Relationships of ore bodies to dikes and sills

Abstract

A review of geologic literature shows many important relationships between ore deposits and associated dikes and sills. Most significant are the structural controls by pre-ore dikes on ore localization. Dikes and sills commonly are competent, brecciated bodies that act as host rocks or as channelways for ore solutions. Incompetent dikes and sills serve as dams, ponding ore solutions at their contacts. Fracturing at dike contacts also creates channelways and loci for deposition; the nature of this fracturing is variable, and depends on relative competency and on the nature and direction of differential stress at the contact. Intersections of dikes and sills with fault zones, formation contacts, and other planar structures provide excellent sites for ore deposition. Primary features of dikes and sills, such as permeability, width, and configuration are sometimes important in localizing ore.Contemporaneous and post-ore dikes and sills in a few cases are important as indicators of the factors controlling movements of ore solutions. Post-ore injections may seriously dilute ore deposits, or may by heat action effect changes in mineral composition and distribution.Genetic relationships between dikes, sills, and ore are not well understood. Magmatic segregations commonly take the form of dikes and sills, and other gradational relationships between ore and igneous rock are occasionally noted. Dike injection is predominantly pre-ore, with lamprophyres and diabase apparently closely related in time to mineralization. Most dikes and sills associated with ore are of intermediate composition.