Gold source and ore-forming process of the Linglong gold deposit, Jiaodong gold province, China: Evidence from textures, mineral chemical compositions and sulfur isotopes of pyrite

The Linglong gold orefield is located northwest of the Jiaodong gold province, in the eastern North China Craton (NCC) area. It consists of over 10 gold mines with a total gold resource of approximately 1000 t, and gold mineralization occurs in gold-quartz veins. The Linglong gold deposit underwent four stages of ore-forming processes namely: Pyrite-quartz (stage I) - milky-white quartz vein with euhedral pyrites, Quartz-pyrite (stage II) - smoky quartz veins with euhedral-subhedral pyrites, Polymetallic sulfides (stage III) - quartz veins with large amounts of polymetallic sulfides (pyrite, pyrrhotite, sphalerite, galena), hematite, and native gold, and the Quartz-carbonate (stage IV) - calcite-quartz veins. This study focuses on the investigation of pyrites from three main mineralization stages (I-III), exploring their textures, in-situ major and trace element concentrations, and in-situ sulfur isotopic compositions.The study examined pyrite through various methods including BSE and EMPA major element, LA-ICP-MS trace element, and LA-MC-ICP-MS sulfur isotope analyses. Pyrite from three distinct stages of ore-forming processes were analyzed. Pyrites from stage I (Py-I) exhibited euhedral crystals with homogeneous brightness in the BSE, lacked mineral inclusions, porous microtextures, and oscillatory zones. Py-I possessed low contents of Au, Ag, As, Bi, Cu, Sb, Zn, Co, and Ni. Pyrites from stage II (Py-II) showed fine-coarse grains and euhedral-subhedral features with slight fractures, similar to Py-I, however, had the higher concentrations of As and Sb. Pyrites from stage III (Py-III) were found in the quartz-polymetallic sulfide veins and exhibited subhedral to anhedral features and more significant concentrations of metallic elements, particularly Au and As. The & delta;34S values of Py-I, Py-II and Py-III were in the ranges of 6.76%o-7.47%o, 6.11%o-7.27%o and 6.07%o-8.33 %o, respectively. Analysis of the texture and geochemical composition of pyrite suggested that invisible gold was primarily present in pyrite in the form of solid solution (Au+), accompanied by a small amount of nano-form gold. The ore-forming fluids that led to this mineralization were mostly derived from mantle-derived mafic magma mixed with some minor metamorphic sedimentary material. A decrease in fluids temperature, water-rock interactions and fluid boiling led to the depositions of sulfides and gold. In the Late Mesozoic, lithospheric delamination of the eastern block of the NCC triggered decompression and melting of the upwelling asthenospheric mantle resulting in partial melting of the lithospheric mantle. This lithospheric mantle-derived mafic magma provided the ore-forming fluids for largescale gold mineralization in the Jiaodong gold province.