Chemical Evolution and Zonation of Massive Sulfide Deposits in Volcanic Terrains

In contrast to most of the other mines in the Viburnum Trend, much of the Ozark Lead Company orebody lies at right angles to the depositional strike of the sediments. This divergence is due to localization of much of the ore along the flank of a northwest-trending Precambrian high situated on the upthrown side of a high-angle reverse fault. A second distinctive feature of the orebody is that ore occurs throughout the vertical range of the Bonneterre Formation at certain horizons. Mineralization is both structurally and stratigaphically controlled. Dominant ore minerals are galena and sphalerite. Chalcopyrite, a relatively minor constituent, occurs locally in bedded bodies composed almost exclusively of chalcopyrite. One such body contains significant bornite, and minor covellite, cligenite, and djurleite. Four broad categories of ore have been delineated: (1) bedded or disseminated, (2) breccia, (3) marginal break, and (4) fracture stockwork. Bedded ore is localized or controlled by the flanks of highs. Breccia ore lies within a breccia that in part parallels the flank of the Precambrian ridge. Marginal break ore occurs in a complex system of throughgoing faults or fractures that parallel the breccia but are separated from it by a barren or weakly mineralized zone. Fracture ore cross-cuts the strata and is generally not of economic importance unless the fractures form a stockwork. The breccia is interpreted as due to solution collapse. The marginal breaks probably developed because of a slight shifting of the sediments toward the breccia.