News Archive 2013

The Origin of Banded Iron Ores (BIFs) Illuminated by Geomicrobiology (29 November 2013)

A New Review of my Economic Geology book (10 September 2013)

The Bushveld PGE, Cr, Fe and V Ores – an Integrated Metallogenetic Model (12 August 2013)

Geometallurgical Application of Portable X-Ray Fluorescence (pXRF) Analysers (18 July 2013)

Geoengineering – Salvation or Doom? (21 June 2013)

Engineering for Perpetuity – Tailings Storage Facilities (3 June 2013)

Gold in the Witwatersrand – New Genetic Evidence (10 May 2013)

Rules for Reserve and Resource Estimation Updated: JORC 2012 (8 April 2013)

Impressions from Kivu Province, DR Congo (28 February 2013)

Africa calling - notice of absence (30 January 2013)

There is nothing so ruinous as the search for gold ... (10 January 2013)


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The Origin of Banded Iron Ores (BIFs) Illuminated by Geomicrobiology (29 November 2013)

Yesterday I attended an inspiring lecture by Andreas Kappler (University of Tübingen) who reported on recent results of his group’s research on the role of microbes in the precipitation and diagenesis of Archaean-Proterozoic BIFs. Considering that BIFs are the largest metal concentrations on Earth I assume you will be interested to have the gist of his talk.

We all know, of course, that most scientists relate the precipitation of the giant mass of iron contained in Superior type BIF to the stepwise transition of oceans and atmosphere from a reduced to an oxidized state (the “Great Oxidation Event” GOE between 2.45 and 2.2 Ga).The basic agreement is that the ores are abiotic chemical or biogenic precipitates from seawater. The most common hypothesis is that “The atmosphere may have been nearly free of oxygen when the oxygen in the oceans first started to increase. Blooms of the earliest photosynthetic microorganisms (cyanobacteria) increased oxygen concentration in seawater and caused oxidation of dissolved Fe(II) and precipitation of insoluble Fe3+(OH)3.”

Andreas approached the work by looking at various elements of this hypothesis and using different methods including isotopes, ecophysiological and phylogeny studies, molecular and mineral marker analysis, and sedimentological reconstructions. to investigate the possible role of microbes.

The paper cited below (Posth et al. 2013) provides an overview and references to other papers dealing with details. It can be downloaded using the link provided.

To summarize the results in a few words: The role of cyanobacteria is diminished whereas a number of other iron-oxidising (producing the iron oxide sediments) and iron-reducing bacteria (essential in diagenesis) is recognized and described. Many of them are still around and can be observed doing their work. The difference is that today, little dissolved Fe(II) is available.



Posth, N.R., Konhauser, K.O. & Kappler, A. (2013) Microbiological processes in BIF deposition. Sedimentology 60, 1733-1754.

DOWNLOAD THE PDF:

http://www.geo.uni-tuebingen.de/fileadmin/website/arbeitsbereich/zag/geomikrobiologie/pdf/Paper/2013_Posth_Sedimentology_BIFs_2.pdf


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A New Review of my Economic Geology book (10 September 2013)

Long expectations bring good results: The latest issue of Economic Geology (journal published by the Society of Economic Geologists, Denver, USA) contains a review of my book, written by Eric Anderson from the US Geological Survey, Denver.

Eric gives a very good overview of the contents and concludes with positive verdicts such as

“well organized”

“particularly enlightening”

“helpful reference material when starting new mineral exploration projects”

“suitable textbook for upper-level undergraduate or first-year graduate courses”

“introductory to the economic geology professional”

“nice addition to the libraries of professional geoscientists”

You will, I hope, sympathize with me that I am very pleased and grateful. Praise from the world’s leader in the advancement and promotion of economic geology is a wonderful distinction.



