Gold In Pyrite Research Articles

Fluid Inclusions and H–O–C–S–Pb Isotopic Systematics of the Jinba Gold Deposit, NW China: Implications for Ore Genesis

The Jinba gold deposit is located in the Maerkakuli Shear Zone of the south Altay Orogenic Belt, NW China. Mineralization types are classified as altered rock–and quartz vein–type. Orebodies occur as veins or lenses controlled by NW–trending faults, and are hosted in phyllite (Early–Middle Devonian Ashele Formation) and plagiogranite (Early Devonian Habahe Pluton). Three paragenetic stages were identified: early quartz–pyrite–gold (Stage 1), middle quartz–chalcopyrite (Stage 2), and late calcite–quartz–galena–sphalerite (Stage 3). Fluid inclusions within the deposit are liquid–rich aqueous (LV–type), vapor–rich aqueous (VL–type), carbonic–aqueous (LC–type), and purely carbonic (C–type) FIs. Homogenization temperatures for stages 1–3 FIs were 373–406 °C, 315–345 °C, and 237–265 °C, respectively. Fluid salinities for stages 1–3 were 2.1–13.6 wt%, 3.2–6.1 wt% and 3.9–6.0 wt% NaCl equivalent, respectively. The ore–forming fluids evolved from a CO2–NaCl–H2O ± CH4 to a NaCl–H2O system from stage 1–3. Oxygen, hydrogen, and carbon isotopic data (δ18Ofluid = 1.7‰–8.1‰, δDfluid = –104.1‰ to –91.7‰, δ13Cfluid = –0.4‰–6.3‰) indicate that ore–forming fluids were metamorphic hydrothermal origin with the addition of a late meteoric fluid. Sulfur and lead isotope data for pyrite (δ34Spy = 3.3‰–5.3‰, 206Pb/204Pb = 17.912.3–18.495, 207Pb/204Pb = 15.564–15.590, 208Pb/204Pb = 37.813–38.422) show that the ore–forming materials were mainly derived from diorite and the Ashele Formation. Mineralization, FIs, and isotope studies demonstrate that the Jinba deposit is an orogenic gold deposit.

Micro-Nanoscale Characteristics of Pyrite and Its Implications for Gold Mineralization: Two Cases of Gold Deposits in the Youjiang Basin and Southwestern Tianshan Mountains.

The mineralogical and compositional characteristics of gold-bearing minerals and the occurrence of gold are not only of great significance to exploring the sources of ore-forming materials and their formation mechanisms but also helpful for designing reasonable beneficiations and smelting schemes and achieving remarkable economic benefits. This paper presents an integrated study on the crystal characteristics, elemental composition and distribution of pyrite (the main gold-bearing minerals), on the basis of electron probe microanalysis (EPMA), scanning electron microscopy (SEM), laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and nano-secondary ion mass spectrometry (NanoSIMS). The occurrence of gold in the Shuiyindong gold deposit and Ashawayi gold deposit has been studied by means of microscopy, SEM, and EPMA images, elemental correlations, S-Fe-As ternary diagrams, logAs-logAu diagrams and Au/As ratios. The gold in pyrite of the Shuiyindong deposit is in the form of nano gold inclusions and lattice gold. The gold in pyrite of the Ashawayi deposit dominantly exists in the form of nano gold inclusions or is present as micro-nano gold particles in the cracks or edges of pyrite, some of which can exist as lattice gold. The ore-forming hydrothermal solution of the Shuiyindong gold deposit is mainly underground hot brine, but it may be reformed by a deep magmatic hydrothermal solution or volcanic-subvolcanic hydrothermal solution. The ore-forming hydrothermal solution of the Ashawayi gold deposit is mainly derived from the metamorphic hydrothermal solution formed during the orogenic process, and the ore-forming process or post-mineralization process may be reformed by the leaching of underground hot brine. Finally, the characteristics of ore-forming fluids and evolution of the two types of deposits are determined via pyrite element surface scanning. This paper shows that micro-nanoscale study of gold-bearing pyrite is of great significance to understanding the gold mineralization process and is worth further study.

