High-grade Deposits Research Articles

The re-direction of small deposit mining: Technological solutions for raw materials supply security in a whole systems context

Large-scale mining of low-grade ores is energy-intensive and generates vast wastes. It has limited suitability for production of specialist metals that are required in relatively small quantities. An approach that limits environmental impact by restricting mining to high-grade deposits requires the investigation of small ore deposits as alternative sources of metals. The return on investment from small deposits is incompatible with the expensive surveys needed to secure investment and the high costs of managing risk. But increasing energy and transport costs may create space in the market for small-deposit mining with highly-competitive technological solutions. It can be argued that small-deposit mining is ethical because it must involve cooperation between mining companies and local residents who share a collective expectation and responsibility for their quality of life. However, small-deposit mining tends to be a limited, short-term initiative, which requires consideration of the extended ‘afterlife’ of mines. This manuscript is the culmination of five years of cross-sector dialogue and stakeholder engagement activities. It debates what constitutes a small deposit and describes the interactions between mining and manufacturing, investment, environment and society. It reaches the conclusion that technological innovations will support the re-emergence of small deposit mining as an important part of a diverse raw materials production sector. We do not suggest a return to past approaches, to mining of small, high-grade deposits, but a consideration of alternative narratives of localised, community-orientated mining processes, thus giving social, economic and environmental context to the needs of the present day.

Virtues of fluorite-case of Bou-Izourane fluorite

Fluorite minerals are among the non-metallic natural substances that have played an important role in the industry for decades. The economic importance of each of the grades of fluorite marketed meets precise chemical specifications such as its melting quality and fluor content. They also provide specific and very diverse outlets: iron and steel industry, aluminum metallurgy, plastics manufacturing, solvents, refrigerants, welding, glassmaking, cement industry, etc. In Morocco, fluorite is a very important resource because of its multiple high-grade deposits, which currently make it the 8th largest producer of metallurgical fluorite concentrate in the world with 70 kt produced per year. In the Moroccan High Atlas, the fluorite district of Bou-Izourane, located 40 km south of the city of Midelt, is estimated to be one of the most important fluorite deposits in Morocco. There are at least four violet fluorite sites in this district, the two deposits of Bou-Izourane and Bou-kharouba in the eastern part of the study area. The western part of the Bou-Izourane region hosts the two other deposits (Tabja and Bou-Imtessene). Although the Bou-Izourane fluorite is more or less colored (Violet-Lilac) with remarkable quality and perfect transparency, its uranium content, especially at the Tabja and Bou-Imtessene sites, is quite high (97.4–188.5 ppm). This property of uranium richness is an axis of research in addition to the determination of its physico-chemical characteristics, which will define the virtues and the fields of use of this fluorite. This document has been written in the hope that it will be of some use in highlighting the potential of the fluorite of the Moroccan Bou-Izourane deposit.

