Biogeochemical Studies of the Ra. U. Th and REE Deposit at Morro do Ferro: A Qualitative Application to improve Confidence in Radionuclide Immobilization Processes

Abstract

A 60–80 million year old thorium and rare earth element (REE) deposit located within a small hill (Morro do Ferro or MF) in the state of Minas Gerais, Brazil, contains virtually none of the attributes deemed essential for the isolation of long-lived radionuclides emplaced in deep geological formations. High grade ore (0.5 to 3.0% Th and REE’s) is found within 50m of the hill’s surface on the southern flank with the richest portions within 10m of the surface. The underlying rock at MF (fine-grained nepheline syenite or tinguaite) is so highly altered (down to at least 400m) due to both weathering and hydrothermal activity such that apart from differences in radioactivity levels, one cannot distinguish the original host rock from the “ore” (Barretto and Fujimori, 1984). Perhaps the only “protection” afforded the ore body is a 1–3m surface cover composed of large aggregates of lateritic soil as radioactive as the “ore” beneath it, and several subsurface magnetite dikes (1-5m thick) which outcrop at various points along the southern face and have probably played a role in supporting the hill’s structure. An extensive network of magnetite (and associated oxidation products) veinlets occurs randomly throughout the hill.