Roasting temperature effect on the recovery of refractory gold and silver in pyrite concentrates

Pyrite concentrates with refractory gold and silver were roasted at different temperatures to improve the recovery of the metals by cyanide leaching. Scanning Electron Microscope characterization of the calcine revealed that the gold occluded in the pyrite less than one micron, and roasting produced channels in the concentrate, exposing the gold particles to the leaching solution. Gold and silver recoveries were maximum in the temperature range of 500-600?C due to the calcine high surface area and porosity. The Au and Ag recovery improved from 25 to 86% and 50 to 73%, respectively. The Au secondary encapsulation due to the sintering, the formation of the Ag-Fe-S species (Fe1?xS + Ag2S + Ag) and Ag ferrite in higher roasting temperatures hence Au and Ag recoveries decreased.

“Invisible” Gold in Pyrite and Arsenopyrite from The Pavlik Deposit (Northeastern Russia)

The first study on the distribution pattern and features of the “invisible” gold concentration in pyrite and arsenopyrite was carried out for a typical gold–quartz deposit of the Kolyma region. It was established that the main concentrator of “invisible” gold on the Pavlik deposit is the Late Arsenian pyrite-2. The method of Laser Ablation-Inductivity Coupled Plasma-Mass Spectrometer (LA-ICP-MS) gives an Au content up to 478 g/t; the Electron Microprobe Analysis (EMPA) gives up to 570 g/t by. The As content, determined by LA-ICP-MS is up to 4.1 wt % and up to 3.4 wt % by EMPA. Pyrite-2 overgrows and replaces the early pyrite-1 with a reduced content of As and Au. Microinclusions of the Pb–Zn–Cu–Sb–Ag–Bi–containing phases are concentrated at the boundaries of the pyrite-1 and pyrite-2 blocks. Pyrite-2 is depleted by an order in Cu, Zn, Ag, Sb, Pb, and Bi in comparison with pyrite-1. The max Au/As molar ratio in pyrite-2 is 0.006, which suggests the presence of Au in the form of a solid solution. In another case, pyrite, depleted by trace elements, is cemented with As, Ag, Sb, Au, and Pb-rich marcasite with native gold. In arsenopyrite, there is a homogeneous distribution of gold at low concentrations (up to 3 g/t) in euhedral crystals and a heterogeneous distribution (up to 7 g/t) in deformed fissured grains.

Multi-Stage Introduction of Precious and Critical Metals in Pyrite: A Case Study from the Konos Hill and Pagoni Rachi Porphyry/Epithermal Prospects, NE Greece

The Konos Hill and Pagoni Rachi porphyry-epithermal prospects in northeastern Greece are characterized by abundant pyrite that displays important textural and geochemical variations between the various ore stages. It is commonly fine-grained and anhedral in the porphyry-related mineralization (M- and D-type veins), while it forms idiomorphic, medium- to coarse-grained crystals in the late, epithermal style veins (E-type). Porphyry-style pyrite from both prospects is characterized by an enrichment in Co, Se, Cu, and minor Zn, and a depletion in other trace elements, like Bi, Mo, Ag, etc. Pyrite in epithermal-style mineralization is mostly characterized by the presence of As, Bi, Pb, Ni, and Se. Gold in pyrite from all mineralization stages occurs as a non-stoichiometric substituting element, and its abundance correlates with As content. Arsenic in pyrite from Konos Hill records an increase from the porphyry stage to the epithermal stage (along with gold); however, at Pagoni Rachi, the highest Au and As contents are recorded in D-type pyrite and in the epithermal stage. The composition of the studied pyrite marks changes in the physico-chemical conditions of the ore-forming fluids and generally follows the geochemical trends from other porphyry-epithermal systems elsewhere. However, a notable enrichment of Se in the porphyry-style pyrite here is a prominent feature compared to other deposits and can be considered as an exploration tool towards Au-enriched mineralized areas.

Fluid evolution and gold precipitation in the Muping gold deposit (Jiaodong, China): Insights from in-situ trace elements and sulfur isotope of sulfides

