云南省文山县官房钨矿床矿床地质和流体包裹体研究

Geology and fluid inclusion study of the Guanfang skarn type W deposit,Wenshan County,Yunnan Province

云南省文山县官房钨矿床是华南西部右江成矿带新近发现的大型钨矿床之一,产于滇东南褶皱带文山-富宁褶皱束薄竹山穹窿南翼。该矿床的形成与薄竹山S类花岗岩有关,形成于燕山期陆内碰撞体制。矿体产于燕山期花岗岩与寒武系碎屑岩-碳酸盐建造的外接触带,矿石构造主要是浸染状和网脉状。围岩蚀变类型复杂、蚀变分带明显,自花岗岩体向外依次为金云母-绿帘石化带→透辉石-透闪石化带→镁橄榄石化带。成矿过程包括矽卡岩阶段(早阶段)、石英-硫化物阶段(中阶段)和石英-碳酸盐(晚阶段)阶段。早阶段矽卡岩矿物(透辉石、石榴石)中发育含CH4的水溶液包裹体和含子矿物包裹体,中阶段石英中发育含CO2、CH4、N2的水溶液包裹体和含子矿物包裹体,晚阶段石英中发育含CO2的水溶液包裹体。各阶段矿物中不发育含石盐子晶包裹体。早阶段流体包裹体均一温度集中于379～550℃,盐度为3.17%～9.86%NaCleqv;中阶段包裹体均一温度集中于250～370℃,盐度为8.95%～10.61%NaCleqv;晚阶段流体包裹体均一温度为115～221℃,盐度为1.74%～5.71%NaCleqv。估算的早、中阶段流体捕获压力分别为45～90MPa和10～30MPa,推测最大成矿深度为3km。上述流体包裹体研究表明成矿流体由早阶段高温、低NaCl的H2O-CH4-NaCl岩浆热液,演化为中阶段中温、低NaCl的H2O-CH4-CO2-NaCl热液体系,最终转化为晚阶段低温、含CO2的大气降水。

The Guanfang W deposit, Wenshan County, Yunnan Province, is one of the newly discovered giant W deposits in the Youjiang metallogenic belt, Southwest China. It is located in the south side of the Bozhushan dome, Wenshan-Funing fold cluster. Tungsten mineralization is associated with the Bozhushan granite which has been classified as S-type granite and was formed in the Yanshanian intracontinental collision regime. Orebodies are hosted in the outer contact zone between the Yanshanian granite and the Cambrian elastic-carbonate strata. Disseminations and stockworks are two common ore structures. Both the granite and wallroeks underwent intense hydrothermal alteration, ranging outwardly from phlogopition-epidotization to diposidization-epidotization, and to forsteritation zones with increasing distance from the intrusion. The ore-forming process can be divided into the early, middle and late stages, corresponding to skaru, quartz-sulfide and carbonate-quartz-fluorite, respectively. Primary fluid inelnsions in the early stage minerals （diopside and essonite） are CH4-bearing NaC1-H20 inclusions and daughter mineral-bearing inclusions, in the middle stage minerals are CO2-CH4-N2-bearing NaC1-H20 and daughter mineral-bearing inclusionin quartz, while in the late stage minerals are CO2- bearing NaC1-H20 inclusions. Halite-bearing inclusions can not be observed. The homogeneous temperatures of the fluid inclusions in the early stage are mainly 379 -550℃, with salinities ranging from 3.2% -9. 9% NaCleqv. In the middle stage, the fluid inclusions mainly yield homogeneous temperatures of 250 - 370℃ and salinities of 8.9% - 10. 6% NaCleqv. The fluid inclusions in the late stage are homogenized at temperatures of 115 - 221 ℃, yielding salinities of 1.7% - 5.7% NaCleqv. The estimated pressures range from 45 - 90MPa in the early stage to 10 -30MPa in the middle stage, with the greatest formation depth of 3km. In the words, the ore-forming fluids evolved from high temperature, low NaC1 H20-CH4-NaC1 system to middle temperature, low NaC1, H20-CH4-CO2-NaC1 system finally to low temperature, meteoric fluid containing CO2.