Re-Os isotope dating of molybdenite from Shangalon Cu-Au deposit in the Wunto-Popa magmatic arc, Myanmar and its geological significance
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摘要:
Shangalon铜金矿床位于缅甸Wunto-Popa岩浆弧北段，研究工作薄弱，其成矿地质背景和矿床成因尚缺乏高精度同位素成矿年代学数据的制约。本文选取典型矿石中5件辉钼矿样品通过Re-Os同位素定年方法厘定成矿时代，获得的模式年龄集中变化于38.5±0.6至38.3±0.5 Ma，加权平均年龄为38.4±0.2 Ma，对应的等时线年龄为38.0±1.6 Ma（MSWD=0.17），二者在误差范围内基本保持一致，指示Shangalon铜金矿床的成矿时限为始新世，该年龄数据与矿区的含矿闪长岩和花岗闪长岩锆石U-Pb年龄38~40 Ma相吻合，表明Shangalon Cu-Au-Mo成矿作用与始新世闪长岩–花岗闪长岩侵入体密切相关，为始新世岩浆活动的产物。Shangalon铜金矿床辉钼矿样品的Re含量为82.4~111.2 μg·g－1，平均值为98.88 μg·g－1，指示成矿物质具有壳幔混源的特征。通过综合分析区域成矿动力学背景，认为Shangalon地区始新世铜金成矿作用可能形成于印度与欧亚大陆碰撞背景下的新特提斯洋板片撕裂和断裂，诱发软流圈上涌，新生下地壳部分熔融。
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关键词:
- 辉钼矿 /
- Re-Os同位素定年 /
- Shangalon铜金矿床 /
- Wunto-Popa岩浆弧 /
- 缅甸
Abstract:The Shangalon copper-gold deposit is located in the northern segment of the Wunto-Popa magmatic arc in Myanmar. The research on this deposit is limited, and there is a lack of high-precision isotopic geochronological data regarding its ore-forming geological background and deposit genesis. In this study, five molybdenite samples from typical ores were selected to determine the mineralization age using the Re-Os isochron dating method. The obtained model ages range from 38.3±0.6 to 38.5±0.5 million years ago (Ma), with a weighted average age of 38.4±0.2 Ma. The corresponding isochron age is 38.0±1.6 Ma (MSWD=0.17). Both ages are in good agreement within the error range, indicating that the mineralization timing of the Shangalon copper-gold deposit is in the Eocene epoch. This age data corresponds well with the zircon U-Pb ages of 38 to 40 million years for the mineralized syenogranite and granodiorite in the mining area, suggesting a close relationship between the Shangalon Cu-Au-Mo mineralization and Eocene syenogranite-granodiorite intrusions, which are products of Eocene magmatic activity. The Re contents of molybdenite samples from the Shangalon copper-gold deposit range from 82.4 to 111.2 μg·g－1, with an average value of 98.88 μg·g－1, indicating a mixed source from the crust and mantle for the mineralizing fluids. Based on a comprehensive analysis of the regional metallogenic dynamics, it is suggested that the Eocene copper-gold mineralization in the Shangalon region possibly formed as a result of the fragmentation and faulting of the Neo-Tethys oceanic plate, triggered by the collision between the Indian and Eurasian continents, leading to upwelling of the asthenosphere and partial melting of the lower crust.
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Key words:
- molybdnite /
- Re-Os isotopic ages /
- Shangalon Cu-Au deposit /
- Wunto-Popa magmatic arc /
- Myanmar
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图 1 缅甸地质构造格架（据Gardiner et al., 2016修改）
Figure 1.
图 2 Shangalon铜金矿区地质图（据Mitchell, 2018修改）
Figure 2.
图 5 Shangalon矿床成矿动力学模型（据Li et al, 2018修改）
Figure 5.
表 1 Shangalon矿床辉钼矿Re-Os同位素测试数据
Table 1. Analytical data of Re-Os isotope from the Shangalon deposit
样品编号 样重/g Re/ ng·g－1 普Os/ ng·g－1 187Re/ ng·g－1 187Os/ ng·g－1 模式年龄/Ma 测定值 不确定度 测定值 不确定度 测定值 不确定度 测定值 不确定度 测定值 不确定度 D10-b2 0.01001 96969 760 0.0006 0.0200 60947 478 38.97 0.26 38.36 0.55 D10-b1 0.01543 103259 839 0.0007 0.0152 64900 527 41.60 0.25 38.46 0.54 D10-b3 0.01534 100550 756 0.0007 0.0148 63198 475 40.32 0.26 38.28 0.53 D10-b4 0.01504 111202 1000 0.0007 0.0152 69893 628 44.67 0.27 38.35 0.56 D10-b5 0.01510 82434 614 0.0007 0.0088 51812 386 33.21 0.19 38.47 0.53 注：Re、Os含量的不确定度包括样品和稀释剂的称量误差、稀释剂的标定误差、质谱测量的分馏校正误差、待分析样品同位素比值测量误差，置信水平95%；由于采用混合稀释剂，模式年龄的不确定度不包括稀释剂和样品的称量误差，但依然包括衰变常数的不确定度1.02%，模式年龄置信水平95%。 
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