Mineral Resources Branch
Twentieth Annual Review of Activities, 1996

By D. R. MacDonald, Editor, macdondr@gov.ns.ca

Nova Scotia Department of Natural Resources
Mineral Resources Branch
Information Series ME 24, 1996

Table of Contents

• Program
• Map of Display Area
• Mineral Resources Branch Activities
  • Geoscience Activities in the Geological Services Division Scott Swinden
  • An Overview of Current Mineral Exploration Activity in Nova Scotia M. A. MacDonald and P. D. McCulloch
  • The Murchyville Gypsum Deposit: A Project Update G. C. Adams
  • New Insights in the Meguma Zone of Southern Nova Scotia
    • Preliminary Stratigraphy and Structure of the Meguma Group in the Central Meguma Project Area R. J. Horne
    • The Victoria Goldfields of Australia: Meguma South? R. J. Ryan and W. R. H. Ramsay
    • Lithogeochemistry of the Goldenville-Halifax Transition Zone at North Beaverbank, Nova Scotia M. Feetham
    • Petrochemical and Isotopic Studies of Pelitic Rocks and Associated Veins at Cochrane Hill P. K. Smith and A. K. Chatterjee

Program

Map of Display Area

(Not Presently Available)
Preliminary map of the display area for the Twentieth Annual Review of Activities (not to scale).

Mineral Resources Branch Activities

Geoscience Activities in the Geological Services Division

Scott Swinden hsswinde@gov.ns.ca

The Geological Services Division is the geoscientific arm of the Department of Natural Resources. Divisional programs are delivered through three sections, Geological Mapping, Mineral Resource Evaluation, and Geoscience Information Services. The division maintained an active program of field and office-based projects during 1995-96.

Geological mapping included both reconnaissance and detailed mapping of bedrock and surficial materials. Detailed mapping continued in the central Meguma area. Significant advances have been made in documentation of the stratigraphy, structure and aeromagnetic character of the Meguma Group, which hosts significant deposits of gold, lead, zinc and antimony. Bob Ryan visited the Victoria gold districts of Australia during 1996 and a comparison of geology, mining methods and economics is in progress. Surficial mapping and drilling continued in the Musquodoboit and Shubenacadie valleys, principally in support of exploration for deposits of Cretaceous clay and silica sand. The extent of these deposits was first established by geological mapping in this area and the input provided by our geologists has been instrumental in furthering efforts to explore and develop this resource.

Field work related to the evaluation of metallic mineral resources focused on the potential for large tonnage, low grade gold deposits at several gold districts in the eastern Meguma terrane. Gold occurs in high grade veins and locally as low grade disseminations in the greywacke, siltstone and slate country rocks. A number of exploration programs are underway in an attempt to develop economic targets. A detailed study of the East Kemptville tin deposit is ready for writing. Base metal projects at the Gays River and Walton Zn-Pb deposits, which have been carried out over the past several years in conjunction with Geological Survey of Canada, are complete and will be written up in a series of papers to be published in a special issue of Economic Geology.

Mapping in support of coal resource evaluation was carried out in the Cumberland, Debert-Kemptown and Stellarton basins, including studies of sedimentology, predictive modelling of coalbed methane resources, predictive stratigraphic modelling of coal beds and characterization of chalcophile-enriched metalliferous coal of the Joggins Formation, and paleo-ecological research to refine predictive coal exploration models and to assist in the economic development (e. g. tourism) of the Joggins fossil cliffs. Detailed sedimentology and structural geology of strata overlying the Foord coal seam, western Stellarton Basin, and detailed sedimentological modelling of strata comprising the roof of the Phalen Colliery, Sydney Basin, were continued.

Work also continued on the Mineral Inventory Database with field verification of mineral occurrences in various areas of Cape Breton Island and input of data from recent mineral exploration assessment files. A user-friendly, menu-driven program has been written in FoxPro^®for Windows^®Version 2.6 that allows easy access to the Mineral Occurrence Database. This will be released at the 1996 Open House.

The aggregate program for 1996 focused primarily on the Annapolis Valley as part of a three-year field study to evaluate and document aggregate potential in the region. As well, several promising dimension stone sites in the South Mountain Batholith were identified and evaluated by diamond-drilling. A study to evaluate the potential of rock dust as fertilizer has been brought to a conclusion. After a year of greenhouse and field trials using basalt, metagreywacke and granite fines, it was concluded that these materials promote plant growth in certain crops.

Geochemical programs focused on preparing data from biogeochemical surveys in Cape Breton Island and southwestern Nova Scotia for release.

GIS development continues in support of mapping and integrated resource management. The public access GIS is almost ready for release. This is a display and query system for staff and clients to produce hard copy, colour geoscience maps.

The division maintains an active and productive land-use group. This group has been very involved with the department's Integrated Resource Management process. The province's Mineral Policy, a major recent focus of this group, is essentially complete and is expected to be published in the Fall of 1996. A number of land-use maps have been produced, including a preliminary 1:500 000 Land Designation and Ownership Map of Nova Scotia. Work continued on the development of several land-use data layers and associated databases, which have been used in several derived map products, such as Land Access for Mineral Exploration in Nova Scotia (1:500 000) and a map depicting Areas Closed to Mining in Nova Scotia.

Helping various audiences understand and appreciate the importance of minerals and mining is the key objective of the education and public awareness group. This objective was met by preparing and delivering a variety of programs such as prospecting courses, teachers' workshops, class presentations, articles and newsletters, and public interpretive walks.

The Drill Core Library in Stellarton houses extensive collections of drill core and other sample media. A total of 7858.4 m of additional drill core was received and 90.7 m of core were disposed of in 1995-96, bringing the cumulative fiscal-year-end total to 634 277 m.

