Main Ore Research Articles

Facies architecture and palaeoenvironmental constraints of subaqueous felsic volcanism in the Iberian Pyrite Belt: The Paymogo Volcano-Sedimentary Alignment

The Paymogo Volcano-Sedimentary Alignment (PVSA) is an essentially igneous sequence associated with VHMS deposits of the Iberian Pyrite Belt. Unlike other areas of this mining district, where mafic igneous rocks are abundant, in the PVSA these are essentially felsic. Two facies associations have been distinguished based on petrographic and chemical features: a lower dacite facies association and an upper rhyolite facies association. The main ore horizons appear related to volcanic breccias of the rhyolite facies association. A detailed petrographic study of these breccias suggests they are resedimented hyaloclastite deposits. The analysis of volcanic facies indicates that the volcanism developed at water depths deeper than 500 m, consistent with the minimum depth at which VHMS deposits can form. We conclude that detailed volcanological studies provide effective constraints to palaeoenvironmental interpretations, which are relevant in assessing regional stratigraphy and area selection for VHMS exploration.

ИСПОЛЬЗОВАНИЕ МЕТОДА РАДИО-ТЕПЛОВИЗОРНОЙ ТЕХНОЛОГИИ ДЛЯ ПОИСКА РУДНЫХ ЗАЛЕЖЕЙ МЕТАЛЛОВ ПЛАТИНОВОЙ ГРУППЫ, В ТОМ ЧИСЛЕ ПАЛЛАДИЯ

Рассмотрены возможности метода Радио-Тепловизорной Технологии для поиска рудных залежей металлов платиновой группы, в особенности – палладия, на примере Еланского месторождения Воронежского кристаллического массива. На геотермических разрезах показана столбообразная геологическая структура (интрузия) главного рудного тела, содержащего палладий и другие элементы платиновой группы. Отслежено глубинное происхождение рудных залежей платиноидно-медно-никелево-палладиевых месторождений, связь рудных структур с дайками

Enhancement of Pyro-Hydrometallurgical Technology of Dephosphorization of Brown Iron Ore of the Lisakovsk Field by Hot Leaching Method

Brown iron ore constitutes about 13% of the global ore reserves and is widespread throughout the world. Brown iron ore is characterized by a significant content of harmful phosphorus (0.7 to 3.0%), which is typically present in the lattice of the main iron ore component in a chemically bound form. Based on the case study of the gravity-magnetic concentrate from the Lisakovsk field, OJSC “VNIIMT” has developed and lab-tested a pyro-hydrometallurgical dephosphorization technology, which can be applied while preparing the concentrate for agglomeration. As established earlier, phosphorus leaching proceeds successfully only after a high-temperature roasting of the gravity-magnetic concentrate, when the hydrated phosphorus-containing component decomposes. Free phosphorus then reacts with sulfuric acid. The main difference of the leaching process was that dephosphorization of the preliminary roasted concentrate with weak aqueous solution of sulfuric acid was performed without cooling it (hot leaching). A fixed-bed roasting was performed in a laboratory muffle furnace. After heating to a specific temperature and soaking for 60 minutes, a crucible containing the sample of the material was removed from the furnace. The roasted material was unloaded in hot condition into a previously prepared weak aqueous solution of sulfuric acid containing 5 wt.% of H2SO4 (solid-to-liquid phase ratio — 1:2). Such ratio prevents the solution from boiling during unloading of the hot concentrate. The pulp was mixed inside the ceramic crucible using an overhead stirrer. It has been established experimentally that hot leaching significantly reduces the duration of dephosphorization (by 3 times or more) compared to leaching under normal conditions. Another important advantage is the possibility of reducing the number of pieces of process equipment industry-wide, since cooling and leaching of the roasted gravity-magnetic concentrate from the Lisakovsk field can be implemented in one apparatus. In this case, reduced duration of the leaching process will enable an increase in productivity of the dephosphorization equipment by 3 times or more.

Trace-elements in sulfides of the Dergamysh cobalt-bearing massive sulfide deposit, the Southern Urals: Mode of occurrence and matter sources

Subject of study. The article presents the results of study of trace elements (TEs) in sulfides of the main ore body (borehole 1T) and the northwestern ore body (borehole 200) of the Dergamysh cobalt-bearing massive sulfide deposit hosted in serpentinites (South Urals). Materials and methods. The chalcopyrite-pyrite-marcasite sandstones of the main ore body and pyrite-chalcopyrite-pyrrhotite “gravelites” of its northwestern satellite were studied with laser ablation with inductively coupled plasma. Results. The TE contents, distribution and mode of occurrence differ in sulfides of the main ore body and its northwestern satellite. In ores of the main ore body, most TEs (Ag, Sn, Mn, As, Co, Ni, Te, Pb, Au) accumulate in pyrite-1, pyrite-marcasite aggregates concentrate Tl and Bi, marcasite is a host to Mo and Sb, and chalcopyrite contains Zn, Se and Cd. Pyrite-2 is depleted in TEs relative to other sulfides. In sulfides of the northwestern satellite, most TEs are related to chalcopyrite (Bi, Te, Zn, Cd, Se, Pb, Au, Tl, Ni, Co). Tin accumulates in cubanite, As and Ni are hosted in pyrite-4, Ag, Mn and Mo are concentrated in pyrrhotite, Sb is typical of pyrite-3, and Co accumulates in pyrite-2. Conclusions. Based on the correlation analysis, it is shown that sulfides of the main ore body and its northwestern satellite are characterized by different mode of TE occurrences. The differences are explained by two main reasons: 1) “mafic” and “ultramafic” metal sources for sulfides of the main ore body and its northwestern satellite, respectively, and 2) different degree of diagenetic alteration of sulfides.

