Geological Fieldwork 1981 a Summary of Field Activities of the Geological Branch, Mineral Resources Division Paper 1982 -1

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Geological Fieldwork 1981 a summary of field activities of the geological branch, mineral resources division Paper 1982 -1

Province of British Columbia Ministry of Energy, Mines and Petroleum Resources ISSN 0381-243X

Victoria British Columbia Canada

January 1982 FOREWORD

This is theeighth year of publication of GeologicalFieldwork, a publicationdesigned to acquaint the interested public with the preliminaryresults of fieldwork of theGeological Branch as soon as possible after thefield season. The reportsare written without the benefit of extensivelaboratory or office studies. To speed publication, figures have generally beendraughted by theauthors.

This edition of GeologicalFieldwork has a revisedformat with two sections.Project andApplied Geology includesreports of nletallic and coalfield investigations, reports of District Geologists, and property examinationrelated to some mineralproperties funded in part by Ministry programs. The OtherInvestigations section consists mainly of reports of work done by differentuniversities funded by grants of theMinistry.

The coverphotograph depicts a fly camp in the Monashee Mountains.

Outputof thispublication was coordinated by W.J. McMillan and productionediting and layout by thehtblications Section and D. Bulinckx of Project Geology. R. HOenSOn of theGeological Branch draughting office assisted with layout.

A. Sutherland Brown, ChiefGeologist, GeologicalBranch, MineralResources Division.

TABLE OF CONTENTS

PROJECT AND APPLIED GEOLOGY Page

1 Hora, Z.D.: Mapping of Silica Occurrences in British Columbia 9

2 Church, B.N.: Notes on the Penticton Group- A Progress Report. on a New Stratigraphic Subdivisionof the Tertiary, South-. Central British Columbia (82E/L) ...... 12

3 Church, B.N.: The Riddle Creek Uranium-Thorium Prospect (82E/12W) ...... 17

4 Addie, George G.: The Use of Personal Computers and Open File Geochemical Data To Find New Exploration Targets ...... 23

5 Addie, George G.: The Nelson-Ymir-Salmo Mining Camp- A New Look at Zoning Based on Production Records...... 28

6 Addie, George G.: A New Look at the Rossland and Boundary Mining Camps Using LogCu (lb.)/Log (nu + Ag) (02.) ...... 33

7 Kwong, Y.T. John and Addie, George G.: Tillicum Mountain Gold Prospect (82F/13) ...... 39

8 Grieve, D.A.: Mount Banner Area, Elk Valley Coalfield (82G/15, J/2) ...... 46

9 Grieve, D.A. and N.C. Ollerenshaw: Stratigraphy of the Elk Formation in southeastern British Columbia(82 C, J) .. . . 51

10 White, G.P.E.: A Copper-Silver Occurrence in the Falkland Area (82L/12E) ...... 54

11 White, G.P.E.: The Stirling Molybdenite Showing (82M./8W) ....,, 56

12 White, G.P.E.: A New Zinc Occurrence in the Revelstcke Area (82M/8W) ...... 57

13 White, G.P.E.: The Thanksgiving Tungsten Showing (82M/lE)...It 58

14 Schiarizza, Paul: Clearwater Area (82M/12W; 92P/8E, 9E) .....,, 59

15 White, G.P.E.: Notes on Carbonatites in Central Brit,ish Columbia (83D/6E) ...... 68

16 Eastwood, G.E.P.: Leech River Area, Vancouver Island (92B/5g, 12 b-c) ...... 70

16a Church, B.N., Brasnett, D., and Eastwood, G.E.P.: Gravity Survey of the Colwood Section of the Leech River Fault ... 75

5 TABLE OF CONTENTS (Continued) PRELIMINARY INVESTIGATIONS (Continued) Page

17 Eastwood, G.E.P.: Geology of the Whitehouse Creek Area (92B/13f, 9) ...... 78

18 Eastwood, G.E.P.: Upper Sutton Creek Area (92C/16c) ...... 84

19 Ray, G.E.: Carolin Mine - Coquihalla Gold Belt Project (928/6, 11) ...... 87

20 McMillan, W.J., Armstronq, R.L., and J. Harakal: Age of the Coldwater Stock and Nicola Batholith, near Merritt (92H). 102

21 Church, B.N.: The Black Dome Mountain Gold-Silver Prospect (920/7E, 8W) ...... 106

22 Church, B.N. and Diakow, L.: Geology and Lithoqeochemistry of the Capoose Silver Prospect (93F/3, 6) ...... 109

23 Broatch, Jane: An Investigation of the Palynology of the Peace River Coalfield, Northeastern British Columbia...... 113 24 Schroeter, T.G.: Toodoqqone River (94E) ...... 122

25 Panteleyev, A.: Toodoqqone Volcanics South of Finlay River (943/2) ...... 135

26 MacIntyre, D.G.: Akie River Project (94F) ...... 142

27 MacIntyre, D. and Diakow, L.: Kwadacha Barite Deposit (94F/10W) ...... 149

28 Panteleyev, A. and Diakow, L.J.: Cassiar Gold Deposits, McDame Map-Area (104P/4, 5) ...... 156 29 MacIntyre, D.G.: Midway Occurrence (1040/16W) ...... 162

OTHER INVESTIGATIONS

30 Sinclair, A.J.: Multivariate Models for Relative Mineral Potential, Slocan Silver-Lead-Zinc-Gold Camp (82F)...... 167

31 Matysek, P., Sinclair, A.J., and Fletcher, W.K.: Rapid Anomaly Recognition and Ranking for Multi-element Fegional Stream Sediment Surveys ...... 176

32 Journeay, J. Murray: Structural Setting Along the Northwest Flank of menchman Camp Dome, MOnashee Complex (82M/7)... 187

6 TABLE OF CONTENTS (Continued) OTHER INVESTIGATIONS (Continued) Page

33 Andrew, A., Godwin, C.I., and Sinclair, A.J.: Preliminary Examination of Gold Metallogeny in the Insular Belt of the Canadian Cordillera Using Galena-Lead Isotope Analyses... 202

34 St. Louis, Robert M.: Platinoids in the Tulameen Ultramafic Complex (92H) ...... 218

35 Ross, John V. and Engi, Martin: Mantle Processes as Deduced from Alpine Ultramafics ...... 223 36 Linds, R.K.: Bowron River Progress Report ...... 227 37 Shen, IC. and Sinclair, A.J.: Preliminary Results of a Fluid Inclusion Study of Sam Goosly Deposit,Fiquity Mines Ltd., Houston ...... 229

38 Whittaker, Peter J.: Chromite Occurrences in Mitchell Range Ultramafic Rocks of the Stuart Lake Belt, Cache Creek Group (93N) ...... 234

39 Carmichael, S.M.M.: Depositional Environments and Paleocurrent. Trends in the Gates Member, Northeast Coalfield...... 244

7 PROJECT AND APPLIED GEOLOGY

MAPPING OF SILICA OCCURRENCES IN BRITISH COLUMBIA

By Z.D. Hora

A fieldreconnaissance of silica occurrenceswith mappingand sampling was carried on duringthe 1981 field season. The purposeof the study is; to obtaininformation about the industrial potential of reportedoccurrences in viewof recent interestfor raw mterials to produce ferrosilicon and silicon metal. The studiedoccurrences were those where previousdata did notprovide enough informationeither on sizeor chemical composition of the silica. The followingproperties were examined.

WHITE ELEPHANP (82L/4E, 500 09'-119' 33')

The silicaoccurrence consists ofan oval-shapedquartz plug, 27 metres long and 12 metres wide, in a coarse-grainedhornblende-bicmtite granite. Part of theplug, which is mineralized by massive pyrrhotitcwith a small amount of chalcopyrite and some goldvalues, was mined between 1921 and 1933. The mined-out arealeft a pit 15 metres by 9 metres that is now filled with water. The oldworkings extend to a depthof approximately 66 metres below thesurface.

FAIRVIEW (82E/4E, 49O 12'-119° 38')

A quartzvein, with minor goldvalues up to 7.5 metres wide, was mined Underground from 1933 to 1961 and mre than 350 000 tonnes of smelter flux were shipped toTrail. In outcrop, the vein strikes 118 degreeswith dip 30 to 50 degreesnortheast; the quartz is exposed in an area7.5 metres by 31 metres. The surrounding rocks consist of slightly metamorphosed sedimentaryrocks, mainly dominated by quartzites and metaqreywackes.

SUSIE (82E/4E, 49" 13'-11g0 36')

A body ofmassive, milky white quartz is enclosedin a granitic intrusion andcrops out as a knoll 35 metres long and 20 metres wide.. Most of the outcrop seems relativelyfree of impurities,although limonite staining andsmall amounts of pyrite,galena, and pyrrhotite are prosent. Between 1964 and 1976 some 20 000 tonnes of silica fluxwith minor goldvalu,es was shippedto Trail froman underground operation.

9 SNOWDRIFT (82F/11W, 49O 37'-117O 29')

Massivemilky white quartz forms the core of a pegmatite dyke. The quartz pod is exposedover an area of 45 metres by 60 metres and is surrounded by a large mass consisting of perthitic undergrowthsof feldspar and quartz.In 1971 a smallquarry, 10 metres by 20 metres, produced 500 tonnes of silica which was used locallyas a stuccodash.

LOUMARK (82E/15E, 49O 58'-118"40')

Outcropsscattered 50 metres of strikelength expose an 8-metre-wide vein ofwhite opaque quartz at least 8 metres wide withnorthwest strike that cutsthrough a body ofNelson granite. The quartz is relativelyfree of impuritiesalthough limited areas have disseminated pyrite.

RICE (82F/9E, 49O 34'-116O 04')

A group of outcropsover an area of 15 metres by 30 metres expose a body of hydrothermalquartz that is highlycontaminated by limonitemalachite stains. Small crystals of pyrite are a common accessory component in unweatheredquartz; low gold values are also reported. Foliated Eine- grainedbrown-green pyritic metasedimentscomprise the surrounding rocks. Some 1 400 tonnes was mined and shipped to Trail in 1973.

QUARTZ (93G/8W,53O 22'-122° 26')

A massivewhite quartz vein is exposed in a zone more than 205 metres in length and 21 metres in width. It strikes 140 degreesand, tothe northwest,splits into two branches. The countryrock consists of slightlyfoliated, fine-grained, dark green-black metasedimentary rocks.

CARIBOO GOLD QUARTZ (93H/4E, 53' 04'-121° 31')

The B.C. vein is a massive, mostlybarren white quartz vein. It is exposed inscattered outcrops along 250 metres of strikelength and is up to 10 metres in width. The veinconsists of parallel bandsof massive quartzwith many small fragments of phyllitewallrock between individual bands.

Severalsedimentary siliceous units were also examined:

(1) Monashee quartzites in theRevelstoke area were found to be highly contaminated by muscovite, and to a lesser degree,biotite and other darkminerals. (2) Southof Salmo nearthe abandoned Jersey mine, theQuartzite Range Formationcontains a 75-metre-wide ridge ofmassive quartzitewith onlytraces ofmuscovite.

10 (3) In the Barkerville area the Yanks Peak quartzite is locally pure white with no macroscopically visible impurities. However, many exposures exhibit rusty spots replacing mafic minerals. Secondary quartz and carbonate veinlets are common. (4) Rocky Mountain Formation sandstones in the Flathead area are highly calcareous beds, locally contaminated by micas and feldspar fragments.

ACKNOWLEDGMENTS

Fieldwork was carried out by Margaret Hanna (party chief) and Jaquir! Rublee (assistant) under the supervision ofZ.D. Hora.

Analysis of data information collected during the summer is in progress.

11 NOTES ON THE PENTIC'PON GROUP A PROGRESSREPOW ON A NEW STRATIGRAPHICSUBDIVISION OF THE TERTIARY SOUTH-CENTRALBRITISH COLUMBIA (82E/L)

By B.N. Church

The name Penticton Group has beenproposed for Eocene volcanic and sedimentary rocks of the Okanagan-Boundary region. The areas of recent studyrequired to delineate these rocksare shown on Figure 1.

Figure 1. Index MP of areas of detailed study.

12 The principalresources of thePenticton Group arecoal, precious metal deposits, uranium, and geothermalenergy.

The Group consists of sixwell-defined formations having an aggregate thickness of about 2 500 metres in thetype area near Penticton (No. 4, Figure 2). At thebase are polymictic conglomerates and breccias referredto as the Springbrook Formation and coevalbeds of the Kettle RiverFormation consisting of graniteboulder conglomerate, rhyolite breccia, and tuffaceoussedimentary rocks. Above this is t.he Marron For- mation composed mainly of thickandesite, trachyte, and phonoliticlava flows,succeeded upward by dacitic and some andesitic domes: of the blararna Formation.This is followed by volcanicbreccias and lacustrine and fluvialsedimentary rocks of the White Lake Formationand, uppermost., the Skaha Formationconsisting of alandslide complex and fang1.omeratebeds. The Group rests unconformably on pre-Tertiarygranitoids, metamorphosed Mesozoicsedimentary and volcanicrocks, and olderschists and gneis:oes.

1 2 3 4 5 6 HATCREEK TERRACE KELOWNA PENTICTON MIDWAY REPUBLIC MTN.

W Z

W z W 0 -.7 2 I

TW wz 0 0 W

Flgure 2. Correlation chart of major Tertiary units.

13 The agerange forthe Group, asdetermined by potassium-argonradiometric methods, is 48.4 Ma (wholerock) to 53.1 Ma (biotite) f1.8 Ma. Pre- liminarytests performed on theprincipal lava members indicate normal magneticpolarity. Overlying the Group areisolated patches of Miocene rhyolite(Olalla rhyolite, 13 Ma) 'plateaubsalt', andyounger 'valley basalt. '

In the Kelowna area'plateau basalt' occurs on Carrot Mountain ( 11.8 Ma) and Daves Creek (14.9 Ma). TheLambly Creek basalt (0.762 Ma) is the onlyso-called 'valley basalt' of theregion.

Northand west of thetype area (see Nos. 1, 2, and 3, Figures 1 and 2) theconstitutent formations interfinger and arereplaced by units of the KamloopsGroup (Ewing, 1981). At TerraceMountain near Vernon the names NaswhitoCreek Formation, Rouleau Rhyolite, Attenborough Creek Formation, and Shorts CreekFormation are applied to Eocene volcanic and sedimentary unitsthat only partly correlate with the Penticton Group (Figure 2). Further west at Hat Creek few comparisonscan be made otherthan to say that the Coldwater Beds partlyresemble the basal Tertiary sedimentary rocks in the Okanagan area.Recent studies suggest that some part of thesebasal successions may be Cretaceous (K. Shannon, pers. corn.).

To thesoutheast near Midway in the BOundary area the EOcene section is incompletebut strikingly similar to the type assemblage (Monger, 1968).

In northern Washington Statenear the Republic area the O'Brien Creek Formation and Klondike buntain Formation, at the baseand top of the Eocene sectionrespectively, are correlated in part withthe Kettle River Formationand Skaha Formation of thePenticton Group (Pearson and Obradovich, 1977). However, thedacite-rich Sanpoil volcanics which underlie part of theRepublic graben are lithologically unlike the Plarron Formation and represent a significantuncorrelated unit.

A checkwith Dr. T.E. Bolton in thespecial projects section of tRe Geological Survey of Canada on thepre-occupation of stratigraphic names hascleared the following list for formaluse in south-centralBritish Columbia:

Area Nam Area Age

Hat Creek LakeFinney Beds (Eocene) kdicine Creek Formation (Eocene) Hat Creek Formation(Eocene)

TerraceMountainNaswhito Creek Formation(Eocene) Bouieau Rhyolite (Eocene) Attenborough Creek Formation (Eocene) Shorts Creek Formation (Eocene)

Penticton Penticton Penticton Group (Eocene)

Ke I owna Lambly Creek (Pleistocene)Basalt

It isconsidered that name Hat CreekCoal Formation (Eocene) is sufficientlydifferent from Hat Creek beds (Oligocene)of Wyoming and Hat Creek Basalt(Recent) of northern California.

14 structuralcontrol of thevarious outliers of thePenticton Group relates to some east-west-trendingsynclines and to a pattern of north-south gravityfaults andpronounced conjugate shears of northeast and northwest orientation. These folds and fracturesare viewed as essential elements in a north-southdirected stress scheme thought to be responsiblefor the many graben-likestructures and overallbasin and range-likafabric of the region.

The Hat Creekbasin is a typicalgraben. In this example thecentral zone of thevalley has beendowndropped on a series of north-southtension faultstrending subparallel to the direction of regional maKiman stress, thewalls of this grabenhaving been offset by northwest an,3 northeast- trendingconjugate shears.

Vertical movementon thegraben faults is commonly inthe range of hundreds of metres. As viewed on ShortsCreek near Vernon, theTertiary bedshave been downfaulted inexcess of 700 metres against Bolder limestone and granite; at Hat Creek thevertical displacement is locally in excess of 1 000 metres. As a netresult of this movement, cormnon1:y thebase of thesecontinental beds is displaced well below mean sea levelelevation.

Lateral movement on theshear faults is notreadily documented although it is suspectedthat the southern Okanagan andBoundary areas may have resided on a northeast-trendinggeothermal lineament simi1a:c to the present Reno, Nevada-Billings, Montana volcanic-geothermal belt (Grim, 1977). Thiscould explain the marked similarity of thestrstigraphy and petrography of the Eocene volcanicrocks of the Okanagan an83Roundary areas.This might also partly account for the resetting to Eocene of radiometric dates of crystalline basementrocks inthe region (Ross, 1974).

The hypotheticalrepositioning of Penticton Group rocksin the south Okanagan andBoundary areasto juxtaposition on a northeast-trending geothermal belt would require a southeast-northwesttranslation of ab,out 80 kilometres.Extending the hypothetical geothermal belt and lithologicalcorrelations to the Highwood area of central Wmtana (similarities noted by Church, 1973, p. 75), a translation :in the order ofseveral hundred kilometres muld be required. It is notedthat lateral translations of this magnitu*have been recorded in theNorthern Cordillera(Norris, 1981, G.A.c. abstract, p. 29).

