News Archive 2016
Quantitative X-Ray Diffraction (QXRD) as a Valuable Tool in Exploration and Resource Reporting (27 October 2016)
Looking for a Present? Consider a Diamond for your Love! (8 December 2016)
You may guess that I am not in the diamond retail business. The reason for my question is a lucid new paper (Stern et al. 2016) that describes the ties between the import of H2O and carbon into the mantle by subduction, and kimberlite formation. Of course, understanding kimberlites is the key to diamond origin.
The authors state that their aim is a contribution to the discussion about when plate tectonics began. Present answers number at least 10 different estimates ranging from 4.2 Ga to 0.84 Ga. Kimberlites may be an important new line of evidence. Why? – Let’s first have a look at kimberlites.
If you have ever seen a sample of kimberlite, you may recall that it is an unremarkable fine-grained brecciated volcanic rock. Without instruments such as infrared reflectance spectrometers, the groundmass mineralogy and dispersed phenocrysts and xenoliths of wall-rock, mantle and crustal derivation can hardly be resolved.
In general petrological terms, kimberlites are potassic, volatile-rich ultramafic rocks with high contents of both compatible (Ni, Cr) and incompatible elements (Ti, P, light rare earth elements). Similar to carbonatite, kimberlite liquids originate by low-degree partial melting from enriched parts of the Earth’s mantle, and ponding at continental roots, acquire their different character by resorption of lithospheric peridotite. If the lithosphere-asthenosphere boundary (LAB) is at depths underneath the low-pressure stability limit of diamonds (>140 km), the accumulating melts react with rocks of the lithospheric mantle and may form diamonds, for example by carbonate reduction or methane oxidation. There is evidence that some diamonds crystallized from pegmatitic melts injected into the thermal aureole of kimberlite melt pools. Type II diamonds associated with pegmatitic megacrysts cause the outstanding value of gemstones from Letseng (Botswana), Jagersfontein and Premier mines (South Africa). Eruption of kimberlites is violent because of overpressured volatiles and vigorous exsolution of a fluid phase during ascent.
The crucial point of this paper is the nature and cause of the mantle enrichment. The authors demonstrate that the age distribution of ca. 1500 dated kimberlites is strongly skewed to recent geological time. The increase starts in the Neoproterozoic. They deduce that this pattern reflects a massive rise in water and carbon flux to the mantle beneath the lithosphere. The volatiles augmented fluid pressures at the base of thick cratonic lithosphere to >6GPa, explaining the high potential energy driving kimberlite eruptions. They maintain that the only solid Earth processes capable of delivering large amounts of H2O and CO2 to the mantle beneath the lithosphere are plate tectonics and deep subduction.
The authors conclude that before ca. 1 Ga, there was no modern plate tectonics and no deep subduction, apart from a few aborted Palaeoproterozoic attempts. The flux of water and carbon to the mantle was low.
And what about that present to your love? – In my view it is wonderful to look at a diamond knowing that it originated by deep cycling of water and carbon from ancient seas. Carbon that was refined by heat and pressure into an indestructible mineral! Recall that the term adamas (the invincible, in ancient Greek) was first used for the “stone of kings” in Antiquity.
Stern, R.J., Leybourne, M.I. & Tatsuki Tsujimori (2016) Kimberlites and the start of plate tectonics. Geology 44, 799-802. http://geology.gsapubs.org/cgi/content/abstract/44/10/799?etoc
- Champagne-coloured octahedral diamond crystals from Argyle, Australia. Note the macroscopic (eclogitic) inclusions. Courtesy Rio Tinto © Argyle Diamonds.
back to top
Remarkable Australian Handbooks for Sustainable Mining – Free Download (10 November 2016)
The Australian Government through its Department of Industry, Innovation and Science, and in consultation with the Australian mining industry and other interest groups, publishes a package of seventeen handbooks to address the key issues concerning sustainability aspects of mining.
The informative and user-friendly handbooks provide mine managers, communities, regulators and NGOs with essential information on current sustainable mining practices. They are relevant to all stages of a mine’s life (exploration, feasibility, design, construction, operation and closure) and to all facets of its operation. Case studies included in the publications encourage, assist and lead all sectors of the mining industry beyond the requirements set by legislation.
Each publication was created with the oversight of individual working groups comprising experts in Australian mining, including Australian mining and minerals industry operators, Australian mining bodies and industry training providers, the Minerals Council of Australia, and Australian state and territory government agencies.
Following the success of the single handbooks, a summarizing publication was produced: A Guide to Leading Practice Sustainable Development in Mining (Australian Government 2011). Please note that the text above is taken from the website provided below, with small changes.
My comment: Professionals working in the industry should know these handbooks that are practical, not science publications, but do cite the relevant references. The Handbook on Cyanide Management (Australian Government (2008), for example, informs in detail on nature, usage and hazards of cyanide, including its chemical forms, properties, sampling and sound analytical routines. Protection of humans, wildlife and general nature is explained in great detail. To those of my readers who work in gold mining, or others whose mine employs cyanide, I recommend urgently to download Cyanide Management.
