Radioelement distributions and analysis of microtopographical influences in a shallow covered area, Inner Mongolia, China: Implications for mineral exploration

Abstract Gamma-ray spectrometry is one of the most cost-effective prospecting methods for investigating anomalies in potassium, uranium, thorium and alteration indexes associated with hydrothermal and radioactive ore deposits. In this work, we selected an arid grass covered landscape micro-region in Inner Mongolia as the study area to examine the radioelement distributions and microtopographical influences on a gamma ray spectrometry survey. In general, concentrations of K, U, Th and TC (total count) of intrusive rocks are higher than the overburden cover. Overburden mixing with the eolian dust and in-situ weathered material reduces the gamma radiation penetrating into the Earth's surface. Similar to overburden, the thin layers of eolian dust in the concave areas of intrusive rock also reduce the measured radioelement concentrations. The decreasing order of radioelement concentrations in the study area is: Jurassic granodiorite > Carboniferous biotite porphyry > overburden. Th, U, K and TC increase with elevation, and all show positive correlations with elevation. The Th and TC have stronger correlations with elevation than K and U. Thus, K and U show relative local enrichment in low-lying areas, whilst Th and TC do not; alteration indices proposed to improve the discrimination of potassic alteration also generate false anomalies, caused by local enrichment of the K and U in low-lying areas. Therefore, the geological interpretation of gamma ray surveys for mineral exploration needs to consider the topography in order to reject false anomalies and retain the true anomalies associated with ore deposits.