成矿元素的气相迁移与实验研究

Gaseous transport of mineralizing elements and experimental study

越来越多的野外观测和实验数据表明,气相对成矿元素的迁移和富集具有不可忽视的作用。由高温火山气体形成的升华壳和凝结水中富集多种岩浆组分和成矿金属;中低温的地热田水蒸气中也检测到成矿元素;某些斑岩型铜-金矿床的富气体包裹体比共存的盐水包裹体更富集Cu和Au。金属呈简单氯化物或氟化物、硫化物、含氧酸及原子迁移的理论假设低估了400℃以下气体搬运成矿金属的能力,而必须考虑溶剂化作用(水合作用),有关银、金、铜、锡、钼、钨在水热气相中的溶解度实验证实了这一点,基于实验数据的热力学模拟计算表明,水热气相可运移足够的成矿金属以形成具有经济价值的浅成热液型和斑岩型矿床。此外,实验也证实砷和硼从液相分配至气相中也与水合作用有关,其气液相间的分配系数随温度和水蒸气的压力增大而增强。无疑地,成矿金属被水热气相搬运的理论对理解金属矿床的形成机理和发展诸如深穿透地球化学的地球气找矿方法具有重要意义。

More and more field observations and experimental data show that gas plays a certain role in the transport and enrichment of mineralizing elements. Sublimates and condensates formed from high temperature volcanic gases are enriched with various magmatic components and ore-forming metals. Mineralizing elements are also detected in moderate to low temperature water vapor occurring in geothermal field. The vapor-rich fluid inclusions are enriched in Cu and Au even more than the co-existing brine inclusions in some porphyry copper-gold deposits. The theoretical assumption of gaseous transport of metals as simple chlorides, fluorides, sulfides, oxyacids and atoms underestimates the capacity of the gas phase to transport metals below 400 ℃ hence the solvation or hydration should be taken into account , which is demonstrated by the solubility experiments of silver, gold, copper, tin, molybdenum and tungsten in hydrothermal vapors. Thermodynamic modeling based on the experimental data indicates that hydrothermal vapors can transport sufficient metals to form economic epithermal and porphyry deposits. In addition, experiments show that the partitioning of arsenic and boron into vapor phase from liquid is also related to the hydration, and the vapour-liquid distribution coefficients increase with temperature and vapor pressure. Undoubtedly, the theory of ore-forming metal transported in hydrothermal vapor is significant to the understanding of the forming mechanism of metal deposit and the development of the geogas prospecting methods such as deep-penetrating geochemistry.