Massive sulphide ZnPbCuAg deposits in the Halls Peak district of northeastern NSW are of the submarine volcanogenic
type. They occur as a number of small lenses enclosed in shale and epiclastic rocks, in association with felsic volcanics of
early Permian age. The deposits crop out in steep terrain near the eastern edge of the New England plateau. Local relief of
700 m and slopes up to 50, coupled with an average annual rainfall of about 1000 mm has led to local severe landsliding
in previously mined areas. Mining from the 1890's to the 1960's has also resulted in unconstrained drainage of heavy
metal-bearing acid waters and physical dispersion of finer grained metalliferous sediments into the Chandler River. Waters
emanating from the main landslide area, from underground workings and draining scattered unconfined stockpiles of
massive sulphide ore have pH values of 3 to 4 and contain elevated contents of Zn, Cu, Pb, Cd and Fe. Chemical mobility
of heavy metals into streams occurs under low pH conditions with Zn exhibiting the greatest dispersion. Increasing pH
conditions downstream cause precipitation of Fe phases and coprecipitation of heavy metals. Physical dispersion of
secondary metal-bearing minerals into the surrounding creeks results in wt% levels of Cu, Pb and Zn in the stream
sediments thereby exceeding the regional background values by one to three orders of magnitude. Areas disturbed by mining
are characterised by lack of vegetation, biomagnification of heavy metals into algae and lower plants, and partial
recolonisation by metal-tolerant grass species (Snow Grass, Poa sieberana; Blady Grass, Lomandra longifolia).
Rehabilitation measures will have to include landslide stabilisation, impervious sealing or removal of sulphidic materials,
import of topsoil and revegetation by metal-tolerant, slow-growing native grass and shrub species.