Metalliferous Environments of Nova Scotia - Base Metals
By James M. Patterson, Ph. D.
Nova Scotia Department of Natural Resources
Mineral Resources Branch
Information Series ME 22, 1993.
(This is the main paper of which Information Circular ME 36 is the summary, with the same title, author and date)
This web version includes editorial revisions to the original hardcopy version first published in 1993.
Funded by the Canada - Nova Scotia Cooperation Agreement on Mineral Development.
Table of Contents
Abstract - Metalliferous Environments in Nova Scotia - Base Metals
In Nova Scotia metallic minerals have been produced from deposits hosted in rocks ranging from the Precambrian to the youngest unconsolidated sediments. Base metals have been produced from deposits representing a wide variety of geological environments ranging from Precambrian to Upper Carboniferous in age.
The objective of this study is to identify those geological environments which have contributed to Nova Scotian base metal production in the past and, more importantly, indicate those environments which are worthy of further investigation. The study is not exhaustive but is directed towards encouraging industry decision makers at senior technical levels to have a much closer look at the diversity of legitimate base metal exploration targets present in Nova Scotia.
The better documented environments are represented by volcanogenic, carbonate-hosted, sandstone-hosted deposits plus those deposits associated with granite intrusions. Indications of Precambrian shale-hosted deposits are present and the base metal potential of the Cambro-Ordovician Meguma Group (better known for its gold deposits) is presented. Recent investigations have indicated that Silurian volcanics, limestones and black shales are new exploration targets.
The volcanogenic massive sulphide deposits at Stirling produced in excess of 1 million tonnes of ore from which Cu, Pb, Zn, Ag and Au were recovered. Surface mapping and recent diamond drilling programs indicate that this Precambrian volcanic belt is a prime exploration target. In the northern part of the Antigonish Highlands argillites of Proterozoic age host low grade zinc mineralization in the form of disseminated sphalerite over considerable thickness and remobilization, due presumably to later tectonic activity, has enhanced the grade. Approximately 5 km of strike length has been tested by 9 drillholes and additional work could be rewarding.
In Nova Scotia the Meguma Group rocks, of Cambro-Ordovician age, are best known as hosts to numerous gold deposits which were investigated during the intensive exploration activity of the 1980s. However significant base metal deposits have been discovered and the Eastville deposit, situated north of the Liscomb Intrusive Complex, shows near ore grade mineralization intermittently over a strike length of 10 km. Sphalerite and galena mineralization has been discovered in three zones and grades are higher in areas of fracturing and brecciation. This deposit is the best known along the 1700 km long Goldenville/Halifax transition zone and offers an excellent opportunity for further follow-up. In southwest Nova Scotia, Meguma Group metasediments host Sn deposits with ore grade Zn values and accompanying values in Pb, Cu and Au and Ag. The Meguma Group, with its abundant and widespread mineralization seems to have been overlooked as a target for base metals.
Recent work by federal and provincial geologists has begun to enhance the potential of the Silurian rocks in the province. Thus Lynch and Tremblay of the Geological Survey of Canada have shown that the volcanics hosting the massive sulphides with Au and Ag in the Cheticamp area northwest Cape Breton Island are of Silurian age rather than the Precambrian age to which they had for so long been assigned. Recent drilling by the Nova Scotia Department of Natural Resources (Smith, 1992) has demonstrated the presence of sulphide-rich black shales interbedded with limestones in the New Canaan Formation of Upper Silurian age. The impure limestones at Lochaber Lake, also assigned to the Silurian, host some 3 million tonnes at 0.3% Cu with potential existing down-dip and along strike.
The carbonate hosted deposits of Nova Scotia range from the metamorphosed Proterozoic marble-hosted deposits at Meat Cove and Lime Hill, through the Silurian impure carbonate-hosted deposit at Lochaber Lake to the Windsor Group carbonate-hosted deposits of Zn, Pb, Cu, Ba, Sr and Ag. These Lower Carboniferous deposits have sustained production at various times and the Walton deposit, which was the largest Ba deposit in the world at one time, also produced significant base metals carrying approximately 4.5 million oz. of silver.
The Upper Carboniferous sandstone and shales of Nova Scotia host Zn, Pb, Cu (Ag) deposits and production was achieved from the sandstone-hosted Yava deposit in Cape Breton Island for a short period. This deposit, analogous to the Eocambrian sandstone-hosted deposits along the Caledonian Front in Scandinavia, has a large tonnage but of low grade. Though Yava was solely a lead producer, potential exists for development of zinc deposits and for further lead deposits in the immediate vicinity. Potential exists for both sandstone-hosted and Kupferschiefer-type shale-hosted deposits in the Upper Carboniferous of the Cumberland Basin of northern mainland Nova Scotia.
Mineralization associated with granitic intrusions has been well documented. The porphyry-type Cu, Mo deposit at Coxheath in Cape Breton Island, the Millet Brook U/Ag deposit south of Windsor and the East Kemptville Sn (Cu, Zn, Ag) deposit in southwest Nova Scotia attest to the province-wide distribution of this type of mineralization.
Historically, in Nova Scotia as elsewhere, mineral exploration has been concentrated along or close to geological contacts at or near the surface. Prospecting and geochemistry have been among the more successful techniques. Recent developments in computer technology are rapidly enhancing the role of geophysics and or integrated interpretations. As exploration moves away from near surface control the necessary role of geological deduction and integration of all disciplines will assist in outlining drill targets and diamond drilling will increasingly augment the prospector's pick.
It is hoped that this paper will provide a good starting point from which companies can advance their exploration programs for base metals in Nova Scotia.
1. Introduction
1.1 Objective of This Study
The primary objective of this study is to increase the awareness among the mining and exploration industry of the variety of geological environments in which base metals have been discovered in Nova Scotia. By identifying the main base metal environments in the province and by illustrating each class by a representative deposit H is hoped that company personnel will be encouraged to delve a little deeper into the potential of this province. The deposits selected as representative of each class are, where possible, former producers so that a good database is available from which to expand and develop an exploration model program. By drawing analogies with better known deposits, both nationally and internationally, it is intended to demonstrate the potential for further discoveries of associated deposits within the province.
2.2 Regional Geological Setting
Situated on the eastern seaboard of North America, and with a land area of some 55,000 square kilometres, Nova Scotia lies within the Acadia Composite Terrane (Keppie, 1985) in the northern part of the Appalachian Orogen.
The Appalachian Orogen is a Paleozoic megastructure (Fig. 1) that stretches more than 3000 km from Alabama in the southwest to Newfoundland in the northeast. The chain is bounded to the northwest by the Laurentian craton of Precambrian rocks or by their platform cover. Within the Appalachian Orogen lie strips of post-orogenic early Mesozoic sedimentary and volcanic rocks, deposited in grabens or half grabens. Williams (1978) has attempted to trace tectonostratigraphic belts within the megastructure and interprets these as representing specific geotectonic, fossilized environments reflecting original Ordovician paleogeographic elements which have been tectonically assembled as an orogenic belt.
Bird and Dewey (1970) first proposed the concept of tectonic assembly by suggesting that the northern Appalachians were formed as a result of a collision between Laurentian and the Avalon platform. An oceanic domain comprising continental shelves, island arcs, back-arc basins and associated sedimentary and igneous rocks was postulated between the two. Upon collision this mixed rock assemblage was thrust (obducted) onto the continental edge. Ophiolite sequences (interpreted as remnants of oceanic lithosphere) within the obducted masses mark the suture lines between the collided plates.
Keppie (1992) states that the long lived, though geographically restricted, deformation events which appear to characterize the early Paleozoic evolution of the Appalachians may be related to terrane accretionary events. He suggests that these events were followed by a terminal, diachronous, long-lived event which affected the entire width of the Canadian Appalachians and which may be related to continental collision.
Keppie notes that the Precambrian deformational events in the Appalachians in general and in Nova Scotia in particular are represented by:
- Middle Proterozoic Polyphase structures associated with high grade metamorphism within Grenvillian inliers in northwest Cape Breton Island and eastern Cobequid Highlands, and
- by Late Proterozoic-Cambrian single phase to polyphase structures accompanied by low to high grades of metamorphism in the Avalon Zone.
The Paleozoic deformational events in the Canadian Appalachians are described by Keppie as corresponding to narrow diachronous events in the Ordovician, Silurian and early to middle Devonian, whereas the late Devonian, Carboniferous and Permian deformational events are widespread and broadly synchronous. It is these Paleozoic events which have combined to form the Appalachian Orogeny. Keppie notes that in plan view the shape of this orogen is inherited from the original irregular edge of the North American craton. In general the major structures also follow this sinuous trend in the orogen and Keppie suggests that their surface traces are more a function of the initial geometry of the North American margin rather than of kinematics.
Keppie (1985) introduced the term "composite terrane" to describe the collage of smaller terranes of the Avalon belt and in 1987 proposed a sequence of five terrane categories, from northwest to southeast, for the northern Appalachians. Keppie's terranes 4 and 5 are well represented in Nova Scotia by the diverse Precambrian terranes which comprise the Avalon Composite Terrane and the Chambray-Ordovician metasediments of the Meguma Terrane, the most outboard of the northern Appalachian terranes.
The Avalon Composite Terrane shows signs of several stages of deformation and assembly with docking of individual parts occurring at different times. Thus the Carolina terrane in the south docked in the Ordovician while the Avalon terrane, in southeastern New England, docked in Devono-Carboniferous times.
The Meguma terrane, an important part of Nova Scotia, is bounded on its northern side by a major east-west dextral shear/fault zone-the Cobequid/Chedabucto Fault. The earliest docking was in Devonian times while the boundary between the Meguma and Avalon terranes is overstepped by the earliest Carboniferous unconformity. Other evidence indicates a prolonged period of convergence, ranging from Devonian to early Permian, after initial accretion.
It should be noted that Keppie (1992) has redefined some of these deformational events and has introduced a revised nomenclature for the orogenic phases. However, for the purposes of this paper, the longer established names are retained for the main orogenic events in Nova Scotia.
1.3 Geological Framework of Nova Scotia
A simplified geological map of Nova Scotia (Fig. 2) shows a broad division into three main geological areas. Southern Nova Scotia is separated from Northern Nova Scotia and Cape Breton Island by the prominent Cobequid-Chedabucto Fault System.
