Types Of Pyrite Research Articles

Trace-element composition of pyrite and its implications for hydrothermal process within the Mesoproterozoic metasedimentary sequences of the São Francisco Craton, northeastern Brazil

The distribution of trace elements in pyrite has been documented for the first time in quartz veins hosted in the Mesoproterozoic metasedimentary sequence of the Tombador Formation, São Francisco Craton, northeast Brazil. In this study, Electron Microprobe Analyses (EPMA) were used to determine the trace-element compositions of pyrite in these hydrothermal quartz veins. Three pyrite types have been distinguished and interpreted from petrographical relationships and trace-element patterns. Pre-existing pyrite (Py1), derived from the host-rock quartzite, is Ni-poor with concentrations varying from 600 – 6,100 ppm. Elongated syn-tectonic pyrite (Py2) has similar trace-element composition to the Py1, with Ni amounts ranging between 830 and 7,870 ppm. In contrast, possibly post-tectonic, euhedral to subhedral hydrothermal pyrite (Py3), contains higher contents of Ni (7,970 – 26,120 ppm). Mafic and/or metasedimentary rocks from the Espinhaço Supergroup were probably the source of Ni for this fluid-flow event. Fluid generation is related to the devolatilization of the base of the thickened crust, with migration of fluids by preexisting structures. Several shear zones and large-scale NNW-trending folds were developed during the inversion of the Espinhaço basin, as a result of the ca. 0.6 Ga Brasiliano orogenic event. Regional fluid movement through the crust at this time is supported by several mineralized veins and hydrothermal deposits in the São Francisco Craton and adjacent Neoproterozoic belts.

Pyrite mega-analysis reveals modes of anoxia through geological time.

The redox structure of the water column in anoxic basins through geological time remains poorly resolved despite its importance to biological evolution/extinction and biogeochemical cycling. Here, we provide a temporal record of bottom and pore water redox conditions by analyzing the temporal distribution and chemistry of sedimentary pyrite. We combine machine-reading techniques, applied over a large library of published literature, with statistical analysis of element concentrations in databases of sedimentary pyrite and bulk sedimentary rocks to generate a scaled analysis spanning the majority of Earth’s history. This analysis delineates the prevalent anoxic basin states from the Archaean to present day, which are associated with diagnostic combinations of five types of syngenetic pyrite. The underlying driver(s) for the pyrite types are unresolved but plausibly includes the ambient seawater inventory, precipitation kinetics, and the (co)location of organic matter degradation coupled to sulfate reduction, iron (oxyhydr)oxide dissolution, and pyrite precipitation.

Origin of the Dayingezhuang gold deposit in the Jiaodong district, eastern China: Insights from trace element character of pyrite and C-O-S isotope compositions

The Dayingezhuang gold deposit is a giant gold deposit in the Jiaodong district, with explored gold reserves of 283 t. After decades of research, sources of ore-forming fluids remain controversial, resulting in continuous controversy on the origin of this deposit. In this study, trace elements of pyrite and C-O-S isotopic data are presented to provide constraints on the ore-forming fluids of the Dayingezhuang gold deposit. Two types of gold-related pyrite were identified. Py1, hosted in quartz-pyrite veins, has subhedral to anhedral textures with developed micro-fissures. Py2, hosted in quartz-polymetallic sulfide veins, is generally subhedral to anhedral and intergrown with polymetallic sulfides. Both Py1 and Py2 are characterized by Co/Ni <1, which supports that the ore-forming fluids are metamorphic fluids with the addition of sedimentary materials. The calcite CO isotope suggests a mantle-derived source mixed with sediments. Combined with the anomalously high δ34S values, the ore-forming fluids that generated the Dayingezhuang gold deposits were most likely originated from the mantle lithosphere which is metasomatized and fertilized by the subducted Paleo-Pacific Plate and its overlying marine sediments. This model is similar to the common genesis of worldwide orogenic type gold deposits which suggests that the Dayingezhuang gold deposit may be of orogenic origin.

Two hydrothermal events associated with Au mineralization in the Youjiang Basin, southwestern China

The Youjiang Basin in southwestern China hosts remarkably large amounts of Carlin-type Au deposits. In such deposits, Au is mainly ionically bound to arsenian pyrite characterized by core and rim textures. Understanding the formation mechanism of zoned pyrite may improve our understanding of the genesis of massive Carlin-type Au deposits. This study examined the elemental content, mineral composition, and pyrite texture and chemistry of wall rock and ore from the Lannigou Au deposit, one of the largest Carlin-type Au deposits in the Youjiang Basin, to identify the genetic mechanisms of zoned pyrite.Five distinct types of pyrites, i.e., pyrite 1 (Py1), 2 (Py2), 3 (Py3), 4 (Py4), and ore pyrite (OPy), were identified in the Lannigou Au deposit. Py1, Py2, and Py3 were mainly observed in the wall rock, whereas Py4 and OPy, constituting the core and rim of zoned pyrite, respectively, were only discovered in the ore. Mineral mapping of the wall rock and ore indicated that pyrite is scarce in the wall rock (0.021 vol%). However, the amount of zoned pyrite significantly increased in the ore (1.275 vol%). Py1, Py2, and Py3, showing framboidal, nodular, and fine euhedral microcrystal textures, had high Pb, Co, Ni, Mn, Zn, and Mo contents (medians ranging from 10 to 1,000 ppm) and variable δ34S compositions ranging from −5.1 to 35.4‰, implying a sedimentary (syngenetic or diagenetic) origin. Py4 was homogeneous and contained numerous illite and quartz inclusions and fractures. In contrast, OPy showed multiple As-rich sub-bands and a lack of illite or quartz inclusions and fractures. Py4 had significantly lower Au, As, Tl, and Cu contents than OPy; however, Py4 had Pb, Co, Ni, Mn, Zn, and Mo contents similar to OPy. The range of δ34S values for Py4 and OPy were both narrow, but Py4 (7.6 to 13.3‰, with an average of 9.1‰) had lower δ34S values than OPy (9.4–14.1‰, with an average of 12.4‰). These texture and chemical features indicate that Py4 likely sedimented from a pre-ore hydrothermal fluid, but not at the early stage of the ore-forming fluid.Hydrothermal pyrite cores were also widespread and exhibited textural and chemical differences compared to Au-rich pyrite rims from other Au deposits in the Youjiang Basin. Based on the two geochronological clusters of Au deposits in the Youjiang Basin, we inferred the occurrence of at least two episodes of large-scale hydrothermal events. The two hydrothermal fluid episodes, which contributed to the zoned pyrite formation, likely originated from the mixing of initial magmatic fluid with δ34S values of ∼0 ± 5‰ and basin brine with elevated δ34S values (δ34S > 18‰). Pre-ore hydrothermal pyrite likely resulted in the rapid non-equilibrium crystallization of ore pyrite; thus, more Carlin-suite elements were captured by ore pyrite. Additionally, low-grade Au orebodies may have locally formed during the pre-ore hydrothermal event. These multiple hydrothermal events may have been crucial for the formation of massive Carlin-type Au deposits in the Youjiang Basin.