The branch carried out successful mineral promotion programs on several fronts. We produced a new promotional package of one-page summaries of the geology of Nova Scotia and its mineralized environments, packaged in an attractive folio designed around the theme 'We're Worth Exploring'. These brochures have been widely distributed and form the cornerstone of our promotional materials at trade fairs. During 1995-96, we attended a number of trade fairs and geological conferences to communicate and promote the province's mineral potential, including the Western Miner's meeting in Spokane, the Cordilleran Roundup in Vancouver, the Prospectors and Developers Association of Canada annual meeting in Toronto, and the Investing in the Americas conference in Miami (as part of the 'Team Canada' booth). Our quarterly newsletter, Nova Scotia Minerals Update, was produced again this year and continues to be well received.

The past year has seen significant evolution and progress in the long term planning for government geoscience in Nova Scotia. In late 1995, the Nova Scotia Department of Natural Resources (NSDNR) and the Geological Survey of Canada (GSC) signed a Memorandum of Agreement under the Intergovernmental Geoscience Accord to govern cooperative program planning over the next five years. The agreement mandates the two organizations to form a cooperation committee from senior managers of the two organizations and to determine the geoscience needs of the province prior to program development. A workshop was held in Halifax in May, facilitated by Voluntary Planning (a division of the province's Economic Renewal Agency), to allow geoscience users to express their needs for geoscience information. A report of that workshop was published in June and has served as a resource for internal program planning discussions that have been underway all summer and early fall. This plan, which is being developed in consultation with the Geological Survey of Canada, will be completed by late November and circulated togeoscience users for comment. It is expected that by March, a joint plan of NSDNR and GSC activities in Nova Scotia will be completed and submitted to the National Geological Surveys committee for review. Both organizations recognize the need for cooperation and communication, both within our respective organizations, and with our clients and other geoscience user groups in the province.

An Overview of Current Mineral Exploration Activity in Nova Scotia

M. A. MacDonald and P. D. McCulloch mccullpd@gov.ns.ca

There has been an upswing in the level of mineral exploration and development in Nova Scotia in 1996. Approximately 1 million acres (400 000 ha) are currently under mineral licence, the highest level since 1989. An estimated 21,000 new claims will be issued in 1996, roughly double the 1994 and 1995 levels of 9,500 and 11,300 new claims, respectively. Mineral exploration expenditures for 1996 are estimated at $2.5 million, an increase of approximately 25% compared to 1995. Current estimates indicate roughly 9000 m of diamond-drilling for 1996, up approximately 12% over 1995.

Exploration was carried out for gold, base metals and industrial minerals in a variety of geological environments throughout the province. In 1996, exploration activity was highlighted by a significant increase in industrial mineral exploration and development for several commodities, including limestone, gypsum, kaolin clay and silica sand. The purpose of this summary of mineral exploration activity in Nova Scotia is to present highlights of the year to date. It is not intended to be an exhaustive compilation of all activities.

An estimated 400,000 acres (160 000 ha) under mineral licence are currently being explored for Cretaceous deposits of kaolin clay and silica sand in central to northern Nova Scotia and Cape Breton Island. This activity has resulted from the discovery of high quality kaolin deposits in the Musquodoboit and Shubenacadie valleys by staff geologists Ralph Stea and Phil Finck during a regional mapping project carried out in conjunction with Sue Pullan of the Geological Survey of Canada. Initial analytical results indicate the potential for both filler-grade and calcined coater-grade kaolin that could be used in the manufacture of paper products. The Cretaceous clays may also have applications in the ceramics and manufacturing industries. KaoClay Resources Inc. have carried out diamond-drilling, trenching and test sampling on several properties during the year.

Tusket Mining Inc. has completed some pre-development work and are proceeding with project development at their gypsum deposit in the Murchyville-Elderbank area of Halifax County. The company plans to bring the deposit into production in the near future, with reported reserves of over 400 million tonnes of gypsum (see Adams, this volume: The Murchyville Gypsum Deposit: A Project Update).

Little Narrows Gypsum Company completed a drilling program for gypsum in the vicinity of the company's quarry at Little Narrows, Victoria County.

Pioneer Coal Ltd. began mining coal from the Foord seam in Stellarton, Pictou County, in March 1996. The company has approval to surface mine 2.6 million tonnes of coal at the site, which is located on the western side of the Pictou coalfield and includes the sites of the former Wimpey and Westray test pits.

Kelly Rock Ltd. continued to evaluate limestone and dolomite occurrences hosted by the Precambrian George River Group at Glencoe and Kewstoke in Inverness County.

The lower Paleozoic Meguma Group rocks of southern mainland Nova Scotia continued to be the focus for gold exploration by numerous companies. Tangier Limited Partnership continued a detailed study on the former Coxheath Gold Holdings property at Tangier, Halifax County, to determine the feasibility of re-opening the mine. The company is currently carrying out underground test mining and bulk sampling on the property. Placer Dome Canada Ltd. completed a feasibility study of the former-producing Upper Seal Harbour gold deposit, Guysborough County. The company has relinquished its option agreement with Exploration Orex Inc. Gammon Lake Resources conducted follow-up trenching and prospecting at the former-producing West Lawrencetown gold district, Halifax County. They are continuing their study of a gold-bearing zone intersected during a drill program in 1995.

Moose River Resources Inc. are currently conducting a drilling project to extend known ore reserves and evaluate gold potential of large tonnage, sediment-hosted, stratabound gold deposits in and adjacent to the Touquoy Zone in the Moose River Gold District, Halifax County. Current resource estimates for the Touquoy Zone are 2 million tonnes at approximately 2.1 g/tonne gold, although there are multiple mineralized zones within 500 m of the deposit that were not included in resource estimates. Alan A. Johnson has acquired a large land position, which lies between the Moose River and Goldenville mining districts, and is preparing to conduct an exploration program designed to evaluate this area for high tonnage, low grade, disseminated gold.

