The Muskox Intrusion
Noril'sk / Talnakh deposits
Basal Margin geometries
The Noril'sk/Talnakh Ni-Cu-PGE deposits are associated with sill complexes interpreted as the sub-volcanic conduit system associated with an extensive flood basalt sequence (the Siberian Traps) (Naldrett and Lightfoot, 1997). Seven major deposits are associated with the basal portions of these olivine rich intrusives. The zone of massive ore covered by the Oktyabr'sk and Taimyrsky mines is approximately 1 km by 3 km in extent and averages over 20 m in thickness. The deposit is strongly zoned with typical grades of 27.4 % Cu, 2.5 % Ni, 35.2 g/t Pd and 8.8 g/t Pt in the more Cu rich zones (Naldrett and Lightfoot, 1997). The deposits generally overlap the basal contact of the sills and intrude / assimilate into the footwall host rocks.
These orebodies formed as an immiscible sulphide liquid that scavenged metals from large volumes of magma en route to the surface. Brugmann et al., (1992) has shown that the composition of the massive ores required the sulfide melts to have interacted with 2,500 to 5,000 times their mass of primitive silicate magma. Although the feeder dykes to these sills have not been identified, the association of the orebodies and their sills with the Noril'sk-Karaelakh fault suggests that it may have been focus and source of the primitive magmas.
The orebodies are concentrated in two ore junctions located 25 km apart. A global estimate of the resource represented in these deposits is on the scale of 555 million tons of 2.7 % Ni and 8.1 % Cu containing 160 million ounces of Pt, 530 million ounces of Pd, and 16 million ounces of Rh (Johnson-Matthey, 2002). The total value of these deposits is approximately one trillion dollars (U.S.).
Noril'sk ore junction model applied to the Muskox Intrusion
Comparison to Noril'sk mineralization environments
Section comparison Komsomol'sky Mine section Talnakh with Pyrrhotite Lake section Muskox Intrusion
Cross section (Mineralization Model)
Feeder Dyke /Keel Deposit Model
The keel of the Muskox Intrusion represents the line of entry for the magma from the feeder dyke into the paleo-magma chamber. Within the elongate trough like geometry of the Muskox Intrusion, the Keel is the lowest point within this intrusion and is therefore an obvious site for dense sulphides to settle. Perhaps more importantly it also represents the point of entry of magma into the paleomagma chamber.</p><p>The loss of velocity in the magma and deposition of entrained sulphides at this entry point are analogous to a fluvial system's deposition of suspended solids in a delta at the mouth of a river. For example at Voisey's Bay in Labrador, the Ovoid (~ 30 million tons) and the Eastern Deeps (~ 100 million tons) magmatic sulphide deposits are associated with this entry point to the paleo-magma chamber (Evans-Lamswood et al., 2000). At Jinchuan in China, three deposits totaling approximately 500 million tons are all associated with the keel-shaped geometry portion of the Jinchuan Intrusion (Zongli, 1993). Recent exploration of the Muskox Intrusion is confirming a similar association of magmatic sulphides within its Keel Environment.
Already, with only a 2.5 km long section of the Keel having been investigated in any detail, there are three significant bodies of magmatic sulphide accumulation in evidence.
Basal Margin Deposit Model
High grade PGE-Cu mineralization has been located in the Basal Margin environment of the Muskox Intrusion. As noted above there are obvious similarities between this mineralization in grade, mode of occurrence and geologic environment to that hosted by the Noril'sk Intrusions.
The Muskox Intrusion is postulated to have originally been emplaced as a sill shaped magma reservoir to the overlying Coppermine Flood Basalts. With the 3 Km thick Coppermine Flood Basalt sequence comprised of some 115 individual flows the, potential volumes of silicate magma that moved through this conduit were in the order of 10,000 km3. The interaction of large volumes of silicate magma with immiscible sulphides would thus explain the spectacular PGE grades in sulphides at both the Muskox and at Noril'sk.
Highlights of results from Basal Margin occurrences.
The Muskox Intrusion - Canada's answer to Noril'sk-Talnakh?
Dr. Roger D. Morton - Chairman, Muskox Minerals Corporation
The Precambrian terrain of Nunavut in northern Canada hosts one of the world's largest layered mafic-ultramafic complexes, the Muskox Intrusion (MI). The MI lies 500 km north of Yellowknife and 90 km south of Kugluktuk (formerly Coppermine), on the Coronation Gulf. The overlying flood basalts of the Coppermine Group (up to 5 km thick) and the associated Mackenzie diabase dyke swarm are consanguineous and coeval with the MI. This is one of the world's major Proterozoic (1267-70 ma) magmatic provinces and the earth's largest and best-preserved continental flood basalt terrain. Exploration by Muskox Minerals Corp (MSK.V) reveals that this giant, 470 km long, layered intrusion has the potential to become a major future source of PGM, Cu and Ni in that it exhibits strong analogies to the region of Noril'sk-Talnakh where the world's richest orebodies occur.
