Mineralization and fluid evolution of the Jiyuan polymetallic Cu-Ag-Pb-Zn-Au deposit, eastern Tianshan, NW China

摘要

The newly discovered Jiyuan Cu-Ag-(Pb-Zn-Au) deposit is located in the southern section of the eastern Tianshan orogenic belt, Xinjiang, northwestern China. It is the first documented deposit in the large Aqikekuduke Ag-Cu-Au belt in the eastern Tianshan orogen. Detailed field observations, parageneses, and fluid inclusion studies suggest an epithermal ore genesis for the main Cu-Ag mineralization, accompanied by a complicated hydrothermal alteration history most likely associated with the multi-stage tectonic evolution of the eastern Tianshan. The Jiyuan Cu-Ag ore bodies are located along the EW-striking, south-dipping Aqikekuduke fault and are hosted by Precambrian marble and intercalated siliceous rocks. Early-stage skarn alteration occurred along the contact zone between the marble layers and Early Carboniferous diorite-granodiorite and monzogranite intrusions; the skarns are characterized by diopside-tremolite-andradite-pyrite-(magnetite) assemblages. Local REE-enriched synchysite-rutile-arsenopyrite-(clinochlorite-microcline-albite) assemblages are related to K-Na alteration associated with the monzogranite intrusions and formed under conditions of high temperature (310°C) and high salinity (19.9 wt.% NaCl). Subsequent hydrothermal alteration produced a series of quartz and calcite veins that precipitated from medium- to low-temperature saline fluids. These include early ‘smoky’ quartz veins (190°C; 3.0 wt.% NaCl) that are commonly barren, coarse-grained Cu-Ag mineralized quartz veins (210°C; 2.4 wt.% NaCl), and late-stage unmineralized calcite veins (140°C; 1.1 wt.% NaCl). Tremolite and Ca-rich scapolite veins formed at an interval between early and mineralized quartz veins, indicating a high-temperature, high-salinity (500°C; 9.5 wt.% NaCl) Ca alteration stage. Fluid mixing may have played an important role during Cu-Ag mineralization and an external low-temperature Ca-rich fluid is inferred to have evolved in the ore-forming system. The Jiyuan auriferous quartz veins possess fluid characteristics distinct from those of the Cu-Ag mineralized quartz veins. CO₂-rich fluid inclusions, fluid boiling, and mixing all demonstrate that these auriferous quartz veins acted as hosts for the orogenic-type gold mineralization, a common feature in the Tianshan orogenic belt.View full textDownload full textKeywordsCu-Ag mineralization, epithermal deposit, paragenetic relationships, fluid inclusion, eastern Tianshan orogenic beltRelated var addthis_config = { ui_cobrand: "Taylor & Francis Online", services_compact: "citeulike,netvibes,twitter,technorati,delicious,linkedin,facebook,stumbleupon,digg,google,more", pubid: "ra-4dff56cd6bb1830b" }; Add to shortlist Link Permalink http://dx.doi.org/10.1080/00206814.2011.581800