Trace element composition and significance of quartz and stibnite in the Woxi Au - Sb - W deposit, Hunan

Abstract

We present new mineralogical and chemical data on quartz and stibnite from the Woxi Au-Sb-W deposit in western Hunan. The aim is to elucidate the substitution mechanisms of trace elements and to estimate the ore-forming temperatures within the Woxi deposit. Furthermore, we explore the potential of using trace element compositions in quartz to differentiate between various types of mineral deposits. Based on field investigation and petrographic observation, the mineralization process of the Woxi deposit can be divided into three distinct stages: an early quartz-scheelite stage, a main quartz-sulfide-native gold stage, and a late quartz-carbonate stage. LA-ICP-MS analysis of quartz from different mineralization stages reveals distinct substitution mechanisms for trace elements. In the early-stage quartz, the primary substitution mechanism is (Al³⁺, As³⁺) + (Li⁺, Na⁺) → Si⁴⁺. In the main stage, the substitution mechanism is 2(Sb³⁺, As³⁺) + (Ba²⁺) → 2Si⁴⁺. For the late-stage quartz, the substitution follows the pattern 2(As³⁺, Sb³⁺) + (Ba²⁺, Sr²⁺) → 2Si⁴⁺. Stibnite occurs exclusively during the second stage, with Cu and Pb enrichment in stibnite facilitated by the substitution mechanism of Cu²⁺ + Pb²⁺ → Sb³⁺. The incorporation of As into stibnite is attributed to a substitution equation of Sb³⁺ ↔ As³⁺. Quartz crystallization temperatures inferred from Ti thermometry suggest that quartz crystallization temperatures across different stages to be relatively similar. The temperature obtained through the titanium-in-quartz thermometer likely reflects the crystallization temperature of quartz. Since quartz crystallizes at relatively higher temperatures, the calculated temperature is higher than that indicated by fluid inclusion thermometry. Additionally, by compiling geochemical data from nine different types of Au, Sb, and W deposits and conducting plotting analysis, it was observed that orogenic deposits exhibit relatively balanced Ti, Al, and Ge concentrations, with a relative enrichment of Ge. Epithermal deposits show higher Ti concentrations but lower Al and Ge, with most data points concentrated in the high Ti range. In contrast, porphyry deposits are characterized by higher Al content and lower Ti and Ge. The ternary discrimination diagram of Ti, Al, and Ge effectively distinguishes the quartz characteristics of orogenic, epithermal, and porphyry-type deposits.