Chemical fingerprinting of hydrothermal ore deposit systems

在这个项目中进行的研究将解决关于金矿床的重要类型是如何形成的真正基本问题。到目前为止，地质学家已经了解到，在变质金矿和岩浆金矿中携带和沉积黄金的流体是“低盐度水-碳流体”（H2O-CO2±CH4）。这种描述过于简单，过分简化了已被证明涉及每种矿床类型的具体实例的矿石流体的复杂性，而忽略了流体组成的微妙之处，而这些微妙之处可能对矿石形成至关重要。更有问题的是，这种描述助长了这样一种假设，即这些矿床类型是相似的，尽管它们的基本构造环境显然完全不同。在截然不同的地质环境中，成矿流体真的有可能如此相似、如此简单吗？回答这个问题将有助于地质学家更好地理解金矿形成背后的基本过程，金矿是上个世纪加拿大经济的重要组成部分，也将有助于矿产勘探公司更有效地集中精力开展工作和支出。*******提出的工作将比较加拿大两个著名的黄金地体，它们的年龄、地质背景和黄金禀养都大不相同：一个以变质矿床为主（新斯科舍省的Meguma），另一个则有变质-岩浆混合矿床（安大略省的Abitibi）。所采用的方法将是迄今尚未用于这种矿床（或任何其他矿床）的分析方法的新颖组合。含金矿物和伴生的非含金矿物同时形成，并包含有关金的来源和沉积条件的信息。重要的是，含有金的石英脉捕获了微小体积的矿化流体，称为流体包裹体，可以使用普通和高度专业化的方法对其进行采样和分析。这些方法可以量化流体化学，并直接评估其来源，这是以前从未做过的，然后将为重新评估这些金矿床的成因模型提供基础。伴生的硫化物矿物（如毒砂）也记录了流体化学，就像生长中的树木的年轮一样。这些硫化物的元素映射使人们能够重建流体历史，并间接评估金的起源及其包裹时间。*******在两种截然不同的环境中采用的方法的结合将首次提供金矿化系统中流体化学的绝对数据。这些数据将构成重新评估用于探索这些宝贵资源的遗传模型的基础。所采用的方法也将为应用于其他热液成矿系统的类似研究奠定基础，以便解决类似的悬而未决的问题。******

The research undertaken in this program will address truly fundamental questions about how important types of gold deposits form. Until now, geologists have understood the fluids that carry and deposit gold in both metamorphic and magmatic gold deposits to be `low-salinity aqueous-carbonic fluids' (H2O-CO2±CH4). This description is extremely simple, grossly oversimplifies the complexity of the ore fluids that have been proven to be involved in specific examples of each of the deposit types, and ignores subtleties of fluid composition that may be critical to ore formation. More problematically, this description encourages the assumption that these ore deposit types are similar, even though their fundamental tectonic settings are clearly entirely different. Is it really possible that the ore-depositing fluids in strikingly different geologic settings are so similar and so simple? Answering this question will help geologists understand the fundamental processes behind the formation of gold deposits, a significant part of the Canadian economy for past century, much better, and will also help mineral exploration companies focus their work and their expenditures more efficiently.*******The work proposed will compare two well known gold terranes in Canada of vastly different age, geological setting and gold endowment: one dominated by metamorphic deposits (Meguma; Nova Scotia) and one having mixed metamorphic -magmatic deposits (Abitibi; Ontario). The methods employed will be a novel combination of analytical approaches that has not hitherto been used on such deposits (or any others). Gold-bearing and associated non-gold-bearing minerals form at the same time and contain information about where the gold came from and the conditions under which it was deposited. Importantly, quartz veins hosting the gold traps minute volumes of the mineralising fluid, called fluid inclusions, which can be sampled and analysed using both common and highly specialised methods. These methods permit quantifying the fluid chemistry and a direct means to assess its origin, which has never been done before, and will then provide a basis to reassess the genetic models for these gold deposits. The associated sulphide minerals (e.g. arsenopyrite) also record the fluid chemistry much like rings in a growing tree. Elemental mapping of these sulphides allow one to reconstruct the fluid history and indirectly assess the origin of gold and its time of entrapment.*******The combination of the methods employed in two very contrasting settings will provide for the very first time absolute data on the fluid chemistry in gold mineralized systems. These data will form the basis for reassessing the genetic models used to explore for these precious resources. The methodology employed will also provide a foundation for similar studies to be applied to other hydrothermal ore-forming systems in order to address similar outstanding issues.******