川西尔呷地吉Pb-Zn矿床方解石Sm-Nd等时线年龄及其地质意义

CALCITE Sm-Nd ISOCHRON AGE OF THE ERGADIJI LEAD-ZINC DEPOSIT IN WESTERN SICHUAN PROVINCE:Geological Implication

尔呷地吉中型铅锌矿床位于扬子地块西南缘川滇黔交界地带.矿体主要呈似层状、透镜状赋存于震旦系灯影组白云岩中,顶板为下寒武统筇竹寺组含炭质砂页岩.主要金属矿物为闪锌矿和方铅矿,Zn平均品位5.30%,Pb平均品位3.25%;主要非金属矿物为方解石和石英.矿石结构主要有自形晶结构、交代-侵蚀结构和固溶体分离结构,矿石构造主要有细脉-浸染状、块状和角砾状.矿床中铅锌矿化与硅化、沥青化和方解石化密切相关.对尔呷地吉Pb-Zn矿床成矿期8件与铅锌矿共生的方解石样品进行了Sm-Nd同位素体系研究,结果表明方解石的^(147)Nd/^(144)Nd值变化于0.058489~0.663246,^(143)Nd/^(144)Nd值变化于0.511852~0.512626,获得Sm-Nd等时线年龄为203±6 Ma(MSWD=1.2),该年龄代表了尔呷地吉MVT Pb-Zn矿床的成矿年龄.尔呷地吉Pb-Zn矿床是典型的MVT Pb-Zn矿床,其矿床成矿作用与峨眉山玄武岩岩浆活动无关,与古特提斯洋闭合背景下的造山运动密切相关.

The Ergadiji medium-sized lead-zinc deposit is located on the junction of Sichuan,Yunnan,and Guizhou provinces,southwestern margin of Yangtze block.The orebody is mainly occurred in stratoid and lenticular forms in the dolomite of Sinian Dengying Formation,with the carbonaceous sand shale of Lower Cambrian Qiongzhusi Formation as the roof.The main metallic minerals are sphalerite and galena with the Zn grade of 5.30%and Pb grade of 3.25%averagely.The nonmetallic minerals are mainly calcite and quartz.The ores are in idiomorphic crystal,metasomatism-erosion and solid solution separation textures and veinlet-disseminated,massive and brecciated structures.The Pb-Zn mineralization of the deposit is closely related to silicification,bituminization and calcilization.Through the study on the Sm-Nd isotope system of 8 calcite samples associated with Pb-Zn ores in the metallogenic period,the results show ^(147)Nd/^(144)Nd is 0.058489-0.663246,^(143)Nd/^(144)Nd 0.511852-0.512626,and the Sm-Nd isochron age of 203±6 Ma(MSWD=1.2),also representing the ore-forming age of the deposit.The Ergadiji Pb-Zn deposit is of typical Mississippi Valley type(MVT),with its mineralization closely related to the orogeny after the closure of Paleo-Tethys Ocean,rather than the magma activity of Mount Emei basalt.