Abstract: Bauxite Mining and Stream Salinity in Darling Range, Western Australia

Graham Slessar

The Perth metropolitan region of Western Australia obtains most of its water supply from forested catchments on the adjacent Darling Plateau. Bauxite mining is a major land use in the high-rainfall zone along the plateau's western margin. Economic bauxite deposits extend into drier areas where substantial quantities of salt are stored in the subsoils.

The consequences of possible future mining in the drier portions of the water-supply catchments are presently uncertain. Large-scale agricultural clearing in lower rainfall areas farther east has lead to marked increases in the salinity of local streams. Although mining involves the clearing and subsequent reforestation of relatively small areas, partial devegetation of larger areas could result from the spread of "dieback"--a root fungus disease which affects many plants including the predominant tree species of the local forest. The spread of the disease is accelerated by vehicular activity associated with most land uses, including mining.

CSIRO (Australia) Division of Land Resources Management has developed simple mathematical models to provide estimates of the increase in stream salinity likely to be associated with any forest clearing program. Results from the application of one such model to conceptual long-term mining sequences suggest that mining alone would have minimal effect on catchment salinity levels. However, if "dieback" disease were to spread unchecked in more saline areas, the salinity of some catchments could rise above potable limits. Reforestation of diseased areas would probable maintain salinity levels well within potable limits. Provided "dieback" is not spread through the more saline areas as a result of other land uses, the time frame for resolution of the potential salinity problem as it relates to mining is in excess of 30 years.

AAPG Search and Discovery Article #90962©1978 AAPG 2nd Circum-Pacific Energy and Minerals Resource Conference, Honolulu, Hawaii