金川岩浆铜镍(铂)硫化物矿床中两类橄榄石的发现及其成矿意义  

Discovery and genesis of two types of olivines and it ssignificance to metallogeny in Jinchuan magmatic copper-nickel(PGE)sulfide deposit

作　　者：刘美玉 苏尚国[1] 姚远 吴晓蔓 蔡楠 管秋云 LIU MeiYu;SU ShangGuo;YAO Yuan;WU XiaoMan;CAI Nan;GUAN QiuYun(School of Geosciences and Resources,China University of Geosciences(Beijing),Beijing 100083,China;Institute of Tibetan Plateau Research,Chinese Academy of Sciences,Beijing 100101,China)

机构地区：[1]中国地质大学(北京)地球科学与资源学院,北京100083 [2]中国科学院青藏高原研究所,北京100101

出　　处：《岩石学报》2020年第4期1151-1170,I0001-I0003,共23页Acta Petrologica Sinica

基　　金：中国地质调查局项目(12120114085501);教育部高等学校博士学科点专项科研基金(20130022140001)联合资助.

摘　　要：金川铜镍硫化物矿床是世界第三大岩浆型铜镍硫化物矿床,其成因机制一直备受争议。主要成矿模型有以下两种:(1)岩浆通道堆积模型;(2)深部熔离-多次贯入模型。目前,二者均不能较好解释矿区中存在的各种地质现象。本文重点研究矿区橄榄石的特征,借此来探讨"硫化物矿浆"的迁移方式与侵位能力。本次研究在金川矿床中发现了两类橄榄石:LREE亏损型(Ⅰ型)与LREE富集型(Ⅱ型)。其中,Ⅰ型橄榄石为岩浆正常结晶的原始颗粒,常见复杂的成分环带,由原生橄榄石与晶间硅酸盐熔体/不混溶硫化物熔体发生物质交换所形成,继承了玄武质岩浆稀土含量低的特征,广泛分布于各类超基性岩石与矿石中;Ⅱ型橄榄石常见包裹斜方辉石的反序列包含关系,以稀土含量高(~2个数量级)且相对富Mg而显著区别于前者,为辉石堆晶颗粒经流体触发不一致熔融后再结晶形成的橄榄石,多见于硫化物矿石中。金川矿床硫化物矿石中广泛发育的原生富Cl含水矿物(金云母、角闪石、磷灰石)与Ⅰ型橄榄石边部活动性元素含量的剧增,暗示金川矿体形成过程受富Cl流体影响显著。实验岩石学与动力学模拟的新研究进展表明流体的加入可有效推动高密度硫化物的迁移,流体的加入可能是金川硫化物矿浆上侵运移的主要机制。结合硫化物Cu/Ni西高东低的空间演化规律,橄榄石Fo值西高东低的空间变化趋势与晶体粒度西细东粗的分布特征可以推测,金川铜镍硫化物矿床岩浆通道的前进方向为自西向东。The Jinchuan deposit is the third largest magmatic copper-nickel sulfide deposit in the world.There are still a lot of controversies about its metallogenic mechanism of which two main models can be summarized from former researches:(1) the magmatic conduit accumulation metallogenic model;and(2) the deep segregation-injection metallogenenic model.However,none of them can explain the geological phenomena in the mining area well.This paper focuses on the characteristics of olivines in the deposit to discuss the migration mode and emplacement ability of the sulfide melts.In this study,two types of olivines were found in the Jinchuan deposit,namely the LREE-depleted(type Ⅰ) and the LREE-enriched(type Ⅱ).The type Ⅰ olivine is the primary minerals generated by crystallization of the ultramafic-malic magma,which is widely distributed in various types of ultramafic rocks and sulf’ide ores in the deposit.It always occurred as complex composition bands formed by compositional changes between primary olivine and interstitial silicate/immiscible sulfide melt.This type of olivine inherited the low rare earth element(REE) contents of basaltic parent magma.The type Ⅱ olivine is formed by reciystallization of cumulate orthopyroxene after its incongruent melting by a fluid-triggered process,which is mostly found in sulfide ores,always wrapped by orthopyroxene.It has high REE content(about 2 orders of magnitude higher than that of the type Ⅰ olivine) and relatively rich in Mg#.The wide distribution of primary Cl-rich hydrated minerals(phlogopite,amphibole and apatite) and suddenly elevation of fluid active elements at the margin of type Ⅰ olivine in the sulfide ore indicates that the formation process of the Jinchuan deposit might be significantly influenced by Cl-rich fluids.The new progress in experimental petrology and dynamics simulation shows that fluid addition can effectively promote the migration of high-density sulfide slurry and it might be the main mechanism for the emplacement of the sulfide melts in the J

关 键 词：金川铜镍(铂)硫化物矿床 两类橄榄石 富Cl流体 定量化结构分析 岩浆通道成矿系统 

分 类 号：P578.942[天文地球—矿物学] P611.1[天文地球—地质学]