Zircon U-Pb, molybdenite Re-Os and muscovite Ar-Ar isotopic dating of the Xitian W-Sn polymetallic deposit, eastern Hunan Province, South China and its geological significance
Zircon U-Pb, molybdenite Re-Os and muscovite Ar-Ar isotopic dating of the Xitian W-Sn polymetallic deposit, eastern Hunan Province, South China and its geological significance
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湘东西田钨锡多金属矿床锆石U-Pb、辉钼矿Re-Os和白云母Ar-Ar同位素定年及其地质意义
DOI：
10.1016/j.oregeorev.2016.03.018
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发表时间：
2016
影响因子：
3.3
通讯作者：
Shan Yehua
中科院分区：
文献类型：
--
作者：
Liang Xinquan;Dong Chaoge;Jiang Ying;Wu Shichong;Zhou Yun;Zhu Haofeng;Fu Jiangang;Wang Ce;Shan Yehua
西田钨锡多金属存款矿床是南岭钨锡成矿区近年来发现的最大的钨锡矿床之一。该存款的矿化带包括矽卡岩，云英岩，构造蚀变岩和石英脉类型。该存款主要产于与锡田花岗杂岩接触的泥盆系绿泥质灰岩中。锡田花岗岩杂岩由印支期（晚三叠世，230-215 Ma）和燕山期（晚侏罗世-早白垩世，165-141 Ma）花岗岩组成。采用激光烧蚀-电感耦合质谱法（LA-ICPMS）对两个西田花岗岩样品进行锆石U-Pb年龄测定，得到两个年龄值，分别为225.6 ± 1.3Ma和151.8 ± 1.4Ma，代表了西田岩体中两个幕式侵入体的侵位年龄。含矿石英脉中辉钼矿的Re-Os等时线年龄为149.7 ± 0.9Ma，与150.3 ± 0.5Ma的加权平均年龄非常吻合。含矿云英岩中的两个白云母样品的40 Ar/39 Ar坪年龄分别为149.5 ± 1.5Ma和149.4 ± 1.5Ma。这些热液矿物的同位素年龄比西田地区燕山期花岗岩的锆石U-Pb年龄（151.8 ± 1.4Ma）稍年轻，表明钨锡成矿作用与晚侏罗世岩浆活动有成因联系。西田存款矿床是南岭地区燕山早期（160-150 Ma）区域钨锡成矿事件的一个典型代表。辉长岩中相对较高的Re含量（8.7 ~ 44.0ppm，平均30.5ppm）表明成矿流体和熔体的成因是幔源和壳源的混合。通过对西田早燕山期花岗岩地球化学特征的研究，结合区域地质特征，认为西田钨锡多金属存款矿床的成因是弧后岩石圈拉张作用，其拉张作用可能是古太平洋板块在岩石圈之下的板块断裂所致。
The Xitian tungsten–tin (W–Sn) polymetallic deposit, located in eastern Hunan Province, South China, is a recently explored region containing one of the largest W–Sn deposits in the Nanling W–Sn metallogenic province. The mineral zones in this deposit comprise skarn, greisen, structurally altered rock and quartz-vein types. The deposit is mainly hosted by Devonian dolomitic limestone at the contact with the Xitian granite complex. The Xitian granite complex consists of Indosinian (Late Triassic, 230–215 Ma) and Yanshanian (Late Jurassic–Early Cretaceous, 165–141 Ma) granites. Zircons from two samples of the Xitian granite dated using laser ablation-inductively coupled mass spectrometer (LA-ICPMS) U–Pb analysis yielded two ages of 225.6 ± 1.3 Ma and 151.8 ± 1.4 Ma, representing the emplacement ages of two episodic intrusions of the Xitian granite complex. Molybdenites separated from ore-bearing quartz-veins yielded a Re–Os isochron age of 149.7 ± 0.9 Ma, in excellent agreement with a weighted mean age of 150.3 ± 0.5 Ma. Two samples of muscovites from ore-bearing greisens yielded40Ar/39Ar plateau ages of 149.5 ± 1.5 Ma and 149.4 ± 1.5 Ma, respectively. These isotopic ages obtained from hydrothermal minerals are slightly younger than the zircon U–Pb age of 151.8 ± 1.4 Ma of the Yanshanian granite in the Xitian area, indicating that the W–Sn mineralization is genetically related to the Late Jurassic magmatism. The Xitian deposit is a good example of the Early Yanshanian regional W–Sn ore-forming event (160–150 Ma) in the Nanling region. The relatively high Re contents (8.7 to 44.0 ppm, average of 30.5 ppm) in molybdenites suggest a mixture of mantle and crustal sources in the genesis of the ore-forming fluids and melts. Based upon previous geochemical studies of Early Yanshanian granite and regional geology, we argue that the Xitian W–Sn polymetallic deposit can be attributed to back-arc lithosphere extension in the region, which was probably triggered by the break-off of the flat-slab of the Palae-Pacific plate beneath the lithosphere.