三个锆石U-Pb SHRIMP年龄对雄村特大型铜金矿床容矿火成岩时代的重新厘定  

Collation of age of ore-hosting volcanics in Xiongcun superlarge Cu-Au deposit on basis of three zircon U-Pb SHRIMP ages

作　　者：曲晓明[1] 辛洪波[1] 徐文艺[1] 

机构地区：[1]中国地质科学院矿产资源研究所,北京100037

出　　处：《矿床地质》2007年第5期512-518,共7页Mineral Deposits

基　　金："973"项目<印度与亚洲大陆主碰撞带成矿作用>(项目编号:2002CB412605)资助

摘　　要：位于冈底斯造山带中西段的雄村特大型铜金矿床产于日喀则弧前盆地北缘的旦狮庭组火山岩中。文章通过对雄村矿床矿体外围英安斑岩、矿带内花岗闪长斑岩脉和矿体深部花岗闪长斑岩3个样品的锆石U-Pb SHRIMP年龄测定,获得成岩年龄分别为(195±4.6)Ma(MSWD=1.48)、(179±5)Ma(MSWD=2.6)和(175±5)Ma(MSWD=3.2),表明这套火山岩是形成于早侏罗世而不是此前一致公认的晚白垩世。在已知成矿时代为始新世(38.11Ma)的情况下,这些早侏罗世容矿火山岩时代的确定自然就排除了该矿床属斑岩型或海底喷流沉积型成因的可能性。另外,矿床受NWW向断裂破碎带控制,缺少浅成低温热液矿床的蚀变矿化组合,成矿流体具有岩浆水与大气水混合特征,矿石硫化物与容矿火山岩具有一致的S、Pb同位素组成。这些成矿特征与胶东焦家式金矿具有很大的相似性,推测该矿床很可能属于破碎带蚀变岩型铜金矿床。The superlarge Xiongcun copper-gold deposit in the west-central segment of the Gangdese orogenic belt occurs in volcanic rocks of Danshiting Formation, and its origin remains a problem of controversy. In this paper, zircon U-Pb SHRIMP dating was made for three whole-rock samples collected separately from the dacite porphyry outside the ore body, a granodiorite porphyry dyke within the deposit and the granodiorite porphyry at the depth of 366 m in a drill hole, and the result shows that their formation ages are （195± 4.6） Ma with MSWD = 1.48, （ 179± 5） Ma with MSWD = 2.6 and （ 175 ± 5） Ma with MSWD = 3.2, respectively. These ages suggest that this volcanic suite was formed in Early Jurassic instead of formerly widely-accepted Late Cretaceous. If this age collation is valid for the whole Rigaze forearc basin, the generation age of the Rigaze forearc basin as well as the collision history of the Indian plate with the Eurosian continent should be wholly reconsidered. Under the background that the ore-forming age is already known （38.11 Ma）, the age data of the Early Jurassic orehosting volcanics naturally rule out the possibility that the Xiongcun Cu-Au deposit belongs genetically to theporphyry or seafloor-exhalation type. This Cu-Au deposit is controlled by a NWW-trending fault and lacks the alteration-mineralization association typical of an epithermal deposit. Its ore-forming fluids are characterized by mixture of magmatic and meteoric water, and its ore sulfides contain the same S and Pb isotopic compositions as the ore-hosting volcanics. All these metallogenic features reflect great similarity to the Jiaodong ＂Jiaojia-style＂ gold deposits. The authors therefore tend to believe that the Xiongcun superlarge deposit belongs probably to thealtered cataclastite type Cu-Au deposit.

关 键 词：地球化学 锆石 U-Pb SHRIMP年龄 容矿火山岩 雄村铜金矿床 冈底斯 西藏 

分 类 号：P618.41[天文地球—矿床学] P618.51[天文地球—地质学]