Abundances of radioelements (K, U, Th) in weathered igneous rocks in Hong Kong

Abstract

Gamma-ray spectrometric measurements and geochemical determinations of major and trace element contents using ICP-MS and XRF were conducted on 58 igneous rock samples from Hong Kong. Stripping analyses on the gamma-ray spectra have yielded estimates on the abundance of K, Th and U. Major element contents were used to compute the Parker weathering indices for the samples. Only K shows a systematic variation in concentration with an increasing degree of weathering. The increase in porosity and interconnectivity of microfractures are probably the cause for the observed nonlinear decline in the K content during the weathering process. The concentrations of U and Th in the samples do not show any systematic variations with the weathering index, reflecting the complex mechanisms of dissolution and deposition of the two radioelements in the weathering profile. A curvilinear relationship between eK and Wp has been derived from the measurement data, which possibly provides a quick means of characterizing the extent of alteration in the igneous rocks. © 2007 Nanjing Institute of Geophysical Prospecting.