The Early Cretaceous Muping gold deposit is hosted in the Late Jurassic monzogranite. Crosscutting relations of ore veins implied a presence of multiple fluid pulses, and the mineralization process comprises four mineralization stages. Three generations/types of pyrite (Py1, Py2, and Py3) have been discriminated. Coarse-grained and euhedral Py1 pertains to pyrite-quartz veins. Coarse-fine grained and subhedral Py2 comes from quartz-pyrite veins. Fine-grained and anhedral Py3 is from quartz-polymetallic sulfides veins. Py3 further can be divided into three sub-types (Py3a, Py3b, and Py3c), in which Py3a did not have a core-rim texture, Py3b is the core and Py3c is the rim of pyrite with core-rim texture.Py1 and Py2 contain relatively higher Co (738 and 29 ppm on median) and Ni (30 and 7.6 ppm on median), but lower As (754 and 15 ppm on median) and Au (median < 0.1 ppm) content. However, Py3 has extremely low Co and Ni (medians below detection), but elevated As (from 16,290 to 206 ppm on median) and Au (from 36 to 0.4 ppm on median) content. Co and Ni contents of pyrite gradually decreased but As content increased from Py1 to Py3, implied that the temperature of ore-forming fluids progressively decreases. Extremely higher As content and high δ34S of Py3c could be associated with an incursion of As-rich and heavy δ34S meteoric water which has flowed through meta-sedimentary rocks. Sulfur isotopes revealed a gradual decrease from Py1 (+11.6‰) to Py3b (+7.5‰). As for the pyrite with core-rim texture, the sulfur isotope progressively increased from the core (Py3b, +6.0‰) and the rim (Py3c, +11.8‰). The high δ34S could be derived from the metasomatic and fertile lithospheric mantle, and the difference between Py1 and Py2 attributed to suffering from degassing processes with different condition. Rayleigh fractionation process caused a “reservoir effect” can explain the inside variations of Py2, while the increase of fO2 caused by phase separation is the main factor leading to δ34S decrease for Py3. It is the fluid mixture that resulted in the inter-crystalline sulfur isotope variation of pyrite with core-rim texture. Gold and As contents for all types of pyrite plot well below the solubility limit for gold in arsenian pyrite, indicating that invisible gold occurs as Au1+ in the pyrite lattice. The extent of invisible gold was incorporated into pyrite depending on the arsenic content, but visible gold mineralization mainly was controlled by vapor phase escape and fO2 increase which attributed to phase separation.

Origin and classification of the Late Triassic Huaishuping gold deposit in the eastern part of the Qinling-Dabie Orogen, China: implications for gold metallogeny

The Huaishuping gold deposit is located in the Xiong’ershan Mountains of the Qinling-Dabie Orogen of central China. The mineralisation is structurally controlled and hosted by faulted rhyolite, quartz andesite, volcaniclastic rocks and volcanic breccia assigned to the Jidanping Formation towards the top the Palaeoproterozoic Xiong’er Group. The deposit has a resource of around 32 t with an average grade of 5.5 g/t Au. Alteration at the deposit progressed from an early K-feldspar–quartz–pyrite assemblage through quartz–pyrite–gold, quartz–base-metal sulfides, to a late-stage assemblage of quartz–carbonate. The δ34S (V-CDT) values for pyrite in the ore range from − 13.3 to + 1.6‰. The calcite has C-isotopes ranging from − 6.1 to + 2.5‰ (V-PDB) and O-isotopes from + 10.6 to + 15.8‰ (V-SMOW). The δ18O quartz ranges from 10.5 to 15.1‰, and the δD values for fluid inclusions in quartz range from − 93 to − 76‰. The δ56Fe value for the mineralisation varies between 0.1 and 0.5‰ with corresponding δ57Fe values between 0.2 and 0.7‰. The isotope systematics indicates that the hydrothermal fluids were derived from metamorphic fluid, but the source of gold remains uncertain. Re–Os dating of molybdenite yields a date of 202 ± 8 Ma interpreted as the age of the gold mineralisation. This age is consistent with the Triassic onset of extensional tectonics following the collision between North and South China.

Kinetics of cupric leaching of pyrite in 4 M NaCl solutions

ABSTRACT Cupric chloride leaching is an attractive alternative for the treatment of pyritic refractory gold ores. In this context, the kinetics of pyrite dissolution was studied in cupric chloride solutions containing 4 M NaCl. Pyrite leaching experiments were conducted in a stirred tank reactor for 250 h. The effect of temperature was evaluated at 45°C, 60°C and 75°C, while the effect of [Cu (II)] was evaluated with solutions containing 0.054, 0.252 and 0.512 M. The results showed that the increase in temperature and [Cu (II)] improved the rate of pyrite dissolution. The fraction of pyrite oxidised to sulphate ranged from 52% to 75%. Sulphate formation correlated well with the number of holes and cracks formed on leached pyrite particles. The kinetics of pyrite dissolution fitted well to the shrinking core model with chemical reaction control (T ≤ 60°C and [Cu (II)] ≤ 0.054 M) or mixed control (T > 60°C and [Cu (II)] > 0.054 M). The activation energy was 73.102 kJ/mol and the dependence of [Cu (II)] was proportional to .

