SULPHATE MINERALOGY OF BURNING SHALES AND ACID PONDS - INGNIRYUAT (SMOKING HILLS), NORTHWEST TERRITORIES, CANADA

Ingniryuat (also known as the Smoking Hills), Northwest Territories, Arctic Canada is characterised by auto-combusting pyritic mudstones of the Smoking Hills Formation. The Smoking Hills Formation was deposited in an outer shelf to slope marine environment, during Late Cretaceous Oceanic Anoxic Event 3. Oxidative weathering of this unit creates extensive jarosite-rich deposits, and banded jarosite- and phyllosilicate-rich mudstones. Slumping of these mudstones exposes large masses to atmospheric oxygen leading to generation of high temperatures (sufficient to produce paralavas) through pyrite oxidation, and the subsequent formation of a diverse suite of hydrated metal-sulphate minerals. Weathered combustion sites are characterised by a simpler jarosite-rich mineralogy along with thermally-altered mudstone. Away from sites of auto-combustion (bocannes), pyrite-rich layers within the mudstone oxidise to jarosite, creating a yellow-banded appearance in outcrops. These jarosite-rich layers, similar to those observed interbedded in mudstones on Mars, reflect post depositional oxidation processes - not acidic conditions during the time of deposition. At the same time, pyrite weathering forms local hyperacidic metal-rich brines (pH less than negative 2) forming a host of additional sulphate minerals. The region forms a wonderland of strange and exotic sulphates.