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首页> 外文期刊>Contributions to Mineralogy and Petrology >Trace element geochemistry by laser ablation ICP-MS of micas associated with Ta mineralization in the Tanco pegmatite, Manitoba, Canada
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Trace element geochemistry by laser ablation ICP-MS of micas associated with Ta mineralization in the Tanco pegmatite, Manitoba, Canada

机译：通过激光烧蚀ICP-MS对加拿大马尼托巴省Tanco伟晶岩中与Ta矿化有关的云母进行微量元素地球化学分析

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摘要

In the Tanco pegmatite, one of the world’s major Ta deposits, tantalum mineralization shows a complexity that reflects the complex petrogenesis of its host pegmatite. Micas are common in most of the pegmatite units and are intimately associated with the successive stages of Ta mineralization, from the wall zone to the central zones where micaceous replacement is pervasive. Different generations of micas, both primary and secondary, associated with Ta oxides, were selected for electron microprobe and laser ablation ICP-MS investigation. Their chemical trends are used to constrain the magmatic versus hydrothermal processes that played a role in their crystallization and their associated Ta mineralization. Micas range from dioctahedral muscovite to trioctahedral lepidolite through Al↔Li substitution. Unexpectedly, the most evolved compositions (low K/Rb ratios and high Li contents) occur in the wall zone; they are interpreted to reflect nonequilibrium crystallization from an undercooled melt, with or without boundary layer effects. In the central zones, the fine-grained mica–quartz assemblage hosts some coarser-grained Li-muscovite, which has the highest Ta contents (up to 400 ppm). These Li–F–a-rich micas are interpreted to originate from a magmatic metasomatic event, which was also at the origin of the MQM-style Ta mineralization at Tanco. However, the Li–Ta-poor, muscovite end-member compositions of fine-grained alteration micas suggest crystallization from an aqueous fluid, during a metasomatic (hydrothermal) event involving late pegmatitic fluids. The low Ta concentrations (around 50 ppm) of this fine-grained muscovite suggest that this fluid transported at least small amounts of Ta.
机译：在世界主要的钽矿床之一的坦科伟晶岩中，钽矿化显示出复杂性，反映了其宿主伟晶岩的复杂成岩作用。云母在大多数伟晶岩单元中很常见，并且与Ta矿化的连续阶段密切相关，从壁区到云母替代普遍存在的中心区。选择了与Ta氧化物相关的第一代和第二代云母的不同世代，用于电子微探针和激光烧蚀ICP-MS研究。它们的化学趋势被用来限制岩浆和热液过程，它们在其结晶和与其相关的钽矿化中发挥了作用。通过Al↔Li取代，云母的范围从二面体白云母到三面体锂云母。出乎意料的是，析出最多的成分（低K / Rb比和高Li含量）出现在壁区。它们被解释为反映了过冷熔体的非平衡结晶，有无边界层效应。在中部地区，细粒云母-石英组合具有一些较粗粒的锂白云母，其锂含量最高（达400 ppm）。这些富含Li–F–a的云母被解释为源自岩浆交代事件，这也是Tanco的MQM型Ta矿化的起源。但是，在涉及较晚的岩溶流体的交代（水热）事件中，贫锂云母的白云母末端成员组成的细粒蚀变云母表明从含水流体中结晶出来。这种细粒白云母的低Ta浓度（约50 ppm）表明该流体至少运输了少量Ta。

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