老挝爬奔金矿沉积环境及矿床成因研究

Study on Sedimentary Environment and Genesis of the Phapon Gold Deposit in Laos

爬奔金矿位于老挝西北部琅勃拉邦构造带,是该带内迄今为止发现的唯一大型金矿床。为了解该矿床形成时的沉积环境及矿床成因,对矿区的岩石及矿石进行了微量元素、稀土元素及同位素等方面的地球化学特征研究。矿区岩石的微量元素特征表明,矿床形成时处于相对缺氧的沉积环境;矿石的硫、氢、氧、碳同位素特征证明岩浆流体参与了成矿作用;Eu异常特征说明围岩灰岩不是矿床的成矿母岩;Ce异常特征表明矿区形成于水体深度适中的氧化还原界面附近;Y/Ho特征也说明金矿床与围岩灰岩的源区不同。通过与我国滇黔桂地区的卡林型金矿进行对比研究,爬奔金矿虽然在诸多方面与卡林型金矿有着相似之处,但两者之间更多的是差异性。综合研究认为,爬奔金矿应为与岩浆有关的热液矿床。

The Phapon gold deposit is located in the Luang Prabang tectonic belt in northwestern Laos.It is the only large-size gold deposit discovered in this belt so far.In order to understand the depositional environment and genesis of this gold deposit,this work studied the geochemical characteristics of trace elements,rare earth elements and isotopes of rocks and ores in the mining area.The trace elements characteristics of the sedimentary rocks indicate that the deposit was formed in a relatively anoxic environment,while the characteristics of sulfur,hydrogen,oxygen and carbon isotopes of the ore imply that the magmatic fluid has participated in the mineralization.The Eu anomalies demonstrate that the wall rock(limestone)is not the ore-forming parent rock of the deposit.The Ce anomalies suggest that the mining area was generated near a redox interface with moderate water depth;and the Y/Ho characteristics also indicate that the source of ore-forming material of the deposit is different from wall rock(limestone).In comparison with Carlin-type gold deposits in Yunnan,Guizhou and Guangxi of China,although the Phapon gold deposit has some similarities with Carlin-type gold deposits in many aspects,differences between them are dominant.The comprehensive study suggests that the Phapon gold deposit should be a hydrothermal deposit related with magma.