Abstract
The Annage gold deposit is located at the east part of the eastern Kunlun orogenic belt. The characteristics of ore-forming fluids and metallogenesis were discussed by using fluid petrography, micro-thermometry and hydrogen-oxygen isotope analysis. Three stages, namely quartz-pyrite stage (A), quartz-polymetallic-sulfide stage (B) and quartz-ankerite stage (C) were included in the hydrothermal process as indicated by the results of this study. Inclusions developed in ore-bearing quartz veins from stages A and B are of three types: aqueous inclusions (type I), CO2-bearing inclusions (type II) and pure CO2 inclusions (type III). All three types of inclusions, mainly type I, are presented in stage A, having homogenization temperatures at 180°C - 360°C, and salinities ranging from 0.53% to 21.44%. In addition to development of type I inclusions, type II and III inclusions increase significantly in stage B, with homogenization temperatures ranging from 160°C to 330°C, and salinities are from 1.32% to 22.01%. Based on micro-thermometry, fluids in Annage deposit are of H2O-NaCl-CO2 type with medium-high temperature (140°C - 395°C) and medium-low salinity (0.53% - 22.01%). Results of hydrogen-oxygen isotope analysis show that ore-forming fluid is mainly CO2-rich magmatic fluid, mixed with shallow groundwater or metamorphic hydrothermal in the late mineralization stages. Calculated metallogenic pressures are in the range of 79 - 130MPa corresponding to a maximum depth of 4.8 km. The Annage deposit is a mesothermal quartz vein type gold deposit.
Highlights
The Annage gold deposit is a typical deposit located at the central subzone of eastern Kunlun polymetallic metallogenic belt in Qinghai province, China
All type IIa fluid inclusions are homogenized by disappearance of the CO2 phase at temperatures ranging from 268 ̊C to 366 ̊C (Figure 5(a)), with the most carbonic phases being homogenized to liquid at temperatures from −3.2 ̊C to 30.5 ̊C and two to vapor at 29.6 ̊C and 29.9 ̊C, respectively
Three types of fluid inclusions, aqueous inclusions, CO2-bearing inclusions and pure CO2 inclusions are well developed in stages A and B, having homogenization temperatures range from 140 ̊C to 395 ̊C, and salinities from 0.53% to 22.01%
Summary
The Annage gold deposit is a typical deposit located at the central subzone of eastern Kunlun polymetallic metallogenic belt in Qinghai province, China. The geological characteristics, genesis and ore-forming fluids of typical deposits in this region have been the subjects of several previous studies. Based on analysis of REE, trace elements, sulfur and lead isotope, Hu [1] indicated that ore-forming temperature of Guoluolongwa gold deposit was from medium-high to medium-low, and mineralization fluids derive from deep magmatic hydrothermal rich in SO24− and Cl−. Qi [4] considered the Asiha gold mine as a typical fracture zone type deposit. On basis of geochemistry of wall rock and ore body, fluid inclusions as well as hydrogen and oxygen isotope, Li [5] reports that ore-forming fluid of Asiha deposit is mainly CO2-rich mantle-derived magmatic hydrothermal
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