This southern section conforms to the Meguma Terrane of Keppie, which comprises argillites and greywackes of Cambro-Ordovician age. These rocks were folded during the Acadian Orogeny of Devonian age into northeast- to north trending upright folds. During Devonian and Carboniferous times these rocks were intruded by granites. Throughout the Carboniferous, non-marine and minor (in extent but important economically) marine sedimentation occurred upon the older rocks in downfaulted and warped areas.
The area to the north of the Cobequid-Chedabucto Fault System is geologically more complex and difficult to generalize. On mainland Nova Scotia, lower to middle Paleozoic with minor Proterozoic rocks occur in two areas known as the Cobequid and the Antigonish Highlands. Adjacent to these blocks, thick successions of Permo-Carboniferous non-marine and minor marine sediments occur in faulted and folded rift basins and/or synclinoria of various sizes.
Hadrynian or older Proterozoic sedimentary and volcanic rocks crop out in much of northern Cape Breton Highlands and along SE Cape Breton Island. Smaller basement horsts occur scattered throughout the remaining area. In SE Cape Breton Island these rocks are overlain by a lower Paleozoic sequence of Precambrian to Cambrian sedimentary and volcanic rocks. Granitic and minor basic plutons of Carboniferous, Devonian and possibly Ordovician or older age intrude the older deformed rocks. As on mainland Nova Scotia, a very thick succession of non-marine and minor marine sediments occur in faulted and folded basins and synclinoria that developed adjacent to and on top of the older rocks.
Glaciation has played a major role in moulding the present day topography and Pleistocene glacial deposits, both till and glaciofluvial deposits, mask much of the bedrock.
1.4 Stratigraphic Range of Metallic Mineral Deposits
Nova Scotia has had a long mining history with the first recorded coal export being a shipment from Cape Breton to Boston in 1724. Coal, hosted by Upper Carboniferous siliclastic rocks, and gypsum and salt, hosted by Lower Carboniferous rocks contribute significantly to the provincial mining industry.
Metallic mineral deposits have played an important role in the Nova Scotian economy, and deposits from a wide range of the stratigraphic column have been mined (Fig. 3).
The purpose of this paper is to identify the main geological environments or deposit classes which hold potential for base metal production in the province. The following classification of the main environments is proposed and the deposits representative of each class are shown on Map 1:
-
The Precambrian volcano-sedimentary massive sulphide environment is exemplified by the Stirling deposit in SE Cape Breton Island, the Coxheath Hills Cu (Zn) deposit adjacent to Sydney, Cape Breton Island and the massive sulphide deposits (primarily pyrite) in the southern Antigonish Highlands of northern Nova Scotia. It should be noted that the volcanogenic-hosted deposits in the Cheticamp area of northwestern Cape Breton Island, which formerly were considered to be hosted by volcanics of Precambrian age, have been shown by Lynch and Tremblay (1992) to be of Silurian age.
At Stirling, intermittent mining operations since the late 1920s have milled 1.06 million tonnes of ore grading 6.3% Zn, 1.5% Pb, 0.8% Cu, 74 g/t Ag and 1.1 g/t Au. Total metal production over the life of the mine was 48,684 tons zinc, 10,348 tons lead, 4,920 tons copper, 1,302,776 oz. silver and 16,492 oz. gold (Roscoe, 1986). Exploration is currently underway on the property.
-
The shale-hosted mineralization in the Precambrian sedimentary rocks of the Antigonish Highlands in northern Nova Scotia is considered to be representative of this class of deposit. Elsewhere in Canada shale-hosted deposits have contributed greatly to the base metal inventory.
The type deposit for this class is the Georgeville property where exploration has identified low grade (1%) zinc mineralization over intersection lengths of 17 m with greater lengths (52 m) of lower grade (0.69% Zn). The mineralized horizon has been tested by nine drillholes over a strike length of 5 km and the description of mineralization in fractures may suggest remobilization of syngenetic mineralization or introduction at a later time.
The Kirkmount (Kirkmount) property, in the western part of the Antigonish Highlands, represents a shale-hosted deposit where zinc mineralization is present in silicate form and core assays averaged 1.66% Zn over 21 m in one drillhole. Shorter and higher grade sections occur.
-
The marble-hosted (George River Group) metallic deposits in the pre-Carboniferous rocks of Cape Breton Island comprise two major categories. Polymetallic skarn mineralization is related to a discrete contact metamorphic or metasomatic event and may be hosted both in the carbonates and the intrusives. Stratabound mineralization is generally restricted to a discrete carbonate unit, is not related to a definable contact metamorphic event, and the associated calc-silicate assemblages are interpreted as reflecting regional rather than local contact metamorphism.
Two deposits, Meat Cove and Lime Hill, illustrate the stratabound marble-hosted deposit type. Both have undergone substantial drilling and Meat Cove has been investigated by underground workings. Zn-Pb sulphides are present in both; Meat Cove has associated Ge and Cd values, and wollastonite is associated with the Lime Hill deposit.
-
A significant base metal deposit, hosted in metasediments of the Meguma Group (Cambro-Ordovician), was discovered at Eastville in 1977. Limited drilling along a 10 km strike length intersected Zn-Pb mineralization over 2-10 m sections and grading between 1% to 3% combined Zn-Pb at various stratigraphic positions within a 100 m interval. Best intersections were 3.34% Zn-Pb over 6.1 m and 4.09% Zn-Pb over 9.33 m. The deposit is classified as a distal type sediment-hosted stratiform deposit remobilized by subsequent tectonic activity. Minor base metals have been identified in the Meguma-hosted gold deposits, which abound in southern Nova Scotia, and there may be some association between these two types of deposits.
Of interest are the Meguma-hosted Sn deposits in southwestern Nova Scotia with which significant base and precious metals are associated. These are discussed under granite-associated deposits.
-
The carbonate-hosted environment is represented by the Carboniferous Gays River, Jubilee, Walton, Smithfield, Brookfield and Enon deposits, and the Gays River deposit is illustrative of the class. Production was achieved at Walton (for Ba and Pb, Zn, Ag), Gays River (for Zn, Pb), Brookfield (Ba) and Enon (for Sr). The other deposits have been subjected to fairly intensive exploration including detailed diamond-drilling and underground exploration (Smithfield). a carbonate-hosted Cu deposit of probable Silurian age occurs at Lochaber Lake in Antigonish County and potential exists along the bounding fault.
-
In 1962, exploration programs initiated as a result of exploitation of the argentiferous base metals at Walton, led to the discovery of the Upper Carboniferous sandstone-hosted Yava Pb deposit in the Salmon River Basin of Cape Breton Island. In the period 1962-1978, various drilling programs showed stratiform lead mineralization at the base of the Upper Carboniferous sandstone over a strike of nearly 3 km and for a distance down-dip of 450 m.
Total ore reserves for the three zones identified amount to 12 million tons at 4.0% Pb (3.5% cut-off), or 19.1 million tons at 3.4% Pb (2.5% cut-off). Mining was carried out on one zone from 1979-1981 and 428,000 tons at 4.75% Pb were milled.
The Terra Nova deposit, also within the Salmon River Basin and immediately north of the Lake Enon deposit, is similar, though it does carry significantly higher Zn values than at Yava. Analogies may also be drawn with the sandstone-hosted Cu deposits in the Cumberland Basin of northern Nova Scotia where the Upper Carboniferous, sandstone-hosted Canfield Creek deposit contains drill-indicated reserves of 300,000 tons at 1.2% Cu with minor Ag values. In addition, the shale-hosted Cu deposits in the Cumberland Basin show similarities with the Kupferschiefer deposits of Poland and this potential is currently under investigation.
-
The granite-associated class of deposits includes both granite-and metasediment-hosted bodies. The East Kemptville Sn Mine, which ceased production in January 1992, was the only primary Sn mine in North America and illustrates the granite-hosted sub-class. During the five years of operations some 19 million tonnes were milled at 10,000 tpd and by-product Cu, Zn and Ag were also recovered. This greisen-type granite-hosted deposit was brought into production on published reserves (Moyle, 1985) of 56 million tons at 0.165% Sn.
Mineralization within the southwestern Nova Scotia tin domain consists of both granite- and metasediment-hosted types, which are spatially (and probably also genetically) related to the regional East Kemptville shear zone. The Duck Pond deposit, some 2 km west of the East Kemptville open pit, represents the metasediment-hosted sub-class.
Additional granite-associated mineralization is known at the Coxheath and Deep Cove deposits, both in Cape Breton Island.
- Recent work by Lynch and Tremblay (1992) has shown that the Cheticamp volcanics are of Silurian age. Recent drilling by the Nova Scotia Department of Natural Resources has identified "sulphide-rich black shales" in upper Silurian rocks (Smith, 1992, in press) and the reference to the possible Silurian age of the host limestone the Lochaber Lake Cu deposit all point to the existence in Nova Scotia of an important, but poorly documented, exploration target in the Lower Paleozoic rocks.
1.5 Nova Scotia Mineral Production
Since the mid 17th century the mining industry has contributed significantly to the economic and social life of Nova Scotia. Production over the years has included coal, salt, gypsum, anhydrite, barite, celestite, iron, manganese, copper, lead, zinc, silver, gold, antimony and tin. Though uranium deposits are known, a government moratorium does not permit continued exploration or development of these deposits.
Among the metallic minerals, gold was very significant during the 1800s and, though intense exploration and underground development in the mid to late 1980s confirmed the depth potential of these deposits, no viable commercial production was sustained. It should be noted, however, that in the period 1862-1942 gold production from the Goldenville District amounted to 210,000 oz. (5,800,000 g) (Donohoe, 1984). Figure 4 shows that the majority of this production came in the period 1862-1912.
Commercial production of base metals began in the early 1900s and the intermittent production, (Fig. 4) reflects mining activity at Smithfield, Stirling, Walton, Gays River, Yava and East Kemptville. The Gays River Mine was reopened briefly in late 1990 but by early 1992 all base metal production had ceased in the province. The major tin production came from the East Kemptville operation, which also produced by-product cooper and zinc. Production at this mine ceased in January 1992.
Base metal production came from deposits hosted in a variety of geological environments and stretching the length of the province. The combination of this diversity of this diversity of proven geological environments with the fact that thick glacial deposits mask much of the favourable geology suggests that continuing exploration of these environments will be rewarding.
