News Archive Pre-2012
Coltan Project Meeting at Kigali, Rwanda (21 November 2011) - Reconciling People and Nature with Tantalum Mining
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Adam Smith (1723-1790) and Expectations for the New Year (1 January 2012)
At this time of the year, media like to report on the financial and economic expectations for the New Year. Students and practitioners of economic geology, even those not holding shares in the industry, must be equally concerned about the near future. And we are not only passive recipients as after all, our work concerning raw materials always impacts on the world of economy, even if some its output is at the moment purely scientific.
With the light touch due for an optimistic start into the New Year, I wish to add my voice. Realizing my own limitations in soothsaying, I have searched Adam Smith’s classic, “The Wealth of Nations” (1776) for his views on minerals. Let me cite a few gems which I have found:
"The most abundant mines either of the precious metals or of the precious stones could add little to the wealth of the world. A produce of which the value is principally derived from its scarcity, is necessarily degraded by its abundance."
"Of all those expensive and uncertain projects, however, which bring bankruptcy upon the greater part of the people who engage in them, there is none perhaps more perfectly ruinous than the search for new silver and gold mines."
"Neither are the profits of the undertakers of silver mines commonly very great in Peru. (...) When any person undertakes to work a new mine in Peru, he is universally looked upon as a man destined to bankruptcy and ruin..."
I do hope that the last will not dishearten our friends working in Peru. Even a great man can err. Adam Smith’s negative opinions are influenced by effects of the flood of silver from America which was released by the Spanish conquest (beginning in 1492 with the arrival of Christopher Columbus). All over Europe, the consequent devaluation and financial crisis broke mining and caused havoc in the economy. The “Little Ice Age” with some of the worst cold spells of the last 2500 years and persisting from about 1600 to 1815 CE added food shortages and general misery. But this is another story.
Disproving Adam Smith we have learnt in recent times that gold and silver do have a stabilising role in private and public economy, but alone cannot guarantee wealth. Generally, I still maintain that “well-managed extraction of minerals has every potential to contribute to communal wealth, a sustainable and vital social and natural environment, and peace” (the very last phrase in my Economic Geology book).
In case that Adam Smith is unknown to you, allow me to add a few words. He was one of the stars of the Scottish Enlightenment, together with men such as David Hume and a founding father of geology – James Hutton. Equal to Paris, the Scottish Enlightenment was leading the evolution of new thinking concerning liberty, reason, free speech, and the role of science, religion and the state. This was one of the drivers starting the Industrial Revolution. Adam Smith tought moral and social philosophy. His interest in economy was aroused by contacts with the great French philosophers of his time. His book “The Wealth of Nations” became the base of modern economic thinking, with ideas such as that the self-interest of individuals and the division of labour lead to increasing wealth of society (the “invisible hand”).
If you search for more detail, Wikipedia offers an elaborate biography of Adam Smith
Adam Smith (1776) An Inquiry into the Nature and Causes of the Wealth of Nations (Wikipedia article on the book)
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Coltan Project Meeting at Kigali, Rwanda (21 November 2011) - Reconciling People and Nature with Tantalum Mining
At the beginning of November 2011, 40 participants, 2 representatives of Volkswagen Foundation and 1 senior consultant (myself) followed the call by Bernd Lehmann (the Project Coordinator) to exchange news about work in progress. If you are interested in the project’s evolution, please refer to my “News Archive” (February 24, 2009) and to the entry in “News” (2nd May, 2011).
The papers presented at the meeting will, in due course, be available for download from the Coltan project’s website . In this website, you can also find a short introduction into the structure, methods and aims of the project.
We have found that in many respects, Rwanda is a beacon of well-managed mining in central Africa. The country is in the middle of a mining and exploration boom, concerning tin, tungsten, tantalum/niobium and gold. Yet, modern exploration methods are hardly applied; presently important deposits such as Cyuri in Rwanda, Kabarore in Burundi and the giant Bisie deposits near Walikale in Congo were discovered by traditional methods. Note that the LME price of tantalite is at nearly 300 US $ per kilogram. The reconciliation of mining and the people (from the diggers to small-scale farmers and the women) is rapidly gaining ground. The larger mines have already submitted an Environmental Impact Declaration (EID) under Rwandan law and have submitted to an independent CTC (Certified Trading Chains) audit. The latter describes the operation in detail, including the established certification scheme, and allows a close estimate of the production capacity. This is a response to widespread concern that sales revenues for minerals from the DR Congo feed armed conflict and abuse of its population.
CTC audits and certified trading are obligations resolved by the International Conference on the Great Lakes Region (ICGLR) aiming to enable bona fide legal mines to export minerals whereas conflict minerals originating from sources dominated by illegal armed groups remain excluded from trade. CTC systems buildup is supported by the German Federal Ministry for Economic Cooperation and Development (BMZ) through a mission at Kigali from “BGR (Federal Institute of Geosciences and Natural Resources, Hannover)” . One of the components for control is the Analytical Fingerprint (AFP) method developed by Frank Melcher and his team at BGR, which is able to identify the source of minerals. Of course, some time will pass till the hundreds of mines producing Au, Sn, Ta and W in the Great Lakes Region will have established CTC and been audited.
In Rwanda, the traceability of tin, tungsten and tantalum ore concentrate and gold is largely guaranteed, because the country’s administration is very efficient. The high costs of the controls, however, turn out to be an economic disadvantage as buyers will not pay above international stock exchange prices. In the countries surrounding Rwanda, the introduction of controls is slower but The International Tin Research Institute (ITRI) with its ”Tin Supply Initiative (iTSCi)“ based on due diligence guidelines published by the Organisation for Economic Co-operation and Development (OECD) and the United Nations (UN) offers to assist producers wishing to join the CTC process.
The Congo (DRC) reportedly suffers from a buyers’ strike – export of Sn, Ta and W concentrate has come to a halt. No company trading with the Unites States dares to infringe upon the Dodd-Frank Financial Act (July 2010) which imposes full traceability on imports from conflict regions. The US Securities and Exchange Commission is presently preparing the looming "conflict metals" law. Although another German project tries to introduce CTC in the eastern Congo, nobody knows at present, how and when an effectual CTC system might be working in the forest mountains of the DRC. Meanwhile, the population continues to suffer, but this time from losing their income and going hungry.
Contrary to pilot phase data collected in the Gatumba area, more detailed geochemical work demonstrated that in this mining district, arsenic is not a risk for drinking water. However, arsenic is a common companion of tin, tungsten and tantalum ore in the whole Western Rift Region, and drinking water wells in all mining camps and nearby river valleys must be monitored. Note that eventual pollution need not be related to mining, as demonstrated by the example of Bangladesh (refer to my “Economic Geology”, page 247). The blog posted by Steve Drury in the Earth Pages on November 16, 2011, “South Asian arsenic update” summarises an illuminating new paper which includes exemplary Bengal Basin-wide hydraulic and geochemical modelling.
As demonstrated by results presented at Kigali, the Coltan-Project progresses in great strides. One field of positive results is the research dedicated to identify the best approach to convert pegmatite waste remaining after ore extraction to agricultural use. Greenhouse experiments at Butare and field trials at Gatumba (see Photo Gallery) clearly show that fertility keys are addition of organic substance and adjusting the pH to near-neutral values (all soils at Gatumba are acidic, caused by natural leaching, not by mining).
If you are interested in an authentic source on the human, military and political background of the recent Congo wars and the role of minerals, I recommend the following book:
Dancing in the Glory of Monsters – The collapse of the Congo and the great war of Africa, by J.K. Stearns, 2011, Public Affairs, New York.
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Field Geologists’ Manual – Essential not only for Practitioners (11 October 2011)
In September, the Australasian Institution of Mining and Metallurgy (AusIMM) released the latest (5th) edition of this time-tested source. Since I first joined this society as a young man, previous editions accompanied my professional activities.
First compiled by Don A. Berkman in 1976, the book provides a “comprehensive reference for field geoscience work”. It evolved into one of the best-selling publications of AusIMM. The foreword to the most recent edition presents the work as “bridging the gap between theory and practice and equipping explorers with the resources to undertake field work in Australia and throughout the world”. I can only add my voice to that of the numerous supporters of these statements.
What kind of information can you expect from this book? Before I point out some details, you might look at the Contents pages of the Field Geologists’ Manual (Monograph 9) which are freely accessible in the AusIMM website. And now to selected examples which may characterise the book.
In my opinion, the Index is an important characteristic of a good book. In this Manual, it has grown from 5 pages in the 4th to 10 in the 5th edition. Generally, much of the book reproduces information from the 4th edn. (2001) but there are moderate updates in all chapters. Pages have grown from 395 (2001) to 479 in 2011.
Examples of data which you will not find in Wikipedia, are (1) 21 pages of minerals (listing composition, crystal system, density, hardness, and remarks such as metal content in ore minerals); (2) a brief presentation of diamond indicator minerals and their characteristic geochemical properties; (3) a lucid short description of hydrothermal alteration, veins and breccia related to ore; (4) regolith terminology (Australian, but exemplary for us all wherever we work); and (5) in Chapter 9 – Geophysics (pages 283-303), comprehensive tables of relevant physical properties of ore, minerals and rocks.
Almost wholly new is Chapter 11 - Sampling, Analysis and Quality Control (page 311-333). Text and colour graphs provide a concise but very rich overview of the subject, supported by up-to-date references. Based on the Periodic Table, the most suitable analytical methods are shown for each element (e.g. for lithium ICP-MS, ICP-OES and AAS). Specifics of analysing gold, base metals, iron ores, nickel laterite ore, uranium, REE and PGE are explained.
Updated is Chapter 12 - Reporting (pages 335-362). Here, the reporting requirements for companies listed on the Australian Securities Exchange (ASX), the National Stock Exchange (NSX) or the New Zealand Stock Exchange (NZX) are covered. The chapter includes the JORC Code (2004). Many countries have similar rules, but for practitioners working in those that do not it is very useful to know the obligations.
Chapter 13 - Geometric and Surveying Data (pages 363-397) is thouroughly revised and enlarged compared to the last edition. It starts by explaining projections and coordinate systems, including transformations. This is followed by essentials of using GPS, differential GPS, classical surveying and its instruments, classical tachymetry, and compass and tape traverses.
A whiff of adventure comes with Chapter 15 – Resources, Templates and Further Reading (427-467), which among many others displays tables explaining petroleum industry abbreviations, or should I write slang? What about C&K meaning “choke and kill”? Or JS, “junk sub”, whatever that is. But seriously, I am very much of the opinion that oil and gas are part of economic geology, and we can learn much from our friends working in that industry
Practitioners should find this book an absolutely essential tool. Having the suspicion that many geologists working in research positions have little knowledge of critical procedures such as representative sampling and quality control of analyical data, I strongly suggest that this book should be at hand for all geoscientists.
Rutter, H., Clements, A. & Cooper, C. (Compilers) (2011) Field Geologists’ Manual, 5th edn., 479 pp, Monograph 9, AusIMM, Parkville (available in print or CD format).
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Ancient Life, and Iron Ore at the Redox Interface (6 September 2011)
Life at the cathode is the title of an interesting and highly readable communication by Steve Drury on the Earth-Pages website. He refers to a recent paper in Nature that describes hydrogen as the energy source of life at deep-sea hydrothermal vents. Steve goes on to a more general look at the importance of redox processes in geology. His choice of the title refers to the generalization of the Earth’s largely reduced subsurface as an anode and its surface as the cathode (the “earth battery”). This is, as you know, due to the gradual transition of oceans and atmosphere from a reduced to an oxidized state which is called the “Great Oxidation Event”. The word “event” is somewhat misleading, because even in geological notion the passage took a long time indeed.
During the passage and ever since then, the interface between the two domains was the stage of ore-forming processes such as produced, for example, the unconformity, IOCG and sandstone-hosted uranium deposits. The largest metal concentrations are iron ores related to Precambrian banded iron formations (BIF). Scientific opinions converge on the hypothesis that in the Late Archaean and Early Palaeoproterozoic (2.6-1.8 Ga) “the atmosphere may have been nearly free of oxygen while the oxygen in the oceans started to increase. Seasonal blooms of the earliest photosynthetic microorganisms (cyanobacteria) increased oxygen concentration in seawater that oxidized and precipitated dissolved Fe2+ in the form of oxy-hydroxides” (my Economic Geology page 102). Worldwide, a huge mass of iron oxide mud assembled in the oceans. Little trace, however, remains of the tiny workers that achieved all this; surprisingly, the BIF display extremely small organic carbon contents.
