Abstract

The Magmont mine is about one and a half miles south of Bixby, Missouri, within the northern third of the Viburnum Trend. First intersected by surface drilling in September 1962, the Magmont orebody was outlined by about 200 drill holes. Production began in 1968 and continues at 1,000,000 tons of ore per year.Economic mineralization occurs within the Bonneterre Formation, closely associated with solution-induced collapse breccias, gravity slumps, a favorable bed sequence called the "Silty Marker," and inter-reef calcarenites. The Davis shale overlies the Bonneterre Formation and has acted as an impervious barrier to solution flow. No structural irregularities within the Bonneterre Formation in the mine area can be attributed to underlying Precambrian knobs, which are apparently not present within this part of the "Buick embayment" (a local feature defined by a shallow, east-northeast-trending valley in the basement rocks).A northeast-northwest joint system is present. One north-south, partially open fracture can be traced for 2,500 feet. Bounding, shale-filled subsidence faults mark the north-south trend of high breccia ore zones. Vertically, economic mineralization occurs between the base of the Davis shale and the base of the lower reef horizon of the Bonneterre Formation. Three north-south-trending, parallel ore zones comprise the Magmont orebody.Laterally a roughly concentric mineral zoning is present. From outside to inside it is marcasite, marcasite-galena, and galena-chalcopyrite-sphalerite. Gangue minerals in addition to marcasite are dolomite, calcite, quartz, and minor dickite.Lesser minerals are pyrite, siegenite, and bornite accompanied by minor amounts of other copper minerals.

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