Characteristics Of Fluid Inclusions And Genesis Of Annage Gold Deposit, Qinghai Province

Abstract:The Annage gold deposit is situated in the orogenic belt of East Kunlun, and is attributed to the middle part of East Kunlun metallogenic belt. The deposit has a short discovering history, with a small extent of scientific investigation. Based on field survey of the deposit, study of thin sections and polished blocks, and analysis of fluid inclusion, H-O stable isotope, and rock and ore geochemistry, the characteristics of metallogenic fluid, the genesis of ore and mechanism of mineralization have been inverstigated in this article.The strata of the mining area are Palaeoproterozoic Baishahe group and Ordovician-Silurian Nachitai group. The main structures in this deposit are near EW trending faults and secondary faults. The Varisean to Indosinian intermediate-acidic magmatic rocks are the major intrusive rocks in the mining area.There are7gold belts found in the mining area, the orebodies are mainly formed in the EW trending faults and SN trending extension fractures,and ore types can be classified into quartz vein type and altered rock type. Mineralization history can be divided into hydrothermal ore-forming period and supergene leaching-enrichment period, and hydrothermal ore-forming period can be further divided into quartz pyrite stage, quartz polymetallic sulfide stage and quartz carbonate stage.Three categories of fluid inclusion have been distinguished based on petrographic and microthermometric criteria:two-phase aqueous (Ⅰ), three-phase CO2-bearing (Ⅱ) and two-phase CO2(Ⅲ) fluid inclusion. The homogenization temperature of ore-forming fluid has immiscible characteristics ranging from140℃to395℃, with salinity between0.52to22.01wt.%equivalent to NaCl. The mineralization pressure has be calculated as ranging from80MPa to182MPa.The variation range of δ18OV-SMOW,δ18D and δ18OH2O of gold-bearing quartz vein from Annage gold deposit is respectively10.6×10-3～12.9×10-3,-83.8×10-3～-72.3×10-3and4.2×10-3～6.5×10-3.The H-O stable isotope study and fluid inclusion component analysis indicate that the ore-forming fluid mainly consists of CO2-bearing magma, with mixing of the meteoric water in the late stage.In the aspect of ore genesis, the characteristics of Annage deposit are similar to the typical orogenic gold deposit, the metallotectonic setting is intracontinental orogeny. The genetic type of ore deposit is mesothermal and mesozonal quartz-vein type gold deposit.