Fluid inclusion characteristics of Longmenshan copper-polymetallic deposit in Yueshan, Anhui Province, China

Abstract

The types, composition and physico-chemical conditions of primary fluid inclusions were researched. The results show that the primary fluid inclusions contain vapor and liquid phase type (Type I), daughter mineral-bearing type (Type II) and pure liquid phase type (Type III). The compositions of vapor are mainly H₂O and CO₂ with a tiny amounts of CH₄ and H₂; the liquid phase mainly contains Mg²⁺, Ca²⁺, Na⁺, K⁺, Cl⁻ and SO ²⁻₄ , and w(Na⁺)/w(K⁺)>1; the homogenization temperatures of the primary fluid inclusions can be divided into 190–250 °C, 250–340 °C and 360–420 °C, corresponding to the salinities of 4%–9%, 9%–14%, and 14%–20.43% (NaCl equivalent mass fraction), respectively. The mineralization process can be divided into three episodes: the silicatization stage, the quartz-sulfide stage, and the carbonatization stage, and all of them are associated with the ore-forming hydrothermal fluid activity. The origin of the hydrothermal fluid is from magmatic water mainly, and later it mixes with the groundwater and meteoric water, which lead to the decrease of temperature and salinity. The decrease of salinity, temperature and pressure are the main causes of the metallogenic elements unloading and enriching in the favorable position.