NSDNR, MRB, Report ME 2011-1 - Nova Scotia · 2012. 3. 14. · Title: NSDNR, MRB, Report ME 2011-1 Created Date: 3/14/2012 9:46:12 AM

Report of Activities 2010 145

Introduction The Antigonish Highlands are part of Avalonia (e.g. Hibbard et al., 2006), which represents a revised interpretation of elements of the Avalon zone, Avalon terrane, Avalon terrane sensu stricto, or Avalon composite terrane of earlier workers (e.g. Williams, 1979; Keppie, 1985; Barr and White, 1996; Barr et al., 1998; Nance and Thompson, 1996; O’Brien et al., 1996; Keppie, 1998; Murphy and Nance, 2002; Murphy, 2007). Avalonia is fault-bounded and occurs inboard from Meguma and outboard of Ganderia throughout the northern Appalachian orogen. The Antigonish Highlands are located along the southern margin of Avalonia in northern mainland Nova Scotia (Fig. 1). They are mainly characterized by Late Neoproterozoic volcanic, sedimentary and plutonic rocks overlain by Silurian and younger Carboniferous sedimentary units (Benson, 1974; Murphy et al., 1991; White and Archibald, 2011). A recent petrological study of plutonic units in the southern Antigonish Highlands by Escarraga (2010) showed that the spatial distribution of many of the units needed to be revised. Escarraga (2010) also recognized the potential for rare earth element mineralization and the presence of Zn anomalies in the highlands. As a result, the Nova Scotia Department of Natural Resources has undertaken a bedrock mapping program in the Antigonish Highlands. This mapping, combined with an M.Sc. thesis by D. B. Archibald (Acadia University) on the gabbroic and syenitic plutons, will add to the understanding of the stratigraphy, structure, tectonic setting and mineral deposits of the Antigonish Highlands. Results of the first summer of mapping in the southern Antigonish Highlands (Figs. 1 and 2) are presented in this report.

Geological Setting and Previous Work The earliest mention of the geology in the area was by Jackson and Alger (1829), who described iron ore deposits on the East River of Pictou near Bridgeville (Fig. 2). Dawson (1845) assigned these iron-bearing rocks to the Silurian and noted the similarities to rocks in the Arisaig section farther to the north. The first comprehensive study of the geology was completed by Fletcher (1886) but his maps were not published until later (Fletcher, 1893; Fletcher et al., 1902). Fletcher (1886) considered the oldest rocks in the southern Antigonish Highlands to be “Pre-Cambrian” and composed of the “Crystalline and Schistose Rocks of Moose River, Blue Mountain, and Sutherlands River” intruded by syenite, diorite and felsitic rocks of the “Crystalline Rocks of the Keppoch and Upper Barneys River”, which are overlain by fossiliferous Silurian strata. By the time the maps were published, however, Fletcher (1893) and Fletcher et al. (1902) placed the “Schistose Rocks” into the “Cambro-Silurian division” and subdivided this division into three units (James River, Baxters Brook and Bears Brook, in ascending order), but the distribution of these new units or the type sections were not shown on the maps. Williams (1914) mapped the northern Antigonish Highlands, kept the unit names established by Fletcher (1886), and re-assigned the Cambro-Silurian division to the Lower Ordovician Browns Mountain Group, although Fletcher (1886) is often cited as establishing the group name (Williams et al., 1985). Maehl (1961) mapped the southern Antigonish Highlands and adopted the name Browns Mountain Group for all the pre-Silurian

White, C. E., Archibald, D. B. MacHattie, T. G and Escarraga, E. A. 2011: in Mineral Resources Branch, Report of Activities 2010; Nova Scotia Department of Natural Resources, Report ME 2011-1, p. 145-164.

Preliminary Geology of the Southern Antigonish Highlands, Northern Mainland Nova Scotia C. E. White, D. B. Archibald1, T. G. MacHattie and E. A. Escarraga1

1Department of Earth and Environmental Science, Acadia University, Wolfville, Nova Scotia B4P 2R6

146 Mineral Resources Branch

rocks. He recognized the Bears Brook Formation (upper Browns Mountain Group) as a distinctive mappable unit along the northern flank of the highlands, however, and described it as maroon tuffaceous sandstone and conglomerate interbedded with andesitic and rhyolitic flows. Although rocks of the Bears Brook Formation do not outcrop in Bears Brook, Maehl (1961) retained the name and established a new type section on Wallace Brook (Fig. 2). Although conformable with the underlying “Ordovician” Browns Mountain Group, he considered that this formation could be as old as Cambrian. Maehl (1961) considered the Lower Silurian Beechill Cove and Ross Brook formations to disconformably overlie the Bears Brook Formation. In the southwestern part of the map area, Maehl (1961) defined the Charcoal, Sunnybrae, Glencoe Brook and Kerrowgara formations. The Charcoal Formation is equivalent to the upper part of the Browns Mountain Group, the Sunnybrae Formation is equivalent to the Bears Brook Formation, the Glencoe Brook Formation is equivalent to the Beechill Cove Formation, and Kerrowgara

Formation is laterally equivalent to the Ross Brook and overlying formations. The Antigonish Highlands were mapped between 1962 and 1965 by Benson (1974) and he concluded that the highlands consisted of the Cambrian-Ordovician Browns Mountain Group. In the southern Antigonish Highlands he divided the group into three units: (1) the Keppoch Formation, consisting of felsic volcanic rocks, quartzite and phyllite; (2) the overlying Baxter Brook Formation, consisting of mainly sedimentary rocks and, (3) the laterally equivalent, dominantly volcanic Brierly Brook Formation. The Bears Brook Formation of Maehl (1961) was abandoned and the rocks included as part of the Baxter Brook and Brierly Brook formations. Three phases of Cambrian to Ordovician igneous activity were interpreted to be associated with the Browns Mountain Group and included: (1) hornblende syenodiorite and granodiorite, (2) diorite and gabbro and (3) granite (Benson, 1974). A younger Devonian diabase was mapped close to College Granite. The distribution of Silurian units according to Benson (1974) is similar to that of Maehl (1961).

