新疆葫芦铜镍矿床锆石U-Pb年代学、铂族元素地球化学特征及其地质意义

Zircon U-Pb chronology,platinum group element geochemistry characteristics of Hulu Cu-Ni deposit,East Xinjiang,and its geological significance

新疆东部葫芦岩体地表出露面积0.75km2,是由辉长闪长岩、辉长岩、辉石岩、辉橄岩、橄榄岩组成的复式岩体。LA-ICP-MS锆石U-Pb定年,岩体形成年龄为274.5±3.9Ma,是东天山后碰撞伸展环境的产物。岩石和矿石的PGE总量低,其中IPGE与PPGE含量相近,PPGE略高于IPGE。岩石平均7.90×10-9,矿石平均45.57×10-9。在原始地幔标准化图解上,岩石和矿石具有相似的分配模式,PPGE和IPGE之间分异较弱。Ni/Cu-Pd/Ir关系图显示母岩浆主要为高镁的玄武质岩浆。根据矿石Cu/Pd比值114.67×103～157.42×103(平均136.05×103)和岩石Cu/Pd比值11.07×103～294.35×103(平均125.48×103)推断,葫芦矿床成矿母岩浆演化过程中经历了深部硫化物部分熔离的过程,这可能是导致该矿床PGE明显亏损的原因之一。地壳物质的混染(SiO2、S等的加入)以及橄榄石、辉石等矿物的分离结晶,是引起该矿床硫饱和并发生硫化物熔离作用而成矿的主要因素。

Hulu intrusion lies in the eastern part of Tudun-Huangshan-Jingerquan-Tulargen mafic-ultramafic rocks belts in East Tianshan,and cover an area of about 0.75km2,is a multiple intrusion and composed of gabbro diorite,gabbro,pyroxenite,pyroxene peridotite and peridotite. The zircon LA-ICP-MS U-Pb dating for gabbro diorite of Hulu intrusion yielded 274.5±3.9Ma. The data suggest that the Hulu intrusion was intruded at Early Permian,is the result of a post-collisional extensional setting. The total concentration of platinum-group element (PGE) in ores and rocks is low. The average concentration of PGE in rocks is 7.90×10-9,and 45.57×10-9 in ores. Rock and ore samples have similar mantle-normalized PGE patterns,the diversity between IPGE and PPGE is lower. The diagram of Ni/Cu verses Pd/Ir reveals that the initial magma of Hulu mafic-ultramafic complex is high magnesian basaltic magma. The Ni/Cu ratio of ores and rocks is from 114.67×103~157.42×103(136.05×103 in average) and 11.07×103~294.35×103 (125.48×103 in average) respectively,which show that the magma has occurred sulfide pre-segregation from the magmatic system resulting in parental magma depleted in PGE. Crustal contamination (addition of SiO2 and S) and the fractionation of olivine and pyroxene in the magma revolution process may be the main factors leading to S-saturation and sulfide segregation in deep crust.