The Pyrites Mines of Spain

Southland Times, Issue 12772, 4 December 1893, Page 2

The Pyrites Mines of Spain

By Edw. D. Peters, Jr., M.E. Amongst the musty Latin documents stored in the British-Museum is a brief description of the loss of a vessel while attempting to enter one of the Roman ports daring a storm. She came from Southern Spain, and was la’den with bars of copper, belonging to the Roman Government. But, vessel, crew, and cargo were all lost, and doubtless the price of armour experienced a decided upward tendency. This copper camo from the enormous deposits of pyrites which are found in the southern portion of the Spanish Peninsula, lying west of Gibraltar, and south of Seville. And important and profitable as they doubtless were to the Roman Emperor 2000 years ago, they are infinitely more important and profitable to Englishinvestors and manu> factnrers to-day. The ore occurs in immense masses, several thousand feet in length, from 300 ft to 800 ft in width, and extending in depth to an unknown distance. It is a mass of iron pyrites not a speck of rock being visible in the ordinary ore, and consists mainly of iron and sulphur in equal proportions. It also contains two to four per cent of copper, and half an ounce to one ounce of silver per ton, besides a few grains of gold. Two companies are working and exporting this ore on a very extensive scale—the Rio Tinto Company of London and the Tharsis Company of Glasgow. Each of these great companies owns extensive tracts of land, known to contain many deposits of the ore already described; and each company is a self-contained community, owning its own railway to the port of Huelva, its own mines, workshops, villages, schools, churches, hospitals, &c. The managers and. chief assistants, as well as the heads of the various departments, are nearly all English or Scotch, but the sub-foremen and workmen are natives of the country, and seem an industrious, contented, and prosperous community. The country about the mines is very hilly and broken, and if covered with the luxuriant vegetation proper to this latitude would be picturesque and interesting. But owing to the extreme dryness of the climate the hillsides are practically barren, and in the immediate vicinity of the mines tho sulphurous vapours from the treatment of the orc have destroyed every weed and blade of grass, thus allowing the rains to wash away the thin soil and expose tho naked skeletons of the hills in all their gaunt sterility. But the want of fertility on the surface is made up for a thousandfold by the lavish hand with which Nature has distributed her wealth underground. As it would be impracticable to mine these huge masses of ore by the- ordinary subterranean methods a system of open quarrying has been adopted, and to keep the sides of the huge excavations from falling in they are sloped down in a succession of steps, the bottom of the cut being the exact width of the ore body, whilst tho sides diverge towards the surface.

Some idea of the magnitude of these cuttings may be had from knowing that two thousand miners could work simultaneously in one of them without being crowded, and half-a-dozen locomotives may be seen moving at a time within the excavation taking out the trains of loaded waggons, whilst the empties usually run back by gravity. One of the most interesting features of the work in these excavations is to see the blasting. All the morning the miners have been drilling holes in the' solid ore, and when tire whistle blows for noon they leave the quarry for their midday rest. We spectators are standing on the surface at the edge of the cut, and looking down into the great hole some 4#Oft. below us. A casual observer would pronounce the mine entirely deserted, but a more careful scrutiny reveals half a dozen minute figures crawling about in the abyss and performing certain eccentric evolutions with a stick and what looks like a coil of wire. These are the men loading the holes, and the coil hung over their arms is the fuse, or safety-match, on which their lives depend. But the last hole is loaded, and a man with a horn, standing beside us at the surfaces gives a series of short, startling “toots” to warn everyone that the blast is about to take place. Now- the men below have lighted their torches, and as they bend over each hole for a moment- we see the flash of the fuse, show* ing that it has caught fire. The fuses of the holes that aro to be first lighted are cut a little longer than the later ones, that all the blasts may explode at about the same But we are beginning to feel a little nervous about the safety of our friends below, for scores of fuses are smoking away, and yet the mon move carelessly about, applying their torches to those yet unkindled with aggravating slowness and unconcern. And how are chey ever to find time to climb the 400 ft. which separates them from the surface and safety?