If you wish to read the full text, here is the reference:

Economic Geology (former Bulletin of the Society of Economic Geologists), September-October 2013, v. 108, p. 1517-1518, doi:10.2113/econgeo.108.6.1517


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The Bushveld PGE, Cr, Fe and V Ores – an Integrated Metallogenetic Model (12 August 2013)

Like probably most economic geologists not closely following the discussions regarding layered mafic intrusions and platinum metallogeny, I did notice the contradictory genetic hypotheses being published over the years but felt unable to extract the most likely variants. Now, we have access to what I believe is an excellent paper on the origin of the Bushveld and its mineral treasures: Maier et al. (2013) present an integrated model, from magma derivation in a combined plume and metasomatized subcontinental lithospheric mantle (SCLM) setting through magma emplacement to the formation of layered cumulates and the PGE reefs. All along this narrative, observations and newest hard data (such as the chemical stratigraphy or the composition of parental magmas B1 to B3) are employed in order to deduce the likeliness (or not) of previous major genetic arguments such as in-situ contamination of melt by felsic country rocks, or Boudreau’s magmatic fluid origin for PGE mineralisation. By the way, both hypotheses are considered not applicable by Maier et al. (2013).

It is not possible to mention here all highlights of this rich paper. I’ll only try to trace the main path that leads to PGE enrichment and mineralisation. The story starts with Mid-Archaean extraction of komatiites and formation of the Kapvaal SCLM that was depleted in Pd but retained 4 ppb Pt. In the Neoarchaean and early Proterozoic, subduction metasomatized the refractory residue, introduced sulphur and volatiles, fertilised and oxidised the SCLM. At 2.05 Ga, a mantle plume induced heat and added primitive melts, and caused partial melting of the Kapvaal SCLM resulting in formation of the Bushveld B1 siliceous high-Mg basaltic liquid, which extracted most of the Pt and Pd of the affected mantle and consequently displays concentrations of 33 ppb Pt+Pd at Pt/Pd 1.5. Along its path into the shallow crust, it acquired a strong crustal chemical component. Its progressive fractional crystallisation formed cumulates of olivine, chromite, orthopyroxene, clinopyroxene, plagioclase and sulphide droplets. Reversals of the expected sequence are explained by major replenishments. Lopolithic subsidence caused increasingly inward-dipping layering. This resulted in liquefaction and slumping of relatively liquid-rich, semi-consolidated cumulate layers towards the center, causing features such as potholes, gaps, pipes (including the iron-rich ultramafic “hortonolites”) and numerous smaller deformational patterns. Slurries unmixed under gravity and flow forces into bands of plagioclase, pyroxene, PGE-rich sulphides and oxides (cumulate sorting). This is at the origin of the PGE reefs and the chromite and magnetite seams of the Bushveld.

Maier et al. (2013) terminate the paper with a concise chapter on “Implications for PGE Prospectivity” in layered mafic-ultramafic intrusions that should be useful for explorationists. Scientists will be delighted to study the text in detail and scan the closely printed 10 pages of references. The article is not marked as a review paper but for most of us will be exactly that – a systematic study and an up-to-date interpretation of all genetic elements.

I strongly recommend that whoever needs a profound insight into the Bushveld or the general economic geology of layered mafic-ultramafic intrusions should start with this paper.



Maier, W.D., Barnes, S.-J. & Groves, D.I. (2013) The Bushveld Complex, South Africa: formation of platinum–palladium, chrome- and vanadium-rich layers via hydrodynamic sorting of a mobilized cumulate slurry in a large, relatively slowly cooling, subsiding magma chamber. Miner. Deposita 48, 1-56.


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Geometallurgical Application of Portable X-Ray Fluorescence (pXRF) Analysers (18 July 2013)

In exploration and in mining geology, portable X-ray fluorescence (pXRF) analysers are widely used for on-site data acquisition but there are few refereed published papers that provide information on best practice.

Allow me to remind here the occasional users of geochemistry, citing from my Economic Geology book (page 427), that in some applications such as exploration geochemistry, analytical data need not in all cases be equal to the absolute element content in a sample, or in other words, accuracy may not be essential. Deviations of ±30% from the absolute tenor (e.g. an international or self-produced inhouse laboratory standard) are tolerated, if the relative error remains within narrow limits. In contrast, excellent reproducibility of results, that is high precision, is absolutely required. This is the base for any data evaluation, especially if the contrast between background and anomalies is small. In contrast to exploration, data for reserve estimation must have high accuracy and precision.

