Laterite Profile Geochemistry in Outlining Supergene Gold Deposits: A Case Study from Nilambur, Kerala

A natural example for exceedingly pure gold was recently identified from the laterite weathering profiles of Nilambur, northern Kerala. The laterites are highly ferruginous and nodular, containing saprolite and clayey horizons. Within the various horizons in the laterites, gold is found as small grains or nuggets. In many cases, the oxidised zone contains high concentrations of gold, closely associated with iron oxide/hydroxide matrix and was observed to be crystalline. This occurrence supports dissolution and reprecipitation of gold during weathering.

Laterite samples from different horizons of two representative vertical sections of the weathering profiles in the Maruda area of Nilambur have been analysed for major. minor and trace elements, including gold in this study. The distribution of Fe, Al, Si, Ca, Mg, Na, K, P, Ti and Mn in these profiles can be correlated with the element mobility patterns associated with tropical weathering environment. The results indicate that a predominantly acidic environment is generated during lateritization, which is conducive to gold mobility. Our study confirms that the concentration of naturally purified gold in the laterites was achieved by acidic oxygenated fluids in the weathering front.