PORE GAS COMPOSITION IN WASTE ROCK DUMPS UNDERGOING PYRITIC OXIDATION

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Abstract
We measured oxygen and carbon dioxide concentrations in the pore space of two waste rock dumps that are significant sources of acid and trace metal pollutants to a local river system. The release of these pollutants is a consequence of the oxidation of pyritic material within the dumps, which are at the abandoned Rum Jungle mine in the Northern Territory, Australia. Comparison of oxygen concentration distributions with heat source distributions indicates that oxygen supply is the oxidation-rate-limiting mechanism in most regions of the dumps. Gas transport into the dumps is by diffusion and advection due to both thermal effects and atmospheric pressure changes. The extent to which one transport mechanism dominates reflects the proximity of the edge of the dump and differences in the properties of the material in different regions. In some areas, at least two transport mechanisms determine the pore gas composition. Carbon dioxide levels, which are generally one to three orders of magnitude higher than atmospheric levels, indicate that the bacteria that catalyze pyritic oxidation have a plentiful supply of carbon dioxide, which is essential for their metabolism. © Williams & Wilkins 1985. All Rights Reserved.