Bulletin of the Geological Society of Malaysia, Volume 16, Dec. 1983, pp. 193 – 213
Department of Earth Sciences, University of Manitoba, Winnipeg, Canada R3T 2N2.
Abstract: Two popular beliefs that strata-related deposits (SRD) are a recently introduced category of ore and that SRD are metal sources of the future, are semiquantitatively evaluated using worldwide data.
Two fundamental obstacles to a convincing numerical analysis are 1) the lack of sharp and precise boundaries of SRD; 2) the gaps in data base and a considerable range in data quality. As a consequence, the selection of members that make up the SRD as a cIass of metallic deposits is based on contemporary convention rather than on accurate definition, and the imperfection of data adds a considerable margin of uncertainty to the conclusions.
Historical review of the proportion of SRD to non-strata-related metallic ores throughout human history demonstrates that SRD – gold and tin placers have been among the most ancient mineralization types utilized. Apparently SRD as a class has been in existence since the beginning with the strata-terminology and the reevaluation of the more controversial types and newly discovered ones being introduced during the great genetic controversy of the 1950’s and 1960’s.
The prediction of the future importance of SRD has been based on the assumption that ore grade will continue to decrease. The proportion of SRD among metallic ores has been estimated for periods in which the average grade drops to 75%, 50% and 10% of the present grade. The drop to 75% and 50% causes few abrupt changes-the proportion of SRD of more metals moderately increases. At 10% of the present grade, the grade of the low-factor of concentration metals (Fe, AI, Ti) approaches the mean crustal content and the “ores” will become indistinguishable from rocks. U, Cr, Mn, Pb, Zn, Ag and Au wiII have their greater proportion derived from SRD. Only in the case of Cu, Sn and possibly Ni wilI the SRD represent the minority source.
Overall, the belief that strata-related deposits are the metal sources of the future, has been confirmed.