Main Orebody Research Articles

Sulfur Isotope Constraints on the Conditions of Pyrite Formation in the Paleoproterozoic Urquhart Shale Formation and George Fisher Zn-Pb-Ag Deposit, Northern Australia

Abstract The Carpentaria province (McArthur basin and Mount Isa inlier) in northern Australia is one of the most important districts for clastic-dominated (CD-type) massive sulfide deposits. The George Fisher Zn-Pb-Ag deposit, located in this province, is hosted by the carbonaceous Urquhart Shale Formation (ca. 1654 Ma) in a region that has an active history of metamorphism and tectonism. In this study, paragenetically constrained pyrite in samples from the George Fisher deposit and unmineralized Urquhart Shale have been analyzed in situ using secondary ion mass spectrometry (SIMS) of sulfur isotopes (δ34S values). Samples were taken from four drill cores through the main orebodies at George Fisher and one drill core through correlative, unmineralized Urquhart Shale (Shovel Flats area). Five generations of pyrite were identified at George Fisher and record a protracted history of sulfate reduction under diagenetic and subsequent hydrothermal conditions: (1) fine-grained, subhedral-spheroidal pyrite (Py-0), (2) coarse-grained, anhedral pyrite (Py-1) associated with ore-stage 1 sphalerite and galena, (3) coarse-grained, euhedral pyrite (Py-2) associated with ore-stage 2 sphalerite, galena, and pyrrhotite, (4) massive subhedral to euhedral pyrite (Py-3) associated with ore-stage 3 chalcopyrite, pyrrhotite, galena, and sphalerite, and (5) coarse-grained euhedral pyrite (Py-euh), which occurs only in unmineralized rocks. In the unmineralized Shovel Flats drill core, only Py-0 and Py-euh are present. Whereas pre-ore pyrite (Py-0) preserves negative δ34S values (–8.1 to 11.8‰), the ore-stage pyrites (Py-1, Py-2, and Py-3) have higher δ34S values (7.8–33.3, 1.9–12.7, and 23.4–28.2‰, respectively). The highest δ34S values (7.2–33.9‰) are preserved in Py-euh. In combination with petrographic observations, the δ34S values of pyrite provide evidence of three different processes responsible for the reduction of sulfate at George Fisher. Reduced sulfur in fine-grained pyrite (Py-0) formed via microbial sulfate reduction (MSR) under open-system conditions prior to the first generation of hydrothermal pyrite (Py-1) in ore-stage 1, which most likely formed via thermochemical sulfate reduction (TSR). During deformation, previously formed sulfide phases were then recycled and replaced during a second hydrothermal event (ore-stage 2), resulting in intermediate sulfur isotope values. Another syndeformational hydrothermal Cu event, involving a sulfate-bearing fluid, formed ore-stage 3 via TSR. This study demonstrates that the fine-grained pyrite formed pre-ore under conditions open to sulfate and outlines the role of multiple stages of sulfide formation in producing high-grade Zn-Pb-Ag orebodies in the Mount Isa inlier.

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).

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.

Hydrothermal alteration, mineralization and fluid inclusions in the Pista and Fofão prospects: implications for the genetic model of the Coringa polymetallic deposit, SE Tapajós Mineral Province, Amazonian Craton, Brazil