All 17 handbooks deserve to be presented, but here is not enough room. Mine rehabilitation, for example, is illuminating. Have a look yourselves! If you prefer to read them in another language – they seem to be available in 5 Asian languages, in Spanish and in French, apart from English.
“Green”, or sustainable mining is possible! Laurels to Australia!
Australian Government (2008) Practices for cyanide management. 99 pp. Department of Industry, Innovation and Science. URL http://www.industry.gov.au/resource/Programs/LPSD/. Accessed November 2016.
Australian Government (2011) A Guide to Leading Practice Sustainable Development in Mining. 198 pp. Department of Industry, Innovation and Science. URL http://www.industry.gov.au/resource/Programs/LPSD/. Accessed November 2016.
Australian Government (2016) Mine rehabilitation. 68 pp. Department of Industry, Innovation and Science. URL http://www.industry.gov.au/resource/Programs/LPSD/. Accessed November 2016.
back to top
Quantitative X-Ray Diffraction (QXRD) as a Valuable Tool in Exploration and Resource Reporting (27 October 2016)
In exploration and mining geology, X-Ray Powder Diffraction (XRD), a method that determines the mineral composition of a sample, is often considered to be onerous, slow and expensive. Geochemical methods are preferred, because they deliver rapidly and cheaply reliable data on elements contained. Yet, there are numerous cases where the targeted element (e.g. copper) in the ore occurs in different mineralogical forms (sulphide, arsenide, oxide) that vary across the ore body. During processing, large recovery losses may be the consequence, in spite of good total tenors. Hand-held XRD analyzers such as Olympus Terra are recommended for geometallurgical characterization that may help to presort the ore into different heaps for appropriate treatment.
If very small error margins are required, the more elaborate and precise Quantitative X-Ray Diffraction (QXRD) may be preferred:
Kemp et al. (2016) describe a remarkable case study in great detail that offers some theoretical and much valuable practical information on using QXRD, including its advantages compared with other modern methods such as inductively coupled plasma-atomic emission spectroscopy (ICP-AES) or X-ray fluorescence spectrometry (XRFS). The project in question is the development of Permian potash seams in NE England, called the York Potash Mine, not far from the working Boulby Potash Mine that is based on sylvinite and, since 2010, polyhalite (marketed by Israel Chemicals Ltd).
Most potassium deposits (including Boulby) are formed of chloride minerals (~90%, mainly sylvite KCl at ~60% K2O) and this is the common form of K-fertilizers. Potassium sulphates contribute only 4% of world production; they are recommended for Cl-sensitive crops such as grape-vine, tomatoes, tobacco and potatoes. The York Potash Mine is based on the sulphate mineral polyhalite, with the compositional formula [K2SO4.MgSO4.2CaSO4.2H2O], a density of 2.77 g/cm3 and containing 15.5% K2O.
Exploration comprised 16 km of deep drilling and 4.2 km of coring, to depths of 1.7 km. A total of 1300 samples were analyzed by QXRD. The work resulted in JORC-standard indicated mineral resources of 820 Mt grading 87.3% polyhalite (13.6 equiv K2O%) and an inferred resource of 1840 Mt at 85.2% polyhalite (13.3 equiv K2O%). This is supposedly the world’s highest-grade and largest resource of polyhalite (Kemp et al. 2016).
The genetic setting of potash deposit formation was the post-orogenic relaxation of Supercontinent Pangaea. In wide parts of Europe, the collisional Variscan orogeny had ceased in the Late Carboniferous. In the Permian, extension and gravitational collapse of the orogen and thermal contraction of the lithosphere and extension induced formation of the wide north-central European Permian rift basin. This was an arid land below sea level, which accumulated continental red sandstones, shales and conglomerates, felsic volcanics, minor coal, and playa-lake evaporites of the Rotliegend sequence. The global Late Permian climate was hot and dry. Boreal forests and coal swamps only formed at highest latitudes and reptiles lived within 15 degrees of the South Pole (Torsvik & Cocks 2004). Ice melting led to a sustained sea level rise and at ca. 258 Ma (Late Permian), the Zechstein basin was flooded. The first sediment deposited was a black shale bed (the European Copper Shale). Because the connection to world oceans was restricted and arid conditions unbroken, the basin developed into a large evaporite pan receiving the Zechstein sequence. Four to six evaporative cycles occur; each starts with clastic sediment (commonly clay indicating high water levels) that is overlain by carbonate, sulphate, halitite and Mg-K salts, reflecting progressive desiccation. Total thickness of the sequence varies considerably, from <500-1500 m.
- Palaeogeographic sketch of the Zechstein Basin (white) within Pangaea in the Late Permian before the Atlantic Ocean began to open. Inflow of seawater probably occurred from the North. The basin was at about 20 degrees northern latitude. Inside the giant landmass (blue), the climate was extremely dry. Note the planned York Potash Mine on the Eastern coast of Britain (red dot).
Near the margins of the basin and around islands emerging from the saline inland sea, shallow-water carbonate and sulphate “reefs” (ramps or walls) were building up. Marginal sulphates display shallow-water facies characteristics caused by oscillating water levels that control deposition of alternating shallow-water and subaerial sediments. The future York Potash Mine is sited on such a coastal structure, straddling the lagoon or shelf, the ramp and the basin margin. Polyhalite replaced gypsum/anhydrite (Kemp et al. 2016), possibly during desiccation phases when concentrated K-Mg-rich brine percolated downwards.
