B. Roasting processes. 1. Chloridizing roasting. 2. Sulphate roasting. C. Leaching processes. 1. Acid solvents. (a) Sulphuric acid. 2. Alkaline solvents. (a) Caustic soda. (b) Ammoniacal solutions. D. Precipitation processes. (Same as for sulphide ores.) E. Dry processes. Igneous concentration. DISCUSSION OF THE WORK OUTLINED. MECHANICAL CONCENTRATION OF ZINC SULPHIDE ORES. Most of the zinc recovered from sulphide ores in Utah is from mixtures of lead and zinc sulphides. The usual milling treatment for such ores is to crush, size, or classify the ore, and then separate as cleanly as possible the gangue material from the sulphides with jigs and tables. By this separation of a mixed sulphide ore a lead product and a zinc product are obtained. Sometimes the lead product contains as much as 10 per cent zinc, or even more, as is shown by column 2 of Table 2 (p. 18), and the zinc product contains a considerable quantity of lead. As previously stated, the zinc that accompanies any lead ore sent to the lead smelter is not recovered, and the problems connected with the milling of a zinc sulphide ore are as follows: 1. Effecting a better separation of the lead and zinc minerals. 2. Preventing losses of zinc, or of lead and zinc in the tailing. The Bureau of Mines has studied this problem in Wisconsin and in Missouri. During the fiscal year 1915-1916 the department of metallurgical research of the Utah school of mines had one "fellow" giving his time to a study of the mining and milling of complex lead and zinc ores in the Park City district, Utah. The results of this investigation were embodied in a report to the department, from which the following extract is taken: Introduction. The Park City mining district is situated on the eastern slope of the Wasatch Mountains and 25 miles southeast of Salt Lake City, which is west of the mountains. This district has been a continuous and steady producer of lead-silver ores for 40 years. a Wright, C. A., Mining and milling of lead and zinc ores in the Wisconsin district, Wisconsin: Tech. Paper 95, Bureau of Mines, 1915, 39 pp. Wright, C. A., and Buehler, H. A., Mining and milling of lead and zinc ores in the Missouri-KansasOklahoma lead and zinc district: Bull. 154, Bureau of Mines, 1918, 132 pp. e Stott, G. F., Mining and milling of complex lead and zinc ores in the Park City district, Utah. Production. The total production of the district has been $156,500,000, of which $42,000,000 has been paid in dividends. In 1915 the district shipped 99,795 tons of crude ore and concentrates, valued at about $4,000,000. Gold, ounces. Lead, pounds.. Total value.. Total production of metals up to January 1, 1915.a 4,058, 315 125, 707, 056 1, 136, 145, 128 25, 943, 492 48,081, 726 $152, 454, 585 In addition to the producing mines there are several properties which are now doing development work *** outside the producing area, and without doubt some of these will become producers. Present (war) prices of metals have so stimulated production that, if it continues for another year at the present rate, this district will have produced more metals than in any other year of its history. The names of the shippers from the Park City district during the year 1915 are given in Table 5 following, with the tonnage and kind of products shipped. This table is compiled from the annual review number of the Salt Lake Mining Review, January 15, 1916: TABLE 5.—Names of shippers from Park City di trict during 1915, with tonnage and Daly Mining Co.. .Pb-Fe and Zn concentrates from mill treating tailings. 752 1,801 1,031 236 702 Daly-Judge Mining Co. mill. Federal Leasing Co... Crude Pb-Ag ore and Pb-Fe and Zn concentrates from mine and mill Daly-West Mining Co.........Crude Pb-Ag ore from mine and Pb-Fe and Zn concentrates from .Crude Pb-Ag ore from Ontario mine.... Grasselli Chemical Co. Keep, G. A.. Zn concentrates from mill retreating Zn middlings from other mills. 51 36 Moore, Chas.. Mines Operating Co. .Pb-Fe and Zn concentrates from mill treating creek tailings. 424 1.595 3,249 Silver King Coalition... Total (tons)... 102, 453 Ontario Silver Mining Co......Crude Pb-Ag ore from mine.. .Crude Pb-Ag ore from mine and Pb-Ag-Fe concentrates from mill.. Union Lime & Stone Co.... Lime rock for CaO and for cement manufacture.. Mineral constituents.