Figure 1. Simplified geological map of the Meguma terrane, Nova Scotia, showing the location of the map area (red box) in the Antigonish Highlands.


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The Antigonish Highlands were remapped by Murphy et al. (1991) and divided into several fault-bounded blocks. The southern Antigonish Highlands were placed in the Keppoch block and units previously included in the Browns Mountain Group were assigned to the Precambrian Georgeville Group. The Georgeville Group was divided into an older, dominantly volcanic Keppoch Formation, which was subdivided into two members based on the absence (Fraser Brook Member) or presence (Moose River Member) of mudstone (Murphy et al., 1991). The overlying mainly sedimentary James River Formation was considered to overlie the Keppoch Formation both conformably and unconformably (Murphy et al., 1991). The sedimentary upper South Rights Formation conformably overlies the James River Formation (Murphy et al., 1991). Murphy et al. (1991) re-instated the Bears Brook Formation of Maehl (1961), but greatly restricted the distribution of the unit and mapped the formation as unconformably overlying the Precambrian Georgeville Group, with a conformable to locally disconformable contact with the overlying Beechill Cove Formation. Hence, they considered the formation to be uppermost Ordovician or lowermost Silurian and included it in the basal Arisaig Group. Murphy et al. (1991) abandoned the Charcoal, Sunnybrae, Glencoe Brook and Kerrowgara formations and placed them into either the Georgeville Group or the Beechill Cove and Ross Brook formations. The plutonic rocks of the southern Antigonish Highlands were considered to range from late Precambrian to Devono-Carboniferous (Murphy et al., 1991). The inferred late Precambrian plutons included the gabbroic to dioritic Eden Lake Complex, Black Brook Pluton, and an unnamed pluton around the Haggarts Lake area. The Precambrian to Cambrian plutons included the granitic Ohio and Indian Lake plutons. Several granitic Devono-Carboniferous plutons were recognized in the southern Antigonish Highlands but only two were named, the Barneys River and Gunn Lake plutons (Murphy et al., 1991).

Escarraga (2010) studied the supposedly Devonian-Carboniferous plutonic units of Murphy et al. (1991) and showed that none of them is of that age. He divided them into two suites of different petrological character and age. Suite A consists of quartz diorite, tonalite-granodiorite, and smaller bodies of alkali-feldspar granite and syenogranite, and displays a calc-alkaline chemical signature. A sample from alkali feldspar granite in this suite yielded a U-Pb (zircon) age of 605 ± 10 Ma (M. Hamilton, unpublished data, 2010). In contrast, suite B consists of varying proportions of granitic, syenitic and monzogabbroic rocks with a peralkaline affinity; a syenitic sample from suite B yielded a U-Pb (zircon) age of 469.4 ± 0.5 Ma (Escarraga et al., in press). Geology of the Southern Antigonish Highlands Introduction Geological mapping in the southern Antigonish Highlands the area between the Cobequid-Chedabucto fault zone on the south (Fig. 2) to Highway 104 in the north, and the town of Stellarton on the west to Lochaber on the east, was completed at a scale of 1:10 000 during the summer of 2010 (White and Archibald, 2011). This mapping, combined with the work of Escarraga (2010), resulted in division of the highlands into several stratigraphic formations and plutonic units (Fig. 2). The stratigraphic units include: (1) Keppoch, James River and Chisholm Brook formations of the Georgeville Group, (2) Bears Brook Formation, (3) Arisaig Group and (4) various Devonian to Carboniferous formations. The plutonic units include: (1) Eden Lake plutonic suite, (2) Lorne Station granite, (3) Sandy Gunns Lake pluton, (4) Ohio pluton, (5) Indian Lake pluton, (6) Sutherlands Lake pluton, (7) Burroughs Lake pluton, (8) West Barneys River plutonic suite and (9) Carboniferous gabbroic units. These unit names are tentative at this time as mapping in the


northern Antigonish Highlands has not been completed and may result in the necessity of further changes in terminology. Stratified Units Keppoch Formation The Keppoch Formation of the Georgeville Group (Murphy et al., 1991) makes up the core of the southern Antigonish Highlands (Fig. 2). It consists of white to pink, locally pale green to grey, rhyolitic to dacitic lapilli tuff with abundant crystal and lithic fragments (Fig. 3a). Locally, lithic fragments are greater than 20 cm in size and the rocks are better termed agglomerate following the classification of Schmid (1981). Pink to maroon, flow-banded rhyolitic flows and pyroclastic flows are less common (Fig. 3b). Pale green to grey basaltic to andesitic lapilli tuffaceous rocks with abundant lithic fragments are minor components, as are green, locally amygdaloidal basalt flows. Common throughout the Keppoch Formation are pale grey to green well laminated ‘cherty siltstone’ units that are interpreted, in part, to have been originally volcanic ash layers. Other than laminations, sedimentary structures are not common in the siltstone. Current mapping did not confirm the presence of the Frasers Brook or Moose River members or a volcanic vent complex (c.f. Murphy et al., 1991; Webster et al., 2009). Varied gabbroic, and to a lesser extent granitic, porphyry dykes and sills are common. An indication of the age of the Keppoch Formation is given by the 618 ± 2 Ma U-Pb zircon age from a rhyolite flow (Murphy et al., 1997); a closer inspection of the sample location, however, indicates that the rock is a high-level granitic porphyry dyke or sill and, hence, likely provides a minimum age for the formation. James River Formation James River Formation of the Georgeville Group (Murphy et al., 1991) forms the flanks of the southern highlands with the best exposures in roads and brooks along the northern margin of the highlands (Fig. 2). The contact with the underlying Keppoch Formation is conformable and gradational over 5 to 100 m, and defined where the volcanic