REFERENCES

B.C. Ministry ofEnergy, Mines & Pet. Res.,Geology inBrit.ish Columbia, 1975, pp. G99-Gl18; GeologicalFieldwork, 1978, Paper 1979-1, pp. 7- 15; Prelim. Map 35, Geologyof thePenticton Tertiary Outlier (revised 1980); Prelim. Map 37, Geologyof theTerrace Mountain Tertiary Outlier(revised 1980); Prelim. Map 39, Geoloqy of the Kelowna TertiaryOutlier (West Half), 1980; Prelim. Map 41, Geology of the Rock Creek Tertiary Outlier, 1980; Prelim. Map 45, Geologyof the Kelowna Tertiary Outlier (East Half), 1981.

15 Church, B.N. (1973): Geology of the White Lake Basin, B.C. Ministry of Energy, Mines .s Pet. Res., 5ull. 61, 120 pp. Ewing, T.E. (1981): RegionalStratigraphy and StructuralSetting of the Kamloops Group, South-centralBritish Columbia, Cdn. Jour. Earth Sei., Vol. 19, NO. 9, pp. 1464-1477. GeologicalAssociation of Canada (1981): Symposium on 'The Last 100 Mil- lion Years of Geology and MineralDeposits in theCanadian Cordillera', in Abstracts, pp. 14 and 29. Grim, P.J. (1977): GeothermalEnergy Resources of theWestern United States,National Geophysical and Solar-Terrestrial Data Center. Monger, J.W.H. (1968): EarlyTertiary Stratified Rocks, Greenwood Map- Area (82E/2), British Columbia, Geol. Surv.,Canada, Paper 67-42, 39 PP . Pearson, R.C. andObradovich, J.O. (1977): Eocene Rocks in Northeast Washington - Radiometric Agesand Correlation, U.S.G.S., Bull. 1433, 41 PP. Ross, J.V. (1974): A Tertiary TnermalEvent in South-centralBritish Columbia, Cdn. Jour.Earth Sci., Vol. 11, No. 8, pp. 1116-1122.

16 THE RIDDLE CREEK URANIUM-THORIUM PROSPECT (82E/12W)

By B.N. Church

The Riddle Creek uranium-thorium prospect, 15 kilometres west: Of Summerland, was discovered in 1977 andacquired the same year by British Newfoundland ExplorationLtd. Work on theproperty to dateincludes line- cutting, mapping, soil geochemistry, and severalshort drill holes.

The presentreport is based on recentgeological and scintillometer surveysand a lithogeochemicalstudy sponsored by theMinistry.

GEOLOGICAL SETTING

A large radioactive anomaly coincideswith an Eocene volcanic: centre near theheadwaters of RiddleCreek (Figure 1). The principalradioactive rocksinclude trachytes andmafic phonolites of the Marron Formationand consanguineousigneous intrusions of theCoryell-type.

LOW-RADIOACTIVE COUNTRY ROCKS

At thebase of the Tertiary section and north of the zone of anomalous radioactivity,poorly exposed polymictic boulder conglomerate beds are tentativelyassigned to the SpringbrookFormation. These rocks appear to beunconformably underlain by graniticphases of the Okanagan Batholith (Jurassic-Cretaceous) and overlain byunnamed andesites. The andesiteis form a significantformation in the northeast part of the area where lava and breccia are 250 metres thick.Alkaline andesite dominates (No. 1, Table 1) and is characterized by scatteredmicrophenocrysts of plagioclase and hornblendeusually less than 1 mtllimetre indiameter.

Scintillometer readings on these rocks and other basal andbasement units range from 40 to 80 counts per second.

RADIOACTIVE ROCKS

Rocks that show anomalous radioactivity are principally mafic: phonolites andtrachyte lavas and breccias (Nos. 2 and 4, Table 1). Thetse overlie theandesites and onlap parts of the Okanagan Batholith. They are dated 52.7t1.8 Ma (K/Ar on biotite) and correlatewith the Yellow Lake Member of the Marron Formationnear Penticton.

Mafic phonolites, whichform the base of the Yellow LakeMenher, are exposed on theridges north and northeast of RiddleCreek where interlayeredlava flows and lahardeposits attain a thickness of about 75 metres. Petrographicexamination shows conspicuous rhomb-shaped anorthoclasephenocrysts to 2 centimetres in length and smaller subhedral

Tableof Chemical Analyses

1 2 3 4 !j 6 Oxidesrecalculated to 100 si02 57.89 57.37 63.87 61.39 57 -58 66.51 Ti02 0.96 0.93 0.64 0.84 0.87 0.49 A1203 16.38 19.16 17.92 17.05 16 -21 17.01 Fe2& 4.43 3.01 3.14 3.43 3.83 2.58 FeO 1.03 1.77 0.73 1.07 2.48 0.24 M nO 0.08 0.11 0.09 0.09 0.12 0.14 MgO 4.331.10 2.40 1.99 3.73 0.28 C a0 6.90 4.05 0.64 3.34 5 -22 0.84 Na20 4.12 5.47 4.71 6.05 K%O 3.88 5.39 7.14 5.33 5.25 5.86 lorn mmrr;Crcr mrr;Crcr mm mm Oxidesand elements as determined 0.56 2.02 0.90 +HzO 2.02 0.56 0.20 1.14 0.70 0.58 0.35 0.75 -H;O __ 0.35 0.58 0.18 0 -41 0.70 co2 0.25 0.25 c 0.11 0.25 0.25 0.25 s 0.02.. " <0.01~.~- (0.005~.." 0.G 0.02 0.01 pa os 0.82 0.46 0.25 0.32 0.68 <0.15 BaO 0.30 0.21 0.10 0.20 0.23 0.013 SrO 0.30 0.07 0.42 0.21 0.31 0.02 Molecular Norm Quartz 2.0 1.3- 5.7 6.6 Orthoclase 22.7 31.1 41.8 31.0 30.6 34 .O A1 bi te 36.7 38.8 41.8 48.3 41 ,.8 53.0 Nephel ine - 7.3 - - - Anorthite 14.6 10 .o 3.1 6.1 7,.5 1.9 Woll astoni te 7.7 3.9 - 4.1 7.2 0.9 Enstatite 11.8 5.4- 3.0 0,.6 0.8 Ferrosili te - - - - - Forsteri te - 4.9 - - 7,.2 - Fayal ite - - - - - Ilmenite 1.3 1.3 0.9 1.2 1,.2 0.7 Magnetite 0.4 2.1 0.4 0.7 3.9 - Hematite 2.8 1.90.6 1.9 2.1 Corundum - - 1.4 - -

Key to Analyses 1. Alkalineandesite, basal volcanic assemblage 2. Maficphonolite lava (rhombporphyry), Yellow Lake Member, MarronFormation 3. Trachyte ash flow,Yellow Lake Member, MarronFormation (Skahil Creek area) 4. Trachytelava (rectangular porphyry), Yellow Lake Member, MarronFormation 5. Coryell-typemonzodiorite intrusion 6. Trachyte dyke, on northfork of Riddle Creek and euhedralphenocrysts of green diopsidicaugite, biotite, apatite, and magnetite set in a devitrifiedglassy or fine-grainedfeldspathic matrix. Scintillometer readingsare in the range 140 to 180 countsper second.

The most radioactiverocks are thick trachyte lava Elows thatcomprise the upper part of theYellow LakeWmber in thisarea. This; unit is

19 estimated to be between 150 to 200 metres in thickness. It underlies the ridges and slopes immediately northeast and south of the confluence of the forks of Riddle Creek. The trachyte contains large rectangularor platy mixed feldspar phenocrysts of anorthoclase, sanidine, and plagioclase: otherwise it is petrographically similar to the mafic phonolite (rhomb porphyry) suite. Scintillometer measurements are in the range 300 to 420 counts per second.

Coryell plutonic rocks crop outon the hillsides north and south of the westerly source of Riddle Creek. These are high level miarolitic syenomonzonite and monzodiorite phases (No. 5, Table1) that are mineralogically akin, and feeders to, the overlying Yellow Lake volcanic pile into which the Coryell pluton has evidently stoped. The rockis composed of about80 per cent alkali feldspar, mostly orthoclase with rhomb-shaped anorthoclase cores, and20 per cent smaller phenocrysts and interstitial grains of amphibole and pyroxene with poikilitic inclusions of biotite, magnetite, apatite, and sphene. The average scintillometer reading is 250 counts per second.

SCINTILLOMETER SURVEY

In the course of routine geological investigation of the Riddle Creek area, rock outcrops weretested in a manner outlined by McDermott (1977) using a portable gam ray scintillometer (GeoMetrics/Exploranium Model GRS-101). Guantitative control was obtained for uranium from neutron activation of 24 samples, courtesy ofD.R. Boyle of the Geological Survey of Canada, and €or thorium from spectrometer analysis performedby the Analytical Division of the Ministry. The relationship between counts per second and uranium/thorium composition canbe reduced to two equations:

U = C.P.S. (0.072) - 0.538 Th = c.p.6. (0.231) + 6.913

Accordingly, the following averages are calculated for uranium and thorium levels for the main rock types, basedon C.P.S. values at 93 stations:

Rock Unil U Th PP Ppn Trachyte (Ye1 lo* Lake Vember) 27 94 Maficphonolite (Yellow Lake Member) 11 45 Coryel I Intrusions 18 66 A ndesite Unit Andesite (unnamed) 5 23 Springbrd Formation 4 22 Okanagan Batho I i th 4 22

scintillometer results (Figure1) were contoured using the method outlined in Geological Fieldwork, 1980, Paper 1981-1, page 27. A bull’s- eye arrangement of contours lies immediately south of the main courseof

20 Riddle Creek in an areaunderlain by trachytelavas and a volcanic centre.Thoroughly altered rocks are exposed below thetrachyte on Riddle Creek and mre distally on theslopes to the west. Pervasive hydrothermalalteration of thetrachyte and vent (7) brecciahas produced cream and whitekaolinized rocks of variableradioactive response.

THE PROSPECT

A (diamond-drillprogram consisting of approximately 270 metres in seven holes was completed in 1979. Sixholes were sitedsouth OF Riddle Creek nearthe westboundary of thetrachyte andone holesited north of the creek. The purpose of thedrilling was totest bedrocknear geochemical soil anomalies and projectedstructural traps For uranium-bearing solutions.

Northof Riddle Creek, drill hole No. 7 was directedat a northeast- dippingsection oE strata +30 metresthick OE coarsz nlasticsedimentary rocksthat is overlain by partly welded ashflow brecciaat t:he base 0.E thetrachyte unit. (This stratigraphic-structuraltarget is strikingly similarto the occurrence of radioactivetrachyte ash and breccia in clasticsedimentary beds in thevicinity of Farleigh Lake and &aha Creek, 15 to 20 kilometresto the southeast (No. 3, Table 1 -' unit lb on Preliminary Map 35). Although no significant uranium was Eound, the drilling proved goal porosity of the bedsbelow theash Elar and thus potential €or Eurther exploration.

Most of the drilling in thearea of soil anomaliessouth of XiddleCre,?k intersectedCoryell intrusive rocks. However, hole No. 1 nearthe west boundary oE thetrachyte cut altered rocks showing vestiges of conglomerate and brecciasimilar to the rocks at site No. 7.

A few prominentradioactive high spots were not tested by the drilling. The mst important of these is an easterlytrending Eelsic dyke about 4 metres wide exposed 450 metresnorth oE theconfluence oE the Eorks oE Riddle Creek. This is thoughtto be aEeeder tothe trachyte lavas oE the Marron Forrnation (No. 6, Table 1). Scinttllocneterreadings here averaging 1500 C.P.S. correspondto rock analyses showing 121 ppm U ant3 342 ppn Th. Radiographs of slabbedsamples show thatradioactive elementsare concentrated on lmnganese pitch and dendritic growths on nutnerous small cracks. A similar dyke with scintillometerreadings in therange of 600 to 900 C.P.S. wasEound atthe contact between Coryell plutonicrocks and mafic phonolitelavas in thenorthwest part of the 'nap area &tween Isintok Creek and the westernheadwaters of RiddleCreek.

DISCUSSION

The Riddle Creek Tertiaryoutlier lies near the western extremity of a helt of mcenealkaline volcanic rocks that are characterized by anomalous uranium and thoriumcontents (Church and Johnson, '1978). It is suggestedthat these rocks are the source oE therelatively highuranium

21 levels in streams of the Okanagan-Boundary area found by the 1976 URP survey. The possibilities of secondaryuranium deposition and enrichment inthis setting are numerous, includingdykes, permeable sedimentary rocks and alteration zones associatedwith volcanic vents (Culbert and Leighton, 1978).

High radioactiveresponse near the headwaters of RiddleCreek coincides with what appearsto be a trachytevolcanic centre (Figure 1). In 1978, a program of shortdiamond-drill holes was conductedperipheral to this centre and yielded low uraniumvalues. For future study the volcanic centre and associatedash flow deposits offer the best target.

REFERENCES

AssessmentReports Nos. 7362 and 6750. B.C. Ministry ofEnergy, Mines & Pet. Bs., GeologicalFieldwork, Paper 1981-1, p. 27; Prelim. Map 35 (Revised 1380). Boyle, D.R. andBallantyne, S.B. (1980): Geochemical Studies of Uranium Dispersionin South-central British Columbia, C.I.M., Bull.,Vol. 73, NO. 820, pp. 89-108. Church, B.N. andJohnson, W.M. (1978): Uranium andTnoriun inlkrtiary AlkalineVolcanic Rocks inSouth-central British Columbia,Western Miner,Vol. 51, No. 5, pp. 33-34. Culbert, R.R. and Leighton, D.G. (1978): Uranium in Alkaline Waters, Okanagan area,British Columbia, C.I.M., Bull.', Vol. 71, No. 783, pp. 103-110. McDermott, M. (1977): FieldSurveys Using a Portable Gamma Ray Scintillometer, Western Miner,Vol. 50, No. 8, pp. 16-20.

22 THE USE OF PERSONAL COMPUTERS AND OPEN FILE GEOCHEM.ICAL DATA To FIND N!ZW EXPLORATION TARGETS

By George G. Addie

ABSTRACT

InGeological Fieldwork, 1980, Paper 1981-1, aprogram was presentedfor calculating moving averagesusing a Wang 2200A computer(Church, et al., 1981). The same program slightlymodified has been used with. a TRS-80 Level I1 computer.

PROGRAM MODIFICATION

The individualvalues are multiplied by a factor of l/Log R where 'R' .is theradius from the samplevalue tothe centre OE the computer window. Thishas the eEfect of reducingthe anomaly size.

NELSON-YMIR-SAM0 - Ag

An interesting anomaly is found tothe south of Salmo and moritly west of the Salmo River, an arearelatively unexplored. The geologyindicates Nelson granite in contactwith sediments. Magnetic anomalies are associatedwith this granite. This is an excellent areafor skarn and vein deposits.

GRAND FORKS - Cu

Thisapproach certainly would havefound 'Phoenix Copper' if used prior to discovery.

GRAND FORKS - Mo

A verysubtle molybdenite anomaly exists tothe east of PhoenixCopper. Is a porphyryenvironment present?

GRAND FORKS - Ag

A low levelsilver anomaly exists to thesouth of PhoenixCopper. Is this the centre ofa porphyry model?

23 49'30'

49.15'

49'00'

Figure 1. Moving average contarr nap of sllver values In strem silts fra Nelson-Ymlr-Salm mlnlng camp.

24 GRAND FORKS

Figure 2. Contour plotuslng moving average method of copper Instrew silts fran Grand Forksarea.

Figure 3. Contour plot of molybdenm Instrem slits In Grand Forks areauslng mvlng average method.

.25 ... .. I 1.8 , Ag

GREENWOOD PHOENIXCOPPER

GRAND FORKS

MIDWAY

Flgure 4. Contour plot of gold In stremslits In Grand Forksarea uslng navlng average method.

CONCLUSION

The use of the computer can identify low level anomalies that are not obvious from data plots only. It is on this basis that new target areas can be found in old mining camps.

REFERENCES

Church, B.X., Barakso, J., and Bell, D. (1981): Computer Processing of Geochemical Data showing the Primary Dispersion of Elements near the Equity Mine (Sam Goosly),B.C. Ministry of Energy, Mines& Pet. Res., Geological Fieldwork, 1980, Paper 1981-1, pp. 25-32. Regional Stream Sediment and Water Geochemical Reconnaissance Data, British Columbia, 1976, Geol. Surv., Canada, Open File 409.

26 TABLE 1. TRS-80 Level II ConputerProgran

GRAhUFORKS FEE 23, 1981 BY GEORGEG. AODIE, P. ENG.,GEOL.P.

5 LPRINT "GRAW FORKS" 6 LPRINT "FEE 23, 1981 BYGEORGE G. ADDIE. P-ENG.,P.GEOI.." 10 LFR I NTCHR*(29)" " 20 CLS 40 D=O:X=O:W=O:Y=O 50 INPUT "COORDINATESOF CENTER OF FIRST CIRUE";A,B 60 INPUT "EASTING ANDNORTHING INTERVALS";G,K 70 Z=A:Q=E 80 LFRIN7 TAB(0)"E";TAB(8)"Nt'; 90 LPRINT TAB(15)"ZN";TAE(25)"CU";TAB(35)"W"; I00 LFRINT TAB(45)"AG";TAE(55)"U";TAB(60)'"3'' 110 FOR I=ITO 8:READ A(I):NMT I 120 IF A(2)=-1 THEN 180 130 IF SOR((A(l)-2)f2t((A(2)-Q)12))>100 THEN 110 131 R=SQR((A(l)-Z)I2t((A(Z)-Q)12)) 132 IF R<=l THEN R=l .1 135U=l/LOG(R) 140S=StI:T=TtLOG(A(3)+U) 150 C=C+LOG(A(4)*U) 160 D=DtLOG(A(5)+U) 170 E=EtLOG(A(6)'U) 171 L=L+LOG(A(7)+U) 172 W=WtLOG(A(8)+U) 175 GOT0 110 180 IF S=OTHEN 280 1 90 Y=EXP (T/S 1 200 F=EXP(C/S) 210 H=EXP(O/S) 220 J=EXP(E/S) 230 M=EXP(L/S) 255 X=EXP(W/S) 260 LFRINT TAB(O)Z;TAB(6)Q;TAB(ll)Y;TAB(19)F;TAB(27)H; 270LFRINT TAE(35)J;TAE(43)X;TAE(55)M 280 2=2-50:S=O:T=O:C=0:0=0:E=0:L=0:W=0:Y=0:F=0:H=0: J=0:M=Q:X=0 290IF (A-Z)>G THEN 310 300 RESTORE:GOTO 110 310 L=~:W=O:S=O:T=~:C=~:DIB:E=~:E=~:L=~:W:Q=Q-~~:P=P~I: Y=O:F=O:H=O:J=O:M+:X=O 320 IF INT(P/2)=P/2 THEN 340 330 Z=(ZtG+50):GOTO 350 340 Z=A 350 IF (B*)

By George G. Adrlie

INTRODUCTION

When logarithmeticvalues of mineralproduction were plotted it was found thatvarious minesformed distinctqroupings of 'populations.' Individual mines from eachgroup can then be studiedfor criteria which would leadto discovery of similardeposits elsewhere in the area.

