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Lac des Iles |
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Ontario, Canada |
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Pd Pt PGE PGM
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Super Porphyry Cu and Au
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The Lac des Iles palladium deposit is located 85 kilometres north-west of Thunder Bay in north-western Ontario, Canada.
Mineralisation is hosted by the 2.74 Ga Lac des Iles Complex, a composite gabbroic and ultramafic mass intruded into the granite/granite gneiss terrane of the Wabigoon sub-province of the Superior Province. The Lac des Iles Complex is the largest of a series of mafic intrusives that form the perimeter of a 20 km diameter circle surrounding a central mass of slightly older to contemporaneous hornblende and biotite tonalite.
The Lac des Iles Complex was created by multiple magmatic pulses of varying composition within several closely spaced chambers. The rarity of rhythmic layering, the presence of chaotic lithologic distribution and the presence of magmatic breccia all suggest a dynamic intrusive environment with disruptive magma pulses.
Both the gabbroic and ultramafic parts of the Lac des Iles Complex contain PGE bearing Ni-Ci sulphide mineralisation. The more significant mineralisation is within the "Roby Zone" which comprises the geologically complex junction between the ortho-pyroxene bearing, sulphide poor East Gabbro and the magnetite rich sulphide rich West Gabbro. The Roby Zone is characterised by varitextured gabbro containing pipes and pods of breccia, and large blocks (up to 60m across) of varying lithologies.
Three distinct ore types are recognised within the Roby Zone, as follows:
"Shear Ore" (mean: 7.89 g/t Pd, maximum: 55.95 g/t Pd) which is largely confined to section of a 15 to 25 m thick pyroxenite unit which is in the east-central part of the Roby Zone, in contact with barren East Gabbro. The pyroxenite is planar with a NNW trend, and is subvertical to 250 m below surface where it changes its attitude to a shallower easterly dip at depth. Near surface, "Shear Ore" is found in those parts of the pyroxenite which have been altered to an amphibole (anthophyllite-actinolite-hornblende)-talc-chlorite assemblage.
Grades are in general higher within the western part of the pyroxenite, decreasing toward the contact with the barren East Gabbro, although with depth the higher grades straddle the contact with adjacent gabbro-breccia and below 250 m the volume of "Shear Ore" in some adjacent heterolithic gabbro-breccia sections is greater than in the pyroxenite.
PGMs specific to "Shear Ore" are predominantly fine-grained vysotskite and braggite, merenskyite and kotulskite, commonly disseminated in chlorite, amphiboles and other hydrous minerals.
"North Roby Ore" occurs as a NNE striking, 20 to 40 m thick and 200 m long tabular zone found to the north of the pyroxenite. It strikes NNE with the footwall dipping to the east at 45 to 60° while the hanging wall is steeper. The principal lithology is a coarse grained leucogabbro with irregular masses of varitextured gabbro and medium to coarse-grained gabbronorite. The PGE distribution is erratic with a mean of 1.7 g/t Pd, and maximum assay value of 39.74 g/t Pd that decreases in a northeasterly direction.
"Breccia Ore" is located southwest of the "Shear Ore" zone within a 550 x 350 m oval shaped complex. This ore zone contains as much as 5% chalcopyrite, pentlandite, pyrrhotite and pyrite which occur as fine-grained disseminations and as coarse blebs interstitial to pegmatitic clinopyroxene and plagioclase. The mean grade of this zone is 1.2 g/t Pd, with maximum values of 36 g/t Pd.
A second zone of mineralisation, the "Twilight" Zone which contains 0.25 to 0.5% pyrrhotite and chalcopyrite, is separated from the Roby zone on its western boundary by the 50 to 70 m thick barren East Gabbro, while a 50 to 300 m thick barren, post-mineralisation gabbro dyke separates it from the south-eastern extension of the Roby Zone. However, it has the same style of lithological complexity as does the Roby zone, but is dominated by less heterolithic gabbronorite-breccia, with 75% gabbronorite and 25% gabbro fragments, and contains minor varitextured or pegmatitic gabbro and weak to absent silicate alteration.
Mineralisation at Lac des Iles occurs as a PGE and base metal rich magmatic matrix of breccia, as lower grade mineralisation in vari-textured units, and as high grade mineralisation associated with strong silicate alteration, exemplified by "Shear Ore".
The mine produces a single bulk concentrate containing palladium, platinum, gold, copper and nickel which is trucked to Sudbury, Ontario, for smelting. In 2001 some 2.662 Mt of ore was milled to produce 21 697 tonnes of concentrate containing 3.83 tonnes Pd, 0.33 t Pt, 0.298 t Au, 1450 t Cu, 740 t Ni.
