云南龙脖河铜矿区变火山岩地球化学再研究

龙脖河铜矿床位于滇中地区红河成矿带南段,矿区火山岩发育、与铜矿化时空密切共生。区内火山岩遭受了不同程度的蚀变或区域变质作用,根据矿物组合可分为变安山岩、变次火山岩和变基性火山岩。三类变火山岩均相对富Na,在地球化学分类图解上样品主要位于碱性玄武岩区域。除个别微量元素外,三类岩石的微量元素含量相近,与各种构造环境玄武岩相比,本区变火山岩富集HFSE(Th、Nb等)、亏损LILE(Sr、Ba等),微量元素配分模式出现明显Th、Nb正异常和Sr、Ba负异常。三类岩石的REE含量范围相互重叠,除Eu异常外,其REE配分模式均为相似的LREE富集型。各种地球化学证据表明,本区三类变火山岩为同源岩浆不同演化阶段的产物,其原始岩浆为大陆板内拉张构造环境交代富集地幔部分熔融的产物,结晶分异作用在岩浆演化过程中具有重要地位。

GEOCHEMISTRY OF META-VOLCANIC ROCKS FROM THE LONGBOHE COPPER DEPOSIT, YUNNAN PROVINCE, CHINA-A FURTHER STUDY

The Longbohe Cu deposit,which is situated in the southern part of the Honghe ore-forming zone,Yunnan Province,China,is a typical orefield where volcanic rocks are of wide distribution and related to Cu mineralization in time and space.Volcanic rocks in the orefield,which have experienced different degrees of alteration or regional metamorphism,can be classified as three types,including meta-andesite,meta-subvolcanic rock and meta-basic volcanic rock in accordance with their mineral assemblages.The three types of rocks in the orefield are relatively rich in Na and the main samples plot in the area of alkali basalt in the geochemical classification diagram.With the exception of very few elements,the three types of rocks are similar in the contents of trace elements. In comparison with the basalts of different tectonic settings,the meta-volcanic rocks in the orefield are rich in high field strength elements(HFSE;such as Th,Nb,etc.) and less in large ion lithophile elements(LILE;such as Sr,Ba,etc.) and their primary mantle-normalized trace element patterns show obvious positive Th and Nb anomalies and negative Sr and Ba anomalies.The three types of rocks are similar in the REE content range and the chondrite-normalized REE patterns with the exception of Eu anomaly.Various lines of evidence show that the three types of volcanic rocks in the orefield are of the same source and different-stage magmatic evolution,their original magma is a product of partial melting of the metasomatic-rich mantle,and tectonic settings are of extension in the continent plate,and the crystallization differentiation plays an important role in the process of magmatic evolution.