OCR

$2-Million Mill Expansion Finished Early Thirty-Eight Days Ahead of the planned target date, work was completed in August, 1963, on the expansion of Pima Mining Co.'s copper concentrator from 4,000 to 8, 000 tpd. Located 20 miles southwest of Tucson, Ariz., this project was one phase of a 6-year mine and plant expansion program which will be completed in 1967 at a total cost of $8 million. In enlarging the crushing, grinding and concentrating facilities, every effort was made to revise existing equipment co conform to the new capacity requirements. Actual work was started by the designers and contractors, Utah Construction and Mining Co. , in January, 1963. The $2 million mill expansion consisted of the following changes and additions: (1) a second tertiary crusher was installed; (2) a stockpile-surge pile was formed between the secondary and tertiary crushing; (3) the dust control system was revised; (4) the mill building was extended 80 ft; (5} a new rod mill and two new ball mills were added to the grinding section; (6) the old rod mill was lengthened by 3 ft. ; (7) a total of 50 new flotation cells were added to the flotation circuit; (8) the regrind circuit was revised; (9) a tailings thickener was added; (10) the water reclamation system was revised; (11) instrumentation and partial automation was added to the grinding, classifying, pH control and tailing disposal sections; (12) overhead traveling cranes were installed in the flotation section. Before the recent changes were made, the crushing section of the Pima mill was essentially as follows: ore was delivered by truck to a primary c usher surge bin, and a chain feeder drew the ore over a 7-in. grizzly to feed a 66 x 84-in. jaw crusher set to produce minus 7-in. material. The crushed ore was then transported to the secondary crushing and screenbuilding by a 54-in. conveyor. The ore was screened over two double -screens dressed with 2 x 18-in. rod grizzlies on the top deck and 1/2 x 2-in. clear opening woven wire on the lower deck. Oversize from the top decks passed to a 7-ft. crusher and oversize from lower decks to a 7-ft. crusher. Feed to the screens was split by an adjustable plate. The screens fed their respective products by gravity into the crushers or onto the finished fine ore conveyor. The crushers discharged directly onto a return closed circuiting conveyor. An automatic tripper finally distributed the minus 1/2-in. ore to two 3,000-ton each fine ore storage bins adjoining the concentrator.