Carbonate-hosted clay-type lithium deposit and its prospecting significance

In recent years, the clay-type lithium resources have attracted increasing attention due to their large scale, stable distribution, low cost of mining and utilization. Comparing with the traditional pegmatite-type and brine-type lithium deposits, it has become an important direction of exploration of new type lithium resources. The clay-type lithium resources reported have genetic relationship to volcanic materials. Through systematic research and review, this paper first proposed the genetic concept of “carbonate-hosted clay-type lithium deposit”, which was related to carbonate weathering-sedimentation. Li-rich clay rocks found at present mainly include the Jiujialu formation (C1 jj ) of lower carboniferous in Guizhou Province and Daoshitou formation (P1 d ) of the lower Permian in central Yunnan Province. Although the different formation ages of the two sets of Li-rich strata in this study, their lithology is relatively similar to the section upward, including: (1) Aluminized clay rocks, local iron bearing; (2) compact aluminaceous clay rocks; (3) bean oolitic aluminaceous clay rocks; (4) loose soil-like clay rocks, among which the dense aluminaceous clay rocks and pisolitic aluminaceous clay rocks are the most favorable lithology for lithium enrichment. The results of XRD analysis show that the major minerals of clay rocks are hydralite, bomberite, montmorillonite, illite, kaolinite, anatase, rutile, zircon and pyrite. According to the analysis of more than 1000 samples from more than 30 profiles, it is shown that most of the samples from two sets of Li-rich strata have reached the comprehensive utilization index of lithium in bauxite (Li2O ≥500 μg/g), and the average Li2O content in the clay rocks is about 0.3%, and the highest is 1.1%. The detailed micro-analysis using Tof-SIMS technique has shown that lithium was mainly distributed in clay minerals, and mainly occurred in amorphous clay minerals identified as montmorillonite. The trace and major elements suggest that the weathering of underlying carbonate rocks provides a source of Li-rich clay rocks. Detailed field observations in combination with trace element geochemical analysis (such as high lithium samples of Sr/Ba ratio is generally less than 0.5, MgO/Al2O3 ratio less than 1, Rb/K ratio is less than 0.003, Ni/Co ratio greater than 5), indicate that oxygen-poor and low-energy coastal marshes, lagoons and limited and closed ancient bay (basin) in the transitional environment may be ideal places for Li enrichment to form high-grade deposits. Therefore, the main geological and geochemical characteristics of this new type can be summarized as: (1) The ore-forming material is derived from the underlying carbonate formation; (2) lithium mainly exists in the smectite phase by adsorption; (3) the sedimentary environment plays an important role in the enrichment of lithium, the limnic basin in coastal plain was an ideal place for lithium accumulation; (4) in addition to Li, there may be Ga and REE enrichment occurring in this type clay. According to this new metallogenic model, it has obtained 340000 tons of lithium oxide resources in Dianzhong basin by geological exploration, reaching a super-large class deposit. Due to the numerous regions with similar ore-forming conditions of these type lithium resources, it can be expected that “carbonate-hosted clay-type lithium deposit” will become an important source of lithium resources in China.

Applying Receiver-Operating-Characteristic (ROC) to bulk ore sorting using XRF

As high grade deposits become depleted, the mining industry is challenged by mining lower grades that require the use of non-selective bulk mining methods. Bulk ore sorting can reduce the dilution of the mined ore thereby preventing costly processing of low grade waste while improving the quality of material reporting to the processing plant. X-Ray Fluorescence (XRF) is one of the sensing technologies used for bulk ore sorting. The grade of the bulk material is predicted based on XRF measurement that is correlated to a grade using a calibrated algorithm. The effectiveness of XRF bulk sorting depends on the accuracy of the grade classification of the scanned material. False classification is attributed to poor performance of the sorting algorithm to correlate the measurements with the assay grades.The paper presents an approach to analyze XRF measurements that reduce misclassification of material. Receiver Operating Characteristic (ROC) was applied as the tool in classification of bulk materials. The performance of this approach was compared to conventional sorting algorithm, namely, simple linear regression (SLR), where XRF responses was linearly correlated to the assay grades. The ROC approach was found to result in more accurate classification and enhanced economics performance of the bulk ore sorting system.

Geometallurgical Approach for Implications of Ore Blending on Cyanide Leaching and Adsorption Behavior of Witwatersrand Gold Ores, South Africa