Kemp, S.J., Smith, F.W., Wagner, D. et al. (2016) An improved approach to characterize potash-bearing evaporite deposits, evidenced in North Yorkshire, United Kingdom. Economic Geology 111, 719-742.
Israel Chemicals Ltd (operator of Boulby Mine) www.icl-group.com
York Potash Ltd. (a subsidiary of Sirius Minerals, Plc) http://siriusminerals.com/
back to top
Drones, or Unmanned Aerial Vehicles (UAVs) in Economic Geology Practice (28 September 2016)
Increasingly, drones are employed by economic geologists in order to collect data by “remote sensing” techniques. Interpretation focuses on geospatial features that support exploration, mining or environmental work.
In most legislations, drones are called unmanned aircraft systems (UAS) – yes, they are usually regulated! They come in all sizes but common non-military systems are light and small quadrucopters, typically with payloads between 300 and 5000 g (see photograph A). At all times, the operator should have a clear and direct line of sight to the vehicle. Because of battery limitations, this kind of remotely controlled aircraft is used for restricted areas and limited height above ground.
A range of sensors can be mounted on drones including digital cameras, imaging spectrometers, gravity meters, LIDAR laser systems, magnetometers, and sensors for visible light, near infrared and thermal imaging.
Digital photography with high-resolution cameras provides images of pits and mine surroundings that can be orthorectified and used as a base for topographic (e.g. mine site construction), photogrammetric and geological mapping. Digital Elevation Models (DEM) are derived that assist volume control in tailings, ore heaps, leach pads or in pits.
Imaging spectroscopy (or “spectral geology”) has been used for decades for remote sensing from orbital or aerial platforms. Recent minimization of sensors such as visible-shortwave infrared (VSWIR) imaging spectrometers allows their use on drones. Data yield identification of minerals and rocks, different soils, types of hydrothermal alteration (Greenberger et al. 2015), gossans and the discrimination of healthy and stressed plants. In many cases, alteration mapping will be most in demand (Kruse et al. 2012).
LIDAR (Light Detection and Ranging) technology provides cm-scale elevation models that support precise mapping, especially in heavily vegetated regions because LIDAR is able to image the ground surface beneath a vegetation canopy. The technology is paramount in recording changes of the land surface in 3D, such as those associated with mining, subsidence or bulging, slope creep, landslides and rock falls.
Gravimetric and magnetometric surveys are geophysical methods that help to locate natural or human-induced anomalies in the Earth’s field, and to map its grain induced by rocks. Consult Milsom & Eriksen (2011) for details.
Mine surveyors at large operations have fully embraced the drone technology. We may safely predict, that drones will soon be essential observation and data collection tools for economic geologists. They assist detailed geological mapping of rocks and structures (such as bedding, folds, faults and joints: Thiele et al. 2015), of mineralisation and alteration in exploration prospect and mine work. Advice for good geological mapping practice can be found in Lisle (2011) and Coe et al. (2010). You may read a review of the two books in my Economic Geology News (2 April 2012: http://www.walter-pohl.com/News_Archive_2012.html). In my Economic Geology book, more background information can be found in Part III, The Practice of Economic Geology (pages 411-463).
Enterprising geologists may start their own business in geological drone surveying, but for occasional work, my advice is to employ an experienced service provider for data collection and processing.
- B - UAS cruising above a rock fall that terminated exploitation of this quarry. The drone carries a digital camera and a LIDAR system for precise mapping. Data collected over time are contrasted in order to identify rock movement and eventual acceleration, which may lead to renewed rock falls that threaten traffic on adjacent road and railway.
Coe, A.L., Argles, T.W., Rothery, D.A., Spicer, R.A. (2010) Geological Field Techniques. 336 pp. Wiley-Blackwell.
Greenberger, R.N., Mustard, J.F., Ehlmann, B.L. et al. (2015) Imaging spectroscopy of geological samples and outcrops: Novel insights from microns to meters. GSA Today 25, 12. doi: 10.1130/GSATG252A.1
Kruse, F.A., Bedell, R.L., Taranik, J.V. et al. (2012) Mapping alteration minerals at prospect, outcrop and drill core scales using imaging spectrometry. International J. Remote Sensing 33, 1780–1798. doi: 10.1080/01431161.2011.600350
Lisle, R.J., Brabham, B. & Barnes, J.W. (2011) Basic Geological Mapping. 5th edn. 230 pp. Wiley-Blackwell.
Milsom, J.J. & Eriksen, A. (2011) Field geophysics. 4th edn. 304 pp. The Geological Field Techniques Series, Wiley.
Thiele, S., Micklethwaite, S., Bourke, P. et al. (2015) Insights into the mechanics of en-echelon sigmoidal vein formation using ultra-high resolution photogrammetry and computed tomography. J. Structural Geology 77, 27-54.
back to top
Mineral Sands – a Source of High Technology Metals (27 August 2016)
In my last weblog I presented AES (Applied Earth Science journal) as a highly useful source of practical information for geoprofessionals working in the mineral resources sector.
