玉龙铜矿带马拉松多斑岩体岩石学及成岩成矿系统年代学分析  

Study on geochemical composition and isotope ages of the Malasongduo porphyry associated with Cu-Mo mineralization.

作　　者：梁华英[1] 莫济海[1] 孙卫东[1] 张玉泉[1] 曾提[1] 胡光黔[1] Charllote ALLEN 

机构地区：[1]中国科学院广州地球化学研究所,广州510640 [2]澳大利亚国立大学地球科学研究院

出　　处：《岩石学报》2009年第2期385-392,共8页Acta Petrologica Sinica

基　　金：中国科学院创新项目(KZCX2-YW-QO4-2);国家自然科学基金项目(40772054,40472049)资助

摘　　要：马拉松多斑岩铜钼矿床是玉龙斑岩铜矿带中第二大的大型斑岩铜钼矿床,本文分析了岩体化学组成及用锆石LA-ICP-MS U-Pb法以及黑云母K-Ar法测定了成岩成矿体系同位素年代.赋矿岩体可分为早晚两期,早期岩体主要由石英二长斑岩及碱长花岗斑岩组成,晚期岩体主要由碱长花岗斑岩组成.早期岩体和晚期岩体在化学组成上有一定的差异,早期岩体富Al2O3.MgO,CaO,Na2O,Fe2OT3,TiO2,晚期岩体则相对富SiO2及K2O;马拉松多早期岩体锆石LA-ICP-MS U-Pb年龄(36.9±0.4Ma,MSWD=1.52)与晚期岩体锆石LA-ICP-MS U-Pb年龄(36.9±0.3Ma,MSWD=1.38)相同,也和黑云母K-Ar年龄(36.9±0.6Ma)及前人的辉钼矿Re-Os年龄一致.早期和晚期岩体是在现有同位素体系难以区别的相同的时闻间隔内脉动侵入形成的,马拉松多成岩成矿系统在很短时期内从高温(800℃,锆石U-Pb封闭温度)冷却至中低温(300℃黑云母Ar同位素体系的封闭温度),成岩成矿时间跨度小于1Ma.玉龙矿带主要赋矿岩体锆石年龄表明,玉龙斑岩铜矿带岩浆活动时间跨度4.3Ma内,约发生过四次成岩成矿事件.The Malaosogdou porphyry Cu-Mo deposit is the second largest porphyry Cu-Mo deposit in the Yulong ore belt, eastern Tibet. Geochemical composition, zircon U-Pb, and mica K-Ar isotopic ages of the Malasongduo porphyry are reported here. The Malasongduo porphyry consists mainly of early stage quartz monzonite and K-feldspar porphyry and late stage K-feldspar porphyry. The early stage porphyry and late stage porphyry are different in composition. The first one is relatively rich in Al(2)O(3), MgO, CaO, Na(2)O, Fe(2)O(3)(T), TiO(2) and the second one is relatively rich in K(2)O and SiO(2). The early stage porphyry yields zircon U-Pb age of 36.9 +/- 0.4Ma (MSWD = 1.52) and the late stage porphyry gives zircon U-Pb age of 36.9 +/- 0.3Ma (MSWD = 1.38). Mica K-Ar age of the late stage porphyry that was suffered from potassium alteration is 36.9 +/- 0.6Ma (MSWD = 1.36) The same zircon U-Pb age of both porphyries reveals that the porphyries of these two stages emplaced essentially at the same time. The concordance between zircon U-Pb age, mica K-Ar age and former Re-Os model age for the Malasongduo porphyry suggests that the Malasongduo porphyry ore-froming system cooled down from about 800 degrees C (zircon crystallization temperature) through 500 degrees C (Re-Os closure temperature of molybdenite) to below 300 degrees C (Ar closure temperature of biotite) in a very short time. The lifespan of the Malasongduo ore-forming system is less than 1Ma. Based on the statistics of isotope ages of the main porphyries in the Yulong ore belt, it is also suggested that the duration of magmatic activities in the If Yulong ore-belt is about 4.3Ma and the magmatic-ore-forming activities are less than four stages.

关 键 词：斑岩铜钼矿床 成矿年龄 斑岩成矿系统时间跨度 西藏 

分 类 号：P618.41[天文地球—矿床学] P588.121[天文地球—地质学] P597.3