EARTH SCIENCES
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Geochemical surveys deliver fundamental data, information and knowledge about the concentration and spatial distribution of chemical elements, isotopes and compounds in the natural environment. Typically near-surface sampling media, such as soil, sediment, outcropping rocks and stream or groundwater, are used. The application of such datasets to fields such as mineral exploration, environmental management, and geomedicine has been widely documented. In this presentation I reflect on a sabbatical experience with the Australian Federal Police (AFP) in 2017-2018 that allowed me to extend the interpretation of geochemical survey data beyond these established applications. In particular, with my collaborators we explore ways in which geochemical survey data and maps can be used to indicate the provenance of an evidentiary sample collected at a crime scene or obtained for instance from items belonging to a suspect intercepted at border entry. Because soils are extremely diverse mineralogically, geochemically and biologically, it should theoretically be possible to exclude very large swathes of territory (>90%) from further provenancing investigation using soil data. In a collaboration between Geoscience Australia (GA), the AFP and the University of Canberra (UC), a recent geochemical survey of the urban/suburban Canberra region in southeastern Australia is being used as a testbed for developing different approaches to forensic applications of geochemical surveys. A predictive soil provenancing method at the national scale was also developed and tested for application where no actual detailed, fit-for-purpose geochemical survey data exist. Over the next few years, GA, AFP and UC are collaborating with Flinders University to add biome data from soil and soil-derived dust to further improve the provenancing technique. This Abstract was presented at the 2021 Goldschmidt Conference (https://conf.goldschmidt.info/goldschmidt/2021/meetingapp.cgi)
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We collected 38 groundwater and two surface water samples in the semi-arid Lake Woods region of the Northern Territory to better understand the hydrogeochemistry of this system, which straddles the Wiso, Tennant Creek and Georgina geological regions. Lake Woods is presently a losing waterbody feeding the underlying groundwater system. The main aquifers comprise mainly carbonate (limestone and dolostone), siliciclastic (sandstone and siltstone) and evaporitic units. The water composition was determined in terms of bulk properties (pH, electrical conductivity, temperature, dissolved oxygen, redox potential), 40 major, minor and trace elements as well as six isotopes (δ18Owater, δ2Hwater, δ13CDIC, δ34SSO4=, δ18OSO4=, 87Sr/86Sr). The groundwater is recharged through infiltration in the catchment from monsoonal rainfall (annual average rainfall ~600 mm) and runoff. It evolves geochemically mainly through evapotranspiration and water–mineral interaction (dissolution of carbonates, silicates, and to a lesser extent sulfates). The two surface waters (one from the main creek feeding the lake, the other from the lake itself) are extraordinarily enriched in 18O and 2H isotopes (δ18O of +10.9 and +16.4 ‰ VSMOW, and δ2H of +41 and +93 ‰ VSMOW, respectively), which is interpreted to reflect evaporation during the dry season (annual average evaporation ~3000 mm) under low humidity conditions (annual average relative humidity ~40 %). This interpretation is supported by modelling results. The potassium (K) relative enrichment (K/Cl mass ratio over 50 times that of sea water) is similar to that observed in salt-lake systems worldwide that are prospective for potash resources. Potassium enrichment is believed to derive partly from dust during atmospheric transport/deposition, but mostly from weathering of K-silicates in the aquifer materials (and possibly underlying formations). Further studies of Australian salt-lake systems are required to reach evidence-based conclusions on their mineral potential for potash, lithium, boron and other low-temperature mineral system commodities such as uranium. <b>Citation:</b> P. de Caritat, E. N. Bastrakov, S. Jaireth, P. M. English, J. D. A. Clarke, T. P. Mernagh, A. S. Wygralak, H. E. Dulfer & J. Trafford (2019) Groundwater geochemistry, hydrogeology and potash mineral potential of the Lake Woods region, Northern Territory, Australia, <i>Australian Journal of Earth Sciences</i>, 66:3, 411-430, DOI: 10.1080/08120099.2018.1543208
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This resource includes bathymetry data acquired during the Southern Depths of the Great Barrier Reef survey using Kongsberg EM302 and EM710 multibeam sonar systems. The Southern Great Barrier Reef Shelf Bathymetry survey (FK201122/GA4867); also known as Ice Age Geology of the Great Barrier Reef survey; was led by Queensland University of Technology aboard the Schmidt Ocean Institute's research vessel Falkor from the 22nd of November to the 21st of December 2020. The primary objective of the expedition was to explore ancient undersea features that formed during the last Ice Age, when sea level was around 125 m lower than it is today. While once an exposed part of the Australian coast, these shelf areas were submerged as Earth’s glaciers and ice sheets melted and sea level rose, flooding Australia’s continental shelf. Another objective was to find the southern extent of an older limestone platform that may represent the approximately 20 million-year-old base upon which the present Great Barrier Reef has grown. This V1 dataset contains two 64m resolution 32-bit floating point geotiff files of the Southern Great Barrier Reef Shelf Bathymetry survey area, derived from the processed EM302 and EM710 bathymetry data, using CARIS HIPS and SIPS software. This dataset is not to be used for navigational purposes. This dataset is published with the permission of the CEO, Geoscience Australia.
