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The Major Nickel Deposits of the World
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MODULE 2 - THE AMERICAS
PART B - Canadian Sulphides,
Sun 11 to Sat 17 June, 2000
This PART commenced in Sudbury, Ontario, Canada on the evening of Sunday 11 June, 2000, and included the following seminar, mine visits and major presentations:
This tour was divided into three Modules and five constituent Parts. The other parts were:
- Sudbury Seminar
- Sudbury (2 mines) - Visit Footwall and Contact orebodies (Proterozoic intrusive), and core display of Offset deposit
- Raglan - Well preserved Proterozoic komatiite flow deposit
- Voisey's Bay - Presentation by Peter Lightfoot, and core inspection at Sudbury
- Thompson - Presentation at Sudbury
Yilgarn Sulphides & Laterites, SW Pacific Laterites, Caribbean Laterites & Eurasian Sulphides.
MODULE 2 - THE AMERICAS, PART B - Canadian Sulphides
Sudbury Seminar - Ontario Canada
Click on image for details.
The workshop involved a full day of presentations by local and internationally known experts on:
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- Geologic Setting of Nickel Deposits in the Canadian Shield - Dr Phil Thurston, OGS
- Overview of Magmatic Sulphide Deposits - Dr Tony Naldrett, University of Toronto.
- Sudbury Ni-Cu-PGE Deposits - Dr Tony Naldrett , University of Toronto.
- Sudbury Ni-Cu-PGE Metal Fractionation - Dr M Constantin, MERC.
- What is and is not special about Sudbury - Dr Paul Golightly, INCO & MERC.
- Voiseys Bay Ni-Co Deposit - Dr Peter Lightfoot, INCO.
- Raglan Ni-Cu-PGE Deposits - Prof. Mike Lesher, MERC.
- Thompson Ni-Cu Deposits - Dr O M Burnham, MERC.
Sudbury - Ontario Canada
The Sudbury sulphide nickel deposits are located within the basal layer of the roughly oval shaped 65x25 km, 1.85 Ga Sudbury Igneous Complex (SIC). This complex cuts both Archaean rocks on the southern margin of the Superior Province, and the Lower Proterozoic of the Huronian Supergroup. It is also less than 10 km to the north of the 1.2 to 1.0 Ga Grenville Front, and lies on a regional, 350 km long zone of linear gravity and magnetic anomalies. It is overlain by the Lower Proterozoic Whitewater Group, an older sequence consisting of an upward progression of conformable heterolithic breccias, a carbonaceous and pyritic argillite and a proximal turbidite unit which occupies a basin shaped structure and is only found with the oval shaped outcrop zone of the SIC. The complex dips inward throughout at around 30 degrees and is composed of a sequence of norite, gabbros and granophyres. It comprises two main zones, a lower 500 to 2500m thick Lower Zone of norite and gabbro-norite, grading upwards into quartz- and oxide rich gabbro. The Upper Zone is 1 to 2500m thick and is mainly a granophyre, with an abruptly transitional margin with the underlying quartz-rich gabbro. The granophyre intrudes the basal Whitewater Group. There is no obvious small scale layering within the complex. A third discontinuous layer is found at the base of the SIC, particularly in embayments into the footwall rocks. This is called the "Sublayer" and contains all of the major Ni-Cu sulphide deposits. The contact with the base of the Lower zone varies from sharp to gradational. It has two facies, namely: 1). the Contact Sublayer that is usually <200m thick and composed of discontinuous lenses of gabbro-norite along the basal contact of the SIC, and 2). the Offset Sublayer that constitutes apophyses or dykes of predominantly quartz-diorite that project outwards into the intruded footwall rocks. A contact metamorphic halo around 1200 m thick occurs in the footwall rocks which have been brecciated for up to 80 km from the complex - the Sudbury Breccia. The composition of the SIC is strongly influenced by the crustal rocks, with a differing succession through the complex to the north where it cuts the Archaean of the Superior Province - the North Range, and the southern side - the South Range where it intrudes the Lower Proterozoic of the Huronian Supergroup. Differences are also noted in the ores in the two ranges.