The occurrence characteristics and recovery potential of middle-heavy rare earth elements in the Bayan Obo deposit, Northern China

The Bayan Obo deposit is a world-class Fe-REE-Nb deposit, and its reserves of rare earth element (REE) resources rank the first over the world. In the face of the current situation of insufficient utilization rate of rare earth resources and scarcity of middle-heavy rare earth elements (M−HREE) resources, the Bayan Obo deposit with such a huge amount of M−HREE cannot be underestimated. In this paper, the occurrence characteristics of M−HREE in different types of iron ore in the Bayan Obo main ore body are studied by using field emission scanning electron microscope (FESEM), energy dispersive spectrometer (EDS) and advanced mineral identification and characterisation system (AMICS), and the enrichment mechanism is also discussed. The results show that both Sm and Y are the most abundant M−HREE in each type of iron ore in the main ore body, and the content of M−HREE accounts for 1.41%–5.57% of total REE, among which the content of M−HREE in aegirine type Nb-REE-Fe ore (824.47 ppm) and fluorite type Nb-REE-Fe ore (794.82 ppm) are higher, and the content of M−HREE in massive type Nb-REE-Fe ore is lower (318.49 ppm). The main minerals containing M−HREE are bastnasite, parisite, Huanghoite, monazite, aeschynite and fergusonite, among which the content of M−HREE in fergusonite and aeschynite are the highest. According to the characteristics of mineral paragenetic association of REE in this ore district, it is believed that the REE migrates mainly in many different forms of complexes. Heavy rare earth elements (HREE) mainly experienced carbonatite magmatism stage, sodium-fluorine metasomatism stage and late vein mineralization stage, and finally got enrichment.

Tourmaline as a Tracer of Late-Magmatic to Hydrothermal Fluid Evolution: The World-Class San Rafael Tin (-Copper) Deposit, Peru