Wabana Explorations Inc. carried out exploration drilling for gold at the former-producing Oldham gold district in Halifax County. The company has also conducted drilling at Lake Peter in Lunenburg County to test a zone of vein and disseminated gold. Prodigy Resources are planning to carry out trenching at their Goldenville property in Guysborough County.

Regal Goldfields Ltd. is currently exploring for mafic-and ultramafic-hosted Cu-Ni-Co mineralization in the Trout Lakes region of Cape Breton Island, east of Cheticamp, Inverness County. Their work is focusing on an occurrence of net-textured pyrrhotite-cobaltite-pentlandite hosted by ultramafic rocks that was discovered and subsequently trenched by Inco in the late 1980s. To date, the company has completed a comprehensive digital compilation of previous assessment work along with line-cutting, geological mapping, and prospecting with both ground and airborne geophysical surveys.

Highland Range Minerals Ltd. continued to evaluate the potential for stratabound gold and base metals hosted by Late Ordovician to Early Silurian metavolcanic and metasedimentary rocks in the Faribault Brook area, east of Cheticamp. The company completed a diamond-drilling project in the Fall of 1995 and has subsequently completed a digital compilation of previous assessment data.

BHP Minerals Canada Ltd. has completed a preliminary geochemical and geophysical program over their mineral claims near the Canfield Creek Cu-Ag deposit south of Pugwash, Cumberland County. The company is evaluating the area for sandstone-hosted copper deposits.

Mispec Resources Inc. and Alterra Resources Inc. have conducted geochemical and geophysical surveys in the Bridgeville-Iron Mines area, Pictou County. They are currently exploring for carbonate-hosted polymetallic Pb-Zn deposits with associated siderite and barite that are proximal to fault zones in Carboniferous sedimentary rocks.

Burnt Point Resources Inc. continued a detailed exploration program for porphyry-related copper and gold associated with Hadrynian diorite-granodiorite-monzonite intrusive rocks in the Coxheath area, Cape Breton County. The company drilled three target areas in late 1995, resulting in the delineation of a new zone of gold mineralization. A program consisting of prospecting and stream sediment geochemistry in 1996 has defined an additional target that the company plans to evaluate in the future.

Phelps Dodge Corporation of Canada Ltd. has conducted line cutting with subsequent geophysical and geochemical surveys near the former-producing volcanogenic massive sulphide deposit at Stirling and on their nearby MacKillops Pond property, Richmond County. The company is currently evaluating the results of these surveys with a view to diamond-drilling, should results warrant.

Alterra Resources Inc. is currently drilling near Collingwood, Cumberland County, to evaluate the precious-metal potential of Lower Carboniferous granitic intrusions west of the Williamsdale gold-arsenic prospect.

Caledonia Mining Corp. has completed a preliminary exploration program in central Nova Scotia. Caledonia is evaluating the potential for paleoplacer gold deposits in Carboniferous rocks of the Horton Group in the St. Marys Graben.

In conclusion, Nova Scotia is currently experiencing an increase in levels of mineral exploration and development. These activities are directed toward a wide range of mineral commodities, including coal, industrial minerals, gold and base metals. These factors auger well for the future of the mineral industry in Nova Scotia.

The Murchyville Gypsum Deposit: A Project Update

G. C. Adams

Recently published newspaper articles on Tusket Mining Inc.'s gypsum property in the Murchyville area of Halifax County have been very encouraging. As is the case with all such projects, this development is the result of a lot of effort by a number of agencies.

W. J. Wright of the former Department of Mines documented significant occurrences of gypsum in the Musquodoboit Valley in the late 1960s. Exploration drilling related to the Gays River deposit facilitated geological mapping in the area in the 1970s and 1980s by R. C. Boehner and P. S. Giles of the former Department of Mines and Energy.

In 1985, I was hired by the Department of Mines and Energy to carry out an inventory of Nova Scotia's gypsum and anhydrite resources. During the course of this work, Murchyville was identified as one of a handful of sites worthy of additional investigation. In 1990, 18 diamond-drill holes were completed by the department's drilling section. Results from this program were released late that year as an Open File Report. Although gypsum exploration was subsequently carried out elsewhere in the valley, it was four years later that the Murchyville property was picked up by Tusket Mining Inc.

After a substantial drilling and geophysical program, Tusket has developed an open-pit mine plan to recover a mineable reserve of 330 million tonnes of gypsum. That is approximately 30% more gypsum than has been mined in Nova Scotia since 1862 when records of production were first kept.

Tusket Mining has recently registered the Murchyville Gypsum Project for environmental assessment under the Environment Act. Tusket has identified three different levels of production at Murchyville. The start-up phase (estimated production of 300,000 to 500,000 t per year) will employ 40 to 50 persons in production, trucking and shipping. This should increase to 500,000 to 1,000,000 t per year for normal production and, depending on demand, could increase to 1,000,000 to 2,000,000 t per year. Employment could rise to 80 to 120 persons depending on production levels.

New Insights in the Meguma Zone of Southern Nova Scotia

Preliminary Stratigraphy and Structure of the Meguma Group in the Central Meguma Project Area

R. J. Horne

Introduction

The Nova Scotia Department of Natural Resources is currently conducting a program of geological mapping in the Central Meguma Project Area (NTS sheets 11E/04 and 11D/13). Mapping has been undertaken by Rick Horne and Bob Ryan (NSDNR), Don Fox (consultant funded through the Canada-Nova Scotia Cooperation Agreement on Mineral Development, 1992-1995), and Darcy Baker and Mary Feetham (summer employees for NSDNR). The principal aim of the program is to enhance the stratigraphic and structural knowledge of the Meguma Group in central Nova Scotia. The following is a brief overview of the stratigraphy and structure of the map area.

