Journal of Earth Sciences and Geotechnical Engineering

Mobility of Radionuclides and Rare Earth Elements in the Coastal area of Rio de Janeiro: Implications for Monazite deposits in Offshore Areas

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• Abstract

  Analysis of ground and airborne radiometric data as well as rare earth element abundances in soils in the Saquarema region (Rio de Janeiro, Brazil) has allowed new insights into the mobility of mineral aggregates containing monazites. The regional distributions of radioactive elements, as revealed in results of airborne radiometric surveys, indicate that topography play dominant role in transportation of weathered material. The mobility pattern is characterized by systematic depletion of radioactive elements along the migration paths. Superimposed on this depletion trend are indications of relative enrichment of uranium and thorium with respect to potassium along the migration paths. Analysis of data on rare earth element abundances in soils and beach sands point to the existence of a complementary process responsible for formation of ore-grade deposits of monazites along the coastal regions. The time and distance scales associated with this enrichment process have been estimated based on the regional distribution of Th/K ratios. The results indicate that submerged monazite deposits may be present along the offshore sand banks, in the coastal region of the state of Rio de Janeiro. These results may be useful in locating under-water monazite deposits in other parts of continental shelf with similar geologic context.