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Borden Basin Project: 2006 Field Season
Project Description
Collaborative Project led by Dr E.C. Turner, Department of Earth Sciences, Laurentian University, Sudbury, ON.
Carbonate strata of the Mesoproterozoic Uluksan Group, Bylot Supergroup, Borden Basin (northern Baffin Island, NU), host numerous base-metal showings, including the Zn-Pb-Ag deposit that was mined at Nanisivik (1976 - 2002). The Borden Basin is a Mesoproterozoic aulacogen comprising three northwest-trending grabens that developed in Archean basement rocks. Base-metal showings are concentrated in the Milne Inlet Graben, and are hosted by the Society Cliffs Formation, which is expressed as a peritidal carbonate platform in the eastern part of the Milne Inlet Graben (MIG), and as a laterally equivalent basinal laminite with local deep-water carbonate mounds in the western part. With the exception of one poorly understood and subtle east-directed compressional event that was contemporaneous with deposition of middle to upper Bylot Supergroup strata, and later emplacement of Neoproterozoic Franklin dykes, the rocks have been subjected to no significant tectonic effects. The dykes fill some of the major northwest-trending faults that accommodated basin rifting. The nature and age of the mineralising event at Nanisivik and at showings throughout the basin are controversial. A variety of dating methods have yielded mineralisation ages for the Nanisivik ore-body that range from Mesoproterozoic (ca. 1.2 Ga) to Paleozoic (461 Ma).
Ongoing work indicates that mineralisation is controlled by three structural phenomena. (1) Antiform/gas-cap type replacement-style mineralisation is known only from Nanisivik and two major showings in the western part of the basin. It is localised by subtle folding in the basinal host rocks, which was a function of either the early compressional event, or of compactional folding around the tops of giant deep-water mounds. Such folding and mineralisation are known only from the westernmost part of the MIG. This type of mineralisation is Zn- and Pb-rich. (2) Fracture-controlled mineralisation in the vicinity of major, northwest-trending intra-graben faults is dominant in the central MIG, either in uppermost Society Cliffs Basinal laminites (presumably capped by the shale aquiclude of the overlying basal Victor Bay Formation), or in the lowermost Society Cliffs Formation, just above a sharp contact with underlying shale of the Arctic Bay Formation. Showings here are dominated by galena, with variable but lesser proportions of Cu, Ba and Zn minerals. (3) The graben-bounding White Bay Fault zone on the north side of the MIG juxtaposes basement gneiss with platformal carbonate, and was intermittently active during deposition of the Bylot Supergroup. In the eastern MIG, mineralisation is locally present up to 1 km away from the fault, in replacement-style showings that appear to be partly facies-controlled. These showings are sphalerite-dominated, with lesser volumes of galena.
Field work in 2006 focused on one showing documented in assessment reports and district synopses, two showings not documented in any material submitted for assessment, and one locality that is critical to understanding the four-dimensional facies evolution of the graben and its base metal distribution. One new Cu showing was discovered.
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