Stratigraphy

The Meguma Group has traditionally been subdivided into the lower, metasandstone-dominated Goldenville Formation and the upper, slate-dominated Halifax Formation. Further stratigraphic subdivision has locally been established in southwestern Nova Scotia (e. g. O'Brien, 1988; Waldron, 1990; Schenk, 1990), and similar subdivisions have been recognized during the current mapping program. A brief outline of this stratigraphy follows, but the reader is referred to Horne (1995), Ryan (1994) and Ryan et al. (1996) for further description of the units and discussion of regional correlation.

Goldenville Formation

Five informal units are locally recognized within the Goldenville Formation, all of which are dominated by metasandstone. These include, from oldest to youngest: the undivided Goldenville, Mount Uniacke unit, Long Lake unit, Lewis Lake unit and Steves Road unit. These units have only been established in the Beaverbank-Long Lake area and their lateral extent is being evaluated.

Halifax Formation

The Halifax Formation has been subdivided into three units, including, from oldest to youngest: the Beaverbank unit, Rawdon unit and Glenn Brook unit. The Beaverbank unit is characterized by siltstone, carbonate and manganese enrichment and local coticule horizons, and is represented in varying thicknesses throughout the map area. The Rawdon unit consists of sulphide-rich black slate and lesser metasandstone and occurs throughout the area. The Glenn Brook unit consists of pale grey-green metasiltstone and is restricted to the Rawdon Syncline, although this may simply reflect a lower level of erosion elsewhere.

Structure

Regional Folds (F₁)

Regional folds define the principal structure of the area and are characterized by kilometre-scale wavelengths and northeast-trending axial traces extending over long distances. The present erosional level results in exposure of the Goldenville units primarily in anticlines and exposure of the Halifax Formation units mainly in synclines. Fold-related cleavage (S₁) includes well developed slaty cleavage in fine-grained units and pressure-solution cleavage in metasandstone. Minor F₁folds include decimetre-scale folds, common within synclines of the Halifax Formation, and centimetre-scale parasitic folds, commonly developed in coticule horizons and banded siltstone of the Glenn Brook unit. Bedding, cleavage (S₁), bedding-cleavage intersection lineations (L₁) and the symmetry (i. e. S, Z, M) of parasitic folds help define fold geometry. These data, combined with map patterns constrained by stratigraphy, indicate that, generally, folds are upright-plunging to inclined-plunging, with locally overturned bedding. Younging directions indicated by sedimentary structures and cleavage vergence (bedding-cleavage relationships) indicate that folds are everywhere upward facing. L₁data indicate common local variation in fold plunge, indicating a general non-cylindrical character.

Pressure shadows on regional metamorphic porphyroblasts in slate units and coarse pyrite in metasandstone indicate a component of vertical extension during folding. Flexural-slip folding is locally demonstrated by intense bedding-parallel shear fabric within the slate intervals, with striations and slickenfibres indicating movement perpendicular to the hinge. A detailed study of flexural-slip folding has demonstrated that this was an important process in the Meguma Group (Horne and Culshaw, 1994). Locally, a crenulation cleavage (S₂) is developed within slate intervals of the Halifax Formation. S₂ is confined to bedding-parallel zones with the margins defined by slip planes and is interpreted to reflect flexural folding.

AC Joints

Southeast-trending, steeply dipping ac joints are the most prominent fracture set within the area and are best developed in the metasandstone units. Well exposed areas, such as vertical faces of quarries, illustrate a planar character and regular spacing (approximately 2 m).

Veins

Several vein sets occur within the area, the most common occurring concordant to bedding, particularly abundant within gold districts, and within ac joints. Veins also occur within kink folds and extensional fractures associated with the Rawdon Fault.

Kink Folds

Kink folds are common throughout the map area. Generally, axial planes and hinges are steep, although subhorizontal attitudes occur locally. Both dextral and sinistral rotation have occurred, suggesting development of conjugate kinks; however, this has not been established.

Southeast-trending Faults

Southeast-trending faults are a common structural element of the Meguma Terrane. A regional, southeast-trending fault is exposed on Soldier Lake, where it is characterized by cataclastic textures, including local zones of breccia-cataclasite and a wider zone characterized by slickensided fractures. The zone of influence of this fault is at least several hundred metres wide and it can clearly be seen on aeromagnetic and digital elevation model maps to extend southeast through Lake Major to the Cole Harbour area. The fault locally defines the contact between the Meguma Group and the Musquodoboit Batholith and there is apparent offset of the contact aureole. A sinistral component of offset is apparent on aeromagnetic maps and these structures are generally considered to be Mesozoic in age (Williams et al., 1995).

Rawdon Fault

The Rawdon Fault is a regional, northeast-trending fault along the north margin of the Rawdon Syncline. The fault locally juxtaposes the Meguma Group and Horton Group, Meguma Group and Windsor Group, or the Horton Group and Windsor Group. A vertical to south-dipping attitude is implied from drilling and from a significant Bouguer gravity low over the Carboniferous rocks adjacent to the fault. Juxtaposition of units suggests a large component of northwest-side-down normal faulting (Boehner, 1991).

