拉拉铁氧化物-铜-金-铀矿床成矿时代分析

国内外学者对拉拉铁氧化物-铜-金-铀矿床(IOCG)成矿时代研究认识尚存争议.运用Isoplot软件对矿区黄铁矿、黄铜矿放射性成因的异常铅同位素数据进行处理,得到Pb-Pb等时线年龄为954Ma,与辉钼矿Re-Os年龄928～1005Ma一致,这一年龄与矿床地质事实吻合,代表矿床形成时代,且说明铜、钼、铀为同一期矿化.结合同位素年龄资料及矿床地质特征分析认为:1700Ma左右河口群火山岩喷发沉积形成矿源层;1200Ma左右河口群地层伴随东川运动发生区域变质作用,形成磁铁矿和磷灰石;900～1000Ma伴随着Rodinia泛大陆拼贴事件,康滇地区发生晋宁运动,在变质热液作用下发生铜钼铀矿化;850Ma左右伴随着Rodinia泛大陆裂解事件,矿区地幔柱成因辉长岩浆上涌带来的巨大热量促使成矿元素进一步的活化、迁移、富集成矿.

Metallogenic Epoch Analysis of Lala Iron-Oxide-Cu-Au-U Deposit

Lala deposit is situated in the western margin of Yangtze Block,Sichuan province,China.It is reported as a typical Fe-Oxide-Cu-Au-U deposit(Li Ze-qin et al).The host rock of the deposit is HeKou Group.HeKou Group is mainly composed of quartz albitite,garnet-biotite schist and magnetite quartzite.The protolith of HeKou Group are spilite,keratophyre and keratophyre volcaniclastic rock.The ore bodies of Lala appears to have the forms of lens and vein.A mass of researching works of Lala deposit had been done by the scholars,but the metallogenic age of it is still disputed.In this paper,the authors got the Lead-Lead isochron age(954 Ma)through dealing with the radioactive-caused abnormal lead isotopic data of pyrite and chalcopyrite by Isoplot.The age is consistent with the dating of molybdenite which is 928～1 005 Ma got by Re-Os method,and it is match the geology facts of the deposit,so it is the metallogenic age of Lala deposit.what's more,it is suggested that the Cu,Mo and U mineralization in the same period.Combined with the isotopic data and the geological characteristics,we suggest:about 1 700 Ma,HeKou Group volcanic eruption and formed the sedimentary ore beds;about 1 200 Ma,regional metamorphism occured in HeKou Group accompany with the Dongchuan movement,magnetite and apatite get enrichment;900～1 000 Ma,with the convergent event of Rodinia super-continent,Jinning movement occurred in Kangdian area,Cu-Mo-U mineralization under the action of metamorphic hydrothermal at the same time;About 850 Ma,with the Rodinia super-continent cracking event,the mantle plume formed gabbro magma upwelling with great heat,cause the ore-forming elements further activation,migration and enrichment.