The value of total mineral production in the province has shown a steady increase since the early 1980s (Fig. 5). However, metallic mineral production has accounted for less than 10% of the total and the recent closure of both the Gays river and East Kemptville mines will further reduce the value of metallic minerals production. However, the possibility of recommencement of production at Gays River, together with continuing base metal exploration programs, hold promise for the industry.
Figures: (Not presently available)
Figure 1. North American orogenic and mineral production provinces.
Figure 2. Simplified geological map of Nova Scotia.
Figure 3. Stratigraphic range of main metallic deposits in Nova Scotia.
Figure 4. Nova Scotian historic metallic mineral production (NSDNR Annual Report for 1990).
Figure 5. Value of mineral production in Nova Scotia and sectoral allocation (NSDNR Annual Report for 1990).
2. Volcanogenic Deposits: Stirling
2.1 Introduction
Volcanogenic-hosted massive sulphide deposits are widespread, both geographically and geologically, and contribute a major part of the world's base metal supply.
Typically these deposits consists of >90% iron sulphide, usually as pyrite, but also as pyrrhotite in some deposits. They are generally stratiform, lenticular to sheet-like bodies developed at the contacts between volcanic units or at volcanic--sedimentary interfaces. Typically the deposits are conformable and commonly they are banded; it was only in the 1950s that they were recognized to be syngenetic, submarine sedimentary exhalative, rather than replacement, deposits. The processes of formation of such deposits can be studied today in the deep ocean basins and such research has extended our understanding of the processes involved.
Volcanic-associated massive sulphide deposits show a progression of types based on host rock, paleotectonic setting and mineralogy. Cyprus-type deposits are essentially cupriferous pyrite bodies associated with basic volcanics (ophiolites) which were formed at oceanic or back-arc spreading centres or ridges. Besshi-type volcanogenic massive sulphides are associated with the early part of the main calc-alkaline stage of island arc formation and thus occur in mafic volcanics in complex structural settings which are characterized by thick greywacke sequences. They commonly carry zinc in addition to cooper. The Kuroko-type volcanogenic massive sulphides are associated with the more felsic volcanism characteristic of the late stage of island-arc evolution. They are represented by the copper-zinc-lead ores (+gold and silver) of the Canadian Shield and may contain barite and gypsum.
Stanton (1978) considered these ores to be part of one continuous spectrum showing a progressive chemical evolution coincident with the evolution of calc-alkaline rocks in island arcs. This view assists explanation of the overlap between the various types. It should be noted that Hutchinson (1980) suggested that the polymetallic massive sulphides of the Canadian Shield should be assigned to a new class, the Primitive-type, which he defined as a variation of the Kuroko-type. Evans (1987) concluded that the confusion in determining the class of volcanogenic deposits may indeed by due to overlapping criteria and supports Stanton's view that they probably represent a continuing spectrum.
Whereas the submarine-hydrothermal origin of these deposits is well established and accepted, the ultimate source of the metals is still open to question. Whether the meals originated from a magmatic source or were leached from the crust by circulating waters is the subject of much debate. However, the processes of emplacement and, of equal importance, preservation of the deposits are widely accepted.
The characteristic features of volcanogenic massive sulphide deposits are well described in the literature and can be most useful in guiding exploration both before and after discovery. The major factor, from an exploration viewpoint, is that such deposits tend to cluster around volcanic domes occurring at irregular intervals along volcanic belts. It should be noted that the Kuroko deposits in Japan are associated with Miocene volcanics and sediments for 800 km of strike. More than 100 occurrences are known along the belt and most are clustered into nine districts. Thus, exploration outward from known centres is not only prudent, but is mandatory for continued discovery.
Within Nova Scotia the Stirling Volcanic Belt of southeastern Cape Breton Island is host to a massive sulphide deposit that has sustained production in the past. The Stirling deposit, described by Miller (1979) as a distal exhalative-sedimentary deposit of the Kuroko type, is used to illustrate this class.
2.2 Location
The Stirling deposit, also known as the Mindamar Mine, is located in Richmond County, Cape Breton Island at 60°25' W and 45°44' N (Fig. 6). The deposit, on NTS map sheet 11F/09C, is situated approximately 72 km southwest of Sydney, from where it is accessed by paved and good secondary gravel roads.
2.3 Exploration History
Mineralization was first discovered in Copper Brook in the 1890s and a small copper open-pit was mined very briefly in 1904. During investigations for zinc by Barytes Ltd. In 1915, fine-grained Zn-Pb-Cu sulphides were discovered in trenches. The complex metallurgical nature of this ore prevented exploitation at that time but exploration, including diamond-drilling and a small underground exploration program, continued up to 1925 but without success.
In 1927 British Metals, Operating as Stirling Mines Ltd., deepened the old shaft to 240 m, carried out an underground development program and installed a 250 tpd mill. Mill capacity was increased to 300 tpd in 1930 but operations ceased in December 1931 due to low metal prices. Upon resumption of operations in 1935, 3400 m of development and 8200 m of diamond-drilling were carried out prior to cessation of operations in 1938.
In 1949 Mindamar Metals Corporation carried out an underground development program of sampling and diamond-drilling. Dome Explorations Ltd. assumed management of the Mindamar operation in 1951, installed a 500 tpd mill which was increased again to 650 tpd in 1954, and sank a new four-compartment shaft to 357 m. This operation continued to April 1956.
Between 1965 and 1969, Keltic Mining Corp. conducted ground geophysics and drilled 2500 m within the limits of the old workings without success. Penarroya then optioned the property from Keltic and drilled three holes without much encouragement.
Cominco staked the ground in 1972 and carried out geological mapping, airborne geophysics (EM-Mag-VLF), ground IP and magnetics, and diamond-drilling. In 1975 St. Joseph Explorations carried out airborne EM and magnetometer surveys and Amax Exploration Inc. conducted a reconnaissance silt and soil survey. Six drill holes (700 m) were drilled by Amax in 1981-82 and minor mineralized zones were encountered.
In 1979 Cominco re-flew the area and conducted regional stream sediment geochemical and geological mapping surveys. This program revealed a number of outcrops of pyritic chemical sediments enriched in base and precious metal values some distance from the Stirling Mine. In the same year, A. S. Macdonald discovered mineralized chemical sediments to the south at Point Michaud Beach.
In 1983 Selco carried out an airborne EM survey over the general area. Falconbridge Ltd. carried out an airborne magnetic and EM survey in 1989 over their claim block located northeast of the mine area. They also completed an orientation lithogeochemistry survey. Diamond-drilling was undertaken by Falconbridge during 1991.
The former mine site and adjacent claims are currently held under Special Licence 4/83 issued to A. Douglas Hunter. Exploration has continued at a slow pace and has included 7456 m in 13 diamond-drill holes and a minor amount of orientation geophysics and lithogeochemistry. Further diamond-drilling was carried out in early 1992.
2.4 Evolution of Models
The first systematic mapping of the area was done by H. Fletcher in 1878, who ascribed the volcanic package to a pre-Silurian group. Matthew (1903) remapped the area and assigned a Cambrian age to the volcanics.
Cairnes (1917), in the first description of the Stirling area, interpreted the mineralization to be a metasomatic replacement of the host "andesitic" rocks and this replacement theory was supported by other authors between 1919 and 1959. Watson's detailed petrological studies (1954, 1957 and 1959) interpreted the ore as a replacement phenomenon. Wilband (1962 and 1963) identified a full range of composition from rhyolite to basalt, while Helmstaedt and Tella (1973) indicated a calc-alkaline affinity for the Bourinot Group volcanics.
The emerging recognition that similar deposits elsewhere were volcanogenic in origin caused Poole (1974) to suggest that the Mindamar deposit at Stirling was of synvolcanogenic derivation with superimposed tectonic, metamorphic and hydrothermal effects.
2.5 Regional Geology
The rocks of SE Cape Breton Island are part of the Avalon Platform (Poole, 1967), Belt (Rodgers, 1972) or Zone (Williams et al., 1974), which stretches along the southeastern margin of the northern Appalachians from the Avalon Peninsula of SE Newfoundland through Nova Scotia, New Brunswick and into eastern Massachusetts (Helmstaedt and Tella, 1973). Segments of this belt are characterized by late Precambrian (Hadrynian volcanic and intrusive rocks which have been affected by the Avalonian Orogeny) (Rodgers, 1972) or Ganderian Orogeny (Kennedy, 1976).
Weeks (1954) used lithological evidence to suggest a Lower Cambrian age for the host Bourinot Group volcanic-sedimentary rock package in SE Cape Breton Island. Smith (1978) renamed these rocks the Giant Lake Complex, which he correlated with the Fourchu Group of possible Hadrynian age. Miller (1979) proposed a Middle Cambrian age for the group in the Stirling area. Macdonald (1989) agrees that the rocks in the belt may be a time correlative of the Fourchu Group though he sees some significant differences. He refers to this belt as the Stirling Volcanic Belt.
Macdonald (1989) describes the Stirling Volcanic Belt, extending for 50 km along a northeast-southwest direction, as containing a wide variety of metamorphosed volcanic, volcaniclastic and epiclastic rocks which have been intruded by an abundant suite of mafic sheets and by several granitoid plutons and related dyke rocks. Volcanic and pyroclastic rocks (80%) dominate the sequence and the pyroclastic component (50%) appears to increase gradually toward the northeast. Intermediate to mafic lava flows grade into flow breccias and coarse lithic tuffs, and chemical analyses indicate that these lavas are mainly basalts or basaltic andesites. Felsic lavas are mainly basalts or basaltic andesites. Felsic lavas are also present and are represented by feldspar porphyritic dacites and quartz feldspar porphyritic rhyodacites. a variety of foliated intermediate to felsic tuffs are present throughout the belt but are most abundant in the northeastern part. Doyon and Van Wagoner (1992) recognize a lower unit comprising rhyolite flows, felsic pyroclastic and epiclastic rocks with laminated siltstone, dolomite and minor chert in the northeast part of the belt. This unit is overlain by fine- to coarse-grained epiclastic rocks.
The epiclastic rocks are represented by volcanic wackes which exhibit erosional features and graded bedding and a relatively thick (200-300 m) siltstone sequence with disseminated pyrite. Macdonald (1989) mapped minor carbonate occurrences within the belt and notes that they occur as conformable bands and lenses up to tens of metres thick within tuffs and siltstone or both. The carbonate rock is predominately dolomite with coarse calcite and patches and laminae of "possibly recrystallized chert."
