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Accumulation of heavy minerals, such as gold and cassiterite, on stream 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 exploration geochemical surveys. Hence, it would be beneficial to be able to recognize such accumulations and, if necessary, correct for them. This, however, requires an improved understanding of the sedimentology of heavy minerals in fluvial channels. In this study we use pit-traps to determine relative rates of transport and estimate transport equivalent sizes of cassiterite and sediment on a coarse sand-gravel stream bed in Malaysia. Results show that for grain sizes finer than about 180 μm (80 mesh ASTM) cassiterite grains have the same average transport rate as sediment grains roughly three times larger. This information can be used to identify and correct geochemical data for Sn anomalies resulting from accumulations of cassiterite that develop on the stream bed in response to the high density of cassiterite and changing hydraulic conditions. In principle the same methodology should be applicable to other heavy minerals. |
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