GEOLOGICAL CHARACTERISTICS OF THE HYDROTHERMAL VEIN TYPE GOLDCOPPER DEPOSITS IN NINGWU BASIN:A Case Study of Tongjing Gold-Copper Deposit in Jiangsu Province

Numerous hydrothermal vein type Au-Cu deposits are distributed in the Ningwu basin. Among them Tongjing Au-Cu deposit is a typical one. The ore bodies are hosted in the composite positions of NNW-trending compressive-shearing faults and ancient volcanic edifices in vein, veinoid and lentiform, with the characteristics of isometric en echelon arrangement. Studies show that Tongjing Au-Cu deposit underwent the early stage of quartz sulfide, mid-stage of quartz sulfide carbonate and late stage of carbonate. The sulfur isotope δ³⁴S of chalcopyrite is 3.63‰, averagely, with ³⁴S/³²S of 22.139, suggesting a mantle source. The ore-forming materials of gold and copper are the liquation production in the late period of differentiation and evolution of alkaline basaltic andesitic magma of the Cretaceous Niangniangshan Formation. The ore-forming hydrotherm rose along the compressive-shearing fault structure, and enriched to mineralization in favorable structural spaces. The homogenization temperature of fluid inclusions ranges from 171 to 253℃, with metallogenic depth of 100-400 m. The Tongjing Au-Cu deposit generally belongs to epi-mesothermal filling vein type related to tectono-volcanic activities.