Petrogenesis of the Bakoudou TTGs and high-K biotite granites and associated gold mineralization, southern Gabon: An Archean example of a porphyry–epithermal transitional gold system

The Bakoudou gold deposit, southern Gabon, is hosted in the Archean basement granitoids of the Chaillu Massif. These granitoids of the Bakoudou deposit are subdivided into two main groups: TTGs and porphyritic biotite granites. The TTGs show geochemical characteristics similar to those of other TTGs worldwide, such as high Al2O3 (13.49–18.93 wt%) and Na2O (3.27–4.66 wt%) and low K2O (1.01–1.98 wt%), with low K/Na (0.15–0.32) ratios. Their Mg# (Mg/(Mg + Fe)*100) values vary from 34.81 to 50.76, with low to moderate Nb/Ta and Zr/Sm ratios (7.03–23.43 and 19.13–75.25, respectively). They are characterized by moderate (La/Yb)N (6.70–41.71) and Sr/Y (20.80–72.13) ratios similar to those of adakites, negative Nb, Ta and Ti anomalies and LREE-enriched and HREE-depleted patterns, without significant Eu anomalies (Eu/Eu* = 0.93–1.11, average = 1.00). These geochemical characteristics suggest that the TTG rocks were formed by partial melting of hydrous basaltic crust, such as garnet-rich amphibolite. The porphyritic biotite granites show high-K calc-alkaline affinity. They are characterized by high SiO2 (71.01–74.86 wt%) and K2O (3.29–4.92 wt%) but relatively low MgO (0.38–0.92 wt%), with Mg# values varying between 31.78 and 40.27. The rocks show low to moderate Sr/Y (13.75–26.66) ratios and LREE-enriched and HREE-depleted patterns, with negative Eu anomalies (Eu/Eu* = 0.36–0.58, average = 0.47). These geochemical features indicate that the porphyritic biotite granites originated from partial melting of TTG lithologies.The orebody of the Bakoudou gold deposit occurs as quartz veins hosted in the TTG shear zones. Quartz is the main gangue mineral, with minor sulfides such as pyrite and chalcopyrite. Gold is present in solid solution (Au+1) and as nanoparticles of native gold (Au0) in pyrite and mostly as free gold. Pyrite samples analysed by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) show high Ni (3.24–3600 ppm) and Co (4.68–4140 ppm) and low As (<34.50 ppm) and Au concentrations (<2.90 ppm) compared to Cu, which has rather high concentration of <3570 ppm. Moreover, the Au–As relationships of pyrites show a porphyry–epithermal transitional signature. Therefore, the Bakoudou gold deposit can be considered an example of Archean porphyry–epithermal transitional gold system, formed from magmatic fluids originating from a hidden porphyry system at depth during cooling and emplacement of the potassic granites. The disseminated free gold grains in the quartz veins may have originated from boiling of the mineralizing fluid (phase separation) and/or from remobilization of invisible gold in pyrite by later tectonic events and surficial weathering.

Invisible Gold Paragenesis and Geochemistry in Pyrite from Orogenic and Sediment-Hosted Gold Deposits

LA-ICPMS analysis of pyrite in ten gold deposits is used to determine the precise siting of invisible gold within pyrite, and thus the timing of gold introduction relative to the growth of pyrite and related orogenic events. A spectrum of invisible gold relationships in pyrite has been observed which suggests that, relative to orogenic pyrite growth, gold introduction in some deposits is early at the start of pyrite growth; in other deposits, it is late toward the end of pyrite growth and in a third case, it may be introduced at the intermediate stage of orogenic pyrite growth. In addition, we report a distinct chemical association of invisible gold in pyrite in the deposits studied. For example, in the Gold Quarry (Carlin type), Mt Olympus, Macraes and Konkera, the invisible gold is principally related to the arsenic content of pyrite. In contrast, in Kumtor and Geita Hill, the invisible gold is principally related to the tellurium content of pyrite. Other deposits (Golden Mile, Bendigo, Spanish Mountain, Witwatersrand Carbon Leader Reef (CLR)) exhibit both the Au-As and Au-Te association in pyrite. Some deposits of the Au-As association have late orogenic Au-As-rich rims on pyrite, which substantially increase the value of the ore. In contrast, deposits of the Au-Te association are not known to have Au-rich rims on pyrite but contain nano- to micro-inclusions of Au-Ag-(Pb-Bi) tellurides.

