The Namew Lake nickel-copper deposit, 60 km south of Flin Flon, Man., hosts diluted recoverable ore reserves of 2.58 million tonnes grading 2.44% nickel, 0.9% copper, 0.102 g gold per tonne, 4.11 g silver per tonne, 0.479 g palladium per tonne and 0.651 g platinum per tonne. The ultramafic-hosted deposit is owned 60% by Hudson Bay Mining & Smelting Co., the operator, and 40% by Outokumpu Mines. The deposit is 600 m from the southeast shore of Namew Lake under 6 m of water and 40 m of Paleozoic sedimentary rocks. It was discovered by Hudson Bay in April, 1984, after five years of exploration in the area. In 1980, the company flew a frequency- domain electro-magnetic (EM) survey and outlined several conductors. Airborne work was followed by ground geophysical surveys and a time- domain EM survey in 1984. The discovery hole, RES-13, drilled into a 335-m-long ground EM conductor intersecting the near-surface massive sulphide and semi-massive sulphide aplite breccia portion of the Namew Lake deposit. Regionally, the deposit lies within the southern extension of the northeast/southeast-trending Proterozoic age Flin Flon greenstone belt in the Churchill Province of the Canadian Shield. The Flin Flon greenstone belt has a strike length of 250 km and a minimum width of 150 km. In the southern part of the belt, the Precambrian rocks are unconformably overlain by Paleozoic sedimentary rocks and, hence, the geology is not well known. The area is mapped as gneissic rocks which appear to be derived from intermediate to felsic metavolcanic rocks. Namew Lake is the first nickel-copper deposit to be discovered in the Flin Flon belt.
In the vicinity of the deposit at Namew Lake, the rocks strike roughly north -south and dip approximately 45 to the west. Using field terminology, rock types from east to west are hornblende-biotite-quartz monzonite gneiss, sericitic aplitic quartz monzonite gneiss, and biotite-hornblende- quartz monzonite. The orebody is at the contact of the hornblende-biotite- quartz monzonite gneiss and the sericitic aplitic quartz monzonite gneiss in an ultramafic rock. In the area of the deposit, the rock types noted are in the range of 50 m to 100 m in thickness. These rocks are unconformably overlain by about 40 m of Paleozoic sedimentary rocks.
Typically, the orebody is 375 m long by 0.3 to 4 m wide near the surface and is greater than 375 m in a down- plunge direction. In longitudinal section, the orebody is more clearly defined as tadpole-shaped, with its tail plunging 20 to the north. The widest part is near surface.
There are three main types of mineralization in the Namew Lake orebody. Near surface, the orebody comprises both massive sulphide and aplite breccia, with a matrix of semi- massive to massive sulphide. It ranges from 0.3 m to 4.0 m in thickness, has a strike length of up to 375 m and extends to about 280 m below surface. Mineralization in this, the thickest and highest-grade part of the orebody, includes violaritized pentlandite, violarite, chalcopyrite, and pyrite. Supergene enrichment just below the Paleozoic-Precambrian contact resulted in an increase in the grade.
Near the centre of the orebody and extending down plunge to approximately 375 m below surface, lower- grade disseminated sulphide-rich, ultramafic-hosted ore predominates. On the longitudinal section, this is equivalent to the mid-section of the tadpole. Here, the orebody ranges from 3 m to 30 m in thickness and contains up to 15% of 3- to 10-mm blebs of pentlandite, chalcopyrite, pyrrhotite and/or pyrite, evenly distributed throughout the ultramafic rock. In this area, the margins of the ultramafic rock contain net-textured sulphide minerals.
Serpentinization of the hangingwall margin of the ultramafic rock is associated with slightly higher-grade nickel content.
Similarly, higher-grade nickel content is associated with some talcose sections along the footwall of the orebody. The altered schistose margins of the ultramafic rock contain chlorite, biotite, talc, tremolite- actinolite, and minor anthophyllite- cumming-tonite plus sericite.
Farther down plunge, the deposit grades to a sulphide-poor, ultramafic- hosted type of mineralization which, at present, is sub-economic in grade. Mineralization consists of pentlandite, pyrrhotite, chalcopyrite and pyrite in large sulphide blebs up to 12 mm in diameter in lower abundances than in the mid-section of the orebody. For details on mine development to date, see accompanying story, page 30. Pamela Phillips is a geologist and project co-ordinator for Greenstone Resources. She would like to thank Mr S. M. (Buz) Trevor, chief mine geologist, and Mr J. R. Pickell, senior project geologist, for their assistance.