Abstract The world-class San Rafael tin (-copper) deposit (central Andean tin belt, southeast Peru) is an exceptionally large and rich (>1 million metric tons Sn; grades typically >2% Sn) cassiterite-bearing hydrothermal vein system hosted by a late Oligocene (ca. 24 Ma) peraluminous K-feldspar-megacrystic granitic complex and surrounding Ordovician shales affected by deformation and low-grade metamorphism. The mineralization consists of NW-trending, quartz-cassiterite-sulfide veins and fault-controlled breccia bodies (>1.4 km in vertical and horizontal extension). They show volumetrically important tourmaline alteration that principally formed prior to the main ore stage, similar to other granite-related Sn deposits worldwide. We present here a detailed textural and geochemical study of tourmaline, aiming to trace fluid evolution of the San Rafael magmatic-hydrothermal system that led to the deposition of tin mineralization. Based on previous works and new petrographic observations, three main generations of tourmaline of both magmatic and hydrothermal origin were distinguished and were analyzed in situ for their major, minor, and trace element composition by electron microprobe analyzer and laser ablation-inductively coupled plasma-mass spectrometry, as well as for their bulk Sr, Nd, and Pb isotope compositions by multicollector-inductively coupled plasma-mass spectrometry. A first late-magmatic tourmaline generation (Tur 1) occurs in peraluminous granitic rocks as nodules and disseminations, which do not show evidence of alteration. This early Tur 1 is texturally and compositionally homogeneous; it has a dravitic composition, with Fe/(Fe + Mg) = 0.36 to 0.52, close to the schorl-dravite limit, and relatively high contents (10s to 100s ppm) of Li, K, Mn, light rare earth elements, and Zn. The second generation (Tur 2)—the most important volumetrically—is pre-ore, high-temperature (>500°C), hydrothermal tourmaline occurring as phenocryst replacement (Tur 2a) and open-space fillings in veins and breccias (Tur 2b) and microbreccias (Tur 2c) emplaced in the host granites and shales. Pre-ore Tur 2 typically shows oscillatory zoning, possibly reflecting rapid changes in the hydrothermal system, and has a large compositional range that spans the schorl to dravite fields, with Fe/(Fe + Mg) = 0.02 to 0.83. Trace element contents of Tur 2 are similar to those of Tur 1. Compositional variations within Tur 2 may be explained by the different degree of interaction of the magmatic-hydrothermal fluid with the host rocks (granites and shales), in part because of the effect of replacement versus open-space filling. The third generation is syn-ore hydrothermal tourmaline (Tur 3). It forms microscopic veinlets and overgrowths, partly cutting previous tourmaline generations, and is locally intergrown with cassiterite, chlorite, quartz, and minor pyrrhotite and arsenopyrite from the main ore assemblage. Syn-ore Tur 3 has schorl-foititic compositions, with Fe/(Fe + Mg) = 0.48 to 0.94, that partly differ from those of late-magmatic Tur 1 and pre-ore hydrothermal Tur 2. Relative to Tur 1 and Tur 2, syn-ore Tur 3 has higher contents of Sr and heavy rare earth elements (10s to 100s ppm) and unusually high contents of Sn (up to >1,000 ppm). Existence of these three main tourmaline generations, each having specific textural and compositional characteristics, reflects a boron-rich protracted magmatic-hydrothermal system with repeated episodes of hydrofracturing and fluid-assisted reopening, generating veins and breccias. Most trace elements in the San Rafael tourmaline do not correlate with Fe/(Fe + Mg) ratios, suggesting that their incorporation was likely controlled by the melt/fluid composition and local fluid-rock interactions. The initial radiogenic Sr and Nd isotope compositions of the three aforementioned tourmaline generations (0.7160–0.7276 for 87Sr/86Sr(i) and 0.5119–0.5124 for 143Nd/144Nd(i)) mostly overlap those of the San Rafael granites (87Sr/86Sr(i) = 0.7131–0.7202 and 143Nd/144Nd(i) = 0.5121–0.5122) and support a dominantly magmatic origin of the hydrothermal fluids. These compositions also overlap the initial Nd isotope values of Bolivian tin porphyries. The initial Pb isotope compositions of tourmaline show larger variations, with 206Pb/204Pb(i), 207Pb/204Pb(i), and 208Pb/204Pb(i) ratios mostly falling in the range of 18.6 to 19.3, 15.6 to 16.0, and 38.6 to 39.7, respectively. These compositions partly overlap the initial Pb isotope values of the San Rafael granites (206Pb/204Pb(i) = 18.6–18.8, 207Pb/204Pb(i) = 15.6–15.7, and 208Pb/204Pb(i) = 38.9–39.0) and are also similar to those of other Oligocene to Miocene Sn-W ± Cu-Zn-Pb-Ag deposits in southeast Peru. Rare earth element patterns of tourmaline are characterized, from Tur 1 to Tur 3, by decreasing (Eu/Eu*)N ratios (from 20 to 2) that correlate with increasing Sn contents (from 10s to >1,000 ppm). These variations are interpreted to reflect evolution of the hydrothermal system from reducing toward relatively more oxidizing conditions, still in a low-sulfidation environment, as indicated by the pyrrhotite-arsenopyrite assemblage. The changing textural and compositional features of Tur 1 to Tur 3 reflect the evolution of the San Rafael magmatic-hydrothermal system and support the model of fluid mixing between reduced, Sn-rich magmatic fluids and cooler, oxidizing meteoric waters as the main process that caused cassiterite precipitation.

Comminution and liberation response of iron ore types in a low-grade deposit

Low-grade iron ore deposits in Brazil are typically represented by rocks called itabirites. These deposits contain ores with different characteristics, which present varying degrees of weathering, with direct implications in iron contents, liberation characteristics and comminution response. This work analyzes the five main ore types or lithologies contained in the Serra do Sapo deposit, as part of the Minas-Rio mining complex (near the city of Conceição do Mato Dentro, Brazil). Besides detailed chemical and mineralogical composition, liberation characteristics of the ore types have been analyzed by scanning electron microscopy and QEMSCAN. Samples were also subjected to point-load and abrasiveness tests as well as batch grinding tests. It is evident that at coarse sizes the ore types present significantly different strengths and abrasiveness, with values decreasing, as expected, with increasing degree of weathering. However, such differences partially disappeared as comminution progressed to finer sizes. Amenability of the different ores to slimes generation also varied, with weathered ores presenting significantly higher values. Grade by size deportment results show that selected ore types offer opportunity for early gangue (silica) rejection prior to the grinding stage.

Geochemical Features and Mineral Associations of Differentiated Rocks of the Norilsk 1 Intrusion

The purpose of this study is to show the patterns of distribution of disseminated sulfide in layered rocks based on the numerous geochemical and mineralogical data obtained for eight boreholes of the Norilsk intrusion (southern part of the Norilsk 1 deposit). There is a common trend of sulfide liquid fractionation in the Main Ore Horizon, which is composed of picritic and taxite (or olivine) gabbro-dolerites: the Ni/Cu in both rock types decreases down all sections, indicating an increase in the degree of fractionation of the sulfide liquid from top to bottom. On the contrary, the Ni/Fe ratios in pentlandite increase in this direction due to an increase in sulfur fugacity. However, picrite and taxite/olivine gabbro-dolerites are very distinctly separated by Ni/Cu values: these values are >1 in picritic gabbro-dolerite while they are always <1 in taxite/olivine gabbro-dolerite. These rock types are distinguished by sulfide assemblages. The first includes troilite, Fe-rich pentlandite, chalcopyrite, cubanite, talnahite, bornite and copper (low sulfur association); the second one is composed of monoclinic pyrrhotite, chalcopyrite, Ni-rich pentlandite and pyrite (high sulfur association). A two-stage magma injection with different ore specializations is supposed for picritic and taxite/olivine gabbro-dolerites.

