西藏尕尔穷铜金矿床S、Pb同位素地球化学特征——成矿物质来源示踪

S,Pb Isotope Characteristics of the Ga'erqiong Gold-Copper Deposit in Tibet:Tracing the Source of Ore-forming Materials

尕尔穷铜金矿为近几年在班公湖-怒江成矿带西段取得找矿新突破的与斑岩有关的矽卡岩型铜金-破碎带型铜金(铁)矿床。通过对矽卡岩型矿石中主要的金属矿物黄铁矿、黄铜矿的S、Pb同位素特征进行研究,进一步确定矿床成矿物质来源,并结合区域矿产特征对区域成矿规律给出指示。结果显示,两种金属矿物中的δ34S主要分布于-2.9‰～0.5‰之间,平均值为-1.1‰,其频率直方图具有塔式分布特征,具幔源硫特征;矿石的208Pb/204Pb主要分布于38.384～39.134之间,207Pb/204Pb主要分布于15.577～15.725之间,206Pb/204Pb主要分布于18.112～18.615之间,μ值在9.44～9.69之间,其具有上地壳与地幔混合的造山带铅特征。矿床成矿物质主要来自具幔源特征物质和念青唐古拉基底片麻岩。在班怒带西段伴随着晚白垩世南羌塘-三江复合板片与冈底斯-念青唐古拉板片之间弧-陆碰撞,在措勤-申扎火山岩浆弧内形成了与上地幔或初生下地壳重熔并受上地壳物质混染的斑岩-矽卡岩铜金矿成矿系列。

The Ga＇erqiong copper-gold deposit, a skarn-type and breccia-type copper-gold （iron） deposit related to porphyry, was discovered in recent years in the western Bangong Co-Nujang metallogenic zone, Tibet. Based on the study of the S and Pb isotope characteristics of pyrite and chalcopyrite within the skarn ore, the authors traced the source of ore-forming materials, and indicated regional ore-forming metallogenic regularity based on a comparison with the characteristics of regional mineral resources. It is shown that the δ^345 value of the minerals is in the range of -2.9%0-0.5‰ with an average of-1.1‰, and the δ34S histogram is distributed approximately in a tower shape, which indicates a mantle source. The ^208pb/^204pb value is between 38.384 and 39.134, and the ^207pb/^204Pb value is between 15.577 and 15.725, and the ^206pb/^204pb value is between 18.112 and 18.615, and the μ value is between 9.44 and 9.69, which indicate that Pb was derived from a orogenic belt source composed of the upper crust and the mantle. It is inferred that the ore-forming materials of the Ga＇erqiong deposit was mainly from materials with mantle characteristics and Nyainqentanglha basement gneiss. During the arc-landmass collision between southern Qiangtang-Sanjiang composite plate and Gandise- Nyainqentanglha plate in late Cretaceous, a Cu-Au porphyry-skarn metallogenic series related to magma which was derived from the upper mantle or the juvenile crust and contaminated by the upper crust materials formed in the Coqen-Xainza volcanic-magmatic arc at the south edge of western Bangong Co-Nujang suture zone.