Tectonic setting of mineralization in the southern Kootenay Arc and Purcell Anticlinorium, southeastern British Columbia Ewan R. Webster & David R.M. Pattison Department of Geoscience, University of Calgary, Alberta, Canada

Introduction Geology of the Southern Kootenay Arc and Purcell Anticlinorium Metamorphic Geology and Mineral Zones Contact Metamorphic Bathozones and Mineral Subassemblages

The geoglogically complex region of southeast British Columbia between Nelson, Salmo and Creston is situated Nelson Midge ISOGRAD PATTERN Kootenay Lake 117°10'0"W 117°0'0"W 116°50'0"W 116°40'0"W 116°30'0"W at the interface between three tectonic domains: The Purcell Anticlinorium, Kootenay Arc and the Priest River LAYERED ROCKS & DRIFT Creek Two elongate domains of regional middle am- JURASSIC METAMORPHISM Stock Plutonic Rocks Complex (Figure 1). This tectonic juxtaposition and contemporaneous magmatism, metamorphism, and defor- Drift Based on the abundant Midge phibolite facies rocks merge in the northern part of mation occurred during Cordilleran orogenesis in a time interval spanning the Jurassic to Eocene. This study Hall Formation Nelson 116 Drewry Creek staurolite+andalusite assemblages, con- Lower and Batholith Nelson Eocene the study area, forming a southward facing forked aims to elucidate on the complex tectonothermal history of the area during orogenesis as a means of putting the Upper ELise Formation Point stock Drewry Middle Lower Elise Formation batholith isograd pattern that is separated by a large area of tact metamorphism associated with the areas mineral deposits in context Jurassic q LITHOLOGY Point Cretaceous Archibald Formation greenshcist facies metamorphism. Mine and Wall stocks occurred at 3.5–4 t pluton q The study area is situated mainly within de- l 51 u kbar (Figure 7, yellow domain). Ymir Group P The structure of the rocks in the southern Kootenay Arc and western limb of the Purcell Anticlinorium is affected a { u formed and metamorphosed sedimentary Jurassic F Active Formation r by at least three phases of penetrative deformation, spanning the time interval from the Middle Jurassic to c k REGIONAL METAMORPHIC ZONES Lower Cambrian e rocks of the: Purcell Supergroup, Winder- 111 e Nelway Formation e l Eocene (Fyles, 1964, 1967; Leclair, 1988; Glover, 1987; Brown, 1995). In general there is an increase in struc- to Middle r P The Porcupine Creek stock is situated 4 161 T Three regional amphibolite-facies metamorphic C u r Ordovician Upper Laib Formation mere Supergroup and Paleozoic clastics and e 92 r tural complexity and intensity of deformation going from the west of the area to the east and north, correspond- e km northwest of the Wall stock and has { c n g e zones have been identified within the map area: Laib Formation carbonates. 43 c Mount Skelly d l ing to progressively deeper structural levels. An exception to this overall pattern are the Purcell Trench fault i l Mount Skelly h Regional Metamorphic Zones Midge Creek fault a lower pressure (~3.0–3.5 kbar) con- T f pluton garnet, kyanite and sillimanite. These metamorphic Badshot Formation M a (PTF) and Midge Creek fault (MCF), across which there are marked differences in structural style and metamor- r Pluton e 49°20'0"N u 49°20'0"N tact aureole with cordierite+andalusite Reno Formation A A’ n lt zones are typical of Barrovian metamorphism, with phic grade (Figure 2,3 & 5). c 90 Lower h Garnet (Figures 5, 7). Quartzite Range Formation F the highest metamorphic grade in the footwall of Cambrian Bayonne a Batholith GRANITOIDS 51 Bayonne batholith Hamill Quartzite Baldy u the PTF and MCF, and progressively lower grades The regional metamorphic grade in the study area is dominantly greenschist facies with two discrete, elongate { lt The metasediments described above are host Kyanite CRETACEOUS METAMORPHISM Upper Three Sisters Formation Pluton with increasing distance from the fault zone. domains of amphibolite facies metamorphic rocks (Figure 5). In the northern part of the field area the amphibo- to numerous granitoid intrusions that range in lite facies metamorphism forms a southward facing forked isograd pattern. The western fork is parallel to strike Proterozoic Steeple The mid-Cretaceous, post-kinematic Monk Formation Steeple