component becomes minor (e.g. Murphy et al., 1991). The formation is dominantly light green to green-grey, to locally maroon, well laminated to thinly bedded, cherty siltstone (Fig. 3c) similar to siltstone in the underlying Keppoch Formation. The siltstone is locally interbedded with minor grey fine-grained sandstone (beds up to 30 cm thick) and rare rhyolitic lapilli tuff with abundant crystal fragments and rare lithic fragments. Brown carbonate-rich sandstone beds with rip-up clasts have been noted. Sedimentary structures are not common. This unit has been interpreted to represent a marine turbidite fan deposit (Murphy et al., 1991). The South Rights formation of Murphy et al. (1991) is included here with the James River Formation. Varied gabbroic dykes and sills are common. Chisholm Brook Formation The Chisholm Brook Formation of the Georgeville Group was noted by Murphy et al. (1991) to outcrop only in the northern Antigonish Highlands. A similar package of basaltic flows and sedimentary rocks occurs in the southern highlands, however, and is included here in that formation (Fig. 2). It consists dominantly of green, amygdaloidal basaltic flows and lapilli tuff, interlayered with grey, well laminated cherty siltstone and rare quartzite. Some flows consist of angular clasts up to several centimetres in diameter that appear to have formed by autobrecciation (Fig. 3d), but no pillow-like structures were observed. In the northeasternmost part of the unit, pink to pale green, rhyolitic lapilli tuff is present. The Chisholm Brook Formation is interpreted to be conformable with the underlying James River Formation as a gradational change is generally observed. In the southeastern part of the highlands, however, the formation appears to conformably overlie the Keppoch Formation and, hence, is also likely to be in part the lateral facies equivalent to the James River Formation. Varied gabbroic dykes and sills are common. Bears Brook Formation The Bears Brook Formation of Maehl (1961) outcrops mainly along the northern flank of the highlands (Fig. 2) and consists dominantly of red to


red-brown to maroon conglomerate and arkosic sandstone with minor grey cherty siltstone and tuff. The conglomerate is polymictic, massive and poorly sorted, with silty and sandy beds and lenses (Fig. 4a). Clasts are typically subrounded and include mafic and felsic volcanic rocks and quartzite. Granitic and dioritic clasts have been reported by Murphy et al. (1991), but their presence was not confirmed in this work. The arkosic sandstone varies from poorly to well sorted with well developed graded bedding. Crossbedding is locally preserved. Detrital muscovite is rare but locally appears to be abundant (Murphy and Collins, 2008). The grey cherty siltstone is similar to that in the underlying James River Formation. The volcanic rocks are minor and include red to pale green rhyolitic to dacitic lapilli tuff and green basaltic lapilli tuff, both with abundant crystal and

lithic fragments. As the unit is defined here, no rhyolitic or basaltic flows were observed. Many of these previously interpreted flows (e.g. Maehl, 1961; Murphy 1987; Murphy et al., 1991) are sills or dykes. The contact with the underlying James River Formation appears to be conformable and because of the similarity in the cherty siltstone between the two formations, the Bears Brook Formation is included in the Georgeville Group. This formation has yielded a U-Pb age of 593 ± 10 Ma from the youngest detrital zircon (Murphy et al., 2004), which also appears to support a correlation with the Georgeville Group. Lithologically, however, it is very similar to Late Neoproterozoic to Cambrian detrital muscovite-bearing ‘redbed’ units that overlie typically Late Neoproterozoic volcanic rocks elsewhere in Avalonia (Barr et al., 1996; Barr and White, 1999).

Figure 3. (a) Dacitic lapilli tuff with abundant large lithic and crystal fragments from the Keppoch Formation. (b) Flow-banded rhyolite in the Keppoch Formation. (c) Laminated ‘cherty’ siltstone from the James River Formation. (d) Basaltic flow displaying autobrecciation textures in the Chisholm Brook Formation.


The Early Silurian Arisaig Group unconformably overlies the Bears Brook Formation, hence, a Late Neoproterozoic to Ordovician age is assigned to this unit. Arisaig Group The upper part of the Arisaig Group is not in the current map area and, hence, this report describes only the lower part of the group. Until the remainder of the Arisaig Group is mapped the Beechill Cove and Ross Brook formations, as defined by Benson (1974) and Murphy et al. (1991), are tentatively retained, although the descriptions here differ. The Beechill Cove Formation is well exposed in several brook and

river sections in the highlands and along a few logging roads (Fig. 2). It consists of light grey, poorly to well sorted, fine- to coarse-grained, thinly to thickly bedded, quartz- to feldspathic arenite that varies in thickness from less than 1m to greater than 50 m. Polymictic to quartz-pebble conglomerate beds are a rare component. Detrital muscovite is common. Locally, carbonate-rich fossil-rich horizons occur, and at one locality in Southerlands River the base of the formation is marked by a thin (


conformably overlies the Beechill Cove Formation and consists of black to grey fossiliferous siltstone and shale (Fig. 4c). As defined here, no volcanic rocks, dykes or sills were observed in the Beechill Cove or Ross Brook formations in the southern highlands. Devonian to Carboniferous Units The Devonian to Carboniferous Horton, Windsor, and Mabou groups have not been mapped in detail during this study and the contacts between these groups have been only slightly modified from previous maps and reports (e.g. Giles, 1982; Murphy et al., 1991; O’Reilly, 2005). It should be noted, however, that the Windsor Group unconformably rests on the older units and that the Horton Group is everywhere in faulted contact with the Windsor Group and with the older units of the highlands described above (Fig. 2). Igneous Units Eden Lake Plutonic Suite The Eden Lake plutonic suite is the name proposed by Escarraga (2010) and adopted by White and Archibald (2011) to include dioritic and granitic bodies in the area around Eden Lake (Fig. 2). The suite includes the units identified by Murphy et al. (1991) as the Neoproterozoic Eden Lake complex. It also includes three plutons that were designated as Devonian-Carboniferous by Murphy et al. (1991). Due to the lack of associated metamorphic and/or sedimentary rocks, the term complex is not appropriate for these intrusive units (Escarraga, 2010). A K-Ar age of 582 ± 32 Ma on hornblende (Wanless et al., 1967) indicates that the plutonic suite is likely Late Neoproterozoic. The Eden Lake plutonic suite consists of bodies of quartz diorite, tonalite (gradational to granodiorite), syenogranite and alkali-feldspar granite (Escarraga, 2010). Fine-grained to porphyritic gabbroic dykes cut the plutonic suite. Lorne Station Granite The Lorne Station granite is exposed only in a quarry west of Lorne Station (Fig. 2) and has been interpreted previously to be Carboniferous in age