Gold production in South Africa is projected to continue its decline in future, and prospects for discovery of new high-grade deposits are limited. Many of the mining companies have resorted to mining and processing low-grade and complex gold ores. Such ores are technically challenging to process, which results in low recovery rates, excessive reagent consumption and high operating costs when compared to free-milling gold ores. In the Witwatersrand mines, options of blending low-grade gold ores with high-grade ores exist. Although it is well known that most of the Witwatersrand gold ores are highly amenable to gold cyanidation, not much is known on the leachability of blended ores, especially the effects of mineralogical and metallurgical variability between different gold ores. In this study, we apply a geometallurgical approach to investigate mineralogical and metallurgical factors that influence the leaching of blended ores in a set of bottle shaker and reactor column tests. Three gold-bearing conglomerate units, so-called reefs, i.e., Carbon Leader Reef, Ventersdorp Contact Reef and the Black Reef, all in the Carletonville goldfield, were sampled. The ores were prepared using a terminator jaw crusher followed by vertical spindle pulverizer (20 kg aliquot) and high-pressure grinding rolls (80 kg aliquot). Mineralogical analysis was conducted using a range of complementary tools such as optical microscopy, QEMSCAN and micro–XCT. The results show that Witwatersrand gold ores are amenable to the process of ore blending. Some of the ores, however, contain impervious inert gangue and reactive ore minerals. Leach solution can only access gold locked in impervious gangue minerals through HPGR-induced pores and/or cracks. The optimum ore blending ratio of the bottle shaker experiments (p80 = − 75 μm) comprises 60% Carbon Leader Reef, 20% Ventersdorp Contact Reef and 20% Black Reef and yields 92% recovered Au over a leach period of 40 h. Blended ores with high carbonaceous material (> 1 wt% carbonaceous material, (Black Reef = 36–60%) yield lower recoveries of 60–69% Au). Ore leaching at the mixed-bed reactor column (− 75 μm and − 5.6/+ 4 mm) yields about 70% over a leach period of two weeks. We therefore suggest that the feasibility of ore blending is strongly controlled by the mineralogy of the constituent ores and that a mixed-bed reactor may be a viable alternative method for leaching of the low-grade Witwatersrand gold ores. Material from certain reefs, such as the Black Reef, has synergistic/antagonistic (nonadditive) blending effects. The overall implication of this study is that ore blending ratios, effects of comminution on mineral liberation, an association of gold with other minerals, and gold adsorption behavior will greatly inform future technology choices in the area of geometallurgy.

Advances in mineral processing technologies related to iron, magnesium, and lithium

Abstract Exploitation and utilization of mineral resources have played a vital role in China’s rapid economic developments. Although the history of mineral processing is quite long, technologies in this field have varied with the changes of market demands. This is particularly the case for minerals whose high-grade deposits are depleting. The aim of this review is to present our recent efforts on developing new routes for the utilization of low-grade minerals, such as iron ores and brine-containing lithium. The emphasis on the two minerals lies in the fact that iron plays a vital role in modern-day civilization and lithium is a key component in electric vehicles for transportation. Furthermore, the utilization of magnesium chloride reserves, one of the largest wastes in western China, as raw materials for fabrication of functional materials is also included in this review.

Mineral grades: an important indicator for environmental impact of mineral exploitation

We have collected and analysed grade information for nine metals: copper, gold, iron, lead, manganese, nickel, PGM, tin, and zinc. Based on this analysis, we have developed a proposal of “grade classes”, i.e., what could be considered low-grade, average-grade, and high-grade deposits for all these metals. We discuss the implications of possible developments into the future of the grades of ores, from which these metals are extracted. A focus on high-grade deposits will naturally reduce the environmental impact of mining. For six metals (copper, gold, iron, nickel, PGM, and zinc), we have further analysed the volumes available for the 10% cohort of projects and operating mines with the highest grades. Three metals (iron, PGM, and zinc) show considerable volumes, between 15 and 20% of total metal content in resources in this high-grade percentile. Copper and gold have between 5 and 10% while nickel has only 1.7% in the highest 10% grade percentile.

