塔里木东北缘早二叠世坡东铜镍硫化物矿床成矿特征与岩石成因

Petrogenesis and metallogenic characteristics of the Early Permian Podong Cu-Ni sulfide deposit,northeastern margin of the Tarim plate

新疆北山坡北基性-超基性岩体位于塔里木板块东北缘,形成于早二叠世,赋存了坡一、坡十超大型铜镍硫化物矿床,以贫矿为主,赋存于橄榄岩相中。近年在坡一矿床东部勘探过程中,新发现了海绵陨铁状富矿,赋存于辉长苏长岩相中,命名为坡东铜镍硫化物矿床,为该区找矿对象提供了新的线索。坡北岩体的地质背景、岩石成因与成矿机制存在较大的争议,本研究在坡东矿床最新勘探钻孔中取得一系列样品,从年代学、岩石地球化学、同位素地球化学角度进行了系统剖析,对比坡一矿床的成岩成矿特征。发现坡东矿床中与成矿相关的辉长苏长岩相的全岩m/f值、εNd(t)值及橄榄石的Fo值明显低于坡一矿床,指示坡东矿床中赋矿岩相的岩浆演化程度相对较高,随着岩浆演化程度增高,地壳混染作用影响增强。岩石学与地球化学研究指示:坡东矿床是岩浆在地壳浅部发生分离结晶和地壳混染,岩浆达到硫化物饱和并发生硫化物熔离后成矿;坡一矿床是岩浆在深部发生橄榄石与铬尖晶石结晶,通过岩浆自身结晶分异导致硫化物饱和成矿。结合前人研究成果,提出坡北岩体的形成可能与～275Ma塔里木地幔柱事件有关,岩体的母岩浆来自亏损型地幔,具有OIB特征,地幔源区遭受了流体的交代作用。

The Early Permian Pobei basic-ultrabasic complex hosts Poyi and Poshi superlarge-scale Cu-Ni sulfide deposit at the northeast margin of the Tarim plate,Xinjiang. The ore body hosted by peridotite consists mainly of disseminated sulfides with low Ni grade. The new ore body was discovered at the east of the Poyi deposit during recent exploration,and was named the Podong Cu-Ni sulfide deposit,which was characterized by net-textured sulfides with high Ni grade hosted by gabbro-norite,providing new clues for exploration object. There are still controversies on geological setting,petrogenesis and metallogenic mechanism of the Pobei complex.Therefore,the authors gathered samples from the drill holes of the Podong Cu-Ni sulfide deposit,studied the petrogenesis and metallogenic machenism by geochronology,petrogeochemistry and isotopic geochemistry,and made a comparison with the Poyi Cu-Ni sulfide deposit. The m/f,εNd（t） values of whole rock and Fo values of olivine from the Podong gabbro-norite,are distinctly lower than that of the Poyi deposit,which indicate relatively high magma evolution degrees for the Podong ore-forming petrofacies,and the higher of magma evolution the more intensive of crustal contamination affect. Based on the lithoface boundaries and petrogeochemistry study,the authors infer the Podong deposit is formed by sulfide segregation from basic magma,and the sulfide saturation was caused by magma crystallization and crustal contamination. However,the Poyi deposit is formed by sulfide segregation from ultrabasic magma caused by magma crystallization itself,as the sulfur solubility decreases along with the olivine and Cr-spinel crystallization. Combining with the previous research,the authors put forward that the Pobei complex is spatially and temporally related to the ~ 275 Ma Tarim Large Igneous Province,and was derived from depleted mantle source with OIB-like signature,affected by fluid metasomatism in magma source.