(O’Reilly, 2005). It is mainly a pink to red, medium-grained granite cut by numerous fine-grained gabbroic dykes and is very similar to the granitic parts of the Eden Lake plutonic suite. Although most contacts are sheared it appears to be unconformably overlain by the Carboniferous Mabou Group. U-Pb age determinations from zircons in a standard petrographic thin section were completed using the laser-ablation microprobe – inductively coupled plasma – mass spectrometry (LAM-ICP-MS) system at the University of Alberta following the procedure outlined by Simonetti et al. (2006). Using a spot size of 40 µm, six analyses were conducted on four different zircon grains in one thin section of sample TM07-020. The analyses shows that the data points are either concordant or slightly reversely discordant (Fig. 5a) and yielded a weighted average mean age on five analyses of 615 ± 11 Ma (2σ error) (Fig. 5b). This is interpreted to be the crystallization age of the Lorne Station granite, confirming that it is of Neoproterozoic age and likely related to the Eden Lake plutonic suite. Sandy Gunns Lake Pluton The Sandy Gunns Lake pluton is well exposed along logging roads and brooks around Sandy Gunns Lake (Fig. 2). It includes both the granitic Gunn Lake and quartz dioritic Black Brook plutons of Murphy et al. (1991), and consists of quartz diorite, alkali-feldspar granite and syenogranite (Escarraga, 2010). The quartz diorite and alkali-feldspar granite locally display co-mingling textures. Hornblende from the quartz diorite yielded an 40Ar/39Ar cooling age of 602 ± 3.5 Ma (Keppie et al., 1990) and the previously considered Devonian-Carboniferous Gunn Lake Pluton (Murphy et al., 1991) yielded a U-Pb zircon crystallization age of 605 ± 10 Ma (Escarraga, 2010), confirming that these bodies are coeval and Neoproterozoic in age. Rare fine-grained gabbroic dykes cut the pluton. Ohio Pluton The Ohio pluton (Murphy et al., 1991) is well exposed in Ohio River and along logging roads in


the eastern part of the highlands (Fig. 2). It is mainly a pink to pale grey, medium-grained granodiorite. It is unconformably overlain by the Carboniferous Windsor Group on its eastern margin, has a faulted contact with the James River formation to the south, but an intrusive contact with the Keppoch formation is recognized on its northern margin. The pluton has yielded a U-Pb zircon crystallization age of ca. 606 Ma (M. Hamilton, written communication, 2010), confirming a Neoproterozoic age. Rare fine-grained gabbroic dykes cut the pluton. Indian Lake Pluton The Indian Lake pluton (Murphy et al., 1991) is well exposed along logging roads and brooks around Indian Lake (Fig. 2). Like the Ohio pluton it

is mainly a pink to pale grey, medium-grained granodiorite but locally varies to monzogranite. It also contains abundant dioritic to quartz-dioritic enclaves that are locally mappable units (White and Archibald, 2011). A small body of similar granodiorite is recognized to the east of the main pluton and is included with the pluton. The pluton yielded a K-Ar biotite age of 432 ± 18 Ma (Wanless et al., 1967), which led Murphy et al. (1991) to speculate a late Precambrian to Cambrian age for the pluton. Because it is lithologically similar to the Ohio pluton and displays similar intrusive contacts with the Georgeville Group, however, it is considered here to be Late Neoproterozoic in age (White and Archibald, 2011). Fine-grained to porphyritic gabbroic dykes cut the pluton. Sutherlands Lake Pluton The Sutherlands Lake pluton is a new name proposed by White and Archibald (2011) for a mainly grey, medium-grained quartz diorite exposed around Sutherlands Lake (formally Smith Lake in Benson, 1974) and logging roads in the area (Fig. 2). It is mainly grey, medium-grained quartz diorite, similar to rocks in the Eden Lake plutonic suite. A small body to the south of the pluton is considered to be equivalent. It is intrusive into the Keppoch Formation, and considered to be Late Neoproterozoic. Burroughs Lake Pluton The Burroughs Lake pluton (White and Archibald, 2011) is exposed only in scattered outcrops on new logging roads in the Burroughs Lake area and in a quarry in the central part of the highlands (Fig. 2). It is mainly pink to locally purple, feldspar to feldspar-quartz porphyry with crystals up to 1 cm in diameter. A nonconformable contact with the overlying Beechill Cove Formation is well exposed in the quarry. Contacts with the surrounding Keppoch Formation were not observed, but because it is lithologically and texturally similar to the U-Pb 618 ± 2 Ma “rhyolite” of Murphy et al. (1997) it is considered to be Late Neoproterozoic. The pluton is associated with a strong low gravity anomaly (Belperio et al., 2008, 2009). Fine-grained to porphyritic gabbroic dykes cut the pluton.

Figure 5. U-Pb concordia plot (a) and weighted average 206Pb/238U plot for data collected on zircon from the Lorne Station granite.