Geophysics of the Patterson Lake South Uranium Deposit, northwestern Saskatchewan

The Athabasca Basin’s major uranium deposits and mines are generally proximal to graphitic conductors (reducing environment) and accompanied by an alteration ‘halo’ which is usually a resistive low, but can also be silicified (resistivity high). The sandstone environment is normally highly resistive which makes things ideal for EM detection of weaker graphitic conductors at depth. The Triple R deposit on Fission Uranium Corp’s Patterson Lake South Property is located in Canada’s Athabasca Basin, home to the world’s richest uranium mines. It is the only major, high-grade deposit in the region that is potentially open-pitable and is the largest mineralized trend in the region - currently standing at over 3 km in length. Patterson Lake South is unconventional in that virtually all the major high grade uranium deposits have been inside the basin margins and were on the east side of the Athabasca Basin; whereas Patterson Lake South lies outside the basin margins and is on the west side of the Basin. The Patterson Lake South discovery is chronicled from the initial airborne radiometric and EM surveys, to ground follow-up using DC resistivity and induced polarization, horizontal loop EM, moving loop TEM and radon survey, leading up to the discovery holes. The deposit shows excellent correlation with a VTEM conductive ‘bright spot’, an interpreted conductor and a resistivity low segment. Also significant is the evidence of cross structure seen in the resistivity at the west side of the displayed deposit outline. The continued success of the resource delineation and expansion is attributed to the dedicated Fission staff for their work to bring the project forward. From Discovery to Resource Estimate, the Triple R Deposit was achieved in just two years of drilling.

Mineral Deposits in the Ontario Cobalt Belt

Recent exploration by Battery Mineral Resources Limited has located numerous cobalt-arsenic-(silver, gold, nickel, copper) deposits in eastern Ontario. The deposits are located within a 250 kilometre zone located north of Sudbury and trending east across the Quebec border. Deposit types include sulphide-carbonate vein systems, skarn, massive sulphide and sulphide breccia. This talk provides an update on the geology and exploration of several high-grade cobalt deposits within this belt.

IMPaCT, Integrated Modular Plant and Containerised Tools for Selective, Low-impact Mining of Small High-grade Deposits, Horizon 2020

IMPaCT, Integrated Modular Plant and Containerised Tools for Selective, Low-impact Mining of Small High-grade Deposits, Horizon 2020

Purification of High-grade Calcite Ore by Flotation with Alkyl Diamines

A very high-grade calcite deposit located in northern Norway consists of CaCO3 ore with minor silicate and sulphide impurities. Cationic (Tallow-1,3-diaminopropane, Duomeen T) collector has been used in the purification of calcite by flotation with an aim of achieving calcite concentrate for its use in value-added products in a variety of industries. The feasibility of sulphide flotation from calcite by this cationic collector has been initially judged from Hallimond flotation and zeta potential on pure mineral systems and the results illustrate the removal of sulphide from calcite ore at neutral pH region. The adsorption mechanism of diamine on both the sulphide minerals was found to be the same by zeta potential studies. The variations in zeta potential are in good agreement with the adsorption of diamine molecular and ionic species as a function of pH. FTIR studies also showed the adsorption of diamine species in agreement with the zeta potential and Hallimond flotation results. Furthermore, the removal of sulphide impurities with selective flotation by diamine collector was performed in bench-scale flotation with the calcite ore and the results indeed showed that the calcite concentrate could meet the quality requirements for its use in the paper industry for coating and filler purposes.

Metal endowment reflected in chemical composition of silicates and sulfides of mineralized porphyry copper systems, Urumieh-Dokhtar magmatic arc, Iran

