The relative contents of Au in a series of groundwaters from water bores
and exploration drillholes, located near Au mineralisation at Stawell,
Ararat, Clunes and Ballarat in central Victoria, were found to be clear
indicators of relative proximity to mineralisation in each region. In the
same series, waters with anomalous concentrations of As distinguished
Au mineralisation in bedrock from secondary palaeochannel or deep lead
Au. In some groundwaters, acid pH values, high sulphate relative to other
anions and detectable concentrations of reduced Fe reflected sulphide
minerals associated with bedrock Au deposits. Close to some ore zones,
locally anomalous groundwater concentrations of Mn reflected the Fe
carbonates that accompany Au in these zones. In addition, elevated
concentrations of other elements provided geochemical signatures for the
aquifer lithologies associated with Au mineralisation. Of the lithological
indicators Co and Ni, U and F, Rb and Cs, Mo and Li respectively
reflected the mafic, felsic, potassic rich and quartz zones, principally in
the Stawell mine area and to a lesser extent those at Clunes and Ballarat.
Mineral stability diagrams, based on groundwater activities of K', Mgt
and H`, demonstrated that a series of ore-zone groundwaters follow a
trend that conforms with a biotite to sericite to kaolinite alteration
sequence in aquifer mineralogy. This is a good illustration of how present
day groundwaters under surface conditions can reflect the underlying
mineral sequences that accompany these Au deposits. These observations
around mine areas suggested that groundwater chemistry could provide a
rapid and cost effective method of assessing prospectivity for An of
extensive areas in central Victoria. To test this, regional sampling and
analysis of 355 bore waters was carried out in a region where potential
An bearing rocks are covered by Mesozoic and Cainozoic sediments and
volcanics. Contoured elemental abundances and distribution from this
program indicated five zones in which groundwaters had elevated Au and
despite the cover, appeared to reflect variations in the underlying
Palaeozoic rocks. Three of the Au zones could be in terrain affected by
extensions or intersections of faults, a feature in common with the
established Au deposits in central Victoria. Reflections of concealed
Palaeozoic rocks included a possible zone of concealed Cambrian
greenstones that coincides with three of the Au zones. It was concluded
that each of the An zones represents a groundwater Au focus that warrants
follow-up exploration.