Sources of Au-bearing mineralisation at the Me Xi Au deposit, Central Truong Son Belt, Vietnam: Evidence from sulfur isotopic composition

Abstract

The Truong Son Belt is one of the most prospective gold metallogenic belts in Southeast Asia. Gold mineralization at Me Xi, located in the central part of the Truong Son Belt in Quang Tri Province, Vietnam, represents a hydrothermal gold system that has not yet been extensively explored or studied, particularly in sources of ore-forming components. In this paper, we present new findings on the origin of gold mineralisation at Me Xi based on sulfur isotope (δ³⁴S) analyses of pyrite samples collected from two distinct gold-bearing hydrothermal stages(Stages 2 and 3). The δ34S values of Stage 2 pyrite samples range from -8.61‰ to -0.19‰ (n=11), with the majority ranging from -4.58‰ to -2.47‰ (n=7). These values are characteristic of sulfur from a predominantly magmatic source. However, several low δ³⁴S values (i.e., -8.61‰ and -7.94‰) suggest a partial contribution of sulfur from the black carbonaceous host rocks of the Long Dai Formation. Pyrite from Stage 3 hydrothermal veins displays relatively homogeneous δ³⁴S values, ranging from -4.38‰ to -3.18‰ (n=9), which aligns closely with the main δ34S range observed inStage 2. Integrating these isotopic results with geological setting and the metallogenic history of the Truong Son Belt and Me Xi area, the sulphur isotopic study results suggest that the gold mineralisation at Me Xi was primarily derived from magmatic sources, with minor contributions from sedimentary hostrocks