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Author: Admin | 2025-04-27
Depths, thug giving more exact information on the nature of the ground;(c) if desired, fresh samples can be taken at any depth by sampling the sides of the shaft, provided, of course, that the shaft is not in running or very wet ground.Generally shafts cost more than bores, and the expense of sinking a sufficient number of them to thoroughly test a deposit may be prohibitive, and for this reason boring is the usual practice. In the writer’s opinion a few shafts should always be sunk in conjunction with a boring scheme, both as a check on the values and to give more accurate information as to the nature of the wash. In several cases boring gave a very close approximation to the actual working results, but in other cases the results were ridiculously high, and in one or two other instances rather low. However honestly and carefully the work be done, values as got by boring must always be accepted with caution.As showing the advantage of large over small samples, the following figures are significant:Case I.—All the dirt taken from a drive was treated in a sluice; as an alternative test a smaller sample was got by taking a shovelful from each truck. The result showed that the small sample gave only 53 % of the bulk test.Case II.—Bores were sunk in drift, and shafts were then sunk in the same locality. The bores gave a value of 2.16 lbs. of tin per cubic yard, while the shafts gave 4.1 lbs. —i.e., the bores gave only 53 % of the value given by shafts in the same spot.Case III.—Twelve blind shafts were sunk below a tunnel, and bores were put down on the same sites. Without exception the result of the bore was less than that yielded by the
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