West Barneys River Plutonic Suite The West Barneys River plutonic suite is a new name proposed by White and Archibald (2011) for an assemblage of co-mingled syenite to alkali-feldspar granite and gabbro that includes the Haggarts Lake, Brora Lake, West Barneys River, Leadbetter Road and the McGraths Mountain plutons of Escarraga (2010). This plutonic suite is well exposed in the central part of the highlands (Fig. 2). A sample of quartz alkali-feldspar syenite yielded an early to middle Ordovician U-Pb (zircon) age of 469.4 ± 0.5 Ma (Escarraga, 2010), which indicates that plutonic rocks of this age form a large area in the southern highlands not recognized previously. Escarraga (2010) and Escarraga et al. (in press) concluded that the granitic components of the suite display many of the petrographic and chemical characteristics of the A-type granitoid suites of White and Chappell (1983) and Whalen et al. (1987), and the peralkaline granites (PAG) of Barbarin (1999). Gravity data from the West Barneys River plutonic suite display high and low signatures that correspond to the gabbroic and syenitic units, respectively (Belperio et al., 2008, 2009). Fine-grained to porphyritic gabbroic dykes cut the plutonic suite. Carboniferous Gabbroic Units Along the Cobequid-Chedabucto fault zone (Fig. 2) several small gabbroic intrusions and dykes have long been recognized (e.g. Benson, 1974), including the College Grant, Centerdale and Marshdale gabbros (O’Reilly, 2005; MacHattie and O’Reilly, 2009). These gabbroic bodies are poorly exposed, but where present they intrude the Carboniferous Mabou Group, except the College Grant gabbro which intrudes the Devonian Knoydart Formation (Murphy et al., 1991). Based on their field relations and geochemical signature, MacHattie and O’Reilly (2009) suggested that they range in age from ca. 340 to 315 Ma. Their distribution is defined by a strong magnetic anomaly. Other than the College Grant gabbro these younger mafic intrusions were not observed in the older rocks of the southern Antigonish Highlands.

Deformation and Metamorphism Introduction Based on the distribution of units, the overall structure in the southern highlands represents a domal feature with the Keppoch formation at the core and the James River and Bears Brook formations on the northern, western, and southern flanks, a distribution similar to the description of Murphy et al. (1991). A major unconformity is present between the Silurian to Early Devonian Arisaig Group and the underlying Georgeville Group and Barney River plutonic suite, which indicates at least one pre-Ordovician deformational event occurred in the older rocks. Deformation was accompanied by greenschist-facies (chlorite zone) regional metamorphism locally overprinted by hornblende-hornfels-facies contact metamorphism around the West Barneys River plutonic suite. After deposition of the Arisaig Group and prior to deposition of the Carboniferous Windsor Group the southern highlands were again deformed and the Silurian units folded and cleaved. A third episode of regional deformation occurred after deposition of the Carboniferous units. The significance, absolute age and overprinting effects of these deformational events are as yet uncertain. Deformation Deformation is heterogeneous across the southern Antigonish Highlands and increases in intensity toward the south. As noted by Murphy et al. (1991), no regional folds are present in the southern highlands. Contoured poles to bedding in the Keppoch and James River formations display considerable scatter but define a moderately developed girdle distribution with a shallow, northeast-plunging fold axis (Fig. 6a, b). Poles in the Keppoch Formation cluster in the southeast, northwest, and east, however, attesting to the domal feature observed in the field. Bedding data from the James River Formation are mainly from the northern part of the area and display moderate to steep northerly dips. Contoured poles to foliation in the Keppoch Formation (Fig. 6c) are broadly


similar to those of bedding (Fig. 6a); however, the James River Formation has a well developed, steep, east-striking foliation (Fig. 6d). Minor F1 folds were not observed in the field. Intersection lineations (L1) (bedding/foliation) are scattered in the Keppoch and James River formations but generally have shallow to moderate northeast to northwest plunges (Fig. 6b). This scatter in the poles to bedding and cleavage the scatter in lineation data, suggests that these structural features might have been re-oriented in a later event. Structural data from the Bears Brook Formation, like those from the James River Formation, are from the northern part of the map area. Contoured poles to bedding and L1 data are similar to those in the older formations (Fig. 6e), suggesting the Bears Brook Formation was deformed along with the older formations. Structural data for kink bands are also scattered, but one main set of kinks has steep fold axes with steep northeast-striking kink planes and a minor set has shallow northeast and southwest plunges with shallow kink planes (Fig. 6f). Contoured poles to bedding in the Arisaig Group in the northern part of the map area define a moderately developed girdle distribution with a shallow, west-plunging fold axis, and poles to foliation are consistent with a steep north-dipping axial planar foliation (Fig. 7a). Minor F1 folds are upright and plunge gently to the east and west (Fig. 7a). Intersection lineations (L1) (bedding/foliation) have shallow plunges to the west (Fig. 7a), parallel to the minor fold axes. In contrast, contoured poles to bedding in the Arisaig Group to the south and southwest (Fig. 2) show considerable scatter, although a moderately defined girdle distribution is still evident with a shallow southwest-plunging fold axis (Fig. 7b). Contoured poles to foliations display a prominent, moderately northwest-dipping cleavage and moderately defined girdle distribution with a shallow northeast-plunging fold axis (Fig. 7c). Both F1 folds and L1 lineations are scattered (Fig. 7b, c) and, like those in the underlying Georgeville Group, may have been re-oriented by a younger deformational event.

Faults Several faults and shear zones were interpreted previously to exist in the area (e.g. Murphy et al., 1991). With better exposure due to new logging roads, gravel pits and rock quarries combined with aeromagnetic data, many of these previously interpreted faults are re-interpreted here as unconformities (contacts between older units and Silurian units) or have been moved or removed (White and Archibald, 2011). A narrow protomylonite zone has been recognized locally in rocks of the Keppoch Formation along the southwestern margin of the West Barneys River plutonic suite and along contacts with the James River Formation. Stretching lineations in this zone are defined by elongate volcanic clasts and quartz rods (formally quartz veins) and dominantly plunge shallowly to north (Fig. 7d). Poles to the mylonitic foliation indicate a shallow north-dipping fabric (Fig. 7d). Preliminary kinematic studies indicate sense of movement was top to the south. The significance of this previously unrecognized mylonite zone is unclear but under investigation. The similarity in structural fabrics between the mylonite and foliations/lineations in the Keppoch Formation and southern part of the Arisaig Group suggest that these structures are related and likely post-Silurian in age. Three main faults are recognized in the area: Cobequid-Chedabucto fault zone, Browns Mountain fault and Hollow fault (Fig. 2). The Cobequid-Chedabucto fault zone (CCFZ) marks the contact between the Devonian to Carboniferous Horton Group to the south and the Late Neoproterozoic and Silurian volcanic and sedimentary rocks of the southern Antigonish Highlands to the north (Fig. 2) (c.f. Benson, 1974; Murphy et al., 1991). The CCFZ is also the boundary between Avalonia and Meguma to the south. The fault zone is poorly exposed but forms a major west-trending topographic lineament. Rocks close to the fault zone display brittle deformation features, but no mylonitic rocks were observed. Although the CCFZ had a long deformational history the overall movement along the system has been interpreted to be dextral strike-slip with some dip-slip movement (e.g. Murphy et al., 1991).


