Gold-bearing Pyrite Research Articles

Textures, trace elements, and Pb isotopes of sulfides from the Haopinggou vein deposit, southern North China Craton: implications for discrete Au and Ag–Pb–Zn mineralization

The Haopinggou deposit in the Xiong’ershan district, southern margin of the North China Craton, comprises numerous Au and Ag–Pb–Zn veins hosted in metamorphic rocks of the Late Archean to early Paleoproterozoic Taihua Group. Two stages of mineralization have been recognized: Stage 1 pyrite–quartz veins and Stage 2 Pb–Zn-sulfide veins. Some pyrite–quartz veins are surrounded or cut by Pb–Zn-sulfide veins, others occur as independent veins. Six generations of pyrite have been identified at Haopinggou: Py1 to Py3 in Stage 1 and Py4 to Py6 in Stage 2. Pyrites from Stage 1 are enriched in Au, As, Co, Ni, and Bi, whereas Stage 2 pyrites contain higher Ag, Pb, Zn, Sn, and Sb. Invisible Au mostly occurs as lattice-bound gold in Py2 (up to 92 ppm Au) and Py3 (up to 127 ppm Au) and has a close relationship with As. Native Au grains are also present in Py3 and likely resulted from mobilization and reprecipitation of the invisible Au previously locked in the precursor pyrite. This view is supported by extensive plastic deformation in Stage 1 pyrite as revealed by electron backscatter diffraction analysis. In Stage 2, Ag is mostly present as lattice-bound silver closely associated with Sb in galena (up to 798 ppm Ag). A variety of silver minerals are also present as inclusions within galena or as interstitial grains. These silver minerals were likely formed via Ag–Cu exchange reaction between tetrahedrite and galena or represent exsolution from galena due to a temperature decrease. Pb isotopic compositions differ remarkably between Stage 1 and Stage 2 sulfides, indicating different sources of lead. Pb in Stage 2 Pb–Zn-sulfide veins is consistent with the Haopinggou porphyry close to the veins. The field, textural, compositional, and lead isotopic data led us to conclude that the early gold-bearing pyrite–quartz veins and late silver-bearing Pb–Zn-sulfide veins likely formed from distinct fluid systems related to discrete mineralization events. Our study suggests that Au and Ag–Pb–Zn veins hosted in the same metamorphic terrains may not be genetically related to each other.

Rb-Sr geochronology of single gold-bearing pyrite grains from the Katbasu gold deposit in the South Tianshan, China and its geological significance

The newly discovered Katbasu gold deposit in the South Tianshan region has a gold reserve of 76t at an average grade of 3.84g/t. It is the first large gold deposit in the central segment of the South Tianshan. Gold mineralization is hosted within granite, and is associated with potassic, phyllic and chloritic alteration. Gold-bearing pyrite occurs as disseminations in the host rock and as quartz-sulfide veins cross-cutting the potassic and phyllic alteration assemblage. Rubidium (Rb) - strontium (Sr) analyses on sericite within five individual pyrite grains from a phyllic alteration sample yield an isochron age of 322.5±6.8Ma (MSWD=3.2). The host granite has a SIMS U-Pb zircon age of 351.4±1.1Ma (MSWD=0.13). The Rb-Sr isochron age represents the mineralizing age of the Katbasu gold deposit, which significantly postdates the ore-hosting granite but is consistent with the age of regional porphyry type mineralization at ~320Ma in the South Tianshan. Discovery of the Katbasu gold deposits indicates huge potential for gold exploration in the central segment of the South Tianshan as it is geologically similar to the western and eastern segments of the South Tianshan, which both host many world-class gold deposits.

