GENETIC LINKS AMONG SYNGENETIC METAL ACCUMULATIONS IN SEDIMENTARY BASINS: GIANT SEDIMENT-HOSTED METAL DEPOSITS TO METALLIFEROUS BLACK SHALES

Ancient sedimentary basins host large and economically important metal deposits. Single sedimentary basins often host different types of syngenetic metal deposits in correlative strata. Striking geologic, geochemical, and isotopic similarities exist between these diverse metal accumulations; including metalliferous black shales, Ni-PGE-Mo-Au-V-P, Au-Ba, Ba, PO4, Fe-Mn, and Zn-Pb-Ag-Ba deposits. The genetic processes responsible for these remarkable metal accumulations are important because they are (1) the primary global source for many of these metals, (2) linked to black shale formation and organic matter burial, and (3) indicators of dramatic secular variations in ocean chemistry. Despite their significance, there is little consensus as to the source, means of transport, and deposition of these metals.

This session joins researchers of diverse disciplines to explore genetic relationships of sedimentary basin-hosted metal accumulations by evaluating possible (1) sources of metals (hydrothermal, seawater, and riverine), (2) transport of metals (different hydrothermal fluid and/or seawater chemistries), (3) mechanisms of deposition and accumulation on the sea floor (redox chemistry, biological pathways), (4) mass balance constraints through dynamic modeling that considers sedimentation rate, metal supply fluxes, organic productivity, (5) exploration potential, and (6) the interrelationships between these metal accumulations and secular changes in seawater chemistry. An overlooked aspect of this discussion is the magnitude of brine expulsion events that formed sedimentary-exhalative (Sedex) ore deposits. During these events the metal fluxes delivered to the ocean rival or surpass their entire modern riverine fluxes. The diversity of metals in these strata implicate a variety of fluid compositions. Oxidized brines form enormous Zn-Pb deposits while reduced brines transport Ba and Au. Significant Ni-PGE-Mo-Au-V deposits are best explained by metal transport in petroleum (herein named Petrex deposits). Brine- and petroleum-associated fluxes of biolimiting nutrients such as trace metals, N, reduced C, Si, and S might explain significant eutrophication and anoxia that characterize these metallogenic events.