Illumination comes from a recent paper by Yi-Liand-Li et al. (2011) who trace the continuity of phosphorus (apatite) from (iron-oxidizing) phytoplankton to bacterial Fe(III) reduction on the seafloor. Apatite nano-crystals in the 2.48 Ga Dales Gorge Member of the Brockman Iron Formation in Western Australia ( Economic Geology , Plate 1.67, p. 156-157) resemble modern biogenic apatite and Fe(III) acetate salt implies the presence of microbes in the iron mud. This is an indirect confirmation that loss of carbon in BIF is the result of early diagenetic anaerobic microbial activity that partially reduced Fe(III) and oxidized the carbon to CO2. And it is a strong pointer that the ordinary paragenesis of BIF, comprising magnetite, siderite and many Fe(II)-rich silicates is probably diagenetic, not low-grade metamorphic as often thought.
Although many new questions arise, this paper is a significant and remarkable step forward in our understanding of BIF origin.
Yi-Liang Li, Konhauser, K.O., Cole, D.R. & Phelps, T.J. (2011) Mineral ecophysiological data provide growing evidence for microbial activity in banded-iron formations. Geology 39, 707-710.
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“Diamonds are Forever” (6 August, 2011)
Surely, nearly everybody remembers this classic James Bond 007 movie after a book written by Ian Fleming and adjusted for the screen by Richard Maibaum and Tom Mankiewicz, first shown in 1971. For students of economic geology, however, this phrase has a second, equally thrilling meaning.
Based on the longevity of diamonds and their capability to preserve inclusions intact through geological ages, Shirey & Richardson (2011) investigated age and nature of inclusions in macrodiamonds from five continents. Look at Fig./Plate 3.13 in my Economic Geology book, which shows eclogitic inclusions in the famous champagne-coloured diamonds from Argyle, Australia. Shirey & Richardson find that eclogitic inclusions (characterised by pyrope-almandine, omphacitic pyroxene, and rare kyanite, coesite and sulfides) are always younger than 3 Ga whereas peridotitic inclusions (olivine, pyroxene and Cr-pyrope) occur in both older and younger diamonds. Of course, eclogite is the product of ocean crust subduction. Therefore, the authors suggest that Wilson Cycle plate tectonics only started to operate about 3000 million years ago. Before that time, deep subduction would not have been possible because of several reasons, e.g. too buoyant oceanic crust.
Another recent paper reveals fascinating insights into deep subduction of continental crust and diamond formation (Kotková et al. 2011). The authors take us back to the sensation in 1870 of finding the first diamond in Europe, sourced from gem-quality pyrope garnet placers in Northern Bohemia. With a mass of 57 mg and a size of 4 × 2.5 mm, it was definitly a macrodiamond, although a small one. Only one more stone could be found since, but no kimberlitic source rock, and exploration was finally abandoned in the 1960s. Now, Kotková et al. have taken up the challenge to identify the source of the Bohemian diamonds.
Kotková et al. looked at the Variscan basement rocks in the area, typically garnet peridotites within high-pressure granite-derived granulites. The first yield the beautiful red “Bohemian garnets”. Moldanubian granulites are very pretty white rocks with characteristic flattened quartz, K-feldspar, and minor kyanite and garnets. For diamond search, the authors used graphite as a prospecting tool, because it is easily detected by reflected light microscopy. Close inspection of graphite spots in garnet and kyanite identified microdiamonds, some partly or totally graphitised, others perfectly preserved tiny crystals. The diamond hosts turn out to be the granite-derived granulites. How is that possible?
The explanation is deep subduction of the granulite precursor into the mantle (hence the garnet peridotites), down to at least 140 km. On the way down the rocks experienced ultra-high pressure (UHP) metamorphism and reached the diamond window (marked by high pressure but relatively low temperature) followed by rapid, buoyancy-driven exhumation.
Super-deep subduction of crustal material is not common, nor is tectonic exhumation of diamond. Of course, there is little hope that diamond deposits will be found in these granulites or the associated mantle slivers, but Kotková et al. (2011) have made an important discovery. For my part, I do admit that now I regard the Moldanubian garnet peridotite-granulite bodies outcropping in my neighbourhood with a very different attention. Maybe one day, a little glittering crystal will catch my eye?
The third paper opens up a wholly new image of diamond formation, in the truest meaning of the word, concerning the mantle underneath North America (Faure et al. 2011). The authors present maps and sections of the lithospheric mantle based on a 3D seismic tomography model (revealing composition, temperature and structures) combined with geology, and petrological data of kimberlites, notably xenolith barometry. You must see the images to understand the impact of the work.
Tomography of the lithosphere as a diamond exploration tool is not new, but improved methods and the continental scope of Faure and colleagues’ survey are singular. Interpretation of their results provides valuable insights. Most kimberlites in North America, for example, did not originate from the deepest parts of the lithosphere but rather in areas of abrupt changes and steep slopes surrounding the deepest cratonic keels with a few hundred kilometers in diameter. The flat-bottomed keels at >200 km depth deflect rising protokimberlite liquids to the lateral slopes from where final ascent takes place. All diamondiferous kimberlites erupted from depths between 160 and 200 km. The authors do not hesitate to name prospective regions.
I realise, of course, that not many of my readers work in diamond exploration, but I trust that most of you will enjoy the enlightenment concerning the structure and composition of the continental lithosphere, which all three papers provide. After all, the mantle is a major driver of essential metallogenetic processes.
Shirey, St.B. & Richardson, St.H. (2011) Start of the Wilson Cycle at 3 Ga shown by diamonds from subcontinental mantle. Science 333, 434-436. [DOI:10.1126/science.1206275]
Kotková, J., O'Brien, P.J. & Ziemann, M.A. (2011) Diamond and coesite discovered in Saxony-type granulite: Solution to the Variscan garnet peridotite enigma. Geology 39, 667-670.
Faure, St., Godey, St., Fallara, F. & Trépanier, S. (2011) Seismic architecture of the Archean North American mantle and its relationship to diamondiferous kimberlite fields. Economic Geology 106, 223-240.
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Zero-Emission Electricity from “Dirty” Coal – a Miracle? (12 July, 2011)
We all know that technological advance in directional drilling opened up giant natural gas reserves locked in shale and coal beds. Now, it is the turn of underground coal gasification (UCG) to be awakened from a pre-economic half-dormant state. For many years, there was no lack of research but economic feasibility was not achieved. The former Soviet Union had several plants, but today, only remote Uzbekistan continues to use a commercial UCG operation for fuelling a 100 MW electricity plant.
In-situ gasification of coal is basically a variation of the Fischer-Tropsch synthesis in which mined coal is converted to liquid fuels. The principle is gasification of coal in the presence of steam and some oxygen at high temperature (for which purpose a “burn zone” is established) and pressure (provided by the overburden). The gas produced is “synthetic gas” with the composition CO + H2 (carbon monoxide + hydrogen) and waste CO2. The synthetic gas (or syngas) can be directly burned to produce electricity, purified to hydrogen or converted by hydrogenation in the presence of catalysts into products such as gasoline, diesel fuel, jet fuel or chemical feedstocks.
Similar to longwall panels, UCG burn zones develop a fractured and collapsed roof which is commonly covered by a “pressure arch” that reduces permeability for fluids and gases. This seal protects overlying groundwater and potentially allows sequestration of by-product CO2 in the voids created by burning (Younger 2011) enabling zero emission electricity generation.
Underground production of syngas eliminates costs of coal mining and transport, of dealing with contaminants freed by burning coal, of waste disposal and mine reclamation.
Combined with carbon dioxide capture and storage (CCS), in-situ syngas electricity production has a very small carbon footprint and approaches the “zero-carbon” target.
It is claimed that the UCG process can be applied to deep, high ash, conventionally unexploitable coal, which would immensely widen the resource base of coal. The new developments suggest that now, underground in-situ gasification of coal accessed by boreholes is profitable. Successful industrial large-scale application in a competitive economy, however, has yet to be realized. Linc Energy Limited, Australia demonstrates the strategy and skills of a private enterprise on the way to establishing a large UCG operation in South Australia.
In my Economic Geology book, I refer to aspects of coal gasification and UCG on pages 486 and 511. If you are interested in more details, read the paper by Younger (2011) which also contains useful references to further sources. The website of British Coal Gasification Energy Ltd. informs about its Firth of Forth UCG Project in Scotland and offers explanatory graphics.
Going back to the question asked in the title, let me answer that zero-emission electricity from coal is not a miracle, but another proof of the power of human inventiveness in adapting to new challenges.
Younger, P.L. (2011) Hydrogeological and geomechanical aspects of underground coal gasification and its direct coupling to carbon capture and storage. Mine Water Environ 30, 127-140.
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The Anthropocene – a new Geological Epoch? (8 June, 2011)
If you should be working in the Australian outback or in Asia’s desert mountains, you may not have heard of this subject. Let me introduce two recent first-class sources.
In the Economist, a brilliant article explains the background of the hottest debate raging in the earth sciences these days, namely, should we recognise that humanity by its sheer size is a geological force; and if so, should we declare some point in time as the end of the Holocene and the beginning of the man-made world, the “Anthropocene”?
Individually, all arguments for human impact are known and much discussed, such as the huge changes in the geochemical carbon and nitrogen cycles, the movement of soil, sediment and rocks by farming, building infrastructure and cities, and mining, and the effects on nature and life which are mainly caused by humans altering land according to their needs.
The Economist points out that there is no way back – the discovery of chemical fertilizers some 150 years ago (the “first application of geoengineering”) allowed the number of humans to jump from <1 billion to over 7 billion today, predicted to increase to 12 billion in a few years.
The only way forward is, in the Economist’s opinion, to use the singular new factor in geology, namely human intelligence, to steer the evolution of the System Earth into a potentially bright future, instead of retrenching into a low-impact path and global immiseration.
In an equally brilliant blog, Steve Drury answers the second of the questions raised above in the negative. His main arguments are scientific and technical, such as where to fix the start of the new epoch. Should we choose first farming in the Near East, about 10,000 years BP (before present), or the start of the Industrial Revolution in England around 1760 CE (common era), or else? Various lines of similar reasoning lead Steve to conclude that the proposed new epoch “Anthropocene” should not formally be recognised.
If you find the time besides logging core, mapping prospective geology, or changing planes in Dushanbe read the sources cited for excellent up-to-date information regarding one of the fundamental controversies of the geosciences. And, to place the subject in its true dimension, this is also a discussion about the self-concept of humans in System Earth.
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Tantalum in the Heart of Africa – Metallogeny and Sustainable Mining (2nd May, 2011)
On this subject I shall present on Tuesday 17th of May at 15 hours sharp at the Geological Survey of Austria, 1030 Vienna, Neulinggasse 38 (lecture room). The nearest U-Bahn station is Stadtpark (line 4). Note, that my talk will be in German language although the slides are in English and, of course, discussion in English is welcome.
The background to tantalum metallogeny in the Great Lakes-Congo region is the geological evolution of the Kibara Orogen. The tin-tantalum-tungsten province covers some 200,000 square kilometres; its historic production is estimated at 0.5 Mt Sn and 10,000 t Ta2O5. The geodynamic trigger of Kibaran rare metal deposit formation is the final amalgamation of Supercontinent Rodinia. Contractional pan-Rodinian movements (here called the “Kibaran orogeny”) caused low-degree remelting of restites from previous (1400 Ma) flood granite generation. Recently, Luc Tack et al. (2010) provided modern geochemical and age data on Kibaran intrusive rocks, including SHRIMP U-Pb zircon ages and laser ablation zircon Hf isotope data. This allows a data-supported update to my metallogenetic model of the Kibaran (1994). Of high scientific and possibly, exploration significance is the strong mantle imprint of some parental Sn-Ta (“G4”) granites in the Congo, such as very low εHf (Tack et al. 2010) and initial Sr-ratios (Pohl 1994). A mantle signature in 3He/4He, 143Nd/144Nd, sulphur and carbon isotopes of tin granites of the Tasman fold belt in eastern Australia is believed by Walshe et al. (2011) to indicate either mixing of crustal and mantle melts or metasomatism of mid-crustal melt by mantle-derived fluids (e.g. slab dehydration). In the Kibara Orogen, incubation of the shallow mantle might explain melting and devolatilization in the absence of a mantle plume or of substantial subduction (as proposed by Coltice et al. 2007 for the Mesozoic Atlantic LIP). Although it is possible that very small degrees of mantle melting results in rare metal charged liquids, the more likely source of Sn, Ta, and W in the Kibaran remains the continental crust. High fractionation of felsic crustal melts continues as the central petrogenetic model of rare metal deposit formation. Yet we may wonder if the coincidence of large tin-tantalum deposits in the DRC with G4 granites marked by geochemical mantle signatures is accidental.
