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Open File Report 78

Regolith studies related to the Challenger gold deposit, Gawler Craton, South Australia

Lintern, M.J. and Sheard, M.J.

The Challenger Au Deposit lies in the northern Gawler Craton, South Australia, 750km NW of Adelaide, and 140km NW of Tarcoola. A 1.5km traverse (the regolith line) was chosen for the study of geochemical dispersion and regolith stratigraphy across three zones of mineralisation (Zones 1, 2 and 3) and various landforms in the Challenger area. The principal mineralisation (Challenger 1 or Zone 1) outcrops on the flank of a low rise, referred to as Mt Challenger. Zone 2 mineralisation (Challenger SE) occurs about 400m to the south east of Zone 1. Kelpie, or Challenger 11 (Zone 3), is located beneath about 20m of sediments, presumed to be mostly Tertiary in age, about 800m to the SE of Zone 1. Other zones of mineralisation occur in the area, but were not studied. Mineralisation is associated with silica and arsenopyrite alteration in the Christie Gneiss, a garnet-rich paragneiss consisting of plagioclase, perthitic K-feldspar, quartz, cordierite, garnet and biotite.

Deep weathering of the Christie Gneiss has led to the development of a clay-dominated saprolite of variable thickness (but averaging about 30m) that contains abundant relict quartz. The upper regolith (designated as 60m) is dominated by silicification (silcrete) and calcrete development, with comparatively small quantities of ferruginous material occurring mainly as ferruginous granules (lag) on the surface. The area is of low relief and dominated by a shrubland of bluebush (Maireana sedifolia), with pockets of mulga (Acacia sp.) flourishing in thin (<2m) aeolian dunes.

Thirty holes were specially drilled along the regolith line in order to study the upper regolith in detail. The lower regolith was sampled to about 60m, using cuttings from pre-existing drill holes, at intervals along the regolith line that correspond with the upper regolith samples. A series of eight, 3m deep pits were excavated along the regolith line to enable detailed examination of the relationship (i) between silcrete and calcrete, and (ii) between silcrete/calcrete and mineralised saprolite. In addition to the drill cuttings and pits, sampling and analyses of calcrete, silcrete, lag and vegetation was undertaken using a suite of 50 major and minor elements, XRD and SEM.

Last updated: Thursday, January 06, 2000 01:56 PM


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