NWT, Baffin Is., Canada

Main commodities: Zn Ag Pb
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The Nanisivik zinc, lead, silver deposit is located in the Borden basin, on the Borden Peninsula of northern Baffin Island, north-eastern Canada, approximately 750 km north of the Arctic Circle. The mine began operation in 1976 and closed in the northern autumn of 2002 due to depleted economic reserves at prevailing prices.

The Nanisivik deposit is hosted by Mesoproterozoic sedimentary rocks of the Bylot Supergroup, unconformably overlying an Archean to Paleoproterozoic granite and gneiss basement complex of the Mary River Group . Rifting of the basement during the Late Mesoproterozoic created a series of basins in the eastern Arctic referred to as the Borden, Fury and Hecla, Ashton and Hunting, and Thule basins. These basins are interpreted to represent either separate contemporaneous aulacogens or erosional remnants of a single larger basin. The Borden basin is the largest of these four remnant rift basins and contains the Bylot Supergroup which has been divided into:
  i). a lower volcanic and siliciclastic sedimentary sequence, the Eqalulik Group;
  ii). the carbonate sedimentary rock-dominated Uluksan Group, and
  iii). the upper siliciclastic and carbonate sedimentary rock-dominated Nunatsiaq Group
(Sherlocks, et al., 2004).

In the Nanisivik area, two siliciclastic sedimentary rock formations (the Adams Sound and Arctic Bay formations of the Eqalulik Group) are overlain by two carbonate sedimentary rock formations (the Society Cliffs and Victor Bay formations, of the Uluksan Group) as well as a mixed carbonate and terrigenous clastic sedimentary rock formation (the Strathcona Sound Formation of the Nunatsiaq Group). The Bylot Supergroup is cut by dolerite dikes of the Franklin igneous event, an extensive dike swarm found throughout northern Baffin Island and the mainland dated at around 720 Ma. Palaeozoic rocks of the Arctic platform overlie rocks of the Bylot Supergroup, including the Cambrian to Ordovician Admiralty Group and the Ordovician to Silurian Brodeur Group. In the Nanisivik mine area only the lowermost parts of the Admiralty Group are preserved (Sherlocks, et al., 2004).

Deposition of the Bylot Supergroup commenced with regional extension, thermal doming and crustal thinning accompanied by mafic volcanism and clastic sedimentation. A series of northwest-trending normal faults, some of which are synsedimentary, divide the Nanisivik area into a series of horsts and grabens. These faults have remained intermittently active, suggesting extension has continued, at least locally, to the present (Sherlocks, et al., 2004).

The sulphide bodies at Nanisivik contain around 100 Mt of massive sulphide, mostly pyrite, with low concentrations of base metals. About 18 Mt of the sulphides contained sufficient base metals to be ranked as ore. All of the known sulphide bodies are at the apex of broad open antiforms and hosted by petroliferous dolostones from the upper part of the middle Society Cliffs Formation and in the upper Society Cliffs Formation. The bulk of the zinc-rich massive sulphides is in a horst of Society Cliff Formation, bounded to the north by the Shale Hill fault and to the south by the Keystone fault, both of which have downdropped the Victor Bay Formation (Sherlocks, et al., 2004).

The main Nanisivik deposit comprises a main sulphide lens underlain by a stockwork system, to form a mushroom-like mass. The main sulphide body is elongated and sinuous, with dimension of around 3000 x up to 200 x 20 to 30 m. The mineralogy of this lens is dominated by pyrite, sphalerite, galena, sparry dolomite, calcite and pyrite pseudomorphous after marcasite. Its internal structure is complex, and includes zones that are massive, mineralogically banded or brecciated. Wing-shaped inclusions of dolostone commonly extend many metres into the massive sulfide lens. A zone of stockwork-like veins of pyrite, sphalerite, galena and carbonate underlie the main sulfide lens, commonly centred above east-west trending normal faults, with veins that are irregular (Sherlocks, et al., 2004).

The upper contact of the main sulphide lens with dolostones of the Society Cliffs Formation is almost horizontal, with a vertical variation of only about 3 m over the entire 3000 m strike length of the lens. In contrast, the host dolostones dip about 20° to the north. Within the upper-middle Society Cliffs Formation, the massive sulphides cross-cut stratigraphy, suggesting they were emplaced postfolding and tilting of the host strata (Sherlocks, et al., 2004).

East-trending normal faults are associated with all of the known Nanisivik mineralisation. The western part of the main lens is centered over the Keystone fault zone, which displaces stratigraphy by approximately 150 m. The main splay of the Keystone fault does not displace the upper and lower contacts between the sulphides and host dolostone but displaces stratigraphy by more than 100 m. The minor splays of the fault displace stratigraphy by from 10 to 15 m and juxtapose petroliferous dolostone of the Society Cliff Formation against shales of the Victor Bay Formation. The sulphides show an apparent displacement across these secondary splays, probably resulting from the juxtaposition of different lithologies. As the shale of the Victor Bay Formation is not a favourable host rock, the sulphides replaced the dolostone on the footwall of the fault but did not replace the shale on the hanging wall, resulting in an apparent downdropping of the sulphide body. These minor splays do not displace sulphide accumulation in the lower stockwork zones (Sherlocks, et al., 2004).

Total production amounted to 17.9 Mt @ 9% Zn, 0.72% Pb, 35 g/t Ag (Sherlocks, et al., 2004).

The most recent source geological information used to prepare this summary was dated: 1996.    
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.

  References & Additional Information
   Selected References:
Arne D C, Curtis L W, Kissin S A  1991 - Internal zonation in a carbonate-hosted Zn-Pb-Ag deposit. Nanisivik, Baffin Island, Canada: in    Econ. Geol.   v86 pp 699-717
Ghazban F, Schwarcz H P, Ford D C  1990 - Carbon and Sulfur isotope evidence for in situ reduction of Sulfate, Nanisivik Lead-Zinc deposits, Northwest Territories, Baffin Island, Canada: in    Econ. Geol.   v85 pp 360-375
McNaughton K, Smith T E  1986 - A fluid inclusion study of Sphalerite and Dolomite from the Nanisivik Lead-Zinc deposit, Baffin Island, Northwest Territories, Canada: in    Econ. Geol.   V81 pp 713-720
Olson R A  1984 - Genesis of paleokarst and strata-bound Zinc-Lead Sulphide deposits in a Proterozoic Dolostone, northern Baffin Island, Canada: in    Econ. Geol.   v79 pp 1056-1103
Sherlock R L, Lee J K W, Cousens B L,  2004 - Geological and Geochronological Constraints on the Timing of Mineralization at the Nanisivik Zinc-Lead Mississippi Valley-Type Deposit, Northern Baffin Island, Nanavut, Canada: in    Econ. Geol.   v99 pp 279-293
Symons D T A, Symons T B and Sangster D F  2000 - Paleomagnetism of the Society Cliffs dolostone and the age of the Nanisivik zinc deposits, Baffin Island, Canada: in    Mineralium Deposita   v35 pp 672-682
Turner E C,  2011 - Structural and Stratigraphic Controls on Carbonate-Hosted Base Metal Mineralization in the Mesoproterozoic Borden Basin (Nanisivik District), Nunavut : in    Econ. Geol.   v.106 pp. 1197-1223

Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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