A modern field-based survey and comparative petrogenetic analysis of the Kibaran G4 granites is overdue but will have to wait for peace in the eastern DR Congo. Until today, only near-surface ore, mainly in the regolith of pegmatites, has been exploited. Ore hosted in apical granite (similar to Abu Dabbab in Egypt) is yet unknown. I am sure that large hard-rock deposits of tin and tantalum will be discovered, once science-based exploration can be executed. The potential of well regulated tin-tantalum mining to development in the Western Rift-Congo region cannot be overstated.
Cooling and crystallization of pegmatite melt ejected from G4 granites induces the segregation of immiscible liquid phases. Hydrosaline melt (a highly concentrated aqueous fluid), saline fluids and a vapour phase may appear at certain stages. Inclusions of coexisting melts and hydrothermal fluids in quartz confirm this model. Ordinary unmineralized pegmatites crystallize at temperatures between 690-540 degrees C, whereas the solidus of fractionated melts with elevated contents of fluxes such as boron, fluorine, phosphorous and chlorine is ~450 degrees C. Also, fluxes raise the solubility of water but inhibit its vapourization. The total tenor of fluxes in pegmatite melt is moderate but they are concentrated in boundary layers at crystallization fronts by “constitutional zone refining” (CZR: fluxing components excluded from solids accumulate in the boundary zone where they promote diffusion). The most fractionated liquid to crystallize last is flux-rich, hydrous, sodic and enriched in tantalum (± other rare elements). After solidification, aqueous fluids dominate the system.
Liquidus undercooling of ~200 degrees C of the melt injected into cool host rocks probably is the principle driver in the formation of pegmatite textures and zoning, and is the main difference to systems where crystallization closely tracks the equilibrium surface of the liquidus (London 2008). Undercooled melt in contact with country rock is semisolid. The development of giant crystals so characteristic for pegmatites seems to contradict the concept of undercooling, but a low density of nucleation sites, water-like viscosity of the flux-rich peralkaline and hydrosaline melts adjacent to the growing crystals, and high diffusion rates explain its feasibility.
Tantalum ore deposits are not a particular chemical risk; there is no acid drainage, and toxic elements only occur in relatively low concentrations (for example, 104 ppm arsenic in Greenbushes albitite tin-tantalum ore: Partington et al. 1995). Yet, control of arsenic is vital when considering the significant health hazard. The main problems of mine restitution concern physical remediation of the waste land and a revival of ecosystems services.
Tantalum is considered to be one of the critical metals both by the US and the EU, not because of geological scarcity but due to insecurity of supply. Tantalum sales from Eastern Congo finance various warring militias and feed wanton killing, plunder, rape and oppression of women, men and children. Geoscience cannot end this, but can design measures for environmentally sound exploitation and remediation of tantalum mines. To reconcile people, mining and nature, and especially to improve food production from mining land are central themes of the Coltan Project which I launched in 2006 (see blog below).
After work, you are invited for drinks at nearby "Zur Steirischen Botschaft", A-1030 Wien, Strohgasse 11, Tel./Fax: +43 1 712 33 67.
Coltice, N., Phillips, B.R., Bertrand, H., Ricard, Y. & Rey, P. (2007) Global warming of the mantle at the origin of flood basalt over supercontinents. Geology 35, 391-394.
London, D. (2008) Pegmatites. Mineralogical Association of Canada Spec. Publ. 10, 347 pp.
Partington, G.A., McNaughton, N.J. & Williams, I.S. (1995) A review of the geology, mineralization, and geochronology of the Greenbushes pegmatite, Western Australia. Economic Geol. 90, 616-635.
Pohl, W. (1994) Metallogeny of the northeastern Kibara belt, Central Africa - recent perspectives. Ore Geol. Reviews 9, 105-130.
Tack, L., Wingate, M.T.D., De Waele, B., Meert, J., Belousova, E., Griffin, B., Tahon, A. & Fernandez-Alonso, M. (2010) The 1375 Ma “Kibaran event” in Central Africa: Prominent emplacement of bimodal magmatism under extensional regime. Precambrian Research 180, 63-84.
Walshe, J. L., Solomon, M., Whitford, D. J., Sun, S.-S. & Foden, J. D. (2011) The role of the mantle in the genesis of tin deposits and tin provinces of eastern Australia. Economic Geology 106, 297-305.
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Fish Production in Post-Mining Pit Lakes, an Important Potential Use (1st May, 2011)
Would you mind to look at photograph 12 (of 14) in my photo gallery? This shows an open pit operation in a stream valley and a miners’ village behind. It is obvious that this pit cannot be left in such a state when mining will cease in the future. But imagine the pit after landscaping, with green banks, filled with water, and producing fish – impossible?
Yes, this is possible. Our Coltan-Project (“Sustainable Restitution/Recultivation of Artisanal Tantalum Mining Wasteland in Central Africa”; cf. News Archive, my first blog, dated 24 February 2009) is dedicated to find and work out solutions just like this.
Generally, opencast lakes formed after mine closure may provide a number of useful ecosystem services which include habitats for flora and fauna threatened by man’s land hunger, flood control, drinking, irrigation or industrial water resources, carbon sequestration and recreations such as swimming, rowing, sailing and fishing.
Confronted with the task of feeding the world population of soon 9 billion people healthily and sustainably, mining land and lakes should in all cases be examined for their potential of producing food. True, land use by mining is relatively small (in most countries below one percent of total area) but the growth of food production cannot be realised by expanding the farming area which has reached its limits, but only by “sustainable intensification“ (Godfray et al. 2010). Fish production from pit lakes is one potential application of this principle.
Responsible mine closure must make the best of the given situation. If rational analysis results in the conclusion that fish production is feasible, go for it. Find a fishing consultant able to help you with all details.
But how can one arrive at a “prefeasibility” conclusion that fishing might be a viable afteruse?
This is where an article by Mallo et al. (2010) in the December 2010 edition of the journal of the International Society of Mine Water and the Environment is a great help. The authors describe the assessment of a former quartzite quarry for aquaculture. The study included hydrological and chemical water parameters, nutrients, organic matter, plankton, and the selection of fish species.
Godfray, H.Ch.J., Crute, I.R., Haddad, L., Lawrence, D., Muir, J.F., Nisbett, N., Pretty, J., Robinson, Sh., Toulmin, C. & Whiteley, R. (2010) The future of the global food system. Phil. Trans. R. Soc. B365, 2769-2777. doi: 10.1098/rstb.2010.0180 (free via Creative Commons).
Mallo, J.C., De Marco, S.G., Bazzini, S.M. & del Río, J.L. (2010) Aquaculture: an alternative option for the rehabilitation of old mine pits in the Pampasian Region, southeast of Buenos Aires, Argentina. Mine Water Env. 29, 285-293.
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My “Economic Geology” Book Is Launched (1st April 2011)
Finally, I can report that my “Economic Geology” is available in two print versions, paperback and hardcover. Apart from the binding, everything out- and inside is identical including the use of colour.
In addition, Wiley provides a Student Companion Site from which you can download all Figures (B&W photos and line drawings, in ppt format) and Tables (pdf) free of charge.
You may not know that authoring is only half of book production. Gentle guidance by editors and reviewers is unseen but helps to improve the work. Once typescript and “art work” is ready, a highly professional group takes over, to manage and carry out copy-editing, typesetting, design, handling the first and second proofs, and at the end, printing.
I am exceedingly grateful to all these people who worked hard to produce an attractive book which I think it is.
Actually opening the first printed copy of his latest book is, of course, a happy moment for an author. Don’t grudge me sharing this sentiment with you.
W. Pohl (2011) Economic Geology, Principles and Practice: Metals, Minerals, Coal and Hydrocarbons – an Introduction to Formation and Sustainable Exploitation of Mineral Deposits. 663 Pages, 294 Figures, 28 Tables and 65 Colour Photographs. Wiley-Blackwell, Oxford.
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The “African Surface”, a New Look at an Ancient Surface (10 March 2011)
If ever you had the chance to travel or work in one of the Gondwana continents (Africa, parts of Southern America, Australia, India) you will remember the deep red laterites so characteristic for the landscape. Laterites are soils that originate by intensive weathering in semi-arid and tropical climate zones. Even the casual observer realizes that extensive laterite peneplains are ancient landforms.
Economic geologists know that weathering is an important agent of mineral deposit formation by enrichment of a low-grade metal stock (e.g. aluminium, gold, copper, iron, manganese, nickel, niobium, phosphate). Most tin-tantalum pegmatite ores in Africa’s Western Rift region (e.g. Coltan Project cf. News Archive, February 24, 2009) are only exploitable where the hard-rock host pegmatite is weathered to sandy-clayey soft rock, reducing extraction costs. Even if no laterite cover is present, we know that weathered rock in situ is the lowest horizon of the laterite regolith profile.
For nearly a century, geomorphology distinguished erosion surfaces by elevation (e.g. the Butare surface at 1700 m a.s.l. in Rwanda, the Buganda surface at 1300 m in Uganda) and attributed age and origin to discrete cycles of erosion at changing base levels. Recently, this is increasingly challenged and in that spirit, Burke & Gunnel (2008) present a new interpretation of African morphology with reference to the continent’s overall Mesozoic-Cenozoic geodynamic evolution which was largely driven by mantle processes.
The authors contend that the African Surface is polygenetic and composite, and may locally split in several levels, but is the product of one long-duration cycle of erosion and weathering which started at ca. 180 Ma (Early Jurassic) when Pangaea began to break apart. Note that most laterites and bauxites formed during the great global bauxite-forming episode from 70-40 Ma (end-Cretaceous to Late Eocene). At about 84 Ma (Santonian) Africa experienced a short pulse of compressive deformation which was mapped long ago in the petroliferous Benue and Sirte Rifts. The event was related to collision in the Alpine chains in the North but of only short-lived and minor consequence for the African Surface. This regime changed dramatically at ~30 Ma (Oligocene), however. Since then, the surface was warped, dissected and tectonically displaced by Africa-wide basin-and-swell formation, rifting and intracontinental volcanism. In the three large – the Kalahari, Congo and Chad Basins – and many smaller intracontinental basins of Africa, the surface is buried beneath sediments which are estimated to host >75% of Africa’s onshore petroleum. Sandstone-hosted uranium may occur in the siliciclastic basin fill. The surface is uplifted on the swells as, for example, the above-mentioned Butare surface along a rift-shoulder in Rwanda. In Guinea, Sierra Leone, Mali, Burkina Faso, Côte d’Ivoire, Ghana and in Nigeria on the Jos Plateau the African Surface is bauxite-capped and has been upwarped to ~1500 m. Elsewhere in Africa, ferruginous laterites cover the surface.
Yves Tardy (1993) drew attention to the significance of gibbsite-goethite bauxite versus boehmite-hematite bauxite; the first being marked by hydrated minerals originates in humid and cooler climate, whereas the dehydrated minerals of the second suggest drier and warmer tropical conditions. Of course, climatic changes may cause later re-adjustment of bauxite mineralogy but this can be recognized by appropriate methods.
I believe that this disparity of bauxite and laterite forming environments may provide keys to a better understanding of many of the enrichment deposits mentioned above. Specific deposit types or metals may well be tied to favourable conditions expressed by the hydration level. The ever curious scientists should be interested, but equally, our friends in the exploration business.
Burke, K. & Gunnel, Y. (2008) The African erosion surface: A continental-scale synthesis of geomorphology, tectonics, and environmental change over the past 180 million years. Geol. Soc. America Memoir 201, 66 pp.
Tardy, Y. (1993) Pétrologie des latérites et des sols tropicaux. 461 pp, Masson.
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Mining Alluvial Diamonds in Southern Africa (18 February 2011)
Economic Geology is not only a science which aims to better understand ore formation. It is also a very practical craft which serves to find a resource and to make a profit from its extraction. Being interested in both, I am delighted to report on an article recently published in Materials World, the monthly members’ magazine of the Institute of Materials, Minerals and Mining (IOM3, London, UK).
Everybody knows that rich diamond placers are exploited along the Atlantic margin of South Africa and Namibia, and that the primary kimberlite sources occur around Kimberley, far away in the centre of the country. Many of the kimberlite pipes erupted in the Coniacian (ca. 86 Ma, Late Cretaceous) and the volcanic craters must have had rims of diamondiferous volcaniclastic ejecta. In the Cretaceous and Palaeogene, the source areas experienced erosion and deep weathering which waned in the Neogene, due to falling temperatures and increasing aridity. Nevertheless, the ancient Vaal and Orange Rivers transported eroded material westwards, including diamonds.
