A deeply karsted unconformity separates Proterozoic carbonate rocks of the Wynniatt Formation from overlying Cambrian sandstone near the head of Minto Inlet on Victoria Island, Arctic Canada. Sandstone-filled paleocaverns, hundreds of metres wide and tens of metres high, are present approximately 10 to 15 m stratigraphically below the nominal stratigraphic contact between Proterozoic and Cambrian rocks; the position of the paleocaves relative to the main unconformity surface suggests development along a paleointerface possibly associated with the water table. Gryke networks and karstic towers are present in the Wynniatt Formation at the unconformity. Crossbedded sandstone that overlies the unconformity contains unusual, vertical columnar sandstone structures, decimetres to metres in diameter, which cut sharply across bedding and contain weak concentric layering. These pillar-like structures are attributed to water escape through submarine springs, where groundwater flowing through the karst network emerged onto the Cambrian seafloor. The pillars are most densely clustered in the most northern exposure of the sandstone, and diminish in abundance southward, suggesting that the coastline and the source of hydraulic head were to the north of the study area.

Despite the presence of known economic resources in Canada's Arctic archipelago, Victoria Island remains understudied. This study addresses the fluid history and economic potential of two major carbonate units on Victoria Island by integrating fluid inclusion microthermometry with SEM‐EDS analysis of evaporate mounds. Three cements containing fluid inclusion assemblages (FIA) occur in the Neoproterozoic Wynniatt Formation: saddle dolomite, brown dolomite and calcite, in paragenetic order. The two dolomite‐hosted cements have average homogenisation temperatures (Th) for FIAs (n = 3) of 108°C (saddle) and 101 and 116°C, but metastability precluded determining salinities; most calcite‐hosted fluid inclusions are too small and/or necked to obtain Th values, but rare larger inclusions have salinities from 1.7 to 0.4 wt. % NaCl equiv. SEM‐EDS analysis of evaporate mounds indicates the fluid changed from an early K‐rich (saddle dolomite), to a later K + Na (brown dolomite), and finally Na‐rich (calcite), which suggests mixing of two end‐member fluids (i.e. Na‐rich and K‐rich). Dolostone of the lower Paleozoic ‘Victoria Island formation’ contains two cements: early quartz and late dolomite. Quartz‐hosted FIAs (n = 2) have an average Th value of 126°C, and salinity of 23.2 wt. % NaCl equiv., whereas FIAs (n = 3) in dolomite have average Th values of 109, 116 and 124°C; metastability precluded determining salinity. Evaporate mound analysis for the cements indicates evolution from a Na‐rich to a Na + K fluid through interaction with reservoir rocks. A reduced, metal‐rich fluid was present during quartz precipitation, as implied by the presence of pyrite framboids along growth zones and nanoparticles of barite and sulphide minerals (Zn, Cu and Pb) in evacuated inclusions, which suggests the area may have potential to host base‐metal mineralisation. Importantly, distinguishing different fluid compositions in both of the case studies would not have been possible without evaporate mound analysis and therefore the results emphasise integrating this technique into diagenetic studies.

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