西藏东窝东矿床矿化蚀变过程元素迁移及绢云母^(40)Ar-^(39)Ar年代学及其地质意义

Element Migration during Alteration and ^(40)Ar/^(39)Ar Dating of Sericite from the Dongwodong Deposit,Tibet and Its Geological Significance

东窝东铜多金属矿床位于羌塘地体南缘,多龙铜金矿集区东侧。该矿床尚未开展矿化蚀变时限、成矿作用中元素迁移特征等问题的研究。为确定矿床的蚀变矿化作用时限,本文对东窝东矿床的黄铁绢英岩化蚀变带中的蚀变绢云母进行了^(40)Ar-^(39)Ar年代学测试,获得^(40)Ar-^(39)Ar坪年龄为122.20±0.84 Ma,该年龄与已有的斑岩体侵位时代(122 Ma)一致,说明东窝东矿床黄铁绢英岩化蚀变与斑岩体侵位有密切联系。此外,对比分析地表弱蚀变和钻孔中强黄铁绢英岩化花岗闪长斑岩的岩石地球化学结果,运用"等浓度线(isocon)方程"及其推导方程,探讨黄铁绢英岩化蚀变过程中的不同元素的带入、带出特点及元素迁移特征。结果表明:高场强元素质量基本守恒;轻稀土元素较重稀土元素迁移量较大,但总体上稀土元素的迁移程度较弱;主要的成矿元素Cu、Pb、Zn为带入元素。东窝东矿床含矿斑岩侵位时代和热液蚀变时限均与多龙矿集区内多不杂、波龙、铁格隆南等多个超大型-大型铜金矿床一致,说明东窝东矿床和多龙矿集区内的多个矿床受控于同一构造-岩浆成矿背景,东窝东矿区具有重要的找矿潜力。

The Dongwodong copper polymetallic deposit is located in the southern margin of Qiangtang terrane,east of the Duolong copper gold ore cluster. The study on the timing of alteration and element migration during the alteration has not yet been conducted. To determine the time of alteration,^(40)Ar-^(39)Ar isotopic dating was carried out for altered sericites closely related to beresitizate mineralization. The results show that the plateau age is 122. 20 ±0. 84 Ma,which is consistent with the age( 122 Ma) of ore-bearing porphyry. Thus,there is a close link between the mineralization and granodiorite porphyry. Meanwhile,the geochemical results of weakly-altered and mineralized granodiorite were compared,using the isocon equation and the derivation equation to judge the inclusion or extraction of each element and the element migration during the alteration. Results show that HFSEs are very immobile during the alteration,whereas REEs migrate insignificantly with more obvious migration of LREEs than HREEs. The ore-forming elements( Cu,Pb,Zn) are inclusion elements. The intrusive age of ore-bearing phophyries and the timing of hydrothermal alteration of Dongwodong deposit are consistent with those of other largesuperlarge scale copper-gold deposits( Duobuza,Bolong,Tegelongnan) in Duolong copper gold ore cluster,indicating that they were controlled by the same tectonic-magmatic event and thus a great potential of oreprospecting in Dongwodong mining district can be predicted.