塔吉克斯坦东杜奥巴金矿床岩脉矿体岩石学、地球化学及成矿年代学研究

The research of petrology geochemistry and geochronology of ore-bearing granitic in Dongduaoba gold deposit,Tajikistan

东杜奥巴金矿床位于中亚造山带西南天山褶皱系的西端,区域内岩浆岩体总体呈北西-南东向展布,单个岩体呈岩枝或岩脉状产出。岩体的主要岩性为偏碱性-中酸性的二长岩、二长花岗岩、石英二长岩。其中,部分岩石为赋矿岩石,并对成矿有一定的控制作用。本次研究对6件岩浆岩进行了岩石学、全岩地球化学分析,并对其中4件样品进行了LA-ICP-MS锆石U-Pb定年分析,厘定了成岩成矿时限和构造环境。样品为亚碱-高钾钙碱性的准铝质岩石,属二长岩-石英二长岩系列:SiO2含量变化范围为57.34%~64.13%,K2O含量为3.40%~4.65%,Na2O含量为3.29%~6.17%,全碱含量(ALK)为7.13%~9.57%,固结指数(SI)为10.42~19.95,分异指数(DI)为65.75~94.06,碱度率(A.R.)为2.2~3.78,里特曼指数(σ)为2.52~5.54。岩石稀土总量偏低,∑REE变化于60.93×10^(-6)~133.37×10^(-6)之间,轻重稀土分异明显,显示出右倾的球粒陨石标准化REE配分曲线,HREE曲线相对平坦,其(La/Yb)N=5.45~22.53,(La/Sm)N=2.46~4.28,Nb/Ta值在5.02~8.29之间,并表现出大离子亲石元素K、Rb、U明显富集,高场强元素Nb、Ta、P、Ti相对亏损的特征,并且具有Hf、La和Ce的正异常以及Sr负异常。此外,岩石显示出壳型-壳幔型的主量元素特征,表明岩浆演化过程中可能有幔源物质的加入。LA-ICP-MS锆石U-Pb定年结果显示,206Pb/238 U加权平均年龄值为284.8±2.1Ma(MSWD=2.2),表明东杜奥巴金矿岩脉矿体形成于早二叠世。结合区域地质背景,本文认为该矿床成矿作用发生于晚古生代活动陆缘半成熟的岛弧环境,且偏碱性-中酸性岩浆的产生对金矿的形成具有重要的意义。

Dongduaoba Gold Orefield is located in the western part of the system of folds in south Tianshan of Central Asia Orogenic Belt.The ore-bearing magmatic rock in this field is represented by NW-SE directionally distributed apophysis or vein-like exposed.The magmatic rock is mainly composed of subalkaline-intermediate-acidic monzonite,monzogranite and adamellite.Some rocks are ore-bearing,and play some controlling role in mineralization.In this research,6 ore-bearing magmatic rock samples were collected to carry out whole-rock geochemical analysis,and LA-ICP-MS zircon U-Pb dating analysis on 4 of these 6 samples;on this basis,the diagenetic mineralization time frame and tectonic environment were determined.These samples are mainly Al-Pertarenite rocks of subalkaline-high-k of ca-alkaline,which are belong to monzonite-adamellite.The content of SiO2,K2 O,Na2 O,ALK,solidification index(SI),differentiation index(DI),alkalinity ratio(AR)and Rittmann index(σ)ranges from 57.34%~64.13%,3.40%~4.65%,3.29%to 6.17%,7.13%~9.57%,10.42~19.95,65.75~94.06,2.2~3.78 and 2.52~5.54 respectively.The total content of rare earth elements is low,andΣREE is between 60.93×10-6~133.37×10-6.There is significant differentiation between light and heavy REEs.These rocks can be represented by a normalized REE distribution curve of right-handed chondrites.However,HREE curves are relatively flat.(La/Yb)N =5.45~22.53,(La/Sm)N =2.46~4.28.LILEs like K,Rb and U are accumulated while HFSEs like Nb,Ta,P and Ti are depleted,Hf,La and Ce shows positive anomalies while Sr shows negative anomalies.Additionally,the negative Eu is not very significant(δEu=0.23~0.35),indicating that the source area may contain many depleted mantle components.Besides,major elements of the rocks represent the characteristics of crust type and crust-mantle type,indicating possible addition of mantle-derived material in the process of magma evolution.LA-ICP-MS zircon U-Pb dating results show that the 206 Pb/238 U weighted average age of 4 ore-bearing rock samples is 284.8±2.1 Ma(MSWD=2.2),indicating that the ore-bearing magmatic in Dongduaoba Gold Orefield was formed in the Early Permian.Based on the regional geological background,it is believed that the mineralization in the region occurred in the semi-mature island arc environment of the Late Paleozoic Active Continental Margin,and the formation of subalkaline-intermediate-acidic magmas was of great significance to the formation of gold ore.