Current mapping of the Meguma Group indicates the following features related to the Rawdon Fault. Carboniferous strata, and the unconformity between the Horton Group and the Meguma Group south of the fault, dip steeply to the northwest. Within the Meguma Group the dips of bedding and regional cleavage (S₁) shallow toward the fault (from southeast to northwest) with formation of low amplitude, northeast-trending folds (F₂) adjacent to the fault (McKay Settlement Anticline of Fletcher and Faribault, 1909; and West Gore anticline of Stevenson, 1959). Bedding-cleavage relationships indicate the F₂folds are always upward facing. Bedding-parallel faults are common within the area of F₂folds and, locally, southeast-dipping, discordant, brittle faults occur. Locally, a northeast-trending crenulation (S₂) is developed roughly axial planar to the F₂folds and northwest-trending extensional quartz veins are developed roughly perpendicular to the crenulation lineation (L₂). The structural data for the area, including a constructed cross-section, are consistent with northwest-directed thrusting and related folding of the Meguma Group and Carboniferous rocks.

References

Boehner, R. C. 1991: Seismic interpretation, potential overthrust geology and mineral deposits in the Kennetcook Basin, Nova Scotia; in Mines and Mineral Branch, Report of Activities 1990, ed. D. R. MacDonald; Nova Scotia Department of Mines and Energy, Report 91-1, p. 37-47.

Fletcher, H. and Faribault, E. R. 1909; Windsor Sheet, No. 73.

Horne, R. J. 1995; Update on bedrock mapping of the Rawdon Syncline; in Mineral Resources Branch, Report of Activities 1994, Eds. D. R. MacDonald and K. A. Mills; Nova Scotia Department of Natural Resources, Mineral Resources Branch Report 95-1, p. 57-61.

Horne, R. J. and Culshaw, N. 1994: Preliminary evaluation of flexural slip and its significance in localizing auriferous veins in the Meguma Group, Nova Scotia; in Mines and Mineral Branch, Report of Activities 1993, ed. D. R. MacDonald; Nova Scotia Department of Natural Resources, Mines and Energy Branches Report 94-1, p. 147-160.

O'Brien, B. 1988: A study of the Meguma Terrane in Lunenburg County, Nova Scotia; Geological Survey of Canada, Open File 1823, 80 p.

Ryan, R. J. 1994: Preliminary investigations of the Meguma Group stratigraphy in the Beaverbank area, Nova Scotia; in Mines and Minerals Branch, Report of Activities 1993, ed. D. R. MacDonald; Nova Scotia Department of Natural Resources, Mines and Energy Branches Report 94-1, p. 147-160.

Ryan, R. J., Fox, D., Horne, R. J., Corey, M. C. and Smith, P. K. 1996: Preliminary stratigraphy of the Meguma Group in central Nova Scotia; in Mineral Resources Branch, Report of Activities 1995, Eds. D. R. MacDonald and K. A. Mills; Nova Scotia Department of Natural Resources, Mineral Resources Branch Report 96-1, p. 27-34.

Schenk, P. E. 1990: Events and sea-level changes on Gondwana's margin: The Meguma Zone (Cambrian to Devonian) of Nova Scotia, Canada; Geological Society of America Bulletin, v. 103, p. 512-521.

Stevenson, I. M. 1959: Geology of Kennetcook, Hants County, Nova Scotia; Geological Survey of Canada, Map 1075a, scale 1:63 360.

Waldron, J. W. F. 1990: The Goldenville-Halifax transition, Mahone Bay, Nova Scotia: relative sea-level rise in the Meguma source terrane; Canadian Journal of Earth Sciences, v. 29, p. 1091-1105.

Williams, P. F., Goodwin, L. B. and Lafrance, B. 1995: Brittle faulting in the Canadian Appalachians and the interpretation of seismic data; Journal of Structural Geology, v. 17, p. 215-232.

The Victoria Goldfields of Australia: Meguma South?

R. J. Ryan rjryan@gov.ns.ca and W. R. H. Ramsay¹

The gold deposits of central Victoria, Australia, have been compared to Meguma gold deposits since the last century. Central Victoria comprises the western margin of the Lachlan Fold Belt of Cambrian to Carboniferous age and is juxtaposed against the Delamerian Fold Belt. Both fold belts form part of the Tasman Orogen in southeastern Australia (Ramsay et al., 1996). The oldest rocks exposed in the gold districts of Central Victoria are narrow, fault-emplaced Cambrian lavas (now metamorphosed to greenstones) and associated pelagic and hemipelagic metasediments. These Cambrian rocks are overlain by quartzose turbidites and mudstones of Cambrian to Silurian age and they form a 2-5 km thick sequence which extends over most of Victoria. During the Early Silurian, the turbidites were deformed into tight, upright chevron folds with associated high-angle contraction faults. The folds have been truncated by Late Devonian to Early Carboniferous granitic intrusions. Approximately half of the area underlain by the turbidite sequence is unconformably overlain by poorly consolidated gravels and sands of Tertiary to Quaternary age. Below this unconformity there are deep weathering profiles in the Cambro-Ordovician rocks. These weathered horizons sometimes extend to nearly 150 m below the unconformity. Most of the turbidites in the Ballarat region exhibit similar weathering profiles, even where there are no Tertiary gravels exposed. The Tertiary gravels are overlainby Quaternary to recent (as young as 5000 years old) basalt and associated scoria cones, believed to be the result of a failed rift along the Tasman Orogen.

The gold deposits of central Victoria can be divided into five basic affinities: (1) alluvial or placer deposits, (2) dilational-fill, mesothermal deposits of gold-arsenic-quartz, (3) fault- or shear-related deposits of gold-antimony-arsenic, (4) greenstone-related deposits, and (5) disseminated gold deposits.

The alluvial or placer deposits are hosted in the Tertiary sediments and have been subdivided into shallow and deep 'leads'. These deposits were the first to be exploited in the state of Victoria and yielded nearly 1250 tons of gold, accounting for 51% of the gold produced in the region. Most of the gold was recovered at or near the unconformity between Tertiary sediments and Cambro-Ordovician turbidites. Production from these deposits primarily took place prior to 1885.

