Geodynamic controls on clastic-dominated base metal deposits

Abstract. To meet the growing global demand for metal resources, new ore deposit discoveries are required. However, finding new, high-grade deposits, particularly those not exposed at the Earth’s surface, is very challenging. Therefore, understanding the geodynamic controls on the mineralizing processes can help identify new areas for exploration. Here we focus on clastic-dominated Zn-Pb deposits, the largest global resource of zinc and lead, which formed in sedimentary basins of extensional systems. Using numerical modelling of lithospheric extension coupled with surface erosion and sedimentation, we determine the geodynamic conditions required to generate the rare spatiotemporal window where potential metal source rocks, transport pathways and host sequences are present. We show that the largest potential metal endowment can be expected in narrow asymmetric rifts. This rift type is characterized by rift migration – a process that successively generates hyper-extended crust through sequential faulting, resulting in one wide and one narrow conjugate margin. Rift migration also leads to 1) a sufficient life-span of the migration-side border fault to accommodate a thick submarine package of sediments, including coarse (permeable) continental sediments that can act as source rock; 2) rising asthenosphere beneath the thinned lithosphere/crust resulting in elevated temperatures in these overlying sediments that are favourable to leaching metals from the source rock; 3) the deposition of organic-rich sediments that form the host rock at shallower burial depths and lower temperatures; and 4) the generation of smaller faults that cut the major basin created by the border fault and provide additional fluid pathways from source to host rock. Wide rifts with rift migration can have similarly favourable configurations, but these occur less frequently and less potential source rock is produced, thereby limiting potential metal endowment. In simulations of narrow symmetric rifts, the potential for ore formation mechanisms is low. Based on these insights, exploration programs should prioritize the narrow margins formed in asymmetric rift systems; in particular those regions within several tens of kilometres from the paleo-shoreline, where we predict the highest-value deposits to have formed.