Pista and Fofao are prospects located near the main orebodies of the Coringa polymetallic deposit, in southeastern Tapajos Mineral Province of the Amazonian Craton. In both prospects, the mineralization is hosted in an Orosirian alkali feldspar granite, which is associated with coeval volcanic rocks at Pista. The paleo-hydrothermal system comprises an early post-magmatic stage, characterized by albite and K-feldspar alterations. Silicified and brecciated zones, sericitization of wall-rocks, both with adularia, as well as carbonatization (siderite and Mn-siderite rich stage) are the proximal ore alteration zones. Chlorite – hematite – rutile – epidote veinlets represent weak and distal zones of hydrothermal alteration. The mineralization is polymetallic (Au and subordinate Ag, Zn, Pb, and Cu) and occurs as dissemination and filling fissure veinlets. Gold occurs predominantly as Au-Ag-tellurides included in pyrite, and as free gold in association with pyrite, sphalerite and hematite within quartz veinlets. Fluid inclusions trapped in quartz veinlets show H2O, H2O-CO2-NaCl and CO2-only inclusions. Microthermometric data indicate an H2O-CO2-NaCl fluid, likely of magmatic derivation, with low-salinity (5.4 ± 1.3 wt. % NaCl equiv.) and moderate density (0.36-0.94 g/cm3) trapped between 264 and 370oC, and a low-salinity aqueous fluid (≤11.2 wt % NaCl equiv.) trapped at 280 to 360oC, possibly evolved from effervescence followed by isothermal mixing with an external heated H2O-NaCl fluid, probably meteoric. After this, the fluids were continuously diluted and cooled. This stage is represented by the liquid-rich H2O-NaCl fluid inclusions of low salinity (up to 5.3 wt. % NaCl equiv.) and relatively low trappingtemperature (177 to 113°C). The petrographic and fluid inclusions data suggest that the Au, Ag and base metals precipitation resulted from fluid mixing and dilution, which led to the breakdown of Au(HS)2−. We interpret the Pista and Fofao prospects as part of a magmatic-hydrothermal mineralized system, with some characteristics compatible with those of low- to intermediate-sulfidation epithermal systems, despite the absence of some typical textures from these systems.

Geology, geochronology, and fluid inclusion studies of the Xiaorequanzi volcanogenic massive sulphide Cu–Zn deposit in the East Tianshan Terrane, China

The Xiaorequanzi Cu–Zn deposit is in the westernmost part of East Tianshan Terrane in northwestern China. The deposit is unique in the region being a volcanogenic massive sulphide (VMS) deposit located near a zone (or belt) containing giant late Paleozoic porphyry Cu deposits. Aiming to better understand the genesis of the mineral deposits in the terrane and their tectonic setting, we report our findings of detailed studies on fluid inclusion microthermometry, Re–Os dating of chalcopyrite from the massive ore, and U–Pb dating of zircons from the host volcanic rocks. There are two sulphide stages with early pyrite succeeded by chalcopyrite–sphalerite, which are hydrothermally overprinted and supergene enriched. The hydrothermal overprinting is characterised by quartz–sulphide veins crossed by carbonate-rich quartz veins. Quartz from the chalcopyrite–sphalerite stage is characterised by primary fluid inclusions containing H2O–NaCl(–CO2) and homogenise at 228–392 °C with a salinity of 2.2–13.3 wt.% NaCl equiv. Secondary fluid inclusions related to the hydrothermal overprinting homogenise at 170–205 °C with a salinity of 2.7–12.1 wt.% NaCl equiv. Fluid inclusions in the quartz–sulphide stage of the hydrothermal overprinting contain H2O–NaCl with homogenisation temperatures of 164–281 °C and salinities in ranging from 2.9 to 12.4 wt.% NaCl equiv. Fluid inclusion in the quartz–calcite stage contain H2O–NaCl with homogenisation temperatures of 122–204 °C with salinities of 1.4–12.4 wt.% NaCl equiv. These characteristics are like those of the secondary fluid inclusions in the VMS mineralisation. Combining these findings with H–O isotopic data from previous studies, we propose that the primary mineralising fluid is magmatic in origin. Tuff hosting the mineralisation yields a SHRIMP U–Pb zircon age of 352 ± 5 Ma, which is interpreted as the age of the tuff, and a porphyritic felsite dyke intruding the tuff yields a SHRIMP U–Pb zircon date of 345 ± 6 Ma, interpreted as the emplacement age of the dyke. Chalcopyrite from the main orebody at Xiaorequanzi yields a Re–Os isochron age of 336 ± 13 Ma with an initial 187Os/188Os ratio of 0.25 ± 0.55 (MSWD = 12). Given that the VMS deposit is a syngenetic deposit, we regard the upper ca. 349 Ma limit of the Re–Os date as the approximate age of the chalcopyrite. The three dates are the same within error, and the upper limit of the Re–Os date of ca. 349 is taken as the age of the volcanic, dyke, and mineralisation. The volcanic rocks around the Xiaorequanzi deposit have been previously classified as calc–alkaline to high-K calc–alkaline enriched in large-ion lithophile elements and depleted in high-field-strength elements, which are characteristics indicative of a forearc setting. It is suggested that VMS mineralisation formed in a forearc setting related to the north-directed subduction of the Palaeo-Kangguer or North Tianshan oceanic plates.

