Controls on the fertility of magmas for the genesis of associated hydrothermal ore deposits

岩浆热液矿床是我国铜、钼、Au、银、铼、锡、钨等金属的主要资源。大多数靠近地表的大型矿床已经被发现，要找到新的大型矿床以满足社会日益增长的金属需求，就需要进行深度勘探，成本大大增加。因此，确定最具成矿远景的地区，集中矿产勘探工作是至关重要的。拟议研究的成果将有助于根据地球化学标准确定大陆弧的富矿段，这在应用于具有复杂岩浆历史和构造演化的增生复合弧地形时可能特别有用，如加拿大科迪勒拉山脉。为了实现这一目标，我将结合联合收割机实验和实地研究，以调查硫和矿石金属的命运在所有主要阶段的岩浆演化导致矿石成因，包括1）在地球上地幔的俯冲洋板块的岩浆生成; 2）通过地球岩石圈的岩浆运输，和3）矿石流体生成的岩浆脱气在上地壳深处。将特别注意岩浆的氧化还原状态的演变，因为这定义了硫和许多矿石金属的地球化学行为。例如，还原态硫的存在可能导致岩浆硫化物饱和，这可能极大地影响金属向后期出溶流体的转移。另一方面，在岩浆流体相中存在丰富的氧化硫物种是斑岩和高硫化浅成热液矿床中有效的矿石矿物沉淀的先决条件。因此，我们将：1）通过高压-高温实验和研究跨墨西哥火山带的火山岩，调查俯冲板片衍生流体如何影响弧岩浆的氧化状态和矿石金属收支，该火山带是一个独特的大陆弧，具有多种多样的原始地幔衍生岩浆; 2）在安第斯山脉进行实地研究，以确定矿石金属的富集程度，S和Cl在地壳岩浆分异过程中的变化特别有利于成矿的构造环境，并将其与具有中等成矿潜力的弧段进行比较; 3）实验性地开发新的方法来限制岩浆氧化还原状态的演化，并将这些方法应用于实地收集的岩石样品; 4）实验上限制硅酸盐熔体组成，压力和温度影响矿石金属和硫转移到出溶岩浆流体中的效率，并使用此信息来帮助解释从天然样品拟议的研究将利用我的小组最近许多成功的实验和分析方法的发展，这将使我们能够获得非常强大的和以前无法获得的信息，以促进更好地理解上述过程。

Magmatic-hydrothermal ore deposits are our major resources of metals such as Cu, Mo, Au, Ag, Re, Sn and W. Most large ore deposits near the surface have already been discovered and the finding of new major deposits to cover the increasing metal demand of society requires exploration at depth at greatly increased cost. Therefore, the identification of the most prospective regions for ore genesis to focus mineral exploration efforts on is essential. The outcomes of the proposed research will help to identify ore-fertile segments of continental arcs based on geochemical criteria, which may be particularly useful when applied to accreted composite arc terrains with complicated magmatic history and tectonic evolution such as the Canadian Cordillera.***To achieve this goal, I will combine experimental and field-based studies to investigate the fate of sulfur and ore metals during all main stages of magma evolution leading up to ore genesis, including 1) the generation of magmas in the Earth's upper mantle over subducting oceanic plates; 2) the transport of magmas through the Earth's lithosphere, and 3) ore fluid generation by magma degassing at upper crustal depths. Particular attention will be paid to the evolution of the redox state of magmas as this defines the geochemical behavior of sulfur and many ore metals. For example, the presence of sulfur in reduced state may lead to magmatic sulfide saturation, which may greatly affect metal transfer into later exsolving fluids. On the other hand, the presence of abundant oxidized sulfur species in the magmatic fluid phase is a pre-requisite for efficient ore mineral precipitation in porphyry and high-sulfidation epithermal ore deposits. We will therefore: 1) Investigate how subducted slab-derived fluids influence the oxidation state and ore metal budget of arc magmas by using high pressure-temperature experiments and by studying volcanic rocks in the Trans-Mexican Volcanic Belt, a unique continental arc with a great diversity of primitive mantle-derived magmas; 2) Conduct a field-based study in the Andes to constrain how the concentration of ore metals, S and Cl vary during magma differentiation in the crust in tectonic settings particularly favorable for ore genesis, and compare this to arc segments with moderate mineralization potential; 3) Experimentally develop new methods to constrain the evolution of the redox state of magmas and apply these to rock samples collected in the field; 4) Experimentally constrain how silicate melt composition, pressure and temperature affect the efficiency of ore metal and sulfur transfer into exsolving magmatic fluids and use this information to help interpret data obtained from natural samples. The proposed research will take advantage of numerous recent successful experimental and analytical method developments in my group, which will allow us to obtain very powerful and previously inaccessible information to facilitate better understanding of the above processes.**