IMPROVED AND NEW USES OF NATURAL RADIOACTIVITY IN MINERAL EXPLORATIONAND PROCESSING

Measurement of natural radioactivity has been used in both a qualitati ve and a quantitative way in mineral exploration, particularly in the search for uranium. In the last five years, the Kernfysisch Versneller Instituut (KVI) and British Geological Survey (BGS) have designed, bu ilt and tested a new detector system that greatly improves quantitativ e applications in mineral exploration, especially on the seafloor and in the nearshore zone. The new system is an enhancement of an earlier BGS design. The major improvements comprise the use of a highly sensit ive gamma-ray detector, together with new data processing, from which concentrations of natural radionuclides may be deduced in real time. A fter laboratory analysis of samples, these concentrations can be conve rted into mineral percentages. Once the mineralogy of an area has been characterized, this conversion can also be done in real time. Thus fa r the system has mainly been used to map heavy-mineral concentrations in coastal subtidal and intertidal sediments. For such work the multi- sensor detector probe is towed on the seafloor and various parameters are recorded continuously. The probe contains, in addition to the gamm a-ray detector, a water-pressure sensor (giving water depth) and an ac oustic device to measure bottom roughness. The system, when used toget her with high-precision positioning systems such as D-GPS, enables the production of detailed maps of bathymetry, bottom roughness, and seaf loor radioactivity or mineral distribution. These maps allow mineral c oncentrations to be readily correlated with seabed topography and sedi ment type. In the same way, gamma-ray detectors could be used advantag eously during dredging operations to provide on-line assessment of the mineral content of the dredged sediment as well as to guide the direc tion of dredging. Additionally, the same technique could be used to mo nitor the subsequent fate of a dredge spoil after dumping on the seafl oor. Natural radioactivity arising from potassium and the thorium and uranium decay series has potential use for the fast and reliable asses sment of siliciclastic and phosphatic impurities in limestones. Detect ion of such impurities may preclude the use of the limestone for chemi cal or cement production. Apart from its use in exploration, the techn ique has significant potential in mineral processing, particularly of heavy minerals. It can be applied as on-line quality control in dry an d wet separation processes and for process control, by using decisions based on the results to control valves and other instrumentation. In addition, it can also be used in environmental monitoring of waste ari sing from mineral extraction and processing. In conclusion, the techni que described has a diversity of applications in exploration, mining a nd mineral processing. (C) 1997 Canadian Institute of Mining, Metallur gy and Petroleum.