Figure 6. Equal-area stereonets of structural data from the map area. (a) Contoured poles to bedding in the Keppoch Formation. (b) Contoured poles to bedding in the James River Formation. (c) Contoured poles to foliation in the Keppoch Formation. (d) Contoured poles to foliation in the James River Formation. (e) Contoured poles to bedding in the Bears Brook Formation. (f) Plot of kink-band axes and associated axial planes. Solid great circle shows average orientation of planar features and the red star shows the calculated average fold axis. Contours at 1, 3, 5 and greater than 7% per 1% area; darkest shading indicates highest contour area.


Figure 7. Equal-area stereonets of structural data from the map area. (a) Contoured poles to bedding in the Arisaig Group north of the Browns Mountain fault. (b) Contoured poles to bedding in the Arisaig Group south of the Browns Mountain fault. (c) Contoured poles to foliation in the Arisaig Group south of the Browns Mountain fault. (d) Plot of my-lonitic fabrics. Solid great circle shows average orientation of planar features and the red star shows the calculated aver-age fold axis. Contours at 1, 3, 5 and greater than 7% per 1% area; darkest shading indicates highest contour area.


The Browns Mountain fault (Benson, 1974) is a northeast-trending vertical feature in the northern part of the map area and marks a change in deformational style from north to south (Murphy et al., 1991). It does not display a major topographic lineament but is defined by zones of highly fractured rocks and breccias and marks a major change in aeromagnetic patterns across the fault (King, 2005). Compared to the maps by Benson (1974) and Murphy et al. (1991), the placement of the Browns Mountain fault is farther south and may represent splays from the main fault zone. Although it has been argued that this fault was active in the Late Neoproterozoic (Murphy et al., 1991) it also cuts the Windsor Group, suggesting post-Carboniferous movement (Fig. 2). The tectonic significance or sense of movement of this fault is unknown but the economic potential appears great (see Economic Geology section). The Hollow fault (Benson, 1974) marks the contact between the Carboniferous Mabou Group to the north and the Late Neoproterozoic and Silurian volcanic and sedimentary rocks of the Antigonish Highlands (Fig. 2) to the south (c.f. Benson, 1974; Murphy et al., 1991). Like the Cobequid-Chedabucto fault zone, this fault is interpreted to be a major crustal feature (Murphy et al., 1991). It was not studied during the current mapping project. Metamorphism Regional metamorphism in the map area was under greenschist-facies conditions (chlorite zone with the assemblage chlorite + white mica + albite + epidote) in the pelitic rocks. Intrusion of the Barneys River plutonic suite produced a narrow, poorly preserved contact metamorphic aureole that is superimposed on regional greenschist-facies mineral assemblages and textures. In the aureole, rounded cordierite grains appear along with hornfelsic texture (Fig. 4d). No andalusite or sillimanite was observed. The presence of cordierite is characteristic of the hornblende-hornfels facies of metamorphism (e.g. Yardley, 1989).

Economic Geology The map area has long been known for its iron ore deposits (Jackson and Alger, 1829), many of which have been mined over the years (e.g. Messervey, 1944). Fletcher (1886, 1893) and Fletcher et al. (1902) reported the presence of copper, iron, manganese and one gold mine. The old gold mine site was not confirmed during current mapping. Benson (1974) summarized the previous mining activity in the map area and discovered several small copper, zinc and iron occurrences but none were found to be economic. Bourque (1981) revisited many of the known mineral occurrences and, like Benson (1974), suggested there is little of economic value in the area. Murphy et al. (1991) recognized several distinct tectonic settings in the highlands, each with its own unique mineralization potential. Based on these models, combined with new mapping and lithogeochemistry, Murphy et al. (1991) documented several new mineral occurrences and suggested that some economic potential exists in the highlands. Several reconnaissance stream sediment geochemical surveys have been conducted in the Antigonish Highlands, which recognized zinc, copper and lead anomalies in the West Barneys River drainage basin and zinc in the Kirkmount area (Bingley, 1977a, b; Bingley and Smith, 1976; Sangster, 1980, 1986; Mills et al., 1986; Mills, 1989). From drilling at Kirkmount, willemite (Zn2SiO4) was discovered as fracture-filled veins, and minor fine-grained sphalerite was also noted (Sangster, 1980, 1986; O’Reilly, 2001). Native silver, barite, hematite, siderite and Mn-rich carbonate also occur (e.g. O’Reilly, 2001; O’Sullivan, 2007). The source of the geochemical anomalies in the West Barneys River area was not discovered. Sangster (personal communication in O’Reilly, 2001) suggested that the zinc anomalies represent an area of high background. Moore (2004) concluded that a skarn-related primary base-metal sulphide deposit is the likely source for the elevated zinc.