In a paper that appeared in print this spring, Gazley et al. (2012) describe a geometallurgy application of pXRF: Amphibolite-facies metabasalts at Plutonic Gold Mine, Western Australia, contain an estimated resource of 10.5 Moz of Au. Based on the observation that high As in the mill feed resulted in poor metallurgical performance, a dense network of more than 70,000 core and underground channel samples was extended throughout the ore body. Apart from arsenic, 31 other elements were determined using pXRF. Gold was measured routinely by fire assay in the mine laboratory where all sample preparation and pXRF analysis took place. The visualization software used was Leapfrog 3-D. Different geometallurgical types of Au mineralisation based on Au/As ratios were mapped in three dimensions. Optimising the mill feed by blending ore is expected to essentially improve metallurgical performance. The authors explain that their motive for choosing pXRF analysis was the low cost of ca. 1 US $ per sample analysed.

In one of the last issues of the AusIMM Bulletin, Michael Gazley (2013) provided valuable advice how to use pXRF units for reliable and valid results. To allow you checking if your routine stands up to Michael’s standards, I mention some of the points he discusses:

Gazley, M.F. (2013) Is there reliability and validity in portable X-ray fluorescence spectrometry? The AusIMM Bulletin no. 2 April 2013, 68-72.

Gazley, M F; Duclaux, G; Fisher, L A; de Beer, S; Smith, P; Taylor, M; Swanson, R; Hough, R M; Cleverley, J S (2012) 3D visualisation of portable X-ray fluorescence data to improve geological understanding and predict metallurgical performance at Plutonic Gold Mine, Western Australia. Applied Earth Science 120, 88-96.


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Geoengineering – Salvation or Doom? (21 June 2013)

What is geoengineering? – Mining professionals may be excused if they believe that the term signifies large-scale change of land by mining or by civil works but this activity is correctly called geotechnical landscape engineering. “Geoengineering” designates a large number of conceptual methods that may be useful for reducing global warming. Note that few of these concepts have been practically evaluated. Examples include the reduction of incoming sun light by spreading reflective aerosols such as sulfate in the stratosphere (imitating volcanic eruptions) or spraying condensation nuclei to increase clouds. Remember that spraying clouds with silver iodide is much used already now for rain-making and hail prevention. Where I live now, valuable wine plantations are guarded against hail by small spraying planes circling through the storm clouds.

Another path of geoengineering is fertilizing the oceans with iron. Iron is the main limiting factor of phytoplankton growth in the high oceans. Phytoplankton blooms are followed by an increase in higher life and a rain of dead organic matter to the deep-sea floor and burial in marine sediments. The result is sequestration of carbon from the atmosphere (Boyd 2007). By the way, natural input of iron and other micronutrients is provided by dust; its increase since 1.25 Ma accounted for up to 50% of CO2 reduction and the consequent ice ages (Martínez-Garcia et al. 2011). This is a reminder that we should not overdo things – a new ice age would exterminate our civilization.

In 2012, the largest iron fertilizing project yet was carried out in the Pacific Ocean, financed by the Haida (a North American native people). Two hundred tonnes of iron-rich dust were dumped over an area of one square kilometre in order to acquire carbon credits, boost phytoplankton growth and salmon stocks. For the Haida, salmon is an important food and has great cultural significance. The induced algal bloom spread across about 10,000 km2. If the salmon run improves as hoped will only be known in 2014.

The figures illustrate that the mining industry should not hope for geoengineering to become a major new customer. Consider that the global iron ore production in 2012 was 3000 million tonnes (USGS 2013). Mined sulfur has been displaced by desulfurization sources such as natural gas and petroleum. And silver? Silver is mainly a co- or by-product in lead-zinc, copper and gold deposits. Global mine production in 2012 was 24,000 t of silver and recycling satisfies a considerable part of consumption. The rather low price of the metal does not indicate an impending shortage. More frequent cloud seeding will make little difference.

The tiny intervention by the Haida attracted ethical critics and furious hate attacks. Scientific investigations such as small field trials are not possible. Governments have launched deliberations by commissions and academies but prefer to stay out of trouble. Yet a regulated social bargain on small-scale research leading to international norms of cooperation and transparency is urgently needed (Parson & Keith 2013). The alternative is secret jostling for an advantage in knowledge and capability.

