A crucial mineralization process and gold source in the Zhaoxian gold deposit, Jiaodong Peninsula, China: Evidence from pyrite and sphalerite trace element and sulfur isotopic compositions

Abstract

The Zhaoxian gold deposit, located in the world’s third largest gold area and the largest in China, with a mineralization depth of 1500–2200 m, was the subject of ideal research to unravel gold source and mineralization process. Through comprehensive analyses incorporating petrology, petrography, and in-situ trace element and sulfur isotopic compositions, the study provides a numerical understanding from different microscales. The deposit exhibits distinct mineral precipitation sequences including pyrite (Py1, Py2-a, Py2-b, Py3) and sphalerite (Sp-a, Sp-b), detailed as follows: Py1 is euhedral to subhedral, brittle fracture structure. Py2-a is mostly euhedral and develop porous textures, filled by chalcopyrite, galena and free gold. The homogeneous Py2-b overgrows on the rims of Py2-a. Sp-a exhibits porous textures, filled with mainly chalcopyrite, Py3, galena, free gold and silver, and minor pyrrhotite. The homogeneous Sp-b overgrows on rims of Sp-a, coexisting with magnetite.

Sulfur isotope of Py1 (0.1–11.1 ‰), Py2-a (8.3–8.7 ‰), Py2-b (9.1–10.1 ‰), Py3(7.7–10.7 ‰), Sp-a (9.5–11.4 ‰) and Sp-b (8.4–9.3 ‰) and trace element ratios reveal consistency source of ore-forming fluids, closely associated with subducted paleo-Pacific slab and overlying sediments, as well as the lithospheric mantle, although contributions are also observed from the minor lithophoric mantle, Precambrian rocks, and Mesozoic granite during the early stage of mineralization. However, the contents of ore-forming fluids clear vary across different mineralization stages. Notably, Py1 has poor As (0.22–629.17 ppm) and Au (0.01–0.20), whereas Py2-b has the highest As (up to 12028.83 ppm) and Au (0.59–4.61 ppm). Gold contents in these pyrite generations correlates positively with the As and low-melting-point chalcophile-elements (LMCEs) contents, implying high contents of As play a critical role in Au migration and precipitation, and low contents of LMCEs are also an indispensable factor. Typical porous textures and elemental zoning indicate fluid boiling and accompanied by Au remobilization, resulting in the formation of the high contents of gold or visible gold in pyrite. Based on these information, a mineralization process model of the Zhaoxian gold deposit has been established. We figured that efficient migration and precipitation mechanisms are more crucial than the initial enrichment of source areas for the high contents of gold in Jiaodong.