Sequential Scheelite Mineralization of Quartz–Scheelite Veins at the Sangdong W-Deposit: Microtextural and Geochemical Approach

The Sangdong W (tungsten)-deposit is known as one of the world’s largest W-deposits, a magmatic–hydrothermal ore deposit including both skarn and hydrothermal alteration zones. The strata-bound characteristic of the deposit resulted in three major orebodies (hanging wall, main, footwall). The main ore mineral is a scheelite (CaWO4)–powellite (CaMoO4) solid solution. We examined the fluid evolution and scheelite formation process of the quartz–scheelite veins of the ore deposit, based on the microtextures and geochemical characteristics of the scheelite. After the initial magmatic–hydrothermal fluid release from the granitic body, prograde skarn is formed. In the later prograde stage, secondary fluid rises and precipitates stage I scheelite. Well-developed oscillatory zoning with the highest Mo content indicates continuous fluid infiltration under an open system. Pressure rises as mineralization occurs, generating the pressure release of the retrograde fluid. Fluid migrates downward by the gravitational backflow mechanism, forming stage II to IV scheelites. Dented oscillatory zoning of stage II scheelite is strong evidence of this pressure release. Stage III and IV scheelite do not show specific internal structures with pure scheelite composition. Retrograde scheelites are formed by fractional crystallization under a closed system. The observation of systematical fractional crystallization in the quartz–scheelite vein system is a meaningful result of our research. The geochemical characteristics and microtextural evidence imprinted in scheelites from each stage provide crucial evidence for the understanding of sequential scheelite mineralization of the quartz–scheelite vein system of the Sangdong W-deposit.

PGM assemblages from the lower ore bodies of the North Kamennik palladium deposit, Kola Region, Russia

The low-sulfide palladium deposit North Kamennik is confined to the North platinum-bearing reef in the West Pana intrusion of the Paleoproterozoic Fedorova-Pana layered complex of the Kola Peninsula. The main ore body of this deposit is accompanied by underlying ore bodies, which is not typical of other sites of the North Reef (e.g., Kievey deposit). The lower ore bodies, differing from the main one in composition of the host rocks and geochemical characteristics, are divided into three types. The conducted mineralogical studies allow us to determine each ore type according to the PGM assemblage — stannide-telluride (type 1), arsenide-sulfide-telluride (type 2) and sulfide-telluride (type 3). Mineralogical finds have been made within the ore bodies of stannide-telluride and arsenide-sulfide-telluride PGM assemblages and are presented by arsenopalladinite, isomertieite and kojonenite (new minerals for the North Reef).

Ni-Co Mineralization in the Intex Laterite Deposit, Mindoro, Philippines

The Intex laterite deposit in Mindoro, Philippines is derived from the weathering of the ultramafic rocks under a tropical climate. This study investigates the several types of serpentines and the effect of the degree of chemical weathering of ultramafic rocks and laterites on the enrichment of Ni in the deposit. The five types of serpentines are differentiated based on their textural features and Raman spectral data. Type I, type II, type III, and type IV serpentines contain a low amount of NiO (average 0.15 wt%), and their formation is linked to the previous exhumation of the ultramafic body. Conversely, type V serpentines show the highest NiO contents (average 1.42 wt%) and have the composition of serpentine-like garnierites, indicating a supergene origin. In the limonite horizon, goethite is the main ore mineral and shows high NiO contents of up to 1.68 wt%, whereas the Mn-oxyhydroxides (i.e., asbolane and lithiophorite–asbolane intermediate) display substantial amounts of CoO (up to 11.3 wt%) and NiO (up to 15.6 wt%). The Ultramafic Index of Alteration (UMIA) and Index of Lateritization (IOL) are used to characterize the different stages of weathering of rocks and laterites. The calculated index values correspond to a less advanced stage of weathering of the Intex laterites compared with the Berong laterites. The Berong deposit is a Ni-Co laterite deposit in the Philippines, which is formed from the weathering of the serpentinized peridotite. The less extreme degree of weathering of the Intex laterites indicates less advanced leaching, and thereby the re-distribution of Ni, Si, and Mg from the limonite towards the saprolite horizon may have resulted in the poor precipitation of talc-like (kerolite-pimelite) and sepiolite-like (sepiolite-falcondoite) phases in the studied saprolite horizon. Nickel in the Intex deposit has undergone supergene enrichment similar to other humid tropical laterite deposits.

