Deformation and mineralizing fluid circulation of gold-silver-bearing quartz veins in the Yushishan gold deposit, Altyn Mountain, northwestern China

Abstract

Understanding the coupled process of deformed microstructure and fluid evolution of ore veins therefore provides insight into processes that influence mineralization distribution and its mechanism. Gold is often developed in quartz veins in many gold deposits. This paper presents detailed evidence for solid deformation, hydrothermal fluid, and mineralization in a fault-controlled gold-silver-bearing quartz vein from the Yushishan gold deposit, Altyn Mountain, NW China. Macro-and microstructure combined quartz crystal preferred orientation (CPO) unravel the ductile–brittle transition deformation of quartz veins formed at the deep crustal level ca. 9 ∼ 13 km and the deformation temperature ranging between 180 ∼ 381 °C. The homogenization temperatures and salinities of fluid inclusions change slightly, while the trapping pressure of fluid inclusions has a large fluctuation of ca. 125 ∼ 275Mpa. HO isotopes and the composition of fluid inclusions decipher the source of ore-forming fluid mainly related to the regional magmatic-metamorphic event. Combined with the fluid immiscibility that is evidenced by different types of fluid inclusion coexistence characteristics and the pH increase induced by CO2 degassing in an inhomogeneous fluid system, it is suggested that an obvious fluid overpressure and rapid decompression occur during Au deposition from the quartz vein. The seismically fractured opening and healing of rocks during ductile–brittle deformation controls the formation of the mineralization and fluid circulation. There has positive feedback between the fluid overpressure evolution, strain localization and mineralization through time. The channelized and circulated fluid flow triggered extensive veining, mineral growth, and connections with fluid reservoirs.