Transactions of the Institution of Mining Engineers Volume 6
This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1894 edition. Excerpt: ...crystals of stibnite, is often seen. Generally speaking, the ore has a very variable hardness and composition; it contains a very large variety of metallic sulphides, and must be ' With a soft decomposed ore, or oncin which the gold is very fine, a slow rate of drop is generally to be recommended. Soft and high sulphide ores should usually also be stamped with a low drop. considered as a combined silver and gold orc, containing from to 10 per cent. of sulphides with an average of 2 to 8 per cent.; it approaches the boundary-line dividing a free-milling from a refractory ore. Reviewing the chief characteristics of the milling, we see that the feeding is done by hand and is very rough, being left to boys, instead of employing trained men. The former shirk breaking big pieces of rock, preferring to throw them into the feed-opening, where, if they stick, they are belted-in with a few blows of a sledge-hammer. The result of the absence of rock-breakers and automatic feeders in lieu of this bad handfceding is seen in the excessive wear of the shoes and dies, averaging 1 '5 ounces for the shoe and 7'5 ounces for the die. The feeding is also too high, the batteries being kept choked with ore, which reduces their efficiency.' The mortar-boxes are of the same pattern, whether employed for rapidly crushing soft material or the slower treatment of average ore. As no amalgamation is done inside, they are too wide. When the mortar is merely a pulverizer, the pulp should be expelled as soon as possible; too roomy a box promotes dead-stamping, keeping in ore, after it has been stamped fine enough to escape under ordinary circumstances. When amalgamation takes place inside, the case is different, but at the Thames, it would seem...
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