Red sandstone of the Proterozoic Aston Formation (Nunavut, Canada) is exposed in the same geographic area as the Storm Cu showing in the Paleozoic-carbonate-hosted Polaris Zn-Pb district (Arctic Canada). The similar to 800-m-thick Aston Formation experienced successive burial and exhumation episodes, with maximum burial (>3 km) at the time of the Devonian Ellesmerian orogeny. A petrographic and in situ SIMS oxygen isotope study identified redbed diagenetic events, associated fluid types and temperatures, and their relative timing. The first hematite coat (Hem1) developed in the Proterozoic. Intrusion of Proterozoic dykes and sills heated local formation water to high temperatures (130-223 degrees C), resulting in precipitation of patchy Qz1 cement in a shallow-burial environment. The Fe and Si were probably derived through alteration of non-quartz silicate detritus. In the Paleozoic, a bleaching (reducing) event removed most Hem 1; the reduced fluid may have been related to regional Zn mineralisation throughout the Polaris district during the mid-Paleozoic Ellesmerian orogeny. Ensuing pressure-solution during maximum burial was probably also Ellesmerian. A second hematisation episode (Hem 2) encloses the pressure-solved quartz-grain contacts. Coeval with Hem 2 was pervasive Qz2 cementation from a low- to mid-latitude, meteoric-derived, oxidised hydrothermal (140-180 degrees C) fluid that supplied externally derived Si and Fe, probably in the Early Carboniferous. The nature and timing of the fluid events indicated by the Aston Formation's diagenetic history closely match the fluid history recorded in both Cu and Zn mineralisation in the Polaris district. This relationship strongly supports the concept that Cu in sedimentary-rock-hosted ore deposits can be sourced from redbeds, even those whose depositional age and environment is much older than, and geodynamically unrelated to, the fluid event(s) that caused diagenetic reddening and Cu transfer from source rock to mineralising site.

The Polaris district in Canada’s Arctic Archipelago contains numerous carbonate rock-hosted Zn + Pb showings and rare, anomalous Cu showings in a 450- × 130-km area. As in many metallogenic districts, a genetic relationship between the mined deposit and surrounding showings has been assumed but not tested. This study uses an in situ, multianalytical approach combining optical and scanning electron microscopy petrography, fluid inclusion microthermometry, evaporate mound analysis, trace element analysis, and in situ stable isotope analysis on sphalerite and carbonate gangue to characterize the fluid histories of individual showings and the district as a whole. Results indicate that a regional, marine-derived fluid dissolved subsurface evaporite minerals, interacted with their connate brines, and transported metals and sulfate to sites of mineralization. Initial fluid mixing with local reduced sulfur accumulations resulted in precipitation of sulfides with lower δ34S values; after exhaustion of the local reduced sulfur pool, thermochemical sulfate reduction (TSR) of transported sulfate became dominant, resulting in higher δ34S. Differences in main-stage δ34S values among different showings indicate a variable extent of TSR among sites. The mineralized volume of each showing is predominantly a function of local fluid flux and availability of a local reductant. The nature and consistency of geochemical characteristics throughout the district confirm the genetic relationship between the large deposit (Polaris) and surrounding showings and indicate that a uniform mineralizing fluid, topographically mobilized during the mid-Paleozoic Ellesmerian orogeny, was responsible for the main, district-wide mineralization, after initially mixing at a smaller scale with local, on-site fluids.

