FLUID INCLUSION CHEMISTRY OF MVT DEPOSITS IN THE CANADIAN ARCTIC

Sediment-hosted mineralization is common in the central part of the Canadian Arctic Archipelago. In the Cornwallis Pb-Zn-(Cu) District, Late Devonian-aged Mississippi Valley-Type mineralization is hosted by Ordovician to Devonian carbonates. Mineralization is associated with thrust faults that formed during the Late Silurian Caledonian Orogen and which were reactived during the Late Devonian Ellesmerian Orogeny (e.g. the Polaris deposit). Pb-Zn-(Ag-Cd) showings have recently been discovered in coeval basinward strata on Ellesmere Island, however, this mineralization is poorly understood and unexploited.

In the Cornwallis District, sphalerite and galena replace carbonate or fill cavities. Sparry dolomite is a ubiquitous gangue phase. On Devon and Somerset Islands, Cu-mineralization is additionally present and has locally undergone supergene enrichment. Pb-Zn-(Ag-Cd) mineralization on Ellesmere Island consists of sphalerite and galena with the addition of arsenides and sulphosalts, with sparry dolomite and quartz as the dominant gangue. Fluid inclusion microthermometric data are reasonably consistent throughout the Cornwallis District. The bulk of the homogenization temperatures range from 90 to 120°C, and were derived from high salinity NaCl-CaCl2 fluids (ca. 25-35 wt.% NaCl equiv). Homogenization temperatures from mineralized zones on Ellesmere Island are higher (140-270°C) and were derived from fluids of varied salinity (8-36 wt.% NaCl equiv.) NaCl +/- CaCl2 fluids.

Previous research has concluded that Cornwallis MVT showings formed at the loci of mixing between warmer, metal-rich basinal brine and cooler, reduced, sulphur-rich formation water. It has further been hypothesized that the basinal brines became saline through the evaporation of seawater before being channeled into the mixing zones by sub-vertical faults. Mineralizing fluids on Ellesmere Island may be related to igneous intrusions.

We report the results of a bulk crush-leach analysis of the chemistry of primary fluid inclusions in sphalerite, dolomite, and calcite from showings in the Cornwallis District and from Ellesmere Island. These data will constrain models of fluid genesis and evolution, and compare the fluid chemistry of different deposits.