藏南沙拉岗锑矿稀土和微量元素地球化学示踪及成矿物质来源

藏南沙拉岗锑矿赋存于下白垩统甲不拉组碳质板岩、泥质粉砂岩、硅质岩及燕山期辉绿岩和喜山期辉长岩中，受近东西向层间破碎带和近南北向构造破碎带控制。围岩蚀变较弱，围绕矿体呈对称性的面状、带状分布。稀土和微量元素测试结果表明碳质板岩和硅质岩具有与上地壳和太古宙后页岩非常相似的稀土配分模式。喜山期辉长岩以轻稀土相对亏损、重稀土相对富集和Eu轻度亏损的平坦型稀土配分模式有别于以轻稀土轻度富集、Eu无异常的稀土配分模式为特征的藏南燕山期辉绿岩。锑矿石具有轻稀土强烈富集、分馏程度高、Eu中度亏损、Ce强烈亏损的配分模式，与洋中脊黑烟囱-白烟囱中热液流体和喷流沉积物的Eu强正异常、海水的Ce中等负异常和重稀土富集的稀土配分模式及沃西Sedex型W-Sb-Au矿的稀土配分模式明显不同，但与喜山期辉长岩的稀土配分模式具有明显的互补关系。此外，锑矿石以其强Nb负异常及Ce和Ba正异常的微量元素特征，展示出与喜山期辉长岩的弱Nb负异常和强Rb正异常及碳质板岩-硅质岩的Nb、Ba负异常和轻度Ce、Rb、Th正异常的异同点,矿石δ³⁴S除个别样品为10.3‰和-41.6‰外，均分布在-2.6‰~-4.1‰区间，反映成矿物质主要来源于岩浆的特点。前人测定的流体包裹体氢、氧同位素值分别为δD=-151‰~-166‰,δ¹⁸O=9.4‰~12.3‰，显示岩浆水和地下水的混合性质。因此沙拉岗锑矿是形成于中新世、与藏南拆离系有关的浅成低温热液型矿床，成矿物质主要来源于喜山期辉长岩岩浆，少量来源于围岩，成矿流体部分来源于岩浆期后热液，部分来源于地下水。

Rare Earth Element and Trace Element Geochemistry of Shalagang Antimony Deposit in the Southern Tibet and Its Tracing Significance for the Origin of Metallogenic Elements

Shalagang antimony deposit of the southern Tibet occurs in carbonaceous slate,pelitic siltstone and silicalite in the Jiabula Formation of the Lower Cretaceous,and diabase in Yanshanian and gabbro in Himalayanian.The ore bodies are controlled by E-W striking interlayer faults and S-N striking faults.The weakly country rock alteration distributed along the ore bodies with symmetrical plane and zone.Analytic results show the REE patterns of the carbonaceous slate and silicalite are similar to that of the upper crust and shale in Paleozoic and Mesozoic.The REE patterns of the gabbro with LREE depleted,HREE enriched and slightly Eu depleted flat curves are different from that of Yanshanian diabase in the southern Tibet with LREE enriched and without Eu abnormal curves.The strong enrichment and high fractionation of LREE,moderate depletion of Eu and strong depletion of Ce in the Chondrite-normalized REE patterns of the antimony ores are different from those of hydrothermal fluid and exhalite from the black-and white-smoker chimney within Mid-Atlantic Ridge,North Atlantic seawater and Woxi Sedex type W-Sb-Au deposit,but the Chondrite-normalized REE patterns of the antimony ores have the strong reversed change with that of Himalayanian gabbro.Furthermore,the characteristics of strongly negative anomaly of Nb and positive anomaly of Ce and Ba in the trace element MORB-normalized spider diagram for antimony ores show the similar to and different from those for Himalayanian gabbro,carbonaceous and silicalite.The sulfur isotopic compositions of sulfides from Shalagang antimony deposit(δ34S)range from-2.6‰ to-4.1‰ besides 10.3‰ and-41.6‰.All above show the metallogenic elements were mostly derived from the Himalayanian magma and less from adjacent rocks.The δD and δ18OH2O are-151‰ to-166‰ and 9.4‰ to 12.3‰,respectively,which show the ore-forming fluid was the mixed solution of postmagmatic hydrothermal and underground water.To sum up,Shalagang antimony deposit,which is an epithermal type,formed in Miocene and was related to the formation of the southern Tibet detachment system.The metallogenic elements are mostly derived from Himalayanian gabbroic magma,and less from the adjacent rocks.The water in the metallogenic fluid is derived from Himalayanian postmagmatic solution and underground water.