Boyd, P.W. (2007) Biochemistry - iron findings. Nature 446, 989-991.

Martínez-Garcia, A., Rosell-Melé, A., Jaccard, S.L. et al. (2011) Southern Ocean dust–climate coupling over the past four million years. Nature 476, 312–315.

Parson, E.A. & Keith, D.W. (2013) End the deadlock on governance of geoengineering research. Science 340, 1278-1279.


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Engineering for Perpetuity – Tailings Storage Facilities (3 June 2013)

Engineering structures in mining (such as pit slopes etc.) are commonly dimensioned for temporary use with a low safety margin. There are few exceptions from this rule. Typically, these concern permanent structures left behind by a mine, e.g. roads or dams, that must be durable in the ordinary way of civil engineering with projected life times of ca. 50 years. Life time is controlled by many factors, of which the quality of materials employed stands out. In wide parts of public construction, low costs are imperative and therefore, lower quality (and shorter life time) is accepted. Early damages and constant repairs are the consequence.

In contrast to the common practice sketched above, the Western Australian Department of Mines and Petroleum (below) proposes that the design life of a a tailings storage facility (TSF) in the mining industry should normally be considered to be perpetuity.

For a geologist this raises the question ‘What is perpetuity’? The Chambers Dictionary defines the word as “something lasting forever”. Being involved in the discussions concerning storage of radioactive waste, I am somewhat doubtful of the German demand that safe storage should be guaranteed for 1 Million years (see my post in News Archive August 25, 1999). My doubts increase when facing the word perpetuity.

There is no question, of course, that as a hazard for humans, nature and water, waste should be safely stored. It is truly insupportable when global tailings dams failure incidence is still about one case annually. And I welcome the challenge to the geological profession to investigate and predict the probable long-term evolution of a site. Yet I hesitate to agree with a term that asks for an unlimited look into the future of the Earth.

What is your opinion? Join the discussion in LinkedIn group “Mining Professionals” or respond by email.

Department of Mines and Petroleum (2013) Tailings Storage Facilities in Western Australia – Code of Practice. 15 pp. Resources Safety, Department of Mines and Petroleum, Western Australia (Draft for public comments).

http://www.dmp.wa.gov.au


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Gold in the Witwatersrand – New Genetic Evidence (10 May 2013)

The Witwatersrand District in South Africa is the most remarkable concentration of gold on Earth. Although mining seems to be in decline, understanding the processes leading to formation of the gold-bearing reefs is one of the most important ambitions of economic geology. Recent publications contribute illuminating data.

Read the following extract from my “Economic Geology” (page 220) where you also find microphotographs of uraniferous gold ore (Figure 2.26a and b); text updated:

The scientific consensus on the origin of the Witwatersrand gold reefs is the “modified placer model”. Alternative genetic interpretations persist, however, foremost the hydrothermal-epigenetic, metamorphogenic model described in detail by Phillips & Powell (2012). Yet, geological observations, rhenium-osmium dating and recently published trace elements signatures of uraninite in the reefs (Depiné et al. 2013) support a placer origin of the gold. The latter is based on REE contents of uraninite revealing its origin (Mercadier et al. 2011).

The ultimate source of the giant mass of gold is not exposed and not known. Most probably, the Witwatersrand palaeorivers eroded giant primary gold sources in older granite-greenstone belts. Hydrothermally altered granites and felsic volcanics were present in the catchment area and may have been a source of gold. Predominant pebbles in the reefs (quartz, quartzite, black schists and chert) provide no clear hint at a specific source. Trace element signatures, however, such as elevated Au (up to 67 ppm), Th, W, Bi, Mo, Ta, Y and REE of uraninite occurring with placer gold in the Witwatersrand reefs clearly point to a highly differentiated granitic source (Depiné et al. 2013).

Finally, the extraordinary size of the Witwatersrand gold province (holding resources of about 100,000 tonnes gold) must be sought in processes preparing the fertile parental mantle, and in the major crust-building event, which caused metal extraction and formation of the primary crustal gold concentrations at about 3030 Ma.

SOURCES

Depiné, M., Frimmel, H. E., Emsbo, P., Koenig, A. E. & Kern, M. (2013) Trace element distribution in uraninite from Mesoarchaean Witwatersrand conglomerates (South Africa) supports placer model and magmatogenic source. Mineralium Deposita 48, 423-435.

