Intrusion-related critical metal deposits throughout the Appalachian orogen: constraining melt fertility and the magmatic-hydrothermal transition

加拿大东部边缘由地质地体组成，这些地体是在4.8亿多年前开始的造山事件(阿巴拉契亚造山运动)中“聚集”的(添加到构造板块一侧的物质)。这些地体包含主要由地壳在吸积过程中熔融形成的火成岩侵入体。其中一些侵入体蕴藏着金属(例如锡、钨、锂、铯、铟、稀土元素)，这些金属对加拿大继续向低碳、数字化经济转型至关重要。在新斯科舍省和新不伦瑞克，过去对与侵入有关的矿床的研究历来侧重于使用化学和同位素分析的整体(全岩)方法来限制岩浆的金属“丰度”(特定年龄和成分的岩浆形成金属矿床的可能性)。然而，从大量分析中获得的信息往往是模棱两可的，因为大量火成岩是多种地质过程的最终产物，这些过程可能会抹去或削弱岩浆和相关流体在其演化的不同阶段的原始化学特征。因此，目前阿巴拉契亚造山带与侵入岩有关的矿床的地质模型需要修改。熔体和流体包裹体的分析(以前熔融的岩石和热液溶液的微观样品，在整个地质时期运输和浓缩金属，被困在矿物中)是直接测量古代岩浆和相关挥发物金属含量的最可靠方法。拟议的研究计划将通过对熔体和流体包裹体的研究，限制阿巴拉契亚造山带中可变矿化火成岩的演化。这些包裹体被困在物理和化学相对较强的矿物(如锆石)中，将使用各种微量分析方法进行分析。个别项目将通过调查不同年龄和不同金属天赋的火成岩环境的岩浆史来推进总体研究计划目标。目的是更好地了解主要控制因素(如岩浆源成分、结晶、污染、流体脱气)对岩浆金属赋存和经济潜力的相对重要性。参与拟议研究的受训人员将获得宝贵的技能和知识，这些技能和知识将可用于学术界、政府和私营部门的职业，并产生一系列适合各种最终用户的数据产品和新知识。该项目不仅将对研究区域的成矿模型进行重要更新，还将对全球其他类似地体的成矿模型进行重要更新，更广泛地说，将解决有关阿巴拉契亚造山带岩浆过程的基本问题，检验之前研究的有效性。建议的研究在自然资源领域有明确的应用，旨在提供将对加拿大产生社会经济效益的勘探标准。

The eastern margin of Canada is comprised of geological terranes that were "accreted" (material added to the side of a tectonic plate) during mountain building events (the Appalachian Orogeny) beginning more than 480 million years ago. These terranes contain igneous intrusions formed mainly by melting of the crust during accretion. Some of these intrusions host deposits of metals (e.g., tin, tungsten, lithium, cesium, indium, rare-earth elements) that are critical for Canada's continuing transition to a low-carbon, digitized economy. In Nova Scotia and New Brunswick, past research on intrusion-related deposits has historically focused on using bulk (the whole rock) methods of chemical and isotopic analyses to constrain the metal "fertility" of magmas (the likelihood that magmas of specific ages and compositions could form metal deposits). However, information yielded from bulk analyses is often ambiguous because bulk igneous rocks are end-products of multiple geological processes that can erase, or diminish, the original chemical signature of magmas and related fluids at different stages in their evolution. Consequently, current geological models for intrusion-related deposits in the Appalachian orogen require revision. The analysis of melt and fluid inclusions (microscopic samples of formerly molten rock and hydrothermal solutions that transported and concentrated metals, trapped in minerals throughout geological time) is the most robust approach to directly measure the metal content of ancient magmas and related volatiles. The proposed research program will constrain the evolution of variably mineralized igneous rocks in the Appalachian Orogeny through the investigation of melt and fluid inclusions. These inclusions, trapped in relatively physically and chemically robust minerals (e.g., zircon) will be analyzed using a variety of microanalytical methods. Individual projects will advance overall research program objectives by investigating the magmatic history of igneous settings of different ages and varying metal endowments. The objective will be to better understand the relative importance of primary controls (e.g., the magma source composition, crystallization, contamination, fluid degassing) on magma metal endowment and economic potential. Trainees involved in the proposed research will gain valuable skills and knowledge that will be transferable to careers in academia, government and the private sector and generate a range of data products and new knowledge suitable for a variety of end-users. The program will provide important updates to metallogenic models not only in the study areas, but in other similar terranes globally, and more broadly, will address fundamental questions about magmatic processes in the Appalachian orogen, testing the validity of previous studies. The research proposed has clear application to the natural resource field, aiming to provide exploration criteria that will have socio-economic benefit to Canada.