Reef Horizons Research Articles

Geology of the Viburnum No. 27 Mine, Viburnum Trend, Southeast Missouri

The No. 27 mine lies at the northern end of the Viburnum Trend near a 2.5-mile-long granite high 3 miles west and basinward of the main ore trend.Mineralization, primarily associated with clastic structures, occurs almost exclusively in the digitate stromatolitic reef horizon of the dolomitic Bonneterre Formation. The two most common ore-bearing structures are calcarenite-filled channels between linear algal mounds and calcarenite-filled troughs behind subtidal offshore algal bars. A mineralized local white rock facies is present in an embayment on the eastern flank of a granite peak that rose over 500 feet above the Cambrian sea level, and a major non-mineralized breccia within the Bonneterre Formation contains fragments of the Davis Formation as much as 90 feet below their normal position.Two fracture systems are prominent in the mine. Both systems parallel much of the ancient shoreline as do the major region faults.Mineral zonation is well developed with chalcopyrite generally occurring along the basinward flank and at the base of the galena orebodies, while sphalerite is usually found near the top of the orebodies.

Geology of the Magmont Mine, Viburnum Trend, Southeast Missouri

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.

Stratigraphic Significance of Devonian Coral Reefs in Western Canada: ABSTRACT

Devonian coral reefs occur in both Middle and Upper Devonian in western Canada. They are confined, however, to definite stratigraphic horizons. In order to provide a basis for the study of the reefs, the writers introduce a succession of zones which are applicable to all western Canada and reef horizons are referred to these zones. The stratigraphic significance of the reefs becomes greatly clarified when this is done. End_of_Article - Last_Page 2251------------