Report of Activities 2019-2020 1

Mineralization Associated with Granitoid Rocks in the Eastern Meguma Terrane, Nova Scotia1

D. B. Archibald2, S. M. Barr3, and S. J. Nickerson2

Introduction associated contact metamorphic aureoles, are much less well known. Peak regional metamorphic

conditions in the Meguma terrane were mostly in Granitoid rocks are widespread in the eastern the greenschist facies, but some areas achieved Meguma terrane (Hill, 1991). The Devonian amphibolite facies, and those areas are mostly plutons are peraluminous, biotite-muscovite granite associated with peripheral granitoid plutons in the with minor granodiorite and tonalite that show southwest Meguma terrane, and in the eastern part enrichment in muscovite and total alkalis (Hill, of the terrane (Raeside et al., 1988; White and Barr, 1987, 1988, 1991; Puchalski, 2012; Puchalski et 2012). al., in press). Several of these plutons host rare- element occurrences (e.g., Be, Li, Mo, W, Sn, Ta) Most of the work completed on granitoid rocks in and the region has the potential for exploitable the eastern Meguma terrane involved student thesis rare-element mineralization (Fig. 1). These mineral projects decades ago (Chevalier, 1983; Edmonds, occurrences have received very little academic 1990; Ham, 1988; O'Reilly, 1988; Thomas, 1982) study. This project was a reconnaissance or regional mapping projects (Hill, 1991). The field investigation of the granitoid rocks that host and petrographic data from these studies provide rare-element bearing minerals in the eastern the foundation for the present study, which Meguma terrane, including known mineralization includes more extensive lithogeochemical datasets. related to the Forest Hills, Sherbrooke, and Kelly U-Pb isotopic data from some plutons yielded ages Brook plutons, and their associated pegmatites. between ca. 378 and 370 Ma (Dostal et al., 2006; This project aims to acquire a better understanding Hill, 1991; Keppie and Krogh, 1999). Ar-Ar data of the economic mineral occurrences associated from muscovite and biotite yielded a range of with granitoid plutons and related pegmatites in the plateau ages between ca. 370 and 360 Ma, eastern Meguma terrane, and to assess their indicating the plutons cooled relatively quickly relationship to sustained high heat flow that may (Keppie and Dallmeyer, 1987). In the Canso area, have facilitated gold mobility during the Devonian granitoid rocks are highly felsic and have initial Neoacadian orogeny. 87Sr/86Sr ratios between 0.703 and 0.709, which

indicate magma derivation from a heterogeneous Geological Context continental crust containing pelitic source rocks (Hill, 1988). However, the mixing of crustal and The Meguma terrane is characterized by a thick mantle components has also been suggested (e.g., Cambrian-Ordovician metasedimentary succession Tate and Clarke, 1997; Puchalski et al., in press). intruded by abundant granitic plutons (e.g., White, 2010, and references therein). The largest granitic In addition to directly associated pegmatite-hosted bodies (South Mountain and Musquodoboit mineralization, the heat associated with pluton batholiths) and smaller peripheral plutons in the emplacement may have played a fundamental role southwestern part of the Meguma terrane have had in triggering protracted episodes of gold extensive petrological studies over many decades mineralization. Gold deposits in eastern Nova (e.g., Bickerton et al., 2018; Clarke et al., 1997; Scotia are coincident with the two main MacDonald, 2001; MacDonald and Clarke, 2017; tectonothermal events that affected the Meguma many student theses). However, the less terrane, regional deformation during the ca. 400 Ma voluminous (at current exposure levels) plutons in Neoacadian orogeny, and widespread Devonian the eastern part of the terrane (Fig. 1) and their magmatism (Kontak and Archibald, 2002; Kontak

1This project was supported by a grant from the Nova Scotia Mineral Resources Development Fund (2019-2020) 2Department of Earth Sciences, St. Francis Xavier University, Antigonish, Nova Scotia B2G 2W5 3Department of Earth and Environmental Science, Acadia University, Wolfville, Nova Scotia B4P 2R6

