THE EFFECTS OF GLACIAL ADVANCE ON THE CREATION OF ORE BEARING FLUIDS

Glacial advance is known to increase the pore pressure of fluids in the underlying bedrock; at the same time, glacial ice is an effective thermal insulator compared to bedrock (1.6 W/m°C vs 3.9 W/m°C respectively), retaining geothermal heat that would otherwise be radiated, resulting in a net heating in the rock beneath the ice mass. Glacial advance and retreat may result in a cyclic movement of fluid due to the difference in fluid pore pressure along shifting glacial margins. This would force the movement of warm fluids in the subsurface, which could result in leeching metal ions from bedrock. Further ionic concentration, either from the establishment of thermal convection cells in the rock, or membrane filtration of fluids along shale or mudstone lenses may raise concentrations high enough to produce mineralization at favorable reactive horizons, or in the upper reaches of convection cells where temperatures and pressures are no longer able to keep ions in solution. The proposed source fluids would be connate aqueous fluids or existing groundwater, and movement would occur primarily in fractures, as a lack of interconnected pores would limit motion at greater depths. The system suggested is an analog of classic Mississippi Valley Type, where depositional compression and diagenetic heat are replaced by glacial compression and a raised geothermal gradient.