Sediment-Hosted Zinc-Lead Mineralization: Processes and Perspectives: Processes and Perspectives

The principal geologic and geochemical characteristics of the main classes of sediment-hosted zinc-lead(-silver-barite) deposits (SEDEX, Mississippi Valley-type, and Irish-type) are summarized with emphasis on the similarities and differences among them. Data that constrain sources of fluids, metals, and sulfur in the deposits and proposed ore genesis models are discussed. Preferred models are described, with areas of uncertainty highlighted. Key factors in deposit formation are considered to be the generation of brines in favorable paleogeographic environments and the subsequent interaction of these under appropriate conditions for efficient stripping of metals from source rocks. Sulfide is derived principally from the near-deposit environment, ultimately sourced from seawater sulfate. The secular evolution of seawater chemistry and supercontinent cycles are considered to have played important roles in controlling periods when the formation of different types of deposits was favored.