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发展到更强大的激光和超磁性材料的技术突破正在创造对稀土元素的强劲需求。目前，97%的稀土产量来自中国的矿藏，中国目前正在削减这种商品的出口。目前正在加拿大西北部托尔湖勘探的矿床有可能填补这一即将到来的短缺。这些矿床主要由一个大的硅不饱和过碱性侵入体承载。最重要的是，与其他类似但不经济的矿床不同，托尔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展作为最近NSERC-CRD项目的一部分所进行的研究，该项目已经证明稀土矿化是由层状火成岩复合体主导的，主要的稀土浓度是通过分离结晶和富含稀土的堆积形成的，而热液流体进一步浓缩了稀土。本申请中提出的研究将确定形成Nechalacho矿床上部和下部矿带的累积锆石和双析岩的机制，以及允许初级矿石矿物分解和在Nechalacho层状序列内及其外的卫星体中稀土元素调动的条件。本研究将通过以下方法重建矿床的综合成因模型：1)结合岩石学、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复合体的火成岩成因；2)利用岩石学、矿物化学、流体包裹体、相平衡、实验和热力学分析重建随后的热液动员。这项研究的结果将为一种鲜为人知的战略矿床的起源提供新的线索，并为加拿大和国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.