A discussion on the performance of seven existing models proposed to describe induced polarization

Many types of classical models of the induced polarization (IP) effects of rock ore have been introduced in previous studies. Our focus is on determining the most effective model for describing the rock ore IP effects based on a numerical simulation calculation and a rock mineral spectrum experiment. We have constructed a Delphi 7 program for seven models to calculate the complex resistivity spectrum of phase. We have also evaluated the influences of the parameters on the spectrum and the spectral scope. More than 50 pieces of various natural rock ore samples from 16 regions were selected, and the frequency sweep measurements were completed using an SI-1260 Solartron spectrometer. Another program of seven models was developed using a differential evolution algorithm and least-squares for fitting the experimental spectral data. The purpose was to evaluate the ability of these models for fitting the IP effects. The results found that the influence laws on the spectrum of the different parameters, as well as the spectral scope of the models, were different. The natural samples measured revealed unimodal and bimodal phase spectra. Dias and multi-Cole-Cole models were optimal for characterizing the unimodal and bimodal phase spectra of the selected metal minerals, with the highest fitting precision root-mean-square (rms) error of 2.5% and 1.16%, respectively. Warburg, Cole-Cole, and generalized Cole-Cole models were suitable for the unimodal phase spectra, with the highest fitting precision of 3.67%, 3.01%, and 3.27%, respectively. Madden and Cantwell model was suitable for characterizing the silver-ore- and gold-bearing pyrite, but the rms was [Formula: see text] for other samples. The Debye model had an rms [Formula: see text] for characterizing all our experimental samples.

Comparison of the native antimony-bearing Paiting gold deposit, Guizhou Province, China, with Carlin-type gold deposits, Nevada, USA

The Paiting gold deposit, Guizhou Province, China, has been regarded as a Carlin-type gold deposit by several researchers. Alteration and ore-related minerals from the Paiting deposit were examined, and results were compared with the Cortez Hills Carlin-type gold deposit, Nevada, USA. Similarities include the structural and stratigraphic controls on the orebodies in both deposits and the occurrence of invisible gold ionically bound in arsenian pyrite. Significant differences include the following: (1) The gold-bearing mineral in Nevada is arsenian pyrite. However, gold-bearing minerals in the Paiting deposit include arsenopyrite, arsenian pyrite, and trace pyrrhotite. Also, euhedral or subhedral gold-bearing arsenian pyrite at Paiting contains significantly less As, Cu, and Hg than gold-bearing pyrite from Nevada. (2) Alteration in the Paiting deposit displays significantly less decarbonatization. Instead, dolomite precipitation, which has not been described in Nevada deposits, is associated with deposition of gold-bearing sulfide minerals. (3) Stibnite and minor native antimony typify Paiting late-ore-stage minerals, whereas in Nevada, realgar, orpiment, and calcite are common late-ore-stage minerals. Precipitation of native antimony in the Paiting deposit reflects the evolution of a late-ore fluid with unusually low sulfur and oxygen fugacities. Some characteristics of the Paiting gold deposit, including formation of ore-stage dolomite and precipitation from CO2-rich ore fluids at temperatures in excess of 250 °C, are more typical of orogenic deposits than Nevada Carlin deposits. The presence of similarities in the Paiting deposit to both Carlin type and orogenic deposits is consistent with formation conditions intermediate to those typical of Carlin type and orogenic systems.

MỘT SỐ ĐẶC ĐIỂM HÌNH THÁI VÀ THÀNH PHẦN HÓA HỌC CỦA ARSENOPYRIT, PYRIT TRONG CÁC TỤ KHOÁNG VÀNG - SULFIDE BÓ VA VÀ NAM QUANG (ĐÔNG BẮC VIỆT NAM)