Types of ores of gold-silver deposits of volcano-plutonic complexes in folded belts and methodological aspects of their isolation

The study covers the ores of the three gold-silver type deposits, namely, Lichkvaz-Tei (Armenia), Nevenrekan and Perevalnoe (Russia). These differ in both geological structure and ore localization conditions. Detailed mineralogical studies of these ores were conducted to establish their natural types. The material composition for the ore types, their structural and textural features, the mineral balance of valuable components, and the grain-size composition of their constituent minerals may be used to predict the processing properties of ores at early exploration stages. Along with the traditional approaches, the method of sample pre-classification by factor analysis based on geochemical associations of ore-forming elements was tested. This enabled the development of an algorithm for identifying certain types in each sample and, consequently, the preparation of composite samples for further mineralogical studies. With due account of the geochemical associations, four ore-geochemical types of ores were identified for the Lichkvaz-Tei deposit based on the statistical analysis. These are the gold-arsenide, gold-copper-base metal, copper-zinc, and gold-silver arsenide-antimonide-sulfide types. For all the objects studied, a general ore-mineral parageneses formation sequence has been established: the early pyrite type is replaced by arsenopyrite-pyrite and chalcopyrite-sphalerite types, then by intermediate gold-chalcopyrite-galena-fahlite silver-bearing and late gold-silver-sulfosaline-fahlite and marcasite types. A wide range of natural types of ores have been established, such as: pyrite-arsenopyrite, gold-arsenopyrite, gold-galena-sphalerite, chalcopyritesphalerite types for the Lichkvaz-Tei deposit; gold-pyrite-sulfosaline and oxidized gold-pyrite types for the Nevenrekan mineral occurrence; silver-fahlite-chalcopyrite-galena-sphalerite type for the Perevalnoe deposit. This diversity is due to the different quantitative ratios of ore-mineral parageneses in the composition of the ores.

Bastnäsite U-Th-Pb age, sulfur isotope and trace elements of the Huangshui’an deposit: Implications for carbonatite-hosted Mo-Pb-REE mineralization in the Qinling Orogenic Belt, China

The Huangshui’an deposit is hosted in carbonatite dykes and located in the southern margin of the North China Craton which forms part of the Qinling Orogenic Belt. The genesis of Mo-Pb-REE mineralization associated with carbonatitic magmatism and hydrothermal activity remain poorly understood. Here we present results from field investigation, petrography, in situ sulfur isotope and trace elements of pyrite, and bastnäsite U-Th-Pb age with a view to understand the age and genesis of the Huangshui’an deposit. Three types of pyrite are identified in the Huangshui’an deposit as follows: (i) Py1a is composed of irregular pyrite in stage Ia carbonatite dykes; (ii) the euhedral Py1b coexists with sphalerite and galena in the margin of stage Ia carbonatite dykes; and (iii) Py2 occurs as irregular and anhedral grains in the fluorite + quartz veins. The highly variable Co (Py1a = 0.032–3230 ppm; Py1b = 0.053–779 ppm; Py2 = 0.98–164 ppm) and Ni values (Py1a = 2.1–418 ppm; Py1b = 0.78–28.8 ppm; Py2 = 8.6–373 ppm) indicate heterogeneous material sources. The δ34S values of the various pyrite types range between −9.6‰ and −3.5‰, and the obviously negative values resulted from sulfur isotope fractionation between sulfide and sulfate minerals. The total δ34S value calculated from co-genetic galena and barite is −0.11‰, in combination with previous Sr-Nd-Pb-He-Ar isotopes, indicate a material source dominantly from enriched mantle (EMI) with an additional contribution through partial melting of the thickened lower crust. In situ bastnäsite U-Th-Pb dating results yield mean ages of 211.7 ± 3.1 Ma and 209.6 ± 2.1 Ma, representing the timing of Mo-Pb-REE mineralization in the Huangshui’an deposit. The Late Triassic carbonatite magmatism and associated mineralization were controlled by the fertile source from the enriched mantle and the thickened lower crust, and the post-collisional extension setting facilitated the partial melting and fast propagation of carbonatite magma from the mantle to shallow crustal level.