Mercadier, J., Cuney, M., Lach, P. et al. (2011) Origin of uranium deposits revealed by their rare earth element signature. Terra Nova 23, 264-269.

Phillips, N.G. & Powell, R. (2012) Origin of Witwatersrand gold: a metamorphic devolatilisation‐hydrothermal replacement model. Applied Earth Science: IMM Transactions B120, 112-129.


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Rules for Reserve and Resource Estimation Updated: JORC 2012 (8 April 2013)

Financing the establishment of a new mine or the enlargement of an existing operation are commonly based on selling shares in a company on stock markets. This allows investors to have a part in the fortunes (or the ruin) of an enterprise. Even people with little money to spare can participate because of the generally low price of single shares (mostly from cents to a few hundred dollars). Stock markets are essentially organisations that facilitate the exchange between buyers and sellers of securities (shares). All large and many small mining companies are registered on one ore more of the great exchanges (for example, Rio Tinto on the LSE – the London Stock Exchange).

Early stock markets (say those in the Australian gold fields around 1850) were practically unregulated. Information on underlying assets of shares offered was mostly hearsay. Most investors lost their money.

Since then, the need of buyers for reliable information has increasingly been answered and today, professional societies such as the Australasian Institute of Mining and Metallurgy (AusIMM) take a center role in further development and continuing improvement of the rules of reporting. Reporting signifies first of all the publication of reserves and resources of deposits, but also other company communications that influence the share price. The past excesses of wild promises such as having found masses of pure gold somewhere in a small mine in the outback are not possible any more. Stock markets have their own set of rules (the “listing rules”, for example, concerning transparency) that complement the more technical rules promulgated by professional societies.

If you are curious, have a look at the new Australian Securities Exchange (ASX) Listing Rules.

The most important asset of a mine is the ore in place. In countries with an important mining sector, its qualification and quantification is the subject of codes similar to the one, the update of which is reported here: Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves (The JORC Code). The 2012 edition can be downloaded for free (link below). It may be used already now and must be applied after the end of 2013.

The JORC Code provides minimum standards, recommendations and guidelines for Public Reporting in Australasia of Exploration Results, Mineral Resources and Ore Reserves. It defines terms and provides guidelines. It stipulates that a Competent Person bound by a professional code of ethics signs off the document. The Public Report must contain all relevant information that investors and their professional advisers require. If you ever find the time I suggest that you search for an example of a Public Report in a company’s website directed to shareholders and investors. For professionals such as geologists, metallurgists and miners it makes interesting reading. I assume that many of you will be curious to read the precise definition of Resources versus Reserves. Here it is (extract from JORC 2012):

“A ‘Mineral Resource’ is a concentration or occurrence of solid material of economic interest in or on the Earth’s crust in such form, grade (or quality), and quantity that there are reasonable prospects for eventual economic extraction. The location, quantity, grade (or quality), continuity and other geological characteristics of a Mineral Resource are known, estimated or interpreted from specific geological evidence and knowledge, including sampling. Mineral Resources are sub-divided, in order of increasing geological confidence, into Inferred, Indicated and Measured categories.”

“An ‘Ore Reserve’ is the economically mineable part of a Measured and/or Indicated Mineral Resource. It includes diluting materials and allowances for losses, which may occur when the material is mined or extracted and is defined by studies at Pre-Feasibility or Feasibility level as appropriate that include application of Modifying Factors. Such studies demonstrate that, at the time of reporting, extraction could reasonably be justified. “

The Australian code is an exemplary standard. Companies that try to tap the North American financial markets, even if they operate in say, Africa, often prefer to use the rules set by the Canadian Institute of Mining, Metallurgy and Petroleum (CIM 2013) where links to codes in other countries are also available.

Links

CIM (2013) Standards on mineral resources and mineral reserves. Canadian Institute of Mining, Metallurgy and Petroleum.

JORC (2012) Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves (The JORC Code). The Joint Ore Reserves Committee of The Australasian Institute of Mining and Metallurgy, Australian Institute of Geoscientists and Minerals Council of Australia.


