Concentrations and isotopic variability of mercury in sulfide minerals from the Jinding Zn-Pb deposit, Southwest China

Mercury (Hg) isotopes have been proven as a useful tracer in understanding sources and biogeochemical processes of Hg in the environment. However, the use of this tracer has not yet been explored in economic geology. This paper investigates the concentrations and isotopic compositions of Hg in sulfide minerals from the Jinding deposit, the largest Zn-Pb deposit in China. Total mercury concentration (HgT) is highly variable: with the highest in sphalerite (472-1010 ng.g(-1)), intermediate concentrations in pyrite (195-342 ng.g(-1)) and the lowest in galena (65-310 ng.g-1). The variation was likely due to the fact that Hg2+ can more readily substitute for Zn2+ than for Fe2+ and Pb2+, but an influence of different parental fluids on the isotopic composition of the sulfide minerals cannot be excluded. An overall range of delta Hg-202 from -3.17 to -0.57 parts per thousand is observed in the sulfides. Samples from the early stage feature the enrichments of light Hg isotopes, with delta Hg-202 ranging from -3.17 to -1.59 parts per thousand, suggesting significant mass-dependent fractionation during the transport and/or deposition of Hg. However, the volatilization of aqueous Hg(0) during boiling of hydrothermal fluids was likely the most important process causing the observed fractionation. Relatively higher delta Hg-202 values (-1.84 to -0.57 parts per thousand) of the late stage samples indicate that the Hg was rarely fractionated from its sources. Additionally, small but significant mass-independent fractionations are measured for the deposit with Delta Hg-199 ranging from -0.06 to 0.10 parts per thousand, indicating that the Hg may have been derived from the sedimentary rocks of the Lanping Basin. Finally, we conclude that Hg isotopes have the potential to be a new tracer of sources of ore-forming materials, as well as pathways of fluid evolution in hydrothermal deposits. (C) 2017 Elsevier B.V. All rights reserved

Fluid and melt inclusion study on mineralized and barren porphyries, Jinshajiang-Red River alkali-rich intrusive belt, and significance to metallogenesis

Alkali-rich Cu (Au, Mo) deposits are of increasing economic significance and are an attractive exploration target. They include some of the world's highest grade and largest porphyry related gold resources as well as some of the largest gold accumulations in epithermal settings. The Jinshajiang-Red River alkali-rich intrusive belt, with many porphyry Cu (Au, Mo) deposits, is a representative magmatic belt associated with mineralization. The Jinshajiang-Red River alkali-rich intrusive belt contains several Cu (Au, Mo) mineralized alkali-rich porphyry rocks including the Yulong quartz monzonite porphyry, the Machangqing granite porphyry, the Tongchang quartz syenite porphyry, and the Beiya quartz syenite porphyry. Additionally, there are also some barren alkali-rich porphyry rocks in the belt, such as the Yanshuiqing quartz syenite porphyry. Fluid inclusion petrography and microthermometry on those porphyry rocks are carried out in detail. The results show that the fluid inclusion assemblages in ore-bearing and barren porphyries are distinct: inclusions from barren porphyry are dominated by primary melt inclusions, and contain rare or no fluid inclusions, whereas inclusions from ore-bearing porphyries are dominated by fluid inclusions, and contain rare melt inclusions. Furthermore, halite, sylvite, calcite daughter minerals and an opaque phase in fluid inclusions from ore-bearing rocks are common, but rare in fluid inclusions from barren rocks. The results suggests that the evolution of ore forming fluids especially the halite, sylvite, calcite and opaque daughter minerals bearing fluid inclusions of quartz phenocrysts could be used to judge the degree of metasomatism and mineralization of a porphyry system

Nature and evolution of fluid inclusions in the Cenozoic Beiya gold deposit, SW China

The Beiya Au deposit in the Sanjiang metallogenic belt, SW China, is a porphyry-skarn deposit that formed in an intracontinental setting. Three stages of hydrothermal veins, namely quartz veins (Stage 1), quartz-pyrite veins (Stage 2), and Au-rich sulfide-quartz veins (Stage 3) were identified on the basis of field relationship and petrography under scanning electron microscopy cathodoluminescence (SEM-CL). Intermediate density aqueous fluid inclusions (ID1, ID2), high density brine inclusions (B1, B2), and low density vapor inclusions (V1, V2) have been identified in both Stage 1 and Stage 2 veins. Only liquid-rich fluid inclusions (L3) were found in Stage 3 veins. Raman spectroscopy revealed that all the inclusions contain abundant CO2 center dot H2S was identified in ID2 and V2 inclusions. Salinities and homogenization temperatures of the intermediate density aqueous fluid inclusions (ID1, ID2), high density brine inclusions (B1, B2), and low density vapor inclusions (V1, V2) are 7.4 +/- 1.1-11.9 +/- 2.2, 33.6 +/- 0.5-39.2 +/- 1, and 1.6 +/- 0.7-5.8 +/- 0.8 (wt% NaCl equiv.) and 400 +/- 35-440 +/- 37, 395 +/- 20-414 +/- 6, and 386 5-416 +/- 4 degrees C, respectively. Salinities and homogenization temperatures of the L3 inclusions range from 4.9 1.6 to 9.8 0.7 (wt% NaCl equiv) and from 301 28 to 398 4 degrees C, respectively. Initial intermediate density aqueous fluid inclusions contain 2000-10,000 ppm Fe, 2000-4000 ppm Cu, 200-600 ppm Zn, 200-500 ppm Pb, 17-89 ppm Mo, 1-8 ppm Ag, and 0.9-5.9 ppm Au, comparable to that of intermediate density inclusions in subduction-related porphyry deposits. Brine inclusions are rich in metals and have 9000-24600 ppm Fe, 3400-11,000 ppm Cu, 1200-5200 ppm Pb, 500-3000 ppm Zn, hundreds of ppm Mo, and tens of ppm Ag. The corresponding vapor inclusions contain lower metal concentrations: 400-6000 ppm Fe, 1700-4700 ppm Cu, 50-270 ppm Pb, 100-500 ppm Zn, and minor Mo and Ag. Low to intermediate density fluids are abundant and are inferred to have been the main metal transporting medium. A temperature decrease to approximately 350 degrees C during Stage 3 triggered metal precipitation

