德兴矿集区花岗闪长斑岩锆石U-Pb年龄、Hf同位素特征及其意义

摘要

德兴矿集区位于赣东北地区,是中国东部中生代钦杭成矿带中的大型铜金铅锌矿集区之一,集中了铜厂、富家坞和朱砂红斑岩铜钼(金)矿、银山银铜铅锌多金属矿和金山金矿等大型、超大型矿床.本文在系统的野外地质调查与样品采集的基础上,对铜厂、富家坞、朱砂红及银山花岗闪长斑岩进行了LA-MC-ICP-MS锆石U-Pb定年和原位Hf同位素分析.德兴矿集区花岗闪长斑岩的LA-MC-ICP-MS锆石U-Pb的4组年龄分别为:(171±1.2)Ma(铜厂)、(172±0.68)Ma(富家坞)、(173±1.3)Ma(朱砂红)、(176±1.5)Ma(银山),表明这些岩体均为中侏罗世的产物.样品Hf两阶段模式年龄平均值分别为861Ma、876Ma、904Ma和941Ma,正的εHf(t)平均值在4.34～5.54,Zr/Hf比值接近于上地幔的Zr/Hf比值.锆石Hf同位素组成显示,岩浆源区主要来源于亏损地幔组分,但在岩浆演化中遭受了古老地壳物质的混染,幔源物质在德兴矿集区花岗闪长斑岩的形成过程中发挥了重要作用.德兴矿集区4个矿床成岩成矿的最重要时期在170～175Ma,该矿集区岩浆热液系统持续活动可能是该大型矿集区形成的重要原因.%The Dexing ore concentration area located at the juncture between Qiantang body and Jiangnan body is one of the large ore concentration areas along the Qinhang metallogenic belt of eastern China. It includes Tongchang, Fujiawu and Zhushahong porphyry Cu-Mo-Au deposits, Yinshan Ag-Cu-Pb-Zn polymetallic deposit, Jinshan gold deposit and other large and superlarge ore deposits. Based on systematic field geological survey and sample acquisition, this paper presents in situ zircon U-Pb and Hf-isotopic data of Tongchang, Fujiawu, Zhushahong and Yinshan deposits: 171 ± 1.2 Ma for Tongchang, 172 ±0.68 Ma Ma for Fujiawu, 173 ± 1.3Ma for Zhushahong, and 176 ± 1.5 Ma Ma for Yinshan. These data show that all the granodiorite-porphyry bodies were formed in the Early-Middle Jurassic period. Zircon in-situ analysis of four samples gives the average εHf (t) values of (4.34～5.54) with limited variation and Hf crustal model ages of 861Ma, 876 Ma, 904 Ma and 941 Ma. The Zr/Hf ratios are close to the Zr/Hf ratio of the upper mantle . Zircon Hf isotopic composition suggests that the parental magmas of the rock bodies were mainly derived from a young mande and partly mixed with old continental crust rock during the evolution. Mande material in the Dexing ore concentration area played an important role in the formation of the granodiorite porphyry. The most important rock-forming and ore-forming period of the four deposits should be in 170 ～ 175 Ma. The continual magmatic hydrothermal activation might have been the important factor responsible for the formation of the Dexing ore district.