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178

Results of Experiments made with Potassium Cyanide on Gold-and Silver-ores from Different Mines.

The experiments on the Gregory concentrates, which consist of pyrite, some arsenopyrite and chalcopyrite, with traces of galena and blende, were made by the Gold- and Silver-Extraction Company of Denver, Colorado. These pyrites are usually bought by the Boston and Colorado Smelting Company, which treats them, when mixed with other ores, by matte fusion, modified Ziervogel process, for the extraction of the silver, and a process of its own for the treatment of the rich auriferous bottoms. The De Lamar ore consists of a siliceous and limestone gangue, impregnated with silver sulphides and chlorides and pyrites. Some of the gold is free, but the greater part is in combination. The ores are at present treated by raw pan-amalgamation, which saves from 83 per cent, to 85 per cent, of the contents, and is considered satisfactory. A considerable quantity of this ore has been treated by the cyanide process with flattering results. The ores from the Eevenue Mine, Madison County, Montana, have puzzled metallurgists for many years. They are oxidized surface-ores, containing a considerable quantity of iron. "When the mine was bonded to George D. Eoberts, of New York, considerable attention was paid to the treatment of the ore by the lateE. U.Riotte.who, after making various experiments, tried cyanide. His results were far from satisfactory, although it is now stated by Mr. Turner, the manager of the property, chat they are extracting by the same process of cyanide some 85 per cent. It is also stated that 70 per cent, of the contents of tailings from amalgamation has been extracted at a cost per ton for extraction of £1; but, as the ore is one which would naturally cause a considerable consumption of cyanide, this statement seems doubtful. The Southern Cross Mine, of Deer Lodge County, Montana, has ores which contain from 42 per cent, to 50 per cent, of iron, in the form of limonite, evidently the result of the decomposition of pyrite. The ores have been treated in a ten-stamp gold-mill with amalgamated silver plates and with copper plates, but without extracting over 40 per cent. The gold is so fine that a speck can rarely be seen on panning large samples. The ore assays from £2 to £8 per ton in gold, with but a trace of silver, and its average value may be taken at £3 per ton. In 1890 a number of experiments were made on the ore by the cyanide process with good results, so far as extraction went; also experiments by the chlorination process, applied to raw ore. These were the first successful experiments by this process, as far as has been learned, applied directly to ores without undergoing a previous treatment. When leached by cyanide as much as 93 per cent, was extracted, the results on high-grade ore varying from that figure to 85 per cent. It was observed on treating in a rotating barrel that, whilst in a short time a large percentage of the gold was extracted, the quantity gradually decreased as the time lengthened, so that the results after a number of hours showed an extraction of only 25 per cent. This indicates that the ore either exerts a decomposing action on the solution or else precipitation occurs. It has been stated that experiments made recently on a large scale have proved successful, but in any event the consumption of cyanide would be large, and would increase with the extraction of less decomposed ore. Chlorination yielded on an average some 90 per cent., with a consumption of 101b. of bleach-ing-powder and 151b. of sulphuric acid to the ton. The total expense of treatment by this method would probably fall below 16s. per ton, if a sufficient quantity of ore were treated. The cyanide process, owing to the decomposition of the solution, would cost over £1 per ton. The Chollar Potosi ores have been considered the most rebellious of the Comstock ores, not over 75 per cent., on an average, being saved by pan-amalgamation. Prom the tailings, however, cyanide extracts some 76 per cent, of the gold, and it is probable that the portion previously extracted by amalgamati(*i would be extracted also, which would make a total extraction of 90 per cent, by cyanide. The Consolidated California-Virginia ore contains metallic gold and silver and comparatively rebellious sulphides, such as tetrahedrite, stephanite, and sternbergite. The results, therefore, on both metals were low, but it is probable that the ordinary type of Comstook ore will yield far better results. Nevertheless, considering the perfection which pan-amalgamation has reached, it is extremely doubtful if the cyanide process will ever be introduced under the present management. The ores of the Minas Prietas Mine, of Sonora, Mexico, consist of quartz, with oxides of iron and manganese, and hardly a trace of sulphur. Some of the gold is free, but the silver is more or less rebellious. The following results of the monthly runs of the 40-stamp Boss process, con-

Assay^ •value. Per Cent. o£ Vi Jue extracted. Name of Mine. Goia. Oz. per ton. Silver. Oz. per ton. Gold. Silver. Gregory, Colorado )e Lamar, Idaho ievenue, Montana iouthern Cross, Montana Jhollar Potosi, Nevada linas Prietas, Mexico itlanta, Idaho Jou, California, and Virginia, Nevada 'aradise Valley, Nevada Judter Company, S. Dakota 0-800 1-000 1-350 1-220 0-130 0-277 0-600 2-260 0-090 1-950 1-4 26-0 4-0 0-7 2-6 9-7 5-2 108-6 49-2 90-0 90-0 94-0 93-0 76-2 85-6 63-4 38-8 77-8 21-0 30 830 52-0 50-0 70-4 30-4 78-6 49-8 25-8