The Mariana intraoceanic volcanic arc system in the western Pacific Ocean hosts abundant ferromanganese (Fe-Mn) precipitates. A suite (n = 22) of Fe-Mn precipitates were collected from the southern portion of the arc and their mineralogies and chemical compositions were determined. These results were used to decipher their genetic assemblage, assess their potential as a source of trace metals, and place them into context with respect to Fe-Mn precipitates sampled at higher latitudes in the Mariana arc and from other locations, globally. Minerals identified include vernadite, birnessite, 10 angstrom manganate, manganite, hematite, goethite, maghemite, calcite, rhodochrosite, quartz, phillipsite, various feldspar, pyroxene, and clay minerals. Element discrimination diagrams indicate that the samples are predominantly of hydrothermal and hydrogenetic-hydrothermal (i.e., mixed) origin, with most reflecting some influence of both. Rare earth element and Y (REY) profiles are distinguished by negative Ce and Y anomalies and positive Eu anomalies. Together, the samples form a continuum from the hydrogenetic to hydrothermal endmembers. Samples with the largest hydrogenetic component are friable with branching oxide/oxyhydroxide growth structures, contain mostly vernadite, and have the greatest concentrations of most metals (including the REY elements). Hydrothermal input produces denser, cemented deposits that contain more 10 A and 7 A manganate minerals and lower minor-metal contents. Calculated growth rates range from 6 mm to >190 m Ma(-1). Average metal contents of Fe-Mn precipitates from the southern Mariana arc are low relative to hydrogenetic Fe-Mn crusts and hydrothermal Fe-Mn deposits from the northern Mariana arc and elsewhere, globally, and are therefore unlikely to be viable exploration targets.

The Cornwallis Pb-Zn district in Canada's Arctic has over 80 base-metal showings, in addition to the past-producing world-class Polaris Zn-Pb deposit (Paleozoic). The district can be geographically divided into regions based on their location relative to the Polaris deposit. The majority of showings are hosted in the same Paleozoic carbonate rock as Polaris (Thumb Mountain Formation), but other strata also contain mineralisation. This study uses an integrated multiple in-situ analytical approach to establish fluid histories recorded throughout the district. Consistent paragenetic, textural, delta O-18(Carbonate) (similar to 25 parts per thousand), and fluid inclusion characteristics (T-h and salinity 80-100 degrees C and 25-30 wt.% NaCl equiv., respectively) suggest that a single regional rock-buffered fluid was involved throughout the district. Different delta S-34 values among showings, even in the same region, suggests independent, isolated sources of sulphur for each showing. Shale-normalised REEY patterns of dolomite gangue and trace-element concentrations in sphalerite are shared within regions, but differ among regions, suggesting local stratigraphic influences. Collectively, these results indicate that mineralisation was facilitated by a single regional fluid that interacted with local strata and sulphur sources, and that the size of the Polaris deposit was a function of local structural controls, in addition to local geological and fluid variation.

The Storm Cu deposit in Arctic Canada overlies a Proterozoic red sandstone unit (Aston Formation), which may have had a role in mineralisation. Petrographic analysis of red and grey/white samples of the Aston Formation reveal multiple hematite cement phases, including an early and a late stage. Early hematite is identified by the presence of hematite-coated Aston Formation grains in Mesoproterozoic strata. Late hematite is identified by relationships indicating that it post-dated chemical compaction during maximum burial. Bleaching removed hematite cement locally and is associated with higher amounts of quartz cement and maximum burial. Bleaching implies the circulation of a reduced fluid, whereas oxidised fluid circulation is implied by the presence of hematite post-dating bleaching. The timing relationship of a reduced fluid mobilised during early to maximum burial followed by the circulation of oxidised fluids is similar to that recorded at the Storm Cu deposit. This suggests that the Proterozoic Aston Formation red sandstone may have been a source for metals for the Paleozoic Storm Cu deposit, and that several prolonged episodes of fluid circulation took place.