Application of pseudo-random frequency domain electromagnetic method in mining areas with strong interferences

Abstract Due to the strong electromagnetic interferences and human interference, traditional electromagnetic methods cannot obtain high quality resistivity data of mineral deposits in Chinese mines. The wide field electromagnetic method (WFEM), in which the pseudo-random signal is taken as the transmitter source, can extract high quality resistivity data in areas with sever interference by only measuring the electric field component. We use the WFEM to extract the resistivity information of the Dongguashan mine in southeast China. Compared with the audio magnetotelluric (AMT) method, and the controlled source audio-frequency magnetotelluric (CSAMT) method, the WFEM can obtain data with higher quality and simpler operations. The inversion results indicate that the WFEM can accurately identify the location of the main ore-body, which can be used for deep mine exploration in areas with strong interference.

Reply to comments on “Dehydration of hot oceanic slab at depth 30–50 km: Key to formation of Irankuh-Emarat Pb-Zn MVT belt, Central Iran” by Mohammad Hassan Karimpour and Martiya Sadeghi” by

The Irankuh-Emarat Pb-Zn belt is situated within the forearc Urumieh-Dokhtar zone of western part of Iran and it is classified as Mississippi Valley TYPE Pb-Zn mineralization. According to Karimpour and Sadeghi (2018) deep-seated thrust faults played an important role in the upward migration of hydrothermal fluids from the basement to shallow depths. The style and shape of mineralization are controlled by the host rocks. Rajabi et al. (2019) commented on the model presented by Karimpour and Sadeghi (2018) but the proposed syngenetic MVT model presented by Rajabi et al. (2019) is not acceptable based on the age of the mineralization at Irankuh-Ahangharan belt and also the role of deep-seated thrust faults in the mineralization area and its spatial distribution and association with the main ore bodies was completely omitted. In addition, the work presented by Karimpour and Sadeghi (2018) did not explain metallogenic aspect of all Zn-Pb deposits in the area and other belts and the proposed model is applicable to Pb-Zn deposits in the Irankuh-Emarat belt and not necessary to explain other Pb-Zn mineralization elsewhere in Iran.

Microscopic Blue Sapphire in Nelsonite from the Western Adirondack Mountains of New York State, USA

Microscopic, non-gem quality, grains of blue sapphire (corundum) have been identified in a small (1–2 cm wide), discontinuous, dike of nelsonite hosted by aluminous feldspathic gneiss. The gneiss was excavated during the construction of a hydroelectric plant on the Black River at Port Leyden, NY (western Adirondack Highlands). The sapphire location is 250 m NE of the Port Leyden nelsonite deposit. The small dike may represent a separate intrusion of nelsonite or one sheared from the main nelsonite orebody during Ottawan (circa 1050 Ma) deformation and metamorphism. The sapphires range in size from 0.1 to 2.0 mm, and commonly show parting, pleochroism, and hexagonal oscillatory zoning (from deep blue to clear). Electron microprobe analysis shows comparable levels of Fe in both clear (0.71–0.75 wt. %) and blue (0.38–0.77 wt. %) portions of grains, but clear sections have significantly lower TiO2 levels (0.002–0.011 wt.%) compared to blue sections (0.219–0.470 wt. %). Cr2O3 abundances range from 0.006 to 0.079 wt. % whereas V2O3 abundances range from 0.010 to 0.077 wt. % in blue sapphires. Small amounts of MgO were detected in one of the clear corundum grains (0.013 wt. %) and two of the six blue grains (0.001–0.015 wt. %), but the remaining five grains were below the limit of detection. Ga2O3, however, was detected in five out of six blue-colored grains (0.026–0.097 wt. %) but was below the limits of detection for clear grains. Optical spectroscopic data collected on the blue sapphire grains show broad absorbance in the yellow, orange, and red part of the spectrum (~565–740 nm) consistent with intervalence charge transfer between the next nearest neighbor Fe2+ and Ti4+. A magmatic origin of the sapphire grains is supported by petrologic and trace element data from the blue sapphires, but Cr abundances are inconsistent with this interpretation. Sapphire in a nelsonite host rock represents a new type of occurrence.

