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The Mines at Rio Tinto Spain November 17, 1883—Among the most remarkable mineral deposits known, those of Rio Tinto, Spain, possess more than ordinary interest for Americans, because the company working them is one of the leading competitors in our own markets of the miners of pyrites for sulphuric acid manufacture, and at the same time the one that has during the past few years rivaled our copper producers in placing growing quantities of metal on the markets of the world. An elaborate report by a leading French engineer, M. E. Cumenge, and printed during the current year, throws a flood of light on the present condition and the future of the great mine, and contains many points which deserve the attention of engineers and metallurgists. The deposits of the Province of Huelva, of which Rio Tinto is one, were known to the ancients, Phoenicians and Romans, who, as evidence of their activity, have left more than 180 miles of workings in the Rio Tinto deposit alone, and accumulated no less than twenty million tons of slags and cinders on the neighboring dumps. A met- alliferous zone extends in approximately an east and west direction for a distance of twenty leagues from El Castillo de las Guardias, north of Seville, beyond the Portuguese frontier. It is four leagues wide. Rio Tinto is situated towards the eastern end of the zone, while the mines of the Tharsis Company are located toward the west, there being a series of minor deposits between the two, among them El Castillo, Peña de Hierro, La Cueva de la Mora, Sotill, St. Elmo, La Joja, La Zarga and some others, some of them, like the Buitron mine, being partially exhausted…. The Rio Tinto deposit consists of a com- pact mass of cupriferous iron pyrites occa- sionally showing patches of gray copper, blende, and galena. The ore as mined is divided into two classes, by sorting accord- ing to its contents of copper, about one quarter of the quantity being exported, while the rest is treated on the spot. Samples are taken from every car of ore loaded, and, the entire sample being crushed, a daily average assay is made. M. Cumenge estimates the general average for the year 1882 at 2.88 per cent of copper. The export ore, 250,000 tons annually, is sold by the Cornish assay, which understates the true percentage by 0.75 to 1.0 unit, so that the actual percent- age of copper in this class of ore lies between 3.25 and 3.50 per cent and from 48 to 50 per cent of sulphur. The ore treat- ed on the spot carries on an average 2.50 per cent of copper…. Until now, all the estimates of the engi- neers have referred solely to the mass of ore worked by an open cut, which until a recent date furnished almost all the ore. The ancient workings, which, to a certain depth, were numerous, had evidently the object of mining the seams of richer ore in the mass of average grade, and this fact alone explains the increase in the percent- age of copper when virgin ground was opened. Experience has proved that, in taking five millions of tons out of the open cut, almost the entire mass is uniform and essentially composed of compact iron pyrites, with spots of copper pyrites and black sulphide. In the future, however, the fact must be taken into account that the Western part of the South vein, known as the San Dionisio lode, is more complex. The copper becomes a more important fac- tor. Pure copper pyrites is not found in spots, but true seams, and other copper minerals become more abundant, so that the average thus far is 4 per cent of cop- per, and selected lots assay from 7 to 8 per cent. The Rio Tinto Company bases great hopes upon this part of the ground, and has begun great underground workings…. MARCH 2016 • E&MJ; 67 www.e-mj.com E & M J 1 5 0 Y E A R S