Coupled heat and fluid flow modeling of the Carboniferous Kuna Basin, Alaska: implications for the genesis of the Red Dog Pb-Zn-Ag-Ba ore district

摘要

The Red Dog deposit is a giant 175 Mton (16% Zn, 5% Pb), shale-hosted Pb-Zn-Ag-Ba ore direct situated in the Carboiniferous Kuna Basin, western Brooks Range, Alaska. These SEDEX-type ores are thought to have formed in calcareous turbidites and black mudstone at elevated sub-seafloor temperatures (120-150 deg C) within a hydrogenologic framework of submarine convection that was structually organzied by large normal fautls. The theory for modeling brine migration and heat transport in the Kuna Basin is discussed with application to evaluating flow patterns and heat transport in faulted rift basins and the effects of buoyancyh-driven the conection on reactive flow and ore genesis. Finite element simulations show that hydrothermal fluid was discharged into the Red Dog subbasin during a period of basin-wide crustal heat flow of 150-160 mW/m~2. Basinal brines circulated to depths as great as 1-3 km along multiple normal faults flowed laterally through thick clastic aquifers acquring metals and heat, and then rapidly ascended a single discharge fault zone at rates approx 5 m/year to mix with seafloor sulfur and precipitate massive sulfide ores.