Ore elements in a mid-ocean ridge hydrothermal systemстатья
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Дата последнего поиска статьи во внешних источниках: 28 мая 2015 г.
Аннотация:A thermodynamic model of a mid-ocean ridge convective hydrothermal system was developed. This model is consistent with field observations with regard to many criteria, including the concentration levels of ore elements (Fe, S, Cu, Zn, and Pb) in the solutions. This enables the model to be used to predict ore-element behavior in natural systems. The model suggests that, in the low-temperature, oxidizing part of descending convection, ore-forming metals are leached from the rock as a result of an interaction with seawater. The ore-forming metals are partially deposited in the high-temperature, reduced part. Based on their relative mobility, the ore metals form a series Pb approximate to Zn > Cu. The metal-bearing potential of the solution grows with increasing temperature and decreasing pressure. Ore-metal contents pass through a maximum with the change in the rock/water ratio. Modeling of the evolution of the hydrothermal system with time shows that young systems with an abundance of fresh basalts in their interiors produce solutions relatively rich in Zn (Zn > Cu approximate to Pb). Hydrothermal systems whose interiors were subjected to intense metasomatic reworking are characterized by Cu-rich solutions (Cu > Zn > Pb). This inversion is due to the differences in the solubility of Zn and Cu sulfides determining the different rates of their removal from the hydrothermal system and to the evolutionary trend in the macrocomposition of the solution. The results obtained explain the observed correlation of the Zn-to-Cu ratios in the ore deposits with their geodynamic setting, size, and duration of active life.