On the possibility of determining rates of removal of uranium from crystalline igneous rocks using U-series disequilibria—1: a U-leach model, and its applicability to whole-rock data

The removal of U from granitic rocks is characterised by234U/238U≤1 and 230Th/234U> 1. It is notable, from weathered Eye-Dashwa lakes (Canada) granite samples and from the published data, that230Th/234U ratios seldom exceed a limiting value of about 2. A U-leach model is discussed in detail which may account for these observations. The model assumes that 230Th is practically immobile and that the removal of U can then be measured against the …