Archibald, D. B., Barr, S. M., and Nickerson, S. J., 2020. in Geoscience and Mines Branch, Report of Activities 2019-2020; Nova Scotia Department of Energy and Mines, Report ME 2020-002, p. 1-8. 2 Geoscience and Mines Branch

Figure 1. Simplified geological map of the northeastern Meguma terrane showing the location of granitoid-related rare-element and gold occurrences. The map is modified from Hill (1991), Keppie and Krogh (1999), Puchalski (2012), and White et al. (2009). Pluton abbreviations: BR, Bull Ridge; CA, Canso; FHP, Forest Hill; GL, Glenelg; HC, Halfway Cove; KB, Kelly Brook; LR, Larry’s River; ML, Mulgrave Lake; MQ, Musquodoboit; QP, Queensport; RL, River Lake; SA, Sangster’s Lake; SH, Sherbrooke; TPS, Trafalgar plutonic suite. Granitoid-related mineral occurrences: BI, Bog Island Lake Pb-Zn-Ag; BM, Buchanans Mountain Li-Mo-Be pegmatite; EL, East Lake W; FHB, Forest Hill Be; HL, Hendsbee Lake pegmatite; LC, Lower Caledonia Be-pegmatite; LH, Lazy Head W-skarn; SHT, Sherbrooke Ta; SL, Second Lake W-Mo-Cu; TGL, Tangier Grand Lake W-Fe-Cu-Mo; LA, Lake Charlotte W; TR, Trafalgar Sb. Major gold occurrences: BD, Beaver Dam; CA, Caribou; CH, Cochrane Hill; ES, Ecum Secum; FHG, Forest Hill; FS, Fifteen Mile Stream; GB, Goldboro; GV, Goldenville; HC, Harrigan Cove; KL, Killag; ML, Mooseland; MR, Moose River; TG, Tangier. et al., 1993; Morelli et al., 2005). Therefore, the pegmatite contains xenoliths of the host granitoid rocks were emplaced during a Goldenville Group schist in three separate outcrops tectonothermal disturbance that facilitated (DeMont, 2006). The mineralogy includes large dissolution-reprecipitation reactions, resulting in quartz and microcline megacrysts, with plagioclase, gold mineralization (Cave et al., 2017; Gourcerol et muscovite, beryl, tourmaline, apatite, garnet and al., 2018). pyrite partially replaced by goethite (Fig. 2a; Nickerson, 2020). Zones within the pegmatite Pegmatites contain approximately 30-40 modal percent coarse, euhedral to subhedral beryl that varies from 2 mm to greater than 6 cm in diameter (DeMont, 2006; Lower Caledonia Pegmatite Nickerson, 2020). Beryl crystals are randomly oriented and slightly altered with inclusions of A beryl-bearing pegmatite crops out in Lower quartz, plagioclase and muscovite. Quartz is Caledonia (Fig. 1). Both the pegmatite and the recrystallized and deformed. Microcline and albitic nearby ca. 375 Ma Kelly Brook pluton show plagioclase are also deformed. Muscovite is evidence for dextral transpressive deformation deformed, altered, and occurs as cm-sized books along the Minas Fault Zone during the late within small miarolitic cavities. Tourmaline is Devonian and Carboniferous (Archibald et al., primarily near the contacts with metasedimentary 2018). The pluton consists of recrystallized quartz, xenoliths, commonly with the c-axis oriented microcline, muscovite, plagioclase, chlorite, garnet, normal to the contact of the xenolith. Mn- and zircon, and apatite (Archibald et al., 2018). The Report of Activities 2019-2020 3

Fe-rich garnet is present in the pegmatite core as the area that contain quartz, K-feldspar, mm-sized, euhedral crystals. Apatite is also present plagioclase, muscovite, biotite, and tourmaline. and U-Pb dating methods will be used on these grains to determine the emplacement age of the New Pegmatite Occurrences pegmatite.

