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An attempt is made here to describe occurrences and paragenetic sequences of the supergene Zn and Pb minerals in 3 districts representing varying mean temperatures and humidities. The facts observed in field and laboratory are interpreted in the light of physical chemistry, assuming equilibrium conditions. The stability relationships between smithsonite, hydrozincite, and zinc hydroxide are defined in terms of pH and total carbon dioxide concentrations in the aqueous solution system, or of the partial pressure of carbon dioxide in the dry system. The stability fields of hemimorphite and willemite are also discussed. The study explains the common occurrence of hydrozincite in arid regions, and the scarcity of this mineral in humid regions. The common occurrences of smithsonite and hemimorphite in the southern Appalachian district, and the predominance of smithsonite over hydrozincite and hemimorphite in the Upper Mississippi Valley district can be explained by the pH of the ground waters and soils. The stability fields of supergene lead oxide minerals, wulfenite, cerussite, anglesite, and Cd minerals are calculated in terms of pH, Eh, and total S concentration or total carbon dioxide concentration in solution. The paragenesis of the Pb minerals and the mobilization of molybdate and Cd ions are discussed. The results of the spectrochemical analyses indicate that Mo and As in the supergene facies were derived from galena, whereas V and P were derived from the limestones and shales.

The Glove Mine is located on the southern extremity of an isolated syncllnal sedimentary block of Paleozoic and Cretaceous sediments on the southern flank of the Santa Rita Mountains in Santa Cruz County about forty miles south of Tucson, Arizona. Fluids probably associated with a Laramide (?) quartz monzonite in- trusivehave deposited argentiferous galena, sphalerite, chalcopyrite, pyrite, and quartz along permeable zones caused by fault intersections within a favorable limestone bed of the Pennsylvanian-Permian Naco group. As a result of extensive oxidation, only relics of the primary sulfides exist in the mined portion of the deposit. Cerussite, and lesser amounts of angle- site, wulfenite, smithsonite, and other oxidation products of the primary sulfides have been conten{rated in solution caverns. The ore body can be divided into three general zones on the basis of metal content and mineral assemblage. These zones are (A) the upper oxidized and leached zone, (B) the silver-enriched intermediate zone, and .(C) the sulfide zone. The behavior of individual metals and minerals is dependent upon local Eh-pH conditions as well as other environmental factors affecting mineral stability. In response to changes in environment, mineral and metal assemblages vary not only between the zones but within them as well.