河南桐柏老湾金矿床氢氧氦同位素地球化学及成矿流体来源

河南桐柏老湾金矿床的成矿作用是在变基性火山碎屑沉积岩为矿源层的背景上演化的。本文根据矿床氢氧同位素研究,认为矿床的热液成矿期成矿流体为大气降水和老湾花岗岩岩浆水的混合,成矿Ⅰ阶段和Ⅱ阶段以岩浆水为主,成矿Ⅲ阶段以大气降水为主,但在成矿Ⅱ阶段大气降水已占有很大的比例。氦同位素分析表明,在老湾金矿形成过程中有地幔流体加入,且从成矿Ⅱ阶段至Ⅲ阶段,由于大气降水比例增大,其与地幔流体的混合导致成矿流体的³He/⁴He比值不断减小。

ISOTOPIC GEOCHEMISTRY OF HYDROGEN ,OXYGEN AND HELIUM, AND ORE-FORMING FLUID SOURCES OF LAOWAN GOLD DEPOSIT IN TONGBAI,HENAN PROVINCE

The Laowan gold deposit is geotectonically located in the Tongbai structure area, which is a joint between the Qinling and Dabie orogenic belts,and evolved on basis of the original gold source bed of metamorphic basic rocks and volcano-clastic sedimentary rocks.The host rocks are Guishan Formation, epimetamorphic rock series of Middle Proterozoic. The Laowan granite is located in the south part of the mining area in age of middle-late Yanshanian orogeny during that time the Laowan gold deposit formed. The hydrothermal ore-forming process can be devided into three stages: quartze-oxide stage (stage Ⅰ), quartz-sulphide stage (stage Ⅱ) and quartz-carbonate stage (stage Ⅲ). with ore-forming temperatures being 350℃,290℃ and 180℃ respectively. The study on hydrogen and oxygen isotopes of the gold ore deposit make it sure that the ore-forming fluid is composed of magmatic water and meteoric water. In the stages Ⅰ and Ⅱ the ore-forming fluid is mainly magmatic water; and meteoric water increases gradually from the stage Ⅰ to stage Ⅲ. The comparative study of hydrogen and oxygen isotopic components of Laowan gold deposit and the gold deposits in Tongbai and Xiong’er regions show a latitudinal effect clearly, namely, the meteoric water played an important role in the ore-forming processes. The concentration range of helium isotope is 0.01×10^-6～0.04×10⁶ cm³/g. The values of ³He/⁴He are 0.9R_a～4.1R_a, which shows that the mantle fluid joined the ore-forming hydrothermal fluid during the gold ore deposit formed. Based on the geochemistry of hydrogen, oxygen and helium isotopes of the Laowan gold deposit, the following conclusions can be carried out. The Laowan gold deposit is an example of structure and coupled magmatism ore-forming. In Indosinian orogeny, the collision and compression between the Yangtze and North China Blocks provided dynamic environment, the Laowan ductile shear zone formed. The Laowan granitic magmatism in the Yanshanian orogeny offered thermal dynamic conditions and the upward channel of ore-forming fluid that included mantle emanation. The ore-forming fluid of Laowan gold deposit is mixed fluid including Mesozoic meteoric water, granitic water and mantle fluid and the latter played an important role in the Laowan gold deposit.