冈底斯成矿带林周县程巴矽卡岩铜多金属矿床特征:对藏南区域古新世铜矿床的找矿启示

Chengba copper polymetallic skarn deposit in Linzhou County,Gangdese metallogenic belt:Implications for mineral exploration of regional Paleocene Cu deposits in southern Tibet

冈底斯是全球重要的斑岩-矽卡岩铜矿床的成矿带之一,发育侏罗纪(173~160 Ma)和中新世(26~12 Ma)两期矿化事件。印度与亚洲大陆主碰撞期(65~50 Ma)形成了该带规模最大的壳幔混源岩浆岩,而藏南能否形成大中型规模的斑岩-矽卡岩铜矿床一直是个未解之谜。文章获得冈底斯带东部程巴大型矽卡岩铜多金属矿床中与黄铜矿共生的辉钼矿Re-Os模式年龄和含矿花岗闪长岩U-Pb年龄分别为(58.9±0.9)Ma、(57.6±0.4)Ma,认为它是主碰撞期首例矽卡岩铜矿床。含矿岩体可见自形角闪石早于斜长石,与甲玛超大型斑岩-矽卡岩型铜矿床具有类似的含矿地层、矽卡岩矿物组合和成矿元素分带特征。结合区域构造背景的资料,笔者提出冈底斯成矿带东部具有寻找古新世斑岩-矽卡岩铜矿床的潜力。

The Gangdese belt is one of the world’s major porphyry-skarn copper metallogenic belt,comprises two mineralization events which took place respectively in Jurassic(173~160 Ma)and Miocene(26~12 Ma).The voluminous mantle and crust-derived magmas are genetically associated with India-Asian collision in the Paleocene.However,the reasons for the formation of porphyry-skarn Cu deposits in southern Tibet during the collision stage were rarely reported.This paper reports granodiorite U-Pb age of(57.6±0.4)Ma and molybdenite Re-Os age of(58.9±0.9)Ma in the Chengba copper polymetallic skarn deposit in Linzhou County,which is considered as the first example of the Paleocene porphyry-skarn Cu deposit formed during the collision stage in southern Tibet.The euhedral hornblende earlier than plagioclase is observed in the granodiorite associated with Cu mineralization,and ore-bearing intrusion,skarn assemblage and element zoning in the Chengba copper polymetallic skarn deposit are similar to those of nearby giant Jiama copper porphyry-skarn deposit.Considering regional tectonic setting,this paper argues for the potential of the discovery of Paleocene porphyry-skarn Cu deposits in eastern Gangdese belt.