Salvador of the Twentieth Century

by Percy F. Martin

The principal work which the management has in hand at the present time is cross-cutting the formation, with the object of finding split or parallel veins, and the discovery of such split veins has naturally much improved the position of the company. The whole policy of the management will now be devoted, for some years to come, to proving the mines in depth, and such, indeed, would have been undertaken before now but for the troubles to which I have above referred in regard to labour. The ore indications, which have so far been met with, are of a distinctly favourable nature, the most encouraging, perhaps, being the cutting of the famous Miguel ore-shoot at the 700 feet level. The width of this vein exceeds 3 feet, and it assays over 6 ounces. The Miguel shaft is now down nearly 800 feet, but the deepest working from which the ore has been stoped is the 600 feet level; the shaft will therefore give 200 feet of backs below the present workings.

At present between 25,000 and 30,000 tons of ore are being crushed annually, which yield on the average a value of 1 ounce 7 pennyweights. The working expenses have never been particularly high, owing greatly to the excellence of management and the economy of the reduction plant, which bears the name of the chairman of the company—viz., the Butters' Cyanide Process—but there are nevertheless hopes that these costs will be still further reduced in the near future. There is no question that the Butters' Salvador Mines rank among the most valuable ore deposits to be found in Central America, and it is no less sure that they are being managed in the most expert and most economical manner.

As to the financial situation of the company, the balance-sheet proves that the cash in hand on June 30, 1910, in Salvador, London, and San Francisco, amounted to £5,001, and that on the same date the stores in hand and in transit were valued at £32,228; sundry debtors in Salvador and London amounted to £812, and per contra the amount owing to sundry creditors was £3,642. The profit and loss account showed a net profit for the period of £62,645; while the amount brought forward from the previous account, and which amounted to £19,042, being added to the net profit, showed a total available distributable balance of £81,677. The dividends which have been paid for the twelve months aggregated, as already mentioned, 45 per cent. upon the capital of the company, and which absorbed £67,500, thus leaving a carry-forward of £14,177.

It is worthy of mention that in the directors' report for the period ending June 30, 1910, a graceful tribute is paid to "the continued consideration which the Government of Salvador has extended to the company," and which testimony goes to prove what I have already indicated—viz., that the Government is anxious and willing to encourage in every legitimate manner sound foreign enterprise; but I go further, and say that I know of no other Latin-American Republic which has shown greater good-will to all foreign enterprise in all its phases than that of Salvador.

It is over seven years since the Butters' filter was introduced in connection with mining, and the process may now be met with in all parts of the world, and especially in Mexico, where I have seen it working with excellent advantage upon the famous Dos Estrellas gold-mine at El Oro, as well as in Brazil and in other South American countries.

The need of a filter of some sort was first forcibly presented to the mind of Mr. Charles Butters and his associates at their works in Virginia City, Nevada, U.S.A. The tailing being cyanided there was originally derived from the Comstock Mills, but it had been treated and retreated several times by the Pan-Amalgamation process; as it stands to-day in the dams, it contains about 75 per cent. of material that is leachable, and which may be designated as "slime." The slime is of an exceptional character. In addition to the difficulties connected with the solution of gold and silver contents, the mechanical condition was such that it gave trouble in settlement for decantation. The clarification produced by a coagulant such as lime was perfect, but the subsidence was so slow that the amount of solution recoverable in this way was not sufficient to make the decantation process a practical success. It was proved, in fact, that coagulation was not necessarily accompanied by good settlement.

After experimenting with several forms of vacuum filter units, both cylindrical and rectangular, there was evolved a form of filter which is the recognized present standard, and the preliminary plant of 336 leaves, which was erected at Goldfield seven years ago, is still in full operation to-day. As the filtration process is found working at the Salvador mines and in other parts of the world, the filter-leaf is made on a frame, the upper side of which is formed on wood, and acts as a suspending bar when the leaf is in position in the filter-box. The remaining three sides are made of ¹⁄₂-inch pipe, perforated with holes and connecting to the vacuum pump. The filtering medium consists firstly of a porous mat of such size as to exactly fill the space formed by the pipe frame, and upon either side of this is placed a sheet of canvas, large enough to overlap the frame, around which it is securely sewn. The first containing-box which was used at Virginia City was an electrolytic precipitation-box, which was not needed for its special purpose, and was adopted for the use of the new filter. An air-compressor was converted into a vacuum pump, and with this equipment the vacuum filter of to-day came into existence.

From the beginning it proved a marked success, and the next step in its perfection was the designing of the large Goldfield plant to handle 800 tons of dry slime per diem. When designing the containing-box for the special purpose of the filter, the lines of the original box were slightly departed from as regards the shape of the hoppers, these being given sixty sides to facilitate the better discharge of the cake, and a quick opening valve of large area was placed at the apex of each hopper. Instead of a dry vacuum pump and gravity drainage, a wet vacuum pump was used, permitting the solution pump to be placed above the filter.

The cycle of operation is as follows: (1) Filling the box with pulp; (2) the formation of a cake on each side of the vacuum leaves by suction; (3) emptying the box of pulp and filling with weak solution; (4) drawing through the cake sufficient solution to displace all soluble values; (5) emptying the box of solution and filling with water; (6) drawing through the cake a small quantity of clean water to displace any solution held in the cake; (7) shutting off the vacuum and admitting water through the leaf connection, thereby throwing off the cake, which falls to the bottom of the box, and cleansing the canvas in preparation for the next charge; (8) opening the valve in hopper bottom of box, and allowing the residues to escape to the waste dam; (9) closing the valve, thus rendering the filter ready for the next charge of pulp.

It is a very unusual thing to find in the newer mining companies of Central America such up-to-date machinery and mining processes as are in use in the Republic of Salvador at the Butters' Salvador and the Divisadero Mines. The Government of Salvador has to be congratulated upon the wisdom it has shown in extending consideration to companies engaged in the development of its mines, and to practical men of the type of Mr. Charles Butters and his associates, to induce them to devote their money and their brains to the development of Salvador. The most modern processes and the most up-to-date machinery can be here found at work, and the Government is permitted, by the terms of the franchise which they have granted to the companies, to send Government students to attend at these works to complete their studies in mining and metallurgy. Among the processes at Butters' Salvador Mines are dry-crushing and roasting, electrolytic precipitation as well as electrolytic refining. The cyanide process with the Butters' Patent Vacuum Filter is found here treating gold ore without amalgamation, and making extraction of from 95 to 96 per cent. The mining at this property has been by adits principally. Electrical winding plants and electrical pumping plants are now installed at this property. Both at the mine and at the mill a high efficiency of working has been attained for many years.