DEEP LEVEL MINING AT ST. BATHANS.

Otago Witness, Issue 2924, 30 March 1910, Page 28

DEEP LEVEL MINING AT ST. BATHANS.

The deep levels at St. Bathans have come into a good deal of prominence of late, consequent upon litigation concerning the ownership of portion of the areas comprising them. Interest is further stimulated by a report that steps are being taken to exploit some of the deep levels adjoining the . famous Kildare sluicing claim. This ground has a lower dip on the western side, and the lead can be seen in the outcrop. A gentleman possessing an intimate" and scientific knowledge of the whole area is. of opinion. that the whole deposit is of marine formation, and at the time it was deposited .was horizontal, or nearly so. : ;•' A tremendous upheaval occurred, and this accounts for the tilted position of the layers which dip at angles -varying from 18 degrees to 45 degrees towards the direction of the township—in fact, tne whole township is built upon the quartz drift deposit. The angle of the dip is found to decrease the deeper the seams are traced, and calculations made at the back of the township on the surface layers show a decrease. of about _ 8 degrees in the dip of the - strata, thus indicating that "at a considerable depth the layers will probably flatten, out, and on this flat, which may "extend'for miles, a. rich harvest of gold will probably be won. The ground in the centre of the basin known as "ETildare Hill'" has been taken out to a. depth of 18.0 ft by the.process of hydraulic elevating, and in connection with this, in passing, it can be stated that the highest, single lift in.the world has been used, but all the, ingenuity and modern designs of competent "hydraulic engineers have.6o far failed to reach a greater depth, so that work is confined to the higher levels at the eastern and western ends of the basin, where very profitable returns are being obtained. But it is only a matter of time when this ground will also get beyond the limit,' and it follows that if some new method is not adopted, the rich deposit will remain unworked. " From this basin alone about £300,000 worth of gold has-been _obtained—the surface being ~'only"' scratched, - and the ground worked in the leep levels has given returns of 4000 oz per acre, nearly all the gold haying been obtained from a seam about 4ft in thickness. But ■it is quite apparent that there -is now only one method which can be successfully adopted to win the gold from the deep ground, and that is by sinking, stoping, and tunnelling. Nowhere else it* New Zealand . has Nature been so bountiful, almost ideal conditions for -this class of work having been provided. There are extensive beds of lignite overlying the wash in portions, and where this is so the pay gravel is all concentrated in a seam about Ift in thickness, but stopes require to be 3ft high in order to facilitate working. The lignite could be mined and sent up to generate the power for the engine and winding gear," and would not be wasted, as is the case in hydraulic mining.- Electricity -could also be generated by water power at small cost. In deep-level mining, filling-in is resorted to. as -. it saves timber and prevents creeps in the workings. Adjoining these deep levels are lara'e Quantities of alluvium which could. be used for that, purpose, and wo'uld.. orobably return ; enough gold to pay the cost of sluicing into the stoned around, and while one portion was being- filled in stoping could be carried on elsewhere, the water being pumped to the surface to be used over as-ain. The stratum overlying the gravel, when not composed of lignite, is hard clav, and_ large areas can he stoped with a few props, which can. be withdrawn as the filling proceeds. The latter ,- s highly, important, and has meant success or failure to many similar ventures. There is sufficient drainage water from the surrounding hills to fill in the around and wash the material: consequently bv this method all the gold in the ground will be saved. It is well-known that at present a larere percentage is lost on necounf of the immense volume of-water used and through the wash becoming intermixed with . the greasy clay. The average value of the gravel is about 17dwt oer ton. computed from oast returns extending over many vears of work on the same lf>-"er. and as all' the conditions are fWon'iMe. we have now on-lv to oomnare this *vrtt> other mining ventures. _ At Barewood mine, where the material is quartz, and has to me crushed, the working expenses do not exceed ■£l 1« per ton. A careful estimate of values indicates a nrofit of half an ounce per vard. and that 20.000 vards could he treated ner annum bv the nrooosed method of mining the St. Bathans basin. It. is generallv conceded that it "is onlv a question of a. little time when the available ground will be worked out by the nresent methods in use. and ; f the pronosed svstem could be r>roved to be successful at Pt; Bathans. there sta other lare-e areas which could iimilarlv worked in carious parte of Otago-with eaual nrosnects ■of success. Once established on these lines, deen-level alluvial mining" would receive an immense impetus, and would in all m'obabiiitv be placed on a substantial basis.- and •30uld be reasonably. exDected to produce «teadv and payable returns for many years to come.