云南羊拉铜矿床磁黄铁矿标型矿物学特征及成矿意义  

Mineralogy typomorphic characteristics of pyrrhotite and mineralization significance of Yangla copper deposit Yunnan China

作　　者：杨镇[1] 杨立强[1] 刘江涛[1] 孟健寅[1] 吕亮[1] 孙诺[1] 张广宁[1] 龙斐 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,北京100083 [2]云南迪庆矿业开发有限责任公司,香格里拉674400

出　　处：《岩石学报》2014年第9期2669-2680,共12页Acta Petrologica Sinica

基　　金：国家重点基础研究发展规划(2009CB421008);北京市优秀博士学位论文指导老师科研项目(20111141501);中国地质调查局地质调查项目(12120114013501);高等学校学科创新引智计划(B07011)联合资助

摘　　要：羊拉铜矿床是三江成矿带中段重要的大型铜矿床之一,其矿床成因一直没有明确界定。里农矿段是羊拉铜矿床最主要的组成部分,该矿段矿石中黄铜矿、磁黄铁矿和黄铁矿发育,其中,磁黄铁矿矿石是矿床中含量最高的硫化物矿石。本文选取里农矿段的磁黄铁矿矿石样品,利用矿相学、电子探针和X射线衍射对磁黄铁矿形态、成分和结构标型特征进行分析,探讨其形成环境和沉淀机制,为揭示矿床成因提供有效约束。研究结果表明：羊拉铜矿床矿体具有典型的矽卡岩型矿床特征,多呈层状、似层状产出,且与花岗闪长岩岩体关系密切,受花岗闪长岩岩体和大理岩、变质石英砂岩等地层以及断裂构造的共同控制;磁黄铁矿矿石呈铁黑色、古铜色、铜褐色,块状和浸染状构造;镜下为黄白色、黄褐色,无内反射色,非均质性不明显,他形-半自形粒状结构。局部可见磁黄铁矿被石英±黄铜矿±黄铁矿±方解石脉切断,也见闪锌矿中有乳滴状、叶片状黄铜矿发育。磁黄铁矿中Fe元素含量为59.25%~60.25%,平均为59.71%,S元素为39.10%~39.97%,平均39.52%,化学分子式为Fe6S7~Fe8S9;晶胞参数平均值为a0=11.912,b0=6.859,c0=12.813,磁黄铁矿的粉晶X射线衍射曲线呈强度大致相等的双峰,表明羊拉铜矿床的磁黄铁矿以单斜磁黄铁矿为主。据此判断该区成矿作用过程中富硫、并经历快速降温变化,非均匀应力作用使六方磁黄铁矿转化成了单斜磁黄铁矿;磁黄铁矿中的硫是以S2-的形式存在,在六方磁黄铁矿向单斜磁黄铁矿的转化过程中,磁黄铁矿晶格中的Fe离子略有减少,Fe1-xS的电负性稍有增加,还原性增强;在Fe-S相图中,磁黄铁矿位于单斜磁黄铁矿和黄铁矿共生相区,表明成矿温度在250℃左右。即羊拉铜矿床的磁黄铁矿主体是形成于富硫、非均匀应力、中温的还原环境。该区磁黄铁矿富Co贫Ni,Co/Ni值范围较�Yangla copper deposit is one of the important and large deposit located in the middle part of the Sanjiang Tethys metallogenic belt. However, its ore genesis remains unresolved. In Linong ore block, the most important part of the deposit, the principal metallic minerals include chalcopyrite, pyrrbotite and pyrite. The pyrrhotite ores are the most important sulfide ores type. In this study, we have performed the mineragraphy, electro-probe microanalyzer and X-ray diffraction analysis on the pyrrhotite samples from the Linong to analyze the typomorphic characteristics of morphology, composition and texture of pyrrhotite. The results above reveal the ore forming environment and precipitated mechanism of the pyrrhotite, which provide valid constraints on the ore genesis. The geological characteristics are discussed fully and summarized in detail here. Its ore bodies are typically layered or bedded in the interlayer fissure of stratum, closely related to the granodiorite and skarn and controlled by the combination of the pluton, stratum and structures, which show obvious features of the skarn deposit. The pyrrhotite has iron black, bronze, massive and disseminated structure. Microscopically, it shows yellowish-white, snuff, without internal reflection and heterogeneity, anhedral to subhedral granular structure. Locally, the pyrrhotite is cut by quartz-pyrite-chalcopyrite-calcite vein, and the chalcopyrite developed in sphalerite as droplet or foliaceous shape. The pyrrhotite in the Yangla copper deposit, have content of Fe： 59.25% ~ 60.25%, average： 59. 71% and S element： 39. 10% ~ 39. 97%, average： 39. 52%, and hence the chemical formula is Fe6S7 ~ FesS9. The average value of crystal cell parameters is similar, a0 = 11. 912/~, b0 = 6. 859A, co = 12. 813＆, and the crystal powder X-ray diffraction profiles of pyrrbotite shows a double-peak phenomenon with nearly equal intensity, which are main characteristics of the monoclinic pyrrhotite. Accordingly, in the sulphur-rich, rapid cooling and non-uniform stresse

关 键 词：矽卡岩型矿床 磁黄铁矿 标型特征 羊拉 云南 三江 

分 类 号：P575[天文地球—矿物学] P578.24[天文地球—地质学]