Abstract
毕机沟层状岩体是扬子地块北缘汉南杂岩中最重要的镁铁-超镁铁质侵入体之一,主要由下部带超镁铁质岩、中部带辉长岩和上部带闪长岩组成。本文对该岩体下部带橄长岩、橄榄辉长岩和橄榄辉长苏长岩以及中部带粗粒辉长岩、磁铁辉长岩和角闪辉长岩进行全岩主微量元素及亲铜元素分析,全岩 (La/Sm)<sub>N</sub>(0.43~2.89)和(Tb/Yb)<sub>N</sub> (1.08~1.52)比值以及La/Yb-Sm/Yb图解均表明毕机沟层状岩体源区属于尖晶石二辉橄榄岩。Ni/Cu-Pd/Ir图解显示毕机沟层状岩体母岩浆主要为高镁玄武岩,模拟计算及高的S/Se比值显示其母岩浆经历了~5%的地壳混染并引进了外界硫,导致毕机沟母岩浆在深部发生早期硫化物熔离,造成其极高的Cu/Pd比值(5.21×10<sup>3</sup>~1.67×10<sup>6</sup>)和低的PGE含量。毕机沟母岩浆侵位到浅部岩浆房后,下部带极少量的硫化物熔离进一步导致残余岩浆亏损PGE,但S和Cu含量相对升高;中部带从下部带残余岩浆中结晶分异,具有更低的PGE含量和相对较高的S以及Cu含量。根据毕机沟层状岩体岩浆演化及硫化物熔离过程,推测岩体深部及附近具有寻找Cu-Ni-PGE矿床的潜力,查明其岩浆通道系统及岩浆运移方向对找矿勘查具有重要意义。
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