Porcupine Sillimanite (Windermere age from Middle Jurassic to Eocene and are Mountain 69 Lost Creek pluton (LCP) and Summit and is truncated by the Midge Creek fault. This fork is a continuation of the metamorphic high mapped north of { Irene Formation Porcupine Mountain Creek 55 Supergroup) part of larger intrusive suites extending stock pluton CONTACT METAMORPHISM the west arm of Kootenay Lake by Moynihan and Pattison (2008). The eastern fork is approximately parallel to Toby Formation Creek 141 51 stock (SS) have imparted lowest pres- Stock The study area has been intruded by numerous Ju- the Purcell Trench fault and transects the strike of lithological units. The eastern fork continues south into the Mount Nelson Formation across southeastern BC. 157 sure contact aureoles (2.2-3.2 kbar, Wall rassic and Cretaceous plutons (Figures 2, 5) that Figure 7. Schematic P-T phase diagram showing the relationship of mineral assemblage domains U.S.A and merges with amphibolite facies metamorphism in the Priest River Complex. Dutch Creek Formation Salmo stock 127 69 Shaw Contact Metamorphic Zones to key sub-assemblages. Contact aureoles from the field area are highlighted on the diagram with figure 7 blue domain) on the surround- Wall Next Creek Fault 72 Shaw stock 102 Creek have imparted contact aureoles to the surrounding their corresponding colours. As observed on the P-T diagram these mineral assemblages are very Van Creek Formation Salmo Stock 100 147 ing country rock. Creek stock country rock. The contact aureoles typically have a sensetive to pressure and help constrain the emplacement depth of the intrusions. The Jurassic intru- The MCF juxtaposes greenschist-facies phyllite of the Milford Group against sillimanite-zone schist in the foot- Middle Kitchener Formation Stock Garnet Proterozoic Stock FAULTING sions were genrally emplaced at deeper structural levels relative to the Cretaceous intrusions. Dia- wall. There is also a large contrast in metamorphic grade across the PTF (Figure 5): pelite in the footwall has the Middle Creston Formation Salmo Sheep Creek 155 granoblastic texture, unique mineralogy and a (Purcell Two large Eocene normal faults crosscut the Mining Camp 127 gram modified from Pattison and Vogl (2005). Abbreviations are from Kretz (1983). mineral assemblage sillimanite±kyanite+garnet+muscovite+biotite+plagioclase+quartz+rutile, whereas pelite in Supergroup) Lower Creston Formation 49°10'0"N 49°10'0"N Staurolite±andalusite coarser grain size that make them distinguishable study area: the Purcell Trench fault and the 55 the hangingwall has the assemblage biotite+muscovite+chlorite+albite+quartz (Figure 6). Based on these min- Upper Aldridge Sheep Creek Mine stock 52 Mining Camp 81 from the regional metamorphism. In summary, the Jurassic intrusions were emplaced at 3.5–4 kbar, which, for a pressure of 2.7 g/cc, corresponds to eral assemblages, the contrast in peak metamorphic conditions across the fault is >2 kbar and >150°C. Middle Aldridge Midge Creek fault, across which there are 162 Sillimanite B 156 78 Lower Aldridge marked differences in structural style and an 11–13 km emplacement depth, considerably deeper than the Cretaceous intrusions at 7–11 km. This implies { Mine Stock Summit Huscroft Andalusite±cordierite METAMORPHIC CONTRASTS approximately 5 km of aggregate exhumation between emplacement of the Jurassic intrusions and the Cretaceous The study area has been intruded by numerous Jurassic (I-type) and Cretaceous (S-Type) plutons that have im- INTRUSIVE ROCKS metamorphic grade. stock fault Across the PTF and MCF there are marked differ- intrusions. parted contact aureoles to the surrounding country rock. Based on mapped mineral assemblages and isochemical Eocene Intrusions Salmo Salmo 209 96 Mining Camp Mining Camp Lost Creek 60 104 Andalusite phase diagram modeling the Jurassic intrusions were emplaced at deeper levels in the crust than the Cretaceous Cretaceous Granitic Rocks 58 ences in structural style and metamorphic grade. pluton intrusions (Figure 7). The historic Salmo mining camp is well known for its extensive deformed MVT Pb-Zn de- Mid-Jurassic Granitic Rocks B’ Summit Prospective One exception to the large temperature and pres- STRUCTURE Area posits and Cretaceous W-Mo-Au