Fluid inclusion study has been carried out for the carbonatite dykes/veins and the ore-hosted dolostone of the Bayan Obo superlarge REE-Fe-Nb deposit in order to provide the evidence and constraint for their origin.Ba...Fluid inclusion study has been carried out for the carbonatite dykes/veins and the ore-hosted dolostone of the Bayan Obo superlarge REE-Fe-Nb deposit in order to provide the evidence and constraint for their origin.Based on the detailed geological observation and mineralogical investigation,the heating and cooling stage and laser Raman spectroscopy were mainly used for the laboratory work of this study.Following results have been obtained:(1)The discovery of melt and melt-fluid inclusions from carbonatite dykes/veins in the Dulahara and Jianshan Mountains,combined with the fine-grained(aplitic)texture of rocks,as well as the types and features of fluid inclusions such as CO_2 enrichment,higher homogenization temperature,provides a direct evidence for the magmatic origin of these dykes/veins.(2)The carbonatite dykes/veins distributed in two regions,nearby the axis of the Kuangou anticline and in the east to Bayan Obo town,mainly show coarse-grained texture.No melt inclusion was found,and the fluid inclusions possess features of less CO_2,lower homogenization temperature and higher salinity.They are tentatively identified as veins formed by some carbonate-rich hydrothermal solution.(3)Bedding carbonate layers/lens within the hanging wall and foot wall of ore-hosted dolostone,previously recognized as of magmatic origin,mainly composed by dolomite.The existence of single phase pure aqueous inclusions with very low homogenization temperature indicates their sedimentary origin.(4)The ore-hosted dolostone possesses apparent bedding and laminated structures.No melt inclusion was found,but,both single phase pure aqueous inclusions and CO_2 bearing multi-phase fluid inclusions coexisted in dolostones.In the direction towards ore-bodies,the homogenization temperature and CO_2 contents of fluid inclusion show an increasing tendency.It indicates the sedimentary origin of dolostone superimposed by late fluid metasomatism.展开更多
越来越多的证据表明,白云鄂博超大型稀土矿床与区内分布的火成碳酸岩有密切的成因联系,因此精确约束碳酸岩的侵位时代对研究成矿历史和机制非常关键.然而,由于后期复杂的热液叠加影响,以往的年代学研究结果大多得到后期扰动事件的年龄,...越来越多的证据表明,白云鄂博超大型稀土矿床与区内分布的火成碳酸岩有密切的成因联系,因此精确约束碳酸岩的侵位时代对研究成矿历史和机制非常关键.然而,由于后期复杂的热液叠加影响,以往的年代学研究结果大多得到后期扰动事件的年龄,而对碳酸岩岩浆活动的启动时间的制约则比较缺乏.为重建白云鄂博碳酸岩型稀土矿的岩浆—热液成矿历史,我们利用SHRIMP离子探针对一号碳酸岩墙(吴氏岩墙)及其蚀变围岩样品开展了薄片原位独居石Th-Pb年代学研究.碳酸岩中最老的独居石记录了其侵入时代1401±39 Ma (MSWD=0.57,n=7),这是首次从白云鄂博的独居石得到碳酸岩初始岩浆年龄,证实白云鄂博碳酸岩可能代表了华北克拉通从Nuna超大陆裂解过程中早期岩浆作用产物.同时,碳酸岩和霓长岩化围岩中的独居石还获得了格林威尔期到加里东期的一系列年龄数据,反映了后期构造热事件的叠加—扰动记录.尤其是,本研究识别出泛非期构造事件的独居石年代学记录(529±17 Ma,MSWD=1.01,n=6)并对其地质意义进行了初步探讨.本文的研究结果和认识为理解白云鄂博碳酸岩型稀土矿的岩浆-热液历史及成矿构造动力学背景提供了新的关键证据,所采用的研究方法对解决类似碳酸岩和稀土矿的年代学问题具有启示意义.展开更多
文摘Fluid inclusion study has been carried out for the carbonatite dykes/veins and the ore-hosted dolostone of the Bayan Obo superlarge REE-Fe-Nb deposit in order to provide the evidence and constraint for their origin.Based on the detailed geological observation and mineralogical investigation,the heating and cooling stage and laser Raman spectroscopy were mainly used for the laboratory work of this study.Following results have been obtained:(1)The discovery of melt and melt-fluid inclusions from carbonatite dykes/veins in the Dulahara and Jianshan Mountains,combined with the fine-grained(aplitic)texture of rocks,as well as the types and features of fluid inclusions such as CO_2 enrichment,higher homogenization temperature,provides a direct evidence for the magmatic origin of these dykes/veins.(2)The carbonatite dykes/veins distributed in two regions,nearby the axis of the Kuangou anticline and in the east to Bayan Obo town,mainly show coarse-grained texture.No melt inclusion was found,and the fluid inclusions possess features of less CO_2,lower homogenization temperature and higher salinity.They are tentatively identified as veins formed by some carbonate-rich hydrothermal solution.(3)Bedding carbonate layers/lens within the hanging wall and foot wall of ore-hosted dolostone,previously recognized as of magmatic origin,mainly composed by dolomite.The existence of single phase pure aqueous inclusions with very low homogenization temperature indicates their sedimentary origin.(4)The ore-hosted dolostone possesses apparent bedding and laminated structures.No melt inclusion was found,but,both single phase pure aqueous inclusions and CO_2 bearing multi-phase fluid inclusions coexisted in dolostones.In the direction towards ore-bodies,the homogenization temperature and CO_2 contents of fluid inclusion show an increasing tendency.It indicates the sedimentary origin of dolostone superimposed by late fluid metasomatism.
文摘越来越多的证据表明,白云鄂博超大型稀土矿床与区内分布的火成碳酸岩有密切的成因联系,因此精确约束碳酸岩的侵位时代对研究成矿历史和机制非常关键.然而,由于后期复杂的热液叠加影响,以往的年代学研究结果大多得到后期扰动事件的年龄,而对碳酸岩岩浆活动的启动时间的制约则比较缺乏.为重建白云鄂博碳酸岩型稀土矿的岩浆—热液成矿历史,我们利用SHRIMP离子探针对一号碳酸岩墙(吴氏岩墙)及其蚀变围岩样品开展了薄片原位独居石Th-Pb年代学研究.碳酸岩中最老的独居石记录了其侵入时代1401±39 Ma (MSWD=0.57,n=7),这是首次从白云鄂博的独居石得到碳酸岩初始岩浆年龄,证实白云鄂博碳酸岩可能代表了华北克拉通从Nuna超大陆裂解过程中早期岩浆作用产物.同时,碳酸岩和霓长岩化围岩中的独居石还获得了格林威尔期到加里东期的一系列年龄数据,反映了后期构造热事件的叠加—扰动记录.尤其是,本研究识别出泛非期构造事件的独居石年代学记录(529±17 Ma,MSWD=1.01,n=6)并对其地质意义进行了初步探讨.本文的研究结果和认识为理解白云鄂博碳酸岩型稀土矿的岩浆-热液历史及成矿构造动力学背景提供了新的关键证据,所采用的研究方法对解决类似碳酸岩和稀土矿的年代学问题具有启示意义.
