Authors / CoAuthors
Gray, D. | Reid, N. | Bardwell, N. | de Caritat, P. | Noble, R.
Abstract
Groundwater can be a useful sampling medium for geological investigation and mineral exploration: its composition is highly sensitive to its origin and interaction with minerals in the subsurface, and it responds to faults and other geological structures. Thus there is considerable scope for groundwater adding value to mineral exploration where prospective rocks are covered along basin margins. We are encouraging the uptake of a groundwater hydrogeochemistry to aid mineral exploration through the development of robust and cost-effective methodologies based on numerous site studies. Field guides, notebooks, and field apps are now available. Issues such as bailing vs pumping have been tested, and metrics for contamination and determination of its effects on varying elements have been developed. Vast amounts of groundwater data are publicly available (e.g., http://portal.auscope.org/portal/gmap.html). Mineral systems concentrate various elements in particular zones of the Earth at various spatial scales. For groundwater, this is further complicated by the differing mobilities of various elements depending on the environment. In acidic groundwater environments, for instance, base metals (such as Cu, Zn) are highly mobile, although the background concentrations also can be high due to acid attack on the country rocks. In neutral groundwater environments, base metals commonly have low mobilities but oxy-anions (such as MoO42-, WO42-, AsO43-) can give larger and more consistent haloes. In some terrains, particularly in southern Australia, the upper 20 m of the water column can be 3 pH units lower than deeper groundwater. In such a situation, combining results from shallow and deep groundwaters will give erroneous spatial patterns. Interpreting groundwater geochemical data at the continental scale has required resolving issues related to differing analytical quality, and sometimes differing sampling and analytical methods. Results provide support for litho-chemical discrimination of the Australian continent, and allow assessment of the utility of these methods for varying terrains, e.g., from very acid/saline in southern Australia, through mostly fresh and neutral in the western two thirds of the continent, to sulfate-poor in the artesian-dominated systems of northeastern Australia. In each case, differing element suites and indices should be used for exploration. At the terrain scale, specific groundwater indices delineate large-scale lithological groups and major mineral camps. Such a broad-scale approach may obscure camp-scale variation but does delineate major features, such as the Agnew and Granny Smith gold camps in Western Australia. Other large mineral systems, such as iron-oxide copper gold (IOCG) or copper porphyries may also be observable. At the prospect scale, indicator elements (such as Au, Ni, Cu, Zn, W, As) are commonly valuable, with indices (such as `AuMin or `NiS) developed for specific commodities. Combined with geophysics, this may assist in selecting drilling targets. Hydrogeochemistry, combined with a robust understanding of environmental factors, weathering processes and good quality analytical chemistry, can positively assist exploration at various scales. Continuing research and interaction with explorers has the potential to contribute to the next phase of economic mineral discovery.
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nonGeographicDataset
eCat Id
90059
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Cnr Jerrabomberra Ave and Hindmarsh Dr GPO Box 378
Canberra
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- External Publication
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Earth Sciences
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- Published_Internal
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2016-01-01T00:00:00
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[-44.0, -10.0, 112.0, 154.0]
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