The dilation-fill, mesothermal (or reef) deposits have been the primary producers of gold in central Victoria for the last century. These deposits are the best known and best described in the area (Baragwanath, 1923; Cox et al., 1995). The deposits typically consist of narrow, structurally controlled veins associated with dilatant zones or jogs in contraction faults, or in fold-related dilatant domains. These are the so called 'saddle reef' deposits, although as with the Meguma Terrane true saddle reefs are rare. The term 'reef' is used in Victoria to denote all quartz-vein-hosted deposits and, therefore, caution must be used in reading the Australian literature. These deposits include the famous deep mines (1400 m +) of the Bendigo gold district (Fig. 1). Mesothermal, fold-related deposits account for over 1200 tons of gold production from the area. In 1899, Faribault was the first to point out the similarities between the gold deposits in Victoria and those in Nova Scotia and he strongly believed that the Meguma deposits extend to depths equal to those in the Bendigo region (Faribault, 1899).

Greenstone-affiliated deposits are mesothermal (and possibly epithermal), shear-related deposits spatially associated with Cambrian greenstones. Examples of these deposits are the Stawell Goldfield and the Pitfield Goldfield. Although they are similar to the other mesothermal deposits, their close association with meta-volcanics and shear zones has been used as a criterion to establish them as a separate deposit type.

Occurrences of disseminated gold have been known for a long time in Victoria with the most significant deposit being the Golden Mountain Deposit which produced 6000 oz. of gold. The Golden Mountain Deposit is currently being re-evaluated by diamond-drilling. There are obvious similarities with the disseminated gold deposits of the Meguma Terrane, such as: (1) coticule horizons associated with the deposits, (2) an absence of significant quartz veins in the ore, (3) the presence of exotic metallic alloys and sulphides, and (4) gold with varying Ag content. There are also many weathered occurrences that can be loosely considered as disseminated deposits. The weathered deposits are oxidized, gold-bearing quartz vein horizons that occur primarily along anticlinal axes where weathering has dispersed gold within the oxidized bedrock. Several of these deposits are currently being mined, with grades of 1-2 g/t and total reserves for individual deposits of approximately 1 million ounces. The most notable of the oxidized deposits is the Fosterville Deposit operated by Perseverance Mining.

Fault-related deposits of gold-antimony-arsenic are also present in Victoria. These deposits appear to have been controlled by the presence of quartz veins related to faulting in domal structures. The most notable of these occurrences is located at Costerfield near Bendigo, although there are numerous occurrences to the east in the Melbourne area. Within zones of stibnite mineralization, gold can attain grades of up to 30 g/t. The total tonnage of these deposits is usually low but the combined value of the stibnite-gold ore makes them attractive exploration targets.

The similarities between the Victoria gold deposits and Meguma deposits are: (1) gold occurs primarily in quartz veins; (2) gold is hosted by Cambro-Ordovician, quartz-rich turbidites where carbon-rich slates occur; (3) grades of the vein deposits are 7-12 g/t; (4) hosts include a variety of quartz vein types, such as saddle reefs, fissure veins, stockworks, bedding concordant veins, and combinations thereof; (5) deposits are hosted by tightly folded rocks that are metamorphosed to lower greenschist facies; (6) thickness of the veins; (7) the presence of silicification and carbonate alteration; (8) chemistry and temperatures of mineralization indicate a metamorphic fluid source; (9) the presence of calc-silicates and coticules; (10) the presence of disseminated gold deposits; (11) gold is preferentially concentrated in anticlinal structures; and (12) the presence of gold-antimony deposits. There are many other similarities too numerous to list here.

The differences between deposit settings in central Victoria and the Meguma Terrane are: (1) more abundant quartz veins (mostly barren) in Victoria; (2) the presence of thick, Tertiary, gold-bearing gravels in Victoria; (3) the turbidite sequence is thinner in Victoria; (4) turbidites are usually interbedded with siltstones and slates in Victoria, whereas in the Meguma Terrane there are very thick quartzarenite-dominated sequences in the Goldenville Formation; and (5) the scale of folding is much tighter in Ballarat, with wavelengths of 200-700 m as opposed to 1-4 km in the Meguma Terrane.

Comparison of the central Victoria goldfields and the Meguma deposits has important implications for exploration in the Meguma Terrane. The Victoria example has shown that narrow, quartz-vein gold deposits, similar to those in the Meguma, can be mined profitably. Furthermore, disseminated, low grade concentrations of gold (1-2 g/t) can be mined as economically viable deposits. Extension of the Meguma deposits to depth is virtually untested and the potential for larger deposits exists in Nova Scotia (Fig. 1). Finally, mineralized veins can not be assessed without bulk sampling and, where applicable, declines must be an intricate part of the exploration strategy.

Figure: (Not presently available)
Figure 1. Comparison of the major gold-producing mines of central Victoria and Nova Scotia.

References

Baragwanath, W. 1923: The Ballarat Goldfields; Victorian Geological Survey, Memoir 14, 496 p.

Cox, S. F., Sun S-S., Etheridge, M. A., Wall, V. J. and Potter, T. F. 1995: Structural and geochemical controls on the development of turbidite-hosted gold quartz vein deposits, Wattle Gully Mines, Central Victoria, Australia; Economic Geology, v. 90, p. 1722-1746.

Faribault, E. R. 1899: The gold measures of Nova Scotia and Deep Mining; Journal of the Canadian Mining Institute, v. 2, p. 119-129.