Now the most recent issue of Applied Earth Science – Section B, Volume 125, Number 3 packs nine significant papers in 188 pages that demonstrate current leading practice for geologists working in the fields of exploration, resource estimation and mineral characterisation of mineral sands deposits.
To pick just one example : A non-conventional placer mineralisation type in the Murray Basin (Australia) with giant low-grade resources of fine-grained zircon is hosted in sheet-like beds that represent deposition in low-energy offshore (as opposed to coastal) environments; these are the so-called WIM-style deposits. The mass of zircon contained in this resource is huge but profitable mining depends on improved processing technology. Recently, a feasibility study of giant WIM 150 deposit was completed that extends over 40 km2. Estimates of measured, indicated and inferred mineral resources total 1650 Mt at a tenor of 3.7% heavy minerals (HM); HM from the 20 to 38 μm size fraction contain more than 40% ZrO2 and CeO2 (Klingner & Standing 2016). Based on reserves of 522 Mt at 4.3% HM composed of 21.6% zircon, 11.7% rutile, 5.9% leucoxene & 31.7% ilmenite, commencement of production in 2018 is under consideration by owner Australian Zircon NL.
Klingner, D. & Standing, C.A. (2016) WIM 150 mineral sand deposit, Murray Basin, Australia: geology and mineral resources. Applied Earth Science 125, 3, 121-127. DOI:10.1080/03717453.2016.1199505
back to top
Applied Earth Science (AES), a Useful Journal for Geological Practice (13 August 2016)
If you are tired of papers streaming out of ivory towers, lengthy and full of details, replete with elaborate lab methods and data that are inaccessible for most people working in industry, consider scanning AES for information that may really help you.
You may have noticed that not infrequently in these notes, I refer to articles from Applied Earth Science journal. AES is produced jointly by the Institute of Materials, Minerals and Mining (IOM3, U.K.) and the Australasian Institution of Mining and Metallurgy (AusIMM, Melbourne). Publishers are Taylor & Francis, a British science specialist. AES is “devoted to the application of the earth sciences in the exploration, discovery, development and exploitation of mineral resources”.
Please note that my position is member of the Editorial Board and of both professional societies mentioned above, and as an author – all without any financial interest. So let me tempt you with a few examples of the type of papers that I consider useful:
Are you working in gold exploration? – Look at the very informative article of Pitcairn, I. (2011) Background concentrations of gold in different rock types. Applied Earth Science 120, 31-38.
Heavy minerals and placers? Stanaway, K.J. (2012) Ten placer models from five sedimentary environments. Applied Earth Science 121, 43-51. Jones, G. & O’Brien, V. (2014) Aspects of resource estimation for mineral sands deposits. Applied Earth Science 123, 2, 86–94.
Rare Earth Elements? Hellman, P. L. & Duncan, R. K. (2014) Evaluation of rare earth element deposits. Applied Earth Science 123, 107–117.
Or the somewhat exotic exploitation of brines and salt? Border, S. & Sawyer , L. (2014) Evaporites and brines – geological, hydrological and chemical aspects of resource estimation. Applied Earth Science 123, 95–106.
If these examples intrigue you, you may i) apply for membership with IOM3 or with AusIMM to get free access; or you can ii) directly search the contents of AES in the website of Taylor & Francis and pay for single articles.
Taylor & Francis http://tandfonline.com/toc/yaes20/current/
back to top
Cryogenian Iron Formations of Rapitan Type – do they have Economic Significance? (12 July 2016)
Rapitan Type iron formations were deposited during or immediately following the nearly global Sturtian glaciation (~717- 660 Ma) but are absent from the younger Elatina or Marinoan (640 - 635 Ma: Rooney et al. 2015) glaciation (Cox et al. 2016). The two glaciations define the Cryogenian System (850-630 Ma) of the Neoproterozoic. During the Cryogenian, in a second prolonged oxydation step after the Great Oxydation Event (GOE, a protracted process between 2.5 and 2.1 Ga), modern atmospheric oxygen levels were attained (Kump 2014). The name Rapitan is derived from a Sturtian locality in the Mackenzie Mts., NW Canada. Similar occurrences are known in Africa, South America, South China and Australia (Cox et al. 2013).
During the Cryogenian ice ages, land and even equatorial oceans were widely, and possibly wholly covered with ice (“Snowball Earth” hypothesis: Hoffman et al. 1998).
- Fictional Snowball Earth during the Cryogenian Period of the Neoproterozoic Era (850 – 630 Ma). Source: Wikipedia public domain from Celestia Motherhole 2008
Glacial cover of restricted basins or of whole oceans caused anoxia and the presence of dissolved ferrous iron in seawater. εNd suggests that the source of the iron were mainly basalt-derived sediments (Cox et al. 2016). Inter- and postglacial melting of the ice resulted in deposition of glacial sediments (such as diamictites), re-oxidation of the oceans, and precipitation of ferric iron and manganese oxides. As marine sediments, Rapitan type iron formations consist of interbedded haematite and jaspilite (Cox et al. 2013), similar to Superior type BIF, but at present have little economic significance.
