VulcansFluids:The behaviour of halogens and sulphur in natural high temperature processes

氯、氟和硫是火山排放的气体和高温富水流体的重要成分，这些流体负责运输和沉积许多重要的经济金属。因此，该项目的目的是全面描述火山熔体中氯、氟和硫的行为，从而确定这些元素在脱气和成矿过程中释放到环境中的条件。这些结果适用于在地球、火星和其他原行星和小行星上发生的过程。该项目使用了两种新的实验方法。在一个实验中，我们使用硅酸盐、金属银、碘化银和氯化银(或氟化银)的混合物来确定高温高压下Cl2(或F2)的分压(逸度)。在实验中，金属和卤化银化合物形成两种不相容的液体，控制硅酸盐熔体中的氯(或氟)含量。在高温高压下使用银/硫化银或铂/铂硫化物混合物(在固定的氧逸度下)来固定S2逸度也使用了类似的方法。实验结束后，用微束方法对硅酸盐(现在是玻璃)进行分析，以确定所关注的元素(S)、氯、氟和硫的准确含量。第二种新的实验方法是用熔融的硅酸盐样品在高温下搅拌，以测定氯、氟、S和微量金属的相对挥发度。我们的结果将与大量关于Cl、S和F的流体熔体分配的现有数据相结合，以确定这些元素在卤水和低密度流体中的逸度，从而确定它们的金属迁移能力。众所周知，地球、月球、火星和灶神星的氯/氟比和氯/S比差异很大，所有这些天体都经历了广泛的熔融和挥发损失。我们的结果将使我们能够估计在行星和小行星形成期间发生挥发损失的不同条件。氯和硫是火山流体中氯化物形式的金属迁移和斑岩铜矿中金属硫化物沉淀的主要媒介。我们的结果将使我们能够根据在其演化过程中演化出的流体和气体的组成来识别潜在的经济金属矿床的火山地点。

Chlorine, fluorine and sulphur are important components of the gases emitted by volcanoes and of the high temperature water-rich fluids responsible for transport and deposition of many economically important metals. The aims of this project are therefore to characterise fully the behaviour of chlorine, fluorine and sulphur in volcanic melts and thereby to determine the conditions under which these elements are released to the environment during degassing and ore-forming processes. The results have applications to processes occurring on Earth, Mars and other protoplanetary and asteroidal bodies The project uses two novel experimental approaches. In one we fix the partial pressure (fugacity) of Cl2 (or F2) at high temperatures and pressures using mixtures of silicate, silver metal, silver iodide and silver chloride (or silver fluoride). During the experiment the metal and silver halide compounds form 2 immiscible liquids controlling the Cl (or F) content of the silicate melt. A similar approach is used to fix S2 fugacity at high temperature and pressure using silver/silver sulphide or platinum/platinum sulphide mixtures (at fixed oxygen fugacity). After the experiment the silicate (which is now a glass) is analysed by microbeam methods to determine the exact contents of the element(s) of concern, Cl, F and S. The second novel experimental method uses a furnace in which the molten silicate sample is stirred at high temperature in order to determine relative volatilities of Cl, F, S and trace metals. Our results will be integrated with the numerous available data on fluid-melt partitioning of Cl, S and F to determine the fugacities of these elements in brines and lower density fluids and hence their metal-transport capacities. It is known that there are large differences between the Cl/F and Cl/S ratios of the Earth, Moon, Mars and Vesta, all bodies which have undergone extensive melting and volatile loss. Our results will enable us to estimate the different conditions under which volatile loss occurred during formation of planets and asteroids. Chlorine and sulphur are principal agents in the transport of metals as chlorides in volcanic fluids and in the precipitation of metal sulfides in porphyry copper deposits. Our results will enable us to identify potential volcanic sites of economic metal deposits based on the compositions of fluids and gases evolved during their evolution.