Origin of the Shanggong gold deposit, the southern margin of the North China Craton: Constraints from Rb-Sr ages of sericite, and trace elements and sulfur isotope of pyrite

The Shanggong Au deposit is a world-class Au deposit in the southern margin of the North China Craton. Pyrite, as the primary Au carrier in this deposit, is an ideal mineral for dissecting the complex ore-forming process and origin of this deposit. Four types of pyrite were identified by EPMA, SEM, LA-ICP-MS, and NanoSIMS analyses: the coarse-grained cubic, disseminated pyrite (Py1) in the early ore stage (S1) and three types of the fine-grained pentagonal dodecahedron, disseminated pyrite (Py2-1, Py2-2, and Py2-3) with zoning textures in the main ore stage (S2). Py1 is relatively depleted in most metals but enriched in Co and Bi compared with other types of pyrite in S2. On the other hand, both Py2-1 and Py2-3 contain relatively high contents of As, Au, and other metals, whereas Py2-2 contains highest Au, As, Ag, Cu, Sb, Te, Tl, and Pb. Oscillatory zoning in Py2-1 resulted from repeated local fluid phase separation at the near-surface of pyrite crystal due to sharp fluid pressure fluctuation. The Au and As-rich Py2-2 was probably formed under both extrinsic fluctuations in fluid pressure and composition and intrinsic local crystal-fluid interface kinetic effects (e.g., diffusion-limited self-organization, surface electrochemistry-driven adsorption). Crystallization of Py2-1 and Py2-2 has exhausted the metals in the residual fluids, wherein the trace element-poor Py2-3 crystallized and locally replaced Py2-2 through a dissolution-reprecipitation process. Our new data and previous results suggest the ore-forming fluids were likely initial produced by degassing of the concealed pluton, and the metals were sourced from both the crust (e.g., the Taihua complex and Xiong’er Group) and the mantle. The negative δ34S values for pyrite in the S2 stage might result from both the isotopic fractionation between sulfide and sulfate minerals via oxidation of the ore-forming fluid and the input of biogenic sulfur.

Influence of fluid-rock interaction on gold mineralization in the Dongwan deposit, East Qinling, China: Constraints from systematic sulfur isotope and trace element geochemistry

The Dongwan gold deposit is located in the Xiong'ershan area, East Qinling, China, with gold ore bodies hosted in NE-trending hydrothermal alteration zone and quartz + sulfides veins in structures. Here we present systematic field investigation, petrographic observations, in-situ trace elements and sulfur isotope of pyrite, and sulfur isotope of galena and barite to elucidate the genesis and effect of fluid-rock interaction during hydrothermal evolution of the Dongwan gold deposit. Four types of pyrite are recognized based on their occurrences in different hydrothermal veins, structures and paragenetic sequences, as follows: i) Py1 in the stage I quartz-pyrite vein is composed of coarse-grained cubic pyrite (Py1-1) and medium-grained cubic pyrite (Py1-2); ii) Py2 is characterized by fine-grained disseminated pyrite in stage II vein; iii) Py3 is represented by pyrite that occurs together with galena, sphalerite and chalcopyrite in stage III vein. The early stage Py1-1 and Py1-2 are characterized by high Co/Ni ratios and low contents of As, Au and Ag. The main ore-forming stages represented by Py2 and Py3 show lower Co/Ni ratios and higher concentrations of As, Sb, Au, Ag, Pb and Cu. The Ni contents of all pyrite types are < 10 ppm, indicating that the ore-forming fluid was derived from felsic rocks. The δ34S values of the different pyrite generations range between −16.0‰ and −7.4‰, which are attributed to the fractionation between barite and sulfide minerals. The sulfur isotopic composition of the hydrothermal fluid calculated from co-genetic barite and pyrite is 1.2‰, suggesting that the ore-forming materials were possible derived from mantle source, and were correlated with the Late Mesozoic granitic magmatism. The main mechanisms of gold precipitation are fluid-rock interaction and decrease of temperature, which promote the Fe2+ rich Xiong’er Group wall rocks to reduce the hydrothermal fluid and disequilibrate the gold-sulfur complex causing the precipitation of gold. The overall trace elements and sulfur isotopic signatures suggest that the pyrite is of magmatic-hydrothermal origin, and that the ore-forming materials of the Dongwan gold deposit are probably related to post-magmatic fluids derived from the Early Cretaceous granitoid magmatism in the region.

Distal gold mineralization associated with porphyry system: The case of Hongzhuang and Yuanling deposits, East Qinling, China

The Hongzhuang and Yuanling gold deposits are located in the Shiyaogou ore field within the Xiong'ershan area, East Qinling, China, where the ore bodies are hosted in Xiong'er Group and mainly controlled by EW-trending and NE-trending faults. The gold mineralization mechanism and the possible genetic link with the porphyry magmatism and hydrothermal events remain unclear. Here we present results from systematic field investigation, petrographic observation, in situ trace elements and sulfur isotope of pyrite to elucidate the genesis of gold mineralization in these deposits. Based on the occurrences of pyrite in different hydrothermal veins, three types of pyrite are identified from each deposit, including: i) coarse-grained cubic pyrite (HZ-Py1 and YL-Py1) in stage I milky quartz vein; ii) medium- to fine-grained pyrite (HZ-Py2 and YL-Py2) in stage II polymetallic sulfides veins; iii) coarse-grained pyrite (HZ-Py3 and YL-Py3) symbiotic with calcite in stage III quartz-calcite vein. The LA-ICP-MS trace element analyses of pyrite show that Au occurs as invisible nanoparticles or nano-sized inclusions in pyrite through absorption-chemisorption during the growth of pyrite or as nano-sized Au-bearing mineral inclusions. The δ34S values of different generations of pyrite in the Hongzhuang and Yuanling gold deposits range from 3.92‰ to 6.43‰ and 2.82‰ to 4.46‰, respectively, indicating that the ore-forming materials were mainly derived from mantle-related source with affinity to the Late Mesozoic granitic magmatism. The Hongzhuang and Yuanling gold deposits are spatially and temporally correlated with the Shiyaogou pluton and they show consistent material sources. We propose that the hydrothermal Au mineralization in these deposits were the distal products generated from the post-magmatic fluids of the Shiyaogou porphyry system. The stretching and thinning of the early Cretaceous lithosphere led to the upwelling of magma and migration of fluid, forming the Au mineralization in fault structures in the shallow crust.

