祁连山某地铂－金砂矿的铂族矿物研究及其意义

Platinum Group Minera form a Platinum-Gold Placer in Qilian Mountains and Their Significance

该铂－金砂矿产于超基性岩体山前谷地的第四纪冲积－洪积层中。在６０年代，前人曾对该铂－金砂矿作过初步评价，但对其中的铂族元素矿物未进行过矿物学研究。笔者于１９９２年夏对该砂矿作了调研，并对吕明鸿工程师所提供的该砂矿的铂族矿物样品进行了物理光学性质研究及电子探针和Ｘ射线分析。业已查明，它们主要是铱锇矿、钉铱锇矿、锇铱矿、自然锇、等轴铁铂矿；矿物共生组合为自然金＋上述铂族矿物＋自然银＋铬尖晶石＋铬铁矿＋磁铁矿＋钛铁矿＋辰砂。这表明，该铂－金砂矿的物质来源为含铬超基性岩。

The studied platinum-gold placer occurs in Quaternary alluvial-diluvial sediments within a piedmont valley of ultrabasic rocks,Northwest China.Several platinum group element(PGF)minerals from the placer were studied under microscope and by electron microprobe and X-ray diffraction analysis, The Os-Ir-Ru minerals include iridosmine[Os_(0.51-0.77)Ir_(0.22-0.45)Ru_(0.01-0.09, rutheniridosmine[Os_(0.40-0.56)Ir_(0.29-0.39)Ru_(0.09-0.30) F_(0.00-0.01),Ir_(0.16-0.20) Ru_(0.00-0.03),and osmiridium[Ir_(0.73-0.76)Os_0.22 Fe_(0.00-0.04)Ru_(0.01-0.02), The Pt-Fe mineral is identified as isoferroplatinum(Pt_(2.85-3.00)Fe, a=3.863-3.868mm,The studied mineral asseblage is Os-Ir-Ru minerals + isoferroplatinum+native gold +native silver+chrome-ceylonite+chromite+magnetite+ilmenite+cinnabar,suggesting that the placer is probably derived from the chrome-bearing ultra-basic rocks.The result of the study provides useful mineralogical data for evaluation of the placer,and lso serves as a valuable indicator in the prospe-acting for primary PGE deposits related to chrome-bearing ultrabasic rocks in the area.