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Show 55-ton trucks was then purchased in 1961. Two 65-ton trucks were added to the new fleet in 1963 for hauling waste. Both 65-ton units are considered experimental and are leased on an optional lease-purchase plan. All of the diesel-powered, 2-1/2-cu. yd. shovels were retained in the pit, but two electric shovels were purchased--one in 1961, the other in 1963. One electric shovel has a 7-cu. yd. dipper, the other an 8-cu. yd. dipper. The skip loading station in the pit was originally built so that 20-ton capacity trucks would dump into one of two hoppers which, in turn, would fill the 20-ton capacity skips. Pima's operating staff felt that a cost saving could be realized by the utilization of larger loading and hauling units working in conjunction with the skip hoist. The means of achieving this flexibility involved a modification of the skip loading equipment. The obvious solution was to provide a grizzly and some surge capacity at the loading station. This problem was immediately tackled by Pima and Utah Construction and Mining Co. design engineers. A 40-ton surge bin was placed over each skip measuring pocket, and a Hydrastroke feeder installed in each bin. With this new arrangement, the loaded ore (or waste} trucks' are directed onto the drive-over structure and positioned for dumping by signal lights. The truck driver pulls a switch (a hanging rope by the driver's window) that opens the air-operated steel deck gates, and then dumps the ore or waste load directly into the surge bin. The skip loading operator uses the Hydrastroke feeders to push the right quantity of ore into the skip measuring pockets. As soon as an empty skip is positioned, arc gates are opened at the bottom of the measuring pocket, and the skip is immediately filled and sent to the rim of the pit. A. 7-cu. yd. electric shovel is used for loading 27-ton trucks for haulage to skip loading structure. If an oversize boulder is dumped into the surge bin, the skip loading operator positions a hinged grizzly to the edge of the bin and then pushes the boulder and other ore onto the grizzly with the Hydrastroke feeder. an position, the grizzly rests against the surge bin at an angle of 10 deg.; when not in use it is up-ended to an angle position of about 50 deg. Boulders that do not pass through the grizzly fall to the ground at the bottom of the loading station to be carried away by a front-end loader and later blasted to size. Except for the air-operated deck opening gates, everything at the skip loading station is hydraulically controlled by a single man at a dual control panel. Only the bottom loading station on the skip hoist system has been converted to this new arrangement since the upper two stations are rarely in service now. The new skip loading facilities permit scheduling of only approximately 200 truck trips to fill 300 skip loads per shift instead of the previous 300. The present Pima pit has a depth of 540 ft. and will be deepened four more benches to a final depth of 750 ft. by 1967, |