The unconformably overlying sedimentary cover rocks (the Kelvin Lake Formation) comprise a red clastic sequence and have been assigned an early-middle Cambrian age by Smith (1978) and Keppie (1979) most of these rocks are unmetamorphosed apart from local hornfelsing, and Macdonald (1989), from field relationships, proposes an early Cambrian age, thereby confirming a Late Precambrian age for the underlying metavolcanic basement.
Macdonald (1989) recognises three phases of deformation in the belt, whereas major structural evidence suggests two phases of folding. Fracture cleavage is present and shear zones, subparallel to the regional strike and dipping steeply, are commonly developed within the metamorphic basement sequence. Two strong sets of joints, subparallel and subperpendicular to the main (D1) structural trends are dominant. Large scale faults, subparallel slightly oblique to the main structural trends, have a strong vertical displacement and no direct evidence of strike-slip displacement was found by Macdonald. Macdonald's mapping suggests that the Stirling Fault may not extend as far to the southwest as shown by Weeks (1954) and he concludes "it is probably a much less important structure than previously considered."
The Stirling Belt of rocks are predominantly of low metamorphic grade and the evidence suggests conditions transitional into lower greenschist facies. The petrochemistry suggest that the volcanic rocks are consistently calc-alkaline, presumably generated in an orogenic magmatic arc, whereas the intrusive mafic sheets are tholeiitic in composition and may have been generated in a different tectonic setting.
2.6 Mine Geology
2.6.1 Stratigraphy and Ore Zone Geology
The sulphide bodies at the Stirling Mine occur within a steeply-dipping Mine Volcanic Sedimentary Unit (MVS). Hunter (1984, 1987) has modified Miller's (1979) nomenclature and describes the mine stratigraphy as presented in Figure 7.
The Middle River Formation, comprising massively bedded and siliceous clastics, has an apparent faulted relationship with the underlying mine volcanics and sediments. The Hanging Wall Lapilli Tuff (HLT) is pumiceous lapilli tuff with primary features characteristic of hot ash-flow tuffs. The Crystal Lithic Tuff (CLT), which forms the hanging wall to the Mine Volcanic Sedimentary Unit, is a fine- to coarse-grained massive tuff. Thin mudstones show bedding and the tuff coarsens toward the base of the unit.
The Mine Volcanic Sedimentary Unit (MVS), the ore host, is a bedded sequence of vari-coloured pyritic mudstone/siltstone and chemical sediments (both cherty and calcareous). The upper part of the unit comprises mudstone and siltstone with minor chert. The rocks become increasingly siliceous with depth and dense, massive chert layers are a significant component of the basal beds of this unit. In the lowermost portion, massive siltstone and sericitic tuffaceous layers with angular chert clasts are interbedded with siliceous chemical sediments. Sedimentary features indicate westward facing beds and abrupt contacts at the base of pyrite-rich layers grade upward through diminishing pyrite content. Soft sediment deformation, slump structures and ripple marks are present, though rare, in the dump material (Miller, 1979).
The Quartz-Carbonate-Talc Unit (QCT) is a bedded chemical sediment comprising dolomite, magnesite, quartz, sericite, talc, chlorite, barite, albite and alunite. The QCT, which in places is highly schistose, hosts the majority of the ore lenses with the remained in the overlying cherty, calcareous, pyritic mudstone. Talc content varies within the unit and up to 50% in strongly sheared rock. Talc content up to 80% was reported from the lowest levels of the mine. The massive sulphide lenses occur where the QCT is thickest. Roscoe and Hunter (1976), Roscoe (1986), and Hunter (1984 and 1987) regard the environment as a typical volcanogenic massive sulphide deposit with exhalative activity. Later preferential deformation or 'shearing' was confined to the QCT due to its high clay/mica content (Curtis, 1988)
Richardson (1953) described three large lenticular quartz-carbonate bodies within the Mine Series. Within the quartz-carbonate rock, minor concentrations of sulphides occur as ubiquitous disseminations, isolated blebs, and clasts, or in massive layers 1-2 cm thick. Pyrite Sphalerite and chalcopyrite occur as fine-grained disseminations within the quartz-carbonate rock.
Hunter (1984) states that the QCT unit, (the Quartz Carbonate of Miller) and the ore-bearing stratigraphic entity, has been traced for over 4000 ft. of strike by diamond-drilling. Though generally 50-100 ft., thick it can attain thickness of 200 ft. locally.
Small sulphide concentrations have been found within the adjacent volcanic rocks (James and Buffam, 1937).
The stratigraphic footwall rocks are referred to as the Footwall Rhyolite (FWR) and comprise predominantly massive felsic flows with minor pyroclastics and siltstones. Some of the flows are intensely fractured and brecciated and exhibit a fracture cleavage. Carbonatization is commonly associated with intense shearing and the rhyolite has been transformed into a quartz-calcite-sericite schist. Narrow zones (10-30 cm) of thin-laminate siltstones, similar in chemical composition to the rhyolites, occur between the rhyolite flows. Intermediate to mafic flows occur in the footwall position to the east of the rhyolites and contain up to 10% magnetite which, locally, has been oxidized to hematite.
Within the mine area mafic intrusions account for 30% of the total Mine Series (Richardson, 1953). Miller reports that these intrusions often constitute 50% of the total rock in drill core and that the volume of these intrusives decreases with depth. In fact, the upper levels in the northern part of the mine were uneconomic due to the large volume (30%) of intrusive material. Hunter (1987) reports that only minor intrusives were intersected in his drill program. The major intrusions are sill-like, vary from vertical to near horizontal, and are up to 22 m thick (Watson, 1954). Generally the intrusions are very irregular in form, pinching and swelling laterally and vertically, and locally they can be offset by younger shears (Miller, 1979). These essentially chloritic intrusions have been saussuritized and sheared, and pyrite and magnetite locally constitute 10% of the rock. Watson (1954) and Miller (1979) both conclude that they postdate the mineralization.
2.6.2 Structure
Bedding within rocks of the 'Mine Series' strikes NE and dips vertically or steeply to the east. This is parallel to the strike and dip of the ore zone (Fig. 8) and the banding within the massive sulphides (Miller, 1979). The average strike of the ore zone is 030° and the dip is 80°-85° SE (James and Buffam, 1937). Way-up evidence within the sediments indicates that the beds are westward facing, implying that the rocks of the Mine Series occur on the western limb of a slightly overturned anticline.
The altered quartz-carbonate-talc rock, formerly referred to as the Mine Shear, is approximately 100 m wide and roughly parallel to bedding. It has been traced underground for approximately 120 m along strike and to a depth of 350 m (Watson, 1957), though Hunter, as noted above, states that it has been traced for over 1300 m of strike by diamond-drilling and to a depth in excess of 750 m. Post-ore faults are numerous with two distinct sets closely related to individual ore lenses (Watson, 1957). One set, striking 005° and dipping 70° SE, causes an apparent thinning of the ore zone at depth while a second set, striking parallel to the ore zone and dipping 45° NW, causes a narrowing of the ore zone towards the surface (James and Buffam, 1937). a third set of faults causes apparent horizontal displacements of 15-30 m, and Watson (1957) suggested that the Stirling Fault may dip steeply SE and may truncate the 'Mine Shear'.
2.7 Ore Mineralogy and Metal Distribution
Miller (1979) describes the sulphide mineralogy as comprising idiomorphic pyrite with, in decreasing abundance, sphalerite, galena, chalcopyrite and tennantite.
Pyrite occurs as ubiquitous fine-grained disseminations throughout the massive sulphides and as the dominant component in distinct, sharply bounded layers. Most pyrite grains have been fractured and locally recemented by sphalerite, galena and chalcopyrite.
Sphalerite is concentrated in layers or lenses that parallel or cross the foliation. Though the sphalerite lenses are elongated the individual grains have an equigranular crystalline texture. Sphalerite also occurs as interstitial material in zones dominated by quartz-carbonate or pyrite, and zones of massive sphalerite contain inclusions of galena, chalcopyrite and tennantite.
Chalcopyrite, galena and tennantite may occur as (i) randomly-orientated interstitial infillings to pyrite, sphalerite or quartz-carbonate; (ii) inclusions in, or coatings on, pyrite and sphalerite; and (iii) a cement to aggregates of pyrite grains and as discrete grains. Textural relationships suggest contemporaneous crystallization. Tennantite is closely associated with galena and is commonly rimmed or veined by chalcopyrite. Barite is rare.
Watson (1954) reports that pyrite constitutes about 10% of the entire mineralized zone and about 20% of the actual ore. Sphalerite constitutes 10-15% of the ore, chalcopyrite 3%, galena 1-2% and tennantite <1%. It would appear (Haycock, 1934) that silver is associated with tennantite while gold, which has not been observed in the ore, has not been reported in the zinc concentrate.
Richardson (1953) noted that individual sulphide lenses within the central "quartz-carbonate" body ranged from 12-120 m long, were up to 18 m wide, averaged generally 6 m for the mineable lenses and contained from 10,000 tons to 500,00 tons of ore. The footwall and hanging wall of the higher grade lenses are abrupt but pyrite mineralization is present in the adjacent enveloping rocks (Weeks, 1924). Laterally the ore lenses terminate gradually with an increase in the pyrite content and also with a decrease in the dip of the lens. In some instances lenses are terminated by cross faults (Richardson, 1953) and intrusions (Watson, 1954; Miller, 1979).
2.8 Production Data
Intermittent operations since the late 1920s have milled 1.06 million tonnes of ore grading 6.3% Zn, 1.5% Pb, 0.8% Cu, 74 g/t Ag and 1.1 g/t Au.
A total of 92,931 tons of Zn concentrate grading 52.4% Zn was produced and represented a recovery rate of 73%. Some 43,486 tons of mixed Pb-Cu concentrates were produced and graded 23.8% Pb (66.5% recovery); 11.31% Cu (63% recovery); 29.96 oz. Ag/ton (56.5% recovery) and 0.379 oz. Au/t (47% recovery). Total metal production over the life of the mine was 48,684 tons zinc, 10,348 tons lead, 4920 tons copper, 1,302,776 oz. silver and 16,492 oz. gold (Roscoe, 1986).