Not very far from Kimberley, an old terrace of Vaal River 105 m above the present course is the target of an enterprising small operator by name of Martin Prinsloo. In the article Martin is cited to report what follows:
Exploration for buried terrace gravels relies mainly on aerial photograph interpretation . Likely areas are percussion-drilled in a grid of 50 by 100 metres. Drilling does not allow to estimate grades, but provides data on the geometry and volume of the gravels, and of the calcrete overburden. Basement traps and rock bars are especially sought because they tend to located higher values.
Estimating diamond grade is very difficult. Previous work indicates that diamond concentration is less than one carat (1 ct = 0.2 g) per 100 tonnes but with the high average value of US$ 1400/ct. In view of the high nugget effect (1000 t of paying gravel may only contain one stone), trial mining of bulk samples in the range of 50,000-100,000 tonnes is the only feasible method to determine grade.
By the way, it is not easy to establish the in situ density of gravels which is needed to convert gravel volume in place to tonnes which are needed, for example, for reserve estimation. In order to be deemed a representative sample, the grain size of gravels (2-200 mm) enforces a mass of several 100 kg to a few tonnes. The practical problem is to determine the in situ volume of the sample taken from the ground (e.g. with an excavator). In engineering, generally used gravel density figures have a wide spread (e.g. 1.4-2.3 tonnes per m3 in Bell 1993). The broad spread reflects dense or loose packing of pebbles.
The capital costs of establishing a 50,000 m3/month operation amounts to only US$ 5 million. Operational costs for mining and processing are US$ 6/t, depreciation is not mentioned. Add a 10% royalty to landowners and you can calculate the pre-tax profit of this operation.
Contrary to most stories of this kind, this one is not intended to attract investors. Just take it as an interesting insight into the financial workings of small placer mines.
Bell, F.G. (1993) Engineering Geology. 359 pp, Blackwell Science.
Forrest, M., 2010, On the river bed. Materials World 18/12, p 32-33.
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« It is the Geologist and Palaeontologist only who see the Panorama of Ages Unrolled in Fullest Length and in Truest Reality »
John C. Merriam 1920 (16 January 2011)
Allow me to present the world’s oldest living organisms. I am almost certain that hardly any of my readers will have heard this marvellous story before.
To begin with, let us note that many salt lake brines host prolific numbers of microorganisms. At high salinity, ordinary freshwater organisms cannot survive. However, specialized (halophile and/or alkaliphile) organisms thrive at high salinity and alkalinity, including species of eukaryotes (algae) and prokaryotes (bacteria and archaea). Halobacterium NRC-1, for example, is an archaeon known to be extremely resistant to UV and gamma radiation. Microbes and halophilic algae floating in the sun-lit, aerobic, nutrient-rich brines are characterized by carotenoid and rodopsin pigments which cause the pink to deep red colour of salt lakes and salt pans (Boetius & Joye 2009). These organisms contribute to the frequent occurrence of organic matter, oil shale and petroleum source rocks in fossil salt lakes (e.g. the Eocene Green River Basin, USA). Some ancient bedded halite, and the included brines and microorganisms can remain undisturbed for many millions of years (e.g. >250 My, Vreeland et al. 2000). Long-term survival of prokaryotes occurs within fluid inclusions by transition into “starvation-survival” or spore forms; probably, the miniaturized microbes draw on carbon and energy supplied by decaying members of the trapped microbial community (Lowenstein et al. 2011).
During the last 50 years, a number of scientists reported to have found viable microbes enclosed in tiny fluid inclusions hosted by salt rock (halititite). Strong doubts remained, however, because there was no explanation for this incredible feat of endurance. Biologists maintained that in the absence of a repair mechanism, DNA (deoxyribonucleic acid) should degrade in geologically short time. The significance of the paper by Lowenstein & Colleagues is that they offer a feasible hypothesis suppported by data as summarized above.
We may conclude that these ancient microbes are truly the “world’s oldest living organisms”.
Apart from beating all records, and the glorious scientific advance, is there any practical benefit? – I think there is, for example in the discussion about the durability of the geological barrier between radioactive waste and the biosphere. In the light of the evidence described above, life itself testifies to the unimpaired geological longevity of salt bodies.
Lowenstein, T.K., Schubert, B.A. & Timofeeff, M.N. (2011) Microbial communities in fluid inclusions and long-term survival in halite. Geol. Soc. America, GSA Today 21, 4-9.
Merriam, John C. (1920) Geol. Soc. America, GSA Bull. 31, 233-246, 1920
Reserves and Resources – Terms for Experts only? (16 December 2010)
Economic geologists, mining engineers and specialised traders on stockmarkets seem to be the only people who really understand the difference between reserves and resources. Most scientists do not -- remember the revered Club of Rome’s notorious prediction that in the 1990s, the world would run out of many essential natural resources. In the event, the general public and the media did not even notice that humanity escaped that dire fate although 20 years earlier nobody doubted the imminent catastrophy.
Today is not much different. Everybody “knows” that crude oil will be finished in 40 years time and that uranium is no carbon-free alternative because it will be exhausted by 2050 or so.
Let me explain the two terms in the simplest way possible – your baker, for example, will most surely have a reserve of flour to draw from for weeks or months. If he does not refill his reserves, he will, of course, run out of flour. Yet, there are ample resources of flour out there. To acquire a lot, he needs to pay down in cash or take a credit. This is the same for mining companies and like the baker, they will hardly be interested to pay for reserves which will lie unused into a distant future.
Mineral resources as opposed to reserves are unknown or little known, or known but not economically recoverable at present conditions. They are mother Earth’s vast endowment, out of which reserves are defined by investing in exploration and evaluation.
The heavy investment required for reserve definition explains why dividing mineral reserves by yearly production nearly always results in a “life-time” of 20-40 years. BUT the 20-40 years are NOT the end of the availability of a metal or mineral. They simply mark the length of time for which reserves must be assured in order to support the commitment of funds for the mining investment. Or in other words, reserves are the security for banks providing credits and for investors buying shares in a mining company.
Please help to end the ubiquitous delusion about “the world running out of this or that metal or mineral” wherever you can!
Reserves and Resources Links
CANADA: Standards for the reporting of Mineral Resources, Mineral Reserves and Exploration Results, with useful references and links to other national codes; Canadian Institute of Mining, Metallurgy and Petroleum
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Australian Break-Through in 21st Century Metal Exploration (15 November 2010)
You are aware, of course, that exploration in the oil and gas industry is based on establishing the relations between source, maturation, migration and trapping of hydrocarbons within the geological evolution of the host basin. The generation potential, volume and extent of source rocks are determined so as to provide an estimate of the total oil and gas mobilized. Fluid flow is correlated with the thermal and structural evolution of the basin. Although only a small part of diagenetic hydrocarbon fluids is trapped in deposits, modelling this process system provides extremely valuable insights that are essential for finding oil.
In metal exploration, the concept was understood but hitherto of little practical use because the supporting data – primarily seismic models of large regions – was not available (some sedimentary basins with both oil and diagenetic ores may be an exception).
A spectacular paper in the August 2010 issue of Economic Geology by Willman et al. (citation below) points the path to future metal exploration strategy.
The region described is the Palaeozoic Victorian gold province in the Lachlan Orogen of southeastern Australia that produced >2500 t (80 Moz) of gold. This is the type-region of metamorphogenic shale, or turbidite hosted gold deposits.
Host rocks of Victorian gold are Cambrian to Early Devonian turbidites of the Lachlan orogen deposited in deep submarine fans. Shales and greywackes are part of an accretionary wedge above the west-dipping subduction zone along the Pacific Gondwana margin. Deformation progressed from west to east between 455-390 Ma. Concurrent amphibolite facies metamorphism liberated fluids from deeply buried Cambrian oceanic and arc-related mafic volcanic crust. Fluid flow was channeled laterally for considerable distances by crustal-scale faults. Deposits consist of quartz veins and concentrate in anticlinoria which served as vertical fluid escape zones. Early veins form an interconnected fracture mesh controlled by folds, bedding planes, cleavage and reverse faults and are partly deformed. Most gold mineralization was synchronous with peak deformation and metamorphism but extended into subsequent tensional strain. Fluids were CO2-rich, of low salinity and had temperatures of 135-360o C.
Four hundred kilometres of deep seismic reflection profiles across the Victorian gold province reveal the crustal section down to the Moho at about 40 km below surface. Because the region experienced little later deformation, Palaeozoic crustal structures are perfectly preserved. Remarkable is the characteristic thrust fault pattern of accretionary complexes. Faults are listric, i.e. flat at depth in mafic volcanics and steepen in overlying turbidites. The cross-sectional extent of Cambrian mafic volcanic rocks is perfectly revealed.
With the gold source and the fluid flow paths so clearly defined, we may assume that exploration geologists and modelers are busily calculating and building new exploration models. Good luck to our friends down under!
Willman, C. E., Korsch, R. J., Moore, D. H., Cayley, R. A., Lisitsin, V. A., Rawling, T. J., Morand, V. J. & O’Shea, P. J. (2010) Crustal-scale fluid pathways and source rocks in the Victorian Gold Province, Australia: Insights from deep seismic reflection profiles. Economic Geology 105, 895-915.
A Dam Break, Not Again! (12 October 2010)
Shaming all mining professions, on 4 October, a mud flow broke from a slimes dam near Ajka in western Hungary. An estimated 700,000 m3 of the heavy liquid flooded the 1.5 km distant village Kolontár and two others downstream. Eight persons were killed and many suffered injury and material losses.
The dam enclosed so-called red mud from an alumina factory at Ajka township. Red mud is the residue of bauxite processing. Run-of-mine bauxite is leached with NaOH. From the aluminate solution alumina Al2O3.xH2O is precipitated. After drying, the precipitate is mixed with natural or synthetic cryolite Na3AlF6, fluorite, LiCO3 and NaCl, and is reduced by electrolysis to metallic aluminium in an electric arc furnace. The red mud is pumped as a slurry into the tailings dam.
Insoluble residue of leaching is alkaline (pH 8-13.5) “red mud” which contains mainly quartz, calcite, hematite and goethite. As a mature soil, bauxite is extremely impoverished in soluble elements. Elevated traces of elements such as Sc, Ga, V, U, Th, REE, P and Ti are possible but rarely observed. In some cases, Sc, V and Ga are extracted from red mud. Red mud is not radioactive nor toxic, apart from its caustic nature (Science, 22 October 2010, pp 432-433). Commonly, it is pumped as a slurry and disposed of in settling ponds.
Revegetation of pond sediments after closure is technically an interesting problem. Recently, red mud is investigated for environmental applications such as lining waste disposal sites, for neutralizing acid mine waters, and for immobilization of toxic heavy metals. At the Kwinana aluminium plant, Western Australia, red mud is reacted with CO2 from the power station in order to neutralize negative environmental risks of both waste products.
Numerous karst-type deposits in the Lake Balaton-Bakony area source the bauxite. This district is part of the large Alpidic (Meso- to Cenozoic) metallogenetic bauxite province which extends from Provence (France) to Greece.
Dam breaks, landslides and mud flows are in most cases induced by exceptionally heavy rains. Dam failure by overflow, faulty drainage or by piping (Richards & Reddy 2007) is the most frequent cause for these accidents. Hydrologic studies for licensing and environmental impact statements are often based on only one annual cycle (Brown 2010). It is impossible, however, to predict extreme precipitation and flooding from one year’s data. Yet, extreme events are the common cause of dam breaks, landslides and mud flows. Clearly, the management of tailings dams asks for measuring precipitation with an automatic rain gauge. Time-series analysis of data is required and as years accumulate, upper and lower bounds of all possible hydrologic conditions affecting a facility can be determined with improving confidence.
All this is well known, dam stability and flow nets can be sketched on the back of a used letter envelope. Systematic inspections may provide timely warning of incipient piping or overflow. SP geophysical surveys locate hidden flow in a leaky tailings dam by an effect that is termed “streaming potential”. Urgency measures how to help endangered people must be planned ahead. And so on, and so on.
Let us raise a call throughout industry to comply with the minimum standards of dam safety – or else our social license to operate is ever more reduced.
Brown, A. (2010) Reliable mine water technology. Mine Water Environ 29, 85-91.
Richards, K.S. & Reddy, K.R. (2007) Critical appraisal of piping phenomena in earth dams. Bull. Eng. Geol. Environ. 66, 381-402.
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My “Economic Geology” is in Print (10 October, 2010)
Finally, I can report that my “Economic Geology” is in the hands of Wiley-Blackwell who inform me that the book now goes into production. This appears to be a lengthy process as I am told that the publishers are expecting to publish the book on 11 March 2011.
Admittedly, I invested most of the past three years into the book and the publishers were patient with me. It is my turn now.
