Mineralogical controls on element dispersion in regolith over two mineralised shear zones near the Peak, Cobar, New South Wales C.J. Cairns a,1 , K.G. McQueen a, * , P.A. Leah b a Cooperative Research Centre for Landscape Evolution and Mineral Exploration, University of Canberra, Canberra, ACT 2601, Australia b Peak Gold Mines Pty Ltd, PO Box 328, Cobar, NSW 2835, Australia Received 2 February 2000; accepted 21 August 2000 Abstract Effective exploration for polymetallic ore deposits in the Cobar region is hampered by incomplete knowledge of the mineralogical controls on element dispersion in the different regolith-landform settings throughout the area. A detailed mineralogical and geochemical study of regolith profiles over two major mineralised shear zones in a strongly weathered but dominantly erosional setting has delineated the important host minerals for a range of base metal cations. Iron oxides/ oxyhydroxides, particularly goethite and to a much lesser extent hematite, are major hosts for Pb, Cu, and Zn as substituted/ adsorbed cations and as constituents of associated or intergrown minerals, probably including members of the jarosite–alunite group. Correlations between elements and major regolith minerals suggest that goethite is also a host phase for As, Bi and Sb. Minor manganese minerals, including lithiophorite and cryptomelane group minerals, also host base metals in appreciable amounts. No clear association was found between gold and any particular secondary mineral. It is likely that gold is present largely as elemental gold particles associated with a range of minerals. Sampling strategies for geochemical exploration in variably leached and stripped regolith in the Cobar area should take into account the relative abundance of goethite and manganese oxides/oxyhydroxides within the profiles and overlying lag. Goethite would appear to be the preferred sampling medium for base metals. Highly ferruginous lag has a high proportion of hematite with variable maghemite and very low manganese oxide contents. Most of the base metal content in this surface material is strongly bound to the crystalline oxides/oxyhydroxides. More work is required to understand the effects of surface transforma- tion of goethite to hematite and maghemite on the mobility and distribution of base metal cations in soil and ferruginous lags.  2001 Elsevier Science B.V. All rights reserved. Keywords: geochemical dispersion; base metals; gold; cryptomelane; lithiophorite; goethite; regolith hosts; semi-arid terrain 1. Introduction Major polymetallic sulfide deposits of Cu, Au, Pb and Zn occur in the Cobar Mining Field of northwes- tern New South Wales, Australia. These deposits are structurally controlled, vein and massive lens systems developed in metasedimentary host rocks. The ore veins are typically confined to steeply plunging, pipe-like concentrations within the steeply dipping host structures. Consequently, most orebodies have a small ellipsoidal surface expression and a large down plunge extension (up to 1000 m, Stegman and Pocock, 1996). Geochemical techniques are widely used in the search for these deposits, but the geometry Journal of Geochemical Exploration 72 (2001) 1–21 0375-6742/01/$ - see front matter  2001 Elsevier Science B.V. All rights reserved. PII: S0375-6742(00)00160-6 www.elsevier.nl/locate/jgeoexp * Corresponding author. E-mail address: kmq@scinece.canberra.edu.au (K.G. McQueen). 1 Present address: Lion Ore Australia Pty Ltd, PO Box 906, West Perth, WA 6872, Australia.