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Geology, Geochemistry And Genesis Of The Jijiawa Au Deposit,Western Henan Province

Posted on:2016-12-05Degree:MasterType:Thesis
Country:ChinaCandidate:X K ZhangFull Text:PDF
GTID:2180330461992728Subject:Mineralogy, petrology, ore deposits
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The Jijiawa gold deposit is located in the western part of the Xiong’ershan gold polymetallic ore district, Henan Province. Finally we made the following mainresults andcognition:Two mineralization types could be distinguished: pyritization altered rocks and quartz vein mineralization. The ore-forming process can be divided into four stages as: pyrite-quartz vein stage(Ⅰ), quartz-pyrite vein stage(Ⅱ), quartz-polymetallic sulfides stage(Ⅲ), quartz-carbonate vein stage(Ⅳ).By mean of the studies of fluid inclusion, two types of fluid inclusions in stage Ⅰand Ⅱare indentified as CO2 type and gas-liquid type; but stage Ⅲ and Ⅳ quartz contain exclusively gas-liquid type fluid inclusions. We obtained the ore-forming fluid temperature, salinity, density and the type and source of ore-forming fluid, and discussed the mechanism of mineralization. The results show as follows. The homogenization temperatures of ore-forming fluids from stage Ⅰto stage Ⅳ are 232-333 ℃, 143-266 ℃, 135-227 ℃ and 106-166 ℃ respectively, with the corresponding salinities being 3.76%-16.05%, 1.74%-17.34%, 0.7%-17.26% and 0.35%-11.34%.Along with the metallogenic process, T, P and p H decrease, but lgfO2 and Eh increases. In general, the ore-forming fluid was evolved from CO2-H2O-Na Cl system, which is characterized by medium-low temperature and medium-lowsalinity, to H2O-Na Cl system; from alkaline environment to weak- alkaline environment and from reducing environment to weak reduction-oxidation environment evolution.The C-H-O isotopes composition reveals that the hydrothermal system gradually transited from a magmatic-dominated fluid to a meteoric-dominated fluid. S isotope shows that the mantle and Taihua Group likely contributing partial metallogenic materials; and Sr and Pb isotopes imply that the Jijiawa Au deposit had a mixing origin of the materials from crust and mantle. In this paper, the auther considers that the mantle and Taihua Group contributing partial metallogenic materials.The Rb-Sr isotopic dating is 118.2±2.4Ma, and the deposit was came into being in Early Cretaceous. And the age data is also a constraint on the Xiong’ershan area. the auther suggests that the Jijiawa Au deposit is the product of the regional intensive tectono- magmatic-fluid activity in the Xiong’ershan area in Early Cretaceous, and it also may be a component part of the large-scale gold mineralization in eastern China.The main handing form of Au in ore-forming fluids is Au(HS) and Au(HS)2-. Fluid mixing action and fluid immiscibility are the most important factorsthat caused the gold precipitation and enrichment, and fluid-rock interaction also contributes to the gold precipitation and enrichment.The mineralization of the Jijiawa Au deposit may be as follows. In the late Mesozoic, the lithospheric of the southern margin of the North China Craton occurreddelamination and thinning. It led to the early Cretaceous magmatic activity, mantle material upwelling, lower crustpartial melting and form ore-bearing magma. Then ore-bearing granitic magma rised and occured crystallization differentiation. And ore-fluid migration in tectonic fracture zone. With the change of fluid physic-chemical conditions, ore fluid unloaded Au. Ultimately it precipitatedand formed the Au deposit.
Keywords/Search Tags:Fluid inclusion, Stable isotope, Geochronology, Ore genesis, the Jijiawa Au deposit
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