Hydrocarbon seepage in the mid-Cretaceous greenhouse world: A new perspective from southern Tibet

The mid-Cretaceous greenhouse climate was induced by volcanic outgassing and the release of biogenic or thermogenic methane into the ocean-atmosphere system. During this period, major episodes of oceanic anoxic conditions enabled the large scale deposition of marine black shales rich in organic carbon, serving as a source for methane production. Studies on the anaerobic oxidation of methane, the key biogeochemical process at sites where methane is transported toward the seafloor, and its associated authigenic carbonates from mid-Cretaceous strata can contribute to elucidate such extreme climatic conditions. A total of nine layers of authigenic carbonates were recognized in the sequence of mid-Cretaceous inner shelf sedimentary rocks of the Qiangdong section, Gamba area, southern Tibet. In this study, we decipher the mode and causes of carbonate authigenesis by combining field observation, thin section petrography, mineralogy, and carbon and oxygen stable isotope geochemistry. The lowest obtained δ13Ccarb value of −30.5‰ is not low enough to exclude oil compounds as a carbon source, but since other evidence of oil seepage is lacking, methane is the most likely carbon source that was admixed to dissolved inorganic carbon to form authigenic carbonate. Typical seep carbonate phases including 13C depleted matrix micrite, clotted micrite, and banded and botryoidal cement as well as three types of authigenic pyrite comprising framboids, zoned aggregates with radial overgrowths surrounding a framboidal core, and euhedral pyrite crystals indicate the occurrence of methane seepage in the mid-Cretaceous depositional environments. In situ brecciation and subvertical tubular carbonates – the former reflecting rupture caused by local fluid overpressure and the latter interpreted as part of a plumping system – agree with widespread and vigorous seepage. Expanded shallow and deep-water anoxia in combination with low seawater sulfate concentration prior to the oceanic anoxic event 2 (OAE 2) event apparently caused an increased flux of organic matter to the methanogenic zone, stimulating methanogenesis and enabling a higher flux of methane toward the seafloor. In the water column, aerobic oxidation of methane would have enhanced oxygen depletion, thereby contributing to black shale deposition and providing a positive feedback to organic matter preservation and burial. Based on correlation with coeval authigenic carbonate deposits from the Tethyan continental margin, we conclude that organic matter accumulation and sea-level change were the main factors controlling carbonate authigenesis in the mid-Cretaceous.

One-Pot Synthesis of Pyrite Type Fes2/C by Microwave Heating Method and its Electrochemical Properties for Oxygen Evolution

One-Pot Synthesis of Pyrite Type Fes2/C by Microwave Heating Method and its Electrochemical Properties for Oxygen Evolution

Genesis of a Ag-Pb-Zn-F system: Insights from in situ sulfur isotope and trace elements of pyrite, and rare earth elements of fluorite in the Baiyine'lebu deposit, Inner Mongolia, China

The recently discovered Baiyine’lebu Ag-Pb-Zn-F deposit in the southern Great Xing’an Range is hosted by NNE-trending transgressional fractures within Late Permian granodiorite. The fluorite ore veins in the periphery of the mining area show close spatial association with the Ag-Pb-Zn ore bodies. A total of four mineralization stages are recognized based on the cross-cutting relationships and mineral assemblages, among which three types of pyrite are identified, including: i) coarse-grained pyrite (Py1) from stage I quartz-pyrite vein, ii) fine-grained cubic pyrite (Py2) from stage II quartz sulfide-rich vein, showing association with metallic sulfide minerals, and iii) anhedral, irregular pyrite (Py3) disseminated in Ag-bearing sulfide ore vein from stage III. The stage IV is quartz-fluorite-calcite vein with very rare distribution of pyrite. Here we investigate the texture, trace element and sulfur isotopic composition of pyrite and rare earth elements (REEs) of fluorite to gain insights into the genesis and mineralization process of the Baiyine’lebu Ag-Pb-Zn-F deposit. Systematic trace element analyses indicate that the compatible and some other elements (Co, Ni, Cr and As) were incorporated in the pyrite structure via isomorphism in all pyrite types, whereas ore metals such as Cu, Pb, Zn, and Sn entered pyrite as structurally bound elements or micro/nanosized mineral inclusions. The Ag concentrations significantly increase from Py1 to Py3 in the form of invisible nanoparticles of sulfides or micro- to nano-sized mineral inclusions during the decrease of temperature. The narrow range of sulfur isotopic compositions from −0.80 to 3.88 ‰ (average in 1.17‰) indicates a relatively homogeneous sulfur source. In combination with REE patterns of fluorite, we propose that the ore-forming fluids originated mainly from post-magmatic hydrothermal fluid mixed with meteoric water in stage IV. The hydrothermal fluorite veins in the periphery of the Baiyine’lebu deposit could be genetically linked to the Ag-Pb-Zn veins. The purple fluorites with enriched REEs and positive Eu anomaly can be used as a proxy for prospecting Ag-Pb-Zn deposits. In addition, the high Sn content of pyrite in hydrothermal Ag-Pb-Zn deposit indicates the potential of Sn mineralization in the surrounding area or deeper level of the ore field in the South Great Xing’an Range.

