坦桑尼亚盖塔绿岩带成矿地质特征和成矿时代

Geological Characteristics and Mineralization Era of Geita Greenstone Belt in Tanzania

坦桑尼亚盖塔绿岩带大地构造位置处于坦桑尼亚克拉通的西北部,绿岩带内发育有世界级的大型金矿床——盖塔金矿。通过对盖塔绿岩带的成矿地质特征、典型矿床和成矿时代进行研究,厘定了该绿岩带的成矿时代,总结了其演化历史。研究表明:盖塔绿岩带出露的岩石类型主要为太古宇尼安萨群条带状铁建造、火山碎屑沉积和卡维隆多群砂砾岩,以及同造山期和后造山期花岗岩、煌斑岩和粗面岩等侵入岩体。区内构造发育,多为褶皱和剪切带,构造方向主要为NW-SE、NE-SW和近SN向。区内金矿脉主要产于条带状铁建造与煌斑岩脉的剪切接触带内,及其与煌斑岩平行的石英脉中;地球化学特征显示其矿体为从岩浆分异出的含矿热液流体赋存于构造空间所形成,根据测年资料,初步认为盖塔绿岩带的主要金成矿期为(2699±9)~(2617±17)Ma,其带内发育的盖塔金矿床属于典型的太古宇绿岩带造山型金矿床。

The Geita greenstone belt is located in the northwest of Tanzania craton,and developed a world-class large-scale gold deposit with a 387 t gold resources,namely Geita gold deposit.The main rock type of Geita greenstone belt is banded iron formation(BIF),volcanic clastic sedimentation and kavirondian system conglomerate,both with syn-orogenic granite,lamprophyre and trachyandesite.The structure of folds and shear zones are well developed in the area,and the structure directions are mainly NW-SE,NE-SW and nearly E-W.The gold veins are developed in the contact of BIF and lamprophyre,and found in nearby parallel quartz veins.The characteristics of geochemistry shows that the orebodies were formed from the magmatic hydrothermal,and hosted in the shear zone.Based on the study of geology,typical gold deposits and ore-forming age of the Geita greenstone belt,this paper determines the era of mineralization and summarizes the evolutionary history of Geita greenstone belt.As a preliminary view,the evolutionary history of Geita greenstone belt shows many periods,including volcanic activities,deposit formation,tectonic activities,multi-hydrothermal activities and tectonic reworking.For the tectonic reworking of Geita greenstone belt,determines the main era of mineralization is(2699±9)~(2617±17)Ma,and the Geita gold deposit is a typical greenstone belt gold deposit of orogenic belt type of Archean.