吉林红旗岭1号和7号岩体中含矿超镁铁质岩的矿物化学特征:对岩浆演化过程以及铜镍硫化物矿床形成机制的约束

Mineral chemistry of ore-bearing ultramafic rocks from the Hongqiling Nos.1 and 7 instrusions in Jilin Province:Constraints on the magmatic processes and the metallogenesis of Ni-Cu sulfide deposits

本文对吉林红旗岭1号和7号岩体中含矿超镁铁质岩的主要造岩矿物进行了详细研究。两岩体的主要造岩矿物为贵橄榄石、古铜辉石、单斜辉石、斜长石、角闪石和金云母。岩浆的暗色矿物结晶顺序为:橄榄石→斜方辉石→单斜辉石→角闪石→黑云母,与镜下实际观察一致,是岩浆在不同深度结晶的产物。原始岩浆来自上地幔,两岩体进入高位岩浆房中的熔体的MgO含量分别13.98%和14.22%、Mg#值分别为72.22和71.05,为含水的高镁的苦橄质玄武岩浆。深部岩浆房深度距地表约26～27km,岩浆房内的结晶温度介于1280～1379℃之间,即结晶于下地壳中。岩浆由深部上升到高位(浅部)岩浆房中的过程是近绝热的,也是快速完成的。岩浆可能经历了两次岩浆房的演化过程,岩浆在上升到高位岩浆房之前,在深部曾经历了较短时间的橄榄石和少量辉石的分离结晶作用;但在高位岩浆房中混染了地壳物质,与此同时,还经历了同源岩浆混合作用以及岩浆过冷却作用,这些都有利于岩浆体系中成矿元素含量增高以及硫达到饱和状态,使金属硫化物熔离并晶出,从而使岩体发生铜镍矿化作用。

Systematic studies on the mineralogy of the ore-bearing ultramafic rocks from the Hongqiling Nos.1 and 7 intrusions in east Jilin Province show that the rocks mainly consist of chrysolite,bronzite,clinopyroxene,plagioclase,hornblende and phlogopite. These minerals were crystallized from magma at different depths.In particular,olivine and pyroxene are the best rock-forming minerals that crystallized firstly from the primary magma and could be used to trace the magma,which were derived from the upper mantle.The parental magmas of these intrusions in the intermediate magma chamber are hydrated high-Mg picritic basalt magma and the MgO content were estimated to be about 1 3.98%and 1 4.22%with Mg # of 72.22 and 71.05 respectively.The depth of the deep-level magma chamber,where only olivine and pyroxene fractional crystallization processes took place ephemerally,was estimated to be about 26～27 km.The temperature of magma chamber was 1 280～1 379℃.When magma uplifted from the deep-level to the high-level chamber,this process was nearly adiabatic and completed in a short time.Then,magma maybe experienced double chamber evolutions.Meanwhile,olivine and less pyroxene fractional crystallizations were over before the uplift of magma.But,there was complex process in high-level magma chamber,where crust contamination,mixing with affinal magma and super cooling have been happened.These processes contribute to the increase of ore-forming elements and the saturation of sulfide in the magmatic system,thus Ni-Cu mineralization occurs in the intrusions.