The Namew Lake nickel-copper deposit, 60 km south of Flin Flon, Man., hosts diluted recoverable ore reserves of 2.58 million tonnes grading 2.44% nickel, 0.9% copper, 0.102 g gold per tonne, 4.11 g silver per tonne, 0.479 g palladium per tonne and 0.651 g platinum per tonne. The ultramafic-hosted deposit is owned 60% by Hudson Bay Mining & Smelting Co., the operator, and 40% by Outokumpu Mines. The deposit is 600 m from the southeast shore of Namew Lake under 6 m of water and 40 m of Paleozoic sedimentary rocks. It was discovered by Hudson Bay in April, 1984, after five years of exploration in the area. In 1980, the company flew a frequency- domain electro-magnetic (EM) survey and outlined several conductors. Airborne work was followed by ground geophysical surveys and a time- domain EM survey in 1984. The discovery hole, RES-13, drilled into a 335-m-long ground EM conductor intersecting the near-surface massive sulphide and semi-massive sulphide aplite breccia portion of the Namew Lake deposit. Regionally, the deposit lies within the southern extension of the northeast/southeast-trending Proterozoic age Flin Flon greenstone belt in the Churchill Province of the Canadian Shield. The Flin Flon greenstone belt has a strike length of 250 km and a minimum width of 150 km. In the southern part of the belt, the Precambrian rocks are unconformably overlain by Paleozoic sedimentary rocks and, hence, the geology is not well known. The area is mapped as gneissic rocks which appear to be derived from intermediate to felsic metavolcanic rocks. Namew Lake is the first nickel-copper deposit to be discovered in the Flin Flon belt.
In the vicinity of the deposit at Namew Lake, the rocks strike roughly north -south and dip approximately 45 to the west. Using field terminology, rock types from east to west are hornblende-biotite-quartz monzonite gneiss, sericitic aplitic quartz monzonite gneiss, and biotite-hornblende- quartz monzonite. The orebody is at the contact of the hornblende-biotite- quartz monzonite gneiss and the sericitic aplitic quartz monzonite gneiss in an ultramafic rock. In the area of the deposit, the rock types noted are in the range of 50 m to 100 m in thickness. These rocks are unconformably overlain by about 40 m of Paleozoic sedimentary rocks.
Typically, the orebody is 375 m long by 0.3 to 4 m wide near the surface and is greater than 375 m in a down- plunge direction. In longitudinal section, the orebody is more clearly defined as tadpole-shaped, with its tail plunging 20 to the north. The widest part is near surface.
There are three main types of mineralization in the Namew Lake orebody. Near surface, the orebody comprises both massive sulphide and aplite breccia, with a matrix of semi- massive to massive sulphide. It ranges from 0.3 m to 4.0 m in thickness, has a strike length of up to 375 m and extends to about 280 m below surface. Mineralization in this, the thickest and highest-grade part of the orebody, includes violaritized pentlandite, violarite, chalcopyrite, and pyrite. Supergene enrichment just below the Paleozoic-Precambrian contact resulted in an increase in the grade.
Near the centre of the orebody and extending down plunge to approximately 375 m below surface, lower- grade disseminated sulphide-rich, ultramafic-hosted ore predominates. On the longitudinal section, this is equivalent to the mid-section of the tadpole. Here, the orebody ranges from 3 m to 30 m in thickness and contains up to 15% of 3- to 10-mm blebs of pentlandite, chalcopyrite, pyrrhotite and/or pyrite, evenly distributed throughout the ultramafic rock. In this area, the margins of the ultramafic rock contain net-textured sulphide minerals.
Serpentinization of the hangingwall margin of the ultramafic rock is associated with slightly higher-grade nickel content.
Similarly, higher-grade nickel content is associated with some talcose sections along the footwall of the orebody. The altered schistose margins of the ultramafic rock contain chlorite, biotite, talc, tremolite- actinolite, and minor anthophyllite- cumming-tonite plus sericite.
Farther down plunge, the deposit grades to a sulphide-poor, ultramafic- hosted type of mineralization which, at present, is sub-economic in grade. Mineralization consists of pentlandite, pyrrhotite, chalcopyrite and pyrite in large sulphide blebs up to 12 mm in diameter in lower abundances than in the mid-section of the orebody. For details on mine development to date, see accompanying story, page 30. Pamela Phillips is a geologist and project co-ordinator for Greenstone Resources. She would like to thank Mr S. M. (Buz) Trevor, chief mine geologist, and Mr J. R. Pickell, senior project geologist, for their assistance.
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