Forest Hills Buchanans Mountain Pegmatite Several pegmatite dykes in the Forest Hills area are <1 m wide, and contain quartz, K-feldspar, To the east of the Forest Hill pluton on Buchanans muscovite, tourmaline, garnet, and pyrite (Fig. 2d). Mountain (Fig. 1), a granite dyke was reported to These dykes intrude metasedimentary rocks of the have the mineralogy molybdenite, beryl, Goldenville Group, as well as granite, and tonalite- arsenopyrite, tourmaline, and Li-rich mica diorite plutons. (O'Reilly, 2010). Hill (1991) noted that the Buchanans Mountain pluton and surrounding area Canso appeared to have the highest exploration potential Field study near Canso identified a series of cm- to because of the mineral assemblage, high Sn m-wide pegmatite dykes containing large (>2 cm) concentrations, and alteration/metasomatic effects. garnet and tourmaline, with quartz, perthitic Pegmatite dykes and quartz veins containing K-feldspar, biotite, and muscovite intruding schist muscovite, beryl, pyrite, and arsenopyrite crosscut of the Goldenville Group (Fig. 2e). the host schist (Fig. 2b) Kelly Brook Sherbrooke Pegmatite During mapping near the Lower Caledonia beryl- pegmatite, another beryl-bearing pegmatite was found 1.5 km to the east. It is an approximately 1.5 A narrow (<15 cm) band of aplite and pegmatite m wide dyke that intrudes the Kelly Brook pluton, crops out several hundred metres north of the but a xenolith of the Goldenville Group schist is village of Sherbrooke (O’Reilly, 2002; Fig. 1). The also present (Fig. 2f). The pegmatite contains pegmatite intrudes the Goldenville Group and quartz, K-feldspar, muscovite, beryl, garnet, consists of quartz, microperthitic microcline, albite, chlorite (secondary), and pyrite. Adjacent to the muscovite, garnet, and topaz (Fig. 2c). Small, dark contact with the xenolith are abundant black crystals in the pegmatite are sphalerite and/or tourmaline crystals with their c-axes oriented columbite-tantalite (O'Reilly, 2002), but additional normal to the contact. data are required to confirm the specific composition of these phases. Two other pegmatites were located near Sherbrooke (G. O’Reilly Reconnaissance personal communication, August 2019) that display Lithogeochemical the same field relationships and contain similar minerals to the Sherbrooke Ta-occurrence. Investigation of Granitoid Additional data are required to determine the Plutons and Pegmatites mineralogy of these pegmatites and their relationship to the Sherbrooke pluton. Lithogeochemical data from ninety-six representative rock samples from pegmatite and Forest Hills Pegmatite granitoid rocks in the eastern Meguma terrane showed that all of the granitoid plutons have A survey of the Nova Scotia Department of Energy similar trace element and rare-earth element and Mines Mineral Occurrence Database (O'Reilly concentrations (Fig. 3). et al., 2016) retrieved information about a beryl pegmatite occurrence located near the Forest Hills One of the new pegmatites found near Canso and gold district (Fig 1). These pegmatites reportedly the Buchanans Mountain pegmatite has the highest have beryl (Be) and molybdenite (Mo) SiO2 concentrations (Fig. 3). The Sherbrooke mineralization (Hill, 1991; O'Reilly, 1996; Schiller, pegmatites have the highest concentrations of Sn 1963). Unfortunately, we were unable to locate and Nb+Ta. The Buchanans Mountain pegmatite outcrop of the mineral occurrence in this field and Lower Caledonia pegmatite have Be study. We did find abundant pegmatite boulders in concentrations that are higher than the granitoid 4 Geoscience and Mines Branch

Figure 2. Selected field photographs: (a) the Lower Caledonia pegmatite showing beryl and tourmaline; (b) the Buchanans Mountain beryl pegmatite; (c) the Sherbrooke pegmatite; (d) new pegmatite found in the Forest Hills region with tourmaline and garnet; (e) new pegmatite found in the Canso area with large, euhedral garnet; and (f) the Kelly Brook beryl-bearing pegmatite. The pen is ~15 cm in length in (a), the pen tip in (b), (d) and (e) is ~2 cm in length, the hammer in (c) is ~25 cm in length, and the hammer in (f) is ~35 cm in length.

