扬子地块西南缘大面积低温成矿时代

中国西南地区(川、滇、黔、桂、湘)发育有世界上很典型的低温成矿域,其面积之大(约90万km2)、包含的矿种之多(Au、Hg、Sb、As、P、Pb-Zn、U、Ni-Mo-PGE、重晶石、冰州石和分散元素等)、矿床组成和组合之复杂,在全球十分鲜见。扬子地块西南缘是中国西南大面积低温成矿域的重要组成部分。近年来,作者采用Rb-Sr、Sm-Nd、Ar-Ar等多种同位素定年方法,对扬子地块西南缘产出的磷矿、金矿、锑矿等低温矿床的成矿时代进行了较系统的研究。文章总结了这些研究成果,并结合前人的资料,初步拟定出该区存在三期大规模低温成矿作用,它们分别相当于晚元古代—早古生代(晚震旦世—早寒武世)、晚加里东期(晚志留世—早泥盆地)和燕山期(晚侏罗世—中白垩世)。该区的磷矿、重晶石矿和黑色页岩中的镍钼铂矿主要形成于晚元古代—早古生代,同位素年龄主要为585～540Ma;赋存于前寒武纪浅变质碎屑岩中的金-锑-钨矿床主要形成于晚加里东期,同位素年龄主要为435～380Ma;产于寒武系以后地层中的锑矿床主要是在中燕山期成矿,同位素年龄主要为160～140Ma;而该区的卡林型金矿和汞矿主要在燕山中晚期大规模成矿,同位素年龄主要为170～80Ma。

Epoch of large_scale low_temperature mineralizations in southwestern Yangtze massif

There exists a typical low-temperature metallogenic domain in southwestern China,which covers Sichuan,Yunnan,Guizhou,Guangxi and Hunan.As a unique region in the world,this domain is characterized by its large area(about 900 000 km2),many kinds of mineralization(Au,Hg,Sb,As,P,Pb-Zn,U,Ni-Mo-PGE,barite,calcspar,and dispersed elements),and complicated compositions and associations of ore deposits.The southwestern Yangtze massif is an important part of the low-temperature metallogenic domain in southwestern China.In recent years,the authors have systematically studied the metallogenic epochs of P,Au,Sb low-temperature mineralizations in southwestern Yangtze massif by using Rb-Sr,Sm-Nd,and Ar-Ar isotopic geochronolgical dating methods.With the combination of previous data,this paper has summarized the dating results and pointed out that there exist roughly 3 stages of large-scale low temperature mineralization,which are equivalent to Late Proterozoic-Early Palaeozoic(Late Sinian-Early Cambrian),Late Caledonian(Late Silurian-Early Devonian)and Yanshanian(Late Jurassic-Middle Cretaceous).The phosphorite deposits,barite deposits and Ni-Mo-PGE deposits in the area were formed mainly in Late Proterozoic-Early Palaeozoic,with isotopic ages mainly ranging from 585 Ma to 540 Ma.The Au-Sb-W deposits hosted in the Precambrian low metamorphic clastic rocks were mainly formed in Late Caledonian,with isotopic ages mainly ranging from 435 Ma to 380 Ma.The Sb deposits hosted in post-Cambrian strata were mainly formed in Middle Yanshanian,with isotopic ages mainly ranging from 160 Ma to 140 Ma.The Carlin-type gold mineralization and the Hg mineralization in the area were mainly formed in Middle and Late Yanshanain period,with isotopic ages ranging from 170 Ma to 80 Ma.