Fluid geochemistry of the Serra Pelada Au-Pd-Pt deposit, Carajás, Brazil: Exceptional metal enrichment caused by deep reaching hydrothermal oxidation

Serra Pelada is a high-grade hydrothermal Au-Pd-Pt deposit within the Carajás mineral province, eastern Amazon craton, which shows an exceptional metal enrichment at carbon-enriched hosted ores (>1000’s ppm Au + Pt + Pd). The main orebody is structurally hosted at the hinge of a recumbent syncline, consisting of dolomitic metasandstones at the outer part of the fold, a layer of carbonaceous metasiltstone in which most orebodies are located, and red siltstone in the core of the fold. Distal hydrothermal alteration comprises spatially separated chlorite – carbon (reduced) and hematite (oxidized) alteration zones. The mineralized zones include silicification and argillic (carbon- kaolinite-, and hematite-rich) alteration zones. Fluid inclusions hosted by quartz and dolomite crystals from distal alteration zones and silicified portions within the mineralized zone record a wide range of salinity (5–22 wt% NaCleqv.) but relatively constant homogenization temperatures (170 ± 25 °C). Pressure and temperature estimations based in the fluid inclusion microthermometry and selenide thermometry constrain the formation of the deposit at 250–270 °C and 1.2–1.7 kbar. Element concentrations of alkali metals, Pb, Cs and to a lesser extent Ba correlate with salinity, whereas redox-sensitive elements including U and Ce vary widely. Gold concentrations from 50 to 500 ppb detected in some inclusions are consistent with the highly oxidizing conditions defined by selenide mineralogy. The presence of uranium and gold within fluid inclusions of the distal hematite alteration zone confirms the oxidizing, metal carrier fluids. The occurrence of hydrothermally precipitated carbon implies that a reducing CH4-bearing fluid was also present, and the structural relationships suggest that mixing between this reducing fluid (and interaction with carbon-upgraded rocks) with an acidic, oxidizing and metal-carrying fluids was the main process driving ore metal precipitation. The genesis of the Serra Pelada Au–Pd-Pt deposit shows similarities with sediment-hosted copper deposits and unconformity-related U ± Au ± PGE deposits, having in common the downflow of highly oxidizing fluids into the hydrothermal domain of the Earth's upper crust. Major differences in metal proportions of these broad classes of ore deposits and other sediment-hosted systems in different ore provinces are primarily caused by differences in source rocks available for oxidative leaching and variations in the geometry of the hydrothermal system.

Geochronology and geochemistry of the Dianfang gold deposit, western Henan Province, central China: Implications for mineral exploration