In-situ trace elements on pyrite and arsenopyrite of the Zhengchong gold deposit, Jiangnan Orogen: Insights for the mineralization mechanism

The Zhengchong gold deposit, with a gold reserve of 19 t, is located in the Liling Goldfield, central Jiangnan Orogen, Southern China. The orebodies are structurally bound by NW- and NNE-NE-trending faults, hosted in the Neoproterozoic slates. The ore styles primarily comprise auriferous pyrite-arsenopyrite-quartz vein, disseminated pyrite-arsenopyrite-sericite-quartz mineralized slate, and intense mineralized slate breccia. The gold-bearing sulfide-quartz veins have average Au grades up to 13.5 g/t, generally higher than that of mineralized rock in all orebodies of 0.6–2.0 g/t and intense mineralized breccia within quartz veins of 2.5–4.0 g/t. Three primary and successive paragenetic sequences are identified: (i) Barren quartz – muscovite; (ii) Quartz – polymetallic sulfides – native gold – muscovite – minor chlorite; (iii) Barren quartz – calcite veins. Native gold has only been observed in the fractures of early barren quartz, pyrite and arsenopyrite in NW-trending auriferous veins. According to textural differences, five types of pyrite and four types of arsenopyrite are recognized from NW- and NNE-NE-trending orebodies.Based on LA-ICPMS spot and imaging analyses of different types of pyrites and arsenopyrites, the refractory, invisible gold in pyrites and arsenopyrites range from < 1 to >500 ppm and was incorporated in these sulfides through substitution of As1− for S2− as the Au and As data plotting below the both gold solubility lines for Carlin and orogenic gold deposits. The invisible gold as the form of Au+ concentrates in sulfides. Besides, minor micro-scale gold with Cu-, Pb-, Sb-, Ag-, and Bi-minerals occur in the pores of pyrite and arsenopyrite. The initial ore-bearing fluid with abundant Si, S, Fe, As and minor Au, Co, Ni, Cu, Zn, Sb, Te, Pb, Bi reacting with Neoproterozoic slates to generate low-grade pyrite (Py-I and Py-III) in both-trending orebodies. For NNE-trending sulfide-quartz veins, cyclic fluid pressure dropping resulted fluid phase separation and destabilization of bisulphide-gold. Due to the small fluid flux in narrow NNE-trending faults, Au+ exhausted after the precipitation of high-grade Py-II, Apy-II and Au-rich rim of Py-I with invisible gold. In NW-trending auriferous quartz veins, hydrofracturing under high fluid pressure in thrust shear-faults, generated massive slate breccias. The sharply pressure decrease in dilations along the ore-controlling faults resulted in significant auriferous fluid phase separation and the solubility reducing of trace elements and gold, which in turn led in the deposition of native gold with chalcopyrite, sphalerite and tetrahedrite in fractures of Py-IV and Apy-III.

Establishment of electrochemical methods to examine the adsorption of flotation surfactants onto a mineral surface

AbstractBACKGROUNDSignificant efforts have been devoted to examine the adsorption of flotation surfactants in both mechanistic studies and process implementations. However, quantitative electrochemical methods for flotation surfactant adsorption examination have not been well‐established, despite of their low‐cost, accurate, in‐situ nature.RESULTSIn this paper, voltametric measurement was proven to quantitatively examine the adsorption of activating copper and lead ions onto a pyrite surface. The activation was achieved by abrading minerals in a heavy‐metal‐bearing solution and the measurements were performed by transferring the minerals to a solution free of those heavy metals. This provided a simple but realistic simulation of the mineral grinding process and simplified the adsorption quantification by excluding any other irrelevant electrochemical reactions near the surface. Reliable electrochemical impedance spectroscopy (EIS) upon adsorption with convincing physical models for interpreting the interfacial structures also were obtained in this paper. The additional pseudocapacitive behaviour of the copper sulfide surface layer led to an increased capacitance of the measured EIS. A resistive but ion‐permeable xanthate adsorption layer exhibited its own relaxation process. Voltammetry and impedance studies showed that cyanide competed with both copper and lead for their adsorption, whereas lead activation showed greater tolerance to cyanide than copper did.CONCLUSIONElectrochemical methods have been established to examine the adsorption of copper, lead and xanthate onto pyrite surface, in relation to various flotation conditions, which exhibited significant implication to the flotation of pyritic gold ore using cyanide‐bearing water. © 2020 Society of Chemical Industry