Assessing the role of bitumen in the formation of stratabound Cu-(Ag) deposits: Insights from the Lorena deposit, Las Luces district, northern Chile

Stratabound Cu-(Ag) deposits located in north-central Chile have been grouped into two NS parallel belts according to the age of their volcanic and volcanoclastic host rocks. Deposits from the Cretaceous belt are characterized by an unusual assemblage of Cu sulfides with migrated hydrocarbons, whereas the presence of organic matter has not yet been recognized in deposits from the Jurassic belt. Here we report the first evidence of pyrobitumen in a Jurassic stratabound Cu-(Ag) deposit and evaluate its role in ore formation. We present a micro-analytical study of pyrobitumen associated with Cu-(Fe) sulfides in the Lorena deposit, located in northern Chile. Our approach involved a combination of surface and drill core sample characterization, (FE)-SEM observations, EMPA and μ-XRF mapping of pyrobitumen. In addition, we determined the speciation of sulfur in pyrobitumen by using synchrotron μ-XANES. Two main events of hypogene mineralization were identified at Lorena deposit, i.e., a pre-ore and a main Cu ore stage. The pre-ore stage is characterized by globularly-shaped pyrobitumen and minor pyrite, and a widespread albite alteration of the andesite host rock. Pre-ore pyrite was replaced by chalcopyrite, bornite and chalcocite, providing evidence for a late Cu inception. In the main Cu ore stage, chalcocite is often associated with sharp-edged, angular pyrobitumen, most likely indicating remobilization or a later pulse of hydrocarbons. EMPA data show that pyrobitumen at Lorena is enriched in Fe (0.02–1.74 wt%), Cu (0.02–0.87 wt%), S (0.01–0.43 wt%) and Cl (0.01–0.4 wt%). Other elements detected include V, Co, Ni, Cr, Sb, As, Ag and Au. Both Ag and Au were only detected in a few spots, with Au reaching up to 600 ppm. Desktop and synchrotron μ -XRF mapping shows that S is homogeneously distributed within pyrobitumen, with lower S concentrations observed at grain rims. On the other hand, EMPA-WDS X-ray maps show that Cu precipitated on pyrobitumen grain surfaces, filling fractures and forming veinlets. In addition, textures showing the presence of micro- to nano-sized pyrobitumen inclusions within both pre-ore pyrite and main ore chalcocite grains point, unequivocally, to the interaction of hydrothermal fluids with hydrocarbons during the formation of this deposit. The high S concentrations measured in pyrobitumen and the presence of organosulfur compounds detected by μ -XANES can be attributed to an organic source. The pre-ore assemblage is interpreted as formed from a petroleum-aqueous fluid (connate waters?) mixture that migrated from the sedimentary source rock into the Jurassic host rocks where pyrite and pyrobitumen precipitated in the andesite. Late Cu-bearing hydrothermal fluids interacted with this pyrobitumen-pyrite assemblage to form Cu sulfides, either by replacement of pyrite or precipitation. We conclude that some of the S contained in pyrobitumen could have been released during interaction with the Cu-bearing hydrothermal fluid contributing, at least partially, to the S budget required for sulfide mineralization in the main ore stage. Our results provide evidence supporting pyrobitumen-fluid interaction as a key process in the formation of the Lorena deposit and possibly other stratabound Cu-(Ag) deposits in Chile.

Pit Lake and Drinking Water Intake: Example of Coexistence (Middle Urals, Russia)

The dewatering system of the Lipovsky nickel mining pit (Middle Urals, Russia) has performed a dual role. From 1961 to 1991, while nickel was being mined there, it protected the pit from flooding with groundwater; since 1989, it has been the principal source of drinking water for the town of Rezh (≈ 50,000 residents). After mining ceased, water withdrawal from the drainage wells decreased 2.5 times (to 100 L/s), resulting in a 120 m deep pit lake. A mass balance analysis has shown that water from the pit lake has become the leading source of water intake. However, the concentrations of the water’s basic constituents at the eastern edge of the pit are several times higher than at the western edge. The reason for the significant increase in the water withdrawn by the wells of the western intake is the fact, that during the working of the main ore body, the eastern part of the pit was filled with overburden rock and substandard ore with dispersed sulfide mineralization. Flooding of the pit created a single aquifer between the pit lake and the eastern water intake facility, including an artificial aquifer within the refilled part of the pit. The rise of the groundwater level in the artificial aquifer to an elevation above 150 m (after 1994) led to active chemical weathering of sulfide-containing minerals and dissolution of secondary sulfates, which accounts for the increasing levels of constituents in the eastern part of the pit. The artificial aquifer has become a generator of salts. The dumping of sulfidic wastes and subsequent recovery of the water table have led to the release of sulfate, calcium, and metals into the local groundwater. To prevent the formation of an artificial aquifer, it is necessary to either completely remediate the unflooded portion using non-acid generating material or completely inundate the pit. Partial remediation would be the worst scenario as it could destabilize the hydrogeochemical processes and render long-term coexistence of the drinking water intake and the flooded pit problematic.