In this sturly log Au is plottedagainst log Ag for production from camps: (1) SheepCreek, (2) Ymir, (3) KeystoneMountain, and (4) Hall Forty-nine Creek.

The mines studiedare all past producers and occurin the Nelson-Ymir- Salmo area.'Location of Mines inthe Nelson-Ymir-Salmo Area' includes gold mines as well asthe zinc-lead deposits of the 'Kootenay Arc.'

The mines of the SheepCreek Camp (Figure 1) seem tofall into three naturalgroups based on theproduction figures. The same 'phases' have been usedfor Ymir (Figure Z), KeystoneMountain (Figure 31, and finally Hall and Forty-nineCreek (Figure 4).

Mines relatedto the three phases of mineralization found from theabove graphs are located on theindividual maps designated'Phase 1,' 'Phase 2,' and 'Phase 3' (Figures 5, 6, and 7).

TARGm AREAS

It is proposedthat mines inthe same 'phase' are somehow related. When they are closetogether a dashed linehas beenused to show their possiblerelationships. It is on thesetheoretical lines or projections that I wouldrecommend prospecting.

28 29 +- Y II YII

30 31 Figure 1. Indexof location of former mines of the Rossland mining canp; first phase - location ofmines on Phase 1 linefran graph 2; second and third phase - locationof these phases fran graph 2; geology ofthe Rossland mining canp after Fyles. et ai., 1973; aeromagentic map 84836 ofthe Rosslandmining camp at 58,000 gammas.

32 A NEW LOOR AT THE ROSSLAND AND BOUNDARY MINING CAMPS USING LOG Cu (lb.)/Log (Au + Ag)(oz.) I FROM PRODUCTION DATA

By George G. Addie

INTRODUCTION

up to 1967 goldproduction from theRossland Camp rankedsecond and t.hat from themundary Camp, Eourth, of all themining camps in British Columbia (Grove, 1971, p. 94). Inthe Rossland Mining Camp (thispaper) three'phases' of mineralizationare indicated while the Boundary Camp has one (Addie 1975). At Rosslandthe distribution of the mines by 'phase' indicated a concentricdistribution mre or less centred on the Rossland monzonite. Similarzoning was identified by Thorp2 (1967). He pointsout (p. 11) 'the Ilossland District, thenproduced a veryrare type o€ goldore.' This paper proposesthat the Boundary Camp hassimilar ore.

The Rosslandmonzonite alsohas a coincidentmagnetic anomaly (Figure 1) which seems to be connected to a largemagnetic anomaly to the west that is associatedwith the contact zone of theCoryell Batholith. The Rosslandmnzonite has also been intruded by theCoryell, which my contributeto the magnetic anomaly. The Rosslandmonzonite may have actedas a buttressagainst which theCarboniferous and Jur,assic volcanic and sedimentaryrocks were broken to givethe vein structures. Thrusting inthe area my be related to emplacement of theTrail grantDdiorite (49.5 - 50.5i1.5 Ma) and/orthe Rainy Day Stock (48.7t1.5 Ma). Fyles (1973) suggeststhat the mineralization is relatedto oneof theplutonic masses, probablythe Trail Batholith. All authors(Brock, 1906; Drysdale, 1923; Little, 1963; Fyles, 1973) agree that themineralization is Tertiary. The onlyquestion is thesource of themineralization. Thisauthor proposes that the Coryell intrusions should be examined nore closely. It is clear from theliterature that Coryell pulaskite dykes were emplaced both before, and after, the mineralization. This is importantbecause we now have a direct link to the Coryell 'Batholith, at leastfor timing, as a potentialcause, if not the source, of the economic mineralization. The presence of weak molybdenite mineralizaationsuggests the Coryell as a possiblesource of the RDssland molybdenitedeposits.

Inthe Boundary Camp, thePhoenix Copper ore zone is cutof:€ by a pulaskite dyke (Coryell). The dyke intrudedalong a fault .plane which has had repeated movement, before and after some ofthe minsaralization (Addie, 1964). Recent geochemicaldata from GeologicalSurvey of Canada Open File 409 indicates a molybdenite anomaly adjacent to t'he Phoenix Copper area(Addie, 1981). Tertiarydiorite (McNaughton, 1'336) is just tothe north of thePhoenix Copper pit and contains a showi!ng of mineralizationsimilar to the mine, that is, theprecious mtal/copper

2 33 Figure 2. Boundary district. log CU lib.) versus Log (Au + Ag) (02.).

Log (Au+ Ag)oz

Figure 3. Rossland, Log Cu (Ib.) versus Log (h+ Ag) (02.).

34 Flgure 4. Comparlson of Boundary and Rossland, log Cu (Ib.) versus log I:Au + Ag) (oi:.).

35 ratios are identical (Addie, 1964). These Teritaryintrusions (see also Church, 1970) thereforedeserve a closerscrutiny for other skarn deposits,porphyry deposits, or another mining camp similar to mssland.

SOURCE OF DATA

Productiondata are from 'Index 3 to Publications of the Departmentof Mines. ' Note that 20 of the mines shown on Figure 1 are notused in our studybecause no copperproduction was reported.

CONCLUSION

The copper/goldplus silver mineralization at Rossland seem tobe identical to that at the Boundary Camp except that mre phases are involved.Geologically andfrom argonage dating it is clear thatthe mineralization at Rossland is Tertiary(Fyles, 1973). Thispaper proposes thatthe Boundary area be examined in this light and thatthe Coryell intrusions,especially the edges, be examined for new mining camps. As at Rossland,these may be identified from theaeromagnetic maps.

REFERENCES

Addie, G.G. (1964): Geological Map ofPhoenix Copper, files, PhoenixCopper Division, GranbyMining Co...... (1975): Gold-Silver-CopperMineralization in the Boundary District, B.C. Ministry of Energy, Mines L Pet. Res., Geological Fieldwork, 1975, Paper 1976-1, pp. 19-23...... (1981): The Use of Personal Computersand Open File Data toFind New Exploration Targets (inprint), B.C. Ministry of Energy, Mines L Pet. Res. B.C. Ministry of Energy, Mines L Pet. Res., MineralResources Branch (1955): Index No. 3 toPublications of the Department of Mines. Brock, R.W. (1906): PreliminaryReport on the mossland, British Columbia, Mining District, Geol.Sum., Canada, Rept. 939. Church, B.N. (1970): Geologyof the McCarren Creek, Goosmas CreekArea, Greenwood Mining Division, B.C. Ministry ofEnergy, Mines & Pet. Res., Prelim. Map 2. Department of Energy, Mines and Resources, Canada and B.C. Ministry of Energy, Mines L Pet. Res. (1977): RegionalStream Sediment andWater GeochemicalReconnaissance Data, SoutheasternBritish Columbia, NTS 82E, Open File 409 (NGR 5-1976). Drysdale, C.W. (1915): Geologyand Ore Deposits of Rossland,British Columbia,Geol. Surv., Ottawa, Mem. 77. Feir, Gordon (1964): Identification of 'Daonella' (Triassic): Fossils in the BrooklynLimestone, files, PhoenixCopper Division, Granby Mining co. Fyles, J.T., Harakal, E.I., and White, W.H. (1973) : The Age of Sulfide Mineralizationat Rossland, British Columbia, Econ. Geol., Vol. 68, pp. 23-33.

36 Grove, E.W. (1971): Geology and MineralDeposits of theStewart Area,, NorthwesternBritish Columbia, B.C. Ministry of Energy, Mines & Pet. Res., Bull. 58. Little, H.W. (1963): mssland Map Area, Bkitish Columbia, real. Surv., Canada,Paper 63-13. McNaughton, D.A. (1945): Greenwood-PhoenixArea, British Ccllumbia, Geol. Surv.,Canada, Paper 45-20. Thorpe, R. (1967): Controls of Hypogene Sulphide Zoning, mssland, British Columbia, thesissubmitted to theGraduate School of tlniv. of Wisconsin,University Microfilms, Ann Arbor,Michigan, U.S.A. Thorpe, R.I. and Little, H.W. (1973): The Age of Sulfide MJ.neralizat.Lon at Rossland,British Columbia, Econ. Geol., Vol. 68, pp. 1337-1339.

37 ,'TI1 Flgure 1. Geological settlng of the TIIIlcm goldproperty (A); after Hyndmn (19.58. Geol. Surv., Canada, Map 1234). "l

38 TILLICUM MOUNTAIN GOLD PROSPECT (82F/13)

By Y.T. John Kwong and George G. Addie

INTRODUCTION

The Tillicum Mountain goldproperty with latitude 49 degret?s 59.2 minutes north and longtitude 117 degrees 42.7 minutes wast is located 13 kilometres east of Burton in the Arrow Lakes region of the Kootenay District, south-centralBritish Columbia. The generalge0:logic setting of theproperty is shownon Figure1. It is beingdeveloped under the jointventure between Welcome North Mines Ltd. and mperanza ExplorationsLtd. To the end of August1981, trenchinghas revealed severalhigh-grade gold occurrences within the property including the 16- metre-long Money pit, from which a 21.3-tonbulk sample yielded 3.887 ouncesper ton gold, 2.30 ounces per ton silver, and 1.9 p?r cent zinc. Moreover, according to a recentreport in the George Cross New Letter (No. 167,September 1, 1981 ), geochemicalsurveys have outlined two northwest-trendingbelts with anomalousgold values in soi:lsvarying from 100 to 3250 ppb over a strike length of 500 metres (see Fiqure2).

GEOLOGY

Figure 2 presents a simplifiedgeological map of theTillicum gold property.In detail, the contact betweenthe rocks of the Milford Group and theKaslo Group is apparently marked by a band of argi:Llitethat is generally less than 5 metres in width. The argillite band,considered to be theyoungest member of theMilford Group exposed in the area, consists of layers of differentlithology. These includedark grey,, relatively fissileargillite, whitish, highly siliceous cherty rock, i%ndinterbeds orrather massive, tuffaceous-lookingrocks with streaks of sulphides. For clarity,these rocks are not shown on Figure 2. Similarly, small patches and dykes of garnet-bearingpegmatite, presumably (derived from partial meltingduring the peak of regional metamorphism, (and aplite and lamprophyredykes are omitted from thefigure.

With theexception of thoseoccurring in and adjacent to the Money pit, rocks of theMilford Group nearthe contact zone with Kaslo Group rocks aresilica-rich and resemblealtered rhyolite in places. igowever, binocularmicroscope examination of collectedspecimens and thinsections indicatethat these rocks are fine-grained muscovite-garnet schists with comparativelycoarser grained quartzite lenses and interbeds.Relative proportions of quartz,muscovite, chlorite, K-feldspar, and plagioclase vary. Garnet is generally less than 5 per cent by volume.Opaque mineralsrarely exceed 2 per cent.Schistosity in these rocks is generally marked by subalignedmuscovite and chlorite. At least part of the latter mineral appears to be an alterationproduct of biotite.

39 I I I T 4+50W WOOW 1+50W o+oow Goat Canyon-Halifax Creek stock: ,e Au geochem.anomaly mainlyquartz monzonite ~~ / 100-500 ppbsoill in 5 Kaslo Group amphibolite . Sample location 11Milford (?) Group peliticschist Intensively sampled

Flgure 2. Local geology ofthe TIIIlcm gold property(partly after Crawford,pers. cam.). Soil geochemistrydata are fra George C-oss News Letter, No. 167, September 1, 1981).

40 Metamorphosed, porphyritic, and locallyamygdaloidal hornblende ande:site and hornblendecrystal tuff (?) are among the most common rocktypes of the KaSlo Group adjacent to theMilford contact. Intrusive rocks of the Goat Canyon-Halifax Creek stock to thenorthwest have not ken examined in detail.

Figure 3 shows the geology in thevicinity of the Money pit. and the location of samples collectedfor detailed petrographic and x-ray studies.Biotite-garnet-amphibole schists occurring around the perimeter of the Money pit are generally compact, fine-grainedrocks., Common mineralconstituents include K-feldspar, plagioclase, tremolite, biotite, and chloritewith lesser amounts of garnet (or its alterationproduc.t), quartz, opaque minerals, and rarecalcite. Likethe muscovite-9arne.t schists found away from thepit, schistosity in theserocks are defined by subalignedbiotite and its alterationproduct, chlorite., Tremolite crystals are alignedeither subparallel to theschistosity or at a small angle to it. Occasionally,tremolite also occurs with K-faldspar in patches and bands of varyingdimensions. The proportion of thesep%tches increases toward the Money pit and schistosity in the rock unit is locallydestroyed. In four out of six thinsections cut from these rocks,garnet has been replaced by clusters of biotite and, less commonly, chlorite.Ihus, a secondepisode of alteration featuring the stableappearance of tremolite,chlorite and possibly some K-feldsparand biotite was superimposed on regional metamorphism in which quartz-feldspar-mica-garnetfamphibole were stable.Prehniie and zoisite arelocally associated with chlorite. Besides sulphides, a few samples alsocarry small amounts of amorphous carbon.Fold structures on a microscope scale Occur in specimens from samplingstripes I: and L.

Calc-silicaterocks in the Money pit consist, in order of decreasing abundance,of clinopyroxene (diopsidic augite ?), amphibole (tremolite- actinolite),quartz, K-feldspar, calcite, plagioclase, opaque minerals, and chlorite. Amphibole Occurs eitheras fine-grained clueiters or as elongatedsingle crystals that cut across and include remnantfragments of clinopyroxene.Wartz, calcite, the feldspars, and opaque minera:ts commonly occupy interstitial spaces between theclinopyroxene and amphibolegrains. All of these interstitial minerals appea.r to be in equilibrium with amphibole but mosthave a reactioncontact. with clinopyroxene. Less commonly, quartzoccurs as scattered qranular lenses or coarsefragments in locallybrecciated clinopyroxene-dominated rocks.

Thesefragments and lenses are especiallyobvious in the southeastern corner of the pit where abundantsulphide minerals occur. Geological contacts of the calc-silicaterocks with the biotite-garnet.-amphibolc? rock are sharpbut the calc-silicates pinch out abruptly in a short distance.Consequently the limit of the calc-silicateunit. depicted in thefigure is veryapproximate.

Argillite adjacent to the mney pit are very similar to arqillite bands described above exceptfor the ubiquitous presence of tremolite.In most cases, the amphibole occurs inK-feldspar-rich bands that cut foliation defined by aligned mica and/or chlorite at a small angle.In a bulk sample, however, plagioclase is more abundantthan K-feldSpar.

41 L I

42 Amphibolite west of the argillite unit was probably a porphyritic andesite prior to metamorphism. Subaligned hornblende phenocrysts, which define the foliation, are replaced by clusters of tremolite, biotite, and chlorite. Less abundant plagioclase phenocrysts and fine-grained clinopyroxene in the matrix, however, remain intact. Deformed lenses; of quartz aggregates frequently enclose a carbonate core; they may have been anygdules originally.

MINERALIZATION AND ALTERATION

Native gold and sulphide mineralsoccw in the Money pit. Sulphides include sphalerite, pyrrhotite, galena, pyrite and rarely arsenopyrite, chalcopyrite, and marcasite. Polished sections indicate that native gold, sphalerite, pyrrhotite, and galena were precipitated in equilibrium. Sphalerite commonly includes discontinuous trains of exsolved blebs of chalcopyrite and pyrrhotite along cleavages indicating that it was originally deposited ata relatively high temperature. Many large pyrrhotite grains arereplaced by marcasite and possibly some pyrite. Weathering products occurring in the Money pit have been confirmed by X-ray diffractometry to include colourless gypsum, white hydrozincite, and hemimorphite, black and dark brown goethite, reddish clayey hematite, and yellowish brown limonite.

As the intensity of mineralization decreases away from the Money pit, the sulphide mineralogy also changes. Whereas small amounts of sphalerite and locally galena are present in rocks of the Milford Gronp throughout the property, little orno pyrrhotite persists beyond the occurrence of biotite-garnet-anphibole schists. In the place of pyrrhotite, pyrite and locally arsenopyrite become the predominant sulphide mineralsin the muscovite-garnet schists. Most of these sulphides are conliornable with the schistosity, and hence with the original bedding because the two are parallel. Some sulphides, particularly sphalerite and galena, also 'occur along fractures atan angle to the schistosity or in association wit:h silicate bands and patches at variable angles to the schistosity. Hydrous iron oxides are the predominant weathering product61 observed but locally, for example at the Jennie trench, arsenopyrite altersto abundant greenish yellow scorodite (FeAs04.2H20). In the sphalerite showing lying northeastof the Money pit (see Figure 2 for location), an alteration mineral assemblage similar to that observed at the Money pit is present. However, neither visible gold nor extensive calc-silicate rocks were noted.

SP SURVEY

SP loops by both long and short wire methods got anomalous results at both the Money pit and the Jennie trench (Figure4).

DISCUSSION

Pennsylvanian to Triassic sediments of the Milford Group deposited in the vicinity of Tillicum Mountain were probablymde up of pe1:tte with highly

43 siliceous interbeds and localized pockets and lenses of impure carbonate which were precursors of a Money pit. These sediments might or might not contain small amounts of syngenetic sulphides. Undergoing progressive metamorphism up to the lower almandine-amphibolite facies, the carbonate was gradually converted into a clinopyroxene-dominating rock. The conversion process required a continual supply of silica from the neighboring rocks which accounts for the paucity of quartz in the biotite-garnet-amphibole rocks in comparison with the muscovite-garnet schist. A net transfer of FeO toward the nucleating calc-silicate zone was also likelyso that diopsidic augite rather than diopside was stabilized and that biotite instead of muscovite preferentially occurred in the vicinity. The conversion of carbonate to a calc-silicate assemblage also involved a significant decrease in total volume that might induce incipient porosity and permeability in the resultant rock in the form of microfractures and pore space. Such inherited defects would be accentuated by structural deformation during or subsequent to regional metamorphism resulting in the formation of a highly permeable zone. In this way the Money pit was chemically and structurally prepared as a suitable site for the introduction of ore which probably took place during the intrusion of the Goat Canyon-Halifax Creek stock. Besides deposition of the ore minerals, the intrusive event also initiated an episode of recrystallization in the host rocks. Details of chemical changes and reactions involved in the formationand modification of the rocks in the Money pit and its vicinity willbe dealt with in a later paper. It should be pointed out here that the ore reserve generated in the model would dependon the size of the original carbonate pocket, and consequently the extent of occurrences of deformed calc-silicate rocks.

