The rate of oil feed is regulated by a small plunger pump whose speed can be altered by means of variable-speed pulleys. The length of stroke can also be varied by manipulating a lock nut, thus giving a good control of the amount of oil fed to the pulp as it is discharged from the first centrifugal pump.

After thorough mixing in the Pachuca tank the pulp is distributed to four roughing cells. The froth is collected and cleaned in the first cleaner cell. Tailing from this cell is re-treated in another cell before going to the tailrace.

Tailing from the roughing cells is thickened in Callow cones, and receives further treatment on two Wilfley tables. The product caught on these tables is the coarser material which is not floated. Each table yields lead concentrate, zinc middling, and tailing. The zinc middling is re-treated on a separate Wilfley table.

Considerable difficulty is found in breaking up the flotation froth without using too much water. A patent nozzle known as the Koerting spray has been found very effective in "killing" froth. The froth after passing under the spray is thickened in two Callow cones and the product fed to two Wilfley tables. Each table yields lead-iron concentrate and zinc middling. The zinc middling goes to a centrifugal pump and is elevated to a third Wilfley table. This table yields zinc concentrate and middling, which is returned to the head of the table for re-treatment. This manner of slime treatment yields concentrate having the following analysis: Results of analysis of slime concentrate.

Zinc concentrate is settled in two settling boxes and the product sent to the zinc concentrate bins.

Lead concentrate is thickened in an 8-foot Callow cone before being de-watered in a small settling box, and later taken to the lead-concentrate bins.

SILVER KING COALITION MILLING PRACTICE.

The ore is divided into two classes: First class, crude shipping ore, which contains values in lead and silver to exceed $17 per ton; second, milling ore which is less than $17 in value.

The first-class ore is a combination of lead, copper, and iron, with a high silver value, the silver being associated with pyrite and galena. There is more or less sphalerite and copper sulphides associated with the pyrite and the galena, but not in the same amount and extent as is found in Daly-West and Daly-Judge mines.

Ore bodies have been oxidized almost completely to the 900-foot level, and oxidation extends even to the 1,200-foot level. The case is rare when oxides are found below this point. Thus the milling ore is divided into two classes-oxide and sulphide ores in the ratio of two-thirds sulphide ores and one-third oxidized or "carbonate" ores, as they are termed locally.

In general the practice is to treat these ores separately. The mill bins hold large tonnages of ores, thus the mill will run for several days on sulphide ores and then will operate on carbonate ores. Each received the same treatment in crushing and jigging. Ores are crushed to inch and treated on Hartz jigs. The jig tailing is reground in Marcy ball mills to pass a 30-mesh Callow screen. From this point on the treatment will depend on whether the ore is sulphide or carbonate. Sulphide ores are sent to a Callow system of flotation and carbonate ores are classified and concentrated on Wilfley and Deister tables.

SULPHIDE SECTION.

Undersize from the 30-mesh Callow screens goes to three flotation units, all alike, and each will be described as one individual unit.

Oil is added, a drop at a time, as the pulp is discharged from the Callow screen. One thing to be noted here is the absence of any pulp thickeners. The water ratio in the pulp is controlled by the water fed to the Marcy mills. The pulp dilution is carried at about 20 per cent dry solids, as nearly as can be approximated.

A box distributor sends the pulp to three 3 by 14 foot Pachuca tanks, each of which feeds a flotation unit. In the Pachuca tanks the oil and pulp are emulsified. Two rougher cells receive the pulp from the Pachuca tank. The rougher tailing is elevated by two 4-inch air lifts to a second series of two rougher cells. These cells make froth concentrate which received further re-treatment in one recleaner cell. Tailing from the second rougher is sent to waste. Tailing from the recleaner cell is sent to a small two-spigot V-classifier and two tables. The products from this table are concentrate and tailing which is sent to waste. Concentrates from the first rougher cell, from the recleaner cell, and from the two middling tables are combined and elevated by a centrifugal pump to two 8-foot Callow cones. The thickened product is filtered by an 8 by 8 foot Portland filter.

Extractions previous to the installation of the Callow flotation process, when using Wilfley tables and vanners, were lead, 96 per cent; silver, 82 per cent.

After the installation of flotation the total mill extraction dropped to-lead, 88 per cent; silver, 73 per cent.

This difference is due largely to the attempt at floating a 30-mesh product. Lead sulphide does not float when it is as coarse as this.

Oilused is 1580 Pensocola," and approximately 1.15 pounds is used per ton of dry pulp. These extractions are taken from assay sheets for only two or three days and do not represent any long period of time. The ore to the mill is very changeable and these extractions may be misleading, but will serve in one way to show what this mill is doing. The same applies to the extractions and data on the carbonate-ore treatment. Data on treatment of sulphide ores.

COSTS.

The last annual report published by this company was in 1913. From this report we find that for the year ending April 30, 1913, 81,996 tons of second class or milling ore were treated with the production of 12,996 tons of concentrate assaying: 35.55 per cent Pb, 55.76 ounces Ag, 0.0648 ounce Au.

MILLS ON TAILING FLATS BELOW PARK CITY.

Below the town of Park City there are two large and two smaller mills working over the tailings that have been discarded from Park City mills since 1886. The extent and value of these flats has been discussed under "Early Milling" and "Tailing Leases."

BROADWATER MILL.

This mill is treating about 400 tons of tailing per day, but has a capacity of about 500 tons per 24 hours. From 900 to 1,200 tons per day are taken to the mill. Onehalf to two-thirds of this tonnage is stored as a "winter dump" in order that the mill may operate during the winter months when the ground is frozen.