Pohl, W.L., in print, Economic Geology, Principles and Practice: Metals, Minerals, Coal und Hydrocarbons – an Introduction to Formation and Sustainable Exploitation of Mineral Deposits. With ~700 Pages, 294 Figures, 28 Tables and 65 Colour Photographs. Wiley-Blackwell.
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The Footprint of Major Energy Sources (3 September, 2010)
All new industrial projects and especially those concerning energy are subject to critical scrutiny by affected people and often, by NGOs operating far away. Land use is one of the focused criteria. Think of tropical forests in the Philippines which must give way to biofuel plantations or of hydroelectric dams in China flooding farm land. Today, the world's population consumes ~15 terawatts of power annually. Of this total, 0.5 terawatts are from renewable sources (e.g. hydro, wind, solar, biomass, etc.). Clearly, if the aim is to replace all fossil fuels (including uranium, as some activists demand) with renewables, large swathes of land must be newly dedicated to energy production.
I have written earlier about the “The Footprint of Wind Energy” (News Archive October 22nd, 2009). In one of the recent issues of Science, Kerr (2010) provides comparative footprint figures for some important energy sources.
• Normalized to the energy yield from one square metre of an average oil field or coal mine,
• the same amount of energy from solar plants requires 5-50 square metres,
• from wind farms 10-100 square metres,
• and from biomass 100-1000 square metres.
Shall we conclude that our sustainable energy future requires about 100 times the land surface compared with fossil fuels?
The larger footprint of renewables is only one aspect that is discussed. Others include the lower energy density, the unpredictable and patchy availability of wind and sunshine, and the unsolved problems of energy storage. Remember that the insolation in Europe is strongest in summer when electrical power consumption is lowest and vice versa. A key sentence reads “A big problem is that, for the first time, the world is moving to tap new energy sources that are, in many ways, less useful and convenient than the currently dominant sources: fossil fuels.” This paper is a short “News contribution” within a Special Section in Science issue 5993, 13 August 2010, entitled “Scaling Up Alternative Energy”.
Richard A. Kerr (2010) Do We Have the Energy for the Next Transition? Science 329, 5993, 780 – 781.
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Sediment-Hosted Brines Formed by Freezing of Seawater (August 10, 2010)
Brines are important agents of dissolution, transport and reprecipitation of matter in the crust. The origin of many mineral deposits is closely related to migrating brines. Commonly, brines originate by solar seawater evaporation but other processes such as dissolution of salt, hydrothermal boiling and separation of vapour, and concentration of solutes by hydration reactions during metamorphism may also result in brine formation.
Deep continental brines in sediments and crystalline basement rocks are known from Canada, Finland, Germany and Sweden. Origin and age of these brines remain controversial. One of the discussed genetic models proposes derivation by freezing of seawater ("cryogenic brines"). This appears to be confirmed by the results of recently published data from a 1000 metre deep drillhole in Antarctica:
Frank et al. (2010) report that brines occur in Neogene sediments of the McMurdo Sound, Antarctica, which was affected by continental-scale glaciation since the Oligocene. The authors find that seawater-like ratios of Na/Cl, Br/Cl, KCl and MgCl are retained through wide variations of Cl concentrations. Delta 18O values decrease downcore.
Plots of Na/Cl and SO4/Cl against Br/Cl show that the increase of salinity is best explained by formation of pure H2O ice from seawater. With concentration reaching 3.5 while temperature falls, precipitation of mirabilite (Na2SO4.10H2O) begins instead of gypsum (CaSO4.2H2O) which forms by evaporation and rising temperature. Therefore, brine compositions of the two process systems reveal distinctly different evolution paths.
The authors suggest that their findings have important applications, e.g. in the oil industry and for better understanding the geological evolution of sites investigated as potential repositories for nuclear waste (refer to News Archive August 25, 2009). Note that because of lowered seawater levels during Pleistocene glacial periods reaching 120 m beneath present levels, it is unlikely that cryogenic brines exist under the present continental land surface. An exception may be areas which were submerged beneath thick ice shields, e.g. Scandinavia and the northern shores of Europe.
Frank, T.D., Zi Gui & ANDRILL SMS Science Team, 2010, Cryogenic origin for brine in the subsurface of southern McMurdo Sound, Antarctica. Geology 38, 587-590.
Secular Variation in Economic Geology (July 12, 2010)
This title is a citation from the May issue of SEG’s Economic Geology Bulletin (Goldfarb et al., 2010, eds.). Allow me to introduce the subject by citing a passage from my book (Chapter 1.7 Metallogeny – Ore Deposit Formation in Space and Time):
“The unidirectional evolution of Earth in time is of superordinate rank compared to geodynamic cycles (Holland 2005, Sleep 2001, Windley 1995). In the 4500 million years (Ma) of geological history, Earth systems experienced severe changes reaching from the atmosphere, the biosphere and the oceans down into the mantle. Of course, metallogenetic evolution reflects these changes. This results in deposit-types that occur only in certain periods of geological history. Examples of time-bound ores are the komatiite-hosted nickel sulfides in Archaean greenstone belts (common from 3800 to 2500, rare until about 2000 Ma), banded iron formations of the Superior type (2600-1900 Ma), granite-related tin deposits in the Late Palaeozoic and the Mesozoic, and uranium in sandstones of Cretaceous and Tertiary age. An important factor controlling the distribution of ore deposits in geological time is the preservation potential. Just as some rocks are more prone to erosion than others in long-term geological processes (Hawkesworth et al. 2009), so are ore concentrations. Preferential exhumation of near-surface deposits and their destruction by erosion must have occurred throughout geological time. This is probably the reason why epithermal and porphyry copper deposits are much more frequent in Phanerozoic compared to Precambrian time (Wilkinson & Kesler 2009, Kesler & Wilkinson 2006).”
In my book, the theme is taken up again in the discussion of deposit types and different mineral raw materials from metals to petroleum.
In 11 review papers, the Economic Geology issue edited by Goldfarb et al. presents the current understanding of the time-distribution of metals such as Fe (iron formations), Mn, Cu, Ni, PGE, U, Pb/Zn, and of diamond in great detail. Controls considered range from the hotter state of early Earth (e.g. komatiite nickel) through mantle activity, supercontinent growth and break-up, to the redox evolution of Earth (e.g. the “Great Oxidation Event”, GOE, ca. 2.4 Ga). As a consequence of generalization, many of the papers contain valuable insights such as a useful narrow definition of IOCG (iron oxide copper gold) deposits (Groves et al. 2010), after the term had been so extended as to include nearly all iron ores. The surprising consequence is that worldwide, less than 20 IOCG deposits with resources >100 Mt of ore are known and nearly all originated in the Precambrian.
Whoever has a deeper interest in one of the metals and deposit types described in this Economic Geology issue is strongly advised to consult the related review paper. Exploration strategy is one of the fields which should profit.
Goldfarb, R.J., Bradley, D. & Leach, D.L. (eds.), 2010, Secular variation in economic geology. Economic Geol. 105, 3, 459-712.
BP Statistical Review of World Energy: The Newest Annual Edition is out (June 13, 2010)
At the moment, BP seems to be very much out of favour with the public, media and even the US government. Is this the reason why the reception of its recent online publication of the annual Statistical Review of World Energy was so quiet?
Let us recall that BP does the world a great service by annually collecting and publishing this report, this year in its 20th edition. Be aware that this is essentially a collection of figures, without any interpretation. But the figures are highly revealing. Let us look at a few of the data.
In 2009, the world’s primary energy supply (ca. 11,164 Mt oil equivalent) was provided by 34.8% from petroleum, 23.8% natural gas, 29.4% coal, 6.6% hydroelectricity and 5.5% nuclear power (BP Statistical Review of World Energy 2010, bp.com/statisticalreview). BP sources are limited concerning renewable energy, but do report that geothermal, wind and solar electricity generation combined accounted for approximately 1.7% of global electricity generation (which is a part only of primary energy supply).
World energy consumption habitually grows by ~2-3% per year, but shrank by -1.1% in the crisis year 2009. Growth was restricted to the rich Middle East and to emerging industrial nations (China, Bangladesh, India) and in the second, was mainly based on coal.
Let us now turn to uranium. In civil applications, uranium is almost exclusively used as a fuel for base load electrical power production in nuclear power stations. Worldwide in 2009, 439 power reactors were operating in 30 countries. 57 were under construction, mainly in China (23), Russia, South Korea, India, Japan and Canada (http://www.world-nuclear.org/info/reactors.html).
Annual world mine production of uranium was ~50,600 t U (2009). Main producing countries are Kazakhstan, Canada, Australia, Namibia, Russia and Niger. The balance to annual consumption of ~70,000 t U required by the world’s nuclear reactors is made up from secondary sources, including former nuclear weapons, re-enrichment of depleted uranium and stockpiles.
Many conclusions may be drawn from these figures. China, for example, is an interesting point: Although (or because of?) consuming 46.9% of world coal production, China has the highest number of nuclear reactors under construction (23), is a world leader in wind and photovoltaics technology and its deployment, and acquires oil fields worldwide. This is not difficult to understand – energy is the base of all development and there are still too many Chinese people hoping for a better life.
Dissecting Large Natural Oil Seeps (“Asphalt Volcanoes”) on the Seafloor (May 21, 2010)
A recent paper by Valentine et al. in Nature Geoscience 3, 345 – 348, 2010, describes newly discovered extinct asphalt volcanoes off the coast of southern California. The article must be paid for (US $ 18), but the supplements are complimentary. The link is
I feel that for an earth scientist, the parallels with the oil spill at BP’s MC252 oil well in the northern Gulf of Mexico are of great interest. The downloadable PDF contains images of samples, analytical data, some fauna living on the asphalt and a model of the whole system from the seafloor where oil and gas erupted to the oil slick on the surface. The fauna is well known by earlier and ongoing research (e.g. MacDonald et al. 2004). Similar to black smoker sites it is of high biodiversity, comprising numerous species of archaea and bacteria, giant polychaete tubeworms, clams, mussels and shrimp. Some extinct asphalt volcanoes are settled by deep sea corals.
The article explains that the emitted methane acted on the climate. The activity of two volcanoes was dated by 14C to between 44 and 31 kyr ago. Remember that this was a moderate spell during the last ice age, which saw the invasion of Europe by Cromagnon people (Homo sapiens sapiens). They had a high cultural level, witnessed by cave paintings, earliest musical instruments, and beautiful sculptures such as the “Venus of Willendorf” (URL below) wich was found not far from where I live now. A few thousand years later, temperatures dropped so low that humans had to retreat to southern marginal parts of Europe.
Is the potent greenhouse gas methane erupted from the seafloor off California the final cause for modern humans’ successful conquest of the world? Was this warming phase during the last glaciation the initation of the migration of man into Europe and Asia, from staging quarters in the Near East?
MacDonald, I.R., Bohrmann, G., Escobar, E., et al., 2004, Asphalt volcanism and chemosynthetic life in the Campeche Knolls, Gulf of Mexico. Science 304, 999-1002.
To learn more about the Venus of Willendorf, read http://witcombe.sbc.edu/willendorf/, accessed May 21, 2010. Christopher L. C. E. Witcombe is professor of art history at Sweet Briar Girls College in Virginia’s Blue Mountains.
Oil Well Blowout in the Gulf of Mexico (May 8, 2010)
Everybody must be concerned about the severe accident at BP’s Macondo oil prospect in the Gulf of Mexico on April 20. Of 126 personell on board of the Deepwater Horizon drill rig, 11 died. Technical details are vague. It appears that the last work undertaken was cementing the ring void around the casing, which is known to be a critical stage and cause of accidents. Reported facts are that on April 20, the crew was finishing the drillhole after having drilled to 5486 m below the sea floor beneath 1522 m of water. An explosion occurred – probably a blowout -- and a fire broke out on board. Two days later, another explosion sank the rig. In the event, the well’s blowout preventer on the seafloor failed to close the hole and petroleum started to flow. The consequent oil spill is well covered by the media. With the spill site about 75 km from shore, it endangers the livelyhood of people and the environment.
