赣北大湖塘地区昆山W-Mo-Cu矿床侵入岩锆石U-Pb、辉钼矿Re-Os年代学及地质意义

Geochronological Study of the Kunshan W-Mo-Cu Deposit in the Dahutang Area, Northern Jiangxi Province and its Geological Significance

昆山W-Mo-Cu矿床地处赣北九岭矿集区南部,距大湖塘超大型钨矿床狮尾洞矿区仅3 km。矿床目前处于详查阶段,已探明钨达中型规模,同时伴生中型钼矿及小型铜矿,具有良好的找矿潜力。昆山矿床矿化样式较为单一,W-Mo-Cu矿体以石英脉形式产出,主要赋存在燕山期侵入岩顶部与新元古界双桥山群浅变质岩的外接触带,具有＂上钨中钼下铜＂的特点,明显区别于大湖塘矿床矿体主要产在燕山期侵入岩与晋宁期黑云母花岗闪长岩的内外接触带,具细脉浸染型白钨矿、热液爆破角砾岩型钨铜矿及石英脉型黑钨矿＂三位一体＂的矿化特征。本文在详细的野外地质调查基础上,对昆山W-Mo-Cu矿床的成岩成矿时代进行了详细研究,并探讨了其地质意义。利用LA-ICP-MS锆石U-Pb法获得矿区内呈岩株状产出的似斑状花岗岩的年龄为151.7±1.3 Ma,晚期花岗斑岩脉的年龄为136.6±2.5 Ma;利用辉钼矿Re-Os法,获得辉钼矿Re-Os等时线年龄和加权平均年龄分别为151.0±1.3 Ma和150.0±1.0 Ma,厘定矿床成矿时代为晚侏罗世,且与似斑状花岗岩有关。结合前人所得高精度成岩成矿年龄数据,认为赣北地区燕山期成岩成矿具多期性,可分为160~150 Ma（塔前、朱溪钨多金属矿床）、140 Ma（大湖塘钨多金属矿床）和125 Ma（香炉山钨矿）,主要集中于150~140 Ma。晚侏罗世,华南地区全面进入岩石圈＂伸展-减薄＂的地球动力学背景,赣北地区燕山期成岩成矿可能与这一构造背景有关。昆山矿床具＂上钨中钼下铜＂的分带模式,其成因值得进一步研究。

The Kunshan W-Mo-Cu deposit is located in the southern part of the Jiuling tungsten-polymetallic ore concentration region in northern Jiangxi province, which is only 3 km away from the Dahutang tungsten deposit. Being in the exploration and evaluation stage, the proven reserve of the deposit has now reached medium scale for tungsten, and medium scale and small scale for the accompanying molybdenum and copper, respectively. Evidence shows that the Kunshan deposit has a promising prospecting potential. Unlike the ores of the Dahutang deposit that consist of veinlet-dissemination type, hydrothermal-explosion breccia type, and thick-vein type which occur in the upper part of the Yanshanian granite and the contact zone with the Mesoproterozoic granodiorite, the ores of the Kunshan deposit are tungsten, copper and molybdenum bearing quartz veins occurring in the top of the Yanshanian plutons and the contact zone of the Meso-Neoproterozoic Shuangqiaoshan Group low grade metamorphic rocks, and interestingly, the surface to deep ore zonation of W-Mo-Cu is obvious. LA-ICP-MS dating of zircon grains from the porphyritic granite and granite porphyry dikes yielded ages of 151.7±1.3 Ma, and 136.6±2.5 Ma, respectively. Re-Os analysis of five molybdenite separates from quartz veins in the Kunshan deposit yielded a weighted average of the model ages and isochron age of 150.0±1.0 Ma and 151.0±1.3 Ma, respectively, which indicate that the Kunshan W-Mo-Cu deposit was formed in the Late Jurassic and was related to the porphyritic granite. Combined with the regional magmatism and mineralization chronology data from previous researches, it is concluded that the age of magmatism and mineralization in the northern Jiangxi province can be divided to three stages, which are 160~150 Ma（the Taqian and Zhuxi tungsten-molybdenum deposit）, 140 Ma（the Dahutang tungsten-molybdenum deposit）, 125 Ma（the Xianglushan tungsten deposit）, and mostly concentrated in 150-140 Ma. In the Late Jurassic, the lithosphere of South China was in an overall ＂extension and thinning＂ dynamic setting, which may lead to the Yanshanian magmatism and related mineralization in the northern Jiangxi province. The distinctive mineralization zonation of the Kunshan deposit is worth further investigation.