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
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