滇西伟晶岩型稀有金属矿床成矿规律与找矿方向

Metallogenic regularity and prospecting direction of pegmatitic rare-mental deposits in western Yunnan

滇西处于“三江”特提斯构造域西南缘,稀有金属伟晶岩脉发育,并沿区域构造带成群成带分布。滇西伟晶岩型稀有金属矿化以铍为主,兼有锂、铌、钽、锡等。本文将滇西伟晶岩型稀有金属成矿区划分为高黎贡山成矿带、腾冲-梁河成矿带、西盟成矿带和凤庆-临沧成矿带等四个成矿带。高黎贡山成矿带稀有金属伟晶岩可能为深熔成因,其矿体主要产出于中深变质岩的构造裂隙中;其它三个成矿带稀有金属伟晶岩与其附近的花岗岩有密切的成因关系,其矿体主要产出于花岗岩体内部、内外接触带或远离岩体的围岩构造裂隙中。矿化时代集中于喜山期,涵盖古新世、始新世、渐新世、中新世四个成矿时期,其年龄范围主要集中于62~15Ma。印度板块及欧亚板块的陆-陆碰撞造成“三江”特提斯构造转换带强烈的挤压、走滑、逆冲推覆导致地壳加厚及深熔作用是滇西伟晶岩型稀有金属成矿的主要地质背景。区域锂、铍、铌、钽、锡等稀有金属地球化学异常展布区为首要勘查目标区,钠长石化及云英岩化等热液蚀变发育地段的伟晶岩脉应列为首要勘查目标,同时,滇西地区与淡色花岗岩密切相关的伟晶岩脉在今后的找矿工作中需要重点关注。

Western Yunnan is located in the southwestern margin of the“Sanjiang”Tethyan tectonic domain,with developed rare mental pegmatite which occurred as groups along the tectonic belt.The pegmatitic rare-metal mineralization in western Yunnan is mainly Be,with Li,Nb,Ta,Sn,etc.The metallogenic regionalization of pegmatitic rare-metals in western Yunnan can be divided into four metallogenic belts:Gaoligong Mountain metallogenic belt,Tengchong-Lianghe metallogenic belt,Ximeng metallogenic belt and Fengqing-Lincang metallogenic belt.Pegmatitic rare-metal orebodies mainly occur as veins in the metamorphic rock series,contact zone of granite rocks,or tectonic belt far from the rock but related to the rock.The mineralization of pegmatitic rare-metal in the Gaoligong Mountain metallogenic belt resulted from deep melting,and orebodies mainly occurred in the tectonic fissures of medium-deep metamorphic rocks.In the other three metallogenic belts,the rare metal pegmatites are closely related to the granites,and the ore bodies mainly occur in the granite,contact zones and fissures.The mineralization mainly occurred in the Himalayan Period from 62Ma to 15Ma,including Paleocene,Eocene,Oligocene and Miocene.The continental collision of the Indian plate and Eurasian plate caused strong compression,strike-slip and thrust nappe in the“Sanjiang”Tethyan tectonic zone,which resulted in crustal thickening and deep melting,leading to the pegmatitic rare-metal mineralization in western Yunnan.The distribution area with rare metal(Li,Be,Nb,Ta,Sn)geochemical anomaly is the primary exploration target.The pegmatite with albitization and greisenization or related to leucogranite should be focused in these areas.