Properties and Evolution of Ore-Forming Fluid in Liuju Sandstone Type Copper Deposit,Chuxiong Basin in Yunnan Province
Wu Haizhi;Han Runsheng;Wu Peng;Faculty of Land Resources Engineering,Kunming University of Science and Technology,Southwest Institute of Geological Survey,Geological Survey Centre for Nonferrous Metals Resource;
Liuju copper deposit is one of the typical terrestrial sandstone-type deposits,and which islocated in the Meso-Cenozoic red-bed basin of South China.The mineralization occurred in the interface between the purple and grey beds of medium-fine grained sandstone strata.Besides, Hematite,chalcocite,bornite,chalcopyrite,and pyrite coexist in this transitional zone from the purple bed to grey bed,a horizontal metallic mineral zone.Aiming at the ore-forming fluid evolution and mineralization mechanism,this paper focuses on the characteristics of fluid inclusions on the basis of mineralization types and mineralizing periods.The fluid mineralization of Liuju deposit can be divided into diagenesis period and tectonic-reworked period;the latter can be further divided into early and late stages.In the two stages,fluid inclusions are predominated by pure-liquid type aqueous inclusions and gas-liquid aqueous inclusions with rich liquid.The homogenization temperatures of the three stages experienced an evolution trend as follows:increased from 96-164 ℃to 108-227 ℃,then decreased to 94-159 ℃;while the salinities(w(NaCl))were slightly decreased from 2.7%-16.7% to 2.1%-13.8%,then 1.2%-13.5%,showing little difference.Generally,all the three stages of the ore-forming fluid were mediumlow temperature and medium-low salinity basin brine.By the petrographic feature observation and the laser raman spectroscopy test of the gas component in fluid inclusions,it was confirmed that small amounts of hydrocarbon fluid inclusions were contained in the diagenesis period;while small amounts of three-phase CO_2 inclusions were found in the tectonic-reworked period.Besides,their grouped fluid compositions are different.The ore-forming fluid experienced a trend as follows:the gas component changed from the reducing organic-rich end(CH_4)to the relatively oxidizing end(CO_2)in the N2-CH_4-CO_2 triangular diagram;meanwhile,the ionic component changed from the rich SO_4~(2-)(-Cl-)-Ca~(2+)-K+type to the rich Cl~--Na+type.Different properties of ore-forming fluids played different roles in the mineralization of bedded orebodies and veined orebodies.During the ore-forming fluid evolution,the disseminated or laminated ores in sandstone-type copper deposits were formed in the diagenesis period;while,the high-grade banded,veined ores on the base of bedded orebody controlled by the fracture are formed during the further evolution in tectonic-reworked period.
【Fund】： 高校博士学科点博导类专项科研基金(20115314110010);; 全国危机矿山重大专项(20089943);; 国家自然科学基金项目(U1133602 41102049);; 云南省矿产预测工程实验室及创新团队(2014);; 中科院矿床地球化学国家重点实验室开放研究基金(201109)~~
【CateGory Index】： P618.41
【CateGory Index】： P618.41