Geological, fluid inclusion, and H–O–C–S–Pb isotopic constraints on the genesis of the Shuangqishan gold deposit, Fujian, China

The Shuangqishan Au deposit lies in the Dehua–Youxi–Yongtai Au metallogenic belt in central eastern Fujian Province, SE China. The orebodies are hosted mainly in the Neoproterozoic Dalingyan Formation. Based on the characteristics of mineralization, alteration mineral assemblages, fluid inclusions, and H–O–C–S–Pb isotopic data, the deposit is classified as a granitoid-related deposit. The primary metallic minerals are native gold, electrum, pyrite, chalcopyrite, galena, tellurbimuth, and tetradymite; the main gangue minerals are quartz, calcite, sericite, and illite. The main types of wall-rock alteration are silicification, pyritization, carbonatization, and sericitization. Fluid inclusions in quartz from auriferous polymetallic sulfide-bearing quartz veins from the main ore stage were studied. Two-phase liquid-rich (type I), CO2-rich (type II), and pure CO2 (type III) inclusions were identified. Their homogenization temperatures (196 °C–295 °C) and salinities (0.8–5.0 wt% NaCl equivalent) indicate that the ore-forming fluids of the Shuangqishan deposit were of a medium-temperature, low-salinity H2O–CO2–NaCl system. Gold deposition at Shuangqishan was likely caused by immiscibility of fluids. H isotopic compositions (δDH2O = −68.0‰ to −64.8‰) of inclusion water in quartz and O isotopic compositions (δ18OH2O = 3.8‰ to 6.3‰) of fiuid, which was calculated from δ18O of quartz, imply that ore-forming fluids were mainly of magmatic origin. C isotopic compositions (δ18CPDB = −15.7‰ to −5.7‰) of the fluid inclusions indicate that the CO2 in the ore-forming fluids was predominantly magma-derived, but was contaminated by organic carbon from the Neoproterozoic Dalingyan Formation. δ34S values of sulfide minerals have a narrow range of–2.7‰ to −0.9‰, suggesting that S was derived from a homogeneous magmatic source. Pb isotopic ratios of gold-bearing ores are similar to those of late Mesozoic granodiorite porphyry of the Xianyang pluton, indicating that the granodiorite porphyry was the source of Pb for the ores.

Signs of Vertically Extending Mineralization in the Nizhnetaezhny Polymetallic Ore District (Northern Primorye)

In this work, to study the vertical extent of mineralization, determine the level of erosion, and identify signs of longitudinal placement of silver mineralization of the Nizhnetaezhny ore district (NOD) For this, the main indicator indicators Ag, Au, Cu, Zn, Pb were identified based on the maximum correlation coefficient, Sn, Sb, As, Mo. Then, the ratios of the linear productivities of the indicator elements for the main ore zones of the Scientific and Technological Logging were made: Kumirnoe - Sb * Ag * As / Cu * Sn, Kabaniy - Sb * As * Ag / Cu * Sn, SredniySukhoy - Sn * Pb * Zn / Au * As, Levoberezhnoe -Sn * Pb * Zn / W * Mo. The obtained geochemical data of changes in the multiplicative coefficients allowed us to identify areas according to their erosion: weakly eroded (Kumirny, SredniySukhoy) and significantly eroded (Kabany, Levoberezhnoe), and then divide them into upper ore, ore and under ore. At all sites (except for the SredniySukhoy), at the level of the conditionally subsided horizon, a tendency of gradual increase in productivity was revealed, which indicates the long-range placement of productive ore zones and makes it possible to suggest the presence of powerful and productive silver zones hidden at depth. The data obtained provide the prerequisites for the revaluation of the prospects of the deep horizons of the NOD silver mineralization.

Genesis of the Mingsai Au deposit, southern Tibet: Constraints from geology, fluid inclusions, 40Ar/39Ar geochronology, H–O isotopes, and in situ sulfur isotope compositions of pyrite