There are three main ore types, namely: 1). Contact type massive sulphides in the noritic Sublayer, with a lower layer of massive sulphide enclosing angular wall rock fragments and stringers extending into the footwall, while upwards the massive sulphides grade into a sulphide-matrix breccia and finally to disseminated sulphides; 2). stockworks of more Cu rich ore in the Sudbury Breccia of the footwall, comprising massive stringers and lenses oriented parallel to the dip of the SIC; 3). deposits associated with Offset Dykes of quartz-diorite that are sub-radial to sub-parallel to the margins of the SIC, with sulphides present as either lenticular zones of sulphide blebs, or as sheaths of sulphide bleb bearing quartz-diorite or Sudbury Breccia on the margin of the dykes. The main ores are composed of pyrrhotite, pentlandite, chalcopyrite, pyrite and magnetite. Bornite is locally present in higher grade zones, while higher arsenic as arsenides characterises the South Range. The copper rich veins deep in the footwall are dominated by chalcopyrite and cubanite with lesser pentlandite, magnetite and pyrrhotite. The Sudbury Complex contained around 1650 mt @ 1.2% Ni, 1.03% Cu.
Two deposits were visited, the Falconbridge Craig (Onaping) Mine a Contact deposit, the Falconbridge Fraser Copper Mine, a Footwall deposit. A briefing and core display was also provided by INCO on the Totten Offset deposit. Field traverses were conducted to illustrate the key features of both the North and South Range geology and deposits.
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Raglan - Quebec Canada
The Raglan Project deposits of Falconbridge Limited are located in an east west trending belt of Lower to Middle Proterozoic rocks, the Cape Smith Belt of Northern Quebec. This belt represents a klippen of Hudsonian fold and thrust belt rocks that has been thrust over the northern extremities of the Superior Province. As such the Raglan deposits are now located near the margin of the exposed Superior Province, as are both Sudbury and Thompson, and in similar aged rocks to those at Thompson. The Cape Smith Belt is a recumbently folded sequence which is composed from south to north, and up section, of the Povungnituk Group of shelf sediments and dominantly continental tholeiitic basalts, the Chukotat Group of komatiitic and tholeiitic lavas and the Watts-Spartan Groups of mafic volcanics and intrusive rocks of unknown affinity.
The Raglan deposits are all stratigraphically located at the same position at the transition between the Povungnituk and the Chukotat Groups, and within a series of 1920 Ma dunitic peridotite lenses interpreted to represent original extrusive komatiitic olivine orthocumulates. The current reserve (1998) amounts to 22 mt @ 3.06% Ni, 0.87% Cu in a series of deposits in 6 separate localities, distributed over a strike length of 65 km. These are from east to west Donaldson, Boundary, Katiniq (Katinniq), Zones 2 and 3, and Cross Lake. Mineralisation is typically found in lenses averaging 200 x 200 x 15 to 30 m in dimensions, each containing an averages of 400 000 t, but varying from 18 000 t to 1.2 mt. Each occurs as channels or pods in topographic lows at or near the base of the composite sequence of peridotitic komatiitic basalts. The footwall to the peridotites varies from gabbro to sediments and is typically deeply embayed or channelled in areas where mineralisation is known. The lateral boundaries of the embayments, which are suspected to represent thermal erosion channels, define the limits to mineralisation.
