Ch. 1: Gold and Silver in 1911

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	220	MINERAL RESOURCES.

	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 of 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 mills 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 be 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 following 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 of the bullion, either base or unrefined, is readily known. In the third item the refining loss and in the fourth item the combined concentrating, smelting, and refining losses must be considered. In the case of the precious metals the concentrating losses may be large and must be allowed for, but the smelting and refining losses are known to be very small and in ordinary practice to be more than offset by certain gams. These gains are of small quantities of precious metals (not paid for, but actually recovered from ores of copper, lead, and zinc) and certain differences in quantity of gold and silver between actual recovery and basis of settlement—for

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