Polygenetic Compound Mineralization of Guoluolongwa Gold Field, Qinghai

Abstract

two stages. Based on microthermometic study, three types of fluid inclusions are divided, namely aqueous inclusions (type I), aqueous-CO2 inclusions (type II) and pure CO2 inclusions (type III). The majority of type I and type II inclusions of stage B and type I inclusions of stage C often appear in groups, representing their primary causes. Besides, near the sulfide veinlet of stage C, many type I inclusions of stage B are arranged in rows along the fracture, showing characteristics of secondary inclusions, these inclusions may be formed at the same time with primary type I inclusions of stage C. So, there may be two main stages of inclusion formation, related to B and C stages, respectively. Stage B develops type I, type II, and type III inclusions, while stage C mainly contains type I inclusions. Homogenization temperatures and salinities of fluids are different in different stages. Mineralization of Guoluolongwa is mainly gold bearing quartz veins and quartz sulfide veins superimposed on the milky quartz veins. The early milky quartz veins of stage A may represent the product of low-grade metamorphic hydrothermal activity. Inclusions of stage B, including all these three types, are primary causes. Coexistence of aqueous and carbonaceous inclusions illustrates the separation of H2 O and CO 2. With a medium homogenization temperature ranging from 240℃ to 300℃, and salinities varing between 18~24% and 3~10% for type I and type II inclusions, respectively, fluid of stage B may be derived from metamorphic hydrothermal fluid. Stage C is characterized by type I inclusions with high salinity, ranging from 15% to 22%, shows that fluid may originate from magmatic hydrothermal, belongs to magmatic hydrothermal period. Homogenization