English

Abstract

Iron hydroxide precipitates, generated from acid mine drainage adhere to surfaces in tailings and waste rock piles and accumulate as sludges in ditches and in pond sediments in mine waste management areas. Such precipitates undergo a series of transformations which lead ultimately to the stable mineral goethite. Ground water from piezometers in an below tailings containing 41 % pyrite were stored for 4 years unpreserved in their original, un-sterilized sampling bottles reached pH values around 1. The stored water with the iron precipitates have been able to support Fe-oxidizing and Fe-reducing bacteria and similar microbial populations were identified on slides which were immersed into the piezometers from the same tailings site. A clear relationship between microbial activity and Fe(III) mineral compositions in the iron precipitates from the stored samples and from sludges accumulating in a ditch precipitating from the effluent from underground workings at the same site, could not be established. The relevance of the microbial activity in the formation of secondary minerals occurring in ground water in and below tailings and accumulating on the surface is discussed. The high variability of the output of geochemical modelling (PHREEQC) to the modelling input allowed a wide variety of possible interpretations.