PLANNED REMOTE SENSING AND LABORATORY SPECTRAL CHARACTERIZATION OF RESIDUAL CLAY-HOSTED ION-ADSORPTION TYPE RARE EARTH ELEMENT (REE) DEPOSITS ASSOCIATED WITH DEEPLY WEATHERED LATERITE AND BAUXITE SOILS

Ion-absorption type REE deposits associated with laterite clay deposits, are mined near the city of Longnan, Jiangxi Province, South China, and are the most important global source of heavy REEs. Analysis of spaceborne Hyperion, ALI and ASTER imagery reveal land-use patterns indicative of slash and burn agricultural methods, clear-cut forest and timber harvesting and perhaps some strip mining activities near the locations of known occurrences in Southern China. Such land-use patterns help to expose underlying laterite clay deposits, and allow for the possible detection of REE-rich laterite clays using remote sensing imagery.

Eu, Nd, Sm, and Pr are amongst the most abundant light REEs that form minerals and oxides in their trivalent states, and are detectable using spectroscopic measurements spanning the visible to near-infrared wavelengths (400 – 1000 nm) and beyond. The spectral reflectance patterns of these minerals and oxides are characterized by series of narrow absorption features, with very unique band positions that are attributed to electronic transition processes within these elements. Heavy REEs often found in association with light REEs, and are typically extracted as a by-product.

In order to better understand the genesis and detectability of such REE deposits in analogous granite-associated laterite terranes in the SE US, we are modeling South China laterite clay deposits in the laboratory. Laboratory experiments will include absorbing various concentrations of key REE to laterite soils that best match the spectral characteristics of well exposed laterite areas mapped using remote sensing imagery acquired over South China. In particular, spectral information extracted from the analysis of Hyperion, ALI and ASTER imagery will be used to determine quartz, clay and ferric-iron mineral mixtures and their abundances in laterite soils, yielding the closest spectral matches to soils exposed in South China imagery. The relative changes in REE spectral absorption feature strength will then be compared with those of more conventional and better studied deposits, such as the well exposed carbonatite-hosted REE deposit at Mountain Pass, California in order to assess detectability limits. A similar approach will be used to recreate and study ion-absorption deposits hosted by karst-bauxite soils.