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Impressions from Kivu Province, DR Congo (28 February 2013)

Back from the Congo, I am writing up the scientific and Coltan Project related results of our field studies (cf. previous News dated 30 January 2013). These may be published elsewhere in due time. Here, allow me to share with you some of the vivid impressions, scenes and sights.

Americans – a fleet of heavy SUVs taking elderly donors to visits of humanitarian projects.

Artisanal miners – cassiterite, columbite (coltan) and gold are worked by thousands of men with very simple tools (we saw no women or children labour on the sites that we visited). Eluvial placers in open pits in weathered rock and regolith, alluvial placers along streams, and underground hard rock ore are extracted. Although we have met very knowledgeable and experienced mining professionals managing such operations, lack of capital limits improvement of technology and of working conditions.

Bisie near Walikale in North Kivu – possibly the greatest new tin deposit in the Kibara metal province. About ten years ago, it was found and developed by artisans and quickly became the country’s largest producer of cassiterite. In 2010, the DRC government closed the operation in the fight against conflict minerals. Since then, a junior explorer revealed potential resources of 500,000 tonnes tin metal contained.

Force majeure – in trade and insurance often used to exclude liability; in the Congo, it also designates “closed” areas.

Gold See Photo Gallery. The artisanal gold mine at Mkungwe in South Kivu is a paragon of a well organised non-industrial enterprise. Thousands find work there, and this illustrates the tragic conflict between the interests of the many as opposed to the efficiency, development and progress that only industrial mining can bring about.

Helicopter – the main overland transport vehicle, because of poor roads, force majeure and road blocks.

Industrial mining – the hope for modern exploration know-how and technologies, provision of funds for mine development, efficient and responsible best practices, and contributions to public and private wealth of the country; but feared by artisans because often, they lose informally held ground to the companies taking up licenses. As far as possible, peaceful co-existence should be agreed.

Pakistanis – the UN peace-keeping force in this region is manned by fierce-looking (but undoubtedly kind and helpful) soldiers from Pakistan.

Ruzizi River bridge - the passage from Rwanda into Congo. Ruzizi is the overflow from Lake Kivu down south to Lake Tanganyika. It was the setting that C.S. Forrester had in mind when writing the novel “The African Queen” that refers to the year 1914 and was filmed with Humphrey Bogart and Katharine Hepburn in 1951. Have you seen it?

Metal tracking – mines in the region struggle to establish a system tracking their ore from the mine to licensed buyers, in order to avoid the ban on conflict minerals (eg. the US Dodd-Frank Act 2010; see my News item dated 21 November 2011) and to regain access to world markets.

Twangiza gold mine – a beacon for an increasing contribution of industrial mining to the development of Kivu Province and a paragon of community engagement. Mining started in 2011 based on oxide reserves of 15 Mt at 2.26 g/t gold. At full capacity projected to produce some 120,000 ounces of gold each year.

Women – a stream of women carring heavy loads, apparently mainly food, from Rwanda into Bukavu town, which when we passed through was reportedly cut off from its agricultural hinterland by one of the militias that are the bane of the region.


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Africa calling - notice of absence (30 January 2013)

In February, I’ll be participating as a Senior Consultant in the Annual Workshop of the Coltan Environmental Management Project (CEMP) at Kigali, Rwanda. This year, field studies will take us to tantalum, tin and gold mines in the DR Congo, west of Bukavu town in Kivu Province. For most of this time, I may not be available for contact by internet nor telephone.

The Coltan Environmental Management Project (full name: Sustainable Restitution/Recultivation of Artisanal Tantalum Mining Wasteland in Central Africa) is a research initiative by academics from four countries in the Central Africa Region (Burundi, DR Congo, Rwanda and Uganda, all sharing part of the Kibaran tantalum-tin-tungsten-gold metallogenetic province) and Germany, and is supported by VW-Foundation (Hannover). Recognizing that the prosperity of the region is advanced by exploitation of the rare metals, we aim to reconcile mining with nature and people, and with the environment, by searching best methods of rehabilitating abandoned mines and of environmental and socio-economic management of current mining. Geology, geomorphology, biology, agriculture, and economic, soil and social sciences are involved. A science-based toolbox of mitigation technologies, and guidelines for socially and environmentally responsible tantalum mining and mine closure are being developed.