skarns. Recent work has delineated a large, previously unidentified contact au- Moyie Sills Stock 102 sure contrast across the PTF is an area of garnet- Lost Creek As a result of different episodes of deforma- reole extending around the Summit stock and Lost Creek pluton. Several skarn deposits on the western margin ROCKS OF UNCERTAIN AFFINITY K-Ar data zone rocks in the hangingwall of the Huscroft fault Pluton Prospective tion that are confined to specific regions of of the Lost Creek pluton (Jumbo, Molly, MUT) suggest a potential for further Mo-W mineralization in the ther- Undivided sedimentary rocks Area Creston itself in the footwall of the PTF. The upper- the study area, the structural features are di- Links to Mineralization mally metamorphosed area extending east to the Summit stock (Figure 5). Meta rocks of uncertain affinity Blazed Creek fault Mt Rykert block Blazed Creek Fault greenschist-facies rocks in the hangingwall of the C vided into a western, northern and eastern 101 52 Muscovite K-Ar age (Ma) “Mixed Unit” pelite intruded by 54 Rykert batholith Huscroft fault contrast with the sillimanite-zone granite and pegmatite domain. 49°0'0"N 49°0'0"N Biotite K-Ar age (Ma) C’ rocks beneath the fault, implying a large amount of A 50–75 km wide arcuate belt of Cretaceous intrusions, known as the Bayonne magmatic suite, extends from the FAULT displacement on the fault. Because the PTF cuts Hornblende K-Ar age (Ma) Canada–United States border to north of Quesnel Lake, crosscutting the study area. The Bayonne magmatic suite the Huscroft fault, the throw on the PTF must be Geological Setting 117°10'0"W 117°0'0"W 116°50'0"W 116°40'0"W 116°30'0"W is associated with Sn, W, W-Mo, U and Ag-Pb-Zn-Au deposits (Logan, 2002). The commodities of interest ROAD Rykert Batholith less than implied by the contrast in peak metamor- 0 2.5 5 10 15 20 02.5 5 10 15 20 km varies depending on the emplacement depth of the intrusion (Lang and Baker, 2001). Undeformed mid- Kilometers Kilometers phic assemblages across the PTF outside the Hu- 118 W 116 W Cretaceous intrusions that were emplaced at 7-11 km are found throughout the study area. The Cambrian Laib 52 N 52 N FORELAND scroft block. Formation hosts Mo-W skarns adjacent to the Emerald and Dodger stocks within the historic Salmo mining OMINECA Figure 2: Regional geology map of the study area, compiled from Reesor (1996), Hoy and Dunne (1998), Glombick et al. (2010) and Paradis et al. (2010). The lines of cross sections shown in Figure 3 are displayed. camp (Figure 2 & 5). These two intrusions imparted cordierite and andalusite contact aureoles to the surrounding Inset modified after Wheeler and McFeely, (1991). The eastern and western domains are separated by the thick yellow line. The rocks north of the Wall stock are within the northern domain. Inset modified after Figure 5. Metamorphic and plutonic map of the study area, compiled from Glover (1978), Archibald et al. (1983), Doughty et al. (1997), Leclair (1988) and new data. Areas with no shading are of low metamorphic grade. Blue squares Figure 5. Metamorphic and plutonic map of the study area, compiled from Glover (1978), Archibald et al. (1983), Doughty et al. (1997), Leclair (1988) and new data. Areas with no shading are of low metamorphic grade. Blue squares are Wheeler and McFeely (1991). are occurences of kyanite away from the regional kyanite zone. K-Ar data compiled from Archibald et al. (1983), Leclair et al. (1993) and Brown et al. (1999). country rock in the sparsely distributed pelitic lithologies. On the eastern margin of the Salmo mining camp is R occurrences of kyanite away from the regional kyanite zone. K-Ar data compiled from Archibald et al. (1983), Leclair et al. (1993) and Glombick et al. (2010). M 120°W 60°N the Lost Creek pluton. This intrusion similarly has an extensive cordierite and andalusite contact aureole that ex- o UNDEFORMED qq INTERMONT ANE o c Golden 55°N tends east to the Summit stock (Figure 2). Therefore, the possibility exists for further Mo-W skarn mineralization n k a in the Laib Formation to the east (Figure 5), in the Lost Creek pluton contact aureole. s y h Calgary Revelstoke 135°W e M Geological Cross Sections and Structural Domains INSULAR Metamorphic Contrast across the PTF e