Study on Pre-oxidation of a High-Arsenic and High-Sulfur Refractory Gold Concentrate with Potassium Permanganate and Hydrogen Peroxide

For arsenic-containing refractory gold concentrate, gold recovery by leaching is extremely difficult due to the encapsulation of gold in arsenopyrite and pyrite. In this work, the pre-oxidation of a high-arsenic and high-sulfur refractory gold concentrate in the acidic potassium permanganate or hydrogen peroxide solutions has been investigated. The studied parameters include pre-oxidation time, acidity, pre-oxidation temperature, ethylene glycol addition and oxidant concentration. When potassium permanganate of 0.25 mol/L is used as oxidant, 61.4% of arsenic and 51.8% of iron can be removed, respectively. The results of kinetics analysis indicate that the oxidative dissolution of arsenopyrite during the pre-oxidation process is controlled by the product layer diffusion, with an activation energy of 7.92 kJ/mol. The stability of hydrogen peroxide can be significantly improved by increasing both sulfuric acid concentration and ethylene glycol addition when hydrogen peroxide is used as oxidant. Under optimum conditions, arsenic removal ratio of 57.2% and iron removal ratio of 51.9% have been achieved with hydrogen peroxide of 2.5 mol/L, sulfuric acid of 0.75 mol/L and ethylene glycol of 30 mL/L. The gold extraction of refractory concentrate is only 11.5% in the copper–ammonia–thiosulfate leaching solutions without pre-oxidation. A gold extraction of 71.8% and significant decrease in thiosulfate consumption from 28.2 to 5.7% have been observed for the concentrate after pre-oxidation.

Multivariate Statistical Analysis of Trace Elements in Pyrite: Prediction, Bias and Artefacts in Defining Mineral Signatures

Pyrite is the most common sulphide in a wide range of ore deposits and well known to host numerous trace elements, with implications for recovery of valuable metals and for generation of clean concentrates. Trace element signatures of pyrite are also widely used to understand ore-forming processes. Pyrite is an important component of the Olympic Dam Cu–U–Au–Ag orebody, South Australia. Using a multivariate statistical approach applied to a large trace element dataset derived from analysis of random pyrite grains, trace element signatures in Olympic Dam pyrite are assessed. Pyrite is characterised by: (i) a Ag–Bi–Pb signature predicting inclusions of tellurides (as PC1); and (ii) highly variable Co–Ni ratios likely representing an oscillatory zonation pattern in pyrite (as PC2). Pyrite is a major host for As, Co and probably also Ni. These three elements do not correlate well at the grain-scale, indicating high variability in zonation patterns. Arsenic is not, however, a good predictor for invisible Au at Olympic Dam. Most pyrites contain only negligible Au, suggesting that invisible gold in pyrite is not commonplace within the deposit. A minority of pyrite grains analysed do, however, contain Au which correlates with Ag, Bi and Te. The results are interpreted to reflect not only primary patterns but also the effects of multi-stage overprinting, including cycles of partial replacement and recrystallisation. The latter may have caused element release from the pyrite lattice and entrapment as mineral inclusions, as widely observed for other ore and gangue minerals within the deposit. Results also show the critical impact on predictive interpretations made from statistical analysis of large datasets containing a large percentage of left-censored values (i.e., those falling below the minimum limits of detection). The treatment of such values in large datasets is critical as the number of these values impacts on the cluster results. Trimming of datasets to eliminate artefacts introduced by left-censored data should be performed with caution lest bias be unintentionally introduced. The practice may, however, reveal meaningful correlations that might be diluted using the complete dataset.