The peridotites in the region contain around 1% fine disseminated sulphides, mainly pyrrhotite and pentlandite. In the orebodies, nickel is found in disseminated to heavily disseminated pyrrhotite with up to 10% medium to coarse pentlandite, to net textured to massive sulphides composed of pyrrhotite, pentlandite, chalcopyrite, minor pyrite and traces of sphalerite and magnetite in a peridotitic gangue. Where present, the massive sulphides form the lower one third of the mineralised column. Copper occurs as disseminated chalcopyrite in veinlets and stringers. PGE's generally average a combined 3 g/t. Remobilised ore is very rich in Cu and PGEs and is locally present in the footwall rocks to the normal channel ore. The Katiniq ultramafic lens, which hosts the main orebodies, is a roughly concordant lenticular body of olivine mesocumulate to orthocumulate that is up to 150 m thick and dips at 30 to 60 degrees north. It cuts across section, being overlain and underlain by high Mg basalts to the west, while the footwall is gabbro near the centre and hornfelsed slaty sediments are in both the footwall and hangingwall to the east. Although the base is very irregular the top is planar and locally exhibits spinifex textures. The main underground mine is developed on the Katiniq orebodies, while several small open pits work deposits in the other zones. Mining commenced in late 1997 and the first concentrate was shipped in early 1998. Annual production is 0.8 mt of ore per year for 21 000 t of contained Ni and 5200 t Cu.
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Voisey's Bay - Labrador, Newfoundland Canada
The Voisey's Bay nickel deposit, was described in detail during the Sudbury Workshop by Dr Peter Lightfoot of Inco who has researched the deposit in detail. Core was also inspected at the Inco Exploration facility in Sudbury. Voisey's Bay is located on the Labrador coast of the Canadian Province of Newfoundland, some 1500 km to the north-east of Montreal. It is hosted by a 1334 Ma troctolite sheet belonging to the extensive 1350 to 1290 Ma Nain Plutonic Suite (NPS) emplaced at the boundary between the Nain Archaean Province to the east and the NNW trending 1850 to 1730 Ma Torngat Orogen to the west. The Torngat Orogen is a zone of deformation separating the Nain Province from the Rae Archaean Province further to the west. Archaean granitic, quartzo-feldspathic and mafic orthogneisses of the Nain Province are found to the east at Voisey's Bay. In the west garnet-sillimanite, and sulphide and graphite bearing quartzo-feldspathic paragneisses represent both reworked Archaean gneisses, and Lower Proterozoic intrusives and shelf sediments of the Torngat Orogen. The NPS is batholithic and covers some 20 000 km2 in the district. It comprises a broad spectrum of compositions including anorthosite, granite, troctolite and ferro-diorite representing the episodic coalescence of multiple plutons in an extensional environment, tapping the mantle. The troctolite host to the Voisey's Bay mineralisation comprises two east plunging intrusions, the lower Reid Brook and the upper Eastern Deeps intrusions. These originally had a 2 km vertical separation. They are linked by a steeply dipping dyke, the Feeder Sheet, that varies from 10 to 100 m in thickness.
There are a number of different rock types within these three intrusive bodies, as follows: 1). The higher Eastern Deeps intrusive has an upper olivine-gabbro (OG), grading downwards progressively into a medium grained, even textured troctolite (NT), to a varied texture troctolite (VTT) containing wall rock clasts, to a basal breccia (BBS) at the base, composed of abundant clasts of wall rock and mafics in a troctolite gangue. Various of these lithologies are cut by syenite and granite dykes. 2). The Feeder Sheet generally comprises the following across its thickness in the upper sections, from the hangingwall - an upper chill zone to an un-mineralised feeder olivine gabbro (FOG), to the leopard troctolite (LT) which has 30 to 50% interstitial sulphides with a sharp contact to a basal breccia (BBS) on the footwall. Lower, towards the Reid Brook intrusive, the BBS may occur anywhere in the feeder and grades into the feeder breccia (FB) which is similar, but much more packed, while the FOG and LT are concentric to massive sulphides, where developed. 3). The Reid Brook intrusive - the confluence of the Feeder Sheet in the roof of the Reid Brook intrusive is commonly choked by feeder breccia (FB), which also extends for a distance along the roof of the intrusive. This is underlain by a varied texture troctolite (VTT), which grades into the LT of the feeder sheet. The main mass of the intrusive is a leuco troctolite (LUT) similar in some respects to the olivine gabbro of the Eastern Deeps intrusive. Again the intrusive is cut by granite dykes.