Genesis and Distribution of Pyrite in the Lacustrine Shale: Evidence from the Es3x Shale of the Eocene Shahejie Formation, Zhanhua Sag, East China.

Pyrite is a common mineral in sedimentary rocks and is widely distributed in a variety of different morphologies and sizes. Pyrite is also widely distributed in the Es3x shale of the Eocene Shahejie Formation in the Zhanhua Sag, Bohai Bay Basin. A combination of geochemical and petrographic studies has been applied to address the formation and distribution of pyrite in the Es3x shale. The methods include thin section analysis to identify the representative samples of the shale-containing pyrite, total organic carbon (TOC) content analysis, X-ray fluorescence, X-ray diffraction, electron probe micro-analysis, and field emission scanning electron microscopy (FE-SEM) coupled with the energy dispersive spectrometer, to observe the characteristics, morphology, and distribution of pyrite in the lacustrine shale. The content of pyrite in the Es3x shale ranges from 1.4 to 11.2% with an average content of 3.42%. The average contents of TOC and total organic sulfur (TS) are 3.48 and 2.53 wt %, respectively. Various types of pyrites are observed during the detailed FE-SEM investigations including pyrite framboids, euhedral pyrite, welded pyrite, pyrite microcrystals, and framework pyrite. Pyrite framboids are densely packed sphere-shaped masses of submicron-scale pyrite crystals with subordinate large-sized euhedral crystals of pyrite. Welded pyrite forms due to the overgrowth and alteration of pyrite crystals within the larger pyrite framboids. Pyrite microcrystals are the euhedral-shaped microcrystals of pyrite. The framework pyrite is also observed and is formed due to the pyritization of plant/algal tissues. Based on the growth mechanism, the pyrites can be divided into syngenetic pyrites, early diagenetic pyrites, and late diagenetic pyrites. The presence of pyrite, especially the abundance of pyrite framboids, suggests that the environment during the Es3x shale deposition in the lacustrine basin was anoxic. Their dominant smaller size suggests the presence of an euxinic water column, which is consistent with the lack of in-place biota and high TOC contents. This research work not only helps to understand the pyrite mineralization, role of organic matter, and reactive iron in pyrite formation in the shale but also helps to interpret the paleoredox conditions during the deposition of shale. This research work can also be helpful to other researchers who can apply these methods and conclusions to studying shale in other similar basins worldwide.

Genesis of visible gold in pyrite in the Zhaoxian gold deposit, Jiaodong gold province, China: Constraints from EBSD micro-structural and LA-ICP-MS elemental analyses

Pyrite (FeS2) is one of the most common hosts for gold (Au) in different types of gold deposits, including visible and invisible gold. For visible gold in pyrite, it remains unclear whether it resulted from remobilization of invisible gold in the gold-hosting pyrite or from external input. This paper reports a case study from the Zhaoxian gold deposit, which is the deep extension of the well-known Jiaojia gold deposit, in the Jiaodong gold province. The texture and composition of Au-bearing pyrite from the Zhaoxian deposit were studied with petrographic, Electron Back-Scattered Diffraction (EBSD) mapping, and Laser Ablation – Inductively Coupled Plasma – Mass Spectrometry (LA-ICP-MS) methods. Four types of pyrite (Py-1 to Py-4), corresponding to four generations of veins, i.e., the pre-ore V1, syn-ore V2 and V3, and post-ore V4, were distinguished. Py-2 is volumetrically the most abundant among the four, and is the main host of visible gold. LA-ICP-MS analyses of pyrite indicate that gold contents in most analysis points are below the detection limit, with measured Au contents ranging from 0.02 to 0.17 ppm (median 0.09 ppm) in Py-1, and 0.03 to 2.45 ppm (median 0.07 ppm) in Py-2. EBSD analyses indicate that pyrite (Py-2) display brittle deformation features including microstructures, lattice dislocation, and grain boundary displacement. Visible gold in Py-2 occurs in micro-fractures, cavities, and grain boundaries. The generally low contents of Au in pyrite, including Py-2, and the brittle deformation features, suggest that the visible gold grains did not result from remobilization of invisible gold from pyrite. Rather, the majority of gold was introduced by fluids after the formation of the gold-hosting pyrite. These fluids were derived from the same sources as those precipitating the gold-hosting pyrite, but were more evolved and enriched in Au. Circulation of these auriferous ore-forming fluids in microfractures of pyrite and interstitial space resulted in precipitation of visible gold.

Mineralogical and geochemical research on Pengyang deposit: A peculiar eolian sandstone-hosted uranium deposit in the southwest of Ordos Basin

