Fluid Inclusions and Metallization of the Kendekeke Polymetallic Deposit in Qinghai Province, China

The Kendekeke polymetallic deposit, located in the middle part of the magmatic arc belt of Qimantag on the southwestern margin of the Qaidam Basin, is a polygenetic compound deposit in the Qimantag metallogenic belt of Qinghai Province. Multi-periodic ore-forming processes occurred in this deposit, including early-stage iron mineralization and lead-zinc-gold-polymetallic mineralization which was controlled by later hydrothermal process. The characteristics of the ore-forming fluids and mineralization were discussed by using the fluid inclusion petrography, Laser Raman Spectrum and micro-thermometry methods. Three stages, namely, S1-stage(copper-iron-sulfide stage), S2-stage(lead-zinc-sulfide stage) and C-stage(carbonate stage) were included in the hydrothermal process as indicated by the results of this study. The fluid inclusions are in three types: aqueous inclusion(type I), CO2-aqueous inclusion(type II) and pure CO2 inclusion(type III). Type I inclusions were observed in the S1-stage, having homogenization temperature at 240–320oC, and salinities ranging from 19.8% to 25.0%(wt % NaCl equiv.). All three types of inclusions, existing as immiscible inclusion assemblages, were presented in the S2-stage, with the lowest homogenization temperature ranging from 175 oC to 295oC, which represents the metallogenic temperature of the S2-stage. The salinities of these inclusions are in the range of 1.5% to 16%. The fluid inclusions in the C-stage belong to types I, II and III, having homogenization temperatures at 120–210oC, and salinities ranging from 0.9% to 14.5%. These observations indicate that the ore-forming fluids evolved from high-temperature to lowtemperature, from high-salinity to low-salinity, from homogenization to immiscible separation. Results of Laser Raman Spectroscopy show that high density of CO2 and CH4 were found as gas compositions in the inclusions. CO2, worked as the pH buffer of ore-forming fluids, together with reduction of organic gases(i.e. CH4, etc), affected the transport and sediment of the minerals. The fluid system alternated between open and close systems, namely, between lithostatic pressure and hydrostatic pressure systems. The calculated metallogenic pressures are in the range of 30 to 87 Mpa corresponding to 3 km mineralization depth. Under the influence of tectonic movements, immiscible separation occurred in the original ore-forming fluids, which were derived from the previous highsalinity, high-temperature magmatic fluids. The separation of CO2 changed the physicochemical properties and composition of the original fluids, and then diluted by mixing with extraneous fluids such as meteoric water and groundwater, and metallogenic materials in the fluids such as lead, zinc and gold were precipitated.

Fluid Inclusions and Metallization of the Kendekeke Polymetallic Deposit in Qinghai Province,China

The Kendekeke polymetallic deposit, located in the middle part of the magmatic arc belt of Qimantag on the southwestern margin of the Qaidam Basin, is a polygenetic compound deposit in the Qimantag metallogenic belt of Qinghai Province. Multi‐periodic ore‐forming processes occurred in this deposit, including early‐stage iron mineralization and lead‐zinc‐gold‐polymetallic mineralization which was controlled by later hydrothermal process. The characteristics of the ore‐forming fluids and mineralization were discussed by using the fluid inclusion petrography, Laser Raman Spectrum and micro‐thermometry methods. Three stages, namely, S₁‐stage (copper‐iron‐sulfide stage), S₂‐stage (lead‐zinc‐sulfide stage) and C‐stage (carbonate stage) were included in the hydrothermal process as indicated by the results of this study. The fluid inclusions are in three types: aqueous inclusion (type I), CO₂‐aqueous inclusion (type II) and pure CO₂ inclusion (type III). Type I inclusions were observed in the Si‐stage, having homogenization temperature at 240–320°C, and salinities ranging from 19.8% to 25.0% (wt% NaCl equiv.). All three types of inclusions, existing as immiscible inclusion assemblages, were presented in the S₂‐stage, with the lowest homogenization temperature ranging from 175 °C to 295°C, which represents the metallogenic temperature of the S₂‐stage. The salinities of these inclusions are in the range of 1.5% to 16%. The fluid inclusions in the C‐stage belong to types I, II and III, having homogenization temperatures at 120–210°C, and salinities ranging from 0.9% to 14.5%. These observations indicate that the ore‐forming fluids evolved from high‐temperature to low‐temperature, from high‐salinity to low‐salinity, from homogenization to immiscible separation. Results of Laser Raman Spectroscopy show that high density of CO₂ and CH₄ were found as gas compositions in the inclusions. CO₂, worked as the pH buffer of ore‐forming fluids, together with reduction of organic gases (i.e. CH4, etc), affected the transport and sediment of the minerals. The fluid system alternated between open and close systems, namely, between lithostatic pressure and hydrostatic pressure systems. The calculated metallogenic pressures are in the range of 30 to 87 Mpa corresponding to 3 km mineralization depth. Under the influence of tectonic movements, immiscible separation occurred in the original ore‐forming fluids, which were derived from the previous high‐salinity, high‐temperature magmatic fluids. The separation of CO₂ changed the physicochemical properties and composition of the original fluids, and then diluted by mixing with extraneous fluids such as meteoric water and groundwater, and metallogenic materials in the fluids such as lead, zinc and gold were precipitated.