Prospecting and sampling of potential gold deposits is performed by the prospector who uses his experience and criterion to evaluate preliminary the deposit. There is no rule as to the number of holes that should be studied. It is possible that some drill holes would be required to give satisfactory results, than shafts. If the values are comparatively evenly distributed over the tract to be examined, fewer holes would enable nearer approach to a correct estimate of values than where the value is uneven. In places where the character and gold are comparatively well known in parts of the gravel that have been sampled, less careful examination is necessary on intervening tracts in order to determine most of the conditions and even the gold values.
In comparatively shallow ground, where there is not much water, it is much more economical to sink shafts than to drill, and the results will be found more satisfactory. By proper sampling is meant the determination, from a comparatively small sample, of the values in a much larger volume of the same material. Care, judgment, and experience are necessary, and all such work, whether done by drilling or by sinking shafts, should be put in charge of an experienced man. Gravel lifted by drills or taken from a shaft must be accurately measured or weighed, and proper allowances made for expansion when loosened. Allowance must be made for excess of bowlders not sampled, and for excess of gravel beyond the normal width of the drills that may come in and be lifted.
Errors in sampling frequently occur from the squeezing in of material around the bottom of the hole, so that more gravel than is called for by the size of the hole is lifted. A check on this is to drill and pump in a section and weigh the material. It has been noted that sliming and consequent loss of gold sometimes results when too long a period of churning transpires before pumping the hole. The casing should be kept driven below the point of drilling, whenever possible. When the gold is present as fine particles, the pan and sluice will not recover all of it, but will recover all that the best saving tables in the dredges will recover, and may save considerably more. But when it is considered that if some of the finest gold now being recovered be shaken up in a bottle of clear water it will take one or two hours to settle, there can be no question that some is lost whether the sampling is done by panning or rocking, and also in the sluicing. How much this is could be determined by gathering samples, especially of the water from the pans and rockers and also at the ends of the sluices and subjecting them to proper tests. It would seem that this work should be undertaken and carefully carried out by the dredge people. If much gold is being lost, there is a spur to ingenuity in devising means for recovering it.
When the presence of gravel is important, the depth of the gravel varies from 8 to 15 m, and will average 10 m. It may be comparatively loose, a clean wash, practically free from clay, and contains practically no bowlders large enough to interfere with digging. In the present river channel and adjacent ground there is no need to blast the banks, but in some of the higher ground it has been found advisable to use powder.The false bedrock to which the gravel is dredged is comparatively flat and quite soft, being merely a bed of volcanic tuff carrying other gravels, and may be dredged to sufficient depth to take up all that contains gold.