The present work attempts to discriminate between the geochemical features of magmatic-hydrothermal systems involved in the early stages of mineralization in high grade versus low grade porphyry copper systems, using chemical compositions of silicate and sulfide minerals (i.e., plagioclase, biotite, pyrite and chalcopyrite). The data indicate that magmatic plagioclase in all of the porphyry copper systems studied here has high An% and Al content with a significant trend of evolution toward AlAl3SiO8 and □Si4O8 endmembers, providing insight into the high melt water contents of the parental magmas. Comparably, excess Al and An% in the high grade deposits appears to be higher than that of selected low grade deposits, representing a direct link between the amounts of exsolving hydrothermal fluids and the potential of metal endowment in porphyry copper deposits (PCDs). Also, higher Al contents accompanied by elevated An% are linked to the increasing intensity of disruptive alteration (phyllic) in feldspars from the high grade deposits. As calculated from biotite compositions, chloride contents are higher in the exsolving hydrothermal fluids that contributed to the early mineralization stages of highly mineralized porphyry systems. However, as evidenced by scattered and elevated log (fH2O)/(fHF) and log (fH2O)/(fHCl) values, chloride contents recorded in biotite could be influenced by post potassic fluids. Geothermometry of biotite associated with the onset of sulfide mineralization indicates that there is a trend of increasing temperature from high grade to low grade porphyry systems. Significantly, this is coupled with a sharp change in copper content of pyrite assemblages precipitated at the early stages of mineralization such that Cu decreased with increasing temperature. Based on EMPA and detailed WDS elemental mapping, trace elements do not exhibit complex compositional zoning or solid solution in the sulfide structure. Nevertheless, significant amounts of Cu and Au are contained in pyrite assemblages as micro- to nano-sized inclusions, especially in the high grade fertile porphyry deposits. However, unexpectedly high concentrations of Te, Se, and Re may be associated with early stage of sulfide mineralization, especially when there is no epithermal lithocap. This may highlight the significance of trace metals partitioning in the sulfides formed at the early stages of mineralization in PCDs.

Mineral Resources and Sustainable Development

Mineral resources have been used for millennia and are a key to society9s development. With the growing importance of new technologies and the energy revolution, questions have arisen regarding the future availability of resources of metals and industrial minerals. As discovering large high-grade deposits has become increasingly rare, the concept of “sustainable development” will become viewed as essential to extract metals/minerals from new low-grade deposits. In addition to economic considerations, it is essential to reconcile mining activity with environmental protection and to allay the concerns of local populations. This issue of Elements highlights the progressive movement towards an active environmental and societal strategy for sustainably harnessing mineral resources.

Adhesion Studies of Microorganisms on Natural Ore Material

In the course of the decline of high-grade ore deposits, new effective and eco-friendly bioleaching techniques are of interest. In-situ leaching is an auspicious method, but composition of leaching community should be adapted to the respective external conditions and the ore material. In this study several sulfidic minerals were inoculated into acidic mine water of a mine in eastern Germany, housing members of well-known iron oxidizing bacteria like Acidithiobacillus, Leptospirillum and Ferrovum. The attachment tests were performed in batch and in a continuous way at different temperatures. The analysis of the extracted DNA from adhered cells showed an enrichment of Ferrovum spp. on chalcopyrite surface under in-situ conditions at 11°C. For laboratory batch conditions an accumulation of Leptospirillum spp. was detected for adhered cells probably due to the changes of the physicochemical parameter of the mine water. In more detailed analyses we aim to elucidate possible preferential attachment of the mine water community members to certain minerals.

Sedimentary and Igneous Phosphate Deposits: Formation and Exploration: An Invited Paper

