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[Display omitted] • Pyrite and pyrrhotite reveal homogeneous textures with some micro-inclusions. • Pyrite and pyrrhotite are enriched in Co, Ni, Cu, Pb, Zn, Ag, Bi, Mn, As, Se, and Sb. • The variation of Co, Ni, and Co/Ni ratios is linked with the distance to ore-related granite. • In-situ sulfur isotopes demonstrate a magmatic source for ore-forming materials. • The formation of Ag–Pb–Zn veins are due to a decrease of temperature, salinities, f S 2 and f O 2. Xiasai is the largest magmatic-hydrothermal Ag–Pb–Zn–Sn deposit in the central Yidun Terrane (SW China). Two generations of pyrite are associated with Ag–Pb–Zn mineralization. The coarse-grained pyrite (PyI) occurs together with arsenopyrite and pyrrhotite, and the fine-grained pyrite (PyII) is associated with sphalerite and chalcopyrite. This study documents LA-ICPMS mapping, trace element and LA-MC-ICPMS sulfur isotopic analyses of the two types of pyrite and pyrrhotite, to further constrain the formation of Ag–Pb–Zn veins. Micro-textures reveal that pyrite and pyrrhotite have a homogeneous distribution of trace elements at the individual grain scale, however, some micro-inclusions containing trace elements, including Co, Ni, Cu, Pb, Zn, Ag, Bi, and As, are identified. Pyrite and pyrrhotite are enriched in Co, Ni, Cu, Pb, Zn, Ag, Bi, As, Se, and Sb. However, PyII has higher Cu, Pb, Zn, Ag, and Bi, but lower Co, Ni, As, Sb, and Te concentrations than PyI. The variations of Co and Ni concentrations, as well as the Co/Ni ratios in pyrite and pyrrhotite demonstrate a link with the distance to ore-related granite. PyI has in-situ δ 34S values of –6.8 to –3.4 ‰ (average of –5.9 ‰), and PyII exhibits values ranging from –6.7 to –5.4 ‰ (average of –6.0 ‰). Pyrrhotite has δ 34S values ranging from –6.9 to –5.5 ‰. The in-situ sulfur isotopic compositions demonstrate a magmatic source for ore-forming materials, which were derived from the Early Cretaceous monzogranite. Trace elements and sulfur isotopic compositions of pyrite and pyrrhotite indicate that the formation of the Ag–Pb–Zn veins at Xiasai is due to a decrease of temperature, salinities, f S 2 and f O 2 of the hydrothermal fluids. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Nageng Ag mineralization age is limited to ca. 217–207 Ma. • Pyrite trace elements and δ 34S suggest a magmatic-hydrothermal origin. • Ag-Pb-Zn veins formed due to temperature, f S 2 , and f O 2 decrease. The Nagengkangqie'er (Nageng) silver deposit, situated in the Eastern Kunlun Orogenic Belt (EKOB), Northwestern China. It contains 5,070 tons of contained silver at a silver grade of 325 g/t. Nonetheless, the genesis of the Nageng silver deposit is still under debate, due to the absence of definitive constraints the mineralization age and the metal sources. The U-Pb data analysis of a post-ore calcite vein established the minimum age of the mineralization at 207 ± 3 Ma, whereas the maximum age of 217 ± 4 Ma was determined from zircon U-Pb data obtained from the altered and mineralized rhyolitic porphyry host-rock. These temporal limitations suggest that the mineralization formed at ca. 217–207 Ma, and it is associated with the post-collisional setting of the Paleo-Tethys evolution in the EKOB. The distinct textural patterns, as revealed by petrographic observations, suggest three types of pyrites: py1 is composed of euhedral pyrite in the early barren quartz vein at stage 1, py2 is represented by subhedral-anhedral grains in massive ore veins at stage 2, and py3 forms euhedral crystals of varying sizes, which are interspersed with early-formed marcasite in the quartz + calcite + silver-bearing sulfosalt-dominated veins at stage 3. In-situ δ 34S values of pyrites range between −2.33 ‰ and −0.37 ‰, indicating a dominantly magmatic origin. EPMA studies have revealed that silver in the Nageng deposit predominantly occurs as silver-bearing galena at stage 2, whereas silver is enriched in sulfosalts of stage 3. From py1 to py3, a decrease in the Co-content indicates a decrease in the ore-forming fluid temperatures. The presence of stage 3 sulfide, sliver-bearing sulfosalt, and calcite-quartz in a fracture-filled vein indicates low-pressure conditions during its formation, compared to stages 1 and 2. In summary, the Nageng deposit is a typical magmatic-hydrothermal vein-type Ag-Pb-Zn deposit. Fluid cooling and decrease in pressure, coupled with decreases in f O 2 and f S 2 , are the parameters inferred to have led to a decrease of silver solubility in the hydrothermal fluids and, successively, promoted extensive Ag deposition. [ABSTRACT FROM AUTHOR]

Sulfur isotope signatures of Au-bearing pyrite from Lannigou Au deposit, a typical Carlin-type Au deposit in SW China, provide valuable information about the origin of the ore-forming minerals. Analysis by NanoSIMS was used to determine S isotope compositions of Au-bearing pyrite and to map the grain-scale distributions of Au, Cu, As and S in pyrite from the deposit. Based on different textural pattern of pyrites revealed by back-scattered electron (BSE) images, they are divided into three types: Py-1 diagenetic pyrite without core-rim structure, Py-2 pyrite with an Au-free core and a rhythmically-zoned Au-bearing rim, Py-3 Au-bearing pyrite with rhythmic zoning across the entire grain. The element distributions and S isotope compositions of four paragenetic stages are recognized on the basis of textural observation. Py-1 grains and the Au-free homogeneous cores of zoned crystals were formed in Stage 1 while the Au-bearing rims of the zoned crystals with rhythmic zonation of As and Cu, and to a lesser degree Au, were formed in two superimposed stages: stage 2 formed the inner zone that is enriched in As alone; and stage 3 formed the outer zone that is enriched in both Au and As. Other sulfides such as realgar, cinnabar and stibnite are formed in the last stage. The relationship between Au and As distributions in pyrite rim is complicated, changing from coupled to decoupled at the nanoscale. Such complexity is interpreted to reflect fluctuation of fluid composition and temperature with time, which in turn affect the modes of occurrence of As and Au. It is inferred that As mainly occurs in the crystal lattice replacing S whereas Au is mainly present as nanoparticles that were trapped in pyrite during crystal growth. The Au-bearing rims of the zoned pyrite crystals are characterized by highly variable δ 34 S values from 1.1 to 18.1‰, which exceed the values of the Triassic calcareous host rocks (10–14‰). In contrast, the δ 34 S values of the Au-free cores of zoned pyrite crystals vary over a narrower interval and are mainly between 6 and 12‰, close to the values of pyrite crystals in the sedimentary country rocks. Our new analyses also reveals that the δ 34 S values of the Au-bearing fluids generally increase during the formation of the deposit. The observed S isotope variations are consistent with mixing between a magmatic-related fluid with mantle-like δ 34 S value (∼0‰) and a sedimentary or deep basin brine fluid with elevated δ 34 S value (>18‰), with an increasing contribution from the latter with time. The notably varied values of δ 34 S and the disseminations of Au and other trace elements such as As and Cu in pyrite crystals indicate that the process responsible for Au precipitation in this deposit occurred in an open hydrothermal system. [ABSTRACT FROM AUTHOR]

[Display omitted] • Pyrite of Carlin-type Au deposits in the Youjiang Basin were analyzed by Nano-SIMS. • The δ34S values Au-bearing pyrite of Linwang vary inversely with Au concentrations. • Initial auriferous fluids of Linwang were sourced from magmatic-hydrothermal systems. • Reduced sulfur in ore-forming fluids of Badu was dominated by sedimentary sulfur. • Sedimentary sulfur contamination result in variable δ34S values of Au-bearing pyrite. The Youjiang Basin in Southwest China is the world's second largest Carlin-type gold (Au)-producing region. However, the source of reduced sulfur that accounts for Au transport in ore-forming fluids remains controversial. Finely characterizing the sulfur isotopic compositions (δ34S values) in micron-scale zonation of Au-bearing pyrite is the key to clearly identify sulfur source. Here, we used high-resolution nanoscale secondary ion mass spectrometry (Nano-SIMS) to characterize the temporal variation in δ34S values and its relationship with metal contents across Au-bearing pyrite from the Linwang and Badu deposits in the Youjiang Basin, with the aim of monitoring the source and evolution of reduced sulfur in auriferous fluids. The Au-bearing pyrite rims in the Linwang deposit contain three growth stages that record episodic injections of Au- and As-rich fluids. Within these rims, the δ34S values vary inversely with Au concentrations. The inner rims with the high Au contents have δ34S values of −1.7‰ to +3.3‰ that are comparable to those of magmatic sulfur. The outer rims with decreasing Au contents have δ34S values of +1.3‰ to +15.7‰ that gradually approach those of pre-ore pyrite in the host rock. Such a variation indicates that the reduced sulfur in the initial Au-bearing ore-forming fluids was primarily originated from deep magmatic-hydrothermal systems while the host rock-derived 34S-enriched sulfur increasingly dominated through fluid-rock interactions during mineralization. In contrast, Au-bearing pyrite from the Badu deposit has positive δ34S values ranging from +9.0‰ to +25.8‰, which overlap those of diagenetic pyrite in the Devonian sedimentary rocks. Combining the intimate spatial association between Au mineralization and the Devonian strata, we propose that the initial ore-forming fluids have leached substantial sulfur from the Devonian strata. Significant contaminations of sedimentary sulfur erased the primary sulfur isotopic signals of the initial auriferous fluids. Our interpretations of these two deposits may also apply to other Carlin-type Au deposits in the Youjiang Basin, where δ34S values of Au-bearing pyrite show host rock-dependent variations. This study demonstrates that high-resolution Nano-SIMS sulfur isotope and elemental analysis of Au-bearing pyrite is a potent tool for tracing the source and evolution of reduced sulfur in ore-forming fluids for sedimentary-host Au deposits worldwide. [ABSTRACT FROM AUTHOR]

• Xinqiao and Taoyuan deposits are typical stratabound massive sulfide deposits. • Colloform (Py1), fine-grained (Py2) and medium- to coarse-grained (Py3) are identified. • Pyrites are magmatic-hydrothermal origin. • Stratabound ore precipitated from the magmatic-hydrothermal fluid. • A sedimentary component was involved in the stratabound mineralization. Stratabound massive sulfide deposits are widely distributed along Middle-Lower Yangtze River metallogenic belt, in eastern China. There has much debate as to whether these deposits were associated with Late Mesozoic igneous or Carboniferous sedimentary exhalative (SEDEX). Three-type pyrites, i.e., colloform (Py1), fine-grained (Py2) and medium- to coarse-grained (Py3), from Xinqiao and Taoyuan stratabound massive sulfide deposits in Tongling region were investigated using electron probe microanalysis (EPMA), in-situ laser-ablation inductively-coupled plasma-mass spectrometry (LA-ICP-MS) and sulfur isotopic analysis. The analytic data indicate that the three-type pyrites have high S and As, and relatively consistent Au contents. The Au, Ag, Bi, Sb and Pb elements are mainly of lattice bound appearance in the Xinqiao and Taoyuan pyrites. Low Au (mainly < 5 ppm) and Ni (commonly < 10 ppm) contents, high Co/Ni (mainly > 1), Se/Tl (mainly > 1) and δ34S CDT (4.0‰ to 5.9‰) values of the studied Xinqiao and Taoyuan pyrites imply a magmatic-hydrothermal origin. High Bi (>1 ppm) and Mo contents, and low Co/Ni ratios (<0.1) of the studied Xinqiao and Taoyuan pyrites reflect a sedimentary contribution to the magmatic-hydrothermal system. Combined with previous results, the Xinqiao stratabound mineralization is most likely to be genetically with the magmatic-hydrothermal fluids by the addition of a sedimentary component. [ABSTRACT FROM AUTHOR]