Regarding the ultimate source of the ore elements, three alternatives are possible and each carries itsown implications on further exploration targets in the region. First, the metals were derived from the intrusive stock and transferred to the Money bypit enriched magmatic hydrothermal fluid. In this case, the entire contact zoneof the stock with the country rocks would be of interest. Besides Au-Zn-Pb, other types of mineralizatin like Cu-Mo would also be expected to occur closer to the stock. Second, Au+Zn*Pb was scavenged from theKaslo Group amphibolite by hydrothermal fluid emanating from the stock. Under such a situation, the area around Mineral Creek (northwest of the centre of Figure1) where a similar lithologic assemblage crops out shouldbe investigated for similar deposits. Third, the mineralization at the Money pit represents a concentration of remobilized ore elements from the Milford Group rocks themselves. In view of the overall poor permeability of the fine-grained schists, which would readily hinder the formation of an extensive convection system, this alternative seems unlikely. Nevertheless, if it were true, then permeable zones in the Milford Group rocks occurring close to the intrusive stock should be examined for possible mineralization.

44 ACKNOWLEDGMENTS

The property was first visited by GeorgeAddie on August Z;!, 1980, w.ith MI. and Mrs. ArnoldGustafson (Prospectors Assistance Program).

Thanks are extendedto Mr. John Brock, Mr. JohnGuild, and Dr. Jim Crawford of Welcome North Mines Ltd. fortheir cooperation and hospitality. MattHoltz helped conduct the SP survey.Lloyd Addie .acted as an assistant.

REFERENCES

George Cross News Letter, No. 167, September 1, 1981, p. 3 and map. Hyndman, D.W. (1968): Petrology and Structure of NakuspMap-Area, B.C., Geol. SUIT., Canada, Bull. 161, 95 pp. Western Miner, Wide rangingexploration by Welcome North,October 1981, p. 22.

45 Elk Formation

Mist Mountain Formation

MorrisseyFormation (basalsandstone)

Bedding attitude (upright, ji+ top unknown,overturned)

,&,,’ Contact(defined, approximate) MT. BANNER and area Anticline, syncline ELK VALLEY COALFIELD

f Thrust fault (defined, / 1 0 1 3. ,/ approximate) km D A Grieve (1981: Figure 1. Geology of the bunt Banner area,Elk Valley Coalfleld.

46 MOUNT BANNER AREA ELK VALLEY COALFIELD (82G/15, J/Z)

By D.A. Grieve

INTRODUCTION

TheMount Banner area 'is south of Ewin Creek in thesouthern portion of the Elk Valleycoalfield (Figure 11, and adjoinsthe area investigated in 1980 (Grieve,1981). Geological mapping was carriedout to provide new dataconcerning structure, stratigraphy, and coalresources of the coalfield.

Coal rights in thestudy area are held in part by B.C. Coal and in part byCrows NestResources, and bothcompanies areactively engaged in exploration.Proximity to developing mines at Line Creek (Crows Nest Resources) and atGreenhills (B.C. Coal), both areapproximately 10 kilometres away, suggeststhat the study area is strategicallylocated for future mine expansion.

Mount Banner is 10 kilometreseast of Elkford, and is accessible from boththe Fording mine road and theLine Creek minesite.Elevations withinthe area range fran 1 500 to 2 600 metres.

FIELD WORK

Data was plotted directly on British Columbiagovernment airphotographs and transferred to 1:lO 000-scaleorthophotos. Stratigraphic sections of thecoal-bearing Mist MountainFormation were measuredusing 'pogo stick,' chain, and compass.Coal outcrops, roadcuts, and trenches were grab-sampledfor petrographic rank determinations. Channelsamples were collected in certainareas to provide representative material for mceral analyses.

Results of petrographicstudies will be publishedat a laterdate.

STRATIGRAPHY

Sedimentaryrocks of theJurassic-Cretaceous Kootenay Group comprisethe Elk Valleycoalfield. The Kootenay Group, asdefined by Gibson (1979), consists of theMorrissey, Mist Mountain, and ElkFormations.

The basalMorrissey Formation is a prominent,cliff-forming, medium" grainedsandstone unit.

47 F-Approximate contact with Elk Formation

rj"_". .... _"-" "_" "

..<..:: .... :.:<...... ?.<< ...... :::m::.:.:.:.;2: ...:.. .: ...... :e:::_"....<......

...... :::::%B %wTy+T?... "_ _" L"_I """- """-

Ewin Pass BurntRidge

Preddomlnantlysandstone

Sandstone and siltstone

Redom. siltslone and liner Redom. coal NO mposure

Figure 2. Generalizedstratlgraphlc columns of theMlst Mountaln Fornatlon at Imperial Ridge, Ewin Pass, and Burnt Rldge.Coal seam thickerthan 1 metreare notIndlcated. 48 The overlying Mist MountainFormation consists of interbeddedsandstone!, siltstone, mudstone, coal, andminor amounts of conglomerate. It is or1 theorder of 500 metres thick in thestudy area (Figure 2).

In this area the overlying Elk Formation includes an estimate83 250 to 300 metres of strata which resemble those of the Mist MountainFormation. However, coal seams in the Elk rarelyexceed 1.5 metres in thickness. Othercharacteristics of the ElkFormation are describedelsewhere in this paper.

The contact between Mist Mountain and ElkFormations is notreadily identifiedin the study area. Generallythe contact is placedeither at thelowest occurrence ofElk coal,or at a locally mappable, resistant sandstone unit which appearsto separate strata that are characteristic: of the two formations.Because lateraltransitions within the coarse clastics of the Kootenay Group are rapid, some inconsistenciesoccur.

Kootenay Group is overlain at two locations in thestudy area by conglomerateof the Cadomin Formation of the Elairmore Group (Figure 1).

STRUCTURE

The north-south-trendingAlexander Creek syncline is thedominant structure in the Elk Valleycoalfield. In the Mount Bannera.rea it is asymmetricwith a steep west limb (Figure 1). Parallel smaller scale foldswith similar geometryoccur on theeast limb and have the effect of bringing Mist MountainFormation to thesurface in thesmall drainage basin west of the Evin Passproperty (Figure 1).

Thrustfaults are also important structural features in the Mount Banner area. The Ewin Pass(or Fording) thrust crops out on theeast limb of theAlexander Creek syncline throughout the south half of the Elk Valley coalfield(Pearson and Grieve, 1980; Grieve, 1981). It is a west-dipping faultwith at least one major splay in the Mount Banner area(Figure 1). Steeply northwest-plungingdragfolds (Figure 1) occur on boththe hanging and foot walls. Its major effects were to emplace Mist Mountain over ;Elk Formation,especially south of Mount Banner peakand on Mount. Michael, and to create an apparentlyexcessive thickness of Mist Mountain Formation on thesouth side of Evin Creek (Figure 1).

Severalother thrust zones of lesser lateralcontinuity and small to negligiblestratigraphic displacement occur on the east limb;three are noted on Figure 1.

The BurntRidge property, which is on the west limb, alsocontains a significant zone of faulting(Figure 1). Xovement on this zone producced northwest-southeast-trendingdragfolds, and a persistent zonc! of overturned,west-dipping strata.

Assuming thatthese overturned strata are in thefootwall ofan east- dippingfault, there are two possibleexplanations €or their orientati'on:

49 (i)gravity movement toward the core of the syncline, perhaps along an earlier thrust surface; or (ii)early formation of the Win Pass thrust, with subsequent folding around the axis of the syncline.'The second alternative implies that the faulton Burnt Ridge is part of the Win Pass thrust, and that the easterly dip and apparent normal movement were produced by the folding. This alternative is also consistent with the relatively large degree of stratigraphic displacement on thewin Pass thrust considering the proximity of the synclinal axis. This suggests that movement was initiated some distance further to the west. It may also be significant that dragfolds associatedwith the fault have a northwest-southeast trend, compared with the nearly north-south trendof the Alexander Creek synclineand associated minor folds.

Further work is required to testthese two hypotheses.

ACKNOWLEDGMENTS

It is a pleasure to record my appreciation of field assistance provided by Mr. Gerry Pellegrin.

Discussions with Crow8 Nest Resources' staff, especially Dr. Barry Ryan, along with logistical support, were invaluable to the study.

REFERENCES

Gibson, D.W. (1979): The Morrissey and Mist Mountain Formations - Newly Defined Lithostratigraphic Units of the Jura-Cretaceous Kootenay Group, Alberta and British Columbia, Bull., Cdn. Petrol. Geol., Vol. 27, NO. 2, pp. 183-208. Grieve, D.A. (1981): Elk Valley Coalfield, B.C. Ministry of Energy, Mines & Pet. Res., Geological Fieldwork, 1980. Paper 1981-1, pp. 70- 72. Pearson, D.E. and Grieve, D.A. (1980): Elk Valley Coalfield, B.C. Ministry of Energy, Mines & Pet. Res., Geological Fieldwork, 1979, Paper 1980-1, pp. 91-96.

50 STRATIGRAPHYOF THE ELK FORMATION hl SOUTHEASTERN BRITISH COLUMBIA (82 G, J)

By D.A. Grieve British Columbia Ministry of Energy, Mines and PetroleumResources and N.C. Ollerenshaw The Institute of Sedimentaryand Petroleum Geology GeologicalSurvey of Canada

The ElkFormation is the uppermostformation of theJurassic-Cretaceous Kootenay Group (Gibson, 1979). It conformablyoverlies the Mist Mountah Formation,the host formation €or economic coalseam in thesoutheastern British Columbia coalfields. It is overlain,generally unconformably, by the Cadomin Formation of theBlairmore Group.

Changes in thelithology and stratigraphy of theElk Formation caused by rapid lateral facies changes inthe ElkFormation away fromand particularlyeast of thetype section on CoalCreek render it less distinct from theunderlying Mist MountainFormation. A consistentdefinition o€ theElk Formation and identification of a precisecontact with the Mist MountainFormation become increasinglydifficult away from the typesection. Theseproblems prompted the authors to undertake a de- tailedanalysis of the ElkFormation in thesouthern Fernie Elasin area in an attemptto formulate a more consistentdefinition of theformation and todescribe its variations. We attemptto identify the problems and to provide some practicalguidelines for recognition of theElk Formation,.

FIELDWORK

Two weeks havebeen devoted tothe study so far.Stratigraphic sections havebeen measured at Coal Creek (typesection, Newmarch, 191;3), MorrisseyRidge (reference section, Gibson, 1979), FlatheadRidge, and the Lodgepole property(McLatchie Ridge), allwithin the Fernie Basin.

Inaddition, drill-core from theLillyburt property in the Fl.atheadcoal- field was logged.

Sections were measuredusing ‘pogo stick’ and chain.

STRATIGRAPHY

ElkFormation in thestudy area is an eastward-thinningunit of non- marine clastic sedimentaryrocks including sandstone, siltstone, mudstone,local conglomerate, and coal.Clastic units are similar in terms ofcomposition and sedimentary structures tothose in theunderlying Mist Mountain Formation.

51 Severallithological criteria aid in identifyingthe Elk Formation in southeasternBritish Columbia.These are:the abundanceand distribution of coarseclastic material; the distinctive nature of Elk coal:the presence of needlesiltstone: the relative scarcity of coal seams:and theabsence of coal seams greaterthan about 1.5 metres in thickness.

A thin-bedded,dark grey to black, well-indurated, carbonaceous siltstone is adistinctive feature of the Elk Formation. It weathersa distinctive light greycolour, and where it is exposed toweathering the bedding surface is irregular and hummocky. This unit is informallycalled 'needlesiltstone' because it containsfragments of needlecoal (Gibson, 1977, p. 782).

Coal in the ElkFormation is of two main types. Themore common is bright and vitrain-rich and occursin thin lenticular beds that are generallyless than 0.5 metre and nearlyalways less than 1.5 metres in thickness. It is indistinguishable in outcrop from some coal seams of the Mist Mountain Formation. The other coal type is a brittle and resistant cannelcoal containing alginite, referred to by theauthors as 'Elkcoal.' A conspicuousvariety of Elk coal,needle coal, consists of algalneedles which resemblepine needles. Elk coalcomprises thin, usually less than 0.3 metre,lenticular, discontinuous beds. These commonly directly overlie needle siltstone.

The contact between the Elk and Mist MountainFormations is gradational. The prominentbasal, cliff-forming sequence of conglomerate and sandstone units in the Coal Creek area (Newmarch, 1953) is alocal phenomenon. Elsewhere,selection of abasal contact often involves a compromise, or an arbitraryplacement. In theseinstances, the contact is nottraceable for mapping purposes.

A more detaileddiscussion of the results of this ongoingstudy will be published at a later date.

ACKNOWLEDGMENTS

Thisstudy was initiallysuggested and planned by D.E. Pearson,formerly with theBritish Columbia Ministry of Energy, Mines and Petroleum Resources.

REFERENCES

Gibson, D.W. (1977): SedimentaryFacies in theJura-Cretaceous Kootenay Formation,Crowsnest Pass Area, Southwestern Alberta and SoutheasternBritish Columbia, Bull., Cdn. Petrol.Geol., Vol. 25, NO. 4, pp. 767-791...... (1979): The mrrissey and Mist MountainFormations - Newly DefinedLithostratigraphic Units of theJura-Cretaceous Kootenay

52 Group, Alberta and British Columbia, Bull., Cdn. Petrol. Geol., Vol. 27. No. 2, pp. 183-208. Newmarch, GB. (1953): Geology of the Crowsnest Coal Basin, withSpecial Referenceto the Fernie Area, 9.12. Ministry ofEnergy, Mines & Pet. Res., Bull. 38.

53 A COPPER-SILVER CCCURFSNCE IN THE FALKLAND AREA (82L/12E)

By G.P.E. White

A copper-silver showing on the Top claims ownedby Don Campbell and under option during 1981 to Craigmont Explorations Limited is located 50 at degrees 31 minutes latitude, 119 degrees 36 minutes longitude, 1 190 metres elevation, approximately3 kilometres northwest of Falkland.

Finely disseminated chalcopyrite, bornite, chalcocite, and possibly digenite are found in a coarse volcanic breccia. Fragments are predominately porphyritic green and buff lava, chert, micrite, and rhyolite, generally ina finer clastic crystal fragment-bearing green matrix. The porphyritic green phase is the most common rock type and, in mineralized areas, it has been altered predominatelyto calcite with 20 per cent albite and some chlorite, quartz, and K-feldspar. Phenocrysts are altered to vermiculite-hydrobiotite with small amounts of chlorite, calcite, and amphibole. Away from the mineralized area, the volcanic breccia consists of sericitic to kaolinitic altered porphyryand clasts of altered microlitic volcanic flows. In this unit, relatively fresh augite phenocrysts are present. Apatite is often present in the chert and veinlets of quartz, K-feldspar, and calcite are occasionally present.

This 'augite porphyry' brecciais interbanded with sone rhyolite and light-coloured flow rocks; some of the rhyolites are flow banded.

South of the mineralized area, 1.5-metre green porphyry blocks are set in a fragmental green porphyry matrix. Occasional clasts are mineralized with copper and there are infrequent, well-rounded, 5-centimetre-diameter milled rock fragments.

To the north of the mineralized showing outcropsa innarrw stream valley show 'augite porphyry' and altered basalt breccia in faulted contact with a coarse conglomerate and interbedded calcite-cemented arkosic sandstone. The conglomerate and sandstone are cut by basaltic dykes. Above is basalt clast sandstone that grades upward into sandstone with plant fossils. It is suggested that the fault juxtaposes Triassic and Tertiary rocks.

The mineralization is proximal toa Triassic diatreme. The present topography is related to Tertiary vent systems myand in part represent coincident areas of crustal weakness which also served as volcanic centres during Triassic time.

Using this concept, Mount Martinto the northwest was investigated but so far only one outcrop of relatively unaltered augite porphyry has been found on the north side. However, it is interesting to note that

54 outcrops below 1 200 metres south and east of Mount Martin in Paxton Valley,along St. LaurentCreek, on MailCreek, and on BoleanCreek arc? Permian-Pennsylvanian,not Tertiary. This interpretation is based on lithology,paleogeography, and fossilevidence. Chertylimestones containproductid brachiopods and schwagerinid fusulinids,possibly Parafusulina (Monger, pers. corn.). Monger suggestedthat these rocks are late Early to MiddlePermian in ageand my correlate wit.h the Harper Ranch Group.

Prospector Do2 Campbell on theMinistry’s Grant Program worked in this areaoff and orL for severalyears before mking this find. Thanks are extended to Johr. Kwongwho identifiedminerals, and Bill McMillanand Vic Pretofor their interest and suggestions. M. Hannamade theinitial suggestionthat the fossils were Permian-Pennsylvanianand this was confirmed by J. Monger of theGeological Survey of Canada.

55 THE STIRLING MOLYBDENITE SHOWING (82M/8W)

By G.P.E. White

The Stirling property (MDINO. 082M/087), owned by CJC Explorations Ltd. of Revelstoke, was optionedby Newmont from July 1980 until July1981. The property is located approximately54 kilometres north of Revelstoke at latitude 51 degrees 23 minutes, longitude118 degrees 25 minutes. Most of the showings are easily accessible from the old or new Mica Dam Highway.

Molybdenite occurs in concordant pegmatite-like sills in Lardeau Group metasediments. The sills consist of quartz, albite, pyrite, pyrrhotite, with carbonate, fuchsite, galena, occasional sphalerite, and rare allanite. Sericitic impure quartzite, quartz-chlorite-muscovite schist, graphite schist, crystalline limestone, and chlorite-muscovite-magnetite schist have a general strike of 015 degrees with a 30-degree northwest dip.

During the 1980-1981 season Newmont collected 252 rock, 28 soil, and 10 trench samples for alteration studies and geochemical assaying,did 23 kilometres of magnetometer surveying, and drilled 45 overburden andBQ 10 diamond-drill holes, the latter totalling1 320.8 metres.

