湖南东坡千里山花岗岩和钨多金属矿床稳定同位素地球化学

STABLE ISOTOPE GEOCHEMISTRY OF QIANLISHAN GRANITES AND TUNGSTEN-POLYMETALLIC DEPOSITS IN DONGPO AREA,HUNAN

湖南东坡地区燕山期千里山复式花岗岩具有高^(18)O、高放射成因Pb和和高^(87)Sr特征。研究表明,岩浆来自13亿年前地壳泥沙质沉积变质岩深溶作用。柿竹园矽卡岩型钨锡铋钼矿床及其“卫星”矿床S、C、H、O、Pb同位素资料表明,它们具多阶段多来源特征。早期以再平衡岩浆水成矿为主,从中期至晚期阶段,逐渐被大气降水热液成矿体系所替代。

Qianlishan composite granites in Dongpo area, southern Hunanare characterized by the high δ^(18)O value, the high radiogenic lead andthe high initial ^(87)Sr/^(86)Sr ratio, which indicates that the granitic magmawas derived from deep melting of sedimentary rocks in the upper crust.However,the δ^(18)O value of the whole rock in granites, especially that ofthe whole rock,feldspar and biotite in middle to late intrusions obviourlydecreased, which suggests that the whole system has become open and hasbeen altered by circulating meteoric water during intrusion of middle tolate magmas, From the 1 to 5 metallogenic stage of Shizhuyuan skarn-greisen com-posite W-Mo-Bi ore deposits,the δ^(18)O_(H_2O) value of the whole minerogenicsystem ranges from +4‰ to +9‰,the δD_(H_2O) value-from -70‰ to -40‰and the δ^(34)S_(∑S) value-about +1‰, which indicates that the ore-formingfluid was derived from the reequilibrium magmatic water of W-bearinggranites. The δ^(18)O_(H_2O) value of 'Satellite' ore deposits outsite the southeastcontact of Qianlishan gcanites (cassiterite-sulfide and lead-zinc sulfiedore deposits)is from 0‰ to 3‰, the δD_(H_2O) value-around -80‰ andthe δ^(18)O value of sericitized magmatic rocks-only +5.5‰, which suggeststhat the genesis of 'Satellite' ore deposits is related to Mesozoicmeteoric water circulation. The δ^(34)S value of sulfides in 'Satellite' oredeporits (lead-zinc ore deposits) depends on the ore-hosting strata: inUpper Devonian, the δ^(34)S value is larger than 0,while in Mid-Devonian,the δ^(34)S valne-around 0, inplying that the sulfur came from sedi-mentary rocks. In addition, by comparison the lead isotopic compositionof 'Satellite' ore deposits is different greatly from that of feldspar inthe intrusion.