阿尔泰阿斯喀尔特Be-Nb-Mo矿床年代学、锆石Hf同位素研究及其意义

Geochronology and Hf isotope of zircon for the Arskartor Be-Nb-Mo deposit in Altay and its geological implications

阿斯喀尔特Be-Nb-Mo矿床位于新疆阿尔泰东段可可托海伟晶岩矿集区,Be储量达大型,产出宝石并伴生Nb、Mo、Ga矿化。该矿床同时发育花岗岩型与伟晶岩型两类稀有金属矿化,晚阶段有辉钼矿、黄铁矿等硫化物发育,在阿尔泰伟晶岩省具有独特性。本文对矿区内的白云母钠长花岗岩、Be矿化白云母钠长花岗岩以及条带状伟晶岩进行锆石LA-ICP-MS U-Pb定年及Hf同位素研究,对伟晶岩中不同产状的辉钼矿进行Re-Os同位素定年。获得的锆石238U/206Pb加权平均年龄分别为219.2±2.9Ma、222.6±4.6Ma与218.2±3.9Ma,辉钼矿Re-Os加权平均年龄为218.6±1.3Ma,表明伟晶岩形成稍晚于花岗岩,花岗-伟晶岩系统的演化时间较短;锆石εHf(t)值分别为-0.72^+1.33、-0.36^+1.99与-0.45^+0.38,t DM C模式年龄分别为1169~1298Ma、1130~1279Ma与1229~1282Ma,表明花岗岩与伟晶岩具有类似的源区,以前寒武纪微陆块的壳源物质为主。花岗岩与伟晶岩形成于后造山板内演化阶段,与加厚地壳的熔融有关。根据矿化组合、源区特征并结合大地构造背景,提出阿斯喀尔特伟晶岩属于LCT型。地质、地球化学及年代学特征表明白云母钠长花岗岩为伟晶岩的成矿母岩。

Located in the Koktokay pegmatitic ore cluster,eastern Altay,the Arskartor Be-Nb-Mo deposit is a large beryllium deposit,bearing gemstone and associated with Nb,Mo,and Ga mineralization. Rare-mental mineralization was developed both in granite and pegmatite,with sulfides like molybdenite and pyrite formed in the late stage,which is unique in Altai pegmatite province.A study of LA-ICP-MS zircon U-Pb dating combined with Hf isotope analysis on the muscovite-albite granite,beryllium-mineralized muscovite-albite granite and striped pegmatite is conducted,Re-Os dating of molybdenite from different zones of pegmatite is carried out as well. Weighted mean206 Pb /238 U ages of zircon are 219. 2 ± 2. 9Ma,222. 6 ± 4. 6Ma and 218. 2 ± 3. 9Ma respectively,molybdenite Re-Os age is 218. 6 ± 1. 3Ma,indicate that the formation of granite followed by pegmatite,and a short evolution history of the graniticpegmatite system. The εHf（ t） values are- 0. 72 ~ ＋ 1. 33,- 0. 36 ~ ＋ 1. 99 and- 0. 45 ~ ＋ 0. 38,with t DM C values of 1298 ~1169Ma,1279 ~ 1130 Ma and 1282 ~ 1229 Ma,respectively,implying that the source area for granite and pegmatite are similar and from the crustal material of Pre-Cambrian micro-continental blocks probably. The granite and pegmatite were formed by melting of thickened crust under an intra-plate tectonic setting during the post-orogenic stage. We infer the Arskartor pegmatite is LCT type from the association of mineralized elements,source material and tectonic setting. Characteristics of geology,geochemistry and geochronology imply that the muscovite-albite granite was the parent pluton for pegmatite.