MODERN DEEP.ALLUVIAL MINING.

Dominion, Volume 1, Issue 182, 27 April 1908, Page 8

MODERN DEEP.ALLUVIAL MINING.

MACHINERY FOR UNWATERINC. AN INTERVIEW 'WITH MR, iI."MONTAGUE M.A. Mr. H. Montague Smyth, who lias just returned from a visit to the Cornish, Welsh, and Australian mines, gave some interesting information to a member of our staff. The object of Mr. Smyth's visit was to prepare a-report upon the best and most up-to-date electrically-drivcn pumps for the unwatoring of his company's (Ross Goldfields, Ltd.) mine, and to select the most approved mining plant for treating the wash-dirt., Use of Electricity. During recent years very radical changes, have been made in the design of mining pumps. This has been brought about by the extensive use of electricity for the distribution of power about the mine. The introduction of producer gas plants and tho perfecting of large gas engines have materially helped in thi3 direction: In the Cornish tin and copper mines there are now somo very fino producer gas plants, driving electric generators which supply all, the current for pumping and working the mine. In-.tho Welsh collieries the colto oven gas is now largely used to drive immense gas eiigines direct coupled to alternating current generators. At one mine at Bargoed, where Mr. Smyth was inspecting .and testing .some pumping plant, -JOOO horse-power is at present being generated and distributed underground at a voltage of 3000 volts. The gas engines at this mine are 2000 brake horse-power each,'and three aro at present installed.

A . Difficulty. As soon as mine managers had installed cheaply-generated' electric power in their • mines, they naturally tried to drivo their mine pumps by it, and wero at once faced with the difficulty of connecting a fastmoving motor to a slow-moving pump. They therefore . demanded . and have recently obtained a fast-working pump capablo of being directly connected to an .electric motor.These pumps, aro of two kinds, high speed displacement pumps, and multi-stage: centrifugal pumps. AVhile in England Mr. Smyth tested some very large high-speed pumps and found them most satisfactory in every way. The pumps selected. and ordered for, tho Ross Goldfields aro tlio very latest and best, and- embody patents obtained, only a few months ago. Tho Pclton wheels for the Ross Goldfields aro being built by James Gordon and Co., London, and they .will bo tho finest of, tho kind that have over been introduced into the Dominion. They will bo similar to those supplied to tho Indian Government for its large electric transmission scheme. Tho Pumping Problem. When asked- how. the pumping problem at Ross compared with other large pumping stations ho had .seen, Mr. Smyth replied that he had. inspected and tested a number of plants in both Cornwall and Uales which altogether put the water problem in his mine at Ross into tho shade. On the Victorian mines tlio water problem was simply enormous, in fact a Jargo subterranean river had to be pumped dry. The following mines, which are situated within a mile or so of each other oil tlio samo lead; anr pumping 31,072,640"' gallons per day, made up as -follows:— , . . 1 : Gallons ' t - per day. The Chalks No. 3 Consolidated... 2,000,000 The Junction Deep Loads of Victoria .... ' ... ' ... . ... ' 2,600 000 The Victorian Deep Leads ' .... 2,500,000 ... -...<5,000,000 Loddon; Valley Goldfields ... ... 8,000 000 The New Havillah ... 5,336^320 Ihe Cliarloite" Plains ... ... 5,636,320 Toial •••.- — : 31,072,640' • Thci two . last-mentioned mines - alone up 13 847 w, °! W(l ? ' ■ lulh, ' )od IJ, gallons from their 360 ft. level. Ihe following example's will , givO some idea of what tlieso figures mean. If this water were formed ; into. a river 10ft. deep, and as wide -as Lambton Quay at its widest part .(abojufc. 100 ft.), its total length ' would be.420 miles. Or again, if it.were placed in 400 gallon tanks (4ft. by 4ft.), and these tanks were; placed side by side,-there *?nld 26,227 miles of them, more than sufficient to go round the globe. .Some cf these Victorian deep alluvial mines have to. pump for nearly two years boforo being ablo to reach any of tho gold-bearing wash-dirt. This is duo to the-geological formation of tho country, arid it.is only the:mddern appliances and . methods of working which enable'this ground to be worked at all. ' An Ancient River-Bed./ ' In ancient times there, was a large valley, the bottom and sides of which w T ere, formed of Silurian rock, ; and an rimmonse river flowed down this valley, and deposited'gold all over tho bottom. Tho alluvium in time roso to somo. height; then came an eruptive period,, and a'deposit of lava was made all over tlio valley;, almost iillftig it up. In-later-times soil was deposited on top of this, so that-now the surface (which is good -agricultural land) is almost flat, and . the line of tho old valley can only bo found- by boring. Between the over-lying Basaltic rock and the Silurian bed-rock* tlio ground is all saturated with water, ■ and forms a sort of subterranean lake all down this ancient river-bed. Oiil and New Methods. The old method of working this alluvial auriferous wash was to sing , right on to it from tho surface. The expense, difficulty, and danger of sinking through and' working in this wet ground were too much for the Australian companies• that tried it.. Companies. with larger capital were then; constructed in London, and a different method of unwatering-the ground (namely from, below) was introduced, _ aiid is now universally used. A shaft is sunk some distance away on what was tho higher side of this old valley, striking tho reek above the levfel of this ancient river. This shaft goe3 right down through the Silurian reek,- until" it- is some fifty feet deeper than the bottom of tho old valley. A main level is then put in through the Silurian rock-bed, right across and under the. old valley. Largo pumps are' installed on this level, and three inch bore holes aro put up into the wash, which is gradually drained. Jump-ups and balance, shafts aro then put up from below, arid tho wash taken out and . hauled .to tho surfaco, whore the most modern appliances are used to recover the gold. Some idea of. what can now bo done by usyig modern screens, puddlers, slime tables, otc., can f be gathered from tho fact that 95 per cent, of the gold is now caught at nearly all the large mines. As might naturally bo expected, the water to be dealt with ill the Victorian mines is very heavy at first, and then falls-off rapidly. Ono which was pumping 8,000,000 gallons per day somo short time back is now dealing with only 3,000,000 gallons per day. Ceologioal Conditions*. Tho geological conditions at Ross (says Mr. Smyth) aro altogether different. The water to be dealt with on the most liberal estimate cannot be more than 3,000,000 gallons per day, and the'mines-we're: worked thcro on two separate occasions when less than 1,000,000 gallons per day were being pumped. In Victoria thoro is only ono layer of wash, and the gold-bearing portion is only a few. inches, thick, while at Ross there are eight distinct payable layers of gold-bearing wash, averaging, about five feet in depth. Tho water at Ross which has to be pumped is simply the proportion of the rainfall which finds its way underground through 400 ft.. of overlying gravel. Tho mining plant to be,installed at Ross will bo similar to that usod at present in Victoria. , A Large Field in New Zealand. . Mr. Smyth, is very satisfied with tho results of ■ his visit. Everywhere, Both at Home and in Australia,, ho met with tlio. greatest courtesy and .kindness' from tho mine-managers and directors of the various mines ho visited, and ho was given facility for testing and examining any plant he wished to see. Ho is strongly.of opinion that there is a large field in New Zealand deep alluvial gold-mining, if. only the best modern machmory now available and w-.to-date .methods .of areuJised,