Phosphorus is the central ingredient in fertilizer that allows modern agriculture to feed the world’s population. This element, also critical in a host of industrial applications, is a nonrenewable resource that is sourced primarily from the phosphatic mineral apatite, hosted in sedimentary and igneous ores. World phosphate resources are estimated by the U.S. Geological Survey at ca. 300,000 Mt, of which 95% are sedimentary and 5% are igneous. Current known USGS reserve estimates are sufficient for a maximum of 200 to 300 years; the exploration and discovery of new resources, enhanced mining technologies, and new technologies aimed at the recovery and recycling of P from sewage and agricultural runoff will all contribute to extending P production. Igneous ores are generally associated with Phanerozoic carbonatites and silica-deficient alkalic intrusions that typically average 5 to 15 wt % P 2 O 5 , which can be beneficiated to high-grade concentrates of at least 30 wt % P 2 O 5 with few contaminants. Carbonatites are typically the smallest and youngest parts of a carbonatite-alkaline rock complex that formed during fractional crystallization of a calcic parental alkaline silicate melt, or from liquid immiscibility of a carbonate-rich nephelinite that underwent magmatic fractionation and differentiation during ascent from the mantle source. Fluorapatite generally crystallizes early, near the liquidus, and over a small temperature interval below the apatite saturation temperature that varies strongly with temperature, SiO 2 and CaO concentrations, and the aluminosity of the melt. Carbonatite-alkaline rock complexes commonly possess a concentric, zonal structure thought to reflect caldera volcanism. Pathfinder elements in soils, sediments, tills, and vegetation include Nb, rare earth elements (REEs), P, Ba, Sr, F, U, and Th, and in water, F, Th, and U are indicators. Remote sensing techniques with the ability to identify minerals rich in CO 3 , REEs, and Fe 2+ that are characteristic of carbonatites are also important exploration tools that may provide vectors to ore. Sedimentary phosphorite is a marine bioelemental sedimentary rock that contains >18 wt % P 2 O 5 . While small peritidal phosphorites formed in Precambrian coastal environments, economically significant upwelling-related phosphorite did not accumulate until the late Neoproterozoic and continued through the Phanerozoic. Coastal upwelling delivered deep, P-rich waters to continental shelves and in epeiric seas to drive phosphogenesis and form the largest phosphorites on Earth. High-grade deposits formed as a result of hydraulic concentration of phosphate grains to form granular beds with minimal gangue. The amalgamation of these beds into decameter-thick, stratiform ore zones is generally focused along the maximum flooding surface, which is a primary exploration target in upwelling-related phosphorite. In addition to P, other elements concentrated in igneous and sedimentary phosphorites are Se, Mo, Zn, Cu, and Cr, which are important agricultural micronutrients. Other saleable by-products include U and REEs. The U concentration in sedimentary phosphorite is generally between 50 and 200 ppm, but can be as high as 3,000 ppm, making it an increasingly important source of U for the nuclear industry. The concentration of REEs in some sedimentary phosphorites is comparable to the world’s richest igneous and Chinese clay-type REE deposits. The source of the dissolved P in upwelling ocean water is ultimately derived from the chemical weathering of continental rocks, the process that links igneous and sedimentary phosphorites through time and space. The covarying temporal relationship of igneous and sedimentary deposits suggests that plate tectonics and the concentration of apatite in a progressively more felsic crust underpins the feedback processes regulating the biogeochemical cycling of P. Critical to the generation of greenfield exploration targets is the recognition that large P deposits emerged in the late Neoproterozoic. The geological environments conducive for exploration can be constrained from an understanding of ore-forming processes by the use of complementary petrological techniques, including fieldwork, petrography, sedimentology, sequence stratigraphy, and geochemistry.

Gold and silver resources in Taupo Volcanic Zone geothermal systems

Earlier investigations show that some geothermal systems of the Taupo Volcanic Zone are sites of precious metal transport and deposition. Gold and silver precipitate in hot springs, in subsurface hydrothermally altered rocks, and in two-phase pipelines associated with production wells, as a result of gas loss due to flashing and adsorption on to As and Sb-rich sulfur phases. The amounts of Au deposited in subsurface rocks may exceed several hundred thousand ounces, but the concentrations appear to be very low grade (<1ppm Au). High-grade deposits are forming in hot springs, containing >500ppm Au and >700ppm Ag, but small metal inventories (<10,000oz Au) and very high conservation value eliminate these sites as potential resources.Down hole sampling of production wells shows that deep reservoir waters have Au concentrations that range from <0.1 to >20ppb and Ag concentrations that range from <2 to >2000ppb. The limited data suggest that at modest concentrations, production wells could produce 0.3 to 3.0kgAu/year, but that wells in Rotokawa, might produce 19–70kg Au/year. For modest Ag concentrations, production wells could produce 3–100kg Ag/year, but wells at Mokai and Rotokawa might produce 680–7500kg Ag/year. The total amounts of aqueous Au and Ag in reservoirs could be on the order of tens of thousands of ounces Au and hundreds of thousands of ounces Ag, or more.New technologies need to be developed to extract the metals from the flow stream of production wells without interfering with geothermal energy production for continued metal extraction to be feasible. The alternative is to let precious metals accumulate in two-phase pipelines, to be recovered in intervals, when practical for steam field operations and optimal in terms of profitability.

