CRC LEME
Open File Report 97
ABSTRACT
Hydrogeochemical dispersion of gold and other elements at Baxter,
Western Australia
Gray, D.J.
The hydrogeochemistry of the Baxter study area was investigated,
with a view to understanding the interaction of groundwaters with
mineralized rocks, and the potential for exploration, particularly
in areas of overburden. Groundwaters at Baxter are neutral groundwaters,
with a similar Eh range to other neutral groundwaters from the Yilgarn
Craton. However, they differ from groundwaters investigated at sites
in the southern Yilgarn in having very low salinities and marked
divergence from sea water ratios, suggesting that the major ion
concentrations are strongly controlled by local lithological or
hydrological factors. The groundwaters at Baxter strongly resemble
those at Lawlers, about 300 km to the SE in the north Yilgarn. Elements
that appear to be controlled by mineral equilibration in some or
all Baxter groundwaters are Ba (barite equilibration), Ca, Mg and
HCO3 (carbonate), Pb and V (chervitite Pb2V2O7).
The Baxter groundwaters have extremely low Au concentrations, similarly
to areas of overburden at Lawlers. This suggests that Au is not
expected to be extensively chemically redistributed in the regolith
under present-day conditions, and therefore that it will not be
a useful pathfinder in groundwaters or in soils overlying extensive
overburden. However, Sc, Mo, W and, possibly, Rb were observed to
have greater groundwater concentrations in areas of Au mineralization
and at this site are better pathfinders in groundwater than Au itself.
This elemental suite is similar, though more limited, to those observed
at other sites. These elements may have scope as target elements
for selective extraction of soil or other regolith material. Other
elements can be used in groundwaters to indicate underlying rocks
or other geochemical features. For example, dissolved Cr concentrations
correlate closely with the presence of ultramafic rocks at Baxter
and elsewhere, even though the groundwaters are in contact with
highly weathered lithologies. Dissolved As and, to a lesser degree,
Ni correlate with a zone of As-enriched rocks to the SE of the study
area.
Thus, results indicate exploration potential for groundwater in
such environments, even where highly weathered rock are overlain
by transported material. The elements enriched in mineralized groundwaters
may also form part of a suite of elements that may yield a geochemical
expression by selective extraction.
Last updated: Sunday, August 05, 2001 11:44:42
|
