云南腾冲地块老象坑铁多金属矿矿床地质特征与成矿物质来源示踪

GEOLOGICAL CHARACTERISTICS AND ORE-FORMING MATERIAL SOURCES OF THE LAOXIANGKENG IRON-POLYMETALLIC DEPOSIT IN TENGCHONG BLOCK,YUNNAN

云南腾冲地块老象坑铁多金属矿床位于三江成矿带中南段,成矿条件和成矿潜力优越。通过野外实地勘查,结合主量、微量、稀土元素与Pb同位素分析,探讨其矿床地质特征与成矿物质来源。结果表明:矿体多呈透镜状,似层状等;矿石以致密块状、角砾状为主;镜下可见磁铁矿,磁黄铁矿,黄铜矿等多种金属矿物。磁铁矿矿石和磁铁矿单矿物微量元素变化趋势基本一致,可明显看出呈强不相容元素相对富集的右倾锯齿状;明显富集K,U,P,Ti,Nb,Sr等大离子亲石元素和重稀土元素Lu;而相对亏损Th,Ce,Nd,Zr,Sm,Y等元素;稀土元素分布总体上呈左倾模式,LREE相对亏损,HREE明显富集,LREE分布模式平坦,HREE分布变化大。磁铁矿矿石δEu为0.245~0.866,δCe为0.524~0.969,磁铁矿单矿物δEu为0.330~1.165、δCe为0.445~1.020,均具有明显的Eu负异常和较弱的Ce负异常。磁铁矿的Pb同位素组成(^(208)Pb/^(204)Pb为38.606~39.173,^(207)Pb/^(204)Pb为15.649~15.727,^(206)Pb/^(204)Pb为18.357~19.284)与腾冲地区基性-超基性岩相似,且磁铁矿与基性-超基性岩形成了很好的线性排列,表明其具有同源关系。腾冲老象坑磁铁矿的铅同位素组成主要源于造山过程;结合实际地质特征及矿区内最新的钻孔资料,认为老象坑铁多金属矿矿床类型应为超基性岩浆热液-断裂填充型铁矿床。

Geology and ore-forming material sources of Laoxiangkeng iron polymetallic ore in Tengchong block are studied through field investigation,combined with analysis of main,trace,rare earth elements and Pb isotopes.It shows that the ore bodies are lenticular,or stratiform-like in shape with compacted and brecciaed ore.Microscope observation reveals there are magnetite,pyrrhotite,chalcopyrite and a variety of metallic minerals in the ore.The change trend of trace elements for magnetite ore and magnetite single mineral is basically the same.Highly incompatible elements are relative enriched with right zigzag dip,U,P,K,Ti,Nb,Sr,and Lu are significantly enriched while Th,Ce,Nd,Zr,Sm,Y and other elements are relatively depleted.The REE distribution display left leaning mode with relative loss of LREE and obvious enrichment of HREE.In addition,LREE distribution pattern is flat,and the distribution of HREE is of obvious variation.Magnetite ore and magnetite minerals has obvious negative Eu anomaly,a weak negative Ce anomalies.The composition of magnetite Pb isotope is similar to basic-ultrabasic rock with a good linear arrangement and homologous relationship.It is considered that the compositions of magnetite Pb isotopes in Laoxiangkeng are mainly originated from orogenic process.The data of geological characteristics and drilling wells in mining area indicate that the iron-polymetallic deposit in Laoxiangkeng belongs to ultrabasic magmatic hydrothermal-fracture fill iron deposit.