The Effect of Increased Classification Capacity at the Allenby Concentrator

Considerable thought and discussion had been devoted toward provision for increased milling capacity at the Allenby concentrator of The Granby Consolidated Mining, Smelting and Power Company operations as early as 1940. During the war, plans for the installation of an additional grindi.ng unit were formulated but were not carried out. It took considerable time after the war to prepare the mine again for its highest rate of production since, with the scarcity of men, development work had been sacrificed in favour of maximum ore shipments. In order to prepare for the expected competitive market in copper, the matter of increasing the capacity of the concentrator was again given serious attention. As ore became available in the mine and the output of the mill was increased, limitations for a satisfactory recovery were observed, due to the overloaded condition of the classifier units at the higher tonnages. From a metallurgical standpoint, the ore from the Copper Mountain mine had always been difficult to treat on account of the finely disseminated character of much of the mineralization and the difficulty of grinding to the desired fineness. This trouble has become aggravated with time as an increasing amount of wall-rock has diluted the ore and lower grade orebodies have been mined. It therefore has been, and is, the practice at the concentrator to maintain the maximum amount of reduction in size of material fed to the flotation units as is possible for the daily tonnage to be milled. This means that all the grinding units are operated for the maximum possible time, and that the classifiers are regulated to return as much feed ?as possible to the mills. The number of tons to be milled for ?the day is determined by the concentrator superintendent after ascertaining the availability of ore from the mine, the condition of the concentrator ore bins, and the need for repairs in the rolls plant. In order to maintain the tonnage des1red, hourly estimates are made of the rate of grinding by weighing the amount of ore contained on one foot of each of the belts conveying the feed to the various ball-mills, and adjustments are made accordingly.