The Dianfang gold deposit, located in the Xiong’ershan–Waifangshan region within the southern margin of the North China Craton, consists of eastern and western ore blocks, which are hosted in the Dianfang breccia pipe and Paleoproterozoic volcanic rocks, respectively. The eastern ore block, which occurs within the southern and hanging wall margins of the Dianfang breccia pipe and in fractures in the rhyolites of the Jidanping Formation, consists of rhyolite-hosted and breccia-hosted disseminated gold mineralization structurally controlled by ENE-striking faults. The western ore block contains gold-bearing quartz-sulfide veins and minor disseminated rhyolite-hosted gold mineralization that occurs in the annular fractures around the Hougou breccia pipe. The two ore blocks have long been researched and prospected as two different genetic types. Detailed fieldwork and microscopic observations reveal that the eastern and western ore blocks contain the same hydrothermal alteration and mineral assemblages, which include K-feldspar, quartz, sericite, chlorite, epidote, carbonate, pyrite, galena, sphalerite, marcasite and chalcopyrite, as well as minor magnetite, anatase, cervelleite, matildite, and bismuthinite. Gold occurs as electrum inclusions in pyrite or along microfractures in sulfides and quartz. Zircon U–Pb geochronology of the granite porphyry around the Hougou breccia pipe constrains the timing of breccia pipe formation to 145.9 Ma which is consistent with the formation age of the Dianfang breccia pipe (145.8 Ma), indicating that the two breccia pipes formed coevally at the end of the late Jurassic, rather than during the Paleoproterozoic, as was suggested by previous studies. The hydrothermal sulfides from the main orebody yield a Rb–Sr isochron age of 119.5 ± 1.8 Ma, suggesting that the eastern and western ore blocks formed coevally at the end of the early Cretaceous. In situ mineral trace element data, as well as sulfur and lead isotope data suggest that the eastern and western ore blocks were formed by a common ore-forming fluid that evolved from a magmatic-hydrothermal system that was genetically related to a hidden late Mesozoic granite. Pre-existing fractures and breccia then served as ideal conduits for fluid flow, accumulation, and gold deposition. Consequently, we propose that the ENE-striking faults developed in and around the breccia pipes and the annular brittle faults around the breccia pipes are good targets for future gold exploration at the Dianfang gold deposit. Based on these results and data from other gold deposits of similar ages around the margins of the North China Craton, we argue that the gold deposits in Xiong’ershan region formed under conditions of lithospheric extension from the late Jurassic to the early Cretaceous, which resulted from lithospheric thinning due to the westward subduction of the Pacific Plate.

Coupling Mineralogy, Textures, Stable and Radiogenic Isotopes in Identifying Ore-Forming Processes in Irish-Type Carbonate-Hosted Zn–Pb Deposits

Irish-type deposits comprise carbonate-hosted sphalerite- and galena-rich lenses concentrated near normal faults. We present new data from the Tara Deep resource and overlying mineralization, at Navan, and the Island Pod deposit and associated Main zone orebodies, at Lisheen. Tara Deep mineralization predominantly replaces Tournasian micrites and subordinate Visean sedimentary breccias. The mineralization is mainly composed of sphalerite, galena, marcasite and pyrite. A range of Cu- and Sb-bearing minerals occur as minor phases. At Tara Deep, paragenetically early sulfides exhibit negative δ34S values, with later phases displaying positive δ34S values, indicating both bacterial sulfate reduction (BSR) and hydrothermal sulfur sources, respectively. However, maximum δ34S values are heavier (25‰) than in the Main Navan orebody (17‰). These mineralogical and isotopic features suggest that Tara Deep represents near-feeder mineralization relative to the Navan Main orebody. The subeconomic mineralization hosted in the overlying Thin Bedded Unit (TBU) comprises sphalerite replacing framboidal pyrite, both exhibiting negative δ34S values (−37.4 to −8.3‰). These features indicate a BSR source of sulfur for TBU mineralization, which may represent seafloor exhalation of mineralizing fluids that formed the Tara Deep orebody. The Island Pod orebody, at Lisheen, shows a mineralogical paragenetic sequence and δ34S values broadly similar to other Lisheen orebodies. However, the lack of minor Cu, Ni, and Sb minerals suggests a setting more distal to hydrothermal metal feeder zones than the other Lisheen orebodies. Pb isotope data indicate a very homogeneous Lower Palaeozoic Pb source for all Navan orebodies. Lower Palaeozoic metal sources are also inferred for Lisheen, but with variations both within and between orebodies. Carbon and oxygen isotopic variations at Navan and Lisheen appear to result from fluid-carbonate rock buffering. The emerging spectrum of mineralogical and isotopic variations define proximal to distal characteristics of Irish-type systems and will assist in developing geochemical vectoring tools for exploration.