Both the main and north ore zones plunge moderately northward and Curtis (1988) suggests that potential may exist in this direction.
The mine was accessed by two vertical shafts and tracked mining methods were used. The last production phase ended in 1956 when a 650 tpd mill was in operation.
2.9 Exploration Techniques
Due to the thick overburden cover in the area, outcrop is relatively poor and direct geochemical techniques have not been particularly successful. Hunter (1987), and Falconbridge (1989) on an adjacent property, state that lithogeochemistry is especially useful in locating alteration zones and specially note the marked Na2O depletion in altered tuff zones.
Geophysics have been widely used and the massive sulphide nature of the deposit has made it a target for airborne methods. Several surveys have been flown but with little response and the deposit is noted as a poor conductor by Mersereau (1988). Miller (1984) reports that the Stirling deposit gives a weak EM response and concludes that the conductive sulphide minerals (pyrite, chalcopyrite, galena) are insulated by sphalerite or gangue, but concludes that weak conductors should not be ignored. Ravenhurst (1987), reporting on a downhole pulse EM survey, confirms the weak conductivity but indicates the presence of off-hole anomalies.
Falconbridge report that airborne magnetics are helpful in mapping and EM data indicate areas requiring follow-up. Ground gravity traverses were also tried over the known mineralization in 1984 but a lack of response.
2.10 Mineral Showings Along the Stirling Belt
The Stirling Belt extends for some 50 km in a northeast direction in SE Cape Breton Island and mineralization has been recorded from several localities along the trend. Barr et al. (1988) have traced the favourable geological host rock package along strike in both directions from the mine. These showings comprise stratabound to thin stratiform framboidal pyritic exposures, some of which carry elevated Cu, Zn and Au values (Mosher, 1979; Macdonald, 1982).
Doyon and Von Wagner (1992) document a new showing in the Mine Series some 2 km northeast of the mine and Macdonald (1989) describes stratabound to stratiform disseminated pyrite in Mine Series lithologies at Caledonia Road, (occurrence 8, Fig. 6), approximately 11 km northeast of the shaft. Amax, drilling on the claims southwest of the mine, intersected minor Cu and Au values in a chemical sediment in 1981, and Aurion Minerals (personal communication, 1991) reported an angular massive sulphide boulder in an area approximately 4 km southwest of the shaft. This boulder assayed 12.7% Zn; 4.5% Pb; 0.5% Cu; 6 oz. Ag/t and 0.03 oz. Au/t, but no further information as to the source of the boulder is available.
Stratabound, disseminated pyrite mineralization occurs in the Mine Series lithologies at Point Michaud Beach, (occurrences 14 and 15, Fig. 6), a distance of 20 km southwest from the mine. Macdonald (1989) also describes massive pyrite lenses and pods occurring at the contact between rhyolite and bedded tuffs immediately southwest of the mine and also at Taylors Brook, (occurrence 12, Fig. 6), some 11 km to the southwest. These massive pyrite pods are several metres long and up to a maximum of 30 cm wide, whereas the disseminated style of mineralization occurs in diffuse zones 1-2 m thick and in excess of 10 m long. Within these zones, local richer stratiform concentrations up to a few centimetres thick occur. Pyrite is the dominant sulphide in both types and sphalerite is present in very small amounts in about 30% of the samples collected by Macdonald. Chalcopyrite is very rare. These observations are confirmed by analyses of some of the pyrites.
2.11 Conclusion and Exploration Potential
Much of SE Cape Breton Island has been affected by at least three periods of folding, two periods of granitoid intrusion and at least four episodes of mineralizing activity. Two of these mineralizing episodes occur within Precambrian-possible Cambrian rocks of the Stirling Belt and Macdonald (1989) describes two types of associated mineralization.
Type 1 mineralization is described as exhalative sedimentary Fe-Zn-Pb-Cu-(Ag, Au) within favourable stratigraphic sequences of interfaces. Type 2 is contact metasomatic Fe-Zn-Cu mineralization adjacent to the Loch Lomond pluton. Macdonald describes a third type which is associated with the high level stocks and plutons of Devono-Carboniferous age and suggests that favourable host rocks, both volcanic and sedimentary, exist as potential sites of accumulation for more distal deposits related to these events. In the immediate vicinity of the old mine, Hunter (1987) has shown the presence of the Mine Series with anomalous base metal values some 600 m below the old workings (Fig. 9). Curtis (1988) confirms this and outlines two main target zones within the immediate mine area. The Mine Volcanic Sediments have been intersected along strike to the north and anomalous base and precious metal values reported. One hole assayed 1.64% Zn/22 m within the quartz-carbonate unit. Another hole in this program intersected the Mine Volcanic sedimentary unit approximately 600 m below the old workings (Fig. 9) and a 15.5 m section of this, carrying from 5-25% pyrite, is anomalous in zinc (0.34%). It is reported that the Falconbridge drilling in 1991-92 indicated encouraging results along strike from the mine, while drilling by Outokumpu on the mine property in early 1992 also met with encouragement.
Sangster (1972) suggested that the Mindamar deposit bears many similarities with the Kuroko massive sulphides of Japan, and Miller (1979) regards the deposit as distal sedimentary exhalative. Analogies with similar deposits in the Canadian Shield suggest that additional targets will exist along strike and down dip and plunge. Thus, additional prospective horizons will exists where repeated extrusions of felsic volcanics have taken place.
Recent mapping programs have shown the presence of massive and disseminated pyrite with minor base metal values along the total length of the Stirling Volcanic Belt. It is suggested that a further examination of this prospective belt, using modern geophysical and computer techniques, allied with appropriate lithogeochemistry and geochemical methods, followed by diamond-drilling, could be most rewarding.
Photo: (Not presently available)
Stirling (Mindamar) mine site. Glory holes (flooded) with tailings on right.
Figures: (Not presently available)
Figure 6. Geological map of SE Cape Breton Island showing location of the Stirling deposit (Macdonald, 1989).
Figure 7. Stirling deposit - stratigraphic section (after Miller, 1979, and Hunter, 1984 and 1987).
Figure 8. Stirling deposit - simplified local geology (Hunter, 1984).
Figure 9. Stirling deposit - vertical section showing exploration potential at depth (after Hunter, 1987).
3. Shale-Hosted Deposits: Georgeville
3.1 Introduction
The shale-hosted base metal sulphide deposits of the Selwyn Basin of western Canada contribute significantly to the national mineral inventory. Analogies have been drawn with similar deposits worldwide and essentially they comprise sulphide bodies hosted in carbonaceous shales or other fine-grained clastic rocks ranging in age from Proterozoic to upper Paleozoic. The Selwyn Basin deposits occur in shales ranging from lower Cambrian to upper Devonian in age and are regarded as sedimentary exhalative in origin.
Within Nova Scotia the shale-hosted mineralization in the Precambrian sedimentary rocks of the Antigonish Highlands is considered to be representative of this class of deposit and it is suggested that continued exploration of the deposits identified to date is warranted.
The type deposit for this class is the Georgeville property on the west side of the Cape George peninsula in the Antigonish Highlands (Fig. 10). Exploration has identified low grade (1%) zinc mineralization over intersection lengths of 17 m with greater lengths (52 m) of lower grade (0.69% Zn).
Nine drillholes have tested the horizon over a strike length of 5 km and the description of mineralization in fractures may suggest remobilization of syngenetic mineralization or introduction at a later time.
3.2 Location
The Georgeville deposit is situated on the west side of the Cape George Peninsula, Antigonish County, at 61°59'32" W and 45°51' N, and some 21 km north of Antigonish town. The Georgeville property, on NTS map sheets 11E/13 and 11E/16, has been the subject of exploration activity since 1953.
3.3 Exploration History
Bridger (1953) described four separate showings in "bands of sediments within the diorite", and though confined to the sediments, the mineralization "appears to be confined at or close to the contact with the diorite." Radioactive minerals were also identified in this survey.
Beavan (1954) reported on an exploration program comprising geological mapping and geophysical surveys by Brinex. The radiometric survey confirmed a small area in pegmatite within which cryolite was confirmed. However, he concluded that only sparse mineralization was indicated in the diorite and no further work could be recommended.
McPhar Geophysics (1955) reported on work in the area on behalf of Eastern Northern Explorations Limited. Geological mapping, and geochemical and geophysical surveys were undertaken and up to 3% Zn was noted in argillite outcrop. Both geochemical and geophysical surveys showed positive responses.
Attention was again focused on the area by the maps published in 1959 by the Geological Survey of Canada reporting on heavy metal stream surveys by R. H. C. Holman. Work conducted by C. G. Cheriton (1960) for Ivan C. Stairs of Bathurst, N. B., confirmed these anomalies by limited soil sampling. Ground magnetometer surveys indicated two "significant" anomalies, while a weak NE-trending anomaly was interpreted as possibly representing a fault or fracture zone.
The first detailed exploration was carried out by new Jersey Zinc from 1967 to 1970, and an assessment report dated 16 November 1970 by C. Cunningham gives a comprehensive description of the work program and results. New Jersey referred to the area as the Greendale property.
In 1976 Noranda optioned the property from Gold Brook Developments and utilized SP and magnetometer surveys to locate drill targets. Noranda hole N-76-2 was sited approximately 450 ft. southwest from NJZ hole #6 (Fig. 11).
3.4 Geology
The rocks in the area comprise sediments of the Morar Brook Formation, represented by shale, slate, argillite, greywacke, minor conglomerate, chert and limestone, and a fossiliferous hematite formation; and volcanics of the Chisholm Brook Formation comprising tuff, andesite and fragmental volcanics. Previously assigned to the Brown's Mountain Group of Ordovician age, mapping by Murphy et al. (1982) has shown these rocks, both sediments and volcanics, to belong to the Georgeville Group of late Precambrian (Hadrynian) age. These are intruded by the Precambrian Greendale Complex of mafic to felsic composition. Late dykes of lower Paleozoic age also occur.
A fault, trending northeasterly, parallel to and approximately 2 km from the Hollow Fault, cuts through the prospect and may be the control to the redistribution of disseminated mineralization.
Cunningham (1970) describes the host argillite as a light to dark grey and fine-grained rock which is extremely fractured with local brecciation. Prominent anastomosing carbonate veining, with extreme distortion in the more brecciated sections, is widespread and at least two generations of veins can be identified. Interbedded light and dark coloured argillites occur and siliceous and graphitic zones are abundant.