Mapping during the current project has confirmed many of the earlier mineral occurrences and some new occurrences (White and Archibald, 2011). Of importance is the recognition that the Kirkmount Zn prospect is located on a wide breccia zone within the Browns Mountain fault. Additional samples were analyzed from the breccia zone exposed on the southern face of the Campbell Quarry and show significant zinc, lead, nickel, iron and manganese concentrations (Table 1). Also significant is the presence of anomalous zinc levels (up to 4500 ppm) in the syenitic and gabbroic rocks of the Barneys River plutonic suite (Fig. 8), which may explain the zinc anomalies in stream sediment data. Along with the elevated Zn levels, the A-type Barneys River plutonic suite has relatively high trace element (Ga, Zr, and Y) and rare earth elements (Lu + Yb) concentrations (Escarraga, 2010), which make the pluton an excellent target for exploration. New occurrences of copper (chalcopyrite, bornite, malachite, azurite) and iron have been documented in fracture-filled quartz/carbonate veins cutting the Sandy Gunns Lake pluton and Eden Lake plutonic suite. These occurrences are probably related to ca. 325 Ma deformation and hydrothermal alteration along the Cobequid-Chedabucto fault zone (Kontak et al., 2008), which is part of the iron

oxide-copper-gold (IOCG) style of mineralization in this area. In addition, similar mineralization in the Kirkmount area is associated with deformation and hydrothermal alteration along the Browns Mountain fault. The map area has high potential for industrial minerals. Sand and gravel deposits are numerous and some are currently exploited. The cherty siltstone in the James River Formation is currently being quarried for local aggregate and asphalt use, and could be used in the future twinning of Highway 104. The Nova Scotia Department of Natural Resources Mineral Occurrences Database for NTS map areas 11E/07, 08, 09 and 10 contains a complete summary of mineral occurrences and former mines in the map area. Summary A major result of the mapping during the summer of 2010 is the identification of previously unrecognized large plutonic units in the southern Antigonish Highlands, including the Early Ordovician West Barneys River plutonic suite and the Late Neoproterozoic(?) Burroughs Lake pluton. In addition, the previously assumed Carboniferous Lorne Station granite has been confirmed to be

Sample lithology Mn ppm Ni ppm Cu ppm Zn ppm Pb ppm

E10-W10-091-1 breccia 24194 1970 0 188 2602

E10-W10-091-3 siderite vein 26316 2699 0 2786 3266

E10-W10-T091-1 breccia 22245 1708 0 764 2066

E10-W10-T091-2 breccia 19992 511 5 3109 257

E10-W10-T091-3 breccia 34588 1344 158 1009 941

E10-W10-T091-4 breccia 1122 0 18 1656 1

E10-W10-T091-5 breccia 25008 1030 0 867 1065

Table 1. Table of geochemical analysis for samples from the breccia zone (Browns Mountain fault) in the quarry at Kirkmount (UTM 537343E, 5035059N Zone 20T). Analysis provided by Nova Scotia Department of Natural Resources desktop X-ray fluorescence device.


Late Neoproterozoic and likely related to similar plutonic units in the southern Antigonish Highlands. The Bears Brook Formation has been demonstrated to not be the base of the Silurian Arisaig Group, but to be older and possibly the youngest unit in the Late Neoproterozoic Georgeville Group. The southern Antigonish Highlands are deformed into a dome-like structure with the Keppoch Formation in the core and younger formations on the flanks. An angular unconformity to nonconformity exists between the Arisaig Group and the underlying Bears Brook Formation, Keppoch Formation, and older granitoid rocks, indicating a pre-Silurian deformational event. Low grade (chlorite zone) regional metamorphism was

synchronous with deformation. The Barneys River plutonic suite is locally in mylonitic contact with the Keppoch Formation along its southeastern margin; however, the original intrusive contact that resulted in hornblende-hornfels facies mineral assemblages in the host rocks are locally persevered. With a better understanding of the geology in the southern Antigonish Highlands and a new geological map (White and Archibald, 2011), the economic potential in the highlands has significantly increased. The newly defined Early Ordovician Barneys River plutonic suite, with its elevated Zn, Ga, Zr, Y and REE concentrations, provides an excellent target for exploration. The Cu

Figure 8. Contoured zinc concentrations from whole rock analysis draped over a DEM for the southern Antigonish Highlands. Samples used in this study were analyzed using the Nova Scotia Department of Natural Resources desktop portable X-ray fluorescence device. Zinc levels range from less than 3500 ppm to 0 ppm.


and Fe mineralization along the Cobequid-Chedabucto fault zone is related to deformation and hydrothermal alteration as is characteristic of IOCG deposits (MacHattie and O’Reilly, 2009). The Zn, Ni, Fe and Mn mineralization in the Kirkmount area is directly linked with the Browns Mountain fault, and is also an IOCG style occurrence. If so, the Browns Mountain fault, which is a major structure that extends tens of kilometres to the northeast, provides an underexplored target for IOGC-style mineral deposits. Acknowledgments S. Barr, G. O’Reilly, G. DeMont and B. Murphy are thanked for numerous discussions regarding the geology of the Antigonish Highlands. Thanks to the numerous aggregate companies for allowing access to restricted quarrying operations. Special thanks to T. Lenfesty and J. Brenton for providing eager and enthusiastic help in the departmental library and to M. Chisholm for providing unexpected sustenance throughout the summer. Comments and edits on the draft manuscript by S. Barr were helpful. References Barbarin, B. 1999: A review of the relationships between granitoid types, their origins and their geodynamic environments; Lithos, v. 46, p. 605–626. Barr, S. M. and White, C. E. 1996: Contrasts in late Precambrian - early Paleozoic tectonothermal history between Avalon Composite Terrane sensu stricto and other peri-Gondwanan terranes in southern New Brunswick and Cape Breton Island, Canada; in Avalonian and Related Peri-Gondwanan Terranes of the Circum-North Atlantic, ed. R. D. Nance and M. D. Thompson; Geological Society of America, Special Paper 304, p. 95–108. Barr, S. M. and White, C. E. 1999: Field relations, petrology, and structure of Neoproterozoic rocks in the Caledonian Highlands, southern New Brunswick; Geological Survey of Canada, Bulletin 530, 101 p.

