GOLD AND SILVER.	237
	The complex nature of western ores, especially, and the gradations from one well-recognized class to another render essential some fixed measures for the terminology used. The dry or siliceous ores com­prise gold and silver ores proper, as well as fluxing ores carrying con­siderable quantities of iron and magnanese oxides and very small quantities of gold and silver, and precious metal bearing ores carrying copper, lead, or zinc in quantities too low to classify them as copper, lead, zinc, or mixed ores. The distinction between gold and silver ores is not here made. The total number of silver mines and the total production of true silver ores are both relatively very small. The copper ores include those containing over 2\ per cent of copper, or less than this in the cases of the great disseminated copper deposits of the West and of the Lake Superior ores; the lead ores are those con­taining 4-1/2 per cent or more of lead, and the zinc ores are those contain­ing 25 per cent or more of zinc, both irrespective of their precious metal content. The mixed ores are combinations of the ones enumerated. Ore production in short tons and average extraction value of gold and silver per ton in 1911, by States and Territories."