The basic rocks comprise pink feldspathic porphyritic volcanics and green, more siliceous volcanics with quartz carbonate and pyrite. Late diorite is slightly chloritized, contains quartz and an unidentified mafic mineral, and exhibits chilled margins with the enclosing argillite.
3.5 Diamond-Drilling
Several diamond-drilling programs totalling 992 m in eight holes, were undertaken by new Jersey Zinc between October 1968 and October 1970. These holes were sited (Fig. 11) to investigate coincident geochemical and geophysical (SP) anomalies located by NJZ personnel.
The 1968-69 drilling comprised 518 m in 5 holes with hole 4 returning 0.69% Zn over 52 m (Cunningham, 1969; Bartlett, 1969). The 1970 drilling program comprised 433 m in 3 holes and glacial overburden did not exceed 20 ft.
The drilling was widely spaced, with DDH 6 (12.2 m at 0.93% Zn) approximately 5 km from DDH 4 (0.69% Zn over 52 m) and including 1% Zn over 17 m. Holes 8 and 9, approximately mid-way between the DDH 6 and DDH 4 areas, both show the mineralized argillite to be present. Hole DDH 8 assayed 0.53% Zn over 15 m, while DDH 9 returned 0.32% Zn over 62 m (Cunningham, 1970).
Noranda DDH N-76-2, which was drilled in 1976, was not completed due to drilling difficulties and did not completely cross the SP anomaly. Results were "similar to those for #6, i. e. graphite, pyrite and minor sphalerite in hornfels" (Graham, 1977).
3.6 Mineralization
Mineralization is represented by pyrite in carbonate veins, while minor chalcopyrite and galena occur as flecks and smears on sheared surfaces and fractures within the argillites. Sphalerite is associated with the carbonate and also occurs as minute disseminations. Bornite occurs in fractures and also as an alteration product of chalcopyrite. In DDH 6 these copper minerals occur in an extremely sheared and altered section of very dark argillite, assaying 0.21% Cu over 3.7 m immediately below a 30 m section of basic volcanics. The Cu minerals also occur within the altered volcanics.
Sphalerite is present in all but one of the drillholes within the argillites of the late Precambrian Georgeville Group. It varies from the light yellow variety, occurring in small veinlets up to 3 mm wide in a 12 m section which assayed 0.93% Zn in DDH 6, to a reddish-brown to black variety occurring in fractures with carbonate. These stringers of carbonate and associated pyrite and sphalerite vary from hairline to 6 mm in width and up to 8 cm in length. The anastomosing veinlets are fractured and offset in the more brecciated sections of argillite. In DDH 8 the sphalerite also occurs as minute disseminations within the argillite and parallel to bedding.
This minute disseminated sphalerite should be considered as a possible indicator of an original syngenetic mineralization which has been remobilized by subsequent tectonic events. Copper mineralization occurs within both the argillites and volcanics but the extent and the controls of this mineralization are unknown.
3.7 Exploration Potential
The mineralization outlined at Georgeville is important because a long strike length (approximately 5 km) of zinc and copper mineralization has been recognized. Grades locally attain significance and long intersections of sub-economic mineralization attest to the large body of mineralized ground. Recognition of the fracture control to the higher grade intersections point to a grade enhancement by later structures. It would appear that the fault parallel to the Hollow Fault and shown on the 1982 map of Murphy et al. may be a major control to mineralization. The wide spacing of the NJZ drillholes and the fact that a large gap between the two mineralized areas has not been tested, makes this a target worthy of further investigation.
The Kirkmount (Kirkmount) property in the western part of the Antigonish Highlands (Fig. 10) represents a different type of shale-hosted deposit. Here the zinc mineralization is present in silicate form and core assays averages 1.66% Zn over 21 sections occur but no sulphides have been noted (Sangster, 1980, 1986). Sangster (1989) identified a willemite (zinc silicate) vein at a depth of 150 m in a drillhole and suggests this as evidence of deep weathering of sulphides in an area of high uplift near the Hollow Fault.
At the Doctors Brook mineral occurrence, about 3 km south of Georgeville, very scattered chalcopyrite mineralization occurs in widely spaced quartz veins and also disseminated in argillites of the Georgeville Group (Northcote et al., 1989). Though not in itself economic or even marginally so, this mineralization supports the contention that the turbiditic, predominantly argillite sequences in the Georgeville Group are exploration targets worthy of further study.
Figures: (Not presently available)
Figure 10. Geology of Antigonish Highlands showing location of the Georgeville deposit.
Figure 11. Georgeville deposit showing diamond-drill hole locations (modified after New Jersey Zinc, 1970).
Photo: (Not presently available)
Dump material at Meat Cove deposit. Adit entrance is to the right of the truck.
4. Marble-Hosted Deposits: Meat Cove and Lime Hill
4.1 Introduction
Hill (1989) recognized two major categories of base metal deposits within the marble-hosted (George River Group) metallic deposits in the pre-Carboniferous rocks of Cape Breton Island.
Polymetallic skarn mineralization is related to a discrete contact metamorphic or metasomatic event and may be hosted both in the carbonates and the intrusives. Further subdivision may be made based on metal association.
Stratabound mineralization is generally restricted to a discrete carbonate unit, is not related to a definable contact metamorphic event, and the associated calc-silicate assemblages are interpreted as reflecting regional rather than local contact metamorphism. Further subdivision of this class may be made based on morphology and metal association.
Earlier investigators (Milligan, 1970 and Chatterjee, 1980) had suggested that the carbonate-hosted deposits of the George River Group of Cape Breton were all skarn-type deposits. The more recent documentation of analogies with the marble-hosted deposits of Quebec and New York State opens up exploration potential. Briefly, these deposits are hosted within the "Marble Belt" of the Grenville Structural Province (Gauthier and Brown, 1986). This belt hosts one major producer, the Balmat-Edwards mine in New York State, and many similar though smaller deposits, several of which have been mined in a small way, occur within the belt. Sulphide mineralization is characteristically hosted in regionally metamorphosed calc-silicate-bearing dolomite marble as coarse-grained, massive to banded, disseminated concentrations of sphalerite ± galena, pyrrhotite, pyrite and chalcopyrite. The deposits are considered to originate from remobilized sediments and display a stratiform control to mineralization. Metamorphism and tectonism have subsequently caused remobilization of the ore into high grade shoots and lenses and orebodies are described as "rod- or pencil-like" because they can continue for long distances along plunging fold axes.
4.2 Location and Access
The marble-hosted deposits at Meat Cove and Lime Hill, in Cape Breton Island, are similar to the Grenville deposits and have been selected to illustrate this base metal environment, which would appear to be confined to Cape Breton Island (Fig. 12).
The Meat Cove Zn, Pb, Cd, Ge, Cu deposit is located in Inverness County, at the northern tip of Cape Breton Island, at longitude 60°35' W and latitude 47°00' N and on NTS map sheet 11N/02A.
The Lime Hill Zn, W, wollastonite deposit is located at 61°009' W and 45°47' N on NTS map sheet 11E/14A in Inverness County. The deposit is located on North Mountain, on the northern shore of the West Bay of Lake Bras d'Or, and approximately 25 km northeast from Port Hastings.
4.3 Previous Work
Fletcher (1881) designated the term George River group to describe the Precambrian metacarbonates of Cape Breton island. Historically, both the Lime Hill and Meat Cove Deposits have been regarded as contact metasomatic Skarn-type deposits (Keating, 1960; Chatterjee, 1977, 1979 and 1980) but more recent workers (Hill, 1987 and 1989; Sangster and Thorpe, 1988; and Sangster, 1990) have drawn analogies with the base metal deposits hosted in Grenville Supergroup marbles in southeastern Ontario, southwestern Quebec and northern New York State.
4.4 Exploration History
Both deposits were discovered in the mid 1950s and have been subjected to several exploration programs in the intervening years.
4.4.1 Meat Cove
Diamond-drilling to test an aeromagnetic anomaly in 1953 led to the discovery of the Meat Cove deposit in northern Cape Breton Island. The initial drilling program, by Mineral Exploration Corp., comprised 5 holes totalling 443 m, and intersected "good" sphalerite mineralization (Nova Scotia Department of Mines, Annual Report 1953).
Between 1953 and 1956, a further 3111 m of surface and 1300 m of underground drilling were completed. The deposit was accessed by a 171 m long adit (Fig. 13) from which some 70 m of crosscuts were developed. This program, under the direction of McPhar Geophysics Ltd., included extensive geological mapping, geochemical surveys, geophysical surveys and the excavation of 62 pits.
By 1957 two zones totalling 3.18 million tonnes grading between 2% to 3% Zn, with Cd and Ge values, were outlined. In 1965 ore reserves were estimated as 4.0 million tonnes grading 4% Zn, and 0.15-0.47 lbs. Cd/t.
A trenching program in 1968 reported grades of 5.65% Zn over a length of 77 m, and included a 31 m section averaging 10.15% Zn (Chatterjee, 1979). Houston and Associates (1972) estimated 3.18 million tonnes grading 2.08% Zn in the Adit zone with a further 0.36 million tonnes at 2.76% Zn in a second zone (Dunbar, 1965).
Belore Mines (Houle et al., 1989) examined the deposit in 1988-89 and reported a total of 6380 m in 67 surface drillholes and 1306 m in 24 holes from underground as being on file at Nova Scotia Department of Natural Resources. The Belore exploration program included line cutting, soil sampling, a magnetometer survey, geological mapping and sampling of the old adit.
4.4.2 Lime Hill
Follow-up of a regional geochemical stream sediment survey in the mid 1950s by Dr. B. Keating led to the discovery of zinc sulphide outcrops in McCuish Brook in 1957. Subsequently named the Lime Hill showing, the deposit was investigated with various trenching and drilling programs by Belcher Mining Corp., Conwest, Cominco, Lura Corp., Patino, Silvermaque and Brascan in the period between 1957-1976.
Eighty-two surface diamond-drill holes, totalling in excess of 4600 m, have been completed on the property. Mineralization has been encountered in many holes and ranges from short, high grade (38.8% Zn/1.2 m) intersections through medium grade (10.17% Zn/7.6 m) to longer sections of low grade mineralization. Four zones of sulphide mineralization have been recognized and Chatterjee (1977) estimated 2 million tons at 2.5% Zn for the deposit as a whole.
