Controls on REE ore formation in peralkaline igneous complexes: Insights from the deposits at Thor Lake, Northwest Territories

从环保混合动力汽车的开发到更强大的激光和超磁材料的技术突破，正在创造对REE的强劲需求。目前，97%的稀土生产来自中国的矿藏，这限制了这种商品的出口。目前在加拿大西北部雷尔湖勘探的矿藏有可能填补这一迫在眉睫的短缺。这些矿床主要赋存于一个大型的硅质不饱和过碱性侵入岩中。最重要的是，与其他地方类似但不经济的矿床不同，雷神湖的矿床经历了强烈的热液蚀变，这增强了稀土矿化。拟议研究的目的是扩大作为最近NSERC-CRD项目的一部分进行的研究，该项目证明稀土矿化赋存于层状火成杂岩中，原生稀土浓缩是通过分离结晶和形成富稀土堆积物实现的，而热液进一步浓缩了稀土。本申请中提出的研究将确定形成Nechalacho矿床上下部矿带的堆积锆石和真透析物的产生机制，以及允许Nechalacho层状层序内和其以外的卫星矿体分解主要矿石矿物和动员稀土元素的条件。这项研究将产生一个全面的矿床成因模型，通过1)结合岩相学、矿物化学、块状岩石地球化学和同位素方法重建层状火成岩杂岩的火成岩成因，以及2)利用岩相学、矿物化学、流体包裹体、相平衡、实验和热力学分析进行随后的热液动员。这项研究的结果将为了解这种知之甚少的战略类型矿床的起源提供新的线索，并为加拿大和海外的勘探确定新的指导方针。

Technological breakthroughs ranging from the development of environmentally friendly hybrid cars to more powerful lasers and supermagnetic materials are creating a strong demand for the REE. Currently, 97% of REE production is from deposits in China, which is now curtailing exports of this commodity. The deposits currently being explored at Thor Lake in the NWT of Canada have the potential to fill this impending shortfall. These deposits are hosted primarily by a large, silica-undersaturated peralkaline intrusion. Most importantly, unlike similar but uneconomic deposits elsewhere, the deposits at Thor Lake have undergone strong hydrothermal alteration, which has enhanced the REE mineralisation. The purpose of the proposed research is to expand on research conducted as part of a recent NSERC-CRD project, which has demonstrated that the REE mineralisation is hosted by a layered igneous complex, that primary REE concentration was achieved by fractional crystallization and the formation of REE-rich cumulates, and that hydrothermal fluids further concentrated the REE. The research proposed in this application will identify the mechanisms that produced the cumulate zircon and eudialyte which constitutes the upper and lower ore zones in the Nechalacho deposit, and the conditions that permitted the breakdown of the primary ore minerals and the mobilisation of the REE both within the Nechalacho layered sequence and into satellite bodies beyond it. This research will lead to a comprehensive genetic model for the deposits that will be achieved by reconstructing 1) the igneous petrogenesis of the layered igneous complex using a combination of petrographic, mineral chemical, bulk rock geochemical and isotopic methods, and 2) the subsequent hydrothermal mobilisation using petrographic, mineral chemical, fluid inclusion, phase equilibrium, experimental and thermodynamic analyses. The results of the study will shed new light on the origin of a very poorly understood strategic class of deposits and identify new guidelines for their exploration in Canada and abroad.