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Mineral exploration
Published in Odwyn Jones, Mehrooz Aspandiar, Allison Dugdale, Neal Leggo, Ian Glacken, Bryan Smith, The Business of Mining, 2019
Odwyn Jones, Mehrooz Aspandiar, Allison Dugdale, Neal Leggo, Ian Glacken, Bryan Smith
Gravity surveys provide a measure of the Earth’s gravity field, which in turn is a subtle expression of variations in the rock density recordable with sensitive devices. The local minor differences in the mass of rock bodies produce an increase or decrease in the gravity field and these high and low mass variations as compared to immediate background mass show up as positive or negative anomalies in gravity data. Gravity is measured as milligal (mGal) and gravity meters measure very minor gravity differences. Gravity has generally been best measured via ground surveys, but developments in the past two decades have allowed better airborne gravity data to be collected. The airborne gravity surveys measure the gravity tensor and its popular version, the gravity gradiometer. The gravity method is used as a direct targeting tool in attempting to detect the higher masses of base metal sulphide deposits as compared to surrounding lower background mass.
Exploration for epithermal Au–Ag deposits in New Zealand: history and strategy
Published in New Zealand Journal of Geology and Geophysics, 2019
Anthony B. Christie, Mark P. Simpson, Richard G. Barker, Robert L. Brathwaite
In 2005, Glass Earth Ltd commissioned regional-scale airborne geophysical surveys of the TVZ. These were a combined aeromagnetic and radiometric survey over a large part of the TVZ and a smaller airborne gravity survey (airborne full tensor gravity gradiometry) within this area. A large database of geological, geochemical and geophysical information, together with the interpretation of the airborne geophysical survey data, identified 22 targets for follow-up exploration (Henderson et al. 2016). Many of these targets have coincident areas of low magnetic and high residual Bouguer gravity anomalies. Wavelength edge detection analyses of the magnetic and gravity data were interpreted to indicate deep crustal structures that were suggested to control the location of some geological features and mineral prospects (Smith et al. 2007). Later, publicly available data were used by Kenex to complete a 2D prospectivity model for epithermal Au–Ag prospects in the TVZ and a 3D model of the Ohakuri epithermal Au–Ag prospect (Payne et al. 2014; Peters et al. 2016).