I take this as occasion to provide you with another sample from my “Economic Geology” book which now is nearly finished. The text is from Chapter 7 and explains pressures and blowouts in technical terms:
“Average reservoir pressure is equal to a water column with the density of 1.1 (a brine with ~8 wt. % dissolved NaCl). Abnormal fluid overpressures are defined by a value above the mean of hydrostatic pressure and lithostatic stress. Even higher pressures are possible but very rare. Overpressures typically occur in sand lenses enclosed by mudrock but may also be a regional feature as in Late Cretaceous chalk in the North Sea (Mallon et al. 2005). In sand enclosed by clay, total vertical stress rests in part or fully on the pore fluid. In the latter case the sand grains float in the fluid and have hardly contact with each other. This is due to inhibited dewatering and compaction of the sand when it was rapidly buried (undercompaction or disequilibrium compaction). A second mechanism for creating overpressures is fluid expansion, which is an increase of fluid volume in a restricted pore space, for example by conversion of kerogen to oil, gas and water (Swarbrick & Osborne 1998). Overpressures dissipate naturally by fluid flow out of the system. The required time is a function of permeability. Compressive tectonic stress fields favour the conservation of high fluid pressures (Sibson 2003). Supralithostatic high-pressure fluids such as gas generated by the decomposition of oil and kerogen in very deep (>3 km) compartments may cause hydraulic fracturing and fluid flow in fractures (Grauls & Cassignol 1992). Transmission of high fluid pressure through fissures, or by uplift and inversion can cause unexpected overpressure at shallow depths (Tingay et al. 2007, Luo et al. 2003). Formations or reservoirs with unexpected overpressure endanger drilling because of the blowout risk. In spite of precautions, fatal accidents, high costs and environmental damages too often result from blowouts (Tingay et al. 2007, Fertit et al. 1994).”
If you should be interested in one of the cited sources I’ll be glad to provide the full citation.
Science Magazine Calls for Urgent Measures to “Head off Shortages of Rare Earths” (April 10, 2010)
You may have noticed that I like to scan Science and Nature for scientific news that regard Economic Geology. When I received the last issue of Science (26 March 2010) I was interested to find two pages dedicated to the above headline (Service 2010). Let me cite a text extract from my book (still in work):
“Main producer countries of rare earth elements (REE) are China, India and Brazil. Annual world production amounts to ~124,000 t REE-oxides (USGS 2010). Largest reserves and resources occur in China which dominates world markets of REE with nearly 97% of world production. Many potential deposits of REE are known elsewhere, however. Demand for, and consumption of different rare earths vary considerably. Generally, light REE are in oversupply whereas demand for Eu and several scarce REE (Nd, Dy and Tb) increases. Presence, price and geopolitics of these latter explain the curious situation that exploration and new mine developments are undertaken in spite of giant REE reserves.”
This appears to be a twist of the more common theme of “the world is running out of oil, metals and minerals” with which we are flooded in the media. But if there are giant reserves, why should we expect shortages?
The key to understanding this lies first of all in the REE market domination of China, based on the large magmatic-hydrothermal (?) deposit at Bayan Obo (Baiyenabo) in Northern China. And note that China not only dominates REE production but also its processing and specialized applications. The second element is the expectation that China’s rapid economic growth is going to reduce its exports of high-tech REE to nil sometime in 2012-2014. And the third is that these scarce elements are the key to industrial competition, for example in photovoltaics and innovative automobile technologies.
An interesting dilemma; should we trust in the global market (sprouting new suppliers) and humanity’s innovative gifts (discovering replacements), or should we call for help? – Leaders of the US magnet industry decided to take the second path and recently approached the Obama administration for a $2 billion loan-guarantee program.
You may consider your own preference for action or inaction. Clearly, the matter is not one of dwindling resources but of industrial policy and geopolitics.
USGS 2010: http://minerals.usgs.gov/minerals/pubs/commodity/rare_earths/mcs-2010-raree.pdf
Service, R.F., 2010, Nations move to head off shortages of Rare Earths. Science 327, 1596-97.
Pohl, W.L., in preparation, Economic Geology, Principles and Practice: Metals, Minerals, Coal und Hydrocarbons -- an Introduction to Formation and Sustainable Exploitation of Mineral Deposits. ~700 pages, 200 figures, 100 photographs and 22 tables.
Bioleaching – How do the Microbes do it? (March 4, 2010)
The precise role of microbes in the oxidation of sulfides is still incompletely understood. However, progress has been made and in the last issue of Science, Newman (2010) summarizes present understanding and open questions.
Essentially, microbes produce biomass from CO2 gas by exploiting the energy available in oxidizing minerals such as chalcopyrite. Or simply said, they grow and multiply by eating minerals.
In the process bacteria and archaea oxidize Fe(II) and produce Fe(III) as a metabolic waste product. The reaction produces heat and acidity which some of the microbes such as the commercially used workhorse Acidithiobacillus ferrooxidans need for optimal growth. The oxidized iron is very immobile and in nature forms residual limonite gossans which are long known as guides to subjacent enriched and primary ore. Sulfur (in the form of sulfate) and metals such as copper and silver are dissolved in the leach solution and can be recovered. This much is confirmation of what was assumed before.
Newman goes on to describe the biochemical details and intracellular processes which enable the tiny organisms (about 1-2 micrometre in length) to “feast on minerals”. Acidophiles attach themselves on sulfides and do the actual feeding with curious little organelles called “fibrils”. The fibrils display the Fe(II)-oxidizing enzymes on their surface. Electron transport chains within the cell have been identified. What a wonderful microcosmos of a chemical factory!
Newman, D.K., 2010, Feasting on minerals. Science 327, 793-794.
Microbes leach metals from Ni-Zn-Cu-Co schist in Finland (February 12, 2010)
For two years now, a large low-grade metal resource is exploited at Talvivaara near the Arctic Circle in eastern Finland. Two aspects are very interesting: The first concerns the recovery of the metals by bioheapleaching, the second the nature of the ore – so-called nickel schists.
Let us first look at the deposit: 642 million tonnes (measured and indicated resources) of graphitic schist with about 15-25% sulfides. The ore grades 0.23% nickel, 0.13% copper, 0.02% cobalt and 0.50% zinc (Pitkäjärvi 2010). Host rocks are of Palaeoproterozoic age and were laid down in a marine rift basin not far from the Cyprus type massive copper sulfide deposits at Outukumpu. Typical for organic-rich mudrocks, the Talvivaara schists are very fine-grained, in spite of amphibolite facies metamorphism and orogenic (Sveko-Fennian) deformation. With normal processing technologies such as flotation, metals cannot be recovered from ore of this kind. This is why the deposit was not developed, although it had been exhaustively investigated already in 1977-1983. Bioheapleaching had even be considered but time was not ripe. In 2008, however, extraction in open pits started, and the ore is treated by comminution and microbial heap leaching.
In recent years, bacteria are increasingly recruited for processing formerly intractable ore. In my comment below (Jan 8) I mentioned that oxidation of reduced matter is assisted by the presence of moisture and thriving communities of microbes. Bacteria such as Acidithiobacillus ferrooxidans “feed” on sulfides by oxidizing sulfur and iron. This makes trace metals contained in the former sulfides accessible for leaching. The helpful microbes work best at acidic conditions (pH 2-2.5) and they produce so much heat that the pregnant leach fluid exiting from the heaps has a temperature of about 50 degrees C. This is the reason why leaching at Talvivaara is not disturbed by arctic winters.
Now let us come to the nickel schists. The origin of elevated metal contents in black shales is a long dispute in economic geology. Of course, all black mudrocks contain more metals than, for example, clean sand. Higher concentrations, however, may be collected from (1) ordinary seawater or (2) from hydrothermal input on the seafloor (e.g. black smokers). The Talvivaara schists are probably derived from ocean-floor hydrothermal fluids pervading organic mud (Loukola-Ruskeeniemi & Heino 1996).
Loukola-Ruskeeniemi, K. & Heino, T., 1996, Geochemistry and genesis of the black shale-hosted Ni-Cu-Zn deposit at Talvivaara, Finland. Economic Geol. 91, 80-110.
Pitkäjärvi, J., 2010, Bioheapleaching of black schist-hosted Ni-Cu-Co-Zn ore in subarctic conditions at Talvivaara, Finland. Bull. Australasian Institute of Mining and Metallurgy no. 1, February 2010, 61-66.
Acid Rock Drainage Mitigation Technology (January 8, 2010)
What is acid rock drainage?
Let me explain the principle for those who have not come across this term before. We have to begin by recalling that the Earth’s atmosphere contains reactive oxygen, whereas the subsurface (the geosphere) is essentially reduced. Where the two meet at the surface, oxidation of reduced matter takes place, assisted by the presence of moisture and thriving communities of microbes. Iron and sulfur are the two most common redox-sensitive elements in rocks. Both occur in their reduced state at depth, very often combined in the form of the mineral pyrite which is disseminated through many quite ordinary rocks such as basalt, limestone, mudstone and schists. When erosion exposes these rocks, and where groundwater infiltrates fractured rock containing pyrite, dilute sulfuric acid is formed. Seepage exiting from these rocks is “acid rock drainage” or short, ARD. There are some famous natural examples of springs, creeks and rivers marked by ARD, such as Rio Tinto in southern Spain (the “Red River” of antiquity, so called long before industrial mining). The typically red to orange colour of ARD is due to the precipitation of colloidal oxidized iron compounds. These brightly coloured oozes are very conspicuous indicators for ARD.
Affected rocks are often strongly decomposed and contain alum. Alum is a hydrous potassium-aluminium sulfate which served humanity from earliest time (e.g. mummification in ancient Egypt) until today’s industry. Where I live now, a former alum mine existed in the outskirts of town.
Natural ARD is ubiquitous but attracts little attention. Concentrated small occurrences form valuable ecological systems. Human actions which expose fresh rocks to oxygen and water such as mining and other excavations (e.g. tunneling) are of a scale that requires precautionary action and mitigation. Over 50 years of research and efforts by the mining industry produced a wealth of knowledge but until now this had not been consolidated into a globally useful form.
In the quest to inform the interested public, professionals and authorities about ARD, the global acid rock drainage guide (GARD Guide) was assembled and published recently (Verburg et al. 2009). The guide adresses ARD issues such as origin, site characterization, prediction, treatment, monitoring and “best practice” management. The drivers behind the effort are several of the largest and most progressive mining companies. Clearly, the freely available GARD Guide sets a high-level standard. In-built updating in wiki-style is to guarantee its actuality.
Verburg, R., Bezuidenhout, N., Chatwin, T. & Ferguson, K., 2009, The global acid rock drainage guide (GARD Guide). Mine Water Environ. 28, 305-310 (www.gardguide.com).
From Primordial Earth to CO2 Sequestration in Geological Formations (December 16, 2009)
You will hardly be able to guess the connection of these two subjects, yet the first leads to the second. This is simply because one of the few commercial CO2 gas fields in the world, Bravo Dome, New Mexico, United States, contains nearly pure carbon dioxide (98.6–99.8%), and trace contents of nitrogen, methane and the six noble gases (helium, neon, argon, krypton, xenon, radon). More than 20 years ago when the significance of the helium isotopic composition was recognised, a magmatic mantle source of the Bravo Dome CO2 field was confirmed.
In a recent issue of Science, Greg Holland and Chris. J. Ballentine from the School of Earth, Atmospheric, and Environmental Sciences, University of Manchester, UK, and Martin Cassidy from the Department of Earth and Atmospheric Sciences, University of Houston, Texas, report that Kr and Xe isotopic compositions in the mantle carbon dioxide of Bravo Dome are different from today’s oceans and atmosphere. Both noble gases must have been concentrated some 15,000 million years ago during the birth of our planet from accretionary material similar to average carbonaceous chondrites (a type of meteorite).
But, you will rightly ask, what exactly is a commercial CO2 gas field? Let us recall that CO2 is an important industrial chemical (e.g. for producing sugar), but is also added to numerous beverages to produce sparkle and intensify flavour. It used to be made into “dry ice” for cool storage of frozen food. Today, however, the carbon dioxide from Bravo Dome is pumped about 800 km to western Texas where it is employed to enhance oil recovery (EOR) in fields where revenues of conventional extraction methods ceased to cover costs. Although there seems to be an oversupply of CO2 in the world, little of this is pure enough for the mentioned uses.
In the Colorado Plateau and the Southern Rocky Mountains region, many similar CO2 fields have been found by oil and gas exploration. Only a few have been developed commercially. Yet, these deposits are very interesting in a time when geological sequestration of CO2 is deliberated. Deposits in this region are typically wide domal structures with thin reservoir strata sealed by mudstone and anhydrite. The Bravo dome natural CO2 field, for example, covers an area of 2000 km2 but the pay horizon’s average thickness is just 30 m. The field is producing from over 250 wells (www.hess.com). In the geological past, there must have been a massive flow of carbon dioxide from the mantle through the crust and to the surface. This region is, therefore, a significant field for studying natural upflow and retention of the gas in geological formations (Pearce et al. 1996). It is interesting to note that despite the abundance of CO2 reservoirs in this large region, and the inferred continuing active flux of CO2 to the surface, no surface CO2 accumulations have ever been encountered.
Holland, G., Cassidy, M., & Ballentine, C.J., 2009, Meteorite Kr in Earth’s Mantle Suggests a Late Accretionary Source for the Atmosphere. Science 326, 1522-1525.