Barr, S. M., White, C. E. and Macdonald, A. S. 1996: Stratigraphy, tectonic setting, and geological history of Late Precambrian volcanic-sedimentary-plutonic belts in southeastern Cape Breton Island, Nova Scotia; Geological Survey of Canada, Bulletin 468, 84 p. Barr, S. M., Raeside, R. P. and White, C. E. 1998: Geological correlations between Cape Breton Island and Newfoundland, northern Appalachian orogen; Canadian Journal of Earth Sciences, v. 35, p. 1252–1270. Belperio, T., Morris, G. and O’Sullivan, J. 2008: Exploration for iron oxide-copper-gold along the Cobequid-Chedabucto structure, Nova Scotia; Nova Scotia Department of Natural Resources, Assessment Report ME 2008-181, 394 p. Belperio, T., Morris, G. and O’Sullivan, J. 2009: Exploration for iron oxide-copper-gold along the Cobequid-Chedabucto structure, Nova Scotia; Nova Scotia Department of Natural Resources, Assessment Report ME 2009-10, 84 p. Benson, D. G. 1974: Geology of the Antigonish Highlands, Nova Scotia; Geological Survey of Canada, Department of Energy, Mines and Resources, Memoir 376, 92 p. Bingley, J. M. 1977a: Stream sediment geochemical reconnaissance program – Antigonish and Cape George map areas; Nova Scotia Department of Mines, Open File Report ME 261, Sheet 3 (zinc), scale 1:50 000. Bingley, J. M. 1977b: Stream sediment geochemical reconnaissance program – New Glasgow map area; Nova Scotia Department of Mines, Open File Report ME 261, Sheet 3 (zinc), scale 1:50 000. Bingley, J. M. and Smith, P. K. 1976: Geochemical evaluation of the Antigonish Highlands; Nova Scotia Department of Mines, Report ME 1976-2, p. 79-82. Bourque, P. D. 1981: A metallogenic study of the Antigonish area, Nova Scotia, with special reference to the copper occurrences of the Ohio-


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Scotia; American Journal of Science, 1, v. 15, p. 132–160, 202–217. Keppie, J. D. 1985: Paleozoic terranes in circum-Atlantic orogens; Episodes, v, 8, p. 196–197. Keppie, J. D. 1998: Birth of the Avalon Arc in Nova Scotia, Canada: geochemical evidence for approximately 700-630 Ma back-arc rift volcanism off Gondwana; Geological Magazine, v. 135, p. 171–181. Keppie, J. D., Dallmeyer, R. D. and Murphy, J. B. 1990: Tectonic implications of 40Ar/39Ar hornblende ages from late Proterozoic-Cambrian plutons in the Avalon composite terrane, Nova Scotia, Canada; Geological Society of America Bulletin, v. 102, p. 16–528. King, M. S. 2005: Airborne magnetic calculated second vertical derivative map for parts of NTS 11E/09, Merigomish area, Nova Scotia; Nova Scotia Department of Natural Resources, Mineral Resources Branch, Open File Map ME 2005-45, scale 1:50 000. Kontak, .D. J., Archibald, D. A., Creaser, R. A. and Heaman, L. 2008: Dating hydrothermal alteration and IOCG mineralization along a terrane boundary fault zone: the Copper Lake deposit, Nova Scotia; Atlantic Geology, v. 44, p. 146–166. MacHattie, T. G. and O’Reilly, G. A. 2009: Timing of iron oxide-copper-gold (IOCG) mineralization and alteration along the Cobequid-Chedabucto fault zone; in Mineral Resources Branch, Report of Activities 2008; Nova Scotia Department of Natural Resources, Report ME 2009-1, p. 63–69. Maehl, R. H. 1961: The older Paleozoics of Pictou County, Nova Scotia; Nova Scotia Department of Mines, Memoir ME 4, 112 p. Messervey, J. P. 1944: Iron Ore Occurrences, Bridgeville Area, Nova Scotia; in Department of Mines, Annual Report on Mines 1943, p. 71–81. Mills, R. F. 1989: Geochemical analyses of bulk stream sediment samples from northern Nova Scotia (parts of NTS Sheets 11E, 11F, 11G, 11J,


11K and 21H); Nova Scotia Department of Mines and Energy, Open File Report ME 1989-7, 367 p. Mills, R. F., Lombard, P. A. and Rogers, P. J. 1986: Regional geochemical surveys; in Program and Summaries, Tenth Annual Open House and Review of Activities; Nova Scotia Department of Mines and Energy, Information Series ME 12, p. 121–122. Moore, C. C. 2004: Distribution of zinc in the West Barneys River drainage basin, Antigonish Highlands, Nova Scotia; B.Sc. thesis, Department of Geology, Acadia University, Wolfville, Nova Scotia, 102 p. Murphy, J. B. 1987: Petrology of upper Ordovician-lower Silurian rocks of the Antigonish Highlands, Nova Scotia; Canadian Journal of Earth Sciences, v. 24, p. 752–759. Murphy, J. B. 2007: Geological evolution of middle to late Paleozoic rocks in the Avalon Terrane of northern mainland Nova Scotia, Canadian Appalachians; a record of tectonothermal activity along the northern margin of the Rheic Ocean in the Appalachian-Caledonide orogen; Geological Society of America, v. 423, p. 413–435. Murphy, J. B. and Collins, A. S. 2008: 40Ar-39Ar white mica ages reveal Neoproterozoic/Paleozoic provenance and an Alleghanian overprint in coeval Upper Ordovician-Lower Devonian rocks of Meguma and Avalonia; Tectonophysics, v. 4, p. 265–276. Murphy, J. B. and Nance, D. 2002: Sm – Nd isotopic systematics as tectonic tracers: an example from west Avalonia in the Canadian Appalachians; Earth Science Reviews, v. 59, p. 77–100. Murphy, J. B., Keppie, J. D. and Haynes, A. J. 1991: The geology of the Antigonish Highlands, Nova Scotia; Geological Survey of Canada, Paper 89-10, 115 p. Murphy, J. B., Keppie, J. D., Davis, D. and Krogh, T. E. 1997: Regional significance of new U-Pb age data for Neoproterozoic igneous units in Avalonian rocks of northern mainland Nova Scotia, Canada;

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NSDNR, MRB, Report ME 2011-1 - Nova Scotia · 2012. 3. 14. · Title: NSDNR, MRB, Report ME 2011-1 Created Date: 3/14/2012 9:46:12 AM