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

加拿大的东部边缘是由在超过4.8亿年前开始的造山活动（阿巴拉契亚造山运动）中“积聚”的地质地块组成的（在构造板块一侧添加的物质）。这些地体包含火成岩侵入物，这些侵入物主要是由地壳在增生过程中熔化形成的。其中一些侵入体中含有金属矿床（如锡、钨、锂、铯、铟、稀土元素），这些金属矿床对加拿大继续向低碳、数字化经济过渡至关重要。在新斯科舍省和新不伦瑞克省，过去对侵入相关矿床的研究历史上主要集中在使用大块（整个岩石）化学和同位素分析方法来限制岩浆的金属“肥力”（特定年龄和成分的岩浆形成金属矿床的可能性）。然而，从整体分析中得到的信息往往是模糊的，因为大块火成岩是多种地质过程的最终产物，这些地质过程可能会抹去或减少岩浆和相关流体在其演化不同阶段的原始化学特征。因此，目前有关阿巴拉契亚造山带侵入体相关矿床的地质模型需要修正。分析熔体和流体包裹体（在整个地质时期被困在矿物中运输和浓缩金属的前熔融岩石和热液溶液的微观样本）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。该研究计划将通过对熔体和流体包裹体的研究来限制阿巴拉契亚造山带变矿化火成岩的演化。这些包裹体，被困在相对物理和化学坚固的矿物（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禀赋的火成岩背景的岩浆历史来推进总体研究计划的目标。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）对岩浆金属禀性和经济潜力的相对重要性。参与拟议研究的学员将获得宝贵的技能和知识，这些技能和知识将转移到学术界、政府和私营部门的职业生涯中，并产生适合各种最终用户的一系列数据产品和新知识。该项目不仅将为研究区域的成矿模型提供重要的更新，而且还将为全球其他类似的地质体提供重要的更新，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，检验以往研究的有效性。这项研究在自然资源领域有明确的应用，旨在为加拿大提供具有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.