Thirty-eight trenches were completed during 1974 and 1975 but the variable depth of weathered bedrock and excessive water flows caused many problems.
In 1977 Chatterjee reported tungsten and wollastonite on the property and in the early 1980s, Bluestack Resources made a geological compilation (Patterson, 1984) of the base metal potential.
In 1986 Bluestack Resources commenced an investigation of the wollastonite potential of the property. Examination of all available drill core at the DAR core storage facility at Stellarton disclosed previously unrecognised sections of wollastonite. a mapping program yielded new showings and a program of 19 trenches was completed (Pegg, 1987).
4.5 Regional Geology
The carbonate-bearing metasedimentary rocks of the pre-Carboniferous of Cape Breton Island have historically been correlated with the George River Group which Milligan (1970) describes as a loosely-defined lithostratigraphic unit comprising interbedded carbonate and clastic metasedimentary rocks and minor volcanic rocks.
Hill (1989) describes the carbonate units as ranging in composition from relatively pure limestone and dolostone of very low metamorphic grade to highly metamorphosed, calcareous, dolomitic or siliceous marble. Associated metasedimentary rocks include quartzite and feldspathic sandstone which enclose carbonate members and are also of variable metamorphic grade. Argillaceous and volcanic rocks are more limited in distribution.
Going northward in Cape Breton Island, correlation of the highly metamorphosed and deformed carbonate-clastic metasedimentary sequences with the George River Group rocks is more difficult than previously implied and carbonate units form a very small component of the clastic sedimentary sequence.
Barr and Raeside (1986) have subdivided the pre-Carboniferous geology of Cape Breton Island based predominantly on intrusive age relationships. Four main tectonostratigraphic divisions are proposed (Fig. 14), namely the "Grenvillian" Blair River Complex, and the Aspy, Bras d'Or and Avalon Terranes. The George River Group rocks, comprising metasediments and metavolcanics, dominate the Bras d'Or zone and are widespread in the Aspy Terrane and in the Blair River Complex, Keppie (1992) suggest that Cape Breton Island comprises one terrane only-the Avalon terrane, and maintains that the divisions recognized by Barr and Raeside are really tectonic features within one single terrane rather than major terrane boundaries. Hill (1989) has discriminated the marble-bearing sequences on the basis of carbonate composition, metamorphism, and structural and stratigraphic relationships. Historically these Precambrian carbonates have all been arbitrarily assigned to the George River Group. Sangster (1990) quotes recent work which shows that the George River Group proper is restricted to the Bras d'Or Terrane and that areas of high metamorphic grade gneissic rocks and marble (as at Meat Cove and Lime Hill) are different.
Thus Sangster (1990) states that the Meat Cove deposit is hosted by dolomite marble of the Blair River Complex. These marbles form a xenolith within a syenite which is regarded as part of the Grenville age basement rocks. The Lime Hill deposit is hosted by dolomitic marbles of the Lime Hill gneissic complex.
4.6 Local Geology
4.6.1 Meat Cove
The host-rock marble is interpreted as large xenolith within the Lowland Brook hornblende syenite which has intruded a high grade gneiss of the Blair River Complex (Fig. 15). The syenite, which carries minor magnetite, show clear intrusive contacts with the carbonate host rock. Previous workers had included these gneisses with rocks of the late Precambrian George River Group, but more recent work (Barr et al., 1987), based on geological relationships, has assigned a much older Grenvillian age. Unconformably overlying both the metacarbonate and the syenite are the Carboniferous age Horton Group clastics.
Houle et al. (1989, for Belore Mines) describe the host carbonate xenolith as a convex tabular body dipping moderately to the NE and striking NW to WNW for some 2 km. The youngest rocks on the property are NE-trending, mafic diabase dykes which intrude all the above noted lithologies.
Two large scale fold styles are described by Houle et al. (1989). a northeast-plunging open anticline is present in the northern part of the property and an open Z-shaped structure occurs within the host metacarbonate and displays a NE- to ENE-striking axial trace. The plunge of these folds follows the footwall syenite contact which dips at 50-60° NE. Subsurface mapping in the adit by Houle et al. delineated a set of isoclinal structures attributed to a second deformational phase.
Two major fault trends have been identified. The ENE fault shows a dominantly sinistral displacement of up to 100 m and with an unknown vertical component. The N- to NE-trending fault has a horizontal offset of about 20 m and appears to throw to the east.
4.6.2 Lime Hill
The mineralized marble at Lime Hill has been historically assigned to the George River Group, which is present at much lower metamorphic grade immediately to the northeast (Sangster, 1990). This difference was noted by Guernsey (1929), and Chatterjee (1980) described the Lime Hill marble as "roof pendants within granitoid rocks."
Mapping by Justino (1985) has defined the Lime Hill gneissic complex (including the mineralized carbonates) to be separate and distinct from the George River Group rocks. Marble accounts for <10% of the exposed area of the gneissic complex, which Raeside (1990) supported as being older than the George River Group rocks.
At Lime Hill (Fig. 16), the gneissic complex consists predominantly of a metacarbonate rocks suite comprising dolomite marble and siliceous dolomite marble, with lesser calcite marble and calc-silicate rocks. This gneissic body was intruded by a small tonalite body and a large number of later granitic and mafic dykes (Sangster, 1990).
Justino and Sangster (1987) defined a strong N-S structural fabric containing the regional foliation and both deeply-plunging and subhorizontal minor fold axes. Sangster (1990) states that the outcrop pattern suggests N-S isoclinal folding, and other structural data suggest that the gneissic rocks structurally overlie the mineralized marble. a major WNW-striking sinistral fault is present and Sangster (1990) suggests that this has offset the mineralization into the present configuration. Several small N-S faults have been mapped.
4.7 Mineralization
4.7.1 Meat Cove
The mineralized carbonate unit at Meat Cove (Fig. 15) strikes southeast for approximately 2 km, is up to 35 m wide and dips moderately to the northeast (Fig. 17). Four styles of sulphide mineralization have been identified as follows:
- Banded sphalerite (blackjack variety)-pyrrhotite-pyrite-chalcopyrite as fine cm-scale bands defining bedding in the metacarbonate.
- Semi-massive disrupted bands and massive pods of sphalerite-pyrrhotite-pyrite-chalcopyrite in the metacarbonate. This is the previously known "zinc ore" type and most commonly occurs on fold hinges.
- Massive sulphide veins of sphalerite-pyrrhotite-bornite occurring both in the syenite and the metacarbonate unit. These veins occupy faults and/or fractures and are commonly associated with the semi massive type near deformation zones. Houle suggests that they may represent the "ore leading channels" of Chatterjee (1977) or may be remobilized banded sulphides.
- Disseminated pyrite-chalcopyrite (plus magnetite) within foliated syenite.
Four zones of "significant" sphalerite mineralization have been outlined as follows (Fig. 15);
- the Adit (underground),
- The Northwest,
- the Road Cut and
- The South Trench
Sampling by Belore Mines (Houle et al., 1989) in the Adit zone returned values of 3.13% Zn/3 m; 6.87% Zn/6 m and 9.52% Zn/3 m with the higher values corresponding to areas of structural grade enhancement. The Northwest showing, the focus of the original work in the mid 1950s and in 1968, returned values of 11.3% Zn/17 m and 6.1% Zn/4.6 m in metacarbonates. Belore reported the highest Zn and Cd assays from this zone with 14.98% Zn/3.5 m and 17.35% Zn/4 m, with best Cd values up to 0.06%.
The South Trench zone, 200 m south of the adit portal, was sampled in 1968 and values of 2.9% Zn/31 m and 10.5% Zn/33.5 m were reported within the metacarbonate.
Several estimates have been made over the years as to 'ore reserves' within the two main zones-the Adit zone and the Northwest showing. In 1965, possible reserves of 4.0 million tonnes grading 4% Zn, and 0.15-0.47 lbs. Cd/t were reported. Huston and Associated (1972) estimated 3.18 million tonnes grading 2.08% Zn in the Adit zone with a further 0.36 million tonnes at 2.76% Zn in a second zone (Dunbar, 1965).
Chatterjee (1979) reported germanium values up to 160 ppm in the sphalerite and Patterson (1987, unpublished data) reported mercury values up to 2.4 ppm in a sample of massive sphalerite assaying 30% Zn.
Metallurgical tests carried out in the 1960s (as reported by Belore Mines) (Houle et al., 1989) on a bulk sample from the Adit zone showed recoveries ranging from 80% for the low grade (>2% Zn) material to 85-90% for a 3.6% Zn head grade. The 18 ton bulk sample returned a concentrate grading "5.2%" (this should probably be 52% Zn) plus 0.16% Cd.
4.7.2 Lime Hill
The sphalerite mineralization is exposed in two zones that parallel the lithological layering and foliation within the marble host rock. The East zone (Fig. 16) comprised three sub-zones, namely the Main, "C" and #2 zones; while the West zone lies 370 m west of the #2 sub-zone. Assay data from previous operators show mineralized intersections ranging from 25 cm to 10 m with grades varying from a few percent to 10% Zn/10 m. Silver values are low and Hg up to 4.32 ppm has been reported (Patterson, unpublished data, 1987) from a high grade (30% Zn) sample.
Patterson (1984) suggested that the sub-zones within the East Zone might be all one zone due to folding. The zone has been traced by trenching and diamond-drill holes over a strike length of 300 m. Within the Main zone, sphalerite occurs as tabular bands ranging from 1-30 cm thick, striking 010° and dipping steeply to the west. The mineralization, averaging 4.5 m in thickness, pinches and swells down dip and along strike from 2-7.5 m and has been estimated to contain 227,000 tonnes at 8.9% Zn (Patterson, 1984). The "C" zone mineralization occurs in a synclinal structure plunging about 30° to the north and also displays wide variation in thickness and grade. The zone averages 2.5 m thick, is 200 m long and has been drilled to a depth of 75 m. Patterson (1984) estimates 112,000 tonnes at 5.46% Zn. The #2 zone is narrow, averaging 1.7 m, and is estimated to contain 36,000 tonnes at 3.49% Zn.
The west zone comprised a series of bands and disseminations of sphalerite in westerly-dipping, tabular bodies of dolomitic limestone. The zone strikes N-S for 200 m, averages 1.8 m in thickness, has been traced down dip for 50 m, and is estimated to contain 50,000 tonnes at 6.25% Zn.
