Previously published
stream quality data and AMD (acid mine drainage) analyses have been collated
into a database (DAME - Database for Assessment of Mine Environments) and
additional samples including NMD (neutral mine drainage) have been collected
from coal mine drainages on the West Coast. Variations in the chemistry of mine
drainage samples can be related to four factors:
1.
regional geology (Brunner Coal Measures or Paparoa Coal
Measures)
2.
mine type (open cast or underground)
3.
hydrogeology
4.
local geology

In
general mines hosted in Paparoa Coal Measures produce NMD whereas mines hosted
in Brunner Coal Measures produce AMD with highly variable chemistry. Differences
in coal mine drainage chemistry between mines hosted in Brunner and Paparoa Coal
Measure sequences can be measured with acid-base accounting geochemistry.
Correlation of ANC (acid neutralising capacity) and MPA (maximum potential
acidity) analysis of rocks with mine drainage samples is substantially better
than correlation of NAG (net acid generation) analysis with mine drainage
chemistry.

It
is likely that NAG analysis over estimates acid generation potential of some
samples due to release of organic acids that are not released under
environmental conditions. In general, differences in mine drainage chemistry
between Brunner and Paparoa hosted mines are attributed to the effect
depositional environment and diagenesis on coal measure composition. Exceptions
to generalisations relating mine drainage to Paparoa or Brunner host rocks are
likely where local geological conditions cause increased deposition of pyrite in
Paparoa rocks and additional analyses are required to confirm
interpretations.

Based on the
interpretation of these results a mine drainage chemistry hazard model has been
constructed. The hazard model predicts likely variations in mine drainage
chemistry based on the four factors listed above. The hazard model has
implications for mine related water quality risks. For example, ecotoxicity,
human health affects and selection of remediation techniques are all sensitive
to mine drainage chemistry.