Genesis of the Meishan iron oxide–apatite deposit in the Ningwu Basin, eastern China: Constraints from apatite chemistry

The Meishan iron oxide–apatite deposit is located in the Ningwu volcanic basin in eastern China. The deposit comprises massive and brecciated ores in the main orebody, located at the contact between a gabbro–diorite porphyry and biotite–pyroxene andesites, and sub‐economic stockwork and disseminated ores. Among the four stages of alteration and mineralization, apatite coexists with magnetite, andradite, and quartz in massive magnetite ore and occurs in disseminated magnetite ore, coexisting with magnetite, siderite (after diopside), and quartz for Stage 2 iron mineralization. Apatite is also present in the altered gabbro–diorite porphyry. The apatites from the massive and disseminated magnetite–apatite ores are fluor‐ and hydroxyl‐ variety. Those from the altered gabbro–diorite porphyry show extensive solid solution between the hydroxyl‐apatite, fluor‐apatite, and chlor‐apatite end members. The apatites at Meishan record oxidized states during formation of the mineral deposit. The SO3 contents of apatite in the Meishan deposit mostly vary from 0.4 to 1.2 wt%, with the highest value of 4.97 wt%. MnO contents in apatites from our study are less than 0.17 wt%, and most values are below detection limit, indicating that the apatite formed in a high ƒO2 magmatic–hydrothermal fluid. The strong Eu depletion in apatites at Meishan resulted from the fractionation of plagioclase. The gabbro–diorite porphyry, magnetite, and apatite show similar LREE‐enriched patterns with significant negative Eu anomalies for apatite and magnetite, and no Eu anomaly for the gabbro–diorite porphyry. The gabbro–diorite porphyry and Stage 2 apatite associated with iron mineralization have also similar primitive mantle‐normalized trace element patterns, suggesting that the mineralization was related to gabbro–diorite porphyry. The REE pattern with significant negative Eu anomalies in apatite from the Meishan deposit is comparable with that of other Kiruna‐type deposits elsewhere in the world.

The occurrences and geochemical characteristics of thorium in iron ore in the Bayan Obo deposit, Northern China

The Bayan Obo deposit in northern China is an ultra-large Fe–REE–Nb deposit. The occurrences, and geochemical characteristics of thorium in iron ores from the Bayan Obo Main Ore Body were examined using chemical analysis, field emission scanning electron microscopy, energy dispersive spectrometer, and automatic mineral analysis software. Results identified that 91.69% of ThO2 in the combined samples was mainly distributed in rare earth minerals (bastnaesite, huanghoite, monazite; 56.43% abundance in the samples), iron minerals (magnetite, hematite, pyrite; 20.97%), niobium minerals (aeschynite; 14.29%), and gangue minerals (aegirine, riebeckite, mica, dolomite, apatite, fluorite; 4.22%). An unidentified portion (4.09%) of ThO2 may occur in other niobium minerals (niobite, ilmenorutile, pyrochlore). Only a few independent minerals of thorium occur in the iron ore samples. Thorium mainly occurs in rare earth minerals in the form of isomorphic substitution. Analyses of the geochemical characteristics of the major elements indicate that thorium mineralization in the Main Ore Body was related to alkali metasomatism, which provided source material and favorable porosity for hydrothermal mineralization. Trace elements such as Sc, Nb, Zr, and Ta have higher correlation coefficients with thorium, which resulted from being related to the relevant minerals formed during thorium mineralization. In addition, correlation analysis of ThO2 and TFe, and REO and TFe in the six types of iron ore samples showed that ThO2 did not always account for the highest distribution rate in rare earth minerals, and the main occurrence minerals of ThO2 were closely related to iron ore types.