Ramsay, W. R. H., Arne, D. A., Bierlein, F. P. and VandenBerg, A. H. M. 1996: A review of turbidite-hosted gold deposits, Central Victoria; in Sedimentary-hosted Mesothermal Gold Deposits-A Global Overview; University of Ballarat, Paper 96-1, p. 5-14.

¹University of Ballarat, Ballarat, Victoria, Australia

Lithogeochemistry of the Goldenville-Halifax Transition Zone (GHT) at North Beaverbank, Nova Scotia

M. Feetham¹

Lithogeochemical variations within the Goldenville-Halifax transition zone (GHT) at North Beaverbank were studied in order to better understand this boundary between meta-quartzarenites of the Goldenville Formation and slates of the overlying Halifax Formation. Geochemical analyses of 35 bulk rock samples were conducted using X-ray fluorescence, and both polished and regular thin sections were used to study the petrology of each of the analytical samples. Statistical analyses using Spearman correlation coefficients were also conducted on the geochemical data.

Based on lithological, petrological, and chemical criteria, the transition zone at North Beaverbank is divided into three zones. Zone A (the coticule horizon), which occurs at the base of the Halifax Formation, consists primarily of grey, sulphide-rich, silty slate with abundant spessartine garnet and Mn concentrations. Zone B, which is stratigraphically below Zone A, is similar lithologically to Zone A but has more abundant fine-grained meta-quartzarenite beds. Garnet and sulphide phases are less abundant in this zone. Zone C, which occurs just above the top of the Goldenville Formation, consists of predominantly medium- to coarse-grained meta-quartzarenite, and contains few sulphides, rare garnet, and minor Mn concretions.

Results from whole-rock geochemistry indicate that the GHT at North Beaverbank is anomalously rich in Mn and Ti due to the presence of spessartine garnet, ilmenite and sphene. Arsenide phases are also distinctive to this zone. Strong positive correlations are observed between Cr and Al₂O₃, K₂O and Al₂O₃, MgO and Fe, and Zn and MgO. No strong negative correlations were observed for any of the elements determined.

In comparison to rocks containing coticules from other areas in the world, the North Beaverbank transition zone is lithologically and chemically similar to the Eastville deposit, with the exception that the Beaverbank section lacks the Zn and Pb mineral phases that are observed at Eastville, Nova Scotia. The coticule rocks of North Beaverbank are also similar to the Andros and Ottre coticules, although the European examples lack the enrichment in Fe, S and Cu that is observed at North Beaverbank. From published discrimination diagrams there is some indication of an active continental margin for the tectonic setting of the clastic material for the North Beaverbank rocks and, of an intermediate (between felsic and basaltic andesite) source.

¹KaoClay Resources Inc., P. O. Box 29, Milford Station, Nova Scotia B0N 1Y0.

Petrochemical and Isotopic Studies of Pelitic Rocks and Associated Veins at Cochrane Hill

P. K. Smith and A. K. Chatterjee

The primary focus of geological investigation into gold deposits in the Meguma Group is currently being directed on two main fronts: (1) systematic petrochemical and isotopic studies of host rocks and vein minerals, and (2) co-operative initiatives with the private sector to assess gold grade and the petrography and geochemistry of selected vein and disseminated styles of mineralization. The new data are expected to provide addition information on relative and absolute timing of gold mineralization, mineral paragenesis, and conflicting metallogenetic models. New data will also provide reliable assay information comparing several analytical techniques on variable lithologies (vein, quartzarenite/greywacke and argillite/shale). A brief summary of ongoing studies at the Cochrane Hill deposit is given below.

Cochrane Hill Gold District

The Cochrane Hill gold district, located at longitude 62°00'38" and latitude 45°14'52", was the site of extensive exploration activity during the 1980s (Northumberland Mines Ltd., Inco Ltd., and Nova Gold Ltd.). Underground bulk sampling by the latter two companies indicated gold grades of ~0.04 oz./ton and ~0.07 oz./ton, respectively.

Quartz veins occur in a 15 to 25 m wide zone and extend for a strike length of ~1200 m. The veins strike east (~075°) and are hosted by interbedded metapelite and metagreywacke along the overturned, north-dipping (75°) limb of the Cochrane Hill Anticline. The anticlinal fold axis passes approximately 75 m north of the deposit. The present investigation is based on samples collected from the open-pit area, adjoining wall rocks and similar regional rock types located well away from the influence of mineralization. Petrography and geochemistry of the wall rocks and veins, as well as Pb isotopic composition of the veins and metamorphic minerals, suggest the following:

1. The porphyroblastic staurolite schist which forms the north and south walls of the deposit (samples collected within 5 m of the vein system) show typical mineral assemblages consisting of quartz + staurolite + garnet + biotite + plagioclase + andalusite + muscovite, indicating amphibolite facies metamorphic conditions. Regional pelitic rocks collected at a distance of 2.5 km from the mine site show identical metamorphic mineral assemblages. On the basis of geobarometric and geothermometric considerations, the estimated P-T conditions were 2.5-3.0 kb and 500-550°C.
2. Geochemically the unaltered pelitic wall rocks are characterized by high Al₂O₃ (av.=21.17), Rb/Sr (av.=0.82), K/Rb (av.=219), Y/Ho (~27) and REE patterns typical of shale (Fig. 1). Gold concentrations in these rocks range from <4 to 6 ppb.
3. Pelitic rocks within the pit area are divided into two groups on the basis of sulphide content. Sulphide-rich pelites occur in zones ranging in width from 1 cm to ~2 m and are spatially associated with sulphide-rich veins. Mineralogically the sulphide-rich pelites are characterized by a marked increase in modal abundance of graphite, carbonates and chlorite when compared to the unaltered wall rocks. Geochemical comparison with the unaltered pelite samples reveals a significant enrichment in As, Au (av.=580 ppb), Sb, Pb and Zn. The associated REE pattern of the sulphide-rich pelites clearly shows depletion of LREE and enrichment of HREE when compared to unaltered pelites (Fig. 2).
4. Hydrothermal veins within the pit area are also divided into two groups on the basis of mineralogy. Sulphide-poor veins have diverse mineralogy but in general can be further divided into three distinct mineral associations. They are:
   1. quartz-feldspar-biotite-muscovite,
   2. quartz-andalusite-garnet-staurolite-muscovite -feldspar ± sillimanite, and
   3. quartz-amphibole-garnet ± diopside ± sphene ± apatite.