Is the latter statement correct? I’d be grateful for any information on mines, exploration, reserves or resources of Cryogenian iron ore.
Cox, G.M., Halverson, G.P., Poirier, A. et al. (2016) A model for Cryogenian iron formation. Earth Sci. Lett. 433, 280-292.
Cox, G.M., Halverson, G.P., Minarik, W.G. et al. (2013) Neoproterozoic iron formation: an evaluation of its temporal, environmental and tectonic significance. Chem. Geol. 362, 232–249.
Kump, L.R. (2014) Hypothesized link between Neoproterozoic greening of the land surface and the establishment of an oxygen-rich atmosphere. Proceedings of the National Academy of Sciences (PNAS) 111, 14062-14065.
Rooney, A.D., Strauss, J.V., Brandon, A.D. & Macdonald, F.A. (2015) A Cryogenian chronology: Two long-lasting synchronous Neoproterozoic glaciations. Geology 43, 459-462.
back to top
Breakthrough: Quick and Safe Carbon Dioxide Sequestration in Basalt (10 June 2016)
Recently in a short report in Science, the feasibility of carbon dioxide storage in basalt, derived from a geothermal power plant in Iceland, and the near- instant mineralisation of injected CO2 by newly formed carbonates was demonstrated (Matter et al. 2016).
The Hellisheidi power plant is the second-largest geothermal power producer in the World. Besides water vapour, it releases 40,000 tonnes CO2 and 12,000 tonnes H2S per year, typical for geothermal plants that are fed from a cooling melt body at depth. Magmatic gases are composed of about 90 mol percent H2O, 5–10 mol percent CO2, 1–2 mol percent sulfur species such as SO2 and (or) H2S, and lesser amounts of H2, HCl and HF. Often, they carry traces of metals such as copper and zinc and other elements. When the plant was built, a research project (CarbFix) was established in order to investigate the potential and feasibility of Carbon Capture and Storage (CCS).
Typical for Iceland, sited on a mid-oceanic rift, the local geology is made up of basaltic volcanic rocks and generally, the stress field is distensive. Basalts are favourable host rocks for carbon storage, because they are highly reactive due to contents of up to 25 weight % of calcium, magnesium, and iron that react with CO2 by forming carbonates such as calcite that are environmentally benign and geologically stable. Once stored within carbonate minerals that have a geological life of millions of years (Lackner 2003), the leakage risk of carbon dioxide is eliminated.
Note also, that basalts are one of the most common rock families on Earth, covering ~10% of the continental surface area and most of the ocean floor. Therefore, demonstration of successful deep storage at Hellisheidi is of global importance.
Novel technologies were tested and proved, such as dissolving the gas into down-flowing water in the well during its injection and injecting gas mixtures rather than pure CO2. Until now, purification of CO2 was a considerable economic burden for projects of this kind. Novel carbon tracking methods by chemical and isotopic tracers included admixture of carbon-14 (14C) in order to acquire precise data on the fate of the injected carbon.
Significant results of Matter et al. (2016) include the evidence that carbonate formation started immediately during injection and >95% of the injected CO2 was fixed (“mineralized”) through water-CO2-basalt reactions between the injection and monitoring wells within 2 years.
Although under different conditions, large-scale capture and geological sequestration of CO2 may still face technological and economic challenges, with this report the potential of CCS to be broadly applied is much improved. Earth scientists and engineers such as Matter et al. (2016) illustrate the potential. It is the governments that must provide clear regulations such as a general tax for carbon dioxide emissions (MacKay 2009) in order to assure companies of a long-term business perspective (Haszeldine 2009). Overall it is expected, that in a few decades, CO2 emissions from coal, oil and gas power stations will be reduced to unproblematic levels similar to the successful mitigation of SO2 and NOx. On that base, fossil fuels can yet provide long-term sustainable energy for the world’s industry and peoples (Haszeldine 2009, Jaccard 2006).
Find more information and images of the Hellisheidi power plant, and how to visit it, at https://www.extremeiceland.is/en/information/about-iceland/hellisheidi-geothermal-power-station
Matter, J.M., Stute, M., Snæbjörnsdottir, S.O. et al. (2016) Rapid carbon mineralization for permanent disposal of anthropogenic carbon dioxide emissions. Science 352 (6291), 1312-1314. [doi: 10.1126/science.aad8132]
back to top
RIO TINTO Brownfield Mines – Remediate or Extract Remaining Resources? (25 May 2016)
The Iberian Pyrite Belt (IPB) in Southwestern Europe with the giant abandoned Río Tinto mines is an outstanding example for this antagonism. Let us first look at the geological and environmental situation:
The IPB is an arcuate volcanic-sedimentary belt of Lower Carboniferous age that contains one of the greatest concentrations of sulphide (mainly pyrite) mineralisation on Earth, with resources in excess of 1700 Mt of sulphide totalling 15 Mt Cu, 13 Mt Pb, 35 Mt Zn, 46 kt Ag and 880 t Au (Adamides 2013). It originated in a supra-subduction setting during the final stages of the collisional assembly of Africa with Iberia, which ended with the formation of Supercontinent Pangaea. About 100 deposits form this metallogenetic province and during >4500 years, hundreds of mines have exploited metals and sulfur. The largest cluster of ore bodies is the Río Tinto mining district that prior to erosion and mining, contained an estimated 500 Mt of massive sulphide and a considerable volume of auriferous gossan.
