Abstract

The Hall Molybdenum deposit near Tonopah, Nevada, has been developed for 1,200 feet in length, and has an average width of 53 feet. It lies in schist along the southern margin of an alaskite stock. Molybdenite, its oxidation product ferrimolybdite, pyrite, chalcopyrite, and limonitic ocher are associated with abundant quartz veins in the contact zone.The region is arid, and the topography is of moderate relief.The oxidized zone is 95 to 150 feet deep, and the bottom of oxidation parallels the surface drainage gradient. The water table lies below the lowest workings, which are 200 feet beneath the bottom of oxidation.In the oxide zone 30 to 40 per cent of the total molybdenum is in the form of sulphide, whereas in the sulphide zone 87 per cent or more of the metal is present in that form. Total assay values, however, show no significant change in passing from one zone to the other.Conditions at the Hall Property favored thorough oxidation, but molybenite oxidizes slowly, and the metal clearly does not migrate readily in any form. In comparison with other molybdenite deposits, oxidation of the Hall orebody has more than average relative importance.The amount and depth of oxidation of molybdenite should be carefully considered in the examination of prospects, because no commercial process has been put in use to recover the metal from the oxide.

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