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

在几种成矿环境中，烃类与金属矿化之间存在密切的空间关联。对于所有这些环境，传统观点认为矿石是由含水流体（通常是热液）沉积而成的。在碳氢化合物的作用中，它通过降低流体的氧化态来促进金属矿物沉积。这被解释为通过使相应的含水金属络合物不稳定和/或将溶解的硫酸盐还原为硫化物（矿石矿物主要是硫化物）而引起矿石矿物的沉淀。很少有研究人员考虑到的另一种解释是，碳氢化合物代表了将金属运送到成矿地点的液体石油的残余物。根据这一假设，矿石金属在随后的石油蒸馏过程中沉淀，从而驱除轻质烃，留下沥青残留物。蒸馏大大增加了金属的浓度，使它们饱和并通过与油中存在的还原硫反应而沉淀为硫化物矿物。这种成矿模式为含有机物（沥青）的沉积岩中富集Ni、Pt、Pd和Hg等金属提供了一个有吸引力的解释，已知这些金属对烃类具有很强的亲和力，不会形成强的水溶性络合物。该假设也可适用于某些金属如Zn的沉积物（例如，密西西比河谷型矿床），虽然它们很容易在热液流体中迁移，但通常也以高浓度存在于原油中。这里提出的研究将开始解决液态烃是否可以形成矿液的问题，通过进行旨在确定选定金属在原油和简单烃液体中的溶解度的实验，通过研究它们在这些液体中的形态，并通过评估它们在烃液体和水溶液之间的分配（例如，盐水），温度高达300 °C。

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.