The newly discovered Pengyang uranium prospect area in the southwest of the Ordos Basin is the world's first uranium deposit hosted in eolian sandstone, which overturned the conventional view of uranium mineralization in fluvial-delta sedimentary strata. Uranium ore body occurring as tabular or lens-shaped is hosted in the gray-green reductive eolian sandstone of Lower Cretaceous Luohe Formation at depths ranging from 700 m to 3000 m. The host eolian sandstone is characterized by the typical high angle cross-bedding, wind sand ripple and grainflow strata. In this study, we conducted borehole log, petrographic observation, whole rock geochemistry analysis, geochemical and mineralogical study of uranium occurrence (SEM), element mapping of uranium minerals and in-situ sulfur isotope determination of pyrite by LA-MC-ICP-MS to reveal the uranium enrichment mechanism. The observations by SEM show that the predominant uranium mineral is pitchblende, primarily occurring as aggregates of nano to micro crystals absorbed on amorphous TiO2 or as colloform replacing the detritus Fe-Ti oxide minerals, both demonstrating the excellent absorption property of small particles of anatase. The contents of altered minerals such as chlorite and pyrite in gray-green sandstone increased significantly under scanning electron microscope (SEM). Whole rock geochemistry analysis data of sandstone samples collected in the target layers display the strong positive correlation between U and S. Whereas, in the elements mapping images, uranium enrichments display complete dissociation with pyrite as the uranium contents adjacent to or around the pyrite grains are under detection limit, demonstrating that uranium precipitation likely occurred earlier than the sulfuration of red eolian sandstone. Sulfur isotope of the two morphological types of pyrite are both characterized by a relatively light signature, ranging from − 19.23 to − 27.22 ‰ and from − 21.60 to − 29.64‰ respectively, implying that they are generated from bacterial sulfate reduction in the open systems with an adequate supply of sulfate. Anaerobic sulfate-reducing bacteria use the hydrocarbon transferred along faults to the sandstone as energy to reduce sulfate (SO42−) to H2S. In addition to the typical vertical red - yellow - gray color zonation, we also observed distinct reverse color zonation of sandstone, which can hardly be interpreted by traditional interlayer-oxidation-zone theory. We attribute the uranium reduction to the encounter of downward penetrating oxygenated groundwater with the upward migrating oil and gas conducted by thrust faults, which are widespread distributed in the west margin of the Ordos Basin. This study gives a new insight into uranium metallogenic mechanism in eolian sandstone and underpins an effective vector for the exploration of sandstone-type uranium deposits in the western of the Ordos Basin.

Intrusion-related orogenic gold deposit in the East Kunlun belt, NW China: A multiproxy investigation

The Wulonggou gold district is one of the most important gold producers of the East Kunlun metallogenic belt in China. Due to its complex geological background and limited investigations, the age of mineralization and ore-forming process remain unclear. Here, we focus on the Yanjingou gold deposit which is the largest and most typical deposit in the Wulonggou gold district, with a view to investigate the metallogenic mechanism and timing of ore formation with a view to evaluate the ore-forming processes and sources through a comprehensive study of the ore mineralogy, monazite and zircon U-Pb dating, in situ trace element analysis and mapping, and in situ S isotopes. Our results show that the magmatism and mineralization were coeval, during 239 Ma and 244 Ma in the Middle Triassic. Four stages of mineralization are identified with distinct textures, mineral assemblages, trace element characteristics and S isotopes. Stage 1 is represented by euhedral pyrite bearing quartz veins, which originated from deep metamorphic fluid, and was rarely affected by magmatic hydrothermal fluids. Stage 2 is characterized by the occurrence of abundant oriented arsenopyrite, which originated from the mixture of deep metamorphic fluid and magmatic hydrothermal fluid. Stage 3 is characterized by the occurrence of polymetallic sulfide of copper, with two generation of pyrite (stage 3 Py1 and Py2). Stage 3 Py1 formed from magmatic hydrothermal fluids whereas Py2 originated from deep metamorphic fluid and was also slightly influenced by magmatic hydrothermal fluids. Stage 4 is represented by late calcite and pyrite combination, which originated from another stage of deep metamorphic fluid. Stage2 and 3 are the main gold mineralization stages, and Au has a close relationship with As, and an obvious inverse correlation with Co and Ni. Combined with the trace element characteristics, we infer that the denudation degree of the Yanjingou gold deposit is very shallow with good prospects for exploration. Through multi-proxy investigation of the different stages and types of pyrite, we postulate that the Yanjingou gold deposit is an orogenic gold deposit related to intrusive rocks formed during Middle Triassic compressional transformation.

Sediment hosted stratiform barite – (Cu-Zn-Pb) deposits in the southwest Mahabad, Iran; implications for geology, ore textural, compositional, and S-O isotopes geochemistry