One of the better intersections in diamond-drill hole81-8 comprised 2 metres of 4.67 per cent MoS2. In diamond-drill hole 81-2 there was 0.39 per cent MoS2 over 2.4 metres.

The above information for the most part was taken from reportsby Denis Bohme of December 29, 1980 and July 10,1981, personal communication with Denis Bohme June 17,1981, and a reportby D.M. Hausen of Newmont dated June 2, 1981.

John Kwong of the Analytical Laboratory identified the allanite.

56 A NEW ZINC OCCURRENCE IN THE REVELSTOKE AREA (82M/8W)

By G.P.E. White

While searching for scheelite north of Revelstoke the Cameron-Jenkins- Campbell prospectors discovered zinc with secondary hydrozinciteat an elevation of 835 metres, north of Mars Creek, latitude 50 degrees 21 minutes, longitude 118 degrees 22 minutes.

Sphalerite and pyrite in a manganese-dioxide-stained metamorphosed siliceous sediment occur in 1-metre bands with an exposed strike length of 10 metres. The host rocks are sericite-chlorite schist, sericite- quartz-albite schist, biotite-chlorite schist, and minor amounts of sericitic quartzite. The regional attitude is 170 degrees, 25 degrees east. Due to the incompetent nature of the schists many crenulations and minor folds are present.

Analysis by our Analytical Laboratory of a grab sample gave a 2.23 per cent zinc, 0.15 per cent lead, and 0.01 per cent cadmium; the cadmium was by spectrographic analysis. THE THANKSGIVINGTUNGSTEN SHOWING (82M/lE)

By G.P.E. White

Scheelite was discovered on theThanksgiving property in the fall of 1980 by the Cameron-Jenkins-Campbell prospecting group of Revelstoke. The showing is locatedabout 25 kilometresnorth of Revelstoke,latitude 51 degrees 12 minutes,longitude 118 degrees 12 minutes,along the new Mica Dam Highway at an elevation of 670 metres.

Skarnnear the crest of an antiformconsists of scheelite,calcite, quartz,K-feldspar, plagioclase, diopside, clinozoisite, vesuvianite, garnet,hornblende, sphene, pyrite, pyrrhotite, and chlorite. The zone is reportedto be stratabound and about 3 metres in thickness.Mineral contentvaries both vertically and laterally and, in one thinsection examined, the rockhas a cherty matrix. The hostrocks are sericitic quartzites and biotite-quartz-plagioclaseschists, with localfissile, micaceous partings.Foliation has a generaleast-west strike anda 30- degreenorth dip. A major low anglenorth-south fault that crosses the property is marked by graphitic shearing. In the easternmosttrenched areatight crenulated folds with axial planes normal tothe major fold axis occur in a calcareousunit.

QuartzEeldspar porphyry with agrey biotite-richmatrix, muscovite- quartz-feldsparpegmatite, and quartzveining occur in closeproximity to scheelite on theproperty but not with theskarn assemblage. No tungsten was detected in a semiquantitativespectrographic analysis of the pegmatite.

Conversationswith Roy Wares representingNorthair Mines were held at various times duringthe field season.

58 CLEARWATER AREA (82M/12W; 92P/8E, 9E)

BY Paul Schiarizza Department of Geology, University of Calgary

INTRODUCTION

Geological mapping of the Fennell and Eagle Bay Formations between Clearwater and Chu Chua muntain was initiated in 1980 (Schiarizza, 1981) and completed during the 1981 field season. Little new ground was covered this season; themin effort was devoted to refining and filling in details of the area covered previously. Extensive sampling of cherty sediments within the Fennell Formation was carried out in an effort to find microfossils. Results from this sampling are not yet available. Structural interpretations advanced after the first seasons' fieldwork were generally confirmed by this year's work. An early stage syncline was outlined with the Lower Fennell Formation between Clearwater and Granite Mountain. Improved understanding of the internal stratigraphy and structure of the Eagle Bay Formation confirms that theof bulk this formation is in discordant fault with adjacent Fennell rocks.

STRATIGRAPHY

EAGLE BAY FORMATION (UNITS1 TO 4)

Considerable time was spent mapping within the Eagle Bay Formation. The work allowed significant refinement and regrouping of EagleMy stratigraphy compared to that advanced by the writer previously.

The structurally highest unit within the formation (unit4; u.nits 3 and 4 of Schiarizza, 1981) consists mostly of rusty weathering, greenish grey feldspathic chlorite-sericite schists. An attempt to map darker green,, more chloritic schists as a separate unit (Schiarizza, 1981) proved untenable, although rocks in the lower part of thedo unitseem to be generally more chloritic. Igneous textures are clearly displayed in weakly schistose specimens from this unit and discrete feldspar grains evident throughout the unit appear to be relict igneous grains. Fragmental rocks OCCUT in the lower parts of the unit, but axe rare.A light grey relatively pure quartzite (4a) was traceable fora. little over 1 kilometre just south of Foghorn Mountain. However, the bulk of this unit is monotonously uniform. It may have been derived from a series of flows, or may represent an intrusive body.

Structurally beneath unit4 is a unit dominated by schists of felsic to intermediate volcanic origin (unit3). The unit is best exposed along lower McDougal and Foghorn Creeks. Along McDougal Creek these rocks are mainly light silvery grey quartz-sericite schists. Substantial chlorite is present in places, and chloritoid porphyroblasts were observed at a number of localities. 'Eyes' of clear quartz are often evident. Thin

:59 sections show that these are embayed quartz phenocrysts. Sedimentary interlayers of dark grey phyllite found throughout this section range up to a few tens of metres in thickness. These same rock types also comprise the succession along Foghorn Creek. There, however, the unit is more varied and includes not only medium green chlorite schist and light grey platy sericitic quartzite but also trachytic rock which hosts mineralization at the Rexspar uranium deposit (Preto,1978). Fragmental rocks that probably represent volcanic breccia are also present, particularly near the Rexspar deposit. Immediately north of the Baldy Batholith at Granite Mountain, outcrops of fine to medium-grained biotite-quartz gneiss with interlayered amphibolite and pelitic hornfels (3a) may be the contact metamorphosed equivalent of 3.unit

Unit '2 consists of medium green chlorite schist with interbedded grey phyllite and limestone. It structurally underlies unit 3 along upper Foghorn Creek. Scattered outcrops of chloritic schist immediately south of Birch Island may also belong to this unit.

Black phyllite with interbedded siltstone, sandstone, and grit (unit1) crops out adjacent to the Fennell Formation immediately southof Clearwater. This unit is truncated on the south bya transverse northeast-trending fault. It does not crop out again until the Fennell/Eagle Bay contact emerges south of the Baldy Batholith. There, it forms a substantial unit which continues southward adjacent to and east of the Fennell Formation, and extends across the Barriere toRiver Johnson Creek (unit 6a of Preto, 1981). Mississippian conodonts were extracted from two lenses of limestone within this unit in the Barriere Lakes area (Okulitch and Cameron, 1976; Preto, et al., 1980). South of Clearwater, unit 1 structurally overlies rocks of the immediately adjacent, east-dipping Fennell Formation, and itself appears to be structurally overlain by felsic schists of unit 3. The nature of these contacts will be discussed in the section on StructuralGeology.

FENNELL FORMATION (UNITS5 AND 6)

The Fennell Formation has been divided into an upper unit consisting almost entirely of massive and pillowed greenstone; and a lower, more heterogeneous unit dominated by greenstone and cherty sediments. Fennell greenstones have suffered varying degrees of low-grade metamorphism and alteration, but appear tobe dominantly of basaltic composition. M.J. Orchard has identified conodonts extracted from Fennell Formation cherts in the Barriere Lakes area. They range in age from Late Mississippian or Early Pennsylvanian to Permo-Triassic (V.A. Preto, pers. comm., April, 1981). Chert samples from the Clearwater area are presently being analysed for microfossils.

LOWER FENNELL (UNIT5)

A wide variety of rock types comprise the Lower Fennell Formation. Individual units are generally discontinuous and often intercalated on a

60 scale that is too fine to be representedat the mapping scale. Greenstone(5a) predominates. It ranges from aphaniticto very coarse grained and includesboth intrusive and extrusivephases. Becauseof metamorphism, the two are generallyindistinguishable; consequently they havenot been separated on the accompanying map (Figure 1). Recognizable extrusivevarieties are generally aphanitic to fine grained: these may be pillowed,but most aremassive. Obviously intrusive dioritic to gabbroic units generallyoccur as concordantsill-like bodies, although irregulardiscordant masses are also present.

Chert to cherty mudstone (5b) is the dominantsedimentary rock type present. It is generally well bedded: bedsrange up to 15 centimetres thick and are separated by thinnerargillaceous partings or interbeds. As with all unitswithin the Lower Fennell,chert horizons tend to lent; out and be discontinuous: however, in placesindividual chert units are persistent andprovide the best local marker unitswithin the succession.

Two substantialconcordant layers, and a number of smaller bodies of light grey,massive to weakly foliatedquartz-feldspar porphyry (5c) occur inunit 5. Theseappear to be mainlyof extrusiveorigin: some were eroded and occur as clasts in overlyingconglomerate.

Conglomerate(56) fom discontinuouslenses throughout the Lower Fennell,but is mst common in a belt thatextends from thevicinity of Axel Lake north-northwestward to Blackpool. Clasts appear to havebeen derivedentirely from surroundingFennell units; they are dominantly chert,greenstone, and argillite.

Bodiesof sandstone, argillite, and phyllite(5e) are most common in the lower part of unit 5. Inplaces, they are well bedded and sandstone layers alternate withfiner grained argillite or phyllite: more comonl.y, bedding is disrupted,giving the rock a lenseyto conglomeratic appearance.

Limestone (5f) is a minorcomponent of the Lower Fennell. It is present as small, discontinouslenses in the lower part of theformation adjacent to the Eagle Bay contact.

UPPER FENNELL (UNIT 6)

The Upper Fennellconsists mainly of aphaniticto fine-grained greenstone.Pillows are commonly present, and thegreenstone appears t:o be largely of extrusiveorigin. Small discontinuous pods of chert are presentin places, and twosomewhat largerbodies of bedded chert(6a) were traceablefor short distances.

Although it was notexposed, the contact between the Lower and Upper Fennell appears to be stratigraphicrather than tectonic. Traverses across thecontact zone alongJoseph Creek and on the slopes west of the Baldy Batholith show a gradualtransition, marked by decrease in the

fil Flgure 1. Generalizedgeologlcal map of theCieanater-Chu Chua area.

62 LEGEND

EOCENE AM) LATER (7)

8 (b) Sku1 I Hi Ii Formation: vesicularandesite (a) Chu Chua Formation:conglanerate. sandstone, shale

CRETACEOUS

7 Biotitequartz monzonite of Baldy Eathollth andJoseph Creek stock

UPPERPALEOZOIC

FENNELLFORMATION

6 Upper Fennel I Formation: pi I lowedand masslvegreenstone, minor chert 6a:bedded chert

5 LoverFennel I Formation (f) I lmestone (e) sandstone, argi I I i te, phyl I i te (d) conglomerate(d) (c)quartz feltspar porphyry (b) bedded chert (a) greenstone

Eagle Bay Formatlon 4 Rustyweathering, greenlsh grey, feldspathlc chlorite-sericlte sch Ist 4a: quartz1te 3 Quartz-sericlte schist with interbedded darkgrey phyl lite; mlnor chloriteschist, platy sericitic quartzite, and tra,:hyte 3a: biotite-quartz gneiss, anphibolite, pelitichornfels 2 Chloriteschist, minorgrey phyllite and limestone 1 Black phyl Ilte wlth Interbeddedslitstone, sandstone, and grlt

Symbo I s

Eeddlng: tops known, overturned;tops not known ...... J/d Schistosity:inclined; horizontal ...... YX Early mesoscopic fold axis ...... -+ Late mesoscopic fold axis ...... + inferred fault ...... NCJ Earlysynclinal axial trace, overturned ...... Geologicalcontact ...... -*‘;./ Mineraloccurrence ...... rn E 4 N-

64 thickness and number of cherthorizons until the succession consists almostentirely of greenstone.

UNIT 7

The Middle Cretaceous(Wanless, et al., 1966) Baldy Batholithoccupies thesoutheast corner of the map-area where it cutsthe Fenne:Ll/Eagle Bay contact. A small body of similar rockoutcrops in theJoseph Creek valleyjust northwest of thebatholith. Coarse-grained biotite quartz monzonite comprises much of thebatholith. It is commonly p

UNIT R

Conglomerate,sandstone, and shale of the Eocene (Campbell and Tipper, 1971) ChuChua Formation(Sa) and overlyingvesicular andesite of the Skull Hill Formation (ab) unconformably overliethe Fennell Formation in Joseph Creek valleyimmediately north of hlnn Lake. A smallerexposure of Skull Hill Formationoccurs 9 kilometres to thenorth. Beddingwit.hin the ChuChua Formation dips consistently at moderateangles tothe ea&, apparently due torotation along late faults that lie east of exposures of theunit.

STRUCTURE

Threephases of foldingare indicated by mesoscopic structureswithin the area. Earlyfolds generally plunge to thenorthwest. The a.ssociated axialplanar schistosity has been variablyreoriented by later structures. Phase 2 foldsplunge northwest or southeast,while phase 3 foldsplunge at low angles east or westward.Axial surfaces of thelater fold sets are relativelyupright; axial planar strain slip cleavage developedlocally during second phase folding, but is not pervasive throughoutthe map-area.

A westerlyoverturned phase 1 syncline in the Lower FennellFormation dominatesthe macroscopic structure between Clearwaterand upper Joseph Creek.This syncline is outlined by thestratigraphy immediately north ofthe Baldy Batholith. There it plungesshallowly toward the north- northwest and theaxial surface dips gently toward thenorth-northeast forseveral kilometres, then swings and takes on a more northerlytrend. The location of theaxial trace is approximatebecause outcxops are sparse,Fennell stratigraphy is discontinuous, and massivesreenstone,, fran which little structuraldata could be obtained,predominates.

West of the Baldy Batholith, in thesouthern half of theare.a, the FennellFormation comprises a west-dipping and facing homocl.ine. Bedding/schistosityrelationships and minor fold asymmetry suggest that

3 65 this homo cline is theresult of a late(phase 2 71, antiformal deflection of thewestern (upright) limb of thephase 1 syncline. Stratigraphic units couldnot be tracedaround this antiform, however, becausethere appears to be azone of faulting betweenJoseph and Axel Creeks. This faulting may be relatedto, or post-date, the second phase of folding.

Units 2 through 4 of theEagle Bay Formationcomprise a relatively flat- lying plate which appearsto be discordant with theadjacent Fennell Formation.Previously (Schiarizza, 1981) a gentlenortherly plunging synform was tentativelyoutlined in this package. However, the zone actuallyappears to represent a slightupturning as it contactsthe FennellFormation. This contact may be an east-dippingthrust fault that post-datesthe phase 1 synclinewithin the Fennell Formation.

Immediatelysouth of Clearwater,unit 1 of theEagle Bay Formation appearsto be roughlyconcordant with rocks of theadjacent Fennell Formation, and to havebeen subjected to the same (phase 1) westerly overturnedfolding. Farther east, felsic schists of unit 3 appear to overlie unit 1, althoughthe contact was notexposed. Units 1 and 3 may beseparated by the same east-dippingfault which has been inferred to separate units 2 through 4 of the Eagle Bay Formation from theFennell Formation. The position where theFennell/Eagle Bay (unit 1) contact emerges south of the Baldy Batholithsuggests that this contact was foldedalong with rocks of theFennel1 Formation. As was thecase south of Clearwater,the metasediments of unit 1 appear to be approximately conformable with adjacentFennell units. However, an apparentthinning (truncation ?) of the Lower Fennellsouthward along the contact, the presence of a tectonized zone between unit 1 and theFennell Formation immediatelysouth of the Baldy Batholith, and theabsence of feeder sills or dykesof theFennell Formation within unit 1, suggestthat this contactmy be a fault.Since the contact appears to havebeen folded by a phase 1 fold,the fault wuld pre-date this folding.

In addition to thosepreviously discussed, conspicuous faults within the area have two dominant orientations.Late faults, in places marked by brecciatedzones, trend northerly and occurmainly along the western side of the map-area.These may be more common thanindicated on the map and occupy a number of northerlytrending valleys, including the North Thompson Rivervalley. Gutliers of theTertiary Chu Chua and Skull Hill Formationsappear to havebeen preserved,at least in part,as a result of movement alongthis system of faults.Northeast-trending faults in thenortheast corner of the map-area areinferred on thebasis of abrupt structuraldiscordances and truncation of stratigraphicunits. These alsoappear to be relativelylate features, imposed afterthe dominant structural geometry had already been established.Intrusion of the Baldy Batholith (MiddleCretaceous) apparently post-dated most of thefolding in thearea. However, there is some deflection and reorientation of contacts and structuresnear its contact.

66 MINERAL DEPOSITS

The locations of the most importantmineral showings in the iarea are indicated on thegeological map (Figure1). TheIUoSt significant of theseare the Rexspar (d, F) (Preto, 1978) and CC (Cu, Zn) (McMillan, 1980)deposits. Mineralization in each of thesedeposits appears to be syngeneticwith theenclosing volcanic hostrocks. In contrast, other showings in thearea occur in crosscuttingquartz or quartz-carbonate veins whichformed late in thegeological history of thearea. These are oftenassociated with local shear zones, suchas at the Queen Bess (Pb, Zn, Ag) and Gold Hill (Au, Pb, Cu, zn, Ag) properties, where Fennel1 greenstones are cut by steepeasterly trending shear zones and altered to rustyferrodolomite.

ACKNOWLEDGMENTS

BruceGaiesky provided able assistance in thefield. Discusl;ionswith P.S.Simony, V.A. Preto, and W.J. McMillan haveproved very helpful and are much appreciated.

