The geochemistry, mineralogy and maturity of gossans derived from volcanogenic Zn-Pb-Cu deposits of the eastern Lachlan Fold Belt, NSW, Australia

The Eastern Highlands of Australia have probably been in existence since th e Late Cretaceous or earlier and so there has been ample time for mature go ssan profiles to form over outcropping volcanogenic Zn-Pb-Cu mineralisation in the eastern Lachlan Fold Belt. The mature gossan profiles are character ised by the upward progression from supergene sulfides to secondary sulfate s, carbonates and phosphates into a Fe-oxide dominated surficial capping wh ich may contain boxwork textures after the original sulfides (as at the Woo dlawn massive sulfide deposit). However, the region has locally been subjec ted to severe erosion and the weathering profile over many deposits is inco mplete (immature) with carbonate and phosphate minerals, especially malachi te, being found in surficial material. These immature gossans contain more Cu, Pb and Zn but lower As, Sn (and probably Au) than the mature gossans. A lthough Pb is probably the best single pathfinder for Zn-Pb-Cu VHMS deposit s of the eastern Lachlan Fold Belt, Ag, As, Au, Bi, Mo, Sb and Sn are also useful, with most of these elements able to be concentrated in substantial amounts in Fe oxides and alunite-jarosite minerals. (C) 2001 Elsevier Scien ce B.V. All rights reserved.