-The primary minerals are in the form of complex sulphides of lead, silver, zinc, iron, and copper, occurring as galena, sphalerite, and some tetrahedrite and chalcopyrite. Silver minerals are known to exist in pyrite, galena, and sphalerite, but like the gold it is not known in what form it exists. Gangue minerals are quartz and calcite. Oxidation of the ores has extended to as great as 1,700 feet, but averages between 600 and 800 feet. The oxidation has not been complete, and sulphide and carbonate ores often occur together. Pyrite is largely oxidized to hematite and limonite. Galena has been altered to cerussite and anglesite. Copper has been altered to the carbonates, malachite and azurite. Zinc minerals are usually unaltered. All of the above minerals are closely associated together. In a few of the ore deposits zinc may be absent, or it may occur in sufficient quantity to warrant shipping direct to zinc smelters without separating it from the lead and iron. This, however, • Heikes, V. C., Gold, silver, copper, lead, and zinc in Utah in 1914, mines report: Mineral Resources 1914, U. S. Geol. Survey, pt. 1, Metals, 1916, p. 743. is unusual. Whenever the ore contains lead and silver minerals in sufficient quantity it is often sent to the lead smelters as crude ore, thus losing all the zinc, in addition to being penalized for the same. HISTORY OF EARLY MILLING IN PARK CITY. As was the case in many western mining camps in the late sixties and early seventies, only the high-grade ore could be hauled 24 miles to the railroad and then freighted to the smelters in Omaha, Nebr. Thus we find in 1874 and 1875 attempts made by the Marsac, McHenry, and Ontario mining companies to crush the ore in small 20-stamp mills and amalgamate the rich silver ores. It In 1879 crude amalgamation gave way to chloridizing roasting and pan amalgamation. The Ontario mill doubled its number of stamps, installed two Stetefeldt furnaces, 24 pans, and 12 settlers, making it one of the largest and best mills of its kind. In 1880 the Marsac mill was remodeled and equipped for a lixiviation process. was here that the Russell lixiviation process was developed. Mr. Russell attempted to treat silver ores containing high percentages of lead. The bullion produced was correspondingly high in lead. He found that lead could be separated from a hyposulphite solution by the addition of sodium carbonate without precipitating any copper or silver, thus removing the main difficulty encountered in the treatment of lead-silver ores by the lixiviation process. The first attempt toward wet concentration was in 1878, when the tailings from the Marsac and Ontario mills were treated on the McKim concentrator-a crude vanner composed of an endless canvas belt on a 5 by 15 foot frame with rollers on the ends. In 1886 the Cresent Mining Co. built the first wet concentration mill, in which they installed fine-crushing machinery and seven Frue vanners. During the next 10 years most of the larger companies installed wet concentration machinery in the shape of Hartz jigs and Frue vanners. Modern wet concentration in the Park City districts began with the installation of the Wilfley table in the Daly West mill in 1895. Wet concentration to this date had been entirely on Hartz jigs and vanners. Zinc was discarded as a waste product until 1907, when the Daly Judge mill began saving zinc middlings for treatment in the Grasselli Chemical Co. mill. Only one other attempt had been made to save the zinc. This was in 1902, when the Park City Metals Co. remodeled the old Peck concentrator and installed six Wilfley tables, a Nowell-Hoyt roaster, and a magnetic separator. The mill burned in 1903 and was never rebuilt. TAILING DISPOSAL. Tailings from all of these mills are sluiced into the creek and are carried down below the town of Park City, where they have been caught by dams placed in the creek in 1880 by the Ontario Mining Co. The farmers on the flats 10 and 12 miles below Park City objected to having these tailings on their land, so they forced the Ontario Mining Co. to put in seven of these dams on the various flats above them. These flats are now being worked over for the zinc minerals they contain. Some idea of the vast tonnage which has been milled and the large amount of lead, silver, and zinc minerals that have been discarded as tailings from the early and even the more modern mills may be obtained from samples and data taken at plants now operaing on three of the largest flats, namely: 1. Broadwater mill, 2 miles below the town of Park City, 450,000 tons, averaging 1 per cent Pb, 4 per cent Zn, and 4-5 ounces Ag per ton. Lead, at 4 cents.. Zinc, at 5.8 cents.. Silver, at 58 cents.... Total..... $8.15X450,000-$3,668,000, total value in minerals. Per ton. 4. 