. The sampling and estimation of ore in a mine . so that each shaftyielded one large sample. From the weight of this andthat of the resulting grains of tin, after panning down,the percentage was calculated. The estimate of quantitywas based upon the length of channel, within the bound-aries of the property, multiplied into an inverted tri-angle, ABC, the base of which was the top width of the —58— SAMPLING AND ESTIMATION OK ORE IN A MINE deposit and the apex the gutter. The cubic yardsthus obtained gave an approximately correct result asto quantity of material, but the estimated average con-te
. The sampling and estimation of ore in a mine . so that each shaftyielded one large sample. From the weight of this andthat of the resulting grains of tin, after panning down,the percentage was calculated. The estimate of quantitywas based upon the length of channel, within the bound-aries of the property, multiplied into an inverted tri-angle, ABC, the base of which was the top width of the —58— SAMPLING AND ESTIMATION OK ORE IN A MINE deposit and the apex the gutter. The cubic yardsthus obtained gave an approximately correct result asto quantity of material, but the estimated average con-tent was all wrong, because the method of calculationdisregarded the fact that the richest stuff was concen-trated at the lowest end of the triangle, and actuallyformed a very small proportion, in weight, of the , the ground was re-sampled. The totaldepth of i8o ft. was, in the case of each shaft, subdividedinto sections of 30 ft., except the last 30, which was fur-ther divided into two portions, one of 20 ft., and a lowest. :/ ^-^/- /~^^- } > F+1 Basalt fiVyj Granite Fig. 7 of all, only 10 ft. thick. The first 30 ft. was found to bealmost barren, the next 30 ft. assayed per cent, of tin,the next 30 ft. per cent., and so on, increasing grad-ually until the last 10 ft. was reached. This was veryrich, per cent., on account of concentration in thegutter or bed of the channel. Each layer was calcu-lated separately as to quantity and average contents, giv-ing results which proved the bottom to be very profit-able, but difBcult to work on account of want of gradientfor hydraulicking operations; while the uppermost por-tions of the deposit were found to be too poor for profit,but yet requiring handling in order to get at the lower-lying part of the gravel. -59- SAMPLING AND ESTIMATION OF ORE IN A MINE The method first described would have given a verymuch exaggerated idea of the cubic yardage and a falsenotion of a uniformity of value, besides ignor
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