Abstract

Simple field observations of megascopic mineralogical relationships have been used to construct a complex model of the orebody found at the Ozark Lead Company mine. Observations which formed the basis of the model are listed without regard to theoretical interpretation:(1) Octahedrons and cubes of galena can be found together and separately in vugs and cross-cutting features.(2) Galena octahedrons may be overgrown by later galena, chalcopyrite, marcasite, or siegenite.(3) Most octahedrons are either etched or partially corroded. Total removal of octahedral-form galena seems an exception.(4) Galena cubes envelop octahedrons and always appear to grow on top of or in the openings between them.(5) Chalcopyrite can be found in varying amounts from individual crystals to nearly solid masses up to 6 feet thick.The model was formulated to explain the development of the orebody. Simply, the model consists of: (1) an early copper segregation, (2) a minimum of three periods of octahedral galena growth, (3) a minimum of one period of colloform galena, and (4) a minimum of two periods of cubic-form galena.Initial precipitation of sulfides in favorable host horizons altered the physicochemical parameters of the solutions. The solutions, still chemically active, were then flushed away from the sites of deposition and reacted with both the country rock and previously existing sulfides in an attempt to regain an equilibrium state. The breccia is thought to have formed by the multiple attack of these undersaturated solutions in previously structurally prepared ground. Penecontemporaneous with breccia development was an exothermic reaction, due to the leaching of sulfides. Dissolution increasements of reduced sulfur followed by temperature drops determined the degree of supersaturation of the regenerating ore fluids. "Hybrid" solutions produced within the Bonneterre host carried a distinctly mixed ore fluid that in turn mineralized parts of breccia and the marginal break ore zones.

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