Galena and Sphalertie in the Mid-Silurian Carbonates in the Vicity of Hamilton, Ontario

Abstract

Field observation at seven outcrops and subsequent polished section studies reveal that lead and zinc mineralization in the Hamilton vicinity occurred after the lithification of the host carbonates. The availability of open structures and the presence of potential reducing agents are the main controlling factors of sulphide deposition, The absence of an igneous source demands an origin of the metals from the sedimentary country rocks. Analysis of 14 shales and 12 dolomites by atomic absorption for Cu, Pb, and Zn indicates that the argillaceous rocks are potential source of the heavy metals. Furthermore, a simple leaching experiment has demonstrated that concentrated brine (sodium chloride solution) can preferentially leach lead and zinc from the shales. A mode of origin involving preferential_leaching can then adequately explain the scarcity of copper minerals in the Mississippi Valley-Type ore. It is suggested that better controlled leaching experiments at various temperatures should be done in conjunction with more extensive field work to check the plausibility of such a theory.