Whilst speculating on this interesting question the men suddenly disappear, and we are relieved to hear that they have found a safe refuge in some of the old Homan galleries that honeycomb most of these masses of mineral. In a moment the entire side of a wall of ore flies outward, and a second later the stunning boom of the explosion reaches our cars. The shots come thick and fast, and a heavy cloud of smoke fills the chasm, warning us to retire a little to the rear, as it makes it impossible for us to dodge the occasional stray fragment that whizzes by us. A long blast of the horn indicates that the last shot litis gone off,.and when the smoke clears away and we can again see the bottom of the pit, we are surprised to find how little its appearance has been changed by all this blasting, and what a small heap of debris appears to be lying there. And yet we are told that no less than 3000 tons of ore has been thrown down before our eyes—enough to load 20 trains of waggons. Anything pertaining to antiquity is interesting to our generation, and few places have so much to offer in this way as these very mines. The country in their vicinity is covered over large areas with Roman slag, most of it over 2000 years old, and yet, on fracture, presenting as fresh a surface as though it had been produced last week. Stone foundations of the little blast furnaces used by the ancients are abundant, and the composition □f the slag, as well as its remarkable freedom from copper, shows that they were no unskilled metallurgists. They did not remove the ore en masse, as the present owners are doing, but followed the richer streaks of copper with a pertinacity and to a depth and extent that is simply surprising, considering that they had but poor tools and no powder for blasting. That they were decidedly skilful and ambitious mechanics is shown by the discovery of various machines, the most interesting and largest being a wheel no less than 18ft. in diameter, used for lifting water from the deeper workings of the mine. It was placed in a chamber hewn out of the solid rock, and rested on two gudgeons (axles) of bronze, which are as perfect as the day they were made. Roman graves have been found in great numbers, and many interesting articles taken from them may be seen in the museum of the Tharsii Mine. One of the most common and curious at tides buried with the dead in those days was the tear-glass, a beautifully blown little vial, shaped something like a chemist’s test tube, and supposed to be filled with the tears of the deceased person’s friends before being placed in the grave. I suppose the sorrow of the deceased’s family circle could be exaotly gauged by the size of the tear-glass that was tilled for him. Many gold rings and coins are found, as well as copper and silver money. Also some pottery of lather rude manufacture, numerous copper and earthern lamps, charms worn by the women about -the neck, tweezers, scissors, bodkins and scores of such small articles.

The Romans worked these mines solely for copper, but the present generation has produced the skill required to extract and utilise all the constituents of the ore.

The pyrites suitable for the manufacture of sulphuric acid is shipped to England in bulk, lhe sulphur is burnt off in kilns to make- acid, and the residues, consisting mainly of iron-oxide, but also containing such copper, gold and silver as was originally in the ore, are calcined with salt, which converts these three valuable metals into such a condition that they can be dissolved out and recovered separately: whilst the last residue, consisting solely of oxide of iron, is sold as an iron ore.

This series of processes is one of the most beautiful applications of science to practice that can be instanced, and enables a splendid profit to be made from an ore that is so poor in any one metal that it would not pay to touch.

But a very large proportion of the ore produced is not suited for the purposes just described, and to extract the copper from this lower-grade ore, it is burnt in great heaps called teleras, the ore smouldering slowly for several months, its own sulphur furnishing the fuel, and thus being slowly driven off. The roasted ore is then formed into terraces, covering the hillsides and taking possession of every available slope in the vicinity, the ore being thus spread over hundreds of acres of surface, and amounting in the aggregate to several millions of tons.

It is here systematically leached with water, intervals of dryness being allowed to render a fresh batch of its copper soluble in the water. The liquors that flow out from the foot of these terraces, as well as all the waters that come from the ore bodies, are heavily charged with copper, and are conducted to a long labyrinth of shallow canals filled with scrap and pig iron. Now these liquors have, as the chemist puts it, a greater affinity for iron than for copper ; consequently they let the copper drop, and take up iron instead. Thus the pigs of iron—of which the precipitating canals contain many thousands of tons—are constantly wasting away and disappearing and requiring fresh iron to replace them, whilst the bright, red, metallic copper is constantly forming in the shape of scales and crusts and powder. This cement-copper is cleaned up every little while, and, after being washed and dried, is shipped in bags to England to be melted into ingots. At Rio Tinto a considerable amount of this cement copper is refined and granulated on the spot, and dissolved in sulphuric acid (also made at the mine) to furnish sulphate of copper (blue vitroil). But Rio Tinto also produces a large amount of ore that is too rich in copper for either export or leaching, and this, after roasting in heaps, is smelted at the mine into a rich made that is shipped to England for refining. A unique feature at Tharsis is a very large body of decomposed schist, that is so impregnated with copper, and so cheaply mined by the quarrying method already described, 'that it is leached by the company at a fine profit. At both mines the feature that will most strike a mining engineer is the enormous extent of the ore reserves that are opened up for the future, and which gives to these corporations a stability and certainty that can seldom be attained by mining companies. Another striking point is the extreme cheapness with which immense quantities of ore and rock are handled ; and the entire mining profession is indebted to these companies for showing them to what an extent this system of open-cast mining may be de-, veloped. Both companies have excellent railways, over which thousands of tons of ore pass daily on their way to the sulphuric plants of the world. Each company also owns a fine iron pier at Huelva, arranged so that the ore is shot from the railway waggons direct into the holds of the vessels.

While it is obviously impossible to publish any details of the business that were kindly given us at the time, I can at least take a few figures from the companies’ public annual report to show the enormous amounts of ore handled by them, and the magnitude of their operations. The average amount of ore extracted from the Rio Tinto mine for the past few years has been 1,400,000 tons per annum, of -which over 400,000 tons has been exported for sulphuric acid manufacture. The balance has been treated at the mine. The annual production of copper at the mines has been about 20,000 tons. Some 5000 tons of blue vitriol are also manufactured. The dividend for 1891 was L 325,000, whilst a large amount of debentures was also redeemed and a considerable sum “written off” for depreciation of property.