The Multiple Factors and Multiple Stages Involved in Sedimentary Ore Genesis

Abstract

Sedimentary mineral deposits cannot be formed by any kind of simple chemical reactions, but are products of a complex multi-episodic process depending on multiple factors. The whole process is governed by a combination of sedimentary, geochemical, biogeochemical, organic geochemical, paleoclimatical. mechanical agents as well as by the properties of relevant earth crust segment and its structural making up and tectonic mobility. A sedimentary ore deposit is nothing but a special kind of sedimentary facies, characterized by definite sedimentary assemblages. Different genetic types of ore deposit and different ore associations characterize different sedimentary assemblages in different ore-forming belts. Crustal movement, including orogenic, epeirogenic and, particularly eustatic events, controls the formation and distribution of all kinds of sedimentary mineral deposits, most of which occur within the transgression front in the lower part of marine transpressive series. Mineral deposits of economic importance cannot be precipitated directly from sea water, but are products of terrestrial imbibition, biological enrichment and pore water concentration instead. Deposits formed above the wave base in the inner continental shelf under strong dynamic condition of sea water are often large and predominantly clastic in texture with commercial grade. Below the wave base in the outer continental shelf environment, where it is more or less dynamically stagnant and oxygen-deficient, the resulted industrial ore deposits are mostly of diagenetic or strata-bound type, formed through deep-burying diagenesis. The theory of multi-factor and multi-episodic metallogenesis includes three major aspects: the ore-forming process, the sedimentary environment and the geological background. The study of the formation process itself and the sources of ore-forming elements would provide useful clues to further prospecting. Whereas, investigations of the sedimentary environments should shed light on the spacial distribution of deposits and the analysis of geological background would contribute a lot to our knowledge of the temporal evolution of sedimentary metallogenesis.