The Lukoganskoe Au–Cu Skarn Deposit (Eastern Transbaikalia): Mineral Composition, Age, and Formation Conditions

Abstract —The Lugokanskoe deposit is located in southeastern Transbaikalia and has been studied for a long time by many researchers. However, the type of its formation is still debatable. In this paper we study the mineral composition of ores by modern methods, recognize and describe the main gold mineral assemblages, and present detailed data on the chemical composition of native gold and sulfide minerals and their isotope composition. We have established that gold–pyrite–chalcopyrite–arsenopyrite and gold–bismuth parageneses localized in skarn deposits are the main productive assemblages. Study of the sulfur isotope composition of sulfide minerals has shown an endogenous source of sulfur of the ore minerals. The carbon and oxygen isotope compositions of carbonates of ore-bearing veins indicate the participation of a magmatic fluid. The established age of the gold mineralization and igneous rocks of the Shakhtama complex, together with direct geological observations, points to their spatial, temporal, and genetic relationships. According to their petrochemical and geochemical characteristics, the igneous rocks of the Shakhtama complex are I-type ilmenite (reduced) granitoids. Study of fluid inclusions by heating and cooling and Raman spectroscopy has shown that the mineral formation was accompanied by a gradual decrease in the content of salts in the ore-forming fluids and by a decrease in their homogenization temperatures. Optical observations demonstrate that the fluid was heterogeneous at the early stages of the mineral formation. The evolution of the ore system was accompanied by a change in the gas phase composition of fluid inclusions from predominantly nitrogen–carbon dioxide to essentially aqueous, with carbon dioxide impurity (H2O + CO2 ± N2 → H2O ± CO2). The research data testify to the magmatic nature of fluids and the participation of meteoric waters at the late stages of the ore-forming process. The data obtained have led to the conclusion that the Lugokanskoe gold deposit is related to reduced intrusions formed at a shallow depth.

Arsenic evolution as a tool for understanding formation of pyritic gold ores: REPLY

Arsenic evolution as a tool for understanding formation of pyritic gold ores: REPLY

Arsenic evolution as a tool for understanding formation of pyritic gold ores: COMMENT

Arsenic evolution as a tool for understanding formation of pyritic gold ores: COMMENT

Geology, mineralogy and stable isotope geochemistry of the Dzuunmod area in northern Mongolia: Constraints for gold ore genesis and sources

The Dzuunmod area located in the North Khentii Gold belt (NKGB) of northern Mongolia includes lode gold deposits such as Gatsuurt, Sujigtei and Boroo with several minor gold deposits and occurrences. They show similar hydrothermal alteration assemblages (sericitic, siliceous and potassic) and ore mineral assemblages (pyrite and arsenopyrite with minor amount of galena, sphalerite and chalcopyrite). Gold occurs as native form and invisible gold in pyrite and arsenopyrite. The major sulfide minerals are separated into earlier non-auriferous stage and later auriferous grains containing invisible gold. Native gold postdates the major sulfide mineralization.Gold and arsenic content of pyrite grains indicates that gold exists mainly as solid solution form (Au+1) in the Gatsuurt and Boroo deposit whereas gold nanoparticle (Au0) is present in the Sujigtei deposit. High Co/Ni and Mo/Ni ratios of pyrite grain suggest a post-sedimentary or hydrothermal origin and the ore-forming fluid was significantly affected by fluid-host rock interactions during mineralization processes.Large variation of δ34S values of pyrite and arsenopyrite from −2.6‰ to 17.2‰ indicates that sulfur seems to be mainly derived from a source with heterogeneous sulfur isotope composition, even though the role of magmatic sulfur as one of possible sulfur sources cannot be ruled out. Consistent with geological evidence, relatively positive δ34S values suggest that sulfidation plays an important role for gold and sulfide precipitation. The calculated δ18O values of hydrothermal fluid from the measured δ18O values of quartz samples (from 14.7‰ to 17.7‰) indicate a metamorphic derivation of ore-forming fluid.Gold mineralization processes in the Dzuunmod area seem to occur several times by multiple input of hydrothermal fluid and fluid-host rock interactions. The gold deposits in the Dzuunmod area are considered to be orogenic gold type influenced by fluid-host rock interactions in the deposit area.