Economic mineralisation, mainly massive sulphides occurs both within the Feeder Sheet and at the base of the Eastern Deeps intrusive, adjacent to the entry point of the Feeder Sheet. Within the Feeder Sheet, massive sulphides are restricted to the wider sections and occur as a series of elongate lenses in the plane of the linking sheet, all raking to the east. These include the Mini-Ovoid orebody and the Discovery Hill zone which are within the leopard troctolite (LT), above the basal breccia (BBS). Further to the west and deeper in the Feeder Sheet, the Western Extensions comprise disseminated mineralisation grading towards the footwall into massive sulphides. The richest body, the Ovoid occupies a 350x600 m basin shaped body that is up to 110 m deep at the thickest point, tapering upwards towards the margins. It overlies a thin band of leopard troctolite (LT) and basal breccia (BBS). This is interpreted to be a depression at the base of the Eastern Deeps intrusive, above the confluence with the Feeder Sheet. Other mineralisation, the Eastern Deeps, is also known from similar positions in the Eastern Deeps intrusive. The massive sulphides of the Ovoid are 75% pyrrhotite (2 to 5 cm crystals), 12% pentlandite (1 to 2 cm eyes), with irregular chalcopyrite and cubanite. Magnetite is scattered through the pyrrhotite. Disseminated ores of the Western Extension are in a similar proportion, but finer. The reserve at the Ovoid body is 32 mt @ 2.83% Ni, 1.68% Cu, 0.12% Co, the indicated resource at Eastern Deeps is 50 mt @ 1.36% Ni, 0.67% Cu, 0.09% Co, while the resource at Western Deeps is in excess of 15 to 20 mt. The total reserve + inferred and indicated resource was stated at 124.4 mt @ 1.66% Ni at the end of 1998. The deposit has not been developed and is owned by Inco Limited.
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Thompson - Manitoba Canada
The Thompson nickel deposits were not visited, but were described in detail during the Sudbury Workshop by researcher working on the orebodies and their formation. The Thompson Nickel Belt of northern Manitoba is located on the margin of the 1850 Ma Trans-Hudson Orogen adjacent to the north-western margin of the Archaean Superior province. The deposits are associated with peridotitic lenses that typically occur in sulphidic meta-pelites, now biotite schists of the Ospwagan Group, a sedimentary-volcanic shelf sequence. This sequence includes siltstone, sandstone, quartzite, shale, phyllite, dolomite, iron formation and pillowed basalts. These rocks have been deformed and a pronounced linearity produced. They have been juxtaposed against the upper amphibolite to granulite facies rocks of the Trans-Hudson Orogen further to the north-west. Several periods of folding and amphibolite facies metamorphism have pervasively reworked the original ore-host relationship in many deposits. Deformation of ores and host rocks at Thompson has been extreme. The parent harzburgite body has been stretched and dismembered into a horizon of ultramafic blocks and boudins that are enclosed in the sulphide rich schist that hosts the ore. The pyrrhotite-dominated nickel sulphide ores are zones in the pelitic schists that contain quasi-conformable lenses and stringers of massive sulphide which enclose numerous wall rock inclusions. Other deposits in the belt - Pipe, Birchtree, Soab, Manibridge, Bucko and Bowden - show similar though less extreme deformation. Most of the komatiitic sulphide rich ores of the belt have been deformed to form sulphide matrix breccias enclosing clasts of wall rocks. The total production plus reserves in the Thompson Belt amounts to approximately 89 mt @ 2.5% Ni, 0.13% Cu.
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For more information contact: T M (Mike) Porter, of Porter GeoConsultancy (firstname.lastname@example.org)This was another of the International Study Tours designed, developed, organised and escorted by T M (Mike) Porterof Porter GeoConsultancy Pty Ltd (PGC) in joint venture with the Australian Mineral Foundation (AMF). While the reputation and support of the AMF contributed to the establishment of the tours, after it ceased trading at the end of 2001, PGC has continued to develop, organise and manage the tour series.
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