Mingsai is a newly discovered Au deposit located in the eastern part of the Tethys Himalayan Au–Sb polymetallic metallogenic belt. The stratiform and lenticular orebodies are hosted within Middle Jurassic metamorphic tuff and quartz-sericite veins and controlled by an interlayer-gliding fracture zone with extensive hydrothermal alteration. In this study, at least three alteration/mineralization stages of the deposit were recognized as follows: (1) pre-ore stage (Stage Ⅰ), forming mainly ore-barren fine quartz veins without sulfides; (2) main ore stage (Stage Ⅱ), forming mainly thick quartz veins with abundant coarse-grained or fine-grained euhedraland subhedral Au-bearing pyrite, arsenopyrite and sericite; and (3) post-ore stage (Stage III), which is characterized by formation of thick barren quartz–calcite veins with few sulfides. Three types of fluid inclusions were identified as follows: (1) pure carbonic (V-type) inclusions, (2) aqueous-carbonic (C-type, including three-phase C1-type and two-phase C2-type) inclusions and (3) aqueous (L-type) inclusions. Fluid inclusions during the pre-ore stage are mainly C1-type, C2-type and V-type. The main ore stage contains mainly C1-type, C2-type, L-type and limited V-type, whereas the post-ore stage contains mainly L-type (with limited C2-type) fluid inclusions. From stages Ⅰ to III, microthermometric data show homogenization temperatures of 292–362 °C (mean = 309 °C), 247–320 °C (mean = 285 °C), and 206–272 °C (mean = 244 °C), respectively, and fluids with salinities of 0.2–8.3 (mean = 2.8) wt% NaCl equiv., 0.2–13.1 (mean = 5.8) wt% NaCl equiv., and 0.8–15.2 (mean = 8.3) wt% NaCl equiv., respectively. The δD values of the fluids from stages I to III range from −129.1‰ to −131.8‰, −137.5‰ to −137.4‰, and −143.6‰ to −138.6‰, respectively. The δ18OH2O values of the fluids from stages Ⅰ to III range from 13.3‰ to 13.6‰, 13.0‰ to 13.2‰, and 11.0‰ to 11.9‰, respectively. The δD and δ18OH2O values may reflect meteoric water involvement in ore-forming fluidssourced from either crustal metamorphism or mantle devolatilization. Fluid mixing is the crucial mechanism that controlled the deposition of the Au-bearing sulfides. In situ δ34S values of the Au-bearing pyrite range from 1.06‰ to 2.41‰, whereas δ34S values of the barren pyrite from the slate range from 8.19‰ to 15.86‰, indicating that sulfur of the Au-bearing pyrite has a deep source. The 40Ar–39Ar plateau age of hydrothermal ore-bearing sericite from the main ore stage is 16.03 ± 0.31 Ma, indicating that the mineralization time of the deposit is Miocene, which is different from other major gold deposits (Eocene) in the Tethys Himalayan Au–Sb polymetallic metallogenic belt. Consequently, taking the data together, it is suggested that the Mingsai is an orogenic-type Au deposit in the Tethys Himalayan Au–Sb polymetallic metallogenic belt.

Multistage pyrites in the Nibao disseminated gold deposit, southwestern Guizhou Province, China: Insights into the origin of Au from textures, in situ trace elements, and sulfur isotope analyses

Nibao is a unique thrust fault-controlled and strata-bound disseminated gold deposit in southwestern Guizhou Province, China. In Nibao, pyrite is the major sulfide mineral and Au is structurally bound (Au+) within the pyrite lattice. In this study, we conducted detailed analyses of the pyrite chemistry and S isotope composition in Nibao using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS), respectively. Through petrographic and pyrite chemical studies, four pyrite generations (Py1–Py4) were distinguished: framboidal pyrite (Py1, pre-ore sedimentary stage), clean pyrite overgrowing framboidal pyrite (Py2, pre-ore diagenetic stage), “spongy” pyrite (Py3, early ore stage), and overgrowth of narrow pyrite rims surrounding Py2/Py3 and disseminated pyrite associated with arsenopyrite (Py4, main ore stage). Among these, Py2 and Py4 are the most abundant.The trace element content in Py2 is characterized by a wide range of As, Cu, Sb, and Pb concentrations (~2480–58100 ppm, ~55.4–1610 ppm, ~29.1–232 ppm, and ~24.1–376 ppm, respectively), while Py4 has the highest Au, As, Cu, and Se contents (~70 ppm, ~4200, ~1630 ppm, and ~38.3 ppm, respectively). The δ34S values of pre-ore pyrites measured by LA-MC-ICP-MS in this study and the available data in the literature range broadly from −53.3 to 114.8‰, indicating that they were most likely generated by bacterial reduction from marine sulfate during sedimentation/diagenesis. Meanwhile, the δ34S values of ore pyrites have relative narrow δ34S values, mostly varying from −5 to 5‰, and indicating that the S was derived either from the average of sedimentary rocks or from a magmatic source.Since igneous rocks are scarce in the region and the exposed (~77–99 Ma) are clearly younger than the mineralization age of the Nibao gold deposit (~141 Ma), a magmatic source is unlikely in Nibao. All pyrites in this study show a positive correlation (R2 = 0.71) between Co and Ni, and the Co/Ni and Zn/Ni ratios of main stage Py4 are close to or within the range defined for a sedimentary–diagenetic origin, suggesting a sedimentary source is more likely in Nibao.

