【摘要】 东秦岭是我国伟晶岩较为发育的地区，也是我国伟晶岩型稀有金属矿产勘查与研究的重点地区。近年来的重要发现是，龙泉坪一带多条伟晶岩脉是高纯石英的重要原料矿。但关于这些伟晶岩的具体岩性特征及分带情况，目前还缺乏深入研究。本文在系统野外地质考察基础上，选择其中的1号含高纯石英伟晶岩脉开展了岩石学、矿物学、地球化学及年代学的分析与研究。锆石、独居石和铌钽铁矿U-Th-Pb同位素分析表明，1号伟晶岩脉形成于早泥盆世（398～404Ma），与区域上广布的伟晶岩浆活动时代相近。锆石和独居石的ε_Hf（t）值和ε_Nd（t）值分别为-5.9～-5.2和-13.7～-11.5，表明该伟晶岩来源于古老地壳物质部分熔融。该伟晶岩脉长约400m，宽5m，是龙泉坪地区规模较大的伟晶岩脉之一，其主要矿物组成包括石英、钾长石、钠长石、电气石和云母。该岩脉的最大特征是它具有明显的对称性结构分带，即由外向内依次为石英-钾长石-白云母-电气石-黑云母外带、石英-钠长石-钾长石-白云母内带和块体石英核部带。详细的镜下观察发现，每个结构带中的石英都表现为两个形成世代。早阶段形成的石英（Ⅰ）呈块状，多分布于核部，阴极发光图像较亮，属于原生结晶石英;而晚阶段石英（Ⅱ）呈粒状，多分布于边部，阴极发光图像较暗，属于重结晶石英。LA-ICP-MS元素成分分析表明，早阶段的原生石英（Ⅰ）比晚阶段重结晶石英（Ⅱ）更富集Li、Al和Ti等晶格元素，相对不利于形成高纯石英，表明后期改造重结晶作用可有效降低石英中杂质元素含量。伟晶岩内带与外带和核部相比，石英中Li和Al的含量明显较低，Ti、B、Na和Ge含量相当，表明内带产出的石英更具有形成高纯石英矿的潜力。上述研究表明，伟晶岩中的石英表现出随分带不同而导致的明显成分变化，是高纯石英勘查需要面对的重要问题。更多还原

【Abstract】 The East Qinling is one of the important pegmatite producing areas,and it is also a key area for the exploration and research of pegmatite rare metal minerals. The most important discovery in recent years is that a number of pegmatites in the Longquanping area are important raw material mines for high-purity quartz. However,there is still a lack of in-depth research on the specific lithological characteristics and zoning of these pegmatites. In this paper,mineralogical,chronological and isotope geochemical analyses of the No. 1 high-purity quartz-bearing pegmatite in this area are carried out on the basis of systematic field geological investigations. The U-Th-Pb dating results of zircon,monazite and columbite indicate that the pegmatite No. 1 was formed in the Early Devonian（ 398 ～ 404Ma）,which is similar to the generation of highly differentiated magmatism on the region. The ε_Hf（ t） and ε_Nd（ t）values of zircon and monazite are -5. 9 ～-5. 2 and -13. 7 ～-11. 5,respectively,suggesting that the pegmatite No. 1 is a product of partial melting of the ancient crust. The pegmatite vein is one of the largest pegmatites in the Longquanping area with 400 meters long and 5 meters wide,and mainly contains quartz,potassium feldspar,albite,tourmaline and mica. The No. 1 vein has obvious symmetrical structural zoning,which can be divided into quartz-potassium feldspar-albite-mica-biotite-tourmaline outer zone,quartzpotassium feldspar-albite-mica inner zone,and quartz core zone from outside to inside. Detailed microscopic observations revealed two types of quartz are developed in all three phases. Quartz（ Ⅰ） is massive and located in the core,with brighter cathodoluminescence images,indicating a primary crystallization property; quartz（ Ⅱ） is granular and located in the edge,with darker cathodoluminescence images,suggesting a recrystallization property. LA-ICP-MS analyses show that quartz（ Ⅰ） is more enriched in Li,Al and Ti than quartz（ Ⅱ） in different lithologies,which is relatively unfavorable to high-purity quartz,suggesting that the later modification recrystallization can effectively reduce the content of impurity elements in quartz. Compared with the outer zone and the core,the inner zone quartz has significantly lower contents of Li and Al,and comparable contents of Ti,B,Na,and Ge,suggesting that the quartz in this zone has more potential to become high-purity quartz. The above studies show that the obvious composition changes of quartz in pegmatites with different zoning are important problems for high-purity quartz exploration.更多还原