COMPONENTS OF A RECOVERY FACTOR IN GOLD AND TIN DREDGING

The usual measure of performance in gold and tin dredging is the R/E f actor. It compares actual production or recovered grade for a given pe riod with that estimated from the original sampling. The factor is a m ultiple of four component factors, each ideally approaching 1.00. The estimation factor reflects the errors involved in determining the grad e and depth of single drill-holes or pits. It is influenced by the cha racteristics of the gold or cassiterite and of the host sediments, the sampling method and the manner in which the sample is evaluated. The results are combined into an ore reserve, from which a planned dredge course is selected. An optimum selection factor is achieved by a highe r drilling density. The drill-hole spacing is dictated by cost, the gr ade variability, the reserve estimation method, the size of the dredge and the cutoff grade relative to the average grade. Any failure of th e dredge to excavate the total volume contained within its course affe cts the excavation factor. An irregular bedrock profile, permafrost an d some operating procedures are important contributing factors. The re quired dredge throughput rate influences not only the success in diggi ng recovery but also the treatment factor, which reflects the equipmen t, the conditions under which the plant is operated and the physical f eatures of the gold or cassiterite. No two alluvial deposits are the s ame, but, in general, the greatest divergence from 1.00 is invariably demonstrated by the estimation factor. A major variation in one of the other three factors may also sometimes be the chief cause of the over all R/E factor being significantly different from the ideal figure of 1.00.