新疆西天山卡特巴阿苏大型金矿床地质地球化学和成岩成矿年代

Geology,geochemistry and metallogenic epoch of the Katebasu large-sized gold deposit,Western Tianshan Mountains,Xinjiang

新疆西天山是"亚洲金腰带"在中国的重要延伸,成矿找矿潜力大。卡特巴阿苏是该区域新发现的大型金矿床,金储量87 t,平均金品位3.84 g/t。矿床形成于中天山北缘靠近那拉提北缘断裂的变形带中,金矿体主要受二长花岗岩体内沿密集韧脆性断裂带分布的蚀变带控制,多呈大型透镜体/似板状体,中部为含金硫化物不规则细/网脉强硅化岩,边部对称出现含金硫化物浸染绢云母绿泥石蚀变岩,黄铁矿和黄铜矿是主要载金矿物,金在黄铁矿中为晶格金,在黄铜矿中为裂隙金或粒间金。卡特巴阿苏金成矿地质体主要为二长花岗岩,锆石U-Pb法测得(346.3±3.3)Ma,为早石炭世成岩;矿石中载金黄铁矿Re-Os法测得(310.9±4.2)Ma,为晚石炭世成矿;成矿比成岩大约晚35Ma。金成矿关键控制因素是南天山洋关闭、塔里木板块与中天山陆块碰撞造山过程中的构造-流体作用。金成矿流体中高温(270~390℃)、中低盐度(7%~16%Na Cl eq.)、富CO2,δ18OH2O(V-SMOW)=1.6‰~6.4‰,δDH2O(V-SMOW)=-64‰^-107‰,为深部/变质成因流体;金矿石中黄铁矿(187Os/188Os)i平均为1.449±0.052,REE配分曲线及铅同位素组成(206Pb/204Pb=18.129~18.773、207Pb/204Pb=15.459~15.554,208Pb/204Pb=37.707~38.123)与中天山地壳不同岩石建造单元具有明显相似或关联性,成矿物质来自中天山地壳;硫化物δ34S值(6.92‰~12.15‰)指示矿石硫源于古生代海相地层中硫酸盐热化学还原。卡特巴阿苏金成矿受晚石炭世塔里木板块与中天山陆块碰撞构造应力驱动,金矿床是中天山地壳岩石经受构造-蚀变的综合产物,属"碰撞造山型"金矿床。研究为在新疆西天山持续实现金矿找矿突破提供了新参考。

The Asian gold belt extends into Western Tianshan Mountains, showing great prospecting foreground and potentiality. The Katebasu gold deposit is a newly- discovered large- sized deposit, with 87 t gold reserves and 3.84 g/t average gold grade. The deposit is situated in a deformation band near the north Nalati fracture on the northern margin of the Middle Tianshan Mountains.Gold orebody, lenticular or tabular in form, is controlled by the alteration zone along with the brittle and ductile fracture zone in the monzonite granite. The center of the gold orebody is silicified rock with gold-bearing pyritization, and the edge is sericite chlorite epidote altered rock with gold- bearing pyritization. The pyrite and chacopyrite are main gold carriers, with ionic gold in pyrite,while embedded-gold and fissure-gold constitute the main forms in chacopyrite. The geological bodies of the Katebasu large-sized gold deposit consist of monzonite granite, with a（346.3±3.3） Ma zircon U-Pb concordia age, suggesting Early Carboniferous. The isochron age of the ore- bearing pyrite is（310.9 ± 4.2） Ma, implying Late Carboniferous, appximately 35 Ma later than monzonite granite. The key to gold mineralization was the tectonic fluidization caused by the closure of South Tianshan Ocean and the collision of Tarim plate with Middle Tianshan landmass. Ore- forming fluids of gold were mesothermal to hyperthermal（270~390 ° C） and low-middle salinity（7%-16% Na Cl eq.） ones rich in CO2, with the data δ18OH2O（V-SMOW）=1.6‰-6.4‰ and δDH2O（V-SMOW）=-64‰-107‰, showing characteristics of deep metamorphism fluids. The average（187Os/188Os）iof the pyrite in gold ore is 1.449±0.052, and the REE patterns and Pb isotope（206Pb/204Pb=18.129-18.773,207Pb/204Pb=15.459-15.554,208Pb/204Pb=37.707-38.123） have similarity or relevance to the earth crust of the Middle Tianshan Mountains, suggesting that the metallogenic material was derived form the earth crust. The δ34S values of the sulfide are 6.92‰- 12.15‰, implying that the S of the ore came from Thermochemical Sulfate Reduction（TSR） of the marine strata of Paleozoic. The Katebasu gold deposit was controlled by the shatter tectonic stresses between the Tarim plate and the Middle Tianshan zone in Late Carboniferous epoch, produced by the structure- altered Tianshan rock and belonging to the collision- orogeny gold deposit. The results achieved by the authors provide valuable guide for the continuous prospecting breakthrough in Western Tianshan Mountains of Xinjiang.