西藏谢通门县雄村铜金矿主要地质体的^(40)Ar/^(39)Ar年龄及地质意义  

^(40)Ar/^(39)Ar isotope ages of main geological bodies in Xiongcun copper-gold deposit,Xietongmen County,Tibet,and their geological significance

作　　者：唐菊兴[1] 张丽[2] 黄勇[3,4] 王成辉[1] 李志军 邓起 郎兴海[3,4] 王友[4] 

机构地区：[1]中国地质科学院矿产资源研究所,北京100037 [2]中国地质调查局成都地质调查中心,四川成都610081 [3]西藏天圆矿业资源开发有限公司,西藏日喀则857000 [4]成都理工大学能源学院,四川成都610059

出　　处：《矿床地质》2009年第6期759-769,共11页Mineral Deposits

基　　金："十一五"国家科技支撑计划项目(编号2006BAB01A01);国家基础研究计划(973项目)"印度-亚洲大陆主碰撞带成矿作用"(2002CB412607)的联合资助

摘　　要：雄村铜金矿Ⅱ号矿体在2007～2008年取得了重大的找矿突破,详细的地质编录成果表明,矿体同样受含眼球状石英斑晶的角闪石英闪长玢岩和角闪石英闪长玢岩控制。含眼球状石英斑晶的角闪石英闪长玢岩和角闪石英闪长玢岩的锆石U-Pb年龄已经确定(164～177Ma),因此,雄村铜金矿不同地质体的云母类、长石类矿物Ar-Ar同位素年龄的测定显得尤为关键。文章通过对穿切I号矿体的黑云母花岗闪长岩、云煌岩脉的黑云母Ar-Ar同位素测年,结合其他研究者的成果,得到一组十分重要的年龄数据。穿插矿体的黑云母花岗闪长岩中的黑云母(样号6187-335)坪年龄(46.96±0.42)Ma,穿插矿体的无矿化的云煌岩(5053-324-4)(Cu含量0.0551%,Au含量0.034g/t,Ag0.6g/t)中的黑云母给出了一个较好的似坪年龄,加权平均年龄为(49.59±0.58)Ma。结合其他研究者测定的中侏罗世侵位的角闪石英闪长玢岩(不含矿)〔锆石U-Pb年龄为(177.1±2.0)Ma〕中黑云母的Ar-Ar同位素年龄为(48.57±0.31)Ma;含矿凝灰岩围岩〔锆石U-Pb年龄为(176±5)Ma,MSWD=0.63〕的蚀变绢云母Ar-Ar年龄为(47.07±0.30)Ma;似伟晶岩中长石的Ar-Ar年龄为(47.62±0.7)Ma,认为不同形成时代、不同产出空间、不同矿化程度的地质体的云母类、长石类矿物的Ar-Ar同位素年龄的一致性,反映了后期岩浆热事件对中侏罗世早期形成的地质体和矿体的黑云母氩同位素体系产生了较强的扰动或置换。谢通门大岩基黑云母花岗闪长岩的侵位致使各地质体发生显著的退变质,形成典型的角岩化带,这种退变质的时限在46～48Ma之间的始新世lutetian期,进而认为各地质体中云母类矿物的40Ar/39Ar同位素年龄不能作为成矿年龄。The exploration of No.II ore body in the Xiongcun copper-gold deposit made signi ficant breakthrough during 2007-2008. Detailed core logging shows that the depo sit is controlled by augen quartz hornblende diorite porphyry and hornblende dio rite porphyry. The zircon U-Pb ages of augen quartz hornblende diorite porphyry and hornblende diorite porphyry are 164-177 Ma, indicating that the Ar-Ar ages of mica and feldspar minerals within different rock types are especially importa nt. In this paper, the authors got a group of age data based on biotite Ar-Ar is otopic dating of biotite granodiorite and lamprophyre in combination with th e re sults obtained by other researchers. The plateau age of biotite （Sample No. 6187 -335） within biotite granodiorite is （46.96±0.42） Ma. The surface ages of six consecutive heating stages are the same within the error range. Released 39Ar accounts for 94.6 % of total 39Ar. The surface ages of the f irst two heating stages are lower than the plateau age. The content of radiogeni c argon accounts for a small percentage of released radioactivity argon at these two stages. This means that the biotite surface was subjected to a very slight loss of argon. At the same time, a small amount of atmospheric argon was adsorbe d on the mineral surface or mixed with the outer crystal lattice of the mineral. The samples don＇t contain excessive argon and have not been polluted by post-ma gmatic minerals, as evidenced by an analysis of the surface age. The formation o f biotite was not subjected to significant thermal event interference, sugge stin g that there did not exist significant heating-magma events after the formation of biotite granodiorite. Argon isotopes are in a closed state. The ages of antiisochron are （46.72±0.81） Ma and （46.84±0.67） Ma respectively , the same as the plateau age in the same error range. This proves that the biot ite cooling age of 46-47 Ma is reliable. According to the intercept from anti-i sochron to the 36Ar/40Ar axis, the initial rati o of 36A

关 键 词：地球化学 AR-AR年龄 退变质 斑岩成矿作用 雄村铜金矿 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]