Radon emanometry in uranium exploration using activated charcoal : Namibian case studies

Abstract

The refinement and implementation of the Radon-on-Activated-Charcoal technique (ROAC), developed in the 1970?s by the South African Atomic Energy Board (Hambleton-Jones and Smit, 1980), is discussed. The objectives were to implement a radon (222Rn) detection technique for uranium exploration which is sensitive, cost effective, and relatively rapid in its application. The refinement of the technique, referred to here as RadonX, has primarily involved improvement of counting statistics and sensitivity. Radon, emanating from buried uranium mineralization, is adsorbed onto activated charcoal contained within a cartridge, fitted into the base of an inverted cup, and buried in the ground. The technique differs from alpha-sensitive radon detection systems in that it measures the gamma radiation arising from the daughter products of the adsorbed radon, namely 214Bi and 214Pb. Two case study datasets are presented. The first is from an exploration area potentially hosting uraniferous granites, where the sand cover varies in thickness from 10 to 100m. Time domain electromagnetic (TDEM) soundings provided cover thickness and conductivity data as a guideline to porosities. The second is from an orientation survey over a known buried palaeo-channel of duricrust-hosted uranium. The results from the latter area, after a 10-day burial period, showed an improved sensitivity compared to a past alpha-detection survey, conducted with a burial period of 30 days. The technique has proven to be highly effective through both residual and transported surficial cover, with good repeatability. A depth of penetration of 80m or more under favourable porosity conditions has been achieved.