The International Nickel Company of Canada (now INCO) performed surface prospecting and drilling during the mid-to-late 1950s. This first exploration on the MI was focused specifically on the discovery of nickel-copper sulphide deposits. During the 1980's several junior companies, hindered by limited financing and by fragmented claim blocks, conducted sampling and some drilling on PGE-bearing sulphide showings.
The MI's geology may be divided into three units: a Feeder Dyke to the intrusion, an outer contact Margin Zone and an upper Layered Series. Due to erosional differences and outcroppings of the intrusion at higher structural levels, north of the Coppermine River the overlying Margin Zone and Layered Series conceal the Feeder Dyke. South of the Coppermine River exposed segments of the Feeder Dyke contain bodies of massive, semi-massive and disseminated PGM-rich Cu-Ni sulphides, some with 16.5 g/t Pd+Pt (Geological Survey of Canada, 1999). The bulk of these bodies are confined to the core of the dyke, unlike similar bodies in the Margin Zone, which tend to concentrate along the intrusion's outer contact and in the adjacent country rocks. The Margin Zone defines the eastern and western boundaries of the intrusion. Sulphide-rich zones outcrop for tens of kilometers along the margins of the MI and carry impressive Pd, Pt, Au, Cu and Ni values. These were the targets of cursory exploration programs in the past. Grab samples taken by previous investigators and by Muskox Minerals have assayed over 160 g/t Pd+Pt+Au and over 20% combined Cu+Ni. Selected grab and trench samples include grades of: 5.5m grading 16 g/t PGMs, 7.6% Cu and 3.2% Ni.
Muskox Minerals Corp began acquisition of mineral tenure to the MI in 1994. Their 2002 land package encompasses the exposed portion of the intrusion, part of its subsurface projection to the north and the feeder dyke to the south. The company is studying the MI's mineral potential, using geological and geochemical surveys, airborne-geophysical data, gravity-, UTEM-, CSAMT-, AMT- and remote sensing-information. The acquired data, plus all pre-existing data sets, have been integrated into a database using advanced 3D Inversion, GIS, orthophotographic and 3D-Integrated Mining Software techniques. This extensive database has defined a variety of mineralization styles, with characteristic geophysical signatures, occurring within the environs of the MI. These mineralization styles include PGMs associated with a Merensky Reef-type chromitite reef and large segregations of PGM-bearing massive and disseminated Fe-Cu-Ni sulfides analogous to those seen at Noril'sk-Talnakh in Russia.
Geophysical conductors directly associated with PGM-bearing sulphide surface showings are now prioritized into immediate drill targets for the program that could commence in the near future.
The subsurface projection of the intrusion to the north, under the cover of the Coppermine flood basalts, has been explored by gravity and magnetic surveys. Gravity anomalies correlating with the buried margins of the intrusion have been located which correlate with 3D inversion magnetic and UTEM four-fold conductivity structures. These are interpreted to be possible massive sulphide accumulations at depth.
Localization of magmatic concentrations of sulphides in the core sector of the Feeder Dyke, the high Cu/Ni and Pd/Pt ratios of the sulfide mineralization in both the Feeder Dyke and the Margin Zone mineralization, as well as other petrological features, clearly demonstrates that the initial magma(s) entering the Muskox intrusion chamber were already sulphide-saturated. It is therefore thought that the extensive outcrops of Margin Zone PGM-rich Cu-Ni sulphide mineralization might be the up-dip extensions of much larger concentrations of sulphides injected along the base of the Margin Zone and into the proximal country rock near the inflection point where the vertical Feeder Dyke flattens out to form the upward dipping (30°) limbs of the Margin Zone. Contrary to earlier exploration hypotheses, which operated on the premise that the Margin Zone sulphide concentrations were the product of local and in-situ contamination of the magma by sulphur-rich country rocks, Muskox's current exploration model suggests that the Margin Zone sulphides may have been injected into their present position by crustal-contaminated and sulphide-saturated magma(s) ascending through the Feeder Dyke.
Although the Margin Zone and Feeder Dyke to the MI contain unprecedented concentrations of Cu-Ni sulphides (most of which are PGM-rich), relative to other large layered intrusions, this does not appear to have impacted on the PGM potentials of the overlying Layered Series. The Layered Series is characterized by a dominance of olivine cumulates and by frequent lithological repetitions. Dunite and peridotite comprise about 66% of the 1800 m thickness of the Layered Series. The Layered Series contains 42 layers of 18 different rock types. The layered rocks are all ultramafic and gabbroic cumulates that range from dunite at the base, through peridotite, various pyroxenites and some olivine gabbro at intermediate levels, to orthopyroxene-bearing pyroxenites and two-pyroxene gabbros at the top. There are two thin chromitite horizons ("reefs") that are at least 100 km2 in areal extent. Grades of 5 g/t Pt+Pd have been found associated with a chromitite horizon in the upper portion of the intrusion. Macroscopically, this horizon is identical in appearance to that of the UG-2 chromitite from the Bushveld Complex of South Africa. As in the Bushveld, the elevated grades associated with the chromitite horizon in the MI are also associated with along-strike structural and lithological transgressions known as "potholes"