64 2. 61 8. 15 2. Beggs mill, one-half mile below the Broadwater mill: Deposit 2,500 feet long, 200 feet wide, and 4 feet deep; 250,000 tons, assaying about the same as the Broadwater; total value of minerals, $2,018,000. 3. Big Four mill, 7 miles below Park City; deposit 34 miles long, 500 feet wide, and 2 feet deep; total tonnage available estimated over 1,000,000 tons. 1.8 per cent Pb, 4.1 per cent Zn, 3.1 ounces Ag, Au 30 cents, 21 per cent Fe, 62 per cent SiO,. Other small flats will bring the total up to over 2,000,000 tons of tailings worth $8 per ton, or $16,000,000, of which a recovery of about 60 per cent of the total mineral values may be expected. TAILING LOSSES OF TO-DAY. Even to-day with modern improvements and up-to-date milling practice the zinc losses are extremely large. At the Daly West mill the "general tails" assayed for six months ending November 1, 1915, 1 per cent Pb, 3.05 per cent Zn, 2.04 ounces Ag, during which time an average of 146 tons per day were treated or approximately 21,900 tons. Economic loss, $433 per day or approximately $65,000 in a period of six months. For the month of September, 1915, 1 per cent Pb, 2.36 per cent Zn, 2.28 ounces Ag, during which time 3,547 tons were treated or 154 tons per day. Lead, at 44 cents..... Zinc, at 5.8 cents.... Silver, at 58 cents.. Total...... Loss, $482.5 per day or $11,700 total. Per ton. $0.90 2.74 1.32 4.96 For the month of October, 1915, 1 per cent Pb, 3.1 per cent Zn, 2.67 ounces Ag. Tonnage milled was small, being only 1,381 or 125.6 tons per shift worked. Owing to the shortage of water, the mill was operated every other day. Sample taken by Stott, November 3, 1915, 0.88 per cent Pb, 2.46 per cent Zn, 1.8 ounces Ag, 4.33 per cent Fe, 79.9 per cent insoluble: Lead, at 4 cents.... Silver, at 58 cents.. Total.. Per ton. .$0.79 2.85 1.04 4.68 At the Daly Judge mill the mill tailing assayed, before the installation of the flotation process, 1 per cent Pb, 3 per cent Zn, and 2.6 ounces Ag. The average tonnage for the year 1914 was 118 tons per day and a total of 49,095 dry tons milled. At the Silver King Coalition the mill tailings assay as follows: General mill tailing from sulphide ores, 0.7 per cent Pb (fire assay), 2.3 ounces Ag, 2.6 per cent Fe (Jan. 10-12, 1916). Lead, at 44 cents...... Silver, at 58 cents... Total General mill tailing from oxide ores, 3.64 per cent Pb., 4.5 ounces Ag. Per ton. 1.33 1.96 The above figures represent the material that is daily being sluiced into the creek as tailing. As a result we find to-day two small leasing mills immediately below each of these larger mills. There have been as many as 10 plants operating on the creek in series but they have been forced to quit on account of the mills above improving their extraction within the last year or two. The two surviving mills have been fairly well designed and are better equipped to handle the poorer grade of tailing. A good insight into the past milling practice was obtained from Mr. Charles Moore, the owner of the two surviving "Creek mills." In 1900 leasers placed sluice boxes with riffles in the creek. A fair shipping concentrate was obtained. The next step consisted of plank riffles across the creek. Crude concentrates were shoveled into a wagon and hauled down to a rather crude mill consisting of one Wilfley table. With one man and a team and another man operating the Wilfley table the leasers were able to make as high as $50 a day and averaged $30 apiece. Thus we can get some idea of how we can to-day go 7 miles below town and find 2,000,000 tons of tailing deposits worth $8 per ton. Up to the last three or four years the tailing from the creek assayed 3 per cent Pb, 7 per cent Zn, and about 10 ounces Ag, indicating that the Daly West and Daly Judge mills were not extracting more than 50 to 60 per cent of the lead, 20 to 30 per cent of the zinc, and 35 to 40 per cent of the silver unless the heading to the mills was considerably higher in metallic values than it is at the present time. |