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The radiometric, or gamma-ray spectrometric method, measures the natural variations in the gamma-rays detected near the Earth's surface as the result of the natural radioactive decay of potassium (K), uranium (U) and thorium (Th). The data collected are processed via standard methods to ensure the response recorded is that due only to the rocks in the ground. The results produce datasets that can be interpreted to reveal the geological structure of the sub-surface. The processed data is checked for quality by GA geophysicists to ensure that the final data released by GA are fit-for-purpose. This radiometric potassium grid has a cell size of 5e-05 degrees (approximately 5m) and shows potassium element concentration of the South Pilbara, Hickman Crater, WA, 2011 in units of percent (or %). The data used to produce this grid was acquired in 2012 by the WA Government, and consisted of 134742 line-kilometres of data at 400m line spacing and 60m terrain clearance.
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The radiometric, or gamma-ray spectrometric method, measures the natural variations in the gamma-rays detected near the Earth's surface as the result of the natural radioactive decay of potassium (K), uranium (U) and thorium (Th). The data collected are processed via standard methods to ensure the response recorded is that due only to the rocks in the ground. The results produce datasets that can be interpreted to reveal the geological structure of the sub-surface. The processed data is checked for quality by GA geophysicists to ensure that the final data released by GA are fit-for-purpose. This radiometric potassium grid has a cell size of 0.00083 degrees (approximately 89m) and shows potassium element concentration of the South Pilbara, Hickman Crater, WA, 2011 in units of percent (or %). The data used to produce this grid was acquired in 2012 by the WA Government, and consisted of 134742 line-kilometres of data at 400m line spacing and 60m terrain clearance.
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The radiometric, or gamma-ray spectrometric method, measures the natural variations in the gamma-rays detected near the Earth's surface as the result of the natural radioactive decay of potassium (K), uranium (U) and thorium (Th). The data collected are processed via standard methods to ensure the response recorded is that due only to the rocks in the ground. The results produce datasets that can be interpreted to reveal the geological structure of the sub-surface. The processed data is checked for quality by GA geophysicists to ensure that the final data released by GA are fit-for-purpose. This radiometric thorium grid has a cell size of 5e-05 degrees (approximately 5m) and shows thorium element concentration of the South Pilbara, Hickman Crater, WA, 2011 in units of parts per million (or ppm). The data used to produce this grid was acquired in 2012 by the WA Government, and consisted of 134742 line-kilometres of data at 400m line spacing and 60m terrain clearance.
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The radiometric, or gamma-ray spectrometric method, measures the natural variations in the gamma-rays detected near the Earth's surface as the result of the natural radioactive decay of potassium (K), uranium (U) and thorium (Th). The data collected are processed via standard methods to ensure the response recorded is that due only to the rocks in the ground. The results produce datasets that can be interpreted to reveal the geological structure of the sub-surface. The processed data is checked for quality by GA geophysicists to ensure that the final data released by GA are fit-for-purpose. This radiometric thorium grid has a cell size of 0.00083 degrees (approximately 89m) and shows thorium element concentration of the South Pilbara, Hickman Crater, WA, 2011 in units of parts per million (or ppm). The data used to produce this grid was acquired in 2012 by the WA Government, and consisted of 134742 line-kilometres of data at 400m line spacing and 60m terrain clearance.
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Total magnetic intensity (TMI) data measures variations in the intensity of the Earth's magnetic field caused by the contrasting content of rock-forming minerals in the Earth crust. Magnetic anomalies can be either positive (field stronger than normal) or negative (field weaker) depending on the susceptibility of the rock. The data are processed via standard methods to ensure the response recorded is that due only to the rocks in the ground. The results produce datasets that can be interpreted to reveal the geological structure of the sub-surface. The processed data is checked for quality by GA geophysicists to ensure that the final data released by GA are fit-for-purpose. This GSWA Hickman Crater TMI Grid Geodetic has a cell size of 5e-05 degrees (approximately 5m). The units are in nanoTesla (or nT). The data used to produce this grid was acquired in 2012 by the WA Government, and consisted of 134742 line-kilometres of data at 400m line spacing and 60m terrain clearance.
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Total magnetic intensity (TMI) data measures variations in the intensity of the Earth's magnetic field caused by the contrasting content of rock-forming minerals in the Earth crust. Magnetic anomalies can be either positive (field stronger than normal) or negative (field weaker) depending on the susceptibility of the rock. The data are processed via standard methods to ensure the response recorded is that due only to the rocks in the ground. The results produce datasets that can be interpreted to reveal the geological structure of the sub-surface. The processed data is checked for quality by GA geophysicists to ensure that the final data released by GA are fit-for-purpose. This GSWA South Pilbara TMI Grid Geodetic has a cell size of 0.00083 degrees (approximately 89m). The units are in nanoTesla (or nT). The data used to produce this grid was acquired in 2012 by the WA Government, and consisted of 134742 line-kilometres of data at 400m line spacing and 60m terrain clearance.
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The radiometric, or gamma-ray spectrometric method, measures the natural variations in the gamma-rays detected near the Earth's surface as the result of the natural radioactive decay of potassium (K), uranium (U) and thorium (Th). The data collected are processed via standard methods to ensure the response recorded is that due only to the rocks in the ground. The results produce datasets that can be interpreted to reveal the geological structure of the sub-surface. The processed data is checked for quality by GA geophysicists to ensure that the final data released by GA are fit-for-purpose. This radiometric uranium grid has a cell size of 5e-05 degrees (approximately 5m) and shows uranium element concentration of the South Pilbara, Hickman Crater, WA, 2011 in units of parts per million (or ppm). The data used to produce this grid was acquired in 2012 by the WA Government, and consisted of 134742 line-kilometres of data at 400m line spacing and 60m terrain clearance.