吉林海沟金矿床同位素地球化学和成矿规律研究

ISOTOPE GEOCHEMISTRY AND METALLOGENIC REGULARITY OF THE HAIGOU GOLD DEPOSIT IN JILIN PROVINCE

同位素地球化学研究表明,中元古界色洛河群绿片岩相变质岩系是海沟金矿床的重要矿源层,它经历了多次构造、变质和混合岩化作用,特别是在燕山早期强烈构造活动中发生了局部深熔作用,形成了海沟二长花岗岩。受热大气降水的淋滤作用,使岩体内金元素活化、迁移和富集,以含金硫化物石英脉群形式沿NE向裂隙带充填于海沟二长花岗岩中,形成了大型沉积变质、深熔岩浆岩源大气降水热液金矿床。

The Haigou gold deposit islocated at the eastern terminal of the Huadian gold ore one in Tilin province, lying along the suture belt between the Old Mongolian oceanic plate and he North China paleoplate.The gold deposit consists of over forty gold-bearing sulfide quartz eins which are distributed northeastward, 1600m in total length, 250m in width and more than 00m in downward extension.Wall rocks include monzonitic granite, diorite porphyrite and etamorphic rocks of middle proterozoic Sehohe Group, whose gold abundance varies in the range . 42—30 ppb. Wall rocks on both sides of the gold-bearing quartz vein have suffered such lterations as silicification, sericitization and carbonatization.The following are isotope eochemical characteristics of the gold deposit.1. Sulfur in both ore veins and wall rocks is ich in ^(32)S, and average δ^(34)S values of sulfide are —7.9‰ and —4.1‰ respectively, xhibiting no obvious temporal-spatial variation. δ^(34)S_(∑S) of ore fluids is —8.8‰. It is onsidered that sulfur might have been derived from volcano-sedimentary-metamorphic rocks.. δD nd δ^(18)O values of Mesozoic meteoric water in this area are —149‰ and —20‰ respectively. uring he ore-forming process, oxygen isotope composition of water and rocks varied considerably, and ^(18)O value of the fluids tended to increase and drift. At the principal ore-forming stage, δD values of he luids were —126——100‰, δ^(18)O values 2—6‰, and δ^(13)C_(CO_2) values —7.8——13.2‰. Ore luids were mainly derived from magmatic source—hot meteoric water, Carbon came from deep arbon and organic Carbon of strata.3. Lead in ores and wall rocks is old lead from two-stage volution, with t_1 being 2398Ma. Model ages of lead in single samples are 1000—1200Ma, with μ alues nearly 9.73. K/Ar closed age of ores is 143Ma, whereas Rb/Sr isochron age of rock body (wall rock) s 181 Ma.Isotope geochemical studies show that greenschist facies metamorphic rock of Middle Proterozoic eluohe Group served as the source bed of gold, monzonitic granite was formed by remelting of the source ed, and meteoric water was the initial source of ore fluids. It is thus inferred that during the early stage of anshanian orogeny, due to the continuous expansion of Mongolian oceanic plate and its subduction owards he bottom of North China plate, strata in this area were intensely folded in company with deep faulting nd agmatic-hydrothermal activity, and this led to the formation of the remeltihg magmatic source—hot eteoric water type gold deposit. The rock-forming and ore-forming process might be divided nto hree epochs consisting of six stages, and the native gold-sulfides-quartz assemblage marks the rincipal oreforming stage of gold during which the temperature was in the range of 250—350℃, e fluids varied from acid to weakly acid, and metallogenic environment was of reduction type.