“Perhaps the most infamous historical mine wastes are those in the Río Tinto Mining District in Andalusia, Spain” (Hudson-Edwards 2016)
Situated at the sources of the Tinto river, the Río Tinto mine is the subject of hot debates in science and environmental communities concerning causation and mitigation of acid drainage and metal contamination affecting the river. Mining at Río Tinto had a first flush in 2500 BCE marked by a metal spike in the river’s estuary (Leblanc et al. 2000) and finally closed in 2001. Remediation at closure was limited; Río Tinto mine was more or less abandoned. Presently, parts of the mine are exhibited as part of a mining museum. In recent years, work is in progress towards opening a new mine (Adamides 2013), though not without opposition.
The Tinto river is 90 km long. Its mean discharge is relatively small—about 15 m3/s; flow ranges from 1 to 100 m3/s depending on seasonal variations, that include dry spells and rainy periods with floods. The Tinto river sediments are gray sands, including quartz, rock particles and abundant detrital pyrite grains that are weakly weathered and slightly rounded (Leblanc et al. 2000). Pebble beds above the water line are coated by ochreous rinds of earthy minerals such as goethite, jarosite and schwertmannite (see Photograph). Ochre formation is one of several processes that induce an attenuation of the solute load along the course of Río Tinto towards the coast (Cánovas et al. 2014).
- Río Tinto some kilometers downstream of the brownfield mining area. The photo dates from the wet season, when the water is not red and the pH tends towards neutral. Riparian vegetation is healthy but the banks are marked by ochre.
There is little doubt that the heritage of large-scale industrial mining that started at about 1850 is a major cause of the present acid mine drainage (AMD) and its effect on the river. Yet, as a geologist, I am sensible to data concerning the state of the river in the geological past. Today, Tinto river is marked by high acidity (pH 1.5–2.5), a high solute load with a rich suite of mineral precipitates and the name-giving red colour in dry seasons, and, surprisingly, a unique, rich fluvial biodiversity of extremophiles (plants, eucaryotes, photosynthetic algae, microorganisms, fungi) that even caught the attention of Mars research (Fernandez-Remolar et al. 2005). Before mining, large supergene copper-silver enrichment ore bodies and auriferous gossans existed at the later Río Tinto mine. Undoubtedly, a large mass of acidity must have passed from the oxidizing sulfides into the river and through the Huelva estuary into the Atlantic Ocean. Indeed, traces of this passage are preserved in three terraces of Río Tinto, the oldest dated at 2 ± 0.1 Ma (Fernandez-Remolar et al. 2005). Ferruginous layers in the terraces display clear evidence that in the geological past, the river precipitated the same minerals and supported the same life forms as at present. And when did the river and its biota acquire their present characteristics? When and how fast developed the singular acidophilic ecosystem? It appears likely, that the supergene history of the district began in the Eocene (early Tertiary), ca. 55 million years ago, when the global climate was hot and humid (the last “hothouse Earth” in geological history). Afterwards and until today, weathering must have progressed in a stop-and-go fashion, as climate varied.
What would be your advice to the authorities in Andalusia? Ban all future mining and remediate at all costs, or encourage the exploitation of remaining ore? The first would have to be paid by the taxpayer, Spanish or European, whereas the second might contribute to restoration costs and develop into a showcase of modern green mining. – I vote for the latter decision!
Adamides, N.G. (2013) Río Tinto (Iberian Pyrite Belt): a world-class mineral field reopens. Applied Earth Science 122, 2-15.
Cánovas, C.R., Olías, M. & Nieto, J.M. (2014) Metal(loid) attenuation processes in an extremely acidic river: The Río Tinto (SW Spain). Water Air Soil Pollut 225: Article 1795
Fernandez-Remolar, D.C., Morris, R.V., Gruener, J.E., Amils, R. & Knoll, A.H. (2005) The Rio Tinto basin, Spain: Mineralogy, sedimentary geobiology, and implications for interpretation of outcrop rocks at Meridiani Planum, Mars. Earth and Planetary Science Letters 240 (1): 149–167.
Hudson-Edwards, K. (2016) Tackling mine wastes. Science 352, 288-290. DOI: 10.1126/science.aaf3354
Leblanc, M., Morales, J.A., Borrego, J. & Elbaz-Poulichet, F. (2000) 4500-year-old mining pollution in southwestern Spain: long-term implications for modern mining pollution. Economic Geol. 95, 655-662.
back to top
Bliss – Geological Underground Mapping (11 April 2016)
Recently, I spent one week dedicated to geological underground mapping. Already as a student, I loved this work and I still do. Assembling data step by step and constructing a 3D image of the geological situation in a confined space from limited exposures is intellectually (and physically) most rewarding.
