Research On Fluid Inclusions Of Guoluolongwa Gold Area In Qinghai Province

The Guoluolongwa gold deposit, located in the Eastern Kunlun orogenic belt, is a mesothermal quartz-vein type gold deposit related to Variscan-Indosinian-Yanshanian intermediate-felsic magmatism. In this paper, the characteristics of ore-forming fluids of the Guoluolongwa gold deposit were discussed, and the conditions of mineralization were studied by means of fluid-inclusion petrography, microthermometry, and component analysis.The metallogenesis of Guoluolongwa gold deposit can be divided into three stages:(Ⅰ) milky white quartz veins stage; (Ⅱ) gold-bearing quartz-pyrite stage; (Ⅲ) quartz-sulfide re-enrichment stage. There are various types of inclusions in the quartz at different stages. The size of inclusions mainly varied from 4 to 8μm, with maximum size of 15 um. Most of inclusions are rounded to irregular in shape, with occasionale presence of ribbon or platy shapes. Five types of fluid inclusions were found in quartz, namely aqueous, aqueous-CO2, CO2-rich, pure CO2, and methane inclusions.The gas component of fluid inclusions are dominantly H2O and CO2, with minor CH4 and H2. The cation ions in fluid inclusions are mainly Na+and K+, and the main anion ions are SO42- and Cl". That is to say, the ore-forming fluids are generally characterized by Cl->SO42- and Na+>K+,which belong to CO2-Na+(K+,Ca+)-Cl-(SO42-,F)-H2O type fluids.The homogenization temperatures of the inclusions fromⅡandⅢstages concentrate between 280℃and 350℃, corresponding to the high salinity groups of 15-22 wt% NaCl equiv. and the middle salinity groups of 4-10 wt% NaCl equiv., respectively. The metallogenic pressure estimated by fluid inclusions is 2962 bars to 3562 bars, equivalent to a depth of 10.5 km.The characteristics of ore-forming fluids show that mineralization is closely related to magmatic hydrothermal, indicating that the deposit is a medium temperature magmatic hydrothermal deposit. Subsequence, phase separation of H2O and CO2 in hydrothermal fluids caused gold transformation and enrichment.