TRANSPORT EQUIVALENCE OF CASSITERITE AND ITS APPLICATION TO STREAM SEDIMENT SURVEYS FOR HEAVY MINERALS

Accumulation of heavy minerals, such as gold and cassiterite, on strea m beds is a well-known phenomenon that results from differences in the rates of transport of the heavy minerals and the sediment as a whole. These accumulations can be both an advantage and a disadvantage to ex ploration geochemical surveys. Hence, it would be beneficial to be abl e to recognize such accumulations and, if necessary, correct for them. This, however, requires an improved understanding of the sedimentolog y of heavy minerals in fluvial channels. In this study we use pit-trap s to determine relative rates of transport and estimate transport equi valent sizes of cassiterite and sediment on a coarse sand-gravel strea m bed in Malaysia. Results show that for grain sizes finer than about 180 mu m (80 mesh ASTM) cassiterite grains have the same average trans port rate as sediment grains roughly three times larger. This informat ion can be used to identify and correct geochemical data for Sn anomal ies resulting from accumulations of cassiterite that develop on the st ream bed in response to the high density of cassiterite and changing h ydraulic conditions. In principle the same methodology should be appli cable to other heavy minerals.