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Gossans resulting from the oxidation of sulphide-rich bedrock occur sporadically across Canada, and these features are routinely indicated on geological maps published by the Geological Survey of Canada (GSC). In the Canadian Arctic Islands, some gossans display reactive zones in permafrost characterized by specific textures and mineralogical facies. In poorly-vegetated areas of the High Arctic, gossans can easily be detected on high-resolution satellite imagery. However, the mechanisms leading to their formation are poorly known. For this study, two reactive gossans located in the early Neoproterozoic Minto Inlier of Victoria Island, Northwest Territories, were investigated to determine if the deposits constitute (1) analogues of mine waste in permafrost and (2) vectors to economic resources. Mineralogy was determined in situ using a portable spectroradiometer, with follow-up laboratory measurements. Site 1, Gossan Hill, is a 75-m topographic high capped by a poorly consolidated, rust-coloured layer overlying pyrite-rich sands, and resembles a classic gossan. Site 2, Gossan Sill, underlies a mineralized gabbroic sill consisting of sulphide-rich veins and pods but appears to be inverted morphologically. Visible–Near Infrared–Short Wave Infrared spectral analyses of surficial materials at Gossan Hill indicate gypsum, goethite and jarosite, and X-ray diffraction (XRD) confirms their presence as well as quartz, illite and feldspar. At Sill Gossan, spectral analyses show gypsum and jarosite; XRD indicates variable amounts of goethite, hematite, pyrite, chlorite, calcite and feldspar. The positive relief and presence of concentric alteration zones at Gossan Hill suggest that cryogenic processes, typical of Arctic regions, are active. Water becomes expelled during the freezing cycle forcing material outwards and along with oxidation of the sulphides, forms variably coloured zones in gossanous material. The inverted stratigraphy at Sill Gossan is more problematic. Constant weathering and mass wasting from the overlying sill and pyrite-rich breccia provide fresh pyrite to the gossan on a regular (seasonal) basis. [ABSTRACT FROM AUTHOR]

Gossan Hill is located within the Minto Inlier in central Victoria Island, Northwest Territories (N 71.36697°, W 114.95155°). A study of the mineralogical associations and geological setting of this deposit indicates that it is an arrested hydrothermal system frozen in permafrost. From above, the hill stands out because of the topographic relief of 75 m and the orange-brown color of the surficial material. The surface of the hill is marked by areas of concentric color zonation up to 3 m across, with light gray centers surrounded by a yellow–orange ring that is surrounded by an orange–brown color that covers the rest of the surface of the hill. Trenches dug into these areas reveal that the central zone contains quartz and pyrite native sulfur in a loose aggregate of sand-sized grains. This central area is surrounded by a zone dominated by gypsum and quartz with some jarosite. Beyond this, the surrounding surface consists of quartz, hematite, and amorphous iron oxides. The radial arrangement of the mineral assemblage indicates an increase in oxidation of sulfur from the center outward. Analysis of isotopic composition of the sulfur indicates the source of sulfur could be the underlying strata. The hill is underlain by inter-bedded carbonate and sulfate-evaporite sedimentary rocks of the Kilian formation in the upper part of the Neoproterozoic Shaler Super group. The sedimentary rocks were intruded by diabase sills of the 720 Ma Franklin igneous event, which crop out 2 km to the south of Gossan Hill. The soft friable nature of the deposit and the topographic relief of the hill indicate a post-glacial (Pleistocene) age of formation. Permafrost has maintained the disequilibrium mineral assemblage since the cessation of fluid flow. Extraction of the permafrost ice from the central zone yields a liquid with a pH of 2.3. The observed long-term persistence of pyrite encased within the acidic permafrost indicates that oxidation and dissolution reactions common in mine waste are slowed, if not stopped, in such an environment. The predicted rise of Arctic temperatures will cause the active layer to move deeper and result in the release of the acidic solutions frozen in the permafrost. Water ice or frozen CO2 just below the Martian surface would also preserve such mineral disequilibrium for very long periods of time. No region exists on Earth where ice has existed continuously for millions of years, but the Gossan Hill deposit is an excellent terrestrial analogue. On Mars, the subsurface ice may be very old. Ancient reactive Martian mineral assemblages and the fluids associated with them will reflect conditions that existed in the past. [ABSTRACT FROM AUTHOR]