Allow me to cite updated text concerning mine mapping from section 5.3.1 of my Economic Geology (2011) book:
Geological mapping of natural outcrops and of man-made exposures is the most important task of the mine geologist. A complete and up-to-date documentation of all geological data is the precondition for both day-to-day management (first of all ore production: Daniels & Mascini 2012) and for serious decisions concerning, for example, a large drilling program, or for the mine and district-scale water management. Field mapping should be carried out at suitable detail (e.g. at 1:1000; note that data in modern software being scalable, such figures rather indicate the needed resolution), whereas display scales of geological mine maps and sections should be equal to the geodetic mine plans. The area surrounding the mine is typically mapped at a scale such as 1:10,000. Airborne or satellite-based synthetic aperture radar interferometry (InSAR) and LIDAR (light detection and ranging) processed into digital elevation models (DEM’s) may provide precise topographical base maps. LIDAR is able to penetrate vegetation cover. Quarry slopes are often surveyed with ground-based LIDAR scanners. Orthophoto-like images are made by surveying pits and the mine near-field with unmanned aerial vehicles (UAVs or “drones”). Acquisition of geological and other field data is increasingly executed through personal digital assistants (PDAs) and tablet PCs (Thum & de Paoli 2015).
Never neglect preparing geological overview sections through the mine. One mine I got to know as a forensic expert suffered a catastrophic mud inrush because a stope was driven upward into water-logged hangingwall sediments. Nobody had ever asked where exactly the hard rock/overburden boundary was. This mine had to be abandoned.
Modern mine management software packages includes components for geological work but GIS software, Leapfrog®, Maptec’s Vulcan® and Micromine®, or powerful 3D modelling tools such as Paradigm GOCAD® may be employed for handling multiple data sources (geological maps and sections, geophysics, drillhole logs; Saalmann & Laine 2014). Integrated digital processing of geological data and of mine planning is standard in most mines. The practical arts of geological mine mapping have been admirably described by McKinstry (1948), but consult also Marjoribanks (2010) and Lisle et al. (2011).
Daniels, A. & Mascini, J. (2012) The benefits of mine-scale three-dimensional structural modelling at Macraes gold mine, central Otago, New Zealand: a case study. Applied Earth Science (Trans. Inst. Min. Metall. B) 12, 3-11.
Lisle, R.J., Brabham, P., Barnes, J.W. (2011) Basic geological mapping. 5th ed., 230 pp., Wiley-Blackwell.
Marjoribanks, R. (2010) Geological methods in mineral exploration and mining. 2nd ed., 238 pp, Springer.
Thum, L. & de Paoli, R. (2015) 2D and 3D GIS-based geological and geomechanical survey during tunnel excavation. Engineering Geol. 192, 19–25.
back to top
Exploring in Europe? Investigate the Minerals4EU Website! (9 March 2016)
If you should be the Exploration Vice President of an overseas enterprise considering to look for potential targets in EU-Europe, you might profitably consult the Minerals4EU facility, as described in their homepage.
The Minerals4EU facility aspires to bring Europe’s minerals related geodata into one, virtual, place through a web portal so that users can more easily get the information they need, directly onto their computer, and free-of-charge. The Minerals4EU facility is based on an EU mineral intelligence network delivering the web portal including a GIS based facility, a European Minerals Yearbook and a Foresight Study. The EU minerals intelligence network comprises foremost EU-European national geological surveys. It publishes data, information and knowledge on mineral resources around Europe. In mid-2015, the website went online. Users may find, view and acquire standardized and harmonized georesource and related data, such as geological and mine maps, information on geophysical data, and papers that locate and describe mineral deposits, districts and provinces.
If you are acquainted with the standard of Australian support for mineral explorers, Mr. VP, you may be somewhat disappointed. This has several causes:
- (1) The European Union is a chessboard of national states with different languages, legal systems and cultures.
- (2) Reporting on geology, minerals and mining is not easily transformed into a standard.
- (3) Geophysical coverage of scales that serve exploration is patchy and rarely transgresses borders.
- (4) There may be more shortcomings, but let us pass ...
Yet, the Minerals4EU initiative must be lauded. In time, it may grow into a wonderful resource such as the services provided by Geoscience Australia . If you, Mr.VP, have the funds to assign staff or a consultant to a thorough search concerning your favoured mineral or metal and deposit type, this will be worth it. Minerals4EU will serve as a spring board to more detailed information.
Europe may not be the first choice for globally operating exploration, but it offers strategic advantages and a great diversity of mineral deposits, from Archaean Ni-komatiites to Proterozoic and Palaeozoic iron, gold, rare and base metals, Mesozoic copper porphyries, and Cenozoic epithermal gold. Along the Mediterranean, subduction-related and volcanogenic deposit formation extends into the Holocene. You are aware that giant Rio Tinto has entered the scene (in former Yugoslavia)?
back to top
What is metallogeny? Is it of any Use? (10 February 2016)
The term METALLOGENY was coined by Louis de Launay (1860-1936), who is described as the greatest French geologist ever (see link below). He is still remembered for his lucid descriptions of the giant gold and diamond deposits in South Africa. Let us commemorate the 80th anniversary of his death.
De Launay (1913) created single handedly the science of metallogeny and discovered most of the principles that we still connect with it, although not necessarily with the same words. Here I refer to concepts such as metallogenetic* districts, epochs, maps, metallotects and provinces. He also established a rational genetic classification of mineral deposits.