o 115° K 50°N A) B) CO AST o u In the western domain at outcrop scale, F1 n P NORTHERN DOMAIN A) folds are typically asymmetrical, upright, Z- o 1 PHASES OF DEFORMATION t CAN A A’ 130°W

u a US A Laib Creek Fault Metres The northern domain has a dominant, regional, north- and S-shaped isoclinal folds with an axial- t 49°N Metres The dominant map-scale structures in the area are tight to isoclinal, up-

r i 2500 Baldy Fault 2500 northeast-striking structural trend that is the result of right to inclined, north-northeastplanar trending foliation, folds as withillustrated subhorizontal in figure axes, 4a. e n Conclusions and Future Work c Laib Syncline U 2000 e 2000 multiple periods of deformation. The deformed, meta- F . These folds are associated with a regionally penetrative, axial-

n 1N f n l In the eastern domain the earliest folds are o 1500 morphosed sedimentary rocks in this domain are in- d 1500 planar cleavage (S ) that is generally subparallel to bedding (S ). The

a l 1N 0N • Eocene extension and exhumation resulted in deeper structural levels, higher metamorphic grade and a l l upright to recumbent, isoclinal to open folds Okanagan e 1000 truded by plutons of the Bayonne and Nelson suites, l 1000 F fold axes are parallel to a mineral and stretching lineation (L ) d 1N 1N younger cooling ages being exposed in the footwall of the Purcell Trench fault and Midge Creek fault. a A f

y which helps separate the timing of the deformation with an axial-planar schistosity (S1; figure o h Nelson 500 500 throughout this domain. Two later crenualtions are also observed in FOOTWALL mineral assemblage:

l n & r 4c). The fold axes (F1) commonly have a a m events. sillimanite±kyanite+garnet+muscovite+bi

t pelitic lithologies.

V A t e s gentle plunge to the north-northeast or • There are three domains with different structural styles and ages of penetrative deformation from the i h otite+plagioclase+quartz+rutile k d

c r r south-southwest.

r Laib Reno Monk La France Jurassic Middle Jurassic to Late Cretaceous. Future Ar-Ar work will focus on addressing the type of interface o Index Quartzite Three Irene Toby Cretaceous

Creston l f c u CANADA C) D) Footwall of PTF F Formation Formation Formation Range Sisters Formation Formation Formation Creek Intrusions Intrusions i o S1E s L2 HANGINGWALL mineral assemblage: between these domains (e.g. fault, gradational or overprinting). Formation Formation Group B) C) E At outcrop scale, F folds are typically asymmetrical, upright, n r d t U.S.A. 1W The F1 folds and S1 schistosity have been