Mineral Resources and Ore Reserves as at 30 June, 2018 (North American Platinum NI 43-101 Technical Report, Oct 2018) were quoted at:
Measured + Indicated Resources - 72.982 Mt @ @ 2.14 g/t Pd, 0.213 g/t Pt, 0.160 g/t Au, 0.06% Cu, 0.07% Ni.
Inferred Resources - 8.235 Mt @ @ 2.22 g/t Pd, 0.216 g/t Pt, 0.146 g/t Au, 0.06% Cu, 0.07% Ni.
Proved + Probable Reserves - 40.877 Mt @ @ 2.31 g/t Pd, 0.209 g/t Pt, 0.174 g/t Au, 0.06% Cu, 0.07% Ni.
NOTE: Mineral Resources are inclusive of Ore Reserves.
The Lac Des Iles mine has been both an open-pit and underground operation. The mine comprises both the Roby zone and the Offset zone, which extend over an area of 86.4 km2 of mineral claims and leases. Open-pit mining began in 1993 and by the second quarter of 2004, underground mining also commenced to access the higher-grade portion of the Roby Zone. The mine was previously owned and operated by North American Palladium, but in 2008, was placed on care and maintenance for a temporary basis as a response to plunging metal prices. It was acquired by Impala Platinum in 2019, and production resumed on 14 April 2010 when prices began to recover.
For more detail consult the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 2002.
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.
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Selected References:
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Barnett P J, 2007 - Overburden geochemical signature of the Lac des Iles platinum group element deposit, northwestern Ontario, Canada : in Can. J. Earth Sci. v44 pp 1151-1168
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Brugmann G E, Naldrett A J, MacDonald A J 1989 - Magma mixing and constitutional zone refining in the Lac des Iles complex, Ontario: genesis of Platinum-group element mineralization: in Econ. Geol. v84 pp 1557-1573
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Djon, M. L., Peck, D. C., Olivo, G. R., Miller, J. D. and Joy, B., 2018 - Contrasting Styles of Pd-Rich Magmatic Sulfide Mineralization in the Lac des Iles Intrusive Complex, Ontario, Canada: in Econ. Geol. v.113, pp, 741-767.
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Duran, C.J. , Barnes, S.-J. and Corkery, J.T., 2016 - Geology, petrography, geochemistry, and genesis of sulfide-rich pods in the Lac des Iles palladium deposits, western Ontario, Canada: in Mineralium Deposita v.51, pp. 509-532
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Hanley JJ and Gladney ER, 2011 - The Presence of Carbonic-Dominant Volatiles during the Crystallization of Sulfide-Bearing Mafic Pegmatites in the North Roby Zone, Lac des Iles Complex, Ontario : in Econ. Geol. v106 pp. 33-54
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Hattori K H, Cameron E M, 2004 - Using the High Mobility of Palladium in Surface Media in Exploration for Platinum Group Element Deposits: Evidence from the Lac des Iles Region, Northwestern Ontario: in Econ. Geol. v99 pp 157-171
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Hinchey J G and Hattori K H, 2007 - Lead isotope study of the late Archean Lac des Iles palladium deposit, Canada: enrichment of platinum group elements by ponded sulfide melt : in Mineralium Deposita v42 pp 601-611
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Hinchey J G, Hattori K H and Lavigne M J 2005 - Geology, Petrology, and Controls on PGE Mineralization of the Southern Roby and Twilight Zones, Lac des Iles Mine, Canada: in Econ. Geol. v100 pp 43-61
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Hinchey, J.G., and Hattori, K.H., 2005 - Magmatic mineralization and hydrothermal enrichment of the High Grade Zone at the Lac des Iles palladium mine, northern Ontario, Canada: in Mineralium Deposita v.40, pp. 13-23.
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Mansur, E.T., Barnes, S.-J. and Duran, C.J., 2021 - An overview of chalcophile element contents of pyrrhotite, pentlandite, chalcopyrite, and pyrite from magmatic Ni-Cu-PGE sulfide deposits: in Mineralium Deposita v.56, pp. 179-204.
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Schisa, P., Boudreau, A., Djon, L., Tchalikian, A. and Corkery, J., 2015 - The Lac Des Iles Palladium Deposit, Ontario, Canada. Part II. Halogen variations in apatite: in Mineralium Deposita v.50 pp. 339-355
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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, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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