The phase diagram and physicochemical properties of the quaternary system Li+, Rb+, Mg2+//borate-H2O at 348 K

Pingluo underground brine, located in the west of China, is a high-grade deposit of lithium, potassium, rubidium, and borates. To study the ways of multipurpose utilization of this resource, the phase equilibrium of the system Li+, Rb+, Mg2+//borate-H2O was investigated at 348 K by an isothermal dissolution method. The solubilities of the components and physicochemical properties of equilibrated solutions, such as density and refractive index were determined. The stable phase diagram, the water content diagram and the physicochemical properties vs. composition diagrams were constructed according to the experimental data. The stable phase diagram consists of one invariant point, three isothermal dissolution curves and three crystallization fields corresponding to single salts MgB4O5(OH)4 · 7H2O, RbB5O6(OH)4 · 2H2O, and Li2B4O7 · 3H2O. The Li2B4O7 · 3H2O salt has the smallest crystallization region, whereas RbB5O6(OH)4 · 2H2O occupies the largest part, so rubidium pentaborate can be more easily separated from solution than other coexisting salts of this system at 348 K.

Evolutionary and geological factors controlling endogenic uranium mineralization and the potential for the discovery of new ore districts

The exhaustion of known surface and near-surface high-grade uranium deposits poses the serious problem of prospecting and exploration of new large endogenic deposits. A comparison of large data sets for endogenic deposits from the world’s major uranium districts allowed the authors to develop an evolutionary geological model of large-scale uranium ore genesis, which reflects the succession and nature of preore, ore-forming, and post-ore processes. The study reveals a combination of general (recurrent) factors controlling the formation of ore districts with large-scale uranium mineralization regardless of the genesis and timing of the mineralization. At the same time, these factors depend on the regional setting and can vary considerably among deposits of the same type localized in different tectonic blocks with different characteristics and structural evolution. In connection with this, the exploration of major genetic types of deposits requires the application of specified criteria. Along with the consideration of the evolutionary geological model of ore formation, the study discusses a variety of tectono-magmatic, mineralogical, geochemical, radiogeochemical, and physicochemical factors and indications in three uranium districts (the Streltsovskoe, Elkon, and Central Ukrainian districts), which can form the basis for further uranium prospecting and exploration. Using a combination of favorable prerequisite conditions the study compares the possibilities for the discovery of large endogenic uranium deposits in several regions of Russia.

Gold concentrations in metamorphic fluids: A LA-ICPMS study of fluid inclusions from the Alpine orogenic belt

Vein and shear-zone hosted gold deposits in orogenic terrains of Archean to Phanerozoic age are formed from dominantly metamorphic fluids. It is debated, however, whether normal crustal source rocks are adequate to generate economic deposits, or whether selectively gold-enriched sources such as mafic to ultramafic lavas, black shales or an input of magmatic fluid make a decisive difference between the formation of high-grade deposits and barren vein systems. As an essential baseline study in this debate, we have analyzed the metal and sulfur content of fluid inclusions in barren veins across a prograde sequence from greenschist to amphibolite facies in the Central Alpine metamorphic belt. Comparison of the analyzed fluid compositions with thermodynamic solubility calculations shows that the fluids record metamorphic dehydration, decarbonation and desulfidation of the continental crust. However, gold with concentrations of 0.003 to 0.03ppm is increasingly undersaturated in the highest-temperature aqueous–carbonic fluids, which otherwise resemble those forming major gold deposits elsewhere. Our results show that the regional-metamorphic fluids could carry 10–1000 times higher gold concentrations, implying that pre-enriched source rocks or hydrous magmas may play an essential role in generating highly gold-endowed orogenic belts.