Pearce, J.M., Holloway, S., Wacker, H., Nelis, M.K., Rochelle, C., and Bateman, K., 1996. Natural occurrences as analogues for the geological disposal of carbon dioxide. Energy Conversion Management 37, 1123-1128.
Mine Disasters (November 13, 2009)
Every year, thousands of miners die while working in underground mineral extraction operations. For more than one hundred and fifty years, preventing underground accidents has received the attention of authorities, science and operators. Results are impressive, but too many disasters still take place.
Therefore, it is most welcome that the mechanism of one of the deadliest hazards in mining, instantaneous coal outbursts, is now understood. For the miner working on the face, a coal outburst is like a sudden explosion, with a large mass of coal pulverized and swept into mine tunnels. People, tools and heavy equipment are irresistibly swept along with the swiftly moving mass flow. Often, with the coal dust, methane is released and a violent gas explosion multiplies damages. In some cases, the admixed gas is incombustible CO2, but this is not less deadly because humans are asphyxiated.
Ping Guan et al. (2009) investigated coal outbursts in their laboratory at Peking University, by building an ingeniously simple device. This was essentially a high-pressure vessel able to house a coal sample, which was saturated in CO2 between 2 and 4 MPa. Remember that this is only about 10 times the pressure of air in car tires. Sudden release of the pressure pulverized the coal sample very much alike the underground outbursts.
The work reveals that the true culprit is natural high gas pressure inside coal, which is released when the coal is exposed to ambient pressure, e.g. by the advancing coal face. Then, the high-pressured gas expands in a shock wave which breaks the coal into small particles. Ping Guan et al. (2009) point out that phenomena such as salt outbursts and volcanic eruptions are very similar, driven by high-pressure gas. They explain that prevention is possible by i) measuring the gas pressure of the seam to be extracted, and b) draining the gas if in situ pressures are found to be hazardous.
One wonders if the advance drainage of high-pressured methane could be made profitable in the form of coal-bed-methane (CBM) recovery operations?
Guan, P., Wang, H. Zhang, Y., 2009, Mechanism of instantaneous coal outbursts. Geology 37, 915-918.
The Footprint of Wind Energy (October 22nd, 2009)
Recently in Texas, the world’s largest wind farm was opened. Owned by E.ON Climate & Renewables, 627 turbines combine toward a total capacity of 780 MW (mega-watts) electricity. The wind farm covers an area of 400 square kilometres.
In my opinion, these figures demonstrate the advantage of centralised as opposed to distributed power generation.
A typical conventional power station of 1,000 MW needs at most 1 square kilometre of land. Its annual fuel requirement is about 3 Mt of coal, which is produced in a pit that may extend over 10 square kilometres. Or if nuclear, 170 tonnes of natural uranium are required annually from a mine with a footprint of less than 4 square kilometres. Of course, seven million tonnes of CO2 and 300,000 tonnes of ash are generated every year by a coal-fired plant, and about 27 t of spent fuel (or 1 t of processed waste) from a nuclear station.
However, these figures are only part of the whole material and energy cycle of electric power generation. Wind turbines, for example, are made from many metals and minerals which have to be extracted, processed, transported, smelted, manufactured, and after years of productivity, must be taken down and recycled, or disposed. The whole cycle must have quite a large invisible footprint, in contrast to the silvery and sleek wind mills in green landscapes we see. The “dirty” and visible part of the cycle – mining, metallurgy and disposal – takes place in far-away regions and is not associated with wind farms.
There is hardly any information on life-cycle aspects of wind power generators, whereas the media report frequently about problems of coal und nuclear-based power production. Do not misunderstand me, I am not arguing against wind power, but for full information and fair dealings in public discussion.
Geological Carbon Dioxide Sequestration (September 26, 2009)
In the recent past, green activists have discovered a new hazard that allegedly endangers humans and the environment -- geological carbon dioxide sequestration. Experience and facts, however, very clearly support a general adoption of this technology.
The principle of geological carbon dioxide sequestration (CCS – Carbon Capture and Storage) is easily explained: At single point sources of CO2 such as coal, oil and gas power stations, hydrogen and biofuel (via fermentation) producers, cement and metallurgical factories, the gas is separated from stack fumes which are commonly dominated by nitrogen. Once separated (“captured”), the CO2 is liquefied and piped overland to underground repositories at over 1,000 m depth. Suitable reservoirs are porous rocks (e.g. sandstone) which can accommodate the gas in the pore space. The reservoir must, of course, be closed against loss of the gas to the surface. Several trapping mechanisms are possible. The most common is enclosure of the reservoir stratum by gas-impermeable shale. Note that many hundred thousands of petroleum and natural gas deposits in the whole world respond to this description. This is one reason why exhausted oil and gas deposits are first choice for deep CO2 storage (“geosequestration”). The second motive is that the CO2 fluid can be used to flush remaining hydrocarbons towards production wells. The additional oil and gas production is expected to support the economic feasibility of CO2 sequestration.
This technology is well known in the oil and gas industry because for many years, supercritical carbon dioxide has been used to displace hydrocarbons from reservoir pore space in order to enhance recovery. The comparable but less proved CO2-enhanced methane recovery (ECBM) from deep unminable coal seams may offer a new path of CO2 geosequestration (Ozdemir 2009). In the Rangely Oil Field, Colorado, loss of injected carbon dioxide by microseepage to the atmosphere is a fraction of natural methane seepage (Klusmann 2003). The safety case for geological CO2 storage is gaining strength (Houston et al. 2007) and in a North Sea oil field CO2 pool, seal performance for >70 million years has been demonstrated (Lu et al. 2009). Therefore, geological sequestration of CO2 may very soon be widely employed (Schrag 2007). Overall it is expected, that in a few decades CO2 emissions from coal (plus oil and gas) power stations will be reduced to unproblematic levels similar to the successful mitigation of SO2. On that base, fossil fuels can yet provide long-term sustainable energy for the world’s industry and peoples (Jaccard 2006, Parson & Keith 1998).
Six main points about geological carbon dioxide sequestration:
1) CO2 is common in the geological subsurface. A steady flow of gaseous CO2 is released by Earth into the atmosphere, both diffused and at point sources (volcanoes). Refer to my blog below (March 26, 2009).
2) At ambient pressure and temperature, carbon dioxide is a gas (density 1.98 g/cm3) that is 1.53 times heavier than air. At moderately low temperatures (31.1 to -56 oC) and a pressure from 5-73 bar CO2 is a liquid heavier than water. Above its critical point at 31.1oC and ca. 73 bar carbon dioxide transforms into a low-viscosity supercritical fluid. This is the state of highly concentrated CO2 in geological reservoirs at depths below about 500-1,000 m.
3) In the oil and gas industry, there is a long experience of the management of natural and injected CO2 at the surface and at depth. Supercritical CO2 is widely used for enhancing petroleum and natural gas recovery from mature fields.
4) Geological storage is generally planned for depths greater than 1,000 m below the surface, in porous rocks that are covered by dense, impermeable beds.
5) Diffusive loss from CO2 repositories will be so small as to be indistinguishable from the steady state degassing of Earth.
6) Storage capacity and time of immobilisation in geological CO2 repositories are very large indeed.
In conclusion, I beg the anti-sequestration activists to accept cool scientific arguments and technical experience as to the feasibility of geological disposal. But, of course, insist on transparency from politicians, firms, and consultants who are involved in specific projects. For prospective storage sites, the main questions which must be answered concern i) the pressure management, and ii) the fate of the displaced pore fluid (Schrag 2009).
If you are interested to learn details about the present state of science and technology in geological carbon dioxide sequestration (e.g. Schrag 2009) I recommend the special section in a recent issue of Science magazine:
Science, 25 September 2009, Vol 325, Issue 5948, Pages 1585-1740 http://www.sciencemag.org/
In addition, you may follow the proceedings of the European Science Foundation Conference on CO2 Geological Storage: Latest Progress. http://www.esf.org/activities/esf-conferences/details/2009/confdetail293.html#c28278
Burial of radioactive waste and climate change (August 25, 2009)
In the last two million years, world climate cycled between glacial conditions with ice shields and mountain glaciers covering large parts of the continents, and subtropical warm periods. Changing ice volumes forced sea levels to rise and fall about 100 metres from today’s norm. Curiously, the Pleistocene climate cycles remain poorly understood, although orbital forcing is undoubtedly one of the factors. The Last Glacial Maximum (LGM from 26.5-19 ka), for example, was terminated by increasing northern summer insolation, not by CO2 which started to rise only about 1 ka later (Clark et al. 2009).
High-heat producing and high-level radioactive waste owes its hazardous nature mostly to radionuclides which are spent after about 100,000 years. The remaining radioactivity is roughly equivalent to ore containing 0.2% U (Plant et al. 2005). Yet, the safety case for a specific nuclear repository demands an assessment of the implications of drastic climate changes for up to one million years. Of course, temporal prediction of future glacial and warm periods is impossible, but their recurrence is geologically certain.
Methods of assessing the impact of extreme climates on disposal sites are now in full development. One important aspect concerns their consequence for groundwater near repositories. Recently, Judith Flügge (2009) published her thesis which explores the hydrogeological ramifications of different climate scenarios. Although the work was mainly directed at testing and improving methods, results include findings of general interest.
As object of the investigations, the Gorleben salt dome in Northern Germany was selected because it is by far the most intensively explored (although not authorised) repository site in the country (Köthe et al. 2007). At Gorleben, waste is supposed to be stored at 800 m depth in massive rock salt. The top of the salt dome occurs at 250 m below ground surface. The cover rocks include Tertiary and Quaternary sediments, mainly aquifers, but with an intercalated aquiclude which is locally perforated. The lower aquifer is in partial contact with the salt and displays salty pore fluid, whereas the upper aquifer contains freshwater. Sluggish flow is generally to the North.
Judith established a hydrogeological model which she calibrated by simulating the Present State (Holocene). Note, however, that the Present State turned out to be transient and a steady state is expected only after 150,000 to 200,000 years, when salt water in the lower aquifer will have been diluted to very low concentrations.
Based on the Present State flow model thus established, Judith calculated flow models and radionuclide dispersion for the three scenarios (1) Constant Climate, (2) Seawater Inundation (during a warm interglacial period), and (3) Permafrost (during a glacial period comparable to the last glaciation). Assuming leakage from the repository and consequent injection of one mol of each nuclide into the deep groundwater, nuclide dispersion was calculated as a function of advection, dispersion, salt concentration, half-life and adsorption characteristics of each element. Nuclides considered include C-14, Zr-93, I-129, Cs-135, U-234, U-238, Th-230 and Ra-226.
In Constant Climate simulations (1), several radionuclides reach the surface although, of course, at very small concentrations. Individual elements show different behaviour. Seawater Inundation (2) virtually ends all flow of groundwater and expansion of nuclides is restricted to diffusion which imposes very different patterns. Cs and I, for example, expand to the surface, whereas Zr forms a very small plume restricted to the lower aquifer. Permafrost (3) is conceived to include a strong southward freshwater inflow from a glacier in the North. This induces south-directed nuclide plumes, mainly in the lower aquifer.
Judith finally provides calculated nuclide concentrations at the surface (e.g. in springs) against time, from 0 to 1 million years. As expected, the strong dilution helps to keep concentrations very low. In the Constant Climate (1) simulation, for example, maximum concentrations of both Cs-135 and U-238 at the surface amount to about 1 times 10(exp -8) mol m(exp -3). These small masses of nuclides arriving at the surface are lost in the ubiquitous natural radioactive background.
Note: I had the pleasure of supervising this work and am proud of Judith’s achievement. The assistance of Wernt Brewitz and other scientists at GRS Braunschweig is kindly acknowledged.
Flügge, J., 2009, Radionuclide transport in the overburden of a salt dome – the impact of extreme climate states. PhD-thesis, Technical University at Braunschweig, Germany, 195 pp, 20 Tables, 64 Figs., Dr. Hut-Verlag, München.
The thesis is available at http://www.dr.hut-verlag.de/9783868531091.html and you can contact Judith by email under Judith.Fluegge@grs.de
Clark, P.U., Dyke, A.S., Shakun, J.D., Carlson, A.E., Clark, J., Wohlfarth, B., Mitrovica, J.X., Hostetler, S.W. & McCabe, A.M., 2009, The Last Glacial Maximum. Science 325, 710-714.
Köthe, A., Hoffmann, N., Krull, P., Zirngast, M. & Zwirner, R., 2007, The geology of the overburden and adjoining rocks of the Gorleben salt dome (in German language). Geol. Jahrb. C72, 201 pp, Hannover.
Plant, J.A., Korre, A., Reeder, S., Smith, B. & Voulvoulis, N., 2005, Chemicals in the environment: implications for global sustainability. Applied Earth Sci. 114, B65-97.
