Hydrocarbons as ore fluids: An experimental study of the solubility of metals in crude oil and its analogues

在一些成矿环境中，碳氢化合物与金属矿化之间存在着密切的空间联系。对于所有这些环境，传统的观点认为，矿石是由含水流体（通常是热液）沉积形成的。碳氢化合物的作用是通过降低流体的氧化状态来促进金属矿物沉积。这被解释为通过破坏相应的水金属配合物的稳定性和/或将溶解的硫酸盐还原为硫化物（矿石矿物主要是硫化物）而导致矿石矿物的沉淀。很少有研究人员考虑过的另一种解释是，碳氢化合物代表了液态石油的残留物，液态石油将金属运送到矿石形成的地方。根据这一假设，矿石金属在随后的石油蒸馏过程中沉淀下来，这赶走了轻烃，留下了沥青的残留物。蒸馏大大增加了金属的浓度，使它们饱和并与油中还原的硫发生反应而沉淀为硫化物矿物。这种成矿模型为含有机质（沥青）沉积岩中镍、铂、钯和汞等金属的浓度提供了一个有吸引力的解释。众所周知，这些金属与碳氢化合物有很强的亲和力，不会形成强的水性配合物。这一假设也适用于某些金属矿床，如锌（例如密西西比河谷型矿床），尽管它们很容易在热液中运输，但也通常以高浓度存在于原油中。这里提出的研究将开始解决液态碳氢化合物是否可以形成矿石流体的问题，通过设计实验来确定选定金属在原油和更简单的碳氢化合物液体中的溶解度，通过研究它们在这些液体中的形态，并通过评估它们在高达300°C的温度下在碳氢化合物液体和水溶液（例如盐水）之间的分配。

In several environments of ore-formation, there are close spatial associations between hydrocarbons and metallic mineralisation. For all of these environments, the conventional wisdom is that the ores form by deposition from aqueous fluids, generally hydrothermal liquids. Where a role is attributed to the hydrocarbons, it is to promote metallic mineral deposition by reducing the oxidation state of the fluid. This is interpreted to cause precipitation of the ore minerals by destabilising the corresponding aqueous metallic complexes and/or reducing dissolved sulphate to sulphide (the ore minerals are dominantly sulphides). An alternative explanation for the association, which few researchers have considered, is that the hydrocarbons represent the relicts of liquid petroleum that transported the metals to the sites of ore formation. According to this hypothesis, the ore metals precipitate during subsequent distillation of the petroleum, which drives off the light hydrocarbons, leaving behind a residue of bitumen. The distillation greatly increases the concentration of the metals causing them to saturate and precipitate as sulphide minerals by reacting with reduced sulphur present in the oil. This model of ore-formation provides an attractive explanation for the concentration in organic-bearing (bitumen) sedimentary rocks of metals like Ni, Pt, Pd and Hg, which are known to have a strong affinity for hydrocarbons and do not form strong aqueous complexes. The hypothesis may also apply to some deposits of metals like Zn (e.g., Mississippi Valley Type deposits), which although they are readily transported in hydrothermal fluids, are also commonly present in high concentrations in crude oils. The research proposed here will start addressing the question of whether liquid hydrocarbons can form ore fluids, by conducting experiments designed to determine the solubility of selected metals in crude oils and simpler hydrocarbon liquids, by investigating their speciation in these liquids, and by evaluating their partitioning between hydrocarbon liquids and aqueous solutions (e.g., brines) at temperatures up to 300 °C.