The Ag–Zn–Pb Blende deposit is located in the Wernecke Mountains, Yukon and is hosted by the middle Proterozoic Gillespie Lake Group dolomitic siltstones. The sulphide mineralization is localized within the axial planar cleavage of a kilometre-scale anticline and is dominated by galena- and sphalerite-cemented mosaic, rubble and crackle breccias with minor pyrite, galena, sphalerite and dolomite veins. 206Pb/204Pb values from galena range from 16.355 to 16.600, 207Pb/204Pb from 15.430 to 15.461, and 208Pb/204Pb from 36.016 to 36.283, respectively, and yield model ages between 1,490 and 1,430 Ma. A hydrothermal alteration zone, which is younger than the mineralization, has a poorly constrained U–Pb monazite age of 1,307 ± 180 Ma, which suggests that the Blende deposit is Proterozoic in age. Dolomites associated with the main- and late-stage mineralization have δ13C values that range from −1.8 to 0.9 ‰ and δ18O values of 15.7 to 21.9 ‰. The total range of δ34S values from pyrite, galena and sphalerite is 9.4 to 58.1 ‰, indicating that the sulphur in the deposit was derived from reduction of seawater sulphate in a closed system. Strontium isotopes suggest there were three fluids involved in the Blende mineralizing system: Fluid 1 was derived from seawater and formed carbonate and quartz veins pre-mineralization; it has an 87Sr/86Sr ratio of 0.70948. Fluid 2 has a high 87Sr/86Sr ratio of 0.73866, and fluid 3 has a Sr isotopic ratio of 0.71602. Fluids 1 and 3 have similar isotopic compositions but different total Sr ion signals (a function of concentration). This suggests that fluids 1 and 3 may have ultimately been derived from Proterozoic seawater but have undergone different amounts of water–rock interaction. The isotopic and geochemical data suggest the mineralization formed when a H2S-rich fluid derived from seawater (fluid 3) mixed with a metal-bearing fluid (fluid 2) in the high permeability zones of the axial planar cleavage. The Blende deposit is an unusual carbonate-hosted massive sulphide deposit which has features of both Irish-type and clastic-dominated Zn–Pb deposits. The deposit formed in response to a change in tectonism from a compressional regime to extension and rifting.

The Polaris deposit, located on Little Cornwallis Island in the Canadian Arctic, was a Mississippi Valley-type Zn-Pb deposit hosted by brecciated carbonate rocks of the Upper Ordovician Thumb Mountain Formation. Mapping indicates that strike-slip faults on the east side of the Polaris deposit were active during the last stage of the Late Devonian Ellesmerian Orogeny. Polaris is on a jog in the north-oriented, Early Devonian Boothia fault system and was the site of localized extension during south-directed Late Devonian Ellesmerian compression. This structural setting elsewhere in the district may be prospective for Zn-Pb mineralisation. Ore fluids rising in the Late Devonian interacted with the host rock causing dissolution, brecciation and collapse. Carbonate beds are thinned, indicating widespread removal of carbonate material. Five breccia types (crackle, pseudo, cobble, mega and collapse) are present in the vicinity of the deposit. Crackle breccia is preserved around the periphery of the deposit and is indicative of structural dilation or the early stages of mineralisation. Dolomite and pseudobreccias are also preserved around, and extend beyond, the periphery of the deposit. These are considered an early stage of alteration directly related to the mineralising fluids and could act as a vector to the centre of the mineralising system where collapse, mega and cobble breccias occur intimately with massive mineralisation. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.

The Polaris Zn–Pb Mine in Nunavut, Canada was one of the largest single Mississippi Valley-type ore deposits in the world. Over 20Mt of sphalerite (ZnS) and galena (PbS) was hosted in brecciated carbonate rocks of the Upper Ordovician Thumb Mountain Formation. Three paragenetic stages are recognized: 1) early dolomite and marcasite; 2) main stage sulphide and dolomite; and 3) late calcite, marcasite and barite. Ore mineral textures range from discrete crystals to massive crystal aggregates and formed as replacements of the dolomite host rock or as fracture- and open space-filling mineralization. Zinc concentration is highest in the core of the deposit where botryoidal aggregates predominate, whereas iron is concentrated in the upper part. Observations of temperature and in situ sulphur isotope fractionation support a genetic model for the Polaris deposit in which thermochemical sulphate reduction occurred within the deposit, with locally generated hydrocarbons acting as a reducing agent. Information from the Polaris Mine indicates that hydrothermal alteration including dolomite, marcasite and barite; complex paragenesis with numerous ore textures; Th values >100°C associated with organic-rich strata; and a geochemical signature that includes in situ sulphur fractionation are effective predictors for determining which showings are prospective in the vast central Arctic Pb–Zn district.

The carbonate strata of the Mackenzie Mountains of Northwestern Canada are host to a large number of mineralized base-metal occurrences, including the Neoproterozoic-hosted Gayna River deposit. Here, we present S and Pb isotopic data on sulphides and sulphates from Gayna River and 7 other smaller showings hosted by Lower Cambrian and Silurian-Ordovican units. The S isotope data suggest that the source of S in all the deposits is variable and may be derived locally. The Pb isotope data have consistent values for most of the showings suggesting a single Pb source for the mineralization. These data allow a model of a regional hydrothermal fluid flow event(s) in the Mackenzie Mountains in the Devonian-Carboniferous that deposited base metals in units of varying ages.

The Mackenzie Mountains have more than 100 Zn-Pb showings. The objectives of the 2005 fieldwork were 1) to assess showings from a wide geographic area and stratigraphic range, 2) verify the assessment files, and 3) rank the showings on exploration potential. TIC, ART-EKWI, BEAR, ICE, KEG, RAIN, TAP, AB, and GAYNA were visited. Most of the showings are hosted in fractures with minor brecciation and very rarely, carbonate replacement. The main economic minerals are sphalerite and galena, but copper sulphide minerals are commonly present. Gangue minerals include dolomite, calcite, quartz, barite, and fluorite. The best targets for further exploration are considered to be showings hosted in strata that were limestone (at the time of mineralization) rather than dolostone; that exhibit strong chemical interaction between the host rock and fluid resulting in carbonate dissolution or replacement; and that have multiple generations of sphalerite and galena. BEAR, GAYNA, AB, and TIC are considered the most attractive exploration targets.