Acid producing potential static tests have been
undertaken on sample lithologies from New Zealand coal
mines, to rank the lithogies into acid producing waste rock and stable non-acid
producing waste rock. Results indicated that the main acid producing waste rock
in the Waikato coal region are the marine
Whaingaroa siltstone and the Glen Massey formations and the main alkaline
producing lithologies were the Tauranga group volcanic-derived sediments (A
& D) and the Mesozoic basement. Coal ash analysis of 28 samples from 28
mines have also been analysed for reactive S percentage and their base potential
has been quantified by the chemical index of alteration (CIA). The results
provide mine management in the Waikato Coal
region with a classification of problematic and stable waste rock types. XRF and
CIA values determined from wash drill cuttings would provide a method of
determining waste rock volumes and magnitude of palaeo-weathering
underground.