   The sulphide-rich veins are characterized by:

   1. quartz-arsenopyrite-gold-pyrrhotite-galena-sp halerite-carbonate,
   2. quartz-pyrrhotite-arsenopyrite-carbonate ± gold, and
   3. rare quartz-carbonate mineral assemblages.
5. Sulphide-poor veins (pegmatoid and calc-silicate) are essentially devoid of gold and the immediate wall rocks show no evidence of hydrothermal alteration. In addition, the composition of garnet, biotite, staurolite and feldspars within the veins and the P-T estimates derived from the coexisting minerals are nearly identical to those observed for the regional metamorphic conditions. The amphibole-garnet-bearing veins are characterized by a positive europium anomaly, a feature associated with Ca-rich mineral assemblages. The sulphide-poor 'pegmatoid veins' are unlike the quartz-feldspar-muscovite pegmatite veins outside the deposit which show a granitic affinity (Fig. 3).
6. Sulphide-rich veins have low concentrations of REE (<10 ppm) but are distinctive in terms of a positive europium anomaly, and (La/Lu)N and (La/Sm)N ratios. The gold content ranges from 4.39 ppm to 7.87 ppm in pyrrhotite-arsenopyrite-dominated mineral assemblages, and 11.28 ppm to 25.02 ppm in arsenopyrite-dominated veins. Both types of mineral associations are characterized by significant enrichment of Pb, Zn and Sb. Note the marked differences in REE pattern for the sulphide-poor and sulphide-rich veins (Figs. 4 and 2, respectively).
7. Preliminary Pb isotope data for hydrothermal and metamorphic minerals (i. e. feldspar, muscovite and andalusite in sulphide-poor veins; arsenopyrite, pyrrhotite and galena from sulphide-rich veins and staurolite from the wall rocks) suggest the following:
   
   1. Galena, pyrrhotite and arsenopyrite are the least radiogenic minerals and all these minerals closely define the initial composition (i. e. pyrrhotite and arsenopyrite contain most of their lead as common lead and their compositions are similar to galena). These compositions lie on or close to the growth curve with a µ value of 9.74. Arsenopyrite from the pyrrhotite-dominated vein sample is slightly more radiogenic than arsenopyrite from the arsenopyrite-dominated vein. It is argued that the gold at Cochrane Hill was deposited from a fluid that would be approximately similar to an average crustal source.
   2. The compositions of lead in feldspar, muscovite and andalusite from barren veins are distinctly more radiogenic than for lead in sulphides, producing a linear array that lies above the growth curve (i. e. higher²³⁸U/²³⁴Pb ratios) and defines a slope of 0.0545965 with an M.S.W.D. of 1.04, corresponding to an isochron age of 396 Ma. Analytical error will cause the observed amount of scatter 41% of the time, as indicated by the M.S.W.D. of 1.04. Staurolite in the unaltered pelites overlaps the composition of muscovite and falls on the same linear array. The combined data for all minerals (i. e. hydrothermal minerals in sulphide-poor veins and staurolite in unaltered pelites) produce an age of 399 Ma.

Conclusions

In summary, host rocks at the Cochrane Hill gold deposit were subjected to amphibolite facies metamorphism. Structurally controlled, sulphide-poor veins within the deposit appear to display similar P-T conditions of regional metamorphism. The REE geochemistry of these veins indicates the influence of wall rocks. Auriferous, sulphide-rich veins appear to show net loss of LREE and net gain of HREE, As, Sb, Pb and Zn, together with graphite and CO₂. From the lead isotopic studies it appears that two distinct fluids were responsible for the generation of hydrothermal veins at Cochrane Hill. In both cases the fluids were dominated by crustal components; however, the²³⁸U/²³⁴Pb ratios of the two fluids were distinctly different. The higher µ fluids were probably pre- to syn-metamorphic while the lower µ fluids were post-metamorphic. These data also suggest that mixing of the two fluids was not responsible for gold mineralization.

Accepting that gold mineralization occurred later than regional metamorphism (i. e. 397-405 Ma) requires that the identical structural site was utilized by later auriferous fluids. This implies that 'site preparation' occurred prior to Acadian regional metamorphism. This observation may have regional metallogenetic implications within the Meguma Zone but requires testing elsewhere.

Figures: (Not presently available)
Figures 1-4. REE distribution patterns for selected rock types in the Cochrane Hill gold district.
Figure 1. shows the REE pattern of sulphide-poor, regional staurolite schist and similar unaltered pelite at the deposit, relative to the average shale (North American Shale composite, NASC: Post Archean Australian Shale, PAAS; and Devonian Belgian Shale, BS.
Figure 2. shows the REE pattern for sulphide-rich pelite from the open pit and indicates depletion of LREE and enrichment of HREE relative to sulphide-poor pelite.
Figure 3. shows the REE pattern for sulphide-rich veins and indicates LREE depletion and HREE enrichment relative to the average unaltered pelite (x 10).
Figure 4. shows the REE pattern for sulphide-poor veins from the deposit and a single pegmatite sample from outside the influence of mineralization.

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