摘要
雪鸡坪斑岩铜矿位于西南三江构造火成岩带义敦岛弧带,其成矿斑岩为印支期石英闪长玢岩和石英二长斑岩。研究对该矿区安山岩、矿化斑岩和矿石矿物系统进行S,Pb同位素分析结果表明:金属硫化物的δ34S值为-3.1‰～+0.7‰,平均值为-1.1‰,与矿化斑岩的硫同位素组成(-1.4‰和-1.5‰)一致,均落入幔源硫范围,表明硫主要来自岩浆;δ34S黄铁矿(-1.8‰～+0.7‰,平均-0.5‰)>δ34S黄铜矿(-2.2‰～0.0‰,平均-1.2‰)>δ34S方铅矿(-3.1‰～-1.3‰,平均-2.4‰),硫同位素分馏基本达到平衡。矿石矿物(208Pb/204Pb=37.917～38.230,平均值38.075;207Pb/204Pb=15.528～15.614,平均值15.571;206Pb/204Pb=17.929～18.082,平均值17.981)与矿化斑岩(208Pb/204Pb=37.832、37.883,207Pb/204Pb=15.529、15.538,206Pb/204Pb=17.906、17.910)以及安山岩(208Pb/204Pb=37.816～37.884,207Pb/204Pb=15.549～15.562,206Pb/204Pb=17.845～17.919)的初始铅组成基本一致,变化范围较小,表明三者具有相同的来源;在铅构造模式图上,所有样品铅同位素均位于造山带演化线上或附近,在铅同位素源区判别图中,均落入造山带和下地壳区域,这表明Pb主要来源于壳幔混合。雪鸡坪铜矿S,Pb同位素组成共同指示成矿物质主要来自于深部岩浆,这种岩浆可能主要起源于俯冲洋壳板片的部分熔融并受到少量地壳物质的混染。
The Xuejiping porphyry copper deposit is located in the Zhongdian arc of the southern Yidun island arc in the Sanjiang structural and igneous district. Its copper mineralization is related to the Indosinian quartz-dioritic porphyrite and quartz monzonitic porphyry. A systematic study on S and/or Pb isotopic compositions of the copper-hearing porphyries, ore minerals and andesite of the deposit shows that S isotopic compositions of ore minerals are similar to those of porphyries. The δ34S values of ore minerals vary slightly from --3. 1‰ to ＋0.7‰ with an average value of --1.1‰ and the δ34S values of the ore-bearing porphyries are --1.4‰ and --1.5‰, indicating that sulfur is mainly derived from the magma of porphyry. The δ34S values of pyrite, chalcopyrite and galena are subsequently decreased as they are --1.8‰-＋0.7‰ （average --0.5‰）, --2.2‰ ~ 0.0‰ （average --1.2‰）, and --3.1‰--1.3‰ （average --2.4‰）, respectively. It implies that the sulfur isotope fractionation among various sulfides has basically reached equilibrium in the ore-forming fluid. The 208Pb/204 Pb, 207Pb/204Pb and 206Pb/204 Pb ratios of ore minerals are in the ranges of 37. 917~38. 230 （average 38. 075）, 15. 528~15. 614 （average 15. 571） and 17. 929~18.082 （average 17. 981） respectively. The 208Pb/204pb, 207Pb/204Pb and 206Pb/204Pb ratios of two ore-bearing porphyry samples are 37. 832~37. 883,15. 529415. 538 and 17. 906~17. 910,respectively, while those of four andesite samples are 37. 816437. 884, 15. 549 ~15. 562 and 17. 845417. 919, respectively. The uniform of Pb isotopic compositions of various kinds of samples from the deposit implies that their Pb could be derived from the same source. The Pb isotopic compositions of all samples are plotted at or near the orogenic belt evolution curves in the plumbotectonic framework diagram,and in the area of orogenic belt or lower crust in the source distinguishing diagram, indicating that the lead could be derived from a mantle-crust mixed source. The sulfur and/or lead isotopic features of ore minerals, copper-bearing porphyries and andesites from the deposit suggest that ore forming materials were mainly from the ore-forming porphyry magma duo to the partial melting of Ganzi-Litang oceanic slab with a little crustal matter in the subduction zone.
出处
《矿物岩石》
EI
CAS
CSCD
北大核心
2008年第4期80-88,共9页
Mineralogy and Petrology
基金
国家自然科学基金(编号为40372049和40873039)
关键词
S同位素
PB同位素
宽岩铜矿
雪鸡坪
滇西北
sulfur isotope
lead isotope
porphyry copper deposit
Xuejiping
Northwest Yunnan