The metallogenetically important Cornwallis Zn district, in Canada's Arctic islands, includes the past-producing Polaris mine and numerous base-metal showings, including Storm copper. Storm is unusual because it is near the southern limit of the district, is Cu- versus Zn-dominated, is overlain and underlain by red sandstone, and is hosted by Silurian strata (rather than Ordovician strata, as at Polaris). Mineralisation styles are primarily carbonate replacement and breccia, and consist of geerite, covellite, bornite, and chalcopyrite, all of which are associated with calcite and dolomite gangue. Multiple in situ micro-analytical techniques (fluid inclusion microthermometry, evaporate mound SEM-EDS, LA ICP-MS, SIMS), plus conventional Cu isotopic analysis were integrated to characterise the nature of the mineralising fluids and events. Fluid inclusions yielded low-temperature (Th < 130 C), moderate- to low-salinity (17.0 to 0.4 wt% NaCI equiv.) fluids. Evaporate mound SEMEDS analysis, which quantified the solute chemistry, show a change from bimodal Na- and Na + K-dominated fluid mixture to a Na + K-dominated fluid. The 8150E120 signature of the mineralising fluid involved reservoirs reflecting involvement of meteoric ( < 0%) and rock-equilibrated (8%) fluids, respectively. The 634S values are nearly homogeneous for pre-ore and second generation sulphides at 0% and 10%, respectively, whereas the third generation (recrystallised) sulphides are more variable, with values from 8.8 to 23.4%. The majority of Cu sulphides have 665Cu values near 0%, but second-generation chalcopyrite shows elevated 865Cu values from +1.31% in the north to + 3.44% in the south, suggesting a probable southward fluid flow. Positive Eu PAASnormalised anomalies in early dolomite cements, which indicate basement involvement, are absent in succeeding cements, suggesting a change in fluid pathways and hence the mineralogical nature of the reservoir. Negative CesN anomalies in main-stage calcite cement indicate an oxidised fluid, but the lack of similar Ce anomalies in the dolomite cements indicates reduced fluids. These data suggest that Storm copper mineralisation is related to basement-equilibrated fluids mobilised during the Ellesmerian orogeny (Devonian), which acquired heat and leached Cu from underlying Proterozoic red sandstone (Aston Formation) and were then focussed up faults where Cu sulphides precipitated. Prolonged meteoric fluid movement from the north, with intermittent episodes of basin-equilibrated fluid influx, produced hypogene and supergene mineralisation. Fluid movement resumed in the Cenozoic, when high-latitude fluids altered Cu minerals to atacamite. Storm copper mineralisation shares characteristics with both red-bed and Irish-type Cu deposit sub-types, but may also highlight a relationship with carbonate-replacement Zn-Pb deposits. Timing of mineralisation is comparable to that of Zn ore precipitation at Polaris, suggesting that Storm may be an integral part of the Cornwallis district, in spite of its unusual composition.

Paleokarst is most commonly expressed as subtle stratigraphic surfaces rather than large void systems penetrating deeply into the paleo-subsurface. In contrast, a regional Precambrian-Cambrian unconformity on Victoria Island (NWT, Canada), is associated with exceptional exposure of large, intact Cambrian paleocaverns (100m diameter; tens of m high). The paleocaves are distributed along a paleo-horizontal plane, and an associated gryke network is present in the 30–60m of Neoproterozoic dolostone between cave rooves and the base of overlying Cambrian sandstone; both are filled by Cambrian sandstone. The formation and preservation of such karst features require aggressive dissolution along a stable paleo-water-table shortly before transgression and deposition of shallow-marine sand over the dolostone. During the transgression, the karst network acted as a conduit for flowing groundwater that was discharged through overlying, unconsolidated Cambrian shallow-marine sand, producing water-escape structures (sand volcanoes and their conduits). The conduits are preserved as cylindrical remnants of the sand volcanoes' feeder pipes. Sediment fluidisation was probably caused by variations in the hydraulic-head gradient in a meteoric lens near the Cambrian coastline under a tropical climate with abundant, probably seasonally variable rainfall that caused pulses in subsurface fluid flow. Spatial distribution of the paleocaves and sand volcanoes suggests their formation on the southeast side of a recently faulted horst of Proterozoic carbonate bedrock that formed a nearshore island during early Cambrian sea-level rise. Fluidisation structures such as those reported here have generally been difficult to interpret owing to a lack of data on the fluid hydraulics of the underlying aquifer. This is the first report linking the hydraulics of a well-characterised paleokarst to development of fluid-escape structures. Such structures are widely known from sandstones overlying the sub-Cambrian unconformity around the circumference of Laurentia.

