Ch. 1: Gold and Silver in 1915

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	GOLD AND SILVER.	785

	(from ores as distinguished from gravels), mainly from underground workings, including those whose ores are valuable chiefly for copper, lead, or zinc, but which contribute precious metals as by-products. In addition to producing mines here enumerated, many properties were being prospected and developed without making any output in 1915, and many other mining claims were being held by assessment work only. The enumeration of placer mines is less satisfactory than that of deep mines, because some of the operations are only temporary and individually small, and because the production is frequently by transitory miners not regularly working placer ground. The unit, so far as possible is, however, as for deep mines, not the operator, but the mining claim or group of claims. Number of producing mines in 1015. °


	a Philippines and Porto Pico not included. b Number of mines contributing to silver production. « Number of mines contributing to gold and silver production. The table shows the number and distribution of mines producing gold and silver in the United States and Alaska. With the exception of (1) some of the Michigan copper mines, (2) all zinc mines in the Eastern and Central States, and a few in the Far West, and (3) all lead mines of the Central States (except a few in Illinois and southeastern Missouri), practically all mines producing copper, lead, and zinc in the United States and Alaska produce gold and silver also. The table, therefore, with these exceptions, is a table of mines producing these five metals. It also includes certain mines producing oxidized manganese iron fluxing ores of Colorado, Utah, and elsewhere, whose ores contain small quantities of precious metals, especially silver, and are smelted as flux.

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