Chatterjee (1977) estimated 2 million tons at 2.5% Zn for the deposit as a whole, but Patterson (1984) estimated a geological reserve of 425,000 tonnes at 7.22% Zn over an average thickness of 2.8 m.
The stratabound carbonate-hosted mineralization occurs in both disseminated and massive forms. Medium- to coarse-grained sphalerite is present in bands that vary from 1 cm to several metres in thickness and parallel the lithological layering in he carbonate. Minor disseminated pyrrhotite and/or pyrite, with rare chalcopyrite, occur. Massive sphalerite layers, from 10-5 cm thick, occur parallel or subparallel to the disseminated sphalerite layers (Sangster, 1990). Pyrite can be dominant in these massive layers, which can be truncate bedding-parrel bodies of disseminated sphalerite. Sangster equates this texture with the "spangle ore" as seen in the Balmat-Edwards deposits in New York State and which are interpreted as the result of mobilization of sulphides during metamorphism.
Chatterjee (1977) identified scheelite and wollastonite and the most recent work on the property, by Bluestack Resources, has concentrated on examining the wollastonite potential (Pegg, 1987).
4.8 Genesis
The Precambrian carbonate-hosted deposits at Lime Hill and Meat Cove have been presented as classic examples of "skarn type" deposits by earlier workers (Keating, 1960, and Chatterjee, 1977, 1979 and 1980). Patterson (1984) suggested that the mineralization might be remobilized syngenetic material and suggested that analogies could be drawn with the Grenville carbonate-hosted deposits in eastern Canada and New York State.
Sangster (1990) presents evidence suggesting that the Lime Hill and Meat Cove deposits are metamorphosed Mississippi Valley type (MVT) or Sedimentary Exhalative (Sedex) type deposits formed from MVT basin brines. The high Hg content of the ore at Meat Cove (Patterson, unpublished data) and the high Hg geochemical dispersion halo (Rogers) would create difficulties for this proposed origin. Interpretation of the lead and sulphur isotope data from Lime Hill caused sulphur isotope data from Lime Hill caused Sangster and Thorpe (1988) to conclude that the origin of the deposit was very similar to that for the Grenville carbonate-hosted deposits. Examination of the composition of pyroxenes in the Cape Breton metacarbonate deposits led Hill the Cape Breton metacarbonate deposits led Hill (1988) to support the theory of a closer association with Grenville deposits rather than with skarns.
4.9 Exploration Potential
The widespread occurrence of Precambrian carbonate rocks has been well established in Cape Breton Island. Work at Lime Hill and Meat Cove has shown the presence of significant sphalerite deposits with associated Cd and Ge values. Though neither of the Cape Breton deposits discussed here are economic it should be stressed that analogies with the probably genetically-associated Grenville deposits of eastern Canada and northern New York State demonstrate that viable deposits may be found. The classic type example of this class is the Balmat-Edwards deposit in New York State, from which 23 million tonnes at 10% Zn were mined between 1915-1979 with a further 23 million tonnes of the same grade in reserve. The former producers in the eastern Canadian Grenville were much smaller tonnage operations but displayed many features similar to the Balmat-Edwards deposit. Typically, these are coarse-grained stratiform sulphides occurring as tabular, pod-like or lenticular bodies, usually elongate in a down plunge direction of fold hinges. The deposits have been described as pencil-or rod-like and are structurally complex.
These analogies with the Grenville type deposits and the widespread distribution of the metacarbonates in Cape Breton (Hill, 1989) suggest that continuing exploration for this type of sulphide deposit, and its associated industrial minerals, could be worthwhile.
Photo: (Not presently available)
High grade massive sphalerite zone at Lime Hill deposit.
Figures: (Not presently available)
Figure 12. Proterozoic stratabound carbonate-hosted base metal deposits in Cape Breton.
Figure 13. Meat Cove, Cape Breton Island, mineralized zone (after Houle et al., 1989).
Figure 14. Tectonostratigraphic divisions in Cape Breton Island (Barr and Raeside, 1986).
Figure 15. Meat cove deposit - geology and mineralization (after Houle et al., 1989).
Figure 16. Lime Hill deposit - geology and mineralization (after Cominco, 1960, and Sangster, 1990).
Figure 17. Meat Cove deposit - vertical section (Houle et al., 1989).
5. Meguma Group-Hosted Base Metals: Eastville (Gold Brook)
5.1 Introduction
In Nova Scotia the Meguma Group rocks of Cambro-Ordovician age have been known since the 1800s as hosts to gold mineralization. Exploration over the years for gold has yielded evidence of massive sulphide mineralization, primarily pyrite, in the host metasediments. Exploration in the southwest part of the province has outlined significant tin mineralization with associated copper and zinc sulphides in Meguma metasediments and these occurrences are described under the granite-associated class of mineralization in Section 8. Antimony and tungsten deposits are associated with veins in Meguma Group metasediments and at West Gore several fissure veins containing auriferous stibnite were exploited to a depth of 250 m. The deposit was re-examined in the late 1980s.
The best-known base metal occurrence within the Meguma Group is the Zn/Pb deposit at Eastville where mineralization in Meguma Group metasediments extends for 10 km along strike. This mineralization occurs around the transition zone between the predominantly greywacke predominantly argillaceous, Halifax Group. This Goldenville/Halifax transition zone is marked by a regional scale enrichment in manganese which several researchers, citing occurrences of manganese, tungsten and tin within the transition zone, have attempted to use as evidence of a widespread mineralizing event at this stratigraphic horizon (Zentilli et al., 1986).
The occurrence of base metal values within the gold deposits, the presence of massive sulphides in close association with the gold deposits, the presence of base metals with the Meguma-hosted tin deposits, and the occurrence of significant base metals at Eastville, make exploration along this 1700 km-long contact between the Halifax and Goldenville Formations a worthy exploration target.
The Eastville deposit, also known as Gold Brook, is the type example for this deposit class in the province.
5.2 Location and Access
The Eastville or Gold Brook deposit is located 2 km southeast of Eastville, Colchester County, and some 35 km southeast of Truro (Fig. 18). The deposit is centred on latitude 45°16'30" N and 62°48'30" W on NTS map sheet 11E/07B and access via a series of paved highways and pulp company gravel roads.
5.3 Previous Work
The area was first mapped by Fletcher and Faribault (1902) and again by Benson for the Geological Survey of Canada in 1962. Neither of these surveys noted any mineralization in the area. Holman (Geological Survey of Canada, 1959), in his regional stream sediment geochemical survey, indicated anomalous Pb and Zn values along Cox Brook which traverses the deposit. Binney et al. (1986) confirmed and extended much of the early Fletcher/Faribault mapping. The area was covered by the Geological Survey of Canada airborne EM survey (1960) and a significant anomaly was interpreted to represent a regional fault.
5.4 Exploration History
The first recorded exploration activity was that of St. Joseph Explorations Limited in 1976 (St. Joseph Exploration Assessment Report 1977). Though primarily focused on gold exploration in the Meguma Group (Cambro-Ordovician) rocks for base metals. a reconnaissance B-horizon soil laid out to follow up the GSC airborne EM anomaly. Highly anomalous Pb values (>1000 ppm) were obtained from the first two lines sampled. Extension of this geochemical program was accompanied by a ground EM survey on widely spaced lines. a strong EM anomaly was located over the length of the claim group and Pb and Zn soil anomalies were detected in two areas coincident with the EM anomalies.
Diamond-drilling in 1977 intersected fine-grained sphalerite and galena and encouraging assays (up to 3.26% Pb and Zn/7 m) were reported. Following this initial success much more detailed geochemical and geophysical programs were initiated and included B-horizon soils, organic-bank stream sediments, and magnetic and EM geophysical surveys.
Between 1977 and 1982 twenty-eight drillholes totalling 3896 m were completed in three widely separated areas on the Eastville deposit (Fig. 18). Early drilling concentrated on geochemical anomalies along the geophysically defined Goldenville-Halifax contact. Later holes tested for down-dip extensions and also along strike in areas of no geochemical response. Australian Mining and Smelting entered into a joint venture in 1980 and an overburden drilling program was completed but no new target areas were identified. The last diamond-drill hole, DDH 28, returned the best intersection with 4.05% Zn + Pb/9.33 m, including a 2.13 m section assaying 4.71% Zn and 1.8% Pb (Binney, 1981).
The mining claims were relinquished by the successor company to St. Joseph Explorations in 1986, since which date the deposit has been under closure by the province.
5.5 Regional Geological Setting
Nova Scotia, south of the Cobequid-Chedabucto Fault System, is to great extent underlain by rocks of Cambro-Ordovician age which are collectively referred to as the Meguma Group. The Meguma Group, comprising sediments of the Goldenville and Halifax Formations, may exceed 10 km in thickness and Schenk (1970) has interpreted the group as a eugeosynclinal-flysch facies.
The basal part of the Meguma Group is the Upper Cambrian (age uncertain) Goldenville Formation which has a minimum thickness of 5500 m (Sangster, 1990). Lithologically it consists of massive, thick bedded, sandy flysch with thinly interbedded (0.1-2 m thick) chloritic slate and siltstone. The overlying Halifax Formation, of Ordovician age, is approximately 3700 m thick and consists of grey to black slate with thin interbeds of flysch. The slate beds are commonly carbonaceous and contain several percent of pyrrhotite, with minor pyrite in the coarser grained and less carbonaceous beds.
The transition between the two formations of the Meguma Group consists of interstratified slate and sandstone and is intermittently exposed over a strike extent of 1700 km in Nova Scotia. It represents a change from the non-carbonaceous sulphide-poor rocks of the Goldenville Formation to the carbonaceous and sulphide-rich rocks of the Halifax formation. The transition zone is characterized by an enrichment in Mn in a distinctive and widespread calcareous argillite unit. This unit, referred to as the coticule (spessartine-rich quartzite) horizon, is locally anomalous in Zn, Pb, Ba, As and Au (Sangster, 1990).
The Meguma Group metasediments are intruded by peraluminous granodiorite-monzogranite complexes ranging in size from bodies of several square kilometres to composite intrusions of batholithic scale. Aplite and pegmatite dykes are indicative of a later magmatic phase.
Regional metam | 