Victoria Island, in Arctic Canada, is one of the largest islands in the world, but its geology has remained largely unmapped and unstudied owing to its remoteness. Base-metal and hydrocarbon showings have been reported from the island, but the origin and prospectivity of these showings remain enigmatic. Regionally extensive, void-filling Phanerozoic diagenetic phases (dolomite, calcite, quartz) are conspicuous in two of the most widespread carbonate units, the Neoproterozoic Wynniatt Formation and the Cambro–Ordovician Victoria Island formation, recording repeated post-depositional movement of fluid through the rocks. These phases were studied to (a) determine whether they could have been associated with movement of metalliferous or petroliferous fluids, (b) establish a diagenetic base-line for a very large and economically unexplored area, and (c) determine whether the fluid-flow events could have been related to known episodes of deformation and mineralisation elsewhere in the Canadian Arctic archipelago. Using an innovative protocol combining in situ SIMS analysis of O and S isotopes with LA-ICP-MS trace-element analysis, the geochemical conditions attending the diagenetic evolution of host dolostone and cement phases were determined. The Wynniatt Formation dolostone contains four Phanerozoic cements: saddle dolomite, brown dolomite, replacive calcite and late calcite. Average δ18O (SMOW) values of Wynniatt Formation saddle and brown dolomite, replacive calcite, and late calcite cements are 24.7‰, 7.7‰, and 6.9‰, respectively. The PAAS-normalised rare earth element patterns of the dolostone, dolomite, and replacive calcite are smooth and flat with slightly positive Ce and Y anomalies and MREE-enrichment; late calcite cement, in contrast, has negative Ce and positive Y anomalies. Recrystallisation of the host dolostone by a reduced, saddle-dolomite-precipitating fluid in a fluid-dominated system altered the isotopic and REE pattern of the dolostone to saddle-dolomite values. This fluid had interacted with shale at depth and then mixed with a relatively high-salinity fluid. Brown dolomite precipitated from this fluid after a decrease in salinity, and oxygenated meteoric water later infiltrated the system and precipitated the calcite cements.The Victoria Island formation dolostone contains two cements: quartz and dolomite. Host dolostone, quartz, and dolomite have average δ18O (SMOW) values of 31.7‰, 18.7‰, and 18.6‰, respectively, whereas δ34S (V-CDT) for framboidal pyrite in the quartz cement averages −7.5‰. The host dolostone has flat PAAS-normalised REE patterns with a positive Eu anomaly, no Ce anomaly, and a zig-zag HREE pattern, whereas the dolomite cements have two REE patterns: one similar to the dolostone (flat) and the other with LREE-enrichment, and negative La and Eu anomalies. These data suggest that a reduced, hydrothermal fluid altered and partially silicified the host dolostone. Quartz precipitated from a seawater-sourced fluid that had incorporated metals at depth and mixed with bacterially reduced sulphur at the site of precipitation. The dolomite cement records the change from a rock-dominant system to a fluid-dominant system. This fluid was sourced from seawater and interacted with REE-phosphate minerals.The results suggest that precipitation of the diagenetic cements took place before peak burial associated with the Ellesmerian Orogeny (late Devonian–early Carboniferous). The most probable cause of fluid migration, therefore, is the Ellesmerian Orogeny for the majority of the diagenetic phases. High-latitude meteoric fluid then infiltrated the system at some time after the Ellesmerian Orogeny. Similar ages, temperatures, compositions, and precipitation mechanisms as those associated with the Cornwallis zinc district (Polaris mine), highlight a possible relation to known base-metal mineralising fluids.The results of this study provide much needed baseline knowledge of the post-depositional history of Victoria Island. It also illustrates that a “less-is-more” approach, using detailed micro-analytical methods on carefully selected and well-constrained samples, allows one to decipher a complex diagenetic history involving the mixing of fluids from different reservoirs and frequent changes in redox state, both of which may be overlooked using conventional macro-scale approaches.

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 (T-h) for FIAs (n=3) of 108 degrees C (saddle) and 101 and 116 degrees C, but metastability precluded determining salinities; most calcite-hosted fluid inclusions are too small and/or necked to obtain T-h 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 T-h value of 126 degrees C, and salinity of 23.2 wt. % NaCl equiv., whereas FIAs (n=3) in dolomite have average T-h values of 109, 116 and 124 degrees 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.