Formation of the Tocantinzinho 1989 Ma gold-only deposit (Pará State, northern Brazil), based on sulfur, oxygen, hydrogen, and carbon isotope data

The Tocantinzinho gold deposit in the Brazilian Amazon region, approximately 1989 Ma in age, contains 16.7 Mt of ore in syenogranite and monzogranite breccias and microbreccias, most with gold in pyrite, silicates and quartz, and a small part in quartz vein pyrites. Three hydrothermal phases are recognised, H1, H2, and H3, where H1, the first hydrothermal phase, is the oldest. The H1 transitional, late-magmatic hydrothermal phase altered feldspar to sericite and mafic minerals to chlorite. During the H2 hydrothermal phase, pyrite, gold, and minor galena were precipitated, followed by intense sericite alteration. The last hydrothermal phase, H3, was coeval with a large number of andesite intrusions that generated high-pressure fluid-driven cataclasis. This event opened veins, tension gashes, and pull aparts that were filled with carbonate, worm-like chlorite, prismatic quartz, galena, pyrite, and rutile, which likely displaced and concentrated the gold near the carbonate-filled structures.The minerals sulfide δ34S values vary between −4.4 and + 5.6‰, which is compatible with a sulfur magmatic source, and indicate that the sulfur and likely the gold are both magmatic. The δ18OSMOW values of carbonates vary between +7.63 and + 21.23‰ in a narrow range of δ13CPDB values between −3.94 and −1.69‰. Two explanations are possible for these values. If that the carbonate fluids were genetically related to the andesite magmatism, this fluid mixed with meteoric water, and degassing of this mixture occurred in the near-surface to produce dissolved inorganic CO2 with high δ18O value. Alternatively, when fluid mixing occurred, the oxidation state of the environment increased, and the δ13C values of the carbonates remained relatively uniform, whereas the δ34S values of the sulfides varied. The δ18O values of the quartz, sericite, and chlorite of the mineralized and barren rocks are consistent with δ18O values > +8 for the fluids that crystallized the chlorites and δ18O > + 4‰ for those that crystallized the muscovite. High δD values of these fluids, estimated from mineral δD values range between −2 and −25‰, and differentiate them from the fluids that form porphyry-type Cu–Au and orogenic deposits. The isotope data for Tocantinzinho present characteristics of an intrusion-related gold deposit that combines the features of equigranular, intrusion-hosted, mesozonal deposits, such as those hosted in reduced granite, with Au-rich porphyry deposits hosted in oxidized granites.

Geochemistry and Fluid Inclusions Analysis of Vein Quartz in the Multiple Hydrothermal Systems of Mankayan Mineral District, Philippines

AbstractSeveral high‐sulfidation epithermal gold orebodies in the Mankayan Mineral District were formed in an environment that has been already affected by earlier porphyry‐type mineralization. This study reports the geologic and geochemical characteristics of the Carmen and Florence epithermal orebodies, which are located in the south of the Lepanto main enargite–gold orebody. The gold‐bearing epithermal quartz veins in the Carmen and Florence areas are of two types: (i) the enargite‐rich veins and (ii) the quartz–pyrite–gold (QPG) veins. The two types of veins are mainly hosted by the Cretaceous Lepanto Metavolcanics basement rocks, with minor veins cutting the Pleistocene Imbanguila Dacite Pyroclastics. The mineral assemblages and homogenization temperatures of fluid inclusions indicate that the Carmen and Florence orebodies were deposited by fluids varying from high to very high sulfidation state. The enargite and QPG epithermal veins of Carmen and Florence cut porphyry‐type quartz veinlet stockworks and veins that host polyphase hypersaline fluid inclusions that did not homogenize at or below 400°C. These high‐temperature quartz exhibits distinctly different mineral chemistry from the quartz of the QPG and enargite‐rich epithermal veins. In particular, the Ti content of quartz of the porphyry‐type veinlet stockwork is elevated (&gt;100 ppm), whereas the Ti concentration of the epithermal vein quartz crystals are below detection limits. The Fe concentration of quartz is high in epithermal vein quartz (&gt;300 ppm), whereas nearly undetected in the porphyry‐type stockwork veinlet quartz. Multiple generations of quartz with different mineral chemistry, fluid inclusions morphology, temperature, salinity and bulk gas compositions, and stable isotopic ratios indicate the variable hydrothermal conditions throughout the mineralization history of the Mankayan District. The temperature, pH, sulfidation state, oxidation state, and fluid composition vary among the orebodies in Carmen and Florence areas. Furthermore, the characteristics of earlier alteration affected the apparent characteristics of subsequent mineralization.