n biotite+muscovite+chlorite+albite+quartz e Black Blu Fault o b S2 Z- and S-shaped isoclinal folds with an axial-planar foliation a E l refolded by gently plunging, north- r e Sheep Creek WESTERN DOMAIN r a B Laib Syncline (S ). These folds are best observed in carbonate layers of the • The Mt. Rykert block of lower grade metamorphic rocks, situated within the footwall of the Purcell G l Anticline B’ 1W northeast-trending, upright to recumbent, i t n The earliest map scale folds in the western domain are S0 S1E CONTRAST in peak metamorphic condi- Metres Metres E Laib syncline and Sheep Creek anticline, as illustrated in Figure u open to tight folds (Figure 4b, d). These F2 Trench fault is probably an extensional klippe, riding on an original low-angle detachment (Figure 3), d 1800 1800 F2 the Laib syncline and Sheep Creek anticline, both of E tions across the fault is >2 kbar and m S1E 4B & C. A shallowly plunging stretching lineation (L ) paral- that was stranded when the steeper PTF developed. This implies that the inferred displacement on 1500 1500 which are isoclines that plunge from north-northeast to folds are the most prevalent outcrop-scale1W >150°C (Figure 6). Priest 1200 1200 lels the fold axes. A later crenulation is evident in pelitic layers. L3 structures and form the dominant map-scale Eocene extensional faults in the area could be much less than previously thought. 48 N River 48 N south-southwest and are inclined to the west. A well- E Hangingwall of PTF 48 N 900 900 All the structures in thisfolds. area are cross cut by the Cretaceous 118 W 116 W 114 W developed sub-vertical cleavage is axial planar to the 600 600 intrusions. folds and is the dominant penetrative foliation in the F1E • The elongate domains of regional middle amphibolite facies rocks merge in the northern part of the Quaternary Late Cretaceous-Palaeogene 300 300 A third episode of deformation (D3) is ob- foreland basin sediments western domain. study area forming a southward facing forked shaped isograd pattern. Despite the apparent continuity of Tertiary Volcanic & served throughout the eastern domain, mani- the isograd pattern it is actually an interplay of multiple periods of metamorphism from the Middle Ju- Sedimentary Rocks Triassic - Jurassic E) fested as a longer wavelength (centimeter- Active Upper Laib Laib Reno Quartzite Three Cretaceous Mesozoic Intrusions Formation Formation Formation Quartzite Range Sisters Intrusions rassic to Late Cretaceous. Future U-Pb monazite dating is planned to better constrain the interface be- D) E) scale) crenulation and microfolding of mica- Formation Formation S1 The earliest folds (F ) are upright to recumbent, Palaeozoic (shelf/slope) L2 E 1E tween the different periods of metamorphism. E ceous layers. Palaeogene Intrusions C C’ EASTERN DOMAIN isoclinal to open folds with an axial-planar schistos- Huscroft S2E Palaeozoic (basinal) Mt. Rykert Overturned Block In the eastern domain there are kilometer-scale, open to ity (S1E; Figure 4D). The fold axes commonly have Summit Homocline Fault In the northern domain tight to isoclinal, up- Quesnel & Slide Mountain Terranes Creston Valley a gentle plunge to the north-northeast or south- tight folds of Belt-Purcell Supergroup. Penetrative struc- S1 Figure 6. Isochemical phase diagram section for an average pelite composition from the Nelson area. Modi- West Creston S0E E right to inclined, north-northeast-trending Gneiss Purcell Trench tures from multiple phases of deformation all have a F2 southwest. The F folds and S schistosity have fied from Pattison and Tinkham, (2009). The chemical system used to model the phase equilibria was Fault E 1E 1E Undi erentiated Gneiss in Neoproterozoic - Lower Cambrian (Hamill & Gog Groups) S1 folds with subhorizontal axes are associated similar north-northeast strike and trend of fold axes. E been refolded by gently plunging, north-northeast MnNCKFMASHT (MnO-Na2OCaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2, with C and P2O5 omitted Metamorphic Core Complexes with a regionally penetrative, axial-planar from the whole-rock analysis, followed by projection from pyrrhotite). The Yellow circle represents the Neoproterozoic (Windermere Supergroup) Rykert Batholith trending, upright to recumbant, open to tight folds L3E stable mineral assemblage in the footwall of the PTF. The red circle represents the stable mineral assem- Palaeoproterozoic Basement cleavage that is generally subparallel to bed- Acknowledgements (Figure 4E). A third period of deformation is locally blage in the hangingwall. Abbreviations are from Kretz (1983). The apparent offset on the fault is approxi- (Laurentian) Mesoproterozoic (Purcell Supergroup) 5 km ding. The fold axes are parallel to a mineral mately 7-12km. F1 observed as a centimetre-scale crenulation. Figure 1. Regional geology map of the southeastern Canadian Cordillera. Study area is highlighted by the white dashed square. Eocene Irene Toby Mount Dutch Kitchener Creston Mixed Upper Middle Moyie Cretaceous E and stretching lineation throughout this This work was funded by a 2011 Geoscience BC grant to Pattison and Webster and by the Natural Sciences and En- core complexes are labelled on the map as; Okanagan, Priest River, Grand Forks, Monashee and Valhalla. Map modified from Moyni- Formation Formation Nelson Creek Formation Formation Unit Aldridge Aldridge Sills Intrusions Formation Formation Formation Formation domain (figure 4f). gineering Research Council (NSERC). The authors would like to thank S. Paradis, D. Moynihan, T. Doughty and D. han and Pattison (in press), originally after Wheeler and McFeely, (1991). The Purcell Anticlinorium is a broad northerly plunging fold Figure 4A) Corn Creek Gneiss with a shallowly plunging stretching lineation, highlighted structure. The Kootenay Arc is a structural arc that is characterised by an increase in metamorphic grade and complexity of deformation, Archibald for there ongoing support. Figure 3. Vertical cross-sections from the study area. The lines of section are shown in Figure 2. Compiled from Leclair (1986; A-A’), Fyles (1959; B-B’), and Brown et al., (1999; C-C’). by the thin black line. B & C) S shaped F1W folds in carbonates of the Laib syncline. D) and a decrease in stratigraphic age. F1E folds showing an axial planar foliation. E) Gently plunging, recumbent F2E fold with sub-horizontal axial plane (S2E). Steeply plunging crenulation lineation (L3E). References

