THE RELATIONSHIP OF NEOPROTEROZOIC CLIMATE CHANGE AND ORE GENESIS

Chemostratigraphic comparison of glaciogenic strata in the Neoproterozoic of Gondwana and Laurentia suggest a strong genetic linkage between severe climatic and environmental perturbations, and subsequent emplacement of Cu-Zn-Pb deposits in carbonates that overly glacial strata or hiatus. This new model suggests that hydrothermal fluids flowing through Neoproterozoic glacial diamictites dissolved and transported metals - from continental crustal sources ground up and deposited by widespread ice sheets, and metalliferous marine cements that lithified the unconsolidated deposits. Redox transformations attendant with the focused fluid flow also resulted in acidic conditions. Injection of these hot, metal enriched solutions, along fractures, into relatively impermeable fine-grained carbonates atop the diamictites further focused fluid flow where neutralization reactions raised pH. Additional sulfur was added to the solutions as bedded sulfate and carbonate associated sulfate dissolved and was thermochemically reduced to sulfide. Cooling of these neutralized solutions caused precipitation of stratabound ore deposits predominantly composed of Cu-Zn-Pb sulfides, silicates, and carbonates. Notably both the stratabound sulfides and structurally bound sulfate in sedimentary carbonates reveal similar levels of ³⁴S enrichment. The extreme ³⁴S enrichment of oceanic sulfate is the expected consequence of high rates of bacterial sulfate reduction in anoxic waters during Neoproterozoic ice ages, and extreme rates of carbonate accumulation in the aftermath. Defining the sources of metals and sulfur for these important Cu-Pb-Zn ore deposits is of critical importance to understanding their genesis. If the sedimentary and metallogenic model proposed here is generalizable, then glaciogenic Neoproterozoic successions with cap carbonates worldwide may become important mineral targets. Rather than a single global ore-forming event, it presently appears that the environmental insults of the Neoproterozoic ice ages set the stage for subsequent mineralization events based on local tectonic and hydrothermal histories.