Experimental Study Of "Fluid-Sulphide" Reaction And The Implication For Genesis Of The Sulphide Assemblages Out-Cropped In Zijinshan Copper Deposit,Fujian

Fujian Zijinshan copper deposit is the largest high sulfidation epithermal deposits in China, the copper ore body under gold ore body is an indication of prospect and exploration.The samples of this thesis collected from drill core in Zijinshan deposit,we grinding them into polished sections and observed by means of optical microscope and EPMA composition analysis. The results show some definite relationships of replacement reaction, interpenetration and component inheritance among copper sulfides, and establish a genesis sequence of Pyrite-Enargite-Anilite、Digenite-Covellite.In an effort to simulate the reaction process of pyrite and copper sulfate solutions, we have designed a series of water-mineral surface and interface reaction experiments.Pyrite were cuttted into cubes (length side about 3mm) and reacted with copper sulfate solution under 100℃、150℃、200℃、250℃ in the reaction pots. The solution concentration is lwt% and 5wt% and the reaction time is 15 and 30 days respectively. Inductively coupled plasma atomic-emission spectroscopy (ICP-AES) was taken to analyze the remaining solutions after reaction. Parts of solid residues were observed by optical microscope and EPMA composition analysis to confirm the components, trend and process.Experimental results show that the temperature and initial concentrations of Cu controled reaction intensity, the higher reaction temperature and initial concentration, the more intense. The reaction time accumulate the effects of temperature and initial concentrations.The stable product in less than 200℃ is digenite,and djurleite between 200℃ and 250℃. The components of products through Cu1.40S to Cu1.96S, the differences of components responded different stage of reaction.This reaction achieved by dissolution and reprecipitation.Combine with the results of grinding sections and experiments, we speculated two phases of hydrothermal alteration in Zijinshan deposite:pyrite and enargite formed in the first phase, other copper sulfides and covellite formed in the second phase. Arsenic carried by the magmatic hydrothermal fluid formed enargite by both replace reaction and precipitation. Most of enargites show characteristic of replacing pyrite, there are also a few enargites formed euhedral columnar crystals in fractures. The minerals in the upper oxidation zone suffered by weathering denudation which formed high sulfidation meteoric solution, and infiltrated downward through fractures. It was heating during its downward infiltrating process, and finally returned as it reached the hot igneous rock, it returned to the top. Through this process pyrite and enargite took precedence being replaced. The epithermal fluid evolved into low temperature and salinity fluid, anilite and digenite generated in the deposite. This phase transformations occurred between deep minerals and the high sulfidation epithermal achieved by dissolution and reprecipitation, and the solutions form a circling of infiltration and heating process.