Report of Activities 2019-2020 5

Figure 3. Summary of lithogeochemical data. (a) Trace-element spider diagram normalized to primitive mantle (Sun and McDonough, 1989); (b) rare-earth element diagram normalized to chondrite (Sun and McDonough, 1989); (c) plot of SiO2 versus Sn; (d) plot of SiO2 versus Nb+Ta; and (e) plot of SiO2 versus Be. 6 Geoscience and Mines Branch rocks and the other pegmatites. Interestingly, one Meguma and Bendigo-Ballarat terranes; The sample of the Sherbrooke pegmatite also has Canadian Mineralogist, v. 55(6), p. 973-999. elevated Be concentrations (~200 ppm) but beryl was not identified in hand samples or thin sections. Chevalier, B.A.M., 1983. Petrography and geochemistry of the Bull Ridge Pluton, Future Work Guysborough County, Nova Scotia; Unpublished B.Sc. Thesis, Acadia University, 104 p.

Lithogeochemical sampling done for this project Clarke, D.B., MacDonald, M.A. and Tate, M.C., provides a foundation for further studies into the 1997. Late Devonian mafic-felsic magmatism in petrogenesis of the granitoid plutons, the tonalite- the Meguma Zone, Nova Scotia; in The Nature of diorite plutons, and the rare-element pegmatites. Magamatism in the Appalachian Orogen, eds. A. The newly discovered pegmatites warrant further K. Sinha, J.B. Whalen and J.P. Hogan; Memoir, investigations, and future work will focus on the mineralogy and petrogenesis of the new pegmatites Geological Society of America, p. 107-127. in addition to the Sherbrooke, Forest Hills, and DeMont, G.J. 2006. Lower Caledonia beryl Buchanans Mountain pegmatites. In addition, U-Pb pegmatite; Geoscience and Mines Branch, Mineral dating of minerals associated with the pegmatites Occurrence Database, 6 p. and the granitoid plutons may better constrain their possible relationship to gold mineralization events Dostal, J., Keppie, J.D., Jutras, P., Miller, B.V. and and the regional tectonic context. Murphy, B.J., 2006. Evidence for the granulite–

granite connection: penecontemporaneous high- Acknowledgments grade metamorphism, granitic magmatism and core complex development in the Liscomb Complex, A 2019–2020 Nova Scotia Mineral Resources Nova Scotia, Canada; Lithos, v. 86(1–2), p. 77-90. Development Fund grant (MRDF-2019-RS-031) to D. Archibald and S. Barr supported this work. We Edmonds, S.L., 1990. Petrology of dioritic and thank C. E. White for providing samples from the gneissic rocks in the Melrose area, eastern Nova Mulgrave Lake pluton and for his thorough review Scotia; unpublished B.Sc. thesis, Acadia of the report. G. O’Reilly is thanked for sharing University, 153 p. photos and knowledge of the Sherbrooke pegmatites. Gourcerol, B., Kontak, D.J., Thurston, P.C. and Petrus, J.A., 2018. Application of LA-ICP-MS References sulfide analysis and methodology for deciphering elemental paragenesis and associations in addition Archibald, D.B., Murphy, J.B., Reddy, S.M., to multi-stage processes in metamorphic gold Jourdan, F., Gillespie, J., and Glorie, S., 2018. settings; The Canadian Mineralogist, v. 56(1), Post-accretionary exhumation of the Meguma p. 39-64. terrane relative to the Avalon terrane in the Canadian Appalachians; Tectonophysics, v. Ham, L.J. 1988. The mineralogy, petrology, and 747-748, p. 343-356. geochemistry of the Halfway Cove-Queensport pluton, Nova Scotia, Canada; unpublished M.Sc. Bickerton, L., Kontak, D.J., Samson, I.M., Murphy, thesis, Dalhousie University. 294 p. J.B., and Kellett, D.A., 2018. U-Pb geochronology of the South Mountain Batholith, Nova Scotia; in Hill, J.D. 1987. Geology of the Guysborough- Targeted Geoscience Initiative: 2017 Report of Country Harbour area, Nova Scotia; in Current Activities, v. 1, ed. N. Rogers; Geological Survey Research, Part A; Geological Survey of Canada, of Canada, Open File 8358, Paper 87-1A, p. 415-422. p. 51–55. Hill, J.D. 1988. Late Devonian peraluminous Cave, B.J., Large, R.R., White, C.E., and granitic plutons in the Canso area, eastern Meguma McKnight, S., 2017. Does tungsten availability Terrane, Nova Scotia; Atlantic Geology, v. 24, p. control the presence of tungsten in turbidite-hosted 11-19. orogenic gold mineralization? Evidence from the Report of Activities 2019-2020 7

