CRC LEME
Open File Report 160
ABSTRACT
Regional Geochemical Surveys: Riverina Pilot Project – Methodology
and Preliminary
Results
P. de Caritat, S. Jaireth, M. Lech and J. Pyke
During financial year 2003-04, we carried out fieldwork and preliminary
analyses for
a collaborative project between CRC LEME and Geoscience Australia
aimed at
testing methodologies and strategies for regional geochemical surveys
in Australia.
The Riverina bioregion, in southern New South Wales and northern
Victoria, was
selected for this pilot project. Overbank sediments were chosen
as sampling media,
with a near-surface sample (TOP: O horizon, from 0-10 cm below
the humus layer)
and a bottom sample (BOT: B-C horizon, ~10 cm interval between
approximately 70-90 cm below the humus layer) being collected.
River Red Gum (Eucalyptus
camaldulensis) leaves were also collected at a small number of
locations. The sample sites were selected to be near outlets or
spill points of large catchments, so that
overbank sediments there could reasonably be assumed to represent
well-mixed, fine-grained composite samples of all major rock and
soil types present in the catchment.
Three field trips visited 143 sites in the Riverina. This report
documents the
methodologies used in this survey and presents results to date.
Sediment samples were subjected to a detailed description
and the determination of
bulk parameters in the field (texture, moist and dry colour, field
pH). In the
laboratory, the samples were analysed for moisture content, EC
1:5, pH 1:5; some
were also subjected to laser particle size analysis. Bulk (<180 µm)
composition was
determined by X-Ray Fluorescence (XRF), Inductively Coupled Plasma
Mass
Spectrometry (ICP-MS) and Instrumental Neutron Activation Analysis
(INAA), and
the samples were also analysed by sequential digestion and prepared
for heavy
mineral separation. At the time of writing, bulk composition of
the samples from the
first fieldtrip (eastern Riverina) only was available. All together
the concentrations of
62 elements were determined, and maps are presented showing the
spatial and
statistical distributions in the TOP and BOT samples and of the
TOP/BOT ratios.
These results will be the basis for further interpretative work
and the backbone of a
forthcoming geochemical atlas of the Riverina.
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