Open File Report 36
Occurrence of gold in hardpan, Youanmi Mine
Gedeon, A.Z. and Butt, C.R.M.
Geochemical, mineralogical and petrological studies of the red-brown
hardpan forming the surface horizon at the Youanmi gold mine were
undertaken to determine the form and origin of the gold within it.
The hardpan itself, apparently typical of the Wiluna Hardpan that
occurs extensively in the Murchison District, is a silica-cemented
unit across the transition from saprolite (in situ weathered bedrock)
to colluvium (locally transported sheetwash deposit). Passing upwards,
it consists of fractured saprolite, untransported saprolite blocks
and poorly sorted colluvial debris cemented by a porous, red-brown
matrix. The matrix contains apparently elastic clay, silt and sand-sized
fragments and aggregates in a silica cement; translucent orange
and clear silica (hyalite) forms a coating on the walls of fractures
and voids. Despite the heterogeneity of the hardpan, the gold content
appears to be fairly uniform within individual profiles. Four polished
sections of hardpan were searched by scanning electron microscopy.
Gold was found in only one section, in which four particles (1-3
microns) were located. These were all situated on open voids, which
could be due to contamination during preparation or analysis of
the samples, or to the late stage mobility of gold, either chemically
or by physical illuviation. Gold probably also occurs throughout
the hardpan matrix as very fine particles below the resolution of
the scanning electron microscope.
Last updated: Thursday, January 06, 2000 08:10 AM