Crystal morphology and chemical composition of arsenopyrite and pyrite in the Nam Quang and Bo Va deposits of the Song Hien basin (Northeast Vietnam) are studied in detail. Arsenopyrite crystals often form elongated crystals. Their chemical composition are relatively poor in As, but rich in S with S/As ratios often > 1.1, impurity elements such as Ni, Co, Sb, and sometimes containing gold (up to 0.02 wt.%). Pyrite is characterized by the stoichiometric composition, but contains relatively high arsenic and sometimes contain gold. The correlation between the concentration of As and Au in pyrite has been recorded. The morphology and chemical composition of arsenopyrite and pyrite of Bo Va and Nam Quang deposits can be correlated to those in the Au-sulfide deposits in black shale in Kazastan and southestern China.ReferencesTrần Trọng Hòa (chủ biên), 1996: Xây dựng mô hình điều tra, sử dụng hợp lý, bảo vệ môi trường trong quá trình khai thác tài nguyên khoáng sản quý hiếm tỉnh Cao Bằng. Lưu trữ Viện Địa chất, Hà Nội. Trần Trọng Hòa, Polyakov G.V., Trần Tuấn Anh, Borisenko A.S., Izokh A.E., Balyakin P.A., Ngô Thị Phượng, Phạm Thị Dung, 2011: Hoạt động magma và sinh khoáng nội mảng miền Bắc Việt Nam. Nxb. Khoa học Tự nhiên và Công nghệ, 368tr. Trần Trọng Hòa, Nevolko P., Ngô Thị Phượng, Trần Tuấn Anh, Phạm Thị Dung, Bùi Ấn Niên, Nguyễn Xuân Huyên, Nguyễn Thùy Dương, Vũ Hoàng Ly, Trần Văn Hiếu, 2013: Các tụ khoáng vàng-sulfide trong các thành tạo lục nguyên - carbonat rift Sông Hiến, ÐBVN. Tuyển tập Báo cáo KHCN toàn quốc năm 2013. ISBN: 978-604-59-0693-4; tr.131-140. Nông Thế Tàng (chủ biên), 1996: Báo cáo Khảo sát và tìm kiếm đánh giá vàng gốc Nam Quang, Bảo Lạc, Cao Bằng. Lưu trữ Trung tâm Thông tin lưu trữ Địa chất, Hà Nội. Chen M.H., Mao J.W., Bierlein F.P., Norman T., Uttley P.J., 2011: Structural features and metallogenesis of the Carlin-type Lannigou gold deposit, Guizhou Province, China. OreGeol. Rev.43 (1), 217-234. Fleet, M.E., Mumin, A.H., 1997: Gold-bearing pyrite and arsenopyrite from Carlin Trend gold deposits and laboratory synthesis: American Mineralogist, v. 82, p.182-193. Kovalev K.R., Kalinin Yu.A., Naumov E.A., Kolesnikova M.K., Korolyuk V.N., 2011: Gold-bearing arsenopyrite in eastern Kazakhstan gold-sulfide deposits. Russian Geology and Geophysics 52, 178-192. Kovalev K.R., Kalinin Yu.A., Polynov V.I., Kydyrbekov E.L., Borisenko A.S., Naumov E.A., Netesov M.I., Klimenko A.G., and Kolesnikova M.K., 2012: ISSN 1075-7015, Geology of Ore Deposits, vol. 54, No.4, 254-275. Peters S.G., HuangJ.Z., Li Z.P., JingC.G., 2007: Sedimentary rock-hosted Au deposits of the Dian-Qian-Guiarea, Guizhou, Yunnan Provinces, and Guangxi District, China. Ore Geol. Rev.31,170-204. Volkova A. V., Genkina A. D., and Academician of the RAS Goncharovb V. I., 2006. New data on invisible gold in disseminated sulfide ores of the Natalka deposit. Vol. 409A, No 6, pp. 879-883. Zhong H.R., Chao S.W., Wu B.X., Zhi T.G., Hofstra A.H., 2002: Geology and geochemistry of Carlin- type gold deposits in China Mineralium Deposita 37:378-39. Zhou T.H., Goldfarb R.J., Phillips G.N., 2002: Tectonics and metallogeny of gold deposits in China. Mineralium Deposita 37, 249-282.

On the use of lignin-based biopolymer in improving gold and silver recoveries during cyanidation leaching

