NEW INSIGHTS INTO THE ORIGIN OF CRITICAL MINERAL RESOURCES IN ORGANIC-RICH BLACK SHALES
Over several decades, intensive study of these shales, and their modern analogs, has revolutionized our understanding of the processes responsible for metal and organic matter accumulation. These constraints have helped unravel the paleo-redox, -oceanographic, -environmental, -climate evolution of the past oceans. Orders of magnitude variations in concentrations of CM are generally viewed as the result of the combined effects of biological productivity, redox, and hydrographic conditions, rather than an external source of elements. However, simple box and oceanographic modeling, suggests that global mass balance of marine systems struggles to explain the largest and highest-grade CM accumulations. It is also increasingly clear that organic-rich black shales correspond with perturbations to the global carbon cycle, OAEs, δ13C excursions, mass extinctions, and environmental/climate change.
Ore genesis research is revealing that many CM-rich organic black shales are distal manifestations of the planet’s largest seafloor hydrothermal deposits - sedex deposits. Evidence that the flux of metals, and importantly, key biolimiting nutrients from these systems can exceed the total modern riverine flux to the ocean, suggests they may be the ultimate source of anomalous CM and the underlying trigger of these global events. Further work is needed to determine whether periodic venting of hydrothermal systems has influenced the evolution of marine chemistry as it raises unprecedented opportunities for mineral assessments and forecasting of CM in shales and the large hydrothermal systems that formed them.