Interpreting U - Th distributions in the continental crust from radiometric data
Abstract
In the mineral system concept, attainment and preservation of extreme levels of concentrations of metals require several critical elements, including a fertile source, a pathway for aqueous and magmatic fluids, and a trap. The processes involved in the transfer of energy and materials in mineral systems are inherently multi-scale. At the same time, the existence of (process-dependent) scaling laws for the trace element concentrations in the Earth's curst has been debated for several decades, with implications in economic geology, such as grade-tonnage relationships. U and Th are incompatible trace elements whose concentrations vary over several orders of magnitudes in the continental crust. They can be mapped at various scales (1 m to hundred's of km) using airborne radiometric surveys or hand-held spectroradiometers. Such data sets offer a new opportunity to examine the spatial organization of Th and U and to re-assess the existence of scaling laws and nested scales in geochemistry. We will present here a) a conceptual and numerical model for a quantitative analyse of airborne radiometric and b) its application to interpretation of radiometric data in the West Africa and Pilbara cratons. Our hypothesis implies that the relative importance of magmatic, fluid-rock and surface processes may be recognized by the analysis of the geostatistical parameters (distribution and variograms). Our model simulates a sequence of elementary geochemical processes (partial melting, fractional crystallization, dissolution - precipitation) and takes into account the scale of radiometric data to simulate U-Th concentrations and geostatistical parameters resulting from various scenarios. The characteristics of the distributions (e.g., normal, log-normal, fractal or multi-fractal) and variograms for Th - U concentrations on mafic and felsic units of the West Africa and Pilbara cratons are tentatively interpreted within this new framework.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMNS31A1945B
- Keywords:
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- 0994 Instruments and techniques;
- EXPLORATION GEOPHYSICSDE: 0999 General or miscellaneous;
- EXPLORATION GEOPHYSICSDE: 1835 Hydrogeophysics;
- HYDROLOGY