The southwestern part of Mahabad town in the northwestern part of the Sanandaj-Sirjan metamorphic zone (SSZ) of Iran hosts seven barite-base metal deposits. They have occurred within the Precambrian-aged metasedimentary succession including black color fine-grained shale, slate, and phyllite with minor calcareous intercalation. This investigation is focused on three main ore deposits including Meraneh, Sorkhab, and Shekarbeig. The mineralized units and host rocks have been metamorphosed to lower greenschist facies in the Post-Cretaceous.Five different stages of mineralization were distinguished based on the field observations, mineralogical and textural relationships, morphology of the orebodies, and mineral chemistry studies. The followings are the stages of evolution: (1) precipitation of framboidal, colloform, and monomineralic pyrite bands and fine-grained barite (2) stratiform accumulation of barite with sulfide and un-mineralized sediment strata (3) stockwork mineralization and associated alteration (4) formation of discrete vent complex associated with massive sulfides and barite in replacement zone, and (5) post-mineralization deformation and shearing process, contemporaneous with regional metamorphism.Pyrite, chalcopyrite, sphalerite, and galena are the major sulfide minerals, in order of abundance, found in the studied deposits, accompanied by the minor amounts of tetrahedrite and covellite. The stratiform, massive and stockwork ores are indicative of the main ore-forming event and are volumetrically the most important facies. The electron probe micro-analyzer (EPMA) data of sulfide minerals indicates a distinct variation in trace element concentrations during the ore formation. Besides, this study focuses on distributions of δ 34S value in sulfide minerals, as well as δ 34S and δ 18O value of barite mineralization in stratiform, stratabound, and stockwork ore zones. The paragenetic relationships, mineral chemistry and isotopic study of minerals reveal that the stages 1 and 2 can be considered as the pre-date hydrothermal input of the stage 3 in all the three ore deposits. In addition, the mineralization event during stage 1 of the ore formation was found out to have occurred in a low temperature environment within the unconsolidated sediments, instantly under the sea floor. During stage 2, the stratiform ore has been deposited due to the diagenetic processes. The up-flow exhalative hydrothermal fluids resulted in the thermal alteration of the organic-rich host rock during stage 3, and formation of the massive mineralized bodies in stage 4. Finally, the lower greenschist facies metamorphism affected both the ore and host rocks during stage 5.On the basis of mineral chemistry inspections, all types of pyrites have high Ni and low Co contents and great majority of them show the Co:Ni ratios of lower than 1. Stratiform pyrites were fine-grained and enriched in As, Au, and Co, in contrast to hydrothermally pyrites. Ni, Pb, Zn, Bi, Hg, and Cu were mostly concentrated in coarse-grained hydrothermally pyrits. Also, the temperature and sulfur fugacity increased from stratiform stage to hydrothermal stage. The Se content of chalcopyrite as well as Bi and Ag contents of Galena increased from feeder to massive and stratiform ore. Sphalerite was generally iron-poor and its Fe content decreases from feeder to massive and stratiform ore. The Co/Ni ratio of pyrite and Zn/Cd ratio of sphalerite can be used to discriminate the VMS, magmatic or SEDEX origins for ore deposits. The Zn/Cd ratio of the sphalerites and Co/Ni ratio of pyrites provided the evidence for SEDEX style mineralization in the studied deposits.Barites with various textures and morphologies show overlapped distributions of δ34S and δ18O values from the stages 2, 3, and 4, range from + 34.1 to + 41.3‰ and + 10.2 to + 12.6‰, respectively. The d34S versus d18O patterns for the stratiform barite resemble the patterns that indicate sulfate is consumed by AOM. Sulfides have different isotopic compositions: stratiform with markedly more positive δ 34S values of + 28‰ to + 33‰; stockwork with δ 34S values of + 8‰ to + 26‰; and massive pyrite with δ 34S between + 8‰ and + 26‰. We suggest that the isotopic relationships (δ34S pyrite ≈ δ34S barite) in the stratiform ore zones may be related to anaerobic oxidation of methane coupled to sulfate reduction (AOM-SR), which has been developed during open system diagenesis. Textural and isotopic evidence indicates that the stockwork and massive ores has grown by thermochemical sulfate reduction (TSR) and reductively dissolving barite. On the other hand, the trend between d18O and δ34S suggest that the growth of the stockwork and massive barite is related to fluid seep on modern continental margins. Textural evidence documented during the different mineralization stages together with concentration and the distribution pattern of trace elements and isotopic investigation in the stratiform, massive, and stockwork ore zones signify that the SEDEX-type mineralization has been occurred in this district.

In situ multiple sulfur isotopes and chemistry of pyrite support a sedimentary source-rock model for the Linwang Carlin-type gold deposit in the Youjiang basin, southwest China

The Linwang gold deposit is a representative example of Carlin-type gold deposits in Youjiang basin, southwest China. High-grade ores are hosted in silicified and brecciated siltstone, sandstone, and mudstone of the Middle Triassic and are controlled by high-angle reverse faults. Optical microscopy pyrite texture, in situ laser ablation-inductively coupled mass spectrometry (LA-ICP-MS) trace elements, and secondary ion mass spectrometry (SIMS) multiple sulfur isotopes analyses are used to examine the different types of pyrites to constrain the sources of reduced sulfur and metals for the Linwang deposit.Petrography and pyrite chemistry studies distinguished three generations of pyrite: Pre-ore pyrite (Py 1) and ore pyrites (Py 2 and Py3). Pre-ore pyrite is framboidal, anhedral to euhedral pyrite with highest concentrations of Co, Ni, and Pb and is interpreted to have a sedimentary (diagenetic) origin. Ore pyrites were formed by hydrothermal fluids via sulfidation of Fe-bearing minerals in the host rocks. They commonly rimed and partially replaced the pre-ore pyrite and have an As-rich inner rim (Py 2) and an Au-rich outer rim (Py 3) with lowest contents of Co, Ni, and Pb. All pyrites contain Au, As, Sb, Cu, Tl, and Se, with increasing concentrations from Py 1 to Py 3.In situ SIMS multiple S isotope analyses show that all pyrites in the Linwang deposit have narrow ranges of δ34S values, with average of +5.13‰ for Py 1, +4.84‰ for Py 2, and +4.53‰ for Py 3, and near zero of Δ33S values (−0.02‰ to +0.03‰), suggesting that the S within the Linwang deposit was most likely sourced from the Triassic sedimentary rocks that host the deposit. A near zero Δ33S signature in all pyrites indicates no record of the assimilation of Archean sulfur, implying the deep basement of Archean rocks beneath the basin were not involved the formation of the Linwang deposit.Oxygen and hydrogen isotope compositions of ore fluids (δ18OH2O = +11.7‰ to +16.5‰, δD = −71‰ to −57‰) indicate a metamorphic origin. Based on these data, we propose a sedimentary source-rock model for the Linwang deposit in which the ore fluids were generated by release of previous Au-bearing sedimentary pyrites during metamorphism of sedimentary rocks. The stress relaxation of Yanshanian orogeny resulted in the ore fluids flowed upward along the fault zones into structural highs where they reacted with Fe-bearing minerals in the host rocks to deposit Au-rich pyrite. The preconcentration of Au, As, and Sb in sedimentary pyrite and gold deposition process are key to the formation of the Linwang deposit and may apply to the genesis of other Carlin-type gold deposits in the Youjiang basin.