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Oil Reserves – are we facing the end of oil? (July 4, 2009)
In June, British Petrol (BP) published its latest assessment of world oil reserves (plus gas and coal: Statistical Review of World Energy 2009*). Most media used this occasion to tell us once more that we are running out of oil. I have no intention to argue that oil is inexhaustible, but I would like to share with you a closer look at the meaning of the term “reserves”, and a few aspects of the future of oil.
The world’s measured (proved) reserves of economically exploitable petroleum at the end of 2008 are estimated by BP at 1,258 thousand million (billion) barrels or 170,800 million tonnes. That represented an increase of around 12 % over the end-1998 figure of 1,068 billion barrels, despite the large cumulative production during the intervening ten years (BP Statistical Review of World Energy 2009). BP defines the term “proved reserves of oil“ as those quantities that can be recovered in the future from known reservoirs under existing economic and operating conditions. World production of oil in 2008 was 3,929 million tonnes, and dividing the reserves by annual production gives an R/P-ratio of ~43. This is the figure that mesmerizes public attention.
So there is only oil for 40 years? – Not so, this figure has been the same for decades in the past, and will almost certainly remain unchanged for decades to come. But how is this possible? – Well, let us have a look at the nature of reserves:
In order to measure the quantity of oil in an oil field and to determine its technical and economic exploitability, extensive work has to be carried out, including many thousand metres of deep drilling. This is very expensive, or in financial terms, it is a giant investment. Because the work must be paid now, and the income from reserves beyond the 40-year mark is uncertain and must be depreciated (another financial term), this is a hopeless business proposition. No bank would provide a credit (not even before the debt crisis). We learn from this that the R/P equal 40 is a typical characteristic of the oil business, not the end of oil.
Do we then conclude that all the worries about a future shortage of oil are unfounded? – Certainly not, although there is undoubtedly a large amount of oil in the ground that is partly unknown, and partly known but not well explored. This category is called resources. Reserves are “made” by search for, and detailed investigation of resources. Future reserves are now in the state of prognostic (undiscovered) or identified (indicated, measured) resources. There is general agreement that resources of oil are giant, but that most of this quantity cannot be extracted with today’s preferred technology including free flow from wells, pumping, or water and gas injection (this is called “conventional” oil). Examples of unconventional oil include oil shale and tar sands. The world’s prognostic oil shale resources are very large. Although estimates vary, extractable (synthetic) oil in place probably amounts to 430-600 thousand million tonnes. The Canadian tar sands host estimated in-situ oil resources of 1.7 to 2.5 x 10 to the power of 12 barrels, more than present proven world reserves. Generally, however, the recovery of this future oil will be more costly, and more of the inherent energy will be used for its extraction from the ground.
Accordingly in the long run, prices of oil are expected to rise. But the main worry concerning future oil is rather geopolitics. Most of the world’s oil reserves are state-controlled. States with giant reserves are powerful and not all pursue benign policies. Industrial and developing nations alike may find that they become political clients of oil powers.
Let me, however, conclude with a positive note. In known and fully developed oil fields, about 50% of the oil in place is left underground, because present economic and technological conditions do not allow its recovery. If human inventiveness succeeds in pushing this limit by only 10%, decades of oil production will be added with little additional costs.
Arctic Oil, or how to quantify undiscovered, assumed resources (June 7, 2009)
In recent years, the media informed us from time to time about the struggle for a share of the Arctic Ocean and its assumed giant submarine hydrocarbon resources. But what is the real amount of the prize for successful nations? This question touches one of the most interesting problems in Economic Geology – how to quantify undiscovered resources.
Several solutions to this problem have been proposed. Some are mainly based on statistics (e.g. Hubbert’s Curve), but to some degree most methods involve geological data. An exemplary sample of the second kind was published in Science (29 May 2009, Gautier et al., pp 1175-1179) by a group of geologists from USGS (United States Geological Survey).
Gautier and co-authors state first that by 2007, more than 400 oil and gas fields had been developed on land north of the Arctic Circle. This is roughly one third of the Arctic, with continental shelves and deep oceans making up equal shares of the remaining area. Offshore fields, however, are yet to be developed.
The authors use the existing limited geological information to map 69 individual “assessment units” (AUs) comprising thick sediments. For each unit, petroleum systems (hydrocarbon fluid generation, migration and trapping) were modeled, based on methods which are commonly used by petroleum geologists. Analogy of AUs with well-known petroleum provinces elsewhere in the world allowed an estimate of size and density of undiscovered hydrocarbon fields. Monte Carlo simulations were employed to find the most probable distribution of fields within AUs. Resulting figures concern conventionally recoverable oil resources, but without considering the technological and financial challenges of establishing oil and gas fields in Arctic waters.
Gautier and co-authors conclude that the “Arctic may contain about 13% of the mean estimated global undiscovered oil resource of about 618 BBO” (billion barrels oil). Very large gas resources are also predicted by the study, but mainly sited in the continental shelf north of Siberia, which should strengthen Russia’s dominance of the Eurasian gas markets.
However, I do not intend to dwell on strategic geopolitical consequences. My motive is simply the wish to acquaint you with a state-of-the-art sample of resource estimation.
Giant Ore Deposits – A Geologic Scandal? (May 6, 2009)
In the latest issue of the SEG (Society of Economic Geology) Newsletter (no. 77, April 2009, pp 1 and 14-16), Dr. Pierre J. Goossens from Belgium reminds us of the exceptional metal endowment of the Proterozoic-Archaean eastern part of the Democratic Republic of Congo. This includes the world’s largest province of stratabound copper ores in the Central African Copper Belt of the Democratic Republic Congo, and Zambia. Its historic production was >1,000 million tonnes (Mt) of ore with about 2.7% Cu and variable amounts of Co, Ni, Au, Ag, U, Pb, Zn, and PGE. It is estimated that more than 190 Mt copper and 8 Mt cobalt metal remain to be extracted. Both primary sulfides and spectacularly enriched bodies of oxide, carbonate and secondary sulfide ore are exploited.
Allow me to pass over descriptions of the geological details. Let us just ask ourselves, what may be causes of the exceptional enrichment of some areas like the eastern Congo compared with the scarcity of raw materials in much wider regions?
I have no intention to bore you with a systematic analysis of this problem. There are too many different geological settings and accordingly, different answers. In principle, we only have to look for processes that concentrate a certain element from crustal background values (for example copper with 60 grams per tonne in average rock) to an exploitable content in ore (5,000 grams or 5 kg per tonne in large deposits that are amenable to open pit exploitation). The concentration process is usually an efficient trapping mechanism. Don’t understand this as purely physical, for example dropping temperature and pressure. Often, chemical traps have an important role, such as an oxidised flow with dilute copper encountering reduced sulfur, which instantly precipitates solid copper (iron) sulfide minerals.
The source rock volume should be very large, because the overall process efficiency of extraction (leaching), of focussing the transport medium into the locality of trapping (the future ore deposit), and of precipitation can hardly be one hundred percent.
To produce giant deposits, both the transport mechanism and the trap have to be enduring and the mass flow very large indeed. This translates into big geological systems which operate for extended times, probably many millions of years.
In the Central African Copper Belt, the scientific consensus says that diagenetic, and in very deep parts of the Katanga basin, possibly metamorphic dewatering of rocks induced a large fluid flow towards the southern basin margins. Probably, profound mafic intrusions provided additional heat energy. Structural and lithological features combined to focus the flow toward basin margins. Precipitation took place in the near-surface by reduction, which may have been induced by i) one of the „Snowball Earth“ events, ii) by microbial sulfate reduction based on organic matter, or iii) by thermochemical sulfate reduction of methane in suitable traps.
Clearly, the “geological scandal” is due to an exceptionally favourable interplay and size of all components that make up an ore-forming process system.
Carbon Dioxide – The Long-Term View of a Geologist (March 26, 2009)
Much emotion and idealism are activated by carbon dioxide and its role in the greenhouse theory of climatic change. Though natural scientists are not free of both, their work must be. In that spirit, let us look at some aspects of carbon dioxide which are not generally discussed in the media.
First of all, carbon is the element of Life on Earth: Six major elements, carbon, hydrogen, nitrogen, oxygen and phosphorous are required to build all biological macromolecules. Carbon dioxide in air, and water, are used by plants in photosynthesis of carbohydrates such as cellulose. Simple bacteria and archaea, and all higher animal life forms, including humans, use carbohydrates as feed and breathe out carbon dioxide. Is this a closed cycle?
Of course, it is not. The Earth contains other reservoirs of carbon and carbon dioxide which take part in the rise and fall of atmospheric carbon dioxide. Examples include the Earth’s interior (mantle, deep crust, shallow crust with sediments, coal and oil), and the ocean floors and permafrost lands with methane gas hydrates. Earth degasses constantly carbon dioxide, but peaks occur with large outpourings of volcanic rocks on the surface.
For the last 600 of 4,500 million years of geological history, carbon dioxide concentrations in the atmosphere are relatively well known (Royer et al. 2007). Throughout geological time, carbon dioxide contents were much higher than today. The present atmospheric level is 0.036 % volume of carbon dioxide in air. At about 635 million years before present, during the Neoproterozoic Marinoan snowball Earth glaciation, it has been as high as 1.25-8% (Bao et al. 2009). Since then, carbon dioxide contents in the atmosphere were drawn down by several processes, but foremost by the expansion of plants on land. Only once in the geological past, carbon dioxide concentrations in the atmosphere fell to about present atmospheric level: This happened in the Permo-Carboniferous, at about 300 million years ago, when huge amounts of peat (carbon) were buried in sedimentary basins. Promptly, a glacial climate period was the result which affected all of today’s southern continents, but had its centre in southern Africa. At this time, the threat of a renewed snowball Earth glaciation was real (just imagine what the media would have made of it...). However, fate intervened – at the end of the Permian, outpouring of the giant Siberian trap basalt province soon put an end to low atmospheric carbon dioxide and glaciation (Kamo et al. 2003). Earth, however, paid for its salvation, paradoxically with a huge sacrifice of life – at this time, more than 95% of all species were lost. This was biggest mass extinction of life in geological history.
After the break, carbon dioxide rose to about 0.2%, climate warmed, and life recovered. But again, drawdown of atmospheric carbon dioxide set in, and about 2 million years ago, Earth entered again a glacial mode which in principle still reigns.
What can we learn from this long-term view on atmospheric carbon dioxide? One conclusion is obvious – Earth does not know a long-term equilibrium, the system is always moving. The general vector, however, is downward, to a fall of atmospheric carbon dioxide by burial in the subsurface. Significant increases of atmospheric carbon dioxide levels are rather caused by punctuated events such as the huge blob of magma rising from the mantle below Siberia, some 250 million years ago. The first is predictable, the second is not.
Bao, Huiming, Fairchild, I.J., Wynn, P.M. & Spoetl, C., 2009, Streching the envelope of past surface environments: Neoproterozoic glacial lakes from Svalbard. Science 323, 119-122.
Kamo, S.L., Czamanske, G.K., Amelin, Y., et al., 2003, Rapid eruption of Siberian flood-volcanic rocks and evidence for coincidence with the Permian-Triassic boundary and mass extinction at 251 Ma. Earth Planetary Sci. Letters 214, 75-91.
Royer, D.L., Berner, R.A. & Park, J., 2007, Climate sensitivity constrained by carbon dioxide concentrations over the past 420 million years. Nature 446, 530-532.
Coltan Research Project and Reconciliation (February 24, 2009)
In 2007, I launched an international research project entitled “Sustainable Restitution/Recultivation of Artisanal Tantalum Mining Wasteland in Central Africa” (short title “Coltan environmental management”) and until the end of 2008, acted as its coordinator. As a Senior Consultant, I remain attached to the project. When I planned the project I was aware of the urgent need to reconcile Coltan mining in Central Africa with the people and with the environment. Alas, we scientists cannot help to end the tragedy of Kivu and other parts of eastern Congo (DRC), but we can help to prepare the ground for a prosperous future peace. As I write in the Preface to my new book*: “Wisely used, mineral resources create wealth, employment, a vital social and natural environment, and peace.”
Coltan is an ore of tantalum and niobium oxide. If you wish to know more, read the sample chapter “Niobium and Tantalum” which I selected from my book* because it provides some background to the Coltan Project. Also, I invite you to look at the photo gallery which should give you an impression of some aspects of the Coltan project.
*W.L. Pohl: Economic Geology, Principles and Practice: Metals, Minerals, Coal and Hydrocarbons -- an Introduction to Formation and Sustainable Exploitation of Mineral Deposits.
About 600 pages, 202 figures and ~30 tables (book in preparation)
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