Archibald, D.A., Glover, J.K., Price, R.A., Farrar, E. & Carmichael, D.M., (1983): Gechrnoogy and Tectonic Implications of Magmatism and Metamorphism, Southern Kootenay Arc and Neighbouring Regions, Southeastern British-Columbia .1. Jurassic to Mid-Cretaceous, Canadian Journal of Earth Sciences, vol. 20, no. 12, pp. 1891-1913. Brown, D. A., Doughty, T. P., and Stinson, P., (1995): Geology and mineral occurrences of the Creston map area (82F/2); B.C. Ministry of Energy, Mines and Petroleum Resources, Open File 1995-15. Brown, D., Doughty, T. P., Glover, J. K., Archibald, D.A., David, D. W., and Pattison, D.R.M., (1999): Field Trip Guide and Road Log; Purcell Anticlinorium to the Kootenay Arc, Southeastern British Columbia; Highway 3 – Creston to Summit Pass, and Northern Priest River Complex; west of Creston. Doughty, P. T., Brown, D.A. & Archibald, D.A., (1997): Metamorphism of the Creston Map Area, Southeastern British Columbia (82F/2), British Columbia Geological Survey.

Fyles, J.T., (1964): Geology of the Duncan Lake area, British Columbia; BC Ministry of Mines, Energy and Resources, Bulletin 49, 87 pages. Fyles, J.T., (1967): Geology of the Ainsworth-Kaslo area, British Columbia; BC Ministry of Energy, Mines and Petroleum Resources, Bulletin 53, 125 pages. Glombick, P., Brown, D.A., and MacLeod, R.F. (Compilers), (2010): Geology, Creston, British Columbia; Geological Survey of Canada, Open File 6152, scale 1:50 000. Glover, J.K.., (1978): Geology of the Summit Creek Area, Southern Kootenay Arc, British Columbia; unpublished PhD thesis, Queen's University. Hoy, T. and Dunne, P.E.K., (1998-1): Geological Compilation of the Trail Map Area, Southeastern British Columbia, scale 1:100 000. Leclair, A.D., (1988): Polyphase structural and metamorphic histories of the Midge Creek area, south east British Columbia: implications for tectonic processes in the central Kootenay Arc; un published PhD the sis, Queens University, Ontario, Canada, 264 pages.

Paradis, S., MacLeod, R.F., and Emperingham, R. (Compilers). (2009): Bedrock Geology, Salmo, British Columbia; Geological Survey of Canada, Open File 6048, scale 1:50 000. Wheeler, J.O., and McFeely, P., (1991): Tectonic Assemblage Map of the Canadian Cordillera and Adjacent Parts of the United States of America: Geological Survey of Canada “A” Series Map 1712A, scale 1:2,000,000.