Essai de revue des concentrations métallifères dans le cycle sédimentaire

The author summarizes the main arguments in the debate between syngenetic and epigenetic deposits and then underlines the importance of the arguments which prove that the formation of the sediments and of the metalliferous concentrations which they bear are contemporaneous. This is strongly suggested by very early syn-sedimentary reworking of the mineralization. This approach leads to a consideration of metallogenesis of syngenetic sedimentary concentrations both as a supply of metal and a sedimentary trap. The exploitability of mineralized rocks is presently such that only the coincidence of an outstanding supply of metal and a receptive sedimentary environment will yield a workable ore deposit. Reviewing all metalliferous sources which could be contemporaneous with sedimentation (terrigenous, exhalative, marine and possibly also fluidogenic) the author stresses the geological and geochemical characteristic of the surrounding sediments. At the same time, the examination of traps in sandy, shaly and carbonate environments permits to the identification of the main characteristics of the concentration on the scale of the deposit and of the ore itself. The search for an understanding of metalliferous concentrations in the sedimentary cycle becomes a question of defining criteria for the quality of supplies and traps. On the level of the trap these would be the duration and the regulation of parameters which govern the efficiency of the concentrating system: the sedimentary features which result from these concentrating processes must be recognized within the lithologic column during tactical exploration. On the level of the metallogenetic province it is the purpose of strategic exploration to search among the available geological and geochemical data for features which favor each type of supply. These are the basic principles of the indirect method of exploration for sedimentary ore deposits.