REACTIVE GOSSANS IN PERMAFROST: CASE STUDIES FROM THE CANADIAN ARCTIC ISLANDS

Gossans are surficial deposits that form through the chemical and physical weathering of the host bedrock. Gossans may produce secondary minerals that reflect the composition of their primary mineral sources, including buried ore deposits. The mineralogy of gossans (e.g. silica, jarosite and goethite) results from the oxidation of sulphides by acidic and oxidizing fluids. Research carried out by the Geological Survey of Canada (GSC) over the past decade has led to new insights on the mapping, morphology, stratigraphy, mineralogy and geochemistry of gossans that form in a permafrost environment. Gossans located on Victoria Island and Axel Heiberg Island were the focus of GSC field and laboratory studies carried out from 2011 to 2015. Study protocols included (1) the identification of gossans using satellite imagery; (2) field mapping, sampling and in situ spectral analyses; (3) mineralogical and geochemical studies; and (4) comparative studies of bedrock and stream sediments located in proximity to gossans. The distinctive colours of the oxide cap allow for the identification of gossans using multispectral and hyperspectral optical remotely sensed imagery especially in the visible-near-infrared (VNIR) portion of the electromagnetic spectrum. The small size of most gossans (a few tens of meters to less than 1 to 2 km in length) requires access to high spatial resolution images such as those provided by the WorldView multispectral sensor. Field observations and sampling of gossans at seven localities suggest that their morphology is complex. For example, the observed stratigraphy does not always match the classic gossan profile of sulphide-depleted and silica-enriched cap underlain by Fe-oxides and other secondary minerals. Gossans were grouped into three categories based on stratigraphy, presence or absence of evaporitic rocks and reactivity with permafrost. In all cases, cryogenic and oxidation processes were clearly ongoing and sulphide oxidation led to acidic conditions and the formation of relatively uniform mineralogical and textural characteristics. We propose that the pumping action of fluids in a permafrost environment, similar to a solifluction process, acts as a concentration mechanism over time and contributes to the transport of materials down slope.