The Greenland Group, Westland, can be characterised with respect to
environmental issues by the application of a GIS database (DAME), and specific
sampling campaigns. Waters draining gold mineralised areas have a distinctive
chemistry characterised by neutral pH and arsenic as a trace element. The acid
neutralising capacity (ANC) from carbonates usually exceeds the maximum
potential acidity (MPA) from sulphides resulting in circum-neutral pH. These
waters are readily distinguishable from waters draining coal mine related areas,
which commonly have low pH (~4) and low As concentrations (~0.1 ppm). In
contrast, dissolved arsenic mobilised from Greenland Group historic gold mining
areas is up to 2.4 ppm. This As mobilisation is controlled by the secondary As
mineral, scorodite (FeAsO22H2O). Maximum dissolved As
concentrations increase with increasing pH, corresponding to the increasing
solubility of scorodite with increasing pH. Dissolved As is attenuated by
dilution, precipitation of scorodite, and/or adsorption to iron oxyhydroxide
(HFO). Adsorption to HFO is an important attenuation mechanism in and adjacent
to many mine sites. HFO is abundant at mine sites where pyrite was abundant in
fresh rock, such as where the mineralised zone is dominated by disseminated
pyrite. Pyrite, and resulting HFO, are relatively rare where mineralisation
occurred as well-defined quartz veins. Localised HFO occurs also where ankerite
oxidises in host rocks. Arsenic output flux (ca. 25 g/day) from historic gold
mine sites is commonly less than the natural background flux from mineralised
rocks (>5000 g/day).