摘要
烂泥塘斑岩铜金矿床位于云南省西北部的中甸地区,矿体主要以细脉—浸染状、网脉状产于石英二长斑岩和石英闪长玢岩之中。矿区热液蚀变作用发育,围绕矿体由深部至浅部依次发育钾化带、绿泥石—绢云母化带、绢云母化带和泥化带。钾化带中发育3种不同产状的磁铁矿,根据磁铁矿产出状态与脉体之间的相互穿插关系,将其划分为浸染状分布的磁铁矿(Ⅰ类)、单一脉状磁铁矿(Ⅱ类)和石英—硫化物脉中的磁铁矿(Ⅲ类)。此外,矿区常见产于成矿期后白云石—石英大脉中的镜铁矿。采用激光剥蚀电感耦合等离子体质谱(LA-ICP-MS)对上述铁氧化物进行了原位微区成分测试。结果表明:3类磁铁矿均富集Ti、V、Cr、Ni、Co、Al、Mg、Mn、Ga和Zn等微量元素。早期Ⅰ类磁铁矿含有钛铁矿出溶体,与Ⅱ、Ⅲ类磁铁矿相比,相对富集Mg、Ni和V等元素,属于岩浆磁铁矿;Ⅱ类磁铁矿相对富集Mn、Zn、Sn和Sc等元素,属于热液磁铁矿。岩浆磁铁矿(Ⅰ类磁铁矿)与后期脉状磁铁矿(Ⅱ类和Ⅲ类)相比,Ti、Al和Cr等元素含量相差不大。这可能是由于后期热液蚀变对Ⅰ类磁铁矿的强烈改造,导致其中Ti、Al和Cr等元素含量降低(通常岩浆磁铁矿比热液磁铁矿更富集Ti、Al和Cr)。Ⅱ、Ⅲ类脉状磁铁矿属于热液磁铁矿且二者微量元素含量差别不大,说明它们属于同一期流体中沉淀的产物。与磁铁矿相比,镜铁矿中的Ti、Al和V元素含量相差不大,而Cr、Ga、Ni和Co等元素含量比磁铁矿低一个数量级。结合前人资料,认为Al、Mn、Mg和Sc元素在磁铁矿中主要以类质同象形式存在,而Ca、S、Cu、Ba、Sr和Zr等元素主要以显微包裹体形式存在。钾化带中广泛发育的磁铁矿—赤铁矿共生组合、镜铁矿以及磁铁矿中异常低的Mn含量表明,烂泥塘矿区成矿流体的氧逸度高达赤铁矿—磁铁矿缓冲线。
The Zhongdian area,located in northwestern Yunnan,is an important porphyry belt in China. It hosts a large number of Triassic intermediate-felsic porphyritic intrusions and porphyry deposits such as Pulang porphyry Cu-Au,Xuejiping porphyry Cu,Chundu porphyry Cu,Langdu Cu skarn and Lannitang porphyry Cu- Au deposit. The Lannitang porphyry Cu-Au deposit is located in west belt of the Zhongdian area. The magnetite in Lannitang porphyry Cu-Au deposit is widespread and it occurred as disseminated and vein types in potassic and chlorite-sericite alteration zone.Specularite is also observed frequently in the post-mineralization dolomite- quartz coarse veins.We conducted the petrography and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS)to determine the texture and composition of iron oxides(magnetite and specularite). In this s tudy,we identified three types of magnetite. Type-Ⅰ magnetite is disseminated in potassic alteration of deposit. It is generally contains ilmenite lamellas. Type-Ⅱ and Type-Ⅲ magnetite are occurred in magnetite single vein and magnetite-bearing quartz stockwork vein separately. Type-Ⅱ and Type-Ⅲ are distributed in potassic and chlorite-sericite alteration zone. The LA-ICP-MS analyses show that Type-Ⅰ magnetite is relatively rich in V, Ni and Mg than other two types of magnetite. Type-Ⅱ and Type-Ⅲ magnetite are more enriched in Mn,Zn,Sn, Sc and high-Ni/Cr ratio than Type-Ⅰ magnetite.Type-Ⅱ and Type-Ⅲ magnetite has similar content of many trace elements. The concentration of Cr,Ga,Ni and Co in specularite is obviously low er than those of magnetite. The il menite lamellae and low-Ni/Cr (Ni/Cr<1)ratio revealed that Type-Ⅰ m agnetite belongs to igneous magnetite. Type-Ⅱ and Type-Ⅲ are distributed in veinlets and displayed high-Ni/Cr ratio(Ni/Cr>1). We suggested that they a re hydrothermal magnetite. Type-Ⅰ magnetite(igneous)is intergrown with hydrothermal minerals including chlorite and sericite and it has quiet similar contents of Ti,Al and Cr wi
作者
郭剑衡
冷成彪
张兴春
张伟
尹崇军
张陆佳
田振东
GUO Jianheng;LENG Chengbiao;ZHANG Xingchun;ZHANG Wei;YIN Chongjun;ZHANG Lujia;TIAN Zhendong(State Key Laboratory of Ore Deposit Geochemistry,Institute of Geochemistry,Chinese Academy of Sciences, Guiyang 550081,Guizhou,China;Chinese Academy of Science University,Beijing 100039,China;State Key Laboratory of Nuclear Resources and Environment,East China University of Technology,Nanchang 330013,Jiangxi,China;Yunnan Huaxi Mineral Resources Co.,Ltd.,Kunming 650200,Yunnan,China)
出处
《黄金科学技术》
CSCD
2019年第5期659-677,共19页
Gold Science and Technology
基金
国家重点研发计划项目“青藏高原大陆碰撞斑岩铜—钼—金矿系统结构与形成机制”(编号:2016YFC0600305)
国家自然科学基金项目“滇西北中甸岛弧印支期斑岩铜矿床的保存与剥蚀程度研究:低温年代学制约”(编号:41373051)联合资助
