老挝万象省爬立山(PHaLek)铁矿床地质特征及成矿作用分析

Geological Characteristics and Metallogenesis of the PHaLek Iron Deposit in Vientiane Province,Laos

爬立山铁矿床位于长山褶皱带北西端,是长山成矿带内与岩浆作用有关的一个大型铁矿床。根据野外地质观察及室内对含矿岩体、赋矿围岩和矿石开展的岩相学和地球化学研究发现:与成矿作用有关的花岗质岩石属钙碱系列准铝质的I型花岗岩,成岩的构造环境为火山弧。矿区内发育致密块状磁铁矿、孔洞状赤铁矿、砂砾土状铁矿等3种铁矿石。结合岩(矿)石微量元素分析,认为爬立山铁矿具有复合成矿作用特征,主要可分为3个成矿阶段:早期以与华力西期岩浆侵入作用有关的接触交代成矿作用为主,形成矽卡岩型磁铁矿;其后,在褶皱造山后形成的断陷盆地中,由于火山喷发(溢)作用形成孔洞状熔岩型赤铁矿;最后随着新生代地壳抬升,发生表生物理化学风化成矿作用,形成如今的砂砾土状型铁矿。

The PHaLek iron deposit is situated in the Northwest end of the Truongson fold belt,an elongate trending belt,which forms part of the Indochian Terrane of SE Asia.It is one of huge iron deposits associated with magmatic activities in the Truongson metallogenic belt.Combined their field geology survey,the micro-petrographic and element geochemical analyses are finished for the oreforming intrusive rock,the wall-rock of the ore bodies and the iron ore.It was shown that the granitic rock related to the mineralization belongs to the ＂I＂type granite,calcium alkali series and metaluminum,and formed in the tectonic environment of volcanic island arc.Three main ore types are recognized in PHaLek mine district,i.e.massive magnetite ore,pore-shaped hematite ore,gravelearthy ore.Based on trace element geochemical analysis of the ore and wall-rock,it was concluded that the PHaLek iron deposit is characterized by composite metallogenesis,which can be divided three main metallogenic epochs.The earliest one is the skarn magnetite mineralization associated with the Variscan intrusive magmatism.Thereafter,the volcanic eruption resulted in pore-shaped lava-type hematite mineralization in continental rift basins,which formed in late stage of continental folding orogenic process.Finally,supergene physical and chemical weathering mineralization caused the gravel-earthy iron mineralization on the surface,due to the crustal uplift in the Cenozoic period.