ZINC-IRON MIDDLING FROM BROADWATER MILL, NEAR PARK CITY, UTAH.

Near Park City, Utah, a large accumulation of old mill tailing is being treated by a number of mills, and large amounts of zinc-iron middling are produced. The question has been raised as to what should be done with it. The sample from the Broadwater mill represents a product such as could have been made during the milling of countless tons of the Park City ores in the past, and could be prepared from the ores now being mined. A marketable zinc concentrate from such zinc-iron middling is possible, as shown by the tests reported in Table 10 following:

TABLE 10.-Results of magnetic concentration of zinc middling from the Broadwater mill.

ORE FROM CARLYLE MINE, STEEPLEROCK, N. MEX.

The ore from the Carlyle mine, near Steeplerock, N. Mex., was tested without removal of the gangue. This was a complex sulphide. ore carrying zinc, lead, copper, and iron. The deposit at this mine. represents a fairly common ore type in this district, the sulphide ore. coming from beneath an old bonanza oxidized gold-ore body. There are many similar mines in which oxidized ores of silver, gold, or copper changes to complex-sulphide ores below the water level. In this sample the sulphides were more or less separable from each other but were intimately combined with the gangue, so that the preparation of products not contaminated with too much gangue was difficult. This was especially true of the zinc concentrate. The only encouraging feature of the test was that the iron products from the magnetic separation carried a good proportion of the copper of the original ore in a concentrate that was marketable. (See Tables 11 and 12.)

The raw ore was ground to pass 20-mesh and then was given a heavy roast in the laboratory roaster. The calcines were then put through the magnetic separator with the magnets set fairly close. The "irons" from the above test were reground to pass 40-mesh and then put over the magnetic separator again, making a magnetic and a

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nonmagnetic product. The zinc concentrate obtained from the roasting and separation of the Carlyle zinc middlings from a table test was treated on the small test table to see what kind of a separation could be obtained after roasting. The results were as follows:

TABLE 11.—Results of maynetic separation of ore from Carlyle mine, roasting without tabling.

In another test the ore was first tabled after being ground to pass a 20-mesh screen. Three products were obtained- -a lead concentrate, a zinc middling, and a tailing. The slime was not recovered; this accounts for the low recovery of copper, as the chalcopyrite slimes badly and was lost. The zinc middling obtained was put through the laboratory roaster and then through the magnetic separator. The concentrate obtained was again sent through the magnetic separator, with the magnets set closer together, to see if any. more iron could be removed. The results of the tests are as follows: TABLE 12.-Results of magnetic separation of ore from Carlyle mine, with tabling.

ORES FROM MINES NEAR CHLORIDE, ARIZ.

The ore from the C. O. D. mine, near Chloride, Ariz., is from a deposit somewhat similar to that in the Carlyle mine. However, this sample yielded commercial grades of concentrate, both of lead and of zinc, as shown in Table 13.

TABLE 13.-Results of magnetic separation of ore from C. O. D. mine, near Chloride, Ariz.

The Middle Golconda mine, near the Chloride, Arizona, district has zinc-iron sulphide ore carrying small amounts of silver, lead, and copper. On account of the small lead content it was difficult to get a clean galena concentrate free from zinc on the concentrating tables. The zinc-iron middling could be separated easily into a zinc concentrate of commercial grade and an iron concentrate, containing some lead and silver, which could either be combined with the lead concentrate produced on the tables, or discarded, according to the distance from a lead smelter. The flotation of the slime of this ore produced a mixed lead-zinc sulphide concentrate that could be marketed, although not to as good advantage as separate lead and zinc concentrates. The results are shown in Table 14.

SUMMARY OF THE MAGNETIC-SEPARATION TESTS.

A number of the less complex mixed-sulphide ores from mines in the western States have been tested for magnetic separation of the iron sulphide with varying degrees of success. Some of them give commercial grades of concentrate.

ROASTING ZINC SULPHIDE ORES.o

CHLORIDIZING ROASTING.

For some years previous to the inception of the work at the Salt Lake City station, various chloridizing processes had been popular in Utah. The large supplies of salt available in this State made chloridizing roasting and brine leaching a logical development in the metallurgical treatment of low-grade and complex ores. The plants of the Mines Operating Co. at Park City and of the Knight-Christensen Metallurgical Co. at Silver City were designed to remove copper, gold, and silver from the low-grade siliceous ores found in many of the western mining districts. Recovery of the lead, in addition to these three metals, had not received much attention, although some lead had been recovered in these plants. Therefore, the Salt Lake City station made a study of the action of the lead and zinc minerals during chloridizing-blast-roasting and leaching, as practiced in the above mills, with the object of determining whether the processes could be extended or modified in order to recover all of the lead and the zinc.

The results of the work on lead have been published by the Bureau of Mines in Bulletin 157. Seemingly, it should be easily possible to modify the processes used in order to make proper recovery of the lead.

The work with the zinc minerals was unsuccessful as only part of the zinc could be chloridized. The question of chloridizing oxidized zinc ores is discussed in another part of this bulletin (p. 120). As regards the zinc-sulphide ores, satisfactory roasting and chloridizing in either the Holt-Dern shaft roaster or the Knight-Christensen downdraft roaster seemed impossible. With an ore containing 5 per cent of zinc as the sulphide, in a quartz gangue, it was found that under the conditions prevailing in the blast roasters the zinc sulphide did not have time to roast, either in the presence or absence of salt. None to 12 per cent of the zinc would volatilize, probably as chlorides, and 5 to 35 per cent of the zinc in the calcine was soluble. Leaching with acidified brine would usually extract not more than half of the zinc in the calcine, including the water-soluble or chloridized zinc.

a Experimenters: W. G. Woolf, C. L. Larson, M. J. Udy, Walter Neal, R. W. Johnson, and J. F. Cullen. Lyon, D. A., and Ralston, O. C., Innovations in the metallurgy of lead: Bull. 157, Bureau of Mines, 1918 176, pp.