LATERITE PROFILE GEOCHEMISTRY IN OUTLINING SUPERGENE GOLD DEPOSITS - A CASE-STUDY FROM NILAMBUR, KERALA

A natural example for exceedingly pure gold was recently identified fr om 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 i s found as small grains or nuggets. In many cases, the oxidised zone c ontains high concentrations of gold, closely associated with iron oxid e/hydroxide matrix and was observed to be crystalline. This occurrence supports dissolution ana reprecipitation of gold during weathering. L aterite samples from different horizons of two representative vertical sections of the weathering profiles in the Maruda area of Nilambur ha ve been analysed for major, minor and trace elements, including gold i n this study. The distribution of Fe, Al, Si, CO Mg, Na, K, P,:Ti and Mn in these profiles can be correlated with the element;mobility patte rns associated with tropical weathering environment. The results indic ate that a predominantly acidic environment is generated during lateri tization, which is conducive to gold mobility. Our study confirms that the concentration of naturally purified gold in the laterites was ach ieved by acidic oxygenated fluids in the weathering front.