28 APRIL 1939, Page 51




THE annual meeting of Crown Mines, Limited, was held on April 21st in Johannesburg.

Mr. John Martin, the chairman? moved the adoption of the report and accounts, and after reviewing operations and financial results for the year 1938, he said the consulting engineer reported that development results had shown no marked change and had been generally satisfactory.

A large proportion of footage on the main reef leader had again been accomplished in the Far Western section, where values dis- closed, though still low, had shown a further slight improvement Footage developed on the south reef had been less than in the pre- ceding year, but values disclosed had shown little alteration.

Development work on the main reef had been continued, and the old No. 2 shaft was being reopened and re-equipped in order to facilitate exploration and exploitation of that reef in the upper levels of the eastern section.


Payable ore developed on the main reef leader and the south reef was estimated to total 3,995,900 tons of an average value of 5.0 pennyweights per ton. That was 39,380 tons more than in the previous year, and its average value was 0.2 pennyweight higher, due to the smaller proportion of ore developed on the lower valued south reef

The re-estimated available ore reserve totalled 20,920,700 tons, averaging 4.9 pennyweights per ton over a stoping width of 47.3 in. In addition there were 5,139,500 tons of payable ore of an average value of 5.7 pennyweights per ton contained in the shaft and safety pillars which could not at present be stoped.

The available reserve showed an increase of 313,200 tons over the previous estimate, its average value and estimated stoping width being lower by 0.1 pennyweight per ton and 1.7 in. respectively.

The comprehensive programme of main vertical shaft sinking, which had been steadily pursued for many years, had now been completed, and the opening up of a reef at greater depths was being accomplished by the sinking of additional incline shafts. The average depth at which development and stoping operations had been conducted last year had been 5,00o feet.

PROVISION OF ADEQUATE VENTILATION The problem of providing adequate ventilation demanded, and was receiving, constant attention. The installation of additional fan equipment at Nos. 14, 15, 16, and 17 downcast shafts and at Nos. 12 and 18 upcast shafts had increased the quantity of passing down the first four shafts to 1,300,000 cubic feet per minute.

The mine workings were steadily extending both laterally and in depth, and it was consequently expected that that quantity of air would have to be increased in due course by the installation of further equipment and the construction of additional upcast airways.

In order to test another means of improving ventilation condi- tions at depth an experimental air-cooling plant had been erected on the 4xst level at No. 14B shaft towards the end of 1936. It had operated successfully on the whole, and although there had been several stoppages due to minor defects they could be over- come in any new plant of similar type which might be required. It had furnished useful information which indicated that, as the workings approached operating limits of depth due to increased rock temperatures and adiabatic compression, further important tonnages of payable ore could, by air cooling, be brought within the workable zone.

Am COOLING Owing to the large quantities of air which could be passed through mine workings the limit of mining depth due to temper- ature had not yet been reached in stoping operations, but the time was not far distant when cooling on a large scale would have to be resorted to. That question was now being considered, and it would Probably be found advisable to erect a large cooling plant at one of the deep level shafts as soon as the arrangements for its in- stallation could be completed.

Every effort was being made by extending the use of mechanical appliances and in other directions to minimise the effects of any ,-lortage of native labour that might be experienced from time


Mechanical scraper truck-loading units had been installed in all naulage developing ends, and the use of mechanical scrapers in topes which had given encouraging results was being steadily ex- nanded. Mechanical shovel loaders had lately been used success- fully in reef drives, and the number of those machines in opera-

ion now be increased.

(Continued at the top of next column) I COMPANY MEETINGS


(Continued from previous column) USE OF DETACHABLE BITS IN DRILLING

A labour-saving device which had beea closely studied during the past two years was the use of detachable bits in drilling opera- tions underground. The current practice of sharpening worn drills on the surface involved the transportation of about 22,000 drills of an average weight of 9 lbs. each in and out of the mine daily, and a very considerable native labour force had to be em- ployed for that purpose.

On the other hand, detachable bits could be transported to the surface for resharpening and back to the working places by the natives engaged in drilling. Preliminary work that had been done in the direction of obtaining detachable bits which would give a satisfactory drilling performance had furnished encouraging results, and the scope of the experiment was now being extended.

The report and accounts were adopted unanimously.