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Regional Geology
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The Turnagain nickel property is hosted by an Early Jurassic (190�1 Ma) Alaskan-type ultramafic intrusion within Paleozoic to Early Mesozoic metasedimentary and metavolcanic rocks formerly assigned to Ancestral North America (Gabrielse, 1998, Erdmer et al., 2005). There is some uncertainty as to the age and origin of the country rocks adjacent to the Turnagain ultramafic complex, and Nixon (1998) presented two contrasting interpretations: 1) that the metasedimentary-metavolcanic rocks are autochthonous (part of the craton) and 2) that the Turnagain intrusion lies within a series of imbricated thrust sheets verging NE. However, new research indicates these rocks likely belong to either the Quesnel terrane or the Yukon-Tanana terrane (Scheel, 2007). The maximum depositional age of the metavolcanic rocks is Late Pennsylvanian-Early Permian (300 Ma) and their rare earth element signature is within the range presented by Ferri (1997) for the Lay Range Assemblage (Quesnellia) and the Klinkit Group (Yukon-Tanana)(Simard et al., 2003). Additionally, the metavolcanic rocks contain Proterozoic detrital zircon, indicative of some sediment input from the craton. These data indicate that the Turnagain ultramafic complex intruded parautochthonous (separated and re-joined to the craton) rather than autochthonous rocks, and is part of an accreted terrane.
The presence of subduction zone-related intrusive rocks, like the Turnagain intrusion, in rocks thought to be part of Ancestral North America is highly suspect as this relationship has not been observed elsewhere in the northern Canadian Cordillera (Mortensen, pers. comm., 2007). The second interpretation of Nixon (1998), that the Turnagain intrusion lies within an imbricated sequence of Late Paleozoic to Triassic sedimentary and volcanic rocks, is partially valid as other Alaskan-type intrusions are found exclusively in accreted terranes. Erdmer et al. (2005), however, observed the contact between graphitic rocks and metavolcanic rocks to be entirely conformable, and this relationship was also observed in drillcore from 2006 - there is no thrust fault contact between the graphitic and metavolcanic rocks. This indicates that the Turnagain ultramafic complex, which intruded these country rocks, intruded a previously unidentified parautochthonous terrane segment. The presence of the Turnagain intrusion proximal to a major structure (the Kutcho Fault) may be similar in tectonic significance to the major nickel-bearing ultramafic intrusions in the Canadian Shield. Indeed, the Quetico intrusions of the southern Superior craton are Precambrian versions of Alaskan-type intrusions (Pettigrew & Hattori, 2006) that occur along major structures.
A number of non-zoned, ultramafic bodies are exposed in rocks of the Cache Creek terrane, south and west of the Turnagain ultramafic body. Most of these are strongly serpentinized and host a number of asbestos and jade occurrances.
The above technical information and all the other technical information on this web-site pertaining to geology and drill hole data is under the supervision of Mr. C. Baldys, P. Eng., a Qualified Person consistent with policy NI 43-101.
Property Geology
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The Turnagain Nickel property covers the known extent of a zoned, Alaskan-type ultramafic intrusion, which measures 8 kilometres by 3.5 kilometres and is elongate in a northwest direction, conformable to the regional structural grain. The ultramafic body is in fault contact with Paleozoic to Early Mesozoic graphitic sedimentary rocks along its northern and eastern margins. The southern contact is not exposed, but several drill holes have penetrated the contact and intersected deformed, graphitic phyllites in fault contact with the ultramafic sequence. Partially digested inclusions of phyllite are also found within the ultramafic body and are abundant in the sulphide-mineralized zones, which suggest the inclusions locally control the nickel sulphide mineralization. Sulphur and lead isotopes from sulphide separates indicate that some crustal sulphur was added to the magmas which formed the Turnagain intrusion and that these inclusions led to the precipitation of sulphides from the melt (Scheel, 2007). Sulphide mineralization is described in more detail in the Resource section.
The ultramafic complex consists of a central, well exposed dunite core and an outer zone of less exposed wehrlite, olivine pyroxenite, pyroxenite and minor hornblendite. All of these rock types and gradations between them have been interpreted as crystal cumulates (Clark, 1980; Nixon, 1998). Narrow bands and schlieren of millimetre-sized chromite crystals have been noted in dunite exposures and drill core. Phlogopite is a minor accessory mineral, but is locally conspicuous in dunite and wehrlite.
Alteration varies from weak to intense serpentinization, with several ages and colours of serpentine present. Most of the prominent magnetic anomaly coinciding with the ultramafic body is thought to result from magnetite produced during serpentinization rather than from cumulus magnetite. Talc replacement of narrow felsic dykes and adjacent wall rock is often intense and is later than most of the serpentine alteration. Fine-grained tremolite often occurs with serpentine alteration but does comprise the majority of some core intervals.
The Turnagain ultramafic body is considered an Alaskan-type intrusion for the following features (Nixon, 1998):
- orthopyroxene is lacking
- clinopyroxene compositions are diopsidic and comparable to other Alaskan-type intrusions
- ultramafic cumulates are restricted to mixtures of olivine and clinopyroxene with minor chromite, rare amphibole and trace phlogopite
- localized chromitite layers in the dunite have been remobilized to form schlieren and syndepositional folds, features that are characteristic of all Alaskan-type intrusions in British Columbia.
References
Clark,T. (1980). Petrology of the Turnagain ultramafic complex, north-western British Columbia. Canadian Journal of Earth Sciences 17, 744-757
Erdmer, P., Mihalynuk, M. G., Gabrielse, H., Heaman, L. M., & Creaser, R.A. (2005). Mississippian volcanic assemblage conformably overlying Cordilleran miogeoclinal strata, Turnagain River area, northern British Columbia, is not part of an accreted terrane. Canadian Journal of Earth Sciences 42, 1449-1465
Ferri, F. (1997). Nina Creek Group and Lay Range Assemblage, north-central British Columbia: remnants of late Paleozoic oceanic and arc terranes. Canadian Journal of Earth Sciences 34, 854-874
Gabrielse, H. (1998). Geology of Cry Lake and Dease Lake map areas, north-central British Columbia. Geological Survey of Canada Bulletin 504, 147p
Kucha, H. (2007). Summary of the mineralogy and geochemistry of pentlandite and related phases from Turnagain, B.C. Unpublished company report.
Nixon, G.T. (1998). Ni-Cu sulphide mineralization in the Turnagain Alaskan-type complex: A unique magmatic environment. Geological Fieldwork 1997, B.C. Ministry of Energy, Mines and Petroleum Resources, Paper 1998-1, 18-1 to 18-11
Pettigrew, N. T. & Hattori, K.H. (2006). The Quetico Intrusions of western Superior Province: Neo-Archean examples of Alaskan/Ural-type mafic-ultramafic intrusions. Precambrian Research 149, 21-42
Simard, R-L., Dostal, J., & Roots, C. F., (2003) Development of late Paleozoic volcanic arcs in the Canadian Cordillera: an example from the Klinkit Group, northern British Columbia and southern Yukon. Canadian Journal of Earth Sciences 40, 907-924
Scheel, J. E. (2007). Age and origin of the Turnagain Alaskan-type intrusion and associated Ni-sulphide mineralization, north-central British Columbia, Canada. Unpublished M.Sc. Thesis, University of British Columbia.
The above technical information and all the other technical information on this web-site pertaining to geology and drill hole data is under the supervision of Mr. C. Baldys, P. Eng., a Qualified Person consistent with policy NI 43-101.
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