Hill, J.D. 1991. Petrology, tectonic setting, and O'Reilly, G.A. 1988. Geology and geochemistry of economic potential of Devonian peraluminous the Sangster Lake and Larrys River plutons, granitoid plutons in the Canso and Forest Hill Guysborough County, Nova Scotia; unpublished areas, eastern Meguma Terrane, Nova Scotia; M.Sc. thesis. Dalhousie University, 312 p. Geological Survey of Canada, Bulletin 383, 96 p. O'Reilly, G.A. 1996. Forest Hills Be occurrence; Keppie, J.D. and Dallmeyer, R.D., 1987. Dating Nova Scotia Department of Natural Resources, transcurrent terrane accretion: an example from the Geoscience and Mines Branch, Mineral Occurrence Meguma and Avalon Composite Terranes in the Database, 2 p. northern Appalachians; Tectonics, v. 6(6), p. 831-847. O'Reilly, G.A. 2002. Sherbrooke Ta occurrence; Nova Scotia Department of Natural Resources, Keppie, J.D. and Krogh, T.E., 1999. U-Pb Geoscience and Mines Branch, Mineral Occurrence geochronology of Devonian granites in the Database. Occurrence F04-014, 3 p. Meguma terrane of Nova Scotia, Canada: evidence for hotspot melting of a Neoproterozoic source; O'Reilly, G.A. 2010. Buchanans Mountain Li, Mo, Journal of Geology, v. 107, p. 555-568. Be occurrence; Nova Scotia Department of Natural Resources, Geoscience and Mines Branch, Mineral Kontak, D.J. and Archibald, D.A., 2002. 40Ar/39Ar Occurrence Database, 2 p. dating of hydrothermal biotite from high-grade gold ore, Tangier gold deposit, Nova Scotia: further O'Reilly, G.A., DeMont, G.J., Fisher, B.E. and evidence for 370 Ma gold metallogeny in the Poole, J.C., 2016. DP ME 002, version 11, 2016, Meguma Terrane; Economic Geology, v. 97(3), p. Nova Scotia mineral occurrence database; Nova 619-628. Scotia Department of Natural Resources, Digital Product ME 002, (version 11). Kontak, D.J., Smith, P.K. and Reynolds, P.H., 1993. Geology and 40Ar/39Ar geochronology of the Puchalski, R., 2012. Field relations and petrology Beaver Dam gold deposit, Meguma Terrane, Nova of the Trafalgar Plutonic Suite, northeastern Scotia, Canada: evidence for mineralization at 370 Meguma terrane, Nova Scotia; unpublished M.Sc. Ma; Economic Geology, v. 88(1), p. 139-170. thesis, Acadia University, 359 p.

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