Heading to the mill assays: Pb, 1 per cent; Zn, 4 per cent; and Ag, 4.5 ounces. Lead-iron concentrates assay: Pb, 20 per cent; Zn, 12 per cent; Ag, 20 ounces; Fe, 20 per cent; SiO2, 4 per cent.

Zinc concentrates assay: Pb, 6 per cent; Zn, 37 per cent; Fe, 11 per cent; SiO2, 8 per cent.

Zinc concentrate is being stored for treatment in the Daly-Judge electrolytic zinc plant which will probably be in operation by the time this report appears in print.

BEGGS MILL.

This millis located about one-half mile below the Broadwater mill.

These tailing deposits were located by Mr. Beggs in 1907 as placer claims. Six claims in all were located on this flat. The deposit varies from 3 to 6 feet deep, and is 200 feet wide and 2,500 feet long.

Tailing from the flat is scraped up into heaps by means of drag-line scraper operated by a steam engine and requiring a crew of two men. The tailing is then shoveled by hand into 16-cubic foot mine cars and trammed to the hopper at the mill.

Tailings from the table were being discharged in so many different and inaccessible places that it was found impossible for us to obtain even a representative tailing sample, so none was taken. However, from data obtained from Mr. Beggs the extraction has been calculated:

Average heading to mill-Pb, 1.5 per cent; Zn, 4 per cent; Ag, 3.5 ounces.

Average lead-iron concentrate: Pb, 23 per cent; Zn, 16 per cent; Ag, 20 ounces; Au, 0.05 ounce; Fe, 18.5 per cent; SiO2, 3 per cent.

Average zinc concentrate: Pb, 6.4 per cent; Zn, 38 per cent; Ag, 10 ounces; Au, 0.03 ounce; Fe, 9.5 per cent; SiO,, 10 per cent.

Mill operated from May 1 to October 30, 1915, and produced 400 tons of zinc concentrate, and 200 tons of lead-iron concentrate. This represents 2.66 tons of zinc concentrate per day, and 1.33 tons of lead-iron concentrate per day.

Calculating from above concentrate assays and from the smelter contract we find

This mill is located at Atkinson, 7 miles below the town of Park City.

$45.75

26. 18

48.60

29.03

The portion of tailing deposits under lease to the Big Four Exploration Co. covers an area 3 miles long, 500 feet wide, and averages 2 feet deep. The tonnage here available is in excess of 1,000,000 tons. Samples taken at 100-feet intervals along the flat indicate that the average metal content of this tailing is as follows: Pb, 1.8 per cent; Zn, 4.1 per cent; Ag, 3.1 ounces; Au, 30 cents; Fe, 2.5 per cent; SiO2, 62 per cent. The tailing is scraped up by means of 8 or 10 teams with scrapers into heaps by the side of the railroad. From these heaps the tailing is scraped over a plankway bridging the tracks and four-ton cars. A converted Cadillac touring car provided with flanged wheels acts as the motor power to a train of four dump cars of 4-ton capacity each.

The mill was operated for a few months last fall, but was closed down for the winter, during which time it has been remodeled and changed. The mill is still being altered.

FLOTATION OF ZINC SULPHIDE ORES."

When the work of the Salt Lake City station began only one mill in the United States-the Butte & Superior, at Butte, Mont.-was using flotation in the recovery of zinc sulphide from slime. As the losses of zinc in slime evidently were rather large and some process that would recover this zinc was necessary, steps were taken to obtain laboratory machinery for testing the applicability of flotation for different slimes. Representatives of Minerals Separation, Ltd., the only flotation company maintaining offices in the United States at that time, did not seem to care to cooperate. The first test machines were built according to the designs printed in the only paper available, the first edition of Hoover's "Concentrating Ores by Flotation." The testing machinery described in the literature was crude and some of the first attempts at flotation at the Salt Lake City station were rather disappointing. It became necessary to visit plants where flotation was practiced before much success was obtained in the laboratory.

By that time small flotation units were being built and tested in scores of mills. In view of the drift of public interest it was decided that the most service possible could be rendered by personal visits to plants that were using or should use flotation, by distributing data, and by making suggestions. Further, much data was published in papers in technical journals. In these ways the Salt Lake City station has encouraged many people to publish their experiences. At the present time the necessity for flotation in many mills has been seen and the process installed. The only metal mining fields in which it has not been adopted to a large extent are the lead-zinc fields of Missouri, Kansas, and Oklahoma, and the Wisconsin zinc field. Here the old milling methods with jigs and tables are often in the control of men who have been slow to see the need of treating the fine slime that escapes concentration on tables. Moreover, in the mills that are under technical control in these fields the amount of slime made in any one mill under present systems of grinding is so small that there is serious doubt as to flotation plants being economical. Small flotation plants would have to be tended by the "table man" of each plant and would necessarily receive only occasional attention. Hence there is need for machines that automatically maintain froth and pulp levels and discharge tailing without attention, and also of automatic oil feeders and other accessories for plants capable of treating small tonnage-10 to 20 tons of slime a day, as determined by C. A. Wright, then assistant metallurgical engineer of the Bureau of Mines.

• Experimenters: G. L. Allen, F. Cameron, H. J. Morgan, C. A. Wright, and O. C. Ralston. Wright, C. A., Mining and milling of lead and zinc ores in the Missouri-Kansas-Oklahoma zinc district: Bull. 154, Bureau of Mines, 1918.

134 pp.