Genesis of the sediment-hosted Haerdaban Zn-Pb deposit, Western Tianshan, NW China: Constraints from textural, compositional and sulfur isotope variations of sulfides

The sediment-hosted Haerdaban Zn-Pb deposit is a newly discovered Zn-Pb deposit in the Sailimu terrane, Western Tianshan (NW China), containing ca. 0.64 Mt of ore at 6.19 wt% Zn and 1.09 wt% Pb. The mineralization consists mainly of veins, breccias and semi-massive sulfide ores within the dolomitic limestone and calcareous slate. Using LA-ICP-MS, this study investigates trace element and sulfur isotope composition of sulfide to constrain the genesis of the deposit. Four pyrite types were identified by variations in texture and composition. Porous pyrite (Py1) shows a significant enrichment in Mn, Ag, Sb, Tl, Ba, Pb, Cu, and Zn, whereas the pyrite overgrowth (Py2) and euhedral pyrite (Py3) are enriched in Co and As, but depleted in all other trace elements. This compositional trend is attributed to the release of trace elements from pyrite during recrystallization from a porous to massive texture. Pyrite (Py4) associated with sphalerite is inclusion-rich, but exhibits a depletion in most trace elements, except Ni and Sb. The underlying carbonaceous sediments are interpreted as a source of Ni, Sb and other metals for the ore-forming fluids. Sphalerite displays a wide variety of colors from dark brown to pale yellow, primarily related to variations in Fe contents. The overall Fe contents (0.25 to 6.12 wt%), Cd contents (524 to 1875 ppm) and Zn/Cd ratios (320 to 1258) in sphalerite are compatible with those of SEDEX Zn-Pb deposit. The contents of other elements in sphalerite are generally low. Calculated temperatures using trace element contents in sphalerite (GGIMFis geothermometer) range from 163 °C to 309 °C, indicating progressive cooling of ore-forming fluid. Pyrite, sphalerite and galena display a wide range of δ34S values from +3.9 to +18.3‰. The association of lower positive δ34S values (+3.9 to +8.8‰) and epithermal suite elements (Ni, As, Sb, and Tl) enrichment in porous pyrite indicate that sulfur in early sulfides was derived from thermochemical sulfate reduction (TSR) with a possible magmatic input. The dominant population of heavier δ34S values (+13.8 to +18.3‰) of massive sulfide support TSR as the main source of sulfur. The intermediate δ34S values (+7.0 to +13.0‰) of vein sulfide are likely a mixing of TSR-derived sulfur with light sulfur leached from diagenetic pyrite. The current data support the classification of Haerdaban as a metamorphosed SEDEX Zn-Pb deposit, where the main mineralization was the product of remobilization and upgrading of early exhalative ores during hydrothermal events.

The genesis and mineralization process of Xiaobaliang VHMS Cu-Au deposit, Central Asian Orogenic Belt: Constraints from the pyrite geochemistry and zircon geochronology

The Xiaobaliang Cu-Au deposit is located in the Hegenshan ophiolite complex belt of the western Xing’an–Mongolia Orogenic Belt (XMOB). Strata-bound sulfide ores are discovered within the Carboniferous volcanic tuff, with the oxidized Au-Cu ores at the top and Cu (-Au) sulfide ores at the bottom. Zircon U-Pb dating on volcanic tuff has yielded a concordia age of 326 ± 3 Ma (n = 21, MSWD = 5.6). Four types of pyrite have been identified, including lamellar pyrite (Py1) in the wall rocks, framboidal pyrite (Py2) in the Zn-rich massive ores, colloform pyrite (Py3) in the massive Cu ores, and euhedral pyrite (Py4) in the fractured Cu ores. Chalcopyrite comprises two types: early massive chalcopyrite aggregates (Cp1) and late chalcopyrite veinlets (Cp2). Here we present the in situ trace elements and sulfur isotopes analyses of different sulfide generations. Elements like Se (44.1 ppm), Co (227 ppm) and Cu (3211 ppm) are enriched in pyrites from Cu ores (Py3&Py4), whereas the pyrites from altered rocks (Py1) take high Mn (5027 ppm), Ti (134 ppm), V (13.0 ppm), Ni (41.9 ppm) and Au (5.07 ppm) concentrations. Similar elemental patterns are observed in chalcopyrite analyses where Co (312 ppm), Se (566 ppm) and Te (31.5 ppm) are enriched in massive Cu ores (Cp1), but Mn (147 ppm), V (174 ppm) and Ti (42.2 ppm) contents are mainly concentrated in chalcopyrite veinlets (Cp2). In situ S isotope analyses exhibit a large variation in Py1 (−30.70 to −1.50‰) and Cp2 (−7.81 ∼ −4.50‰) but are constant in Py2, Py3, Py4 and Cp1 (0.44 to 3.15 ‰). The high Co/Ni ratios and relatively lower δ34S values in Py1 suggest a diagenetic environment where the lower-temperature and extremely reduced conditions facilitate the enrichment of Mn, V and Au. The progressive enrichment of Sn, Te, Bi, Se and Cu in hydrothermal Py3 and Py4 then points out the rising of temperature in the weakly reduced environment. The negative sulfur isotopes in altered rocks (Py1) and fractured ores (Cp2) point out the contribution of the volcanic-sedimentary sequence. These compositional features, combined with sulfur isotopes, have demonstrated that Cu was mainly derived from magmatic-hydrothermal fluids whereas Au was released from Au-rich sediments on the seafloor. The Xiaobaliang Cu-Au deposit belongs to a Cyprus-type VHMS deposit formed in the Carboniferous extensional setting.