REFERENCES

Campbell, R.B. and Tipper, H.W. (1971): Geologyof themnaparte Lake Map-Area, British Columbia,Geol. Sum., Canada, Mem. 363. McMillan, W.J. (1980): CC Prospect, ChuChua Mountain, B.C. Ministry of Energy, Mines & Pet. Res., GeologicalFieldwork, 1979, :Paper 1980-1, pp. 37-48. Okulitch, A.V. and Cameron, B.E.B. (1976):Stratigraphic Revisions of theNicola, Cache Creek,and Mount Ida Groups,Based on Conodont Collections from the Western Marginof the Shuswap Metamorphic Complex, South-CentralBritish Columbia, Cdn. Jour. Earth Sci., Vol. 13,pp. 44-53. Preto, V.A. (1978):Rexspar Uranium Deposit (82M/12W), B.C. Ministry of Energy, Mines & Pet.Res., Geological Fieldwork, 1977, Paper 1978-8, pp. 19-22...... (1981):Barriere Lakes - Adams Plateau Area (82M,14, 5W; 92P/lE), B.C. Ministry of Energy, Mines 6 Pet.Res., Geological Fieldwork, 1980, Paper1981-1, pp. 15-23. Preto, V.A., McLaren, G.P., and Schiarizza, P.A. (1980): Barriere Lakes -Adams Plateau Area (82L/13E; 82M/4, 5W; 92P/lE, EE), B.C. Ministry of Energy, Mines & Pet. Res., GeologicalFieldwork, 197'3, Paper 1980-1,pp. 28-36. Schiarizza, P. (1981):Clearwater Area (82M/12W; 92P/8E, 9E), B.C. Min- istry of Energy, Mines & Pet. Res., GeologicalFieldwork, 1980, Paper 1981-1,pp. 159-164. Wanless, R.K., Stevens, R.D., Lachance, G.R. and Rimsaite, J.Y.H. ( 1966) : Age Determinations and GeologicalStudies, Part 1 - Isotopic Ages, Report 5, Geol. SUrv., Canada,Paper 65-17.

67 NOTES ON CARBONATITES IN CENTRAL BRITISH COLUMBIA (83D/6E)

By G.P.E. white

Carbonatites were examined at the Verity(Lempriere), Paradise Lake, Howard Creek, Mud Lake, and Gum Creek localities as well as at one new site; an extension of the Gum Creek carbonatite which lies to the west of theoriginal locality.

Generallycarbonatite is conformable to the hostingschists or, less commonly, syenite as at Howard Creek. Two ormre bodies of carbonatite separated by schist bands may be present.Beforsite is sometimes interbandedwith sovite and theircontacts are usually well defined. Some texturesresemble flow banding, but others are suggestive of carbon- atephenocrysts in a carbonate matrix.

In the verityarea, coarse olivine is oftenassociated with sovite and apatitecreates banding in trenchedareas; otherwise lateral and vertical mineralzoning is not obvious.

Minerals identified in carbonatite on the JIM property (Mud Lake) are calcite,dolomite, apatite, ilmenite, olivine (ferroan forsterite with secondaryiddingsite and goethite), tremolite-actinolite,chlorite, antigorite,vermiculite, talc, hydromica, and pyrrhotitealong with previouslyreported phlogopite, chondrodite. pyroxene, magnetite, and limonite . From the Howard Creek site zircon,baddeleyite, pyrochlore, sphene, apatite,calcite, pyrite, richterite, and titanite were identifiedas well as traces of ilmenite and hornblende(possibly edenite).

In the Howard Creek areathere is a black,hard, relatively coarse- grainedrock consisting of hornblende,sphene, clinopyroxene (acmite- augite) and apatitewith interstitial calcite, and minormica, for which A. Mariano has tentativelysuggested the name 'lemprierite' (Bent Aaquist, pers. corn.,September 1981).

Columbite and pyrochloreare common to manyof these sites and molybdenite was noted in core from the Gum Creek area.

Attempts at age dating have not been definitiveor correlative to date. Potassium-argondates by Joe ilarakal of theUniversity of British Columbia were 20528 Ma on phlogopite from Howard Creek, and 92.5t3.2 Ma and 80.2t2.8 Ma on richterite from theVerity site. Dr. R. Armstrongof theUniversity of British Columbia hassuggested that we confine our datingwith zircons. Euhedral, coarse-grained zircon is present at the Verity site and zirconhas been noted in thinsections from the Howard Creekcarbonatite.

68 John Kwong of theAnalytical Laboratory in Victoria is responsible for much of themineral identification while Lynn Sheppardcarried out the heavymineral separations. Bill McMillan suggested methods toobtain age dates and thanks are due to MitchMihalynuk who assisted in theField.

BentAaquist OF AnschutzMining Corporation gave freely of his time and discussedresults OF their mrk in thearea.

69 LEECH RIVER AREA, VANCOUVER ISLAND (92B/5g8 12 b-c)

By G.E.P. Eastwocd

INTRODUCTION

Placergold was minedfrom the Leech River in quantity in 1864 and has been theobject of intermittentprospecting and small-scale mining since then. The river name hasbeen used forthe metasedimentary bedrock formation on which theplacer deposits rest and fora major fault which juxtaposesthe Leech RiverFormation against the Eocene Metchosin basalt tothe south. The IeechRiver Formation has not been dated, and suggestionsas to its agehave ranged from Carboniferous to Early Creta- ceous. The formationcontains numerous smallquartz veins carrying trace amounts of gold, and Clapp ( 191 7) concludedthat the placer gold was derived from them.

A prospector, Marvin Richter,did not believe this and in 1980 claimed to havefound nugget gold in shear zones in the Leech RiverFormation. He speculatedthat these were localizedalong fold limbs.There were thus stratigraphic,structural, and economicreasons for taking another look at the Leech Riverarea. In 1981 the writerspent 7 days on a reconnaissance of a strip betweenthe mouth of the West Leech andSooke Rivers. It was thenlearned that the Greater Victoria Water District plans to builda 20-metre dam acrossthe Leech River at the end of the new road on thenorth side and to drive a 4-kilometre tunnel from a point immediately above northeast to Deception Gulch, near Sooke Lake.

Thisarea may be reached on weekends viaa Pacific Logging main haulroad fromSooke, or at any time from the Shawnigan Lake Road viathe Sooke LakeRoad and asuccession of secondaryroads that lead to the old Leechtown site.Ihe formerbridge over the upper Sooke River is gone, so it is necessary to fordthe river immediately above its junctionwith the Leech River.Ihe passable roads and main streamsare shownon Figure 1. A gateacross the new road on the northside of the Leech River is kept locked, and a key was borrowed from theGreater victoria Water District. The north slope and lower part of thesouth slope of the Leech Riverval- leyare mderate, vibereas theupper part of thesouth slope is bluffy. The river is slightlyincised over most of its length. Martins Gulch is actuallya V-shaped creekvalley with a moderate gradient. Bedrock is wellexposed along the beds of the Leech River and Martins Gulch,moder- ately so in road cuts at lower elevations, and not at all on the upper part of the northslope.

GENERAL GEOLOGY

In thisarea exposures of the Leech RiverFormation consist of interbeddedblack phyllite, light to dark grey siltite, and white to lightgrey fine-grained quartzite. The siltite constitutes abouthalf

70 therock and phyllite is least abundant. Most of thebeds are thin: phyllite commonly 0.5-1.0 millimetre, siltite 1-5 millimetres, and quartzite 1-3 centimetres. A few quartzite bedsare metre-thick, and at one placeseveral beds coalesced to form a unit 10 metres wide. Along the Leech River between Martins Gulch and the end of the new road,these thin-beddedrocks have been closely dragfolded; most of the limbs have been stretched and pinchedoff, producing a striped and roddyrock. All gradations can be seenbetween perfectlycylindrical rods, which resemble stretchedpebbles, and flangedrods which are clearlythe thickened axial parts of dragfolds. Thesebeds have a moderate schistosityparallel to thestriping andbedding. Downstream, 680 metresabove the haul road bridge,the beds are notdragfolded and arecleaved to slightlyschis-- tose. Southwest and west of MacdonaldLake mesoscopicdragfolds are scattered and thebeds are onlylocally schistose. Such foldsare abundant up Martins Gulch butnot sheared out; the rocks are cleaved to somewhat schistose.

No definitestratigraphic units could be distinguished. "UE quartzite units exposed in the Leech Rivermight be traceablebut because exposure is largelyrestricted to theriver, the likelihood is notpromising.

Thin sheets of slightlygneissic granitic rock intrude the phyllite and siltite in a road Cut on thenorth side of theriver about 800 metres west of the haulroad bridge.

STRUCTURAL GEOLOGY

Observations of the structuralelements are shownon Figure 1. There is acoherent pattern west from Martins Gulchwhere dragfolds c:onsistent:Ly indicateoverriding (vergence) toward thesouth. They have one long upright limb and one shortoverturned limb. Viewed alongthe east plungingfold axis, the folds resemble a staircasewith narrow treads and high risers. The easterlyplunge of thefolds decreases westwardfrom 35 degrees at Martins Gulch to 20 degrees at the end of the new road. Furthermore,the bedding generally steepens southward, to near vertic.31 at the mouth of Martins Gulch and is overturned at the west end of th,e area. Dips of bedding were necessarily measured on the long limbs of the dragfolds,hence the average true dip of a bed is somewhat less where dragfolds were not dismembered. Inareas with sheared out :Eolds, the averagedip differs little from the true dip.

The Leech River fault was notobserved; its tracehas been.taken from a line of change in topographyseen on airphotos.If it were verticalor north-dippingthe river would presumablyhave eroded downa'Long it. Sincethe trace is part-way up thesouth slope the fault zonemust dip south and hasbeen partially protected from erosion by overhanging erosion-resistantMetchosin basalt. A south dip is alsoconsistent with steepening and overturning of the Leech Riverbeds toward the fault. The fold pattern is consistentwith a largeflexure in beds that have been downfaulted. The pattern of disrupteddragfolds can be understood i€ it is assumed that beds on theconcave side of the flexure were initially

71 \ \'\ ..\' ...... (I: ma L. +: -wt am l?c9 L

72 undercompression and responded by dragfoldingwith relative movement of the upper bed up towardthe fault, and subsequently were under tension and stretched as subsidence of thepackage continued. Thus, on the section of thefault between points oppositethe mouthsof the west Ieech and Martins Gulch the MetchosinFormation has been thrustover the Leech RiverFormation. The plungeof the dragfolds would indicate an eastward component ofmovement.

Inthe eastern part of thearea the structural pattern is less clear.. Near the Sooke Riverthe fault trace approaches Leech River and thelfault may be close to vertical. The vertical and overturneddips south and west of Macdonald Lake appearanomalous and my be unrelated to the faulting. The steep plunge is alsodifficult to accountfor. Farther east, nearGoldstream, Clapp found thatthe Leech River fault dipsnorth.

The thin Leech Riverbeds are particularly susceptible to downhillcreep. Spectacular examplesoccur at the endof theroad along the! northside of theriver and at the end of the lowerroad on thesouth side. At the first, bedsdipping 65 degreesnorth are curvedthrough horizontal to a gentlesouth dip at thesurface. At thesecond, beds overturned to 70 degreessouth in the river bank are bent Over to a gentlesouth dip (upside down) in thebluff above.Shallow cuts on hillsides cannot 'be expected to show true dips.

ECONOMICGEOLOGY

The source of theplacer gold remains undetermined. In 1864 the main placer accumulations were found at the mouthof Martins Gu:Lch and at the junction of the Leechand Sooke Rivers. A weekend placer:?rospector told the writer hehad tracedgold by panning up the Leech Rive:c and Cragg Creek asfar as themiddle of SurveyMountain, but had fownd no lodegold on the mountain. The writer's assistant panned a few grai.ns of gold from mid-channel gravelpatches opposite the mouth of Martins Gulch, butcould find no gold in bech Rivergravels immediately above this. The gold grains were well-rounded, almond shaped, and possiblylaminated; they could haveformed either by deformation of individualnuggets or by poundingtogether of a numberof small flakes. The Razzoshad a small1 placeroperation in Martins Gulch but declinedto report results. lllese observationshint at a zone or zonesof gold mineralization passing throughSurvey Mountain and the upper part of Martins Gulch. Several1 shearzones were seenabout the middle of Martins Gulch butthey appeared barren. A 1922 report on theInvereck talc deposit on EeceptionCreek notesthat trace gold was found in thetalc, and a 1924 reportnotes; that colours oE goldcan be panned from the gouge between the talc and the enclosing Leech Riverbeds. Quartz veins in Leech River he& are so A significant post-Nanaimo fault is indicated by theabrupt termination of the basal conglomerate and by a large notch in theriver wall. A major component ofthe movement had to be southside up.Not enough work hasbeen done to indicate its westward extension, and to the east it passes under extensiveglacial cover.

73 The Nanaimo-Sicker contacthas been offset 30 metres to the left on a tightvertical fracture which anglesacross the river bed. A possible thrustin the Nanaim beds has beennoted above. And becausethe basal grit is notrepeated there may be a faultalong the south side of the Sickerinlier in the Chemainus River.

ECONOMIC GEOLOGY

No significantmineralization was found. Pyriteoccurs in theschist belt and inthe mafic volcanic rocks. The shonkinitescontain sporadic grains of chalcopyrite.

REFERENCES

Clapp, C.H. (1917): Sookeand Duncan Map-Areas, Vancouver Island, British Columbia, withSections on Sicker Series and the Gabbrosof East Sookeand Rocky Point by H.C. Cooke, Geol.Surv., Canada, Mem. 96, pp. 125-172, Map 42A. Eastwood, G.E.P. (1979): SickerProject - Mount Richards Area, B.C. Ministry of Energy, Mines & Pet. Res.. GeologicalFieldwork, 1979, Paper 80-1, pp. 49-51...... (1980): Geology of the Mount Richards Area, B.C. Ministry of Energy, Mines 6 Pet. Res., Prelim. Map 40. Eyles, J.T. (1955): Geology of the Cowichan Lake Area, Vancouver Island, B.C. Ministry of Energy, Mines & Pet. Res., Bull. 37. Muller, J.E. (1980): The Paleozoic Sicker Group ofVancouver Island, British Columbia,Geol. Surv., Canada, Paper 79-30.

74 GRAVITY SURVEY OF THE COLWOOD SECTION OF THE LEECH RIVER FAULT

By B.N. Church, D. Brasnett, and G.E.P. Eastwood

The purpose of thissurvey is to determine the position of the Leech River fault in an area of glacialcover between Langford Lake and Esquimalt: Lagoon throughthe Colwood area of greaterVictoria.

The approximateposition of the fault is known from the early worksof Clapp (1912). It crosses 60 kilometres of the southerntip of Vancouver Island, trending in an east-southeastdirection from a pointnear the west entrance ofJuan de mca Strait to thevicinity ofBrochy Ledge inthe strait immediatelysouth of theFairfield-James Bay area of Victoria.

The fault is a major geologicalboundary that marks the con,tactbetween oceanic and continentalplates. The success of thegravity survey relies on thedensity difference betweenthe Metchosin oceanic basalts (specific gravity -3.0) south of thefault and the Leech Rivermetasedimentary and volcanicrocks (specific gravity -2.67) to the north.

The surveycomprises 43 stations on threenortheast-trending lines across theprojected course of thefault (Figure 1 ). The precise route of the surveytakes advantage of recentlypublished municipal topographic bench marks (British Columbia Ministry of hvironment, Map Projeat No. 79-087 T-C) and various well-known thoroughfaresincluding Jacklin Road. on the west, Lagoon Roadon theeast, and Wishart Road-SookeRoad-Old Bland Highway in thecentre. The gravityreference station for the survey i.s No. 9282-60 with a localgravity value of 980959.31, established on the window s.ill at the northeastcorner of the main LegislativeBuilding in Victoria.

The course and attitude of thefault is defined by inflectionsin the profile of observedgravity readings (Figure 2a, b, and c)., The pro:Eile alongJacklin Road is most definitive owing to godspacinq of thestations andprobably thin glacial cover in this area. One point on the fau1.t is indicated by a sharpinflection in readingsobserved near station 5. A flat profile on thenorth passes to a steadyincrease in gravity values 011 the south. The profilefor the Wishart Road-SookeRoad section which places the faultnear station 27 is similar.Control of the exactpositions of the faultin this case is notas good owing to a large gapbetween stations 27 and 28. TheLagoon Road section is least definitive of thethree lines showingonly a gradualincrease in gravityreadings to thesouth. T'his relatively subdued profileprobably results from a great thickness OE relatively low specificgravity sand and gravelover the Metchosinb.asalts. A small notch in theprofile near station 38 maymark the psition of the fault.

The combined evidence from thethree profiles seems to give a fairly accuratelocation for the Leech River faultthrough the Colwood area. "ne fault strikes 117 degrees, bisectsJacklin Road and Esquimalt Lagoon, and

75 Figure 1. The projectedposition of the Leech Rlverfault in the Colwood area frm gravity statlons on the Jacklln Road, Wlshart Road-SookeRoad, and Lagoon Road sections.

76 JACKLIN ROADSECTIONROAD LAGOONSECTION

e- - .4 .? III f a ITA

Figure 2. Relativegravity sections in the Cold area. passes just north of thenorth end of Wishart Road. "be steadyincrease in gravityreadings south of thefault suggests sone decrease :in thickness of sialic crust southward and suggeststhat the fault dipssouthward. There is no evidence from thisstudy on the directionor magnitude of motionalong thefault although the marked geologicaldifferences suggeat that it is large. It is anticipatedthat additional gravity readings in thearea and carefulmodelling of theresults will provide mre informationabout the attitude and displacement of this importantfault.

REFERENCE

Clapp, C.H. (1912): Geology of the Victoria and Saanich Map-Areas, Vancouver Island, B.C., -01. Surv., Canada, Mem. 36, 143 pp.

77 GEOLOGY OF THE WHITEHOUSE CREEK AREA (92B/13f, 9)

By G.E.P. EastWood

INTRODUCTION

The Whitehouse Creek area (Figure 1) overlaps the Mount Richardsarea on thenorthwest and represents a continuation of the Sicker mapping project. Some of the mapping was done in 1978 and 1979 but most was done duringfour weeks in 1981. The principalobject of thestudy is to relatethe Sicker rocks north of the Chemainus Riverto the section established on Mount Richards.

Physiographicallythe area includesthe widening valley of the Chemainus River, thenorth footslope of Big and Little SickerMountains, and the extremesoutheast footslope of Mount Brenton. The valleynarrow to a notchin the west part of the area. Within it the river has been incised throughthick drift and, along most of theincluded length, deeply into

LEGEND

NANA IM) GROUP

4d Sandstonedyke 4c Siltstone and shale 4b Sandstone 4a Conglomerate and grit

INTRUS I VE ROCKS

3 Hornblendeshonklnite 2 Quartzfeldspar porphyry

SICKER GROUP

ld Quartz-mica schist IC Siltlte and finequartzite ib Hornblendetrachyte la Maficla trachyte; chlorite schlst

Symbols

Outcrop; outcroparea ...... + ...... Geologicalcontact ...... ,..’ Bedding; schlstoslty ...... /A Orientationof sandstone dyke ...... /r Trend and plungeof minor fold; canbindwith bedding ..... f,/ Directionof overriding (vergence) on minorfolds ...... r Fault ......

