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Gold in Carlin-type gold ores is commonly hosted in the arsenian pyrite rim, but the formation of arsenian pyrite and its contribution to Au adsorption are poorly understood. Based on our previous NanoSIMS Au mapping, we conducted SEM and HR-TEM analyses to examine the Au deportment and nanoscale texture of individual auriferous arsenian pyrite grains from the giant Carlin-type Lannigou gold deposit, SW China. The results indicate that the arsenian pyrite rim is composed of numerous nanoparticulate pyrite grains (rather than a single crystal), and gold nanoparticles (Au0) occur mainly in sub-rim with the highest Au content, which are porous and have lower degrees of order. We propose that nanoparticulate arsenian pyrite attachment and aggregation is the main mechanism for the arsenian pyrite rim growth, and such mechanism is crucial for the Au efficient enrichment for this giant gold deposit. [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]

• There are three types of pyrite with sector zoning, massive overgrowth, and replacement relics. • Two principal types of sphalerite were identified with fragmented and replacement textures. • Different generations of pyrite have variable trace elements, reflecting an evolving hydrothermal system. • Trace element contents of pyrite indicate that the Qilinchang deposit was formed from low temperature hydrothermal fluids. The Qilinchang Pb-Zn deposit (̴ 5Mt of sulphide ore at mean grades of 2.3–9.2% Pb and 2.7–22.5% Zn) is hosted in Early Carboniferous carbonate rocks and mainly controlled by NE-, NS-, and NW- trending structural belts between the Xiaojiang and Zhaotong-Qujing buried faults. Ore minerals are sphalerite, galena, pyrite, chalcopyrite, and marmatite, whereas gangue minerals are dolomite, calcite, and quartz. Three generations of pyrite are recognized; these include fine-grained anhedral pyrite (Py-I), medium-grained anhedral to subhedral hydrothermal pyrite (Py-II), and coarse-grained subhedral to euhedral hydrothermal pyrite (Py-III), while the sphalerite occurs in two forms as fine-grained intergrown with galena and associated with Py-I and Py-II. Laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis was performed to evaluate trace element compositions of pyrite and sphalerite from different generations of ores. Py-I has relatively higher concentrations of Mg, Mn, Co, Ni, and Tl. Py-II in Cu, As, Se, Mo, and Sb relative to pyrite of other generations. The contents of trace elements in Py-III are variable but significantly enriched in Ti, V, Bi, Ag, and Pb compared to Py-I and Py-II. This variation indicates that these elements occur as micro mineral inclusions of possible Ag-Pb-bearing phases. Sphalerite of stage I has higher concentrations of Mn, Fe, Co, Ni, Cu, Ga, Ge, As, Ag, Cd, In, Sb, Hg, and Pb than stage II. These elements are homogeneously distributed in all samples analyzed. The incorporation of these elements is primarily through simple substitution mechanisms (e.g., 2Zn2+ ↔ Cu+ + In3+) as indicated from binary plots. Principal component analyses (PCA) applied to LA-ICP-MS dataset for pyrite reveal two main clusters; Py-I enriched in Ni, Co and As, Py-II and Py-III high in with V, Mn, Cu, Zn, Se, Mo, Ag, Sb, Au, and Bi. Likewise, the PCA also confirms two clusters of elements for sphalerite; Ge, Cu, As, Sb, Ag, Fe, and Cd corresponding to Sph-I and In, Sn, and Ga corresponding to Sph-II. Py-I has higher Co/Ni ratio ranging from 0.04 to 1.6 compared to Py-II and Py-III having Co/Ni ratios from 0 to 0.706 and 0 0.696, respectively. We report that the pyrites from the Qilinchang deposit have Co/Ni ratios slightly lower than typical Mississippi Valley-Type (MVT) deposits (0.2–7.2) and different from iron oxide copper-gold (IOCG) and porphyry Cu deposits. Considering these geochemical signatures, it can be suggested that the Qilinchang deposit was not related to magmatic activities. We thus propose that the ore-forming fluids responsible for the formation of the deposit were generated from a low-temperature environment, similar to typical MVT deposits. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ge is mainly coupled with Cu in sphalerite, locally associated with Pb, Ag, and Mn. • The substitution mechanism of Ge will vary with textures and color of sphalerite. • Crystal structure or planes, texture, and temperature affect Ge, Ga, In contents. • Ge, Ga, and In behave differently during sphalerite precipitation. The low-medium temperature Zn-Pb deposits in the Sichuan-Yunnan-Guizhou (SYG) metallogenic region contain not only Pb and Zn but also abundant critical metals such as Ge, Ga, and In. The majority of previous studies focus on the genesis of Pb and Zn metals, and the research on Ge, Ga and In in the SYG region has become a topic in recent years due to economic importance of these metals. In this review, the distribution, occurrence, and enrichment mechanism of Ge, Ga, and In in Zn-Pb deposits in the SYG region is summarized. Sphalerite is the main host mineral of Ge, Ga, and In, with contents of up to ∼1300 ppm, ∼600 ppm, and ∼1191 ppm, respectively. Pyrite from the Fule Zn-Pb deposit is also rich in Ge (up to 340 ppm), which may be due to involvement of magmatic components in the ore-forming fluids. Germanium, Ga, and In mainly appear in the form of isomorphism in sphalerite. Independent minerals of Ge such as ruizhongite (Ag 2 □)Pb 3 Ge 2 S 8), are only found in the Wusihe Zn-Pb deposit. Copper is the main coupling ions for substitution of Ge, Ga, and In in sphalerite. However, the positive correlation of Ge with Pb, Mn and Ag in the sphalerite of Huodehong, Shaojiwan, Shanshulin, and Qingshan Zn-Pb deposits may indicate other means of substitution or existence of nanometer Ge minerals with similar composition to the ruizhongite. The substitution mechanisms of Ge and Ga vary with layers in the zoned sphalerite from the Nayongzhi Zn-Pb deposit, possibly indicating that physical or chemical variations in fluids will affect the substitution ways of Ge and Ga in sphalerite. The growth direction and crystal structure of ZnS also exert control over the contents of Ge, Ga, and In. The enrichment degree of Ge, Ga, and In changes between (1 1 0) and (1 1 1) crystal planes, and the wurtzite structure is beneficial to the infiltration of large ions (Ge, Ga, and In). Compared to sphalerite with euhedral texture, colloform sphalerite is conducive to the enrichment of Ge. For zoned sphalerite such as the rhythmic banding and the conventional zone, the former lacks zoning of Ge, Ga and In but the latter shows elemental zonation and Ge is enriched in the black domains. The correlation between the contents of Ge, Ga, and possible In in sphalerite and Pb or Zn isotopes of sulfides indicates the significant contribution of basement rocks for the enrichment of these metals. During the mineralization process, Ge tends to be enriched in dark or early sphalerite, including the Daliangzi, Tianbaoshan, Huize, Nayongzhi, Fule, Fuli, Wusihe, and Maoping deposits, which may be due to the variations in temperature or fluid evolution. The opposite variation trend of Ge and Ga with sphalerite color or stage in the Daliangzi, Nayongzhi, Maoping, Shaojiwan, and Wusihe Zn-Pb deposits indicates that Ge and Ga may behave differently during precipitation of sphalerite. [ABSTRACT FROM AUTHOR]

• Zn dominates early mineralization stage, whereas late stage features Pb-Sb. • Sulfur is mainly of magmatic source, with a small amount of sulfur from TSR. • Mixing of sulfur-rich fluid with metalliferous brine caused sulfide precipitation. • Temperature is the most important factor to control the metal precipitations. The Lanuoma deposit, located in the Sanjiang Tethyan metallogenic domain, shows a characteristic assemblage of Pb-Zn-Sb mineralization, distinguished from those in other sediment-hosted base metal deposits of this region. The ore textures reveal two mineralization stages: the early stage is characterized by Zn mineralization with occurrences of porous pyrite (Py2) and yellowish-brown sphalerites (Sp1), and the late stage is characterized by Sb-Pb mineralization with occurrences of subhedral-euhedral pyrite (Py3), yellowish-white sphalerites (Sp2), sulfosalts consisting of boulangerite, zinkenite, sorbyite and plagionite and calcite veins. The framboidal pyrites (Py1) predate Pb-Zn-Sb mineralization. Py2 has higher Zn contents (16.97–621.67 ppm, mean: 181.17 ppm) than Py3 (Zn: 0.76–323.44 ppm, mean: 29.58 ppm) by up to one order of magnitude. The Se contents of Py2 (Se: 5.46–87.82 ppm, mean: 50.96 ppm) are also one order of magnitude higher than those of Py3 (Se: 1.64–10.99 ppm, mean: 4.35 ppm). Sp1 is characterized by one order of magnitude higher contents of Fe (381.99–9046.64, mean: 4875.50 ppm) and Se (4.02–72.51 ppm, mean: 34.70 ppm) than Sp2 (Fe: 287.53–584.02 ppm, mean: 416.75 ppm; Se: 2.89–10.80 ppm, mean: 6.20 ppm). However, the average content of Cd (4256.38 ppm) in Sp2 is almost twice that in Sp1 (2635.74 ppm). The higher Se contents in Py2 coupled with higher Se and Fe contents in Sp1 indicate that Py2 and Sp1 had higher precipitation temperatures than Py3 and Sp2. Sulfur isotope compositions of pyrites and sphalerites acquired by NANO-SIMS and LA-MC-ICP-MS suggest two origins: the sulfur of Py2 (δ34S: −3.0 to 2.3‰), Sp1 (δ34S: 0.2–0.9‰) and Sp2 (δ34S: 0.7–2.5‰) was mainly of magmatic source, and sulfur reduced via thermochemical sulfate reduction participated in the formation of Py3 (δ34S: 0.2–6.0‰) and S-Sb-Pb minerals intergrown with Py3. The sulfur isotope compositions of Py1 (δ34S: −31.8 to −19.4‰) indicate a biogenic origin associated with bacterial sulfate reduction. A fluid mixing model is suggested to interpret the genesis of the Lanuoma Pb-Zn-Sb deposit: mixing of a reduced S-bearing fluid with a metalliferous basinal brine resulted in the precipitation of sulfides. Temperature was the most important factor controlling metal precipitation in the Lanuoma deposit. [ABSTRACT FROM AUTHOR]