Ch. 1: Gold and Silver in 1912

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	232	MINERAL RESOURCES, 1912.

	The data for the mines' report of the United States Geological Survey may be classified as follows: (1) Gold and silver from placers in nuggets, dust, and bullion; (2) gold and silver in mill bullion (obtained by amalgamation, cyanidation, chlorination, etc.) from mills of mine companies treating their own ores, tailings, dumps, etc.; (3) gold and silver in base bullion, matte, etc. (by assay value), from smelters treating their own ores; and (4) gold and silver in crude ore, concentrates, old tailings, slags, etc. (by assay value), shipped to custom mills and smelters—all four of these classes of data being for material treated at the mines or shipped from them during the calendar year. The first item is the native gold (with silver in natural alloy) produced from placer mines and sold to Government mints and assay offices, and to refineries, banks, and traders. It is difficult to obtain accurate figures for this item only in some parts of Alaska, or from transitory miners elsewhere, or from miners who report only value received for their output. The second and third items cover metal production by mining companies whose mills and smelters treat their own ores and whose products go to the mints and refineries and are covered by confidential mine reports to the Survey. The fourth item, which covers raw mine products shipped for treatment, gives rise to the main apparent discrepancies between mine and mint-refinery reports on the production or gold and silver for the same calendar year. The discrepancies are due largely to the lapse of time between the disposal by shipment of the ore as reported from the mines and its arrival and metallurgical treatment at the mill or smelters, followed by the refining of the products, an interval in which large quantities of metals in ores reported from the mines as shipped in one year may be reported from refineries as produced in marketable form in the following year. For instance, ore shipped in November may be smelted in the following January, and the metal content would be reported from the mines for the calendar year preceding that for which it would be reported in marketable form by the smelters and refineries. The miners furnish the United States Geological Survey with confidential reports on assay values and tonnages of ore and concentrates shipped as the measure of their output, and the mine figures are reported by the Survey so far as possible in terms of recoverable metal; and the smelters and refineries report the metals eventually produced, first as unrefined and finally as refined. In using the mines report it should be noted that tonnages and metal output given are based not on ore mined but on ore treated or sold during the year. Of course most of the ore treated or sold is also mined during the same year, but some of it is necessarily mined during the preceding year. It must not bo overlooked also that the mines' report aims to give the recoverable content, not the assay content, of ore treated or sold. A part of the actual recovery is of course made during the early part of the fodowing year for ores treated or sold late in the year under review, but the basis of the report is essentially metal recovered at whatever time from the tonnage treated or sold during the year covered by the report. For the second and third items enumerated the recovery figures are easily had, as the ore is treated on the ground, and the metal content

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