东秦岭古生代伟晶岩稀有金属成矿特色与成矿条件分析

东秦岭伟晶岩区是秦岭造山带规模最大、稀有金属矿化最丰富的伟晶岩区.该区稀有金属矿化种类齐全,产出贫矿、铀矿化、铍矿化、锂矿化和复杂稀有金属矿化伟晶岩,以锂矿化和铀矿化伟晶岩为主.稀有金属伟晶岩类型丰富,包括绿柱石-铌铁矿亚型、锂辉石亚型、锂云母亚型和钠长石-锂辉石型.伟晶岩内部结构分带型式多样,包括对称分带、分层和均一结构.铀矿化伟晶岩分带简单,铍矿化和复杂稀有金属矿化伟晶岩以对称分带结构为主,锂矿化伟晶岩具有多种内部结构分带型式.伟晶岩分异演化程度跨度大.结晶分异影响着复杂稀有金属矿化伟晶岩的成矿过程.该区主要产出古生代伟晶岩,形成于晚志留世—中泥盆世,集中于两期,处于晚造山-造山后阶段.伟晶岩形成时代与伟晶岩空间分布、岩浆岩分异演化程度、稀有金属矿化类型等关联不大.东秦岭地区中大面积不同时代花岗岩体的侵位、变质沉积岩地层的发育以及长期复杂的造山演化历史,包括地壳加厚和抬升,是形成高度分异演化的伟晶岩岩浆的有利地质条件.该区具有寻找铍矿和复杂稀有金属矿的潜力,且需要关注长石、石英和云母等矿物的综合利用.稀有金属伟晶岩的岩浆成因是未来研究的重要方向.

The features of geology and rare- elemental enrichment of the East Qinling pegmatite district

The East Qinling pegmatite district is the largest pegmatite district hosting abundant rare element (REL) in the Qinling orogenic belt. It has many mineralization types including barren, uranium- , beryllium- , lithium- and multi REL- mineralized pegmatite dykes. The lithium- mineralized and uranium- mineralized pegmatite dykes dominate other REL pegmatites. Various types of REL pegmatite dykes, including beryl- columbite, spodumene and lepidolite subtypes and albite- spodumene types are present. There are three internal structural zoning patterns for the pegmatites namely symmetrical zoning, layered zoning and homogeneous. The uranium- mineralized pegmatites are weakly zoned. The beryllium- and multi REL- mineralized pegmatites mainly display symmetrical zoning pattern, while lithium- mineralized pegmatites have various internal structure zoning patterns. The degrees of fractionation and evolution of the pegmatite dykes display a wide range. Fractional crystallization plays an important role in the REL metallogenic process of the multi REL- mineralized pegmatite dykes. The pegmatites in the East Qinling are mainly Paleozoic pegmatites that formed in late Silurian- middle Devonian and were concentrated in two episodes during the late to post orogenic stages of the North Qinling orogen. Formation times of the pegmatites are unrelated to the distribution of pegmatites, the degree of fractionation and evolution of magma, and REL mineralization types. The multiple emplacements of many granites with different formation times, metapsammitic rocks of the North Qinling unit, and the long and complex orogen evolution history including crust thickening and uplift were favorable for the formation of highly evolved pegmatite magma in the East Qinling. The East Qinling orogenic belt is a potential area for beryllium- mineralized pegmatites and multiple REL- mineralized pegmatites. We also should pay attention to the comprehensive utilization of feldspar, quartz and mica in this region. The origin of the rare- elemental pegmatite dykes should be an important future research focus.