Nature and evolution of fluid inclusions in the Cenozoic Beiya gold deposit, SW China

The Beiya Au deposit in the Sanjiang metallogenic belt, SW China, is a porphyry-skarn deposit that formed in an intracontinental setting. Three stages of hydrothermal veins, namely quartz veins (Stage 1), quartz-pyrite veins (Stage 2), and Au-rich sulfide-quartz veins (Stage 3) were identified on the basis of field relationship and petrography under scanning electron microscopy cathodoluminescence (SEM-CL). Intermediate density aqueous fluid inclusions (ID1, ID2), high density brine inclusions (B1, B2), and low density vapor inclusions (V1, V2) have been identified in both Stage 1 and Stage 2 veins. Only liquid-rich fluid inclusions (L3) were found in Stage 3 veins. Raman spectroscopy revealed that all the inclusions contain abundant CO2 center dot H2S was identified in ID2 and V2 inclusions. Salinities and homogenization temperatures of the intermediate density aqueous fluid inclusions (ID1, ID2), high density brine inclusions (B1, B2), and low density vapor inclusions (V1, V2) are 7.4 +/- 1.1-11.9 +/- 2.2, 33.6 +/- 0.5-39.2 +/- 1, and 1.6 +/- 0.7-5.8 +/- 0.8 (wt% NaCl equiv.) and 400 +/- 35-440 +/- 37, 395 +/- 20-414 +/- 6, and 386 5-416 +/- 4 degrees C, respectively. Salinities and homogenization temperatures of the L3 inclusions range from 4.9 1.6 to 9.8 0.7 (wt% NaCl equiv) and from 301 28 to 398 4 degrees C, respectively. Initial intermediate density aqueous fluid inclusions contain 2000-10,000 ppm Fe, 2000-4000 ppm Cu, 200-600 ppm Zn, 200-500 ppm Pb, 17-89 ppm Mo, 1-8 ppm Ag, and 0.9-5.9 ppm Au, comparable to that of intermediate density inclusions in subduction-related porphyry deposits. Brine inclusions are rich in metals and have 9000-24600 ppm Fe, 3400-11,000 ppm Cu, 1200-5200 ppm Pb, 500-3000 ppm Zn, hundreds of ppm Mo, and tens of ppm Ag. The corresponding vapor inclusions contain lower metal concentrations: 400-6000 ppm Fe, 1700-4700 ppm Cu, 50-270 ppm Pb, 100-500 ppm Zn, and minor Mo and Ag. Low to intermediate density fluids are abundant and are inferred to have been the main metal transporting medium. A temperature decrease to approximately 350 degrees C during Stage 3 triggered metal precipitation

Composite metallogenesis of sediment-hosted Pb-Zn-Ag-Cu base metal deposits in the Sanjiang Collisional Orogen, SW China, and its deep driving mechanisms

A great number of sediment-hosted Pb-Zn-Ag-Cu deposits occur in the Meso-Cenozoic sedimentary basins within the Sanjiang Tethyan orogeny, SW China, which compose a significant base metal metallogenic belt with an extension over 1000km along the northeastern margin of the Tibetan Plateau. For it is an important type in the continental collision-related deposit spectrum, further study upon these deposits is greatly helpful to understand and improve the theories of the continental collision metallogenesis and guide the exploration. Many studies suggest that these deposits are distinct from the SEDEX and MVT model in terms of ore controls, host rocks and other features, and that multiple sourced fluids associated with mineralization should have been driven by deep processes. However, it is intensively debated on the geotectonic settings of ore formation and spatial-temporal association with the collisional orogeny due to lack of highly resolved chronological data. Some studies indicate that they were resulted from composite mineralization, but these studies did not well document its mechanisms. A comprehensive study has thus been carried out on the geochronology, ore-forming fluids and metal sources, composite metallogenesis and mechanisms for the Pb-Zn-Ag and Cu polymetallic deposits in the Lanping and Changdu basins. The results show that the Cu deposits were mainly formed in 48 similar to 58Ma and the Pb-Zn deposits were formed in 28 similar to 33 Ma. Also, three types of composite mineralization have been recognized: 1) metamorphic fluids and basinal brines or meteoric water, represented by the Jinman-Liancheng Cu deposits; 2) basinal brine and meteoric water, represented by the Jinding deposit; and 3) basinal brine and magmatic fluid with an example of the Lanuoma Pb-Zn-Sb deposit. The Cu deposits happened synchronously with the main collisional compression of the India-Asian continental collision and metamorphic fluids were probably generated by subduction-caused high-pressure metamorphism. The Pb-Zn deposits were formed by basinal brine-dominated fluids driven by orogenic uplift as well as tectonic compression in the stage of the late collisional tectonic transform. Contemporaneous magmatism may have mainly played as heat sources or provided ore materials