Chemical fingerprinting of hydrothermal ore deposit systems

该计划中进行的研究将解决有关重要类型金矿如何形成的真正根本问题。到目前为止，地质学家认为变质金矿床和岩浆金矿床中携带和储存黄金的流体都是“低盐度的水-碳酸盐流体”(H2O-CO2±CH4)。这种描述极其简单，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，并忽略了可能对成矿至关重要的流体成分的微妙之处。更有问题的是，这种描述鼓励了这样的假设，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了解金矿形成背后的基本过程，金矿是加拿大过去一个世纪经济的重要组成部分，也将有助于矿产勘探公司更有效地专注于工作和支出。 这项拟议的工作将比较加拿大两个著名的金矿地体，它们的年龄、地质环境和金矿资源截然不同：一个以变质矿床为主(Meguma；新斯科舍省)，另一个具有混合变质-岩浆矿床(Abitibi，安大略省)。所采用的方法将是迄今为止尚未用于此类矿床(或任何其他矿床)的分析方法的新组合。含金矿物和伴生的非含金矿物同时形成，并包含有关黄金的来源和沉积条件的信息。重要的是，承载金矿的石英脉捕获了极少量的矿化流体，称为流体包裹体，可以使用普通和高度专业的方法进行采样和分析。这些方法可以量化流体化学，并提供一种直接评估其成因的方法，这是以前从未做过的，然后将为重新评估这些金矿的成因模式提供基础。伴生的硫化物矿物(如毒砂)也记录了流体化学，就像生长的树上的年轮一样。这些硫化物的元素填图使人们能够重建流体历史，并间接评估金的来源及其圈闭时间。 在两种截然不同的环境中使用的方法的结合将首次提供关于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类似研究应用于其他热液成矿系统提供基础，以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.