AN ASSESSMENT OF SULFIDE OXIDATION IN ABANDONED BASE-METAL TAILINGS, TE AROHA, NEW-ZEALAND

Tailings from the Tui base-metal mine were characterised using a varie ty of techniques including scanning electron microscopy (SEM) and flam e atomic absorption spectroscopy (FAAS), to assess their potential for use as a plant growth medium. With the notable exception of Pb (10 56 8 mg kg(-1)), 'total' metal concentrations in the surface tailings (0- 200 mm) were relatively low (Cu, 113; Fe, 3660; Zn, 486 mg kg(-1)). Th e theoretical acid generating potential (TAGP) and 'total' concentrati ons of Cu, Fe and Zn of the tailings, were found to increase greatly w ith depth, reflecting an increase in the abundance of chalcopyrite (Cu FeS2), pyrite (FeS2) and sphalerite (ZnS), as detected by X-ray diffra ction (XRD) analysis. SEM micrographs indicate that the distribution o f sulphide minerals in the tailings was originally uniform with depth. The depletion of Cu, Fe and Zn in the surface tailings is considered to be a result of sulphide oxidation, as evidenced;by the craggy and h ighly irregular morphology of the sulphide particles and the high hydr ogen ion activity (pH 2.3-4.0) in this zone. The persistence of high c oncentrations of acid-generating sulphide minerals between 200 and 600 mm has important implications in determining strategies for revegetat ing the tailings. (C) 1997 Elsevier Science Ltd.