【摘要】 近年来,大兴安岭南段维拉斯托矿区深部Sn-Li找矿取得重大突破,但人们目前对与成矿作用密切相关的深部花岗岩体成因与演化及其对稀有金属矿化存在怎样的制约尚不清楚.为此,针对该岩体开展了年代学、地球化学和Sr-Nd-Hf同位素组成研究,获得的锆石LA-ICP-MS U-Pb年龄为130.7±0.5Ma(MSWD=0.53),属早白垩世岩浆活动产物.化学组成上表现为高硅、富碱(高钠),贫钙、镁、铁和极低P2O5(<0.01%)含量特征,铝饱和指数(A/CNK)集中于1.02～1.08,全岩Rb/Sr、Nb/Ta比值高,Zr/Hf比值低(<4).岩体富Cs、Rb、Th、U、Nb、Ta以及Li、F等元素,亏损Ba、Sr、Ti和稀土元素,轻重稀土比值小,并具显著的四分组效应和Eu负异常(δEu=0.02～0.15),锆石饱和温度(691～727℃)和Zr+Nb+Ce+Y含量均低于A型花岗岩,以上综合特征反映其应属准铝-弱过铝质高分异I型花岗岩类.岩体具正的εNd(t)(+1.10～+3.75)值和相对均一的εHf(t)(+4.2～+8.7)以及年轻的二阶段模式年龄(T(Nd)DMC=607～829Ma;T(Hf)DMC=627～914Ma),说明成矿岩体的岩浆源区可能来自于含大量幔源组分新生下地壳的部分熔融.Sn-(稀有)成矿受岩浆后期的高度分异演化和晚期流体-熔体相互作用共同影响,并与外围的脉状矿体共同构成岩浆-热液成矿系统.更多还原

【Abstract】 In recent years,great breakthroughs have been made in the deep Sn-Li prospecting in the Weilasituo area of the southern of Great Xing’an Range.However,the genesis and evolution of deep hidden rock mass closely related to the minerali-zation has not been studied in depth.In this paper,this cancealed granite was selected as example for a detailed geochronological,geochemical and Sr-Nd-Hf isotopic composition study in order to elucidate their petrogenesis.LA-ICP-MS U-Pb zircon age for Weilasituo pluton was 130.7±0.5Ma(MSWD=0.53),indicating that it was generated in Early Cretaceous.Chemically,Weilasituo granite is metaluminous-(weakly)peraluminous(A/CNK concentrated in the range of 1.02-1.08),which shows high contents of silica,alkalis and natrium,low abundances of calcium,magnesium,iron and extremely low P2O5(<0.01%),with high Rb/Sr,Nb/Ta and low Zr/Hf ratios.They are also enriched in Cs,Rb,Th,U,Nb,Ta,Li,F and depleted in Ba,Sr,Ti,REE elements with low LREE/HREE ratios and obviously negative Eu abnormality(δEu=0.02-0.15).Zircon saturation temperatures(691-727℃)and Zr+Nb+Ce+Y contents of Weilasituo pluton are less than those of the low-limit values of the A-type granite.Integrated geological and geochemical data suggest that the pluton was highly fractionated I-type granite.The granite has positiveεNd(t)(+1.10-+3.75)and relatively highεHf(t)(+4.2-+8.7)and young two-stage Nd and Hf model ages(T(Nd)DMC=607-829Ma;T(Hf)DMC=627-914Ma),suggesting that the rock was dominantly derived from the partial melting of a juvenile lower crust with a mass of mantle magma mixed into the crust,followed by fractional crystallization during magma ascent.The Sn-(rare-metal)mineralization of the pluton was controlled jointly both by high fractionation of the magma and fluid-melt interaction during the late stage.A complete magmatic-hydrothermal system was revealed by the Sn-(rare-metal)mineralization granite with the surrounding vein ore bodies.更多还原