Today, the “Glossary of Geology” (Neuendorf et al. 2005) defines the term as follows: Metallogeny - the study of the genesis of mineral deposits, with emphasis on their relationship in space and time to regional petrographic and tectonic features of the Earth’s crust.
The scale of metallogenic studies is always regional in extent; I believe that the term should not be applied for the genetic study of one specific deposit. Often, metallogenetic studies include the whole crustal section and may involve parts of the mantle. Fundamental questions typically asked are the source of metals and the circumstances of their mobilisation, migration and eventual enrichment resulting in ore deposit formation.
Ore deposit formation is a function of the Earth’s process systems. Like our understanding of these systems, metallogeny is not a consolidated body of knowledge but an assemblage of structured and unstructured information in perpetual flux.
Most tangible is metallogeny in the printed metallogenetic maps that were produced in the second half of the 20th Century, in order to allow a synopsis of metallogenetic, geological (metallotects) and basic economic data (e.g. the size of deposits). This work improved understanding, but the promised boost of exploration successes was meager. New finds were rather due to application of novel technologies such as remote sensing. The almost global availability of mineral deposit data, however, must have guided numerous investment decisions and exploration programmes.
Currently, digital media and supporting mineral deposit data banks are replacing the printed maps; stacked data (including geology, geophysics, geochemistry etc.) are analysed in GIS or comparable software, often draped over satellite images or digital elevation models (DEMs). Spatial metallogenetic information still serves scientific interests, but its main use is practical, for estimates of undiscovered resources and mineral deposits, and for mapping mineral prospectivity that facilitates strategic planning of exploration (e.g. Carranza & Sadeghi 2010). Modern mineral prospectivity modelling relies on a process-based, or “mineral systems” approach; although the processes cannot be directly observed or mapped, they can be translated into proxies such as wide alteration halos or syngenetic faults that may be recognizable.
Would you support my conclusion that although printed metallogenetic maps are a thing of the past, research of ore deposit formation and its mappable proxies ("metallotects") remains an essential component of high-tech resource estimates, prospectivity modelling and exploration?
*A linguistic note: In British English, the word “metallogenic” refers to an element that occurs as an ore or a naturally occurring metal (e.g. gold). Metallogenetic, in contrast, is something relating to metallogeny (The Chambers Dictionary, 10th ed. 2006).
Carranza, E.J.M. & Sadeghi, M. (2010) Predictive mapping of prospectivity and quantitative estimation of undiscovered VMS deposits in Skellefte district (Sweden). Ore Geology Reviews 38, 219–241.
Launay, Louis de (1913) Traité de métallogénie : gîtes minéraux et métallifères : gisements, recherche, production et commerce des minéraux utiles et minerais, description des principales mines (3 volumes), Paris, C. Béranger.
http://www.annales.org/archives/x/launay.html (Louis de Launay’s life and work; in French language; accessed 10 February 2016)
back to top
Anthropocene Revisited – Is Formalisation Useful for Geology? (16 January 2016)
Recently, a paper in Science (Waters et al. 2016) described the profound influence of humans on Earth surface processes. In conclusion, the two dozen authors support formalisation of the Anthropocene as a new Epoch (equal to Holocene or Pleistocene) in the Geological Time Scale. Recognizing that human impact started with ice age hunters and accelerated to our days, the authors do not settle on a specific event or year but propose more research. Yet they state, that the start of the Anthropocene may be defined by a Global Standard Stratigraphic Age (GSSA) coinciding with detonation of the Trinity atomic device at Alamogordo, New Mexico, on 16 July 1945 CE, or with global fall-out signatures from nuclear tests that peak in about 1963.
The impact of humanity on the Earth is excellently summarized and the paper* is a very useful source of hard data on man-made global change. Yet I feel that there is one big misunderstanding on the part of the authors – they do not describe rocks but mainly processes and their signatures, such as nuclear fall-out, accelerated extinction of species, increase of CO2 in the atmosphere, and climate change. And, strangely, they describe the onset of a geological epoch; rather a point in geological time, or an initial event, than its evolution.
In arguing for the formalisation of the Anthropocene as a new geological Epoch the authors neglect to ask if this will be of any use for geological practice and research. – I would not deny, however, that it will make catchy headlines in grant applications and in the media, but what about the geologist in the field?
Waters et al. refer to waste dumps (of mines or cities) as examples of Anthropocene deposits. But already now it is common practice to depict such features on geomaps. Is it of geological interest to separate pre- and post-1945 waste? Shall we measure traces of fall-out nuclides in dumps or soil in order to determine an Anthropocene age? Or, because practically the whole Earth is already impacted by humans, certainly by nuclear fall-out, shall we simply call all surfaces Anthropocene in age?
In my opinion, formalisation of the term “Anthropocene” as a new geological Epoch is useless for geologists and is therefore redundant.
You may also look at an earlier News Weblog on my website (News Archive 2015): The Anthropocene – a Voice of Reason (24 March 2015)
*Waters, C.N., Zalasiewicz, J., Summerhayes, C. et al. (2016) The Anthropocene is functionally and stratigraphically distinct from the Holocene. Science 351, pp. DOI: 10.1126/science.aad2622
back to top