HYPOGENE ALUNITE FROM THE EL SALVADOR DISTRICT, CHILE, INDICATES POTENTIAL FOR A BLIND PORPHYRY COPPER CENTER

AbstractSurface samples of hypogene alunite that cement late breccia bodies from the El Salvador porphyry copper district of Chile were recently dated. One alunite sample over the principal Turquoise Gulch porphyry deposit has a 40Ar/39Ar total gas age of 40.64 ± 1.04 Ma, overlapping the age of a late latite intrusion. Two other samples associated with quartz-alunite replacement of rhyolite, ~750 m southwest of the collapse zone over the block cave of the porphyry copper deposit, are distinctly younger, at 38.12 ± 0.66 and 38.04 ± 0.22 Ma (averages of duplicate analyses, with ±2σ errors).Previously reported U/Pb ages of zircons from 15 Eocene-age diorite, granodiorite, and granite porphyry intrusions have weighted mean ages that range from about 44 to 41 Ma, with peak magmatic flux interpreted at 44 to 43 Ma. Porphyry copper ores in the El Salvador district formed at about the same time as porphyry intrusions, with intrusive centers that migrated in a south-southwest direction, from the small deposits at Cerro Pelado (~44.2 Ma), to Old Camp (~43.6 Ma) and M Gulch-Copper Hill (~43.5–43.1 Ma), to the main ore deposit at Turquoise Gulch (~42 Ma). The granodiorite porphyry intrusions at Turquoise Gulch are associated with ~80% of the known copper ore of the district; they record waning stages of magmatism at 42.5 to 42.0 Ma, followed by weakly altered latite dikes at 41.6 Ma. Molybdenite in quartz veins returned Re-Os ages of 41.8 to 41.2 Ma.The two alunite samples from our study with coincident dates of ~38 Ma provide evidence for magmatic-hydrothermal activity younger than any recognized to date, consistent with the alteration overprint of quartz-alunite on older muscovite after erosion. This younger activity must have been associated with a blind intrusion, likely located south of the Turquoise Gulch deposit, based on the distribution of alteration minerals, and offset from the zoning associated with the Turquoise Gulch center. Stable isotope values (δ34S, δ18O, δD) of the ~38 Ma alunite indicate a high-temperature hypogene origin, consistent with formation in a lithocap environment that typically is located at shallow levels over and on the shoulders of porphyry copper deposits. Both observations—alteration overprint and markedly younger age of alunite—indicate the potential for porphyry copper mineralization south of Granite Gulch, as much as 1,000 m below the level of the coeval outcropping quartz-alunite replacement, perhaps near ~2,000-m elevation; this is hundreds of meters deeper than the known copper ore of Turquoise Gulch.

Sulfide ore facies, fluid inclusion and sulfur isotope characteristics of the Tappehsorkh Zn-Pb (± Ag-Ba) deposit, South Esfahan, Iran

The stratiform, stratabound Tappehsorkh Zn-Pb (±Ag-Ba) deposit, located in the southeastern part of the Malayer-Esfahan Metallogenic Belt of Iran, formed during Lower Cretaceous back-arc extension. Sulfide mineralization occurs within dolostone, black siltstone, and crystal lithic tuff and andesite associated with the Gushfil-Baghabrisham synsedimentary normal fault. Three sulfide ore facies (massive, bedded, and stockwork) occur in the deposit. Sulfide minerals are sphalerite, galena, tetrahedrite and pyrite with minor chalcopyrite and bornite, and gangue minerals are barite, dolomite and quartz. Sulfide mineralization textures are massive, replacement, vein-veinlet, laminated, disseminated, and brecciaThree mineralization stages are distinguished: early, main and post-ore. An early fine-grained sulfide ore (early ore, stage I) occurs in the bedded facies which has synsedimentary textures such as laminated, disseminated and framboidal pyrite, galena and sphalerite. Coarse-grained sulfides in the brecciated, massive replacement, and vein-veinlet textures comprise main ore stage of mineralization (main ore, stage II) and formed during diagenesis via sub-seafloor replacement of protore by mixing of hydrothermal brines with cold seawater. Late, coarse-grained sulfides (post-ore, stage III) were formed during deformation and orogenic events and occur as strain fringes, foliation-like, and spindle textures. Pervasive hydrothermal alteration styles are predominantly dolomitization and silicification and minor sericitization occurs in all host rocks in the hanging-wall of the GBF.Fluid inclusions within massive sphalerite of the main ore stage have trapping temperatures ranging from 118–199 °C, and salinities ranging from 6.2 to >23.32 wt. % NaCl equivalent. The δ34S values of the sulfide minerals from main ore stage ranges from -2.4 to -34.1‰, whereas barite ranges from +10.3 to +16.9‰. The negative values of the δ34S as well as the narrow range of δ34S in galena and sphalerite suggest that sulfur was derived by bacterial reduction of seawater sulfate.The back-arc extensional tectonic setting, presence of a normal fault controlling sulfide mineralization and hydrothermal alteration, the siliciclastic-carbonate-volcanic lithology of the host rocks, magmatism in the region (pyroclastic and volcanic rocks, that also host the sulfide mineralization), the distribution of the three ore facies, and the negative sulfur isotope values all support a sub-seafloor diagenetic replacement SEDEX-type classification for the Tappehsorkh deposit, which was then affected by Laramide (?) orogenic events which imparted the post-ore stage mineral textures.

Accurate and precise in situ U–Pb isotope dating of wolframite series minerals via LA-SF-ICP-MS

We present an analytical protocol for in situ U–Pb isotope dating of wolframite series minerals [(Fe,Mn)WO4], the main ore mineral for tungsten, by LA-SF-ICP-MS.