Lead isotope constraints on the genetic relationships among different ore types in the Dongshengmiao deposit, northern China

The giant Dongshengmiao Cu-Zn-Pb-S deposit is the most representative Proterozoic sedimentary exhalative (SEDEX) deposit in China. A detailed investigation of Pb isotope compositions of sulfides from various types of ores and associated host rocks has been carried out to determine the genetic relationships among different ore types and to provide important insights on whether younger fluids have contributed mineralizing materials in the formation of the Dongshengmiao Cu-Zn-Pb ores. The substantial similarity of the Pb isotope composition between the studied stratiform Cu-Zn-Pb and S orebodies suggests that the bulk of the Dongshengmiao Cu-Zn-Pb ores belong to the same polymetallic metallogenic system with the syngenetic S ores of the Proterozoic age. Comparatively, vein-type ores show relative scattered Pb isotope signatures that fall along a well-correlated linear trend, whereas their less radiogenic end member projects towards the Pb isotope compositions of the overlying stratiform main orebody. In addition, the overall Pb isotope compositions of these vein-type ores have shown an apparent overlap and similar trend with the radiogenic disseminated pyrites in the mica schists, indicating their radiogenic Pb most likely originated from host rocks as well. The scatter of Pb isotope compositions of the Dongshengmiao Cu-Zn-Pb ores shows that lead was not homogenized regionally during subsequent metamorphism, ruling out the possibility of a deposit-scale remobilization. Furthermore, the significant difference and lack of intermediate Pb isotope values between the previously studied Hercynian feldspars and the bulk of the Dongshengmiao sulfide ores suggest that a significant introduction of metals from, or overprinting by, fluids derived from Hercynian magmatism is unlikely to have played an important role in the metal endowment. Taken together, all sulfide orebodies associated with various ore types in the Dongshengmiao deposit belong to an integrated and progressive hydrothermal ore-forming system of the Proterozoic age, and a portion of the vein-type ores and associated disseminated pyrites experienced a minor addition of evolved rock lead during subsequent greenschist face metamorphisms.

A Review of Flotation Separation of Mg Carbonates (Dolomite and Magnesite)

It is well documented that flotation has high economic viability for the beneficiation of valuable minerals when their main ore bodies contain magnesium (Mg) carbonates such as dolomite and magnesite. Flotation separation of Mg carbonates from their associated valuable minerals (AVMs) presents several challenges, and Mg carbonates have high levels of adverse effects on separation efficiency. These complexities can be attributed to various reasons: Mg carbonates are naturally hydrophilic, soluble, and exhibit similar surface characteristics as their AVMs. This study presents a compilation of various parameters, including zeta potential, pH, particle size, reagents (collectors, depressant, and modifiers), and bio-flotation, which were examined in several investigations into separating Mg carbonates from their AVMs by froth flotation.

Geology of the western flanks of the Oktyabr’skoe deposit, Noril’sk district, Russia: evidence of a closed magmatic system

The Oktyabr’skoe deposit in the Northern Siberian Platform is one of the world’s largest deposits in terms of platinum-group elements and nickel reserves. The genesis of this deposit has been inferred from the inner geological structure of its central portion and remains a matter of long-lasting and heated discussions. The current dominant hypothesis is that the ores were produced in an open magmatic system. This study is devoted to only one aspect of the complicated problem of ore formation, i.e., the geological structure of the Kharaelakh intrusion to which the huge orebodies are related. Recently, new data have been acquired on the structure and composition of the western flanks of the Kharaelakh intrusion, which pinches out in this direction and does not coincide with basalts as has been suggested in many publications. A distinctive feature of this part of the deposit is that it is cut by numerous relatively thin intrusions of contrasting compositions (from picritic gabbro-dolerite to leucogabbro) that are spatially separated in contrast with the central portion of the deposit, where these rocks occur as discrete layers of a single intrusion. These bodies taper off westward and are “blind” apophyses of the intrusion to which various ore types are related. The inner structure of this part of the vertical section of the intrusion is analyzed based on detailed data on the core material recovered by a number of boreholes and on the chemical and mineralogical characteristics of the ores, which differ from those in the main orebodies in that they possess lower Cu and PGE concentrations (up to 3.5 wt% and 9 ppm, respectively) and hence result in the dominance of pyrrhotite and limited amounts (and smaller grain sizes) of platinum-group minerals. Peripheral sills of the Kharaelakh intrusion were formed by portions of initial magma with different melt/cumulus minerals proportions, forming separate bodies of picritic and olivine-bearing gabbro-dolerite. The last rock varieties comprise disseminated ore, in contrast with the central parts of the intrusion, where these ores are located in the picritic and taxitic horizons. No peripheral sills or dikes connected with lava flows have been found inside the studied area. These facts evidence ore formation in a closed magmatic system.

Using Gravity and Magnetic Data for Insights into the Mesoproterozoic St. Francois Terrane, Southeast Missouri: Implications for Iron Oxide Deposits

Gravity and magnetic data in conjunction with available drill hole data were used to decipher the nature of the volcanic lithologies and their relationship to iron oxide ore deposits within the northwest portion of the Mesoproterozoic St. Francois Terrane in southeast Missouri. Analyses of the data included creating a deep-seated gravity anomaly map by removing the gravitational effect of the Paleozoic sedimentary units, residual gravity and magnetic anomaly maps, and two and one-half dimensional gravity and magnetic models. The residual gravity and magnetic anomaly maps highlighted a series of short-wavelength maxima and minima anomalies that could be interpreted to be granitic within collapsed caldera systems surrounded later by ring intrusions. The gravity and magnetic models illustrate that the sources of the anomalies are situated mainly within the upper 5 km of the crust and help to constrain the location of suspected calderas. The iron oxide deposits, some of which contain significant quantities of REE minerals, are rarely associated with both residual gravity and magnetic maxima but may be on the edge of these maxima and/or occur over gravity minima. The REE-rich Pea Ridge deposit is located over a gravity minimum where modeling shows the main ore body extending down to 1.5 km with a low-density region extending to 5 km below the ore body. The cause of this low-density body is unknown but may be associated with the formation of the ore deposit. Potential iron oxide deposits may occur to the south and southwest of Pea Ridge based on our analysis while to the northeast of the Pea Ridge deposit an anomaly pattern similar to that over Pea Ridge was found.

Mineralization and Genetic Environments of the Central and Main Orebodies in the Manjang Deposit, Goesan

Mineralization and Genetic Environments of the Central and Main Orebodies in the Manjang Deposit, Goesan

3D Geological Modelling and Prospecting Prediction of the Pulang Porphyry Copper Deposit, Yunnan Province, China

In this paper, we propose 3D model and prospecting application of Pulang copper deposit which is a typical super large scale porphyry copper deposit in Yunnan, southwest China. Geological, geophysical and geochemical data have been collected and integrated in a spatial database in order to model the surface and sub-surface geological bodies of the study area. 3D structure model of Pulang porphyry copper deposit (11.0 km × 5.0 km × 1.8 km) is established on the basis of these data defining temporal and spatial relationships among geological objects. The 3D grade property model of KT1 (the main orebody) is used to reflect the distribution of copper element in space and to infer or deduce the extension of orebody. In view of the nature of the mineralization, tectonism, multi-phase porphyry rocks, and wall-rock alteration, the deeper levels of KT1 at its northern and eastern limits are potential target zones for prospecting.

Primary geochemical haloes study of the possibly Carlin-like Dashui gold deposit for gold exploration in southern Gansu Province, central China

To increase the reserves of the possibly Carlin-like Dashui gold deposit in Maqu county, Gansu Province, central China, exploration techniques to detect mineralization in the subsurface of the mining district are required. Orebodies in the Dashui deposit are usually controlled by structures closely associated with the Ge'erkuohe granitoid. Samples collected from the deposit area indicate that the mineralization is primarily associated with the indicator elements, Au-Ag-As-Hg-Te-Sb, and less so with the indicator elements, K 2 O-Rb-F-Ba. The supra- and/or near-ore haloes are characterized by an As-Sb-Hg-Te-Au-Ag association and sub-ore haloes by a W-Mo-Bi-Co-Sc-Ni-V-Cd association. The primary geochemical haloes of the two main orebodies show that they were formed by up to three hydrothermal events. These results indicated that the two orebodies may extend downward to great depths, as was later confirmed by drilling down to depths of c. 3500–3400 m.