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Jo Dandy Mill, Raven Hill.
This sadly not so great view of the Kavanaugh-Jo Dandy Mill on Raven Hill shows a plant that is treating a large mine-dump on Raven hill and is right at its source of supply of ore.
The ore is shoveled and trammed by hand from the dump to the mill, where it is dumped over a grizzly into a 10 by 20-in. Blake crusher set to break to about 1½ inches. Two stands of 16 by 36-in. rolls take the product of the crusher. The product of the rolls is elevated to a hexagonal trommel screen 8 ft. long and set with 1 ft. inclination in the 8 ft. This screen is 3-mesh No. 12 wire and runs at 15 r.p.m. Oversize from this screen returns to the rolls again; and the undersize is delivered to a belt-conveyor which transfers the material to the leaching vats.
There are four of these leaching vats, 5 ft. deep and 30 ft. in diameter, and of about 125-ton capacity, in use. In charging the material into the vats, considerable care must be exercised to avoid channeling later on account of the large range in size of the material treated. Solution is first applied from below for the same reason. But one strength of solution is used, from 1½ to 2 Ib. per ton. The first solution stands on the ore for 12 hours and is then withdrawn and the ore allowed to drain for aeration. The cyanide leaching treatment is continued for about three days, the vats being allowed to drain well between applications of solution to promote oxidation as thoroughly as time permits, the complete cycle for one charge being about seven days. Just enough water wash is used at the last to keep up the solution in the mill; and then the exhausted ore is shoveled out of the vat by contract and trammed in hand-pushed cars to the dump.
This would seem to be one of few mills in the district not troubled by a lack of convenient dumping room.
The pregnant solutions are precipitated by zinc shavings in the usual 6-compartment boxes, the barren solution going to the storage vats. The cyanide solutions are made up to strength by adding the salt at the head of the zinc-boxes to keep the precipitation good.
Thomas Kavanaugh, who is operating both this and the Homestake plants, says the rock is a sylvanite ore containing considerable arsenic and manganese and is extremely refractory, with not over 10% of free gold. He says he is securing about an 85% extraction and that the ore runs about $2 grade, which is an extremely good result on such coarse refractory material.
Image Note:My Collection; Scanned from page 298 in the August 23, 1913 issue of The Mining and Scientific Press; from a 300dpi scan.
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- Page 298; The Mining and Scientific Press [Vol. 107, No. 8] - Published in 1913.
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