Geology, isotope geochemistry and ore genesis of the Shanshulin carbonate-hosted Pb–Zn deposit, southwest China

The Shanshulin Pb–Zn deposit occurs in Upper Carboniferous Huanglong Formation dolomitic limestone and dolostone, and is located in the western Yangtze Block, about 270km west of Guiyang city in southwest China. Ore bodies occur along high angle thrust faults affiliated to the Weishui regional fault zone and within the northwestern part of the Guanyinshan anticline. Sulfide ores are composed of sphalerite, pyrite, and galena that are accompanied by calcite and subordinate dolomite. Twenty-two ore bodies have been found in the Shanshulin deposit area, with a combined 2.7milliontonnes of sulfide ores grading 0.54 to 8.94wt.% Pb and 1.09 to 26.64wt.% Zn. Calcite samples have δ13CPDB and δ18OSMOW values ranging from −3.1 to +2.5‰ and +18.8 to +26.5‰, respectively. These values are higher than mantle and sedimentary organic matter, but are similar to marine carbonate rocks in a δ13CPDB vs. δ18OSMOW diagram, suggesting that carbon in the hydrothermal fluid was most likely derived from the carbonate country rocks. The δ34SCDT values of sphalerite and galena samples range from +18.9 to +20.3‰ and +15.6 to +17.1‰, respectively. These values suggest that evaporites are the most probable source of sulfur. The δ34SCDT values of symbiotic sphalerite–galena mineral pairs indicate that deposition of sulfides took place under chemical equilibrium conditions. Calculated temperatures of S isotope thermodynamic equilibrium fractionation based on sphalerite–galena mineral pairs range from 135 to 292°C, consistent with previous fluid inclusion studies. Temperatures above 100°C preclude derivation of sulfur through bacterial sulfate reduction (BSR) and suggest that reduced sulfur in the hydrothermal fluid was most likely supplied through thermo-chemical sulfate reduction (TSR). Twelve sphalerite samples have δ66Zn values ranging from 0.00 to +0.55‰ (mean +0.25‰) relative to the JMC 3-0749L zinc isotope standard. Stages I to III sphalerite samples have δ66Zn values ranging from 0.00 to +0.07‰, +0.12 to +0.23‰, and +0.29 to +0.55‰, respectively, showing the relatively heavier Zn isotopic compositions in later versus earlier sphalerite. The variations of Zn isotope values are likely due to kinetic Raleigh fractional crystallization. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of the sulfide samples fall in the range of 18.362 to 18.573, 15.505 to 15.769 and 38.302 to 39.223, respectively. The Pb isotopic ratios of the studied deposit plot in the field that covers the upper crust, orogenic belt and mantle Pb evolution curves and overlaps with the age-corrected Proterozoic folded basement rocks, Devonian to Lower Permian sedimentary rocks and Middle Permian Emeishan flood basalts in a 207Pb/204Pb vs. 206Pb/204Pb diagram. This observation points to the derivation of Pb metal from mixed sources. Sphalerite samples have 87Sr/86Sr200Ma ratios ranging from 0.7107 to 0.7115 similar to the age-corrected Devonian to Lower Permian sedimentary rocks (0.7073 to 0.7111), higher than the age-corrected Middle Permian basalts (0.7039 to 0.7078), and lower than the age-corrected Proterozoic folded basement (0.7243 to 0.7288). Therefore, the Sr isotope data support a mixed source. Studies on the geology and isotope geochemistry suggest that the Shanshulin deposit is a carbonate-hosted, thrust fault-controlled, strata-bound, epigenetic, high grade deposit formed by fluids and metals of mixed origin.