The Tantalum-Niobium International Study Center (TIC) estimates that “most likely” global resources of tantalum comprise 260,000 t (contained metal). World mine production in 2011 was about 1,000 t Ta, 25 % of which originated from artisanal mines in Central Africa (essentially North and South Kivu in DRC, Rwanda and Burundi). The Kibara metallogenetic province is a large region affected by an intracontinental orogenic phase due to the final welding of Supercontinent Rodinia (~ 1000-900 Ma; “pan-Rodinian orogenic events”: Li et al. 2008). Tin-tantalum (Be-Li) pegmatites are related to granites of S-type character. Eluvial and proximal alluvial placers often host rich ore, whereas to my knowledge, industrial-scale hard rock mining has not yet been tried in the region. In the past, the province was systematically investigated by classical propecting methods but is drastically underexplored by modern technologies.

If you should be interested in more details concerning the metallogeny of tantalum and its companions niobium and scandium, look up the sample chapter “Niobium and Tantalum” under the heading “Economic Geology Book” on this website.

More information on the Coltan Project such as participating scientists and institutions, and the results of a pilot phase in 2007 can be found at: Coltan Environmental Management Project ("Sustainable Restitution/Recultivation of Artisanal Tantalum Mining Wasteland in Central Africa")


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There is nothing so ruinous as the search for gold ... (10 January 2013)

Yesterday I attended a lecture on Earth resources, given by the leader of one of the largest geoscience research institutions in Europe. The speaker somewhat hurried through his excellent presentation from satellite geophysics through conventional and unconventional hydrocarbons to global warming, but one fact caught my eye: Gold reserves will last only 18 years. In principle, this is wonderful news for explorers, miners and investors: Gold is scarce and prices must continue to rise.

Wishing you a properous New Year, allow me to entertain you with some thoughts on gold exploration:

Together with platinum and rhenium, gold is one of the rarest elements. Surprisingly, gold deposits are quite common, in numbers, geographic spread and genetic diversity. Clearly, relatively common melts and crustal fluids are able to mobilize, transport and concentrate gold. Metamorphic and magmatic fluid systems are prolific producers of primary gold deposits. This is illustrated by thousands of gold deposits that formed in orogenic belts from large volumes of crustal rocks with a near-ordinary geochemical background. The group is called “orogenic gold deposits”, which are understood as products of crustal-scale massive flow of aqueous-carbonic metamorphic fluids and of more local magmatic-hydrothermal fluids during orogeny. The majority of primary gold deposits originated in subduction, accretion and collision settings. The “unified” metallogenetic model by Hronsky et al. (2012) proposes that fertile lithospheric mantle provides a source of gold, which can be extracted by transient events of melting or fluid generation; lithospheric-scale structures allow the focused transport of fertile magmas or fluids to the upper crust.

Exploration for gold is exceptional because even today, prospectors and small companies may, with luck, find a new viable deposit. The relatively high probability of success, low stakes and big rewards contribute to gold being the most explored-for metal. Projects are based on geological concepts (e.g. the “unified genetic model” of Hronsky et al. 2012 for large areas, scaling down to structural and lithological controls, metamorphic gradient, etc.) and involve mineralogical, geochemical and geophysical methods. Note that “data by itself does not make a discovery”; it is the intellectual input (Phillips 2012).

Are you interested? Before investing all your money in the shares of a promising junior exploration team, read what the Scottish founder of modern economic science, Adam Smith, thought about gold exploration:

“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” (Adam Smith 1776)

Be not discouraged, however. My opinion is still what I wrote in my Economic Geology book (the third and forth paragraphs above).


References

Hronsky, J.M.A., Groves, D.I., Loucks, R.R. & Begg, G.C. (2012) A unified model for gold mineralisation in accretionary orogens and implications for regional-scale exploration targeting methods. Miner. Deposita 47, 339-358.

Phillips, N.G. (2012) Gold exploration success. Applied Earth Sci. (Trans. Inst. Min. Metall. B) 120, 7-20.

Adam Smith (1776) The Wealth of Nations. Book IV/VII. Of Colonies.


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