In the present paper, influence of a lignin-based biopolymer in improving gold and silver recoveries during cyanidation leaching is discussed. Series of laboratory cyanidation leaching testworks at the absences and the presences of the biopolymer were performed under variations of the biopolymer concentration, NaCN concentration, slurry density and particle size distribution. The ore samples used were from Pongkor Gold Mine of PT. Antam, Tbk. in Indonesia. The biopolymer additive was found to reduce slurry viscosity that leads to a higher dissolved oxygen concentration in the leach solution. The testwork results show that the use of biopolymer improves gold and silver recoveries as well as leaching kinetics. At biopolymer dosage of 800mg/L, the increases of gold and silver recoveries were 4.5% and 6.4%, respectively. The lignin-based biopolymer is able to disperse fine solid particles and stabilizes the ore suspension in the leach-slurry that results in a better contact between the ore and the leaching agents. The effect of biopolymer on the gold and silver recoveries was found to be more significant at lower cyanide dosages. The addition of biopolymer resulted in the increase of cyanide consumption, lowering final pH and higher dissolved iron which is associated with gold-bearing pyrite dissolution. Enhanced dissolution of gold-bearing pyrite at higher dissolved oxygen concentration was found as the major factor that improves gold recovery at the presences of the biopolymer in addition to lowering slurry viscosity that leads to higher dissolved oxygen concentration and effect of fine particles dispersion.

Occurrence of gold in hydrothermal pyrite, western Taupo Volcanic Zone, New Zealand

The Taupo Volcanic Zone (TVZ) on the North Island of New Zealand is located above the subducting Pacific slab and hosts hydrothermal systems related to subduction, arc magmatism and crustal extension. In these systems, gold is transported primarily as sulphide complexes, with gold being deposited in response to boiling and mixing of the deep geothermal fluids. Conglomerate cobbles and hydrothermal fumaroles from the upper Retaruke River in the western TVZ are mineralised deposits that have been eroded from the nearby Miocene alluvial sedimentary plateau. Abundant gold-bearing pyrite was precipitated in the conglomerates and fumaroles by late hydrothermal process, primarily occurring as veinlets, disseminations and fine-grained aggregates which consists discrete euhedral microcrystals. Scanning electron microscopy combined with X-ray energy disperses spectroscopy shows that pyrites are commendably affected by late hydrothermal fluids, possibly by the carbonate fluid. Electron probe microanalysis revealed that the pyrite contains 20–120 ppm Au (averaging 60 ppm). Wavelength dispersive spectral elemental mapping suggests that gold is distributed uniformly in pyrite, indicating structurally bound gold (solid solution) in pyrite. Gold mineralisation recognised in the conglomerates and fumaroles demonstrates that the upper Retaruke River is a promising target for future gold exploration.

Geological setting of the Wassa gold deposit, SW Ghana

Including past production, current indicated and inferred resources, Wassa is a 5 Moz poly-deformed early-orogenic gold deposit located on the eastern flank of the Ashanti Belt, in southwest Ghana. It is hosted by metamorphosed volcanic, intrusive and sedimentary rocks of the Sefwi Group (ca. 2260–2160 Ma). Early mineralization has an Eoeburnean age (2164 ± 22 Ma, Re–Os on pyrite) and is characterized by quartz veins, by a carbonate alteration of the host rocks, and by deformed gold-bearing pyrite. Remobilization of this gold occurred during the late stages of the Eburnean Orogeny (~ 2.1 Ga) and is associated with quartz-carbonate veins with visible gold and euhedral pyrites.

Local and Regional Mass Transfer During Thrusting, Veining, and Boudinage in the Genesis of the Giant Shale-Hosted Paracatu Gold Deposit, Minas Gerais, Brazil

Multiscale structural and geochemical studies have been applied to understand the genesis of the Paracatu deposit in Brazil, a shallow-dipping, bulk-tonnage, vein-style low-grade Au(-Ag-Pb-Zn) orebody hosted in ~1000 Ma black phyllites of the Paracatu Formation, associated with intense shearing accompanying thrusting during the ~680 Ma Brasiliano orogeny. Massive to laminated quartz-sulfide-carbonate veins and associated alteration and Au mineralization formed early in the deformation history, and these veins were boudinaged during subsequent progressive increase in shear strain. Geochemical profiles across the ore allow recognition of a relatively homogeneous protolith at 100-m scales with respect to Ti, Al, Zr, V, and rare earth elements, including a footwall with protolith attributes similar to those of the ore. Oxygen, hydrogen, and sulfur isotopes do not reveal a distinctive external fluid source; rather, they reflect fluid-rock equilibration with the host phyllites during greenschist facies regional metamorphism. Detailed geochemical sampling around a prominent population of smaller boudinaged veins shows that Si, Ca, and Sr were removed and Al, K, and Ti were residually concentrated during formation of synboudinage dark selvages. This process of mass transfer occurred at scales more local than the processes responsible for ore genesis. Despite the local processes of chemical equilibration and redistribution, many of the main ore components appear externally derived at scales broader than the orebody. Gold, As, Ag, Sb, Bi and, to some extent, Pb and Zn show a strong spatial and statistical correlation with boudinaged quartz-sulfide ± carbonate veins, and these are surrounded by a broader (10–50-m vertical scale) halo of enriched K, Ba, and volatiles (loss on ignition), with depleted Na and Sr. The majority of gold is present as inclusions in pyrite and arsenopyrite within and immediately surrounding the veins, and gold-bearing pyrite shows mineral chemistry consistent with a hydrothermal origin. The main population of large veins locally preserve preboudinage, complex internal vein textures, including sulfide-rich wall-rock laminae similar to laminated fault-fill veins in many orogenic-style vein deposits. These larger veins contain most of the gold in the Paracatu resource. Metals were most likely sourced distal to the Paracatu Formation and were precipitated in sheeted shear or tensile veins during the early stages of the Brasiliano thrusting. The oblate strain recorded by the boudinaged, mineralized veins is anomalous and distinctive to Paracatu at km scales, even though the thrusting is regional. Although the orebody may have been physically dislocated by thrusting from the place where the early veins formed, the anomalous strains recorded suggest a perturbation in the footwall to the regional thrust or, perhaps, a spatially restricted competency contrast within the stratigraphy, which contributed to the localization of the present mineralization during the thrusting.

Error analysis in ore particle composition distribution measurements

Measurements of ore particle composition distribution, commonly termed mineral liberation distribution, are used in assessing process performance in mineral processing. In many applications, comparisons are made between particle composition distributions (for example comparing the products of fine and coarse grinds) and in such comparisons it is useful to understand the errors in the measurements in order to decide whether any differences are significant. A statistical approach based on bootstrap resampling has been applied to estimate the confidence intervals for ore particle composition distribution measurements obtained using the MLA automated mineralogy system.In this approach confidence intervals for each individual composition class are estimated as compared to a previous analytical solution which provides this information for particle composition data in cumulative form (Leigh et al., 1993). The effects on the magnitude of the error associated with measured values of particle composition distribution of the number of ore particles measured in the analysis and the complexity of the particle texture are investigated. Examples from a gold-bearing pyrite ore and an iron oxide copper gold ore are presented to demonstrate the practical application of this approach.

Quantifying mineral grain size distributions for process modelling using X-ray micro-tomography

Recent advances at JKMRC in modelling mineral liberation required the development of a method to measure ore textural characteristics such as the mineral grain size distribution and the spatial location of mineral grains in three dimensions.This paper describes the development of this method which uses X-ray micro-tomography to provide three-dimensional (3D) measurement of the grain size distribution and spatial location of the minerals in an ore. The methodology was developed on a gold-bearing pyrite ore and used to quantify the textural characteristics which are key inputs for modelling mineral liberation in this ore during comminution. The measurement and image processing steps required to quantify the grain size distribution of the mineral of interest, pyrite, are described together with the image analysis method. The quantification of 3D mineral characteristics together with corresponding two-dimensional (2D) sections through the same particle, provided the opportunity to explore the relationship between 2D and 3D grain size data.

The Wassa deposit: A poly-deformed orogenic gold system in southwest Ghana – Implications for regional exploration

The Ashanti greenstone belt in southwest Ghana hosts many gold deposits distinguished by different timing and structural contexts. This study investigates the evolution of the Wassa system by integrating field and geophysical observations. This 4 million ounces (past production and current resources) gold deposit is interpreted to represent the oldest gold mineralization event in West Africa with gold-bearing pyrites aligned and stretched within the S1 ductile fabric. Mineralized quartz-carbonate veins were strongly deformed during the D1 deformation event. Three additional folding events are characterized by hectometer-scale tight to isoclinal folds, by a kilometer-scale synform fold centered on the mine and by a late recumbent metric-scale folds. Because of its early timing, the Wassa system represents a new poly-deformed deposit type in West Africa and highlights a potential for new discoveries in the underexplored meta-volcanic and meta-sedimentary Sefwi Group. Timing of the gold mineralization at the Wassa mine makes this deposit type a possible candidate for the source of the gold contained in the Tarkwa paleoplacer.

Geology, geochronology and sulphur isotope geochemistry of the black schist-hosted Haoyaoerhudong gold deposit of Inner Mongolia, China: Implications for ore genesis

The Haoyaoerhudong gold deposit is located in the Urad Middle Banner area of Inner Mongolia in China, and is hosted by black schist of the Bilute Formation in the Mesoproterozoic Bayan Obo Group. The gold mineralization is within a 4500m long and 100m wide zone associated with sulphide(–quartz) veins following the schistosity and crosscutting fractures in the host-rocks; locally as disseminated sulphide in altered black schist. The sulphide mineral assemblage is pyrrhotite–pyrite(–arsenopyrite–chalcopyrite–sphalerite) and is associated with a weak hydrothermal alteration characterized by a silica halo with variable amounts of biotite, sericite and carbonate.The Bilute Formation was intruded by multi-stage dykes; these include metamorphosed porphyritic diorite that pre-dates mineralization, unmetamorphosed amphibole olivine gabbro that pre-dates mineralization, and tourmaline-bearing pegmatite that post-dates mineralization. In order to constrain the timing of the gold mineralization and host rocks, zircons from the porphyritic diorite, amphibole olivine gabbro and tourmaline-bearing pegmatite were extracted for U–Pb dating. Gold-bearing pyrite samples were analysed for δ34S to help determine the possible source of S in the mineral zones. A weighted mean 206Pb/238U age date of 288±3Ma (MSWD=2.4) was obtained for the porphyritic diorite, a weighted mean 206Pb/238U age date of 282±1Ma (MSWD=0.58) was obtained from the amphibole olivine gabbro, and a weighted mean 206Pb/238U age date of 182±1Ma (MSWD=1.04) was obtained from the tourmaline-bearing pegmatite. These dates constrain the timing of gold mineralization to between 282±1 and 182±1Ma, and are consistent with the hydrothermal alteration ages of ca. 267–246Ma reported from the literature. These new zircon dates indicate that the regional metamorphism of the Bayan Obo Group ceased by the time the Haoyaoerhudong gold mineralization was deposited and the genesis of mineralization is not related to the regional metamorphic event. The gold-bearing pyrites gave positive δ34SV-CDT values between 6.8 and 13.4‰, and are different from the δ34S widely distributed values for the typical black rocks, indicating that the sulphur is not derived from the black Bilute Formation, but sourced from some other relatively uniform reservoir. Widespread contemporaneous granitic magmatism is developed in the Haoyaoerhudong area and we suggest that the sulphur forming the gold-bearing sulphides is probably sourced from a carbonate-contaminated granitic magma reservoir. The new zircon dates for the dykes and the δ34S data for gold-bearing sulphides indicate that the gold mineralization did not form from metamorphosed black schist in the Bayan Obo Group, but is associated with magmatic–hydrothermal activity.

Iron Recovery by Two-Stage Roasting the Gold-Bearing Pyrite Concentrate and Gold-Leaching from the Pyrite Cinder by Thiourea

Pyrite cinders, which are the waste products of sulphuric acid manufacturing plants, contain hazardous but valuable heavy metals. This passage introduced that iron recovery by two-stage roasting the pyrite concentrate and gold-leaching from the pyrite cinder by thiourea. After re-floating and two-stage roasting of the gold-bearing low-grade pyrite concentrate, the final cinder contains about 0.056% As and 61% Fe and high grade gold and silver. The thiourea gold-leaching experiment for the pyrite cinder shows the gold-leaching rate is up to 90.4% in the case of grinding fineness of 60%-0.074mm, pH = 1~2, R=1:2, thiourea dosage of 10g / L, ferric sulfate dosage of 3g / L, leaching time of 6h.

Rb‐Sr Dating of Pyrite and Quartz Fluid Inclusions and Origin of Ore‐forming Materials of the Jinshan Gold Deposit, Northeast Jiangxi Province, South China

AbstractThe Jinshan gold deposit is located in the Northeast Jiangxi province, South China, which related to the ductile shear zone. It contains two ore types, i.e. the alteration‐type ore and the gold‐bearing quartz vein ore. Rb‐Sr age dating is applied to both gold‐bearing pyrite in the alteration‐type ore and fluid inclusion in the gold‐bearing quartz vein to make clear the time of the gold mineralization of the Jinshan deposit. Analytical results of this study yielded that the age of the alteration‐type ore bodies is about 838±110Ma, with an initial 87Sr/86Sr value of 0.7045±0.0020. However, the age of the gold‐bearing quartz vein‐type ore is about 379±49Ma, and the initial 87Sr/86Sr is 0.7138±0.0011. Based on the age data from this work and many previous studies, the authors consider that the Jinshan gold deposit is a product of multi‐staged mineralization, which may include the Jinninian, Caledonian, Hercynian, and Yanshanian Periods. Among them, the Jinninian Period and the Hercynian Period might be the two most important ore‐forming periods for Jinshan deposit. The Jinninian Period is the main stage for the formation of alteration‐type ore bodies, while the Hercynian Period is the major time for ore bodies of gold‐bearing quartz vein type. The initial values of the 87Sr/86Sr from this study, as well as the previous isotope and trace element studies, indicate that the ore‐forming materials mainly derived from the metamorphic wall rocks, and the ore‐forming fluids mainly originated from the deep metamorphic water.

Electrochemical Behavior of Carbon Paste Electrode with Gold-Bearing Pyrite in Bioleaching

The dissolution of gold-bearing pyrite plays an important role in bioleaching of gold. This paper describes a fundamental study on the electrochemical behavior and reaction mechanisms of gold-bearing pyrite leaching in the form of Carbon Paste Electrode (CPE) with and without microorganisms using Cyclic Voltammetry (CV) and polarization curve. A two step process was suggested from Cyclic voltammetry. Electrode passivation by elemental sulphur was observed below 700mV (vs. SCE), elemental sulphur was then oxidized to sulphate when the electrode potential further increased from 700mV. The polarization current density of CPE and the oxidation rate of pyrite are further enhanced by the presence of microorganisms. Analyses of EDS and XPS confirmed the formation of elemental sulphur and sulphate. This electrochemical method successfully showed its simplicity and reliability to measure oxidation rate of gold bearing pyrite.

Recovery of Zinc during the Pre-Treatment of a Refractory Gold-Bearing Ore

Mesophilic bacteria were enriched from samples collected from acid mine drainages in La Carolina (San Luis, Argentina). Two enrichments, E1 and E2, showed suitable rates for iron or sulphur oxidation, respectively. Both enrichments were characterized by FISH analysis. They were mainly composed by Leptospirillum ferrooxidans and Acidithiobacillus ferrooxidans respectively. Studies with both, mixed and individual enrichments, showed biooxidation (measured as iron solubilisation) of a refractory gold-bearing pyrite ore from Hualilán (San Juan, Argentina). Pyrite and sphalerite were the main mineral species in the ore with 7% w/w and 8% w/w of iron and zinc and approximately 25 ppm of gold. Leaching experiments (2% w/v ore, 1.8 initial pH, 180 rpm and 30°C) were carried out with the addition of different alternative energy sources (6.67 g/L sulphur powder, 1 g/L ferrous iron, 0.02% w/v yeast extract). Redox potential, pH, ferrous iron concentration and total Fe and Zn were measured regularly. A 100% of iron leaching (after 28 days in the best experimental condition) was observed in some of the cultures. In other systems high zinc release was obtained (100% of dissolution after 28 days in the best experimental condition). Our results strongly suggest that under the correct operating conditions, biooxidation pre-treatment can be used to recover zinc as a subproduct of gold extraction from refractory ore.

Recovering Gold from a Gold-Bearing Pyrite by Flotation and Chemical Process

The ore assays 2.5g/t Au, 23.4% S and 56.6% Fe. This research enriched the gold by flotation, and recovered it by a chemical process. The obtained flotation concentrate contains 66.35%g/t gold and 37.06% S with recovery 96.14% and 96.42% respectively. A roasting process was conducted at 900-1000°C for 5.5hrs, followed by cyanide leaching of the residue. The gold leaching rate reaches 87.4% with an adsorption rate of 97.6%. Furthermore, the regrinding of the concentrate to 95% -0.18μm was conducted, and followed by cyanide leaching at pH11.5 for 12hrs. The results show the amount leached gold reaches 92.5% with an adsorption rate of 99.21%, which increases by 1.61% and 5.1% in comparison with the roasting-leaching process.

LA-ICPMS and EPMA studies of pyrite, arsenopyrite and loellingite from the Bhukia-Jagpura gold prospect, southern Rajasthan, India: Implications for ore genesis and gold remobilization

The Bhukia-Jagpura gold prospect is hosted by a Paleoproterozoic metasedimentary rock sequence that constitutes the lowermost part of the Aravalli Supergroup, lying in close proximity to the basement-cover contact. A combined ore petrographic, LA-ICPMS and EPMA studies of iron sulfides and sulfarsenides from the prospect has revealed four varieties of pyrite and two varieties of arsenopyrite with different trace element compositions. The data indicates a sedimentary-diagenetic origin for the earliest Pyrites (Py) I and II, which are devoid of any gold, in contrast to hydrothermal Py III and IV with a minor, but significant content of invisible gold (0.3–1.6ppm). Associated loellingite (35–51ppm) and Arsenopyrite (Aspy) I (0.28–10ppm) contain the maximum concentration of invisible gold, while it is substantially lower in Aspy II (0.06–1.5ppm). The compositions of the gold-bearing pyrites (low Ni:Co ratios), arsenopyrites and loellingite (rich in Co), and the presence of Au–Bi–Te mineral phases within arsenopyrite, support a magmatic hydrothermal model for the origin of gold–sulfide mineralization, which appears to have taken place during the peak of regional metamorphism, or at an earlier stage. The different stages of deformation and metamorphism released and remobilized gold in invisible and discrete forms from the sulfarsenides. During prograde metamorphism of Aspy I, gold was partially incorporated and relatively enriched within the structure of loellingite. Later, during retrograde metamorphism gold was exsolved as visible grains at the interface of loellingite and Aspy II and/or within loellingite.

Giant Mesozoic gold provinces related to the destruction of the North China craton

Lode gold deposits in Precambrian cratons represent the world's major gold source and were mostly generated during formation and stabilization of the cratons. However, there is an extraordinary exception in the North China craton (NCC), where lode gold deposits formed after prolonged stabilization of the craton. Molybdenite Re–Os and hydrothermal sericite and biotite 40Ar/39Ar dating of major gold deposits from the Xiaoqinling district, southern NCC, bracket their emplacement in the range of 154.1±1.1 to 118.9±1.2Ma (n=23), postdating formation of the craton by more than 1.7 billion years. Fluid inclusions extracted from gold-bearing pyrite have elevated 3He/4He ratios (1.52–0.22Ra) and mantle-like Ne isotopes (20Ne/22Ne=10.02−9.22 and 21Ne/22Ne=0.033−0.027), indicating presence of mantle-derived fluids in the ore system. Measured δ34S of pyrite and δD and δ18O of hydrothermal micas and fluid inclusion waters in auriferous quartz further confirm a magmatic/mantle source for sulfur and ore fluids. Gold deposits of similar ages also widely occur in the eastern and northern margins of the NCC, which, together with those in the Xiaoqinling district, have a total reserve of ∼2500t gold, forming the only known giant late Mesozoic gold province in the world's Precambrian cratons. These deposits formed coevally with extensive felsic to mafic magmatism, development of intracontinental rift basins, and exhumation of metamorphic core complexes across the eastern NCC, events interpreted as indicating thinning and destruction of the lithosphere beneath the craton. Rising of asthenosphere coupled with destruction of the lithosphere has generated voluminous mafic and felsic magmas that provided sufficient fluids, sulfur and, by inference, other ore components to form the giant gold provinces.