78 79 bedrock. In summer it is possibleto walk longstretches of the river on bedrockpavement and gravelbars, crossing where necessary by rock- hopping or wading. Two canyons in the west part areinaccessible but the section between them can be reachedwith the aid of a rope.

Thick drift in thevalley extends up the slope of Big SickerMountain, andoutcrops are mstly confined to a few exposures in watercourses and roadcuts. Mostof this slope is covered by tall timber, and airphotos arevirtually useless. Mapping here was done by altimeter and compass traversesusing a contour map at 1:2500 obtainedthrough the courtesy of Serem Limited.

GENERAL GEOLOGY

Volcanic and sedimentaryrocks of thePaleozoic Sicker Group havebeen intruded by smallbodies of quartzfeldspar porphyry, deformed,then intruded by largerbodies of hornblendeshonkinite. The thick Lower Mesozoic section seen elsewhere on Vancouver Island is missingfrom this area, and the olderrocks are directly and unconformablyoverlain by clasticsedimentary rocks of the Upper Cretaceous Nanaimo Group. The Nanaimbeds form a lobe extending some distance up theancestral ChemainusRiver valley.

SICKER GROUP

Trachytecharacterized by medium to coarse-grainedhornblende phenocrysts is the dominant Sicker rock north of the Upper Cretaceouslobe. It is similar to a band of hornblendictrachyte traced through the Mount Richardsarea. Outcrops are massive and erosion-resistant,forming low hills and ridges. The outcroparea south of Banon Creek is interpreted as a hill in the pre-Nanaimo surface. The inlier in the lower Cnemainus River may be a similar hill or it may represent tilting on apost-Nanaimo fault.Coarse volcanic breccia occurs in thearea of hornblendic trachyte in Banon Creekboth near the Nanaim contact and atthe base of a transmissionpylon east of thecreek. It is probablethat the hornblendicphase was repeatedseveral times in thevolcanic sequence, so the BCLnon Creek unitcannot be positioned in thesequence from the present mapping.

Mildlydeformed sedimentary rocks are exposed in the Chemainus River upstream from the NanaimoGroup basalconglomerate. They consist of dark grey to blackargillite, chert-like siltites, and fine-grainedlight grey quartzite. The siltites are mre or less banded in white andshades of grey. A few tuffaceous beds areintercalated. Theserocks resemble the upper,sedimentary part, of theSicker Group in the Cowichan Lake areato the west and areprobably somewhat youngerthan unit Id of the Mount Richardsarea. Mafic volcanicrocks appear to overlie these beds in a smallbluff south of theNanaim contact, but this section is complicated by faulting and themafic rocks do notoccur in an equivalent stratigraphic position in the river bed.

80 A belt of volcanicrocks occurs south of theSicker and Nanaimo sedimentaryrocks. The volcanicrocks are mostly mafic, though a few thin bands of thehornblendic phase are intercalated. The rocks are variablychloritized and slightlyto completely schistose. A hornblen'de band appears to overliethe Sicker beds in theright bank of theriver near thesouthwest limit o€ mapping, but the contact is sheared and is close to a projectedfault. The position of these mafic volcanicrocks in theSicker sequence is uncertain.

UnitId has been traced along Crofton andBreen Ridges, north of Mount Richards,across the flats, and alongthe north slope ofBig Sicker Mountain tothe mine road. Where least deformed, the rock is a white to light grey siltite. Most of it is schistose, and theintensity of schistingincreases northward; the outcrops shownon Figure 1 are white tolight brown quartz-micaschists. This schist belt is interpreted to be a diffusefault zone. The largestsingle movement apparentlyoccurred in the siltites atthe contact with the mafic volcanic rocksbut the total movement was distributedover a considerablethickness of rock. Bandsof chloriteschist indicate that somemovement took placein the volcanicrocks. An undisturbedshonkinite dyke anglesacrosg the contact,consequently the movement is pre-shonkinite.

INTRUSIVE ROCKS

A few small dykes of quartzfeldspar porphyry occur in the schist belt., and are schistedalong with the siltites, but none have been found tothe north.

Three,or possibly four, bodies of shonkinite(mafic hornblende syenite) were found in themap-area. One extendsout of the area to the north and appears to be a stock. A secondappears to be a thicksheet dipping gently westward up the Chemainus River. It rests on Sickersedimentary rocks and is overlapped byNanaimo sedimentaryrocks. A small outcrop south of WhitehouseCreek may represent a faulted segment of thissheet or perhaps a completelyseparate body. A relatively narrow dyke angles throughthe schist belt inthe south part of thearea and appears to tle an extension of the much thicker body that underlies CroftonRidge.

NANAIMO GROUP

TheNanaimo bedsare well exposedalong the walls and bed of the Chemainus River and sporadicallyelsewhere. me earlysedimentation varied from place to place. Along the west edge of the lobe there is a thick,coarse basal conglomerate.In Banon Creek this conglomeratethins to 30 metres. Inboth places it is overlain by sandstone which fines upward. Inthe river near the highway, 4.5 metres ofhard grit (granule conglomerate and poorlysorted sandstone) overlies the Sicker rocks. The sandstone and grit are overlain by a thicksection of darkgrey siltstones and blackshales, which in turn are overlain by fine-grainedsandstone which is exposedalong the highway. South of Banon Creek siltstone

81 appears to rest directly on theSicker inlier. In the Chemainus River south of Banon Creek,a 5-metre grit bed has a discordantstrike and rests on rumpled siltstone; it may be thebasal unit thrust northwest overthe youngerbeds.

Fossiliferoussandstone dykes cut thesiltstones in two places:just abovethe discordant grit bed,south ofBanon Creek in Chemainus River at theplace marked 4d. The attitude symbol is for the largest dyke, one which is 20 to 30 centimetresthick. Others are as thin as 5 centimetres and curved. Onewas seen to bifurcate upward.

STRUCTURAL GEOLOGY

Pre-shonkinite and post-Nanaimo episodes of faulting occurred. In additionthe Sicker sedimentary rocks (IC) havebeen folded and thedip of the Nanaimo beds suggeststhat the area has been tiltedeastward. The overalldip of theSicker beds is to thesouth-southwest. A syncline- anticlinepair indicate overriding or vergence to thenorth. A shear zone on theflank of theanticline dips 32 degreessouth and is probably a thrust. The timing of thisfolding and faulting is unclearbut it is probably pre-Nanaimo.

The sense ofmovement in theschist belt is unclear. If the mafic volcanic rocks to thenorth are correlative with those on Mount Richards then atleast acomponent of the movementwas northside up.However, themafic volcanics may be intercalated in thesediments in thisarea.

A significant post-Nanaimo fault is indicated by theabrupt termination of thebasal conglomerate and by a large notch in theriver wall. A major componentof the movement had to be southside up.Not enough work hasbeen done to indicate its westward extension, and to theeast it passes under extensiveglacial cover.

The Nanaimo-Sicker contacthas been offset 30 metres to the left on a tightvertical fracture which anglesacross the river bed. A possible thrust in the Nanaimo bedshas been noted above. And becausethe basal grit is notrepeated there may be a faultalong the south side of the Sicker inlier in the Chemainus River.

ECONOMIC GEOLOGY

No significantmineralization was found. Pyrite occurs in theschist belt and in themafic volcanic rocks. The shonkinitescontain sporadic grains of chalcopyrite.

REFERENCES

Clapp, C.H. (1917): Sooke and DuncanMap-Areas, Vancouver Island, British Columbia, withSections on SickerSeries and the Gabbros of

82 East Sooke and Rocky Point by H.C. Cooke, Geol. Sum., (!anada, Mea. 96, pp. 125-172, Map 42A. Eastwood, G.E.P. (1979): SickerProject - Mount Richards Arc!a, B.C. Ministry of Energy, Mines & Pet.Res., Geological Fieldwork, 1979, Paper 80-1, pp. 49-51...... (1980): Geology of the Mount RichardsArea, B.C. Ministry of Energy, Mines & Pet. Res.,Prelim. Map 40. Fyles, J.T. (1955): Geology of the CowichanLake Area,Vancouver Island, B.C. Ministry of Energy, Mines & Pet. Res., Bull. 37. Muller, J.E. (1980): The PaleozoicSicker Group of Vancouver Island, British Columbia,Geol. Sum., Canada,Paper 79-30.

133 UPPER SVTTON CREEK AREA (92C/16c)

By G.E.P. Eastwood

INTRODUCTION

Thisarea lies south of Cowichan Lake and may be reached fra either HoneymoonBay or Caycuse by main loggingroads. Local access is provided by Truck Road 3,which is badlyeroded but was still passable by four- wheel-drivevehicle as far as Sutton Creek in 1981 (seeFigure 1).

SuttonCreek flows down asteep V-shaped valley between two spurridges ontoa flat-floored valley followed by the main haulroad. The west ridge is fairlyflat crested. Much of thearea is coveredwith second- growthtimber, and growth is thick on the Gordon Riverslope.

About1971 Western ForestIndustries leased the mineral rights to a tract ofland extending westward from upperSutton Creek from theFsquimalt and NanairmRailway. In 1980 the company instructed its prospector, V. Allan, to assessthe mineral potential. He askedfor assistance with the geology, and the writer spent an aggregate of13 days in 1981 cruising roads in and east of thearea of Figure 1 andmapping on the west ridge. The company kindlyprovided free accommodation for the writer and his assistant.

GENERAL GEOLOGY

Mostof thearea between Cowichan Lake and the main haulroad is underlain by Bonanza volcanicrocks, but alongthe section of the Gordon Riverroad (Figure 1) the rocksare dark greenish grey or grey amygdaloidalKarmutsen Formation lavas. On thesouth nose of the west ridgethe rock is generally much sheared and rubbly, a featurecharacter- istic of the Bonanza, but creekexposures show thatthe rocks are Kannut- Sen.

A solid mass of blue-greyQuatsino limestone occupies part of the summit and west slope of the =st ridge. It is massive,a typical feature of Quatsinolimestone that has beenmoderately metamorphosed. A few andesite dykes occur in thelimestone at the north end of theexposure. Both north and souththe area is largelycovered, but numerous sink holes indicateextension of thelimestone. On thesouth part of theridge crestsmall outcrops of limestone are interspersedwith outcrops of massiveandesite, and limestone is exposed in two roadcuts. No limestone was foundbelow theroad. In the Kennedy Lake area and elsewhere on Vancouver Islandthe Quatsino limestone is extensivelyintruded by massive andesiteor basalt, which is believed to representa resurgence of Karmutsen volcanism.Intrusion into the lower part of thelimestone

84 LEGEND Symbols

5 Areasof abundant porphyry dykes ...' ..: 4 Bonanza Formation Areaof continuous outwop .... :...,. 3 Parson Bay formationalFormationInferredcontact .. ./' . 2 Quatsino2 Formation .A' 2a: limestonermnants In intruslveandesite Mineraloccurrence ...... X 1 KarmutsenFormation Figure 1. Upper SuttonCreek area.

on the west ridgehas completely disaggregated the limestone ;so it now occursas blocks in theandesite. Along thesouth part of thethird ley of Truck Road 3 therock is mostlyamygdaloidal JCarmutsen lava. 'Ryo outcrops of limestoneoccur on theeast rid* and suggestthat the limestone body strikesnortheastward. Here thelimestone is succeeded .to thenorth by areddish grey volcanic rock which is assumed to be Bonanza. Near the end of the east branch of Truck Road 3 thereddish rock passesnorthward toa chert-like rock such as is seen in lower Bonanza in otherareas. Westward, thelimestone doesnot reach the Gordon Riverroad within the map-area. It must either be faultedor dip at a low angle to thenorth and pass under thecovered area around the first switchback.

After a coveredinterval, the secondleg of Truck Road 3 cutsthrough andesitecontaining bands of limestone and calcareousargillite. Some thinlimestone bands areblack and resembleParson Bay Formation,but one comprises 10 metres of thinly banded light greylimestone. This section has no counterpart on theeast ridge. The andesite is intruded by a 4.5- metremonzonite dyke and by many small dykes of fine-grainedlight grey feldsparporphyry. Shear zones cut allthe rocks in severaldirections.

On theeast ridge the Bonanza-like rocks are cut by diorite dykes up to 25 metres wide.These in turnare cut by small dykes of feldspar porphyry. At theroad junction on the west ridgea similar porphyry dyke intrudeslimestone and intrusiveandesite, and farthernorth another intrudesa nondescript grey rock.

STRUCTUm GEOLOGY

The distribution of theQuatsino limestone suggests that: it dips moderatelynorthwestward on the east ridge and *ntly towardthe west- northwest on the west ridge. A flow contactin Kannutsen on the Gordon Riverroad, 365 metres south of thefoot of Truck Road 3, strikeseast- west and dips 25 degreesnorth. The bandedlimestone strikes 050 degrees and dips 55 degreesnorthwest. However, the belt south of Cowichan Lake is intricately faulted and isolated attitudes may notbe significant.Individual shear zones arelegion, but no major faults have beendemonstrated.

ECONOMIC GEOLOGY

. Two mineraloccurrences havebeen found in the map-area. At thepoint indicated on Truck Road 3 (Figure 1) a littlechalcopyrite and arsenopyriteoccur with pyrite in arusty, altered, dense rock. At the pint indicated in Sutton Creeka little wire silveroccurs with pyrite in ashear zone in Kannutsenlava. However, there is much barren shearing in thearea and theprospects are poor. There is alsoa lack of skarndevelopment in andesiteintrusions into Quatsino limestone; such alterationusually occurs where mineralizingsolutions migrate through therocks.

REFERENCE

Eastwood, G.E.P. (1968): Geology of the Kennedy Lake Area,Vancouver Island,British Columbia, B.C. Ministry of Energy, Mines & Pet. Res., Bull. 55, 63 pp.

86 CAROLIN MINE - COQUIHALLA GOLD BELT PROJ~T (92H/6, 11 )

By G.E. RAY

INTRODUCTION

Thisproject was initiated in June 1981, and hasbeen centred around the Carolingold mine (MDI No. 092H/NW/007), situatedapproximately 18 kilometresnortheast of Hope. The main objectivesare:

Regional mapping to outlinethe relationship between %he Coquih.slla Serpentine Belt and theadjoining Ladner Group. The contact betweenthese units is of economic interest because the Carolin mine, severalformer gold producers, and numerous goldoccurrences lie close to it. Regional mapping duringthis initial. season wss confined to an areastretching 13 kilometressouth and 5 kilometres east of theCarolin mine (Figure 1 1.

Detailed mapping at theCarolin gold mine, with particularemphasis on interpretingthe structuralhistory of the rockshosting the goldmineralization (Figures 2, 3, and 4; Table 1).

Geochemical analysis and, where possible,microfossil identification on rocksamples collected from the entire region. Mineralogical and traceelement studies will be undertaken on undergroundore samples taken from theIdaho 7nne at(arolin mine and from otherformer gold mines inthe area.

TABLE 1. STRUCTURALHISTORY OF THECAROLIN MINE AREA

Sporadicaliy developed, minor conjugatefolds associated with kink banding and crenulation cleavage.

Open to tight, disharmonicfolds having sub-vertlcai to easterlydipping, southeast-striking axlal planes and northwest to southeast, gentlyplunging axes. it is the domin.snt fold episode In the area and is assoclated with awldesproad axialplanar slaty cleavage and minerallineation. Some disruptionalong fold limbs and axial planes.

Widespread structuralinversim of the Ladner Group and greenstonevoicanics, probably related to maJor recumbent folding. No associatedaxial plane fabric recognized.

Early to MiddleJurasslc 7 Unconformable depositim of the Ladner Group !sediments on a greenstonevolcanic unit of unknownage.

HISTORY AND PREVIOUS WORK

By theearly part of thiscentury, numerous gold-bearingquartz veins had beendiscovered in rocks adjacent to theeastern edge of theCoquihalla

87 Flgure 1. Reglonalgeology of the CoqulhallaRlver area.

88 89 C

...... ,. . .

...... 0 100 I .:;;?.;,7,,,,;, . .I .: "...... ' ...~ -

Flgure 3. Geologicalsectlons AB, Bc (see Figure 2) In theCaroiln mine area.

Figure 4. Geologicalsections CD, DE (see Figure 2) acrossthe Idaho Zone, Carolln mi ne.

90 Serpentine Belt. These discoverieseventually led to underground production from threedeposits, the Pipestem, Rnancipation, and Aurum mines (Figure 1 ). All threeproperties are now closed and the mineralization and geology at these sites are described by Cairnes(1914, 1929).Mineralization at theEmancipation mine was inquartz veins cuttingaltered volcanic rockswhereas at Pipestem the gold-hearing veins cutsedimentary rocks of theLadner Group. In bothdeposits gold is associatedwith silver, pyrite, and arsenopyrite,while pyrrhotite, chalcopyrite, and calciteare reported from theEmancipation property. The Rnancipitation area was recently re-examined by rquariusResources Ltd. (Cardinal, 1981 ).

In 1927, the Aurum gold mine was discoveredjust south of theIdaho Zone. Spectacularvalues of freegold, hosted in a talcoseshear, rare found in the Hozameen fault which is a major fracture marking the eastern marginof the CoquihallaSerpentine Belt. At Aurum, gold is associatedwith pyrrhotite,pyrite, chalcopyrite, arsenopyrite, and possibly millerite (Cairnes,1929).

Surfaceexposures of the Idaho Zone (Figure 4), thegold deposit which comprisesthe current Carolin mine operation, were originallydescribed by Cairnes(1929). At that time the goldvalues were not economic butthe increasedprice ofgold inthe early 1970's led Carolin Mines LU. to conduct a major exploration and developmentprogram on thepr(3perty. Current outlined orereserves are as follows: Tonnes Oz./tonneCut-off Grade 2 OM1 000 0.128 0.05 oz./ton Au 1 500 000 0.141 0.08 oz./ton Au

Carolin mine startedproduction in December 1981, and the mill. should handleapproximately 1,500 short tons of oreper day.

Briefdetails on the geology of the Idaho Zone were given by Barr (1980), but most wrk on thedeposit is inunpublished form; this includes work by Cochrane. et al. (1974). Griffiths (1975), and a mineralogi.ca1 and petrographicstudy on theore zone by Kayira(1975).

The regionalgeology, involving early major workby Cairnes(1924, 1929), was compiledby Monger (1970).Additional work relevant to thearea includesthat by McTaggart and Thompson ( 1967),Coates ( 1970, 1974),and Anderson (1976).

REGIONAL GEOLOGY

In theCarolin mine vicinity,the Coquihalla Serpentine Belt formsan elongatenorth-northwest-trending unit that separatesrocks of the Ladner and Hozameen Groups to the east and west respectively(Figure 1); both margins of the belt appear to represent major long-livedtectonic fractures. In theCoquihalla River area, thebelt exceeds 2 kilometres in width,but it graduallythins to the north and southuntil in the

9 'I Flgure 5. Schematlc stratlgraphlc successlon In the Carolfn mlne area (not to scale): (1) F2 folding of the Ladner Group sedlmentary rocks contalnlng carbonaceous argillites (black); (2) late F2 high-angle reverse faulting localized along the carbonaceous horizon (black) withinthe F2 fold limb; (3) hydrothermal eplgenetlc emplacement of sulphlde-gold nlnerallzatlon tstlppled) along the fault shatter zone; and(3) late normal faultlng (F) causlng displacement of the mlnerallzed zone.

92 Boston Bar and Manning Park areas (Monger, 1970; Coates, 1974) the Hozameen and Iadner Groups are in direct faultcontact. The Hozameen Fault marks the eastern boundaryof the belt while the fracturealong the belt's western margin (Figure 1) is currently unnamed. Near Carolin mine the belt is dominated by two major rock types: massive darkserpentinite of probableperidotite parentage (Cairnes, 1929) and medium to coarse-. grained, massive and highlyaltered hornblende diorite. The basalts, diabases, and multiple sheeteddykes observed by Anderson (1976) were not seen in thisportion of thebelt.

Serpentinite is the dominantrock type and characterizes the belt, except in theSerpentine Lake vicinity(Figure 1) where diorite is abundant and forms sub-parallelsheets and lenses up to 250 metres in width. The age and geneticrelationships between these two rocktypes are rmknown becausetheir rarely observed contacts are highlysheared.

TheHozameen Group in the map-area consists of phyllitic argillites interlayered with both massive and ribboncherts. They have been subjected to intensedeformation and lower greenschist metamorphism, ,and otherthan the ribbon layering in thecherts, no sedimentarystructurces havebeen positivelyidentified. Some schistoseargillites contain highly deformed clasts, but it is uncertainwhether these represent sedimentary or tectonicfeatures. Elsewhere, the HozameenGroup includes spil- litic basalts(greenstones) andminor limestonesinterlayered with cherts and plites (Daly, 1912; Cairnes, 1924; McTaggartand 'Ihompeon, 1967; Monger, 1970). Monger (1975) interpretsthe group as a supracrustal oceanicsequence of possibly hiassic or pre-Triassic age.

The Ladner Group (Cairnes, 1924) consists of a thicksequence of fine- grained,poorly bedded, blackslaty argillites andwell-bedded, grey- colouredsiltstones with minoramounts of coarseclastic sedimentary rocks. Most outcrops show evidence of low grade metamorphiam with the imposition of a weak to intenseslaty cleavage, butin many instances theoriginal sedimentary structures are clearly preserved. Gradedbed- ding is commonly observed in thesiltstones and coarse clastic units, whileother, less common, sedimentarystructures present include crossbedding,ripple marking, scouring, flame, load cast, ball and pillow structures, and chaoticslumping. Gradedbedding and scourstructures indicate that most Ladner Group rocksadjacent to theSerpe,ntine Belt, includingthose hosting the gold mineralization at Carolin mine, are structurallyinverted (Figures 3 and 4).

A broadstratigraphic sequence is recognized in the Ladner Croup consisting of a thin, lowermost unitcharacterized by a heterogeneous; assortment of coarseclastic, partly volcanogenic, sedimentary rocks, thatpass upwards into a thicker sequenceof fine to medium grained vel1 bedded siltstones. These are overlain in turn by a thickunit of very fine-grained,organic, and iron-richargillites (Figure 5). The lower clastic unithosts the Carolin gold mineralization; it includes discontinuous wedges of qreywacke, lithic wacke, conglomerate,and possible reworked tuffswith intervening units of argillite and finely beddedvolcanogenic siltstones. Pebbles of volcanicorigin are common

93 with lesser amounts of quartz, jasper, and chert; one extensive conglomerate unit contains fragments of limestone that are derived from an unknown source. Cochrane, et al. (1974) mentions possible welded tuffs and volcanic bombs in the lowermost section, while Anderson(1976) notes the presence of 'serpentine (clasts) recognizably derived from Coquihalla Belt rocks' but these observations were not verified in this study.The overall upward fining of the Ladner Group suggests a progressive temporal change from shallow to deeper water conditions. The initial rapid and chaotic deposition of near-shore clastics was superceded by early siltstones (proximal turbidites) and later argillites (distal turbidites).

The Ladner Group overlies a volcanic greenstone (Figure5) of unknown age, whose relationship to the other major rock units in the area is controversial (see Discussion). Consequently, the greenstone is pro- visionally separated from the Ladner Group (Figures1, 2, and 5). This greenstone unit can be traced discontinuously for 13 kilometres along the eastern side ofthe Hozameen fault, and now structurally overlies the Ladner Group because of the regional tectonic inversion. Thus, its thickest development, up to400 metres in outcrop width, occurs on higher ground, while along the bottom of the Ladner Creek valley, ofsouth Carolin mine the unit disappears, and the Ladner Groupis in faulted contact with the Coquihalla Serpentine Belt (FigureI). The greenstone is a highly altered, fine to medium grained rock of probable andesitic composition (Cairnes, 1924). Outcrops vary from massive to very weakly layered and, in places, excellent pillow structures are preserved with some interpillow breccias, which in one instance include chert clasts. Many greenstone outcrops contain numerous dark green angular fragments, in a lighter green matrix which could represent evidence of autobrecciation within the lavas. Some greenstones northof Carolin mine also show evidence of tectonic brecciation and shearing (Shearer, pers. COmm.) .

In the vicinity of the Emancipationmine, the Ladner Group and the greenstones are separated by a fault whereas further south the contact appears to represent an unconformity. Near the junction of Dewdney Creek and the Coquihalla River, the pillowed greenstones are overlain directly by finely laminated, volcanogenic siltstones of the Ladner Group, but northeast of Serpentine Lake the contact is markedby a coarse conglomerate varying from1 to 200 metres in outcrop width (Figure1).

A variety of intrusive rocks cut the Ladner Group. East of Ladner Creek the metasediments are intrudedby the Needle Peak Pluton which has been dated at 39 Ma by K-Ar methods (Monger, 1970). The metasediments adjacent to this granodiorite body are characterizedby a thermal metamorphic aureole up to0.75 kilometre wide, which is marked by the growth of biotite and cordierite.

Other intrusive rocks within the Ladner Group are broadly separable into granitic and mafic types. The latter form dykes, sills and sub-rounded masses up to 0.3 kilometre in width that comprise a highly varied suite ranging from leucogabbroic to ultramafic rocks (Figure1). Granitic

94 intrusive rocks form narrow dykes and sills generally less10 thanmetres wide that have been mapped as either quartz or feldspar porphlyries; the latter are locally of syenitic composition (Cairnes,1924). Some dykes contain disseminated pyrite and arsenopyrite and are by cut quartz veining; Cairnes (1924, 1929) considered these bodies to be genetically related to some of the reef-hosted gold in the district.

GEOLOGY AND STRUCTURAL HISTORY OF THE CAROLIN MINE VICINITY

The surface geology around the Carolin mine is shown on 2 Figun?and the structural history of the area summarized on Figure6 and in 'Table1. The Hozameen Fault dips steeply northeast, and detailed geOlO'giCa1 sections across the mine area reveal that most of the stratigraphic sequence, including that hosting the gold-bearing Idaho Zone, is structurally inverted (Figures 3 and 4). After this early F1 tectonic overturning, the supracrustal rocks were deformedby the F2 folding andl overprinted by a weak to intense slaty cleavage which forms the d0minan.t tectonic foliation in area. Thus, the slaty cleavage was imposedon inverted beds. Several generations of fault movement subsequently occurred, particularly along theF2 fold axial planes and limbs. An early phase of fault shattering appears to be spatially related to several zones of alteration which are markedby either quartz, calcite, or feldspar veining and pervasive sulphide mineralization (Figure4). However, most of the fractures shown on Figures3 and 4 belong to a lat.er phase of generally normal faulting which post-dates and displaces the earlier alteration zones. The Idaho Zone (Figure 4), 150 metres east of the Hozameen fault, forms the largest surface exposure of alteration and is the only one to date in which economic gold mineralization has been found. At a cut-off grade of0.05 ounce per ton gold it appearsto form an irregular, steeply inclined ore body approximately35 metres wide, 1100 metres deep, and over300 metres in length which is still open down plunge (R. Niels, pers. comm.). The deposit passes upward into unmineralized chloritic schists, and the top of the ore zone plunges gently northward at approximately25 degrees (W. Clarke, pers. comm.). The predominant mineral assemblage in thezone comprises quartz, plagioclase (AII~-~), carbonate, chlorite, pyrrhotite, arsenopyrite, and pyrite; other rarer opaque minerals, in decreasing order of abundance, include magnetite, chalcopyrite, bornite, and gold (Kayira, 1975). In outcrop, the zone is characterized by abundant sulphides, intense hydrothermal alteration which weathers to give a distinctive black or grey-coloured rock, and a multi-stage networkof quartz, calcite and albite veining. Many veins are orientated parallel to the slaty cleavage, demonstrating thatsome alteration in the Idaho Zone post-dat.es the main F2 structural event. Mineralization involved the spasmodic introduction of silica, carbonate, Na,Fer Cu, As, Mo, Sb, and Au, and Table 2 shows the results of some trace element analyses completed on fresh, underground samples collected from mineralized and unmineralized portions of the Idaho Zone. Cochrane (pers. comm.) notes that soils over the surface exposures of the Idaho Zone contain anomalous mercury value!s, but underground ore samples (Table2) show no significant enrichment in this element. Thus a vertical zoning of mercury could existin the deposit.

95 West East

Lodner Creek erosion level

~~~~~~~ ~ ~

Figure 6. Postulatedevolutlonary history of theCoquihalla Serpentine Belt:

(1) pre-Trlasslc toTrlasslc deposition of the tbzameenGroup (HG) oceanlcsupracrustal rocks (bnger, 1975). Jurassic(Calrnes, 1924; Coates. 1974) depositlon of the Ladner Group(LG) arctrench gap sedimentsonto ocean volcanicrocks (Anderson, 19761. IX = oceanlccrust; OV = oceanicvolcanic rocks. (21 eastwardoverthrusting of the tbzameen Grwpalong a horlzonof serpentinized ocean crustcauslng F1 structuralinversion in the Manning Parkarea (hates, 1974); E = presenterosion level inthe Carol in mine area. (3) F2 foldlngresulting In a steepenlng of all unitsincluding the CoquihallaSerpentine Belt (CSE), withlater developnent of the Hozameen fault (HFI. 035 = Dewdney Creek Series(Cairnes, 1924). NOTE: Graniticplutons aitted; length of section 3 approximately 15 ki Imtres.

96 W oomoPoo c oommmoo m """C VI v v -vvvv 0 .-c

L 0

r-In F?...;rsssu)mr.or-o w0-(o000

0000000 ""C" vvvvvvv m + 2 W

-,unE

~m -. Y no d

97 4 The eyact controls of mineralization areunknown. Clarke (pers. corn.) notes that selective replacementhas occurred in the ore zone with preferential enrichment of the more brittle, coarse-grained sediments and a tendenc'y for less mineralization to be present in the finer grained argillites. Detailed surface mapping indicates that the Idaho Zone is located close to the disrupted limb of F2 an fold (Figure 4) and it is noteworthy that the topof the ore zone and theF2 fold axes both have very simi'.ar plunges. Consequently, the Idaho Zone is believedto represent an epithermal replacement deposit (Kayira,1975) that was laid down alonq a high-angle reverse fracture of lateF2 age (Figure 7). The presenceof carbonaceous metasediments adjacentto the orebody (Cochr,me,et al., 1974: Kayira, 1975) could also be significant. InitiaLly this incompetent horizon may have localized the reverse fault movements and later provided a favorable reducing geochemical environment

West East

Figure 7. Postulated development of the Idaho Zone, Carolinnlne.

98 forthe deposition of sulphides and gold when hydrothermalsolutions passed up thefracture (Figure 7). Thispostulated lithostructural control of thegold mineralization may helpoutline underground exten- sions of theIdaho Zone and assist explorationfor similar daposits in the region.Subsequent to goldemplacement, late normal faul-tin9rejuve- natedthe mineralized, pre-existing fracture zone.This intense late faultingcut the orebody (R. Niels, pers. comm.) butapparently played no role in oregenesis (Figure 7).

DISCUSSION

The pillowedvolcanic greenstones which separatethe Ladner Group from the Hozameen fault in theCarolin mine areaare a problematicunit becausethe following stratigraphic relationships are possib:Le:

(1) They could form part of theoceanic supracrustal Hozamf?enGroup as suggested by Cairnes (1924). However, this seems unlikelybecause theyare separated by thefault-bounded Coquihalla Serpntine Belt, which has probably been thelocus ofmajor tectonic movements.

(2) They couldbelong to theCoquihalla Serpentine Belt, a possible oceaniccrustal assemblage, as advocated by Anderson ('1976). This interpretation would suggestthat relatively minor movements occurredalong the Hozameen Fault, and thatthe Ladner Group unconformablyoverlies an olderoceanic volcanic basement. This possibility is indirectlysupported by observationsin the Emancipation mine area where thevolcanic rocks are intruded by dioritebodies (Cairnes, 1924,1929) that bear a superficial resemblance to dioriteswithin the Coquihalla serpentine Belt (Cardinal, pers. comm.), while theseintrusives have not been observedcutting the Ladner Group. Furthermore, no proof exists that volcanismoccurred during the Ladner Group sedimentation in thisarea, and the volcanogeniccharacter of thecoarsely clasti,?, lowermostsediments may merely reflect theirerosional derivation froman oldervolcanic terrane.

(3) The greenstones may have no geneticrelationship with any rocks west of the Hozameen fault, and insteadrepresent the :Lowest exposedportion of theLadner Group, as suggested by Cochrane (pers. comm.). Ifthis is correct,the volcanic-sedimentary unconformity is probably of relatively minorimportance!.

Detailedstructural mapping alongthe Coquihalla River suggests that the volcano-sedimentarysequence between Ladner Creek and the Hoxameen fault occupies the invertedlimb of a major F1 synform which is overturned b, theeast andwhose axialtrace probably lies alongLadner Creek (Figurce 6). Furthersoutheast, in Manning Park,the Coquihalla Serpentine Belt is absent and theLadner Group forms an essentially upright sequence even adjacent to the Hozameen fault (Coates, 1974).Thus, the tectonic

'39 inversion of the L3dner Group appears to be spatiallyrelated to the CoquihallaSerpentine Belt ratherthan the Hozameen fault.This raises the pssibility that the belt and the F1 recumbentfolding share a geneticrelationship. One possibleexplanation is thatthe Coquihalla Serpentine Belt originated as a thin,sub-horizontal unit of obducted oceaniccrust over which the Hozameen Group was thrust in an easterly direction(Figure 6). Serpentinizationpresumably accompanied this movement with the belt forming the lubricated,sub-horizontal sole below a nappe structure whose easterlytransport resulted in the F1 tectonic inversion of the underlying Ladner Group (Figure 6). This mechanism would explainthe absence of a F1 tectonicfoliation in the Iadner Group which was probably unlithified and notdeeply buried during this overturningevent. Subsequent F2 deformationcaused a refolding of the F1 synformalstructure (Figure 6) and steepenedthe Coquihalla Serpentine Belt into its presentsub-vertical position, as suggested by McTaggart and Thompson (1967) andAnderson (1976). This model implies that major tectonicdislocations occurred along both margins of the Serpentine Belt and thatthe Hozameen fault is a late, normaland relatively minor fracturelying close to one of theearly thrust planes (Figure 6). If thisinterpretation is correct, other'Alpine-type' serpentinebelts in theregion may also representobducted oceanic material marking early,refolded thrust zones.

CONCLUSIONS

The Carolin mine orebody(Idaho Zone) is hosted in a structurally invertedsequence of Iadner Group sedimentaryrocks, close to their faultedcontact with the CoquihallaSerpentine Belt.

The Idaho Zone representshydrothermal replacement mineralization that involvedthe multistage introduction of silica, carbonate, Na, Ek, As, Mo, Sb, Cu, and Au.

Mineralization was emplaced alongan early reverse fault that occupies thedisrupted limb of anoverturned fold. Incompetent carbonaceous sedimentaryrocks lying close to the ore zone may have localized the reversefaulting and geochemicallycontrolled the subsequentgold mineralization.

The widespread tectonic inversion of the Ladner Group appears to be spatially and geneticallyrelated to theCoquihalla Serpentine Belt. The Belt couldrepresent oceanic crust that was obducted and serpentinized duringeasterly directed, subhorizontal thrusting. These mvements caused the structuralinversion in the Ladner Group and subsequent foldingsteepened the belt into its presentsub-vertical position.

ACKNOWLEDGMENTS

The authorwishes to thankthe management and staff of Carolin Mines Ltd. and WuariusResources Ltd. fortheir willing cooperation and helpin

100 thisproject, particularly D.G. Cardinal, R.J.E. Niels, P.W. Richardson, and J.T. Shearer.Stimulating discussions in the field with W.E. Clarke, D.R. Cochrane, T. H6y, W.J. McMillan, J.W.H. Monger, and A. sutherland Brown are gratefully acknowledgedwhile Patrickttesjardins gave invaluablesupport as a geologicalassistant.

REFERENCES

Anderson, P. ( 1976): Oceanic Crust and Arc-trench Gap Tectonicsin SouthwesternBritish Columbia,Geology, Vol. 4, pp. 443-446. Barr, D.A. (1980): Gold inthe CanadianCordillera, C.I.M., Bull., Vol. 73, No. 818, pