Apatite fission track and ⁴⁰Ar/³⁹Ar age spectrum data from sandstone drill-core minerals taken from depths of 2–5 km in nine wells from the Scotian Basin are presented and interpreted in terms of the thermal history of the basin and the provenance of its sediments. The focus of the study is a comparison of the data from these thermochronometers with each other and with previously published vitrinite reflectance and aromatization–isomerization (A–I) reactions in biomarker compounds from the same or nearby wells.Apatite fission track ages are generally in agreement with expectations in that they trend to zero at a depth of ~4 km (corrected bottom-hole temperature ~120 °C). Shallower (lower present temperature) samples are partially annealed; the degree of partial annealing correlates closely with the degree of A–I reactions. Both thermal indicators are activated over the temperature range 60–120 °C.Samples from two wells, Mic Mac J-77 and Erie D-26, are anomalous. They are more annealed than present formation temperatures would predict, an anomaly that is also indicated by the A–I data. These samples are interpreted as having experienced higher than present temperatures subsequent to deposition, possibly resulting from the passage of hot fluids related to localized volcanism or the sudden venting of an overpressured reservoir.K-feldspars record minor (< 20%) argon loss as a result of burial heating in the basin only at the greatest depths of the sampled range (> 4.3 km). This result is in agreement with the thermal models of the Scotian Basin and extrapolation of the A–I and fission track data to greater depths. The inferred argon loss implies an activation energy of 40 ± 4 kcal/mol for the smallest diffusion domains.The argon age spectra for samples that have not lost argon during residence in the basin provide evidence on the provenance of the sediments. K-feldspars from the Early Cretaceous Missisauga Formation have spectra that are similar to those obtained from K-feldspars from the Grenville Province of the Canadian Shield, whereas muscovites from the same formation give Cambrian to Carboniferous argon ages (mean 387 Ma), an indication of contributions from other source rocks. Corresponding data from the Jurassic Mohican Formation are similar to those reported for plutons from the southern Nova Scotia mainland (ca. 250–350 Ma argon ages). By implication, the Mohican Formation, which is the earliest postrift deposit, was derived from local sources inferred to be adjacent flank uplifts, whereas the Missisauga Formation was derived in part either directly or indirectly from the Grenvillian-aged interior of eastern Canada.

It is surprising to encounter active saline spring activity at a constant 6°C temperature year-round not far away from the North Pole, at latitude 79°24′N, where the permafrost is ca. 600 m thick and average annual temperature is -15°C. These perennial springs in Expedition Fiord, Queen Elizabeth Islands, Canadian Arctic Archipelago, had previously been explained as a recent, periglacial process. However, the discovery near White Glacier (79°26.66′N; 90°42.20′W; 350 m.a.s.l.) of a network of veins of hydrothermal origin with a similar mineralogy to travertine precipitates formed by the springs suggests that their fluids have much deeper circulation and are related to evaporite structures (salt diapirs) that underlie the area. The relatively high minimum trapping temperature of the fluid inclusions (avg. ~200 ± 45°C, 1σ) in carbonate and quartz in the vein array, and in quartz veins west of the site, explains a local thermal anomaly detected through low-temperature thermochronology. This paper reviews and updates descriptive features of the perennial springs in Expedition Fiord and compares their mineralogy, geochemistry, and geology to the vein array by White Glacier, which is interpreted as a hydrothermal predecessor of the springs. The perennial springs in Axel Heiberg Island are known for half a century and have been extensively described in the literature. Discharging spring waters are hypersaline (1-4 molal NaCl; ~5 to 19 wt% NaCl) and precipitate Fe-sulfides, sulfates, carbonates, and halides with acicular and banded textures representing discharge pulsations. At several sites, waters and sediments by spring outlets host microbial communities that are supported by carbon- and energy-rich reduced substrates including sulfur and methane. They have been studied as possible analogs for life-supporting environments in Mars. The vein array at White Glacier consists of steep to subhorizontal veins, mineralized fractures, and breccias within a gossan area of ca. 350 × 50 m. The host rock is altered diabase and a chaotic matrix-supported breccia composed of limestone, sandstone, and anhydrite-gypsum. Mineralization consists of brown calcite (pseudomorph after aragonite) in radial aggregates as linings of fractures and cavities, with transparent, sparry calcite and quartz at the centre of larger cavities. Abundant sulfides pyrite and marcasite and minor chalcopyrite, sphalerite, and galena occur in masses and veins, much like in base metal deposits known as Mississippi Valley Type; their weathering is responsible for brown Fe oxides forming a gossan. Epidote and chlorite rim veins where the host rock is Fe- and Mg-rich diabase. The banded carbonate textures with organic matter and sulfides are reminiscent of textures observed in mineral precipitates forming in the active springs at Colour Peak Diapir. Very small fluid inclusions (5-10 μm) in two generations of vein calcite (hexagonal, early brown calcite we denominate “cal1” lining vein walls; white-orange sparry calcite “cal2” infilling veins) have bulk salinities that transition between an early, high-salinity end-member brine (up to ~20 wt% NaCl equivalent) to a later, low-salinity end-member fluid (nearly pure water) and show large fluctuations in salinity with time. Inclusions that occupy secondary planes and also growth zones in the later calcite infilling (deemed primary) have Th ranging from 100°C to 300°C (n=120, average~200°C; independent of salinity), 2 orders of magnitude higher than average discharging water temperatures of 6°C at Colour Peak Diapir. Carbon isotope composition (δ¹³C_VPDB) of the White Glacier vein array carbonates ranges from approximately -20 to -30‰, like carbonates formed by the degradation of petroleum, whereas carbonates at Colour Peak Diapir springs have a value of -10‰. Oxygen isotope composition (δ¹⁸O_VSMOW) of vein carbonates ranges from -0.3‰ to +3.5‰, compatible with a coeval fluid at 250°C with a composition from -3.5‰ to -7.0‰. These data are consistent with carbonates having precipitated from mixtures of heated formational waters and high-latitude meteoric waters. In contrast, the δ¹⁸O_VSMOW value for carbonates at Colour Peak Diapir springs is +10‰, derived from high-latitude meteoric waters at 6°C. The sulfur isotope (δ³⁴S_VCDT) composition of Fe-sulfides at the perennial springs is +19.2‰, similar to the δ³⁴S_VCDT of Carboniferous-age sulfate of the diapirs and consistent with low-temperature microbial reduction of finite (closed-system) sulfate. The δ³⁴S_VCDT values of Fe-sulfides in the vein array range from -2.7‰ to +16.4‰, possibly reflecting higher formation temperatures involving reduction of sulfate by organics. We suggest that the similar setting, mineralogical compositions, and textures between the hydrothermal vein array and the active Colour Peak Diapir springs imply a kinship. We suggest that overpressured basinal fluids expelled from the sedimentary package and deforming salt bodies at depth during regional compressional tectonic deformation ca. 50 million years ago (Eocene) during what is known as the Eurekan Orogeny created (by hydrofracturing) the vein array at White Glacier (and probably other similar ones), and the network of conduits created continued to be a pathway around salt bodies for deeply circulating fluids to this day. Fluid inclusion data suggest that the ancient conduit system was at one point too hot to support life but may have been since colonized by microorganisms as the system cooled. Thermochronology data suggest that the hydrologic system cooled to temperatures possibly sustaining life about 10 million years ago, making it since then a viable analogue environment for the establishment of microbial life in similar situations on other planets.

The supergiant Chuquicamata porphyry Cu-Mo deposit in northern Chile is truncated on its west side by a N-S-trending regional fault (the West fault), juxtaposing its ore to a relatively barren granodiorite (Fortuna Igneous Complex). There has been much speculation about the fate of, and extensive exploration for, the “missing half” of the deposit. It has been proposed that the west side of the fault hides the ore at depth, or that it was uplifted and the ore eroded; however, regional geologic mapping suggests that the West fault had a postore left-lateral strike-slip displacement of ca. 35 km. Accordingly, exploration, so far unsuccessful, has been focused in an area 35 km south near the Loa River and the city of Calama. In 1989, the Mina Ministro Hales (MMH) deposit was unexpectedly discovered west of the fault, under thick gravels, only 7 km south of the main mine. A previous study at MMH had suggested that mineralization was as old as 39 Ma, hence its ores were correlated with deposits of that age near Calama. Our recent U-Pb and Re-Os dating indicates that MMH mineralization was formed between 35 and 31 Ma, thus concurrently with Chuqui. The geochemistry of host Triassic and Eocene porphyry intrusions, ore mineralogy, and common Pb isotope ratios of hypogene sulfides at MMH and Chuqui proper are indistinguishable. Fluid inclusion data for paragenetically early porphyry assemblages at MMH closely mimic Th-salinity data from earlier studies at Chuqui, showing little or no evidence of boiling but indicating widely fluctuating confining pressures, compatible with hydraulic fracturing and fault movement during and after mineralization at a minimum initial lithostatic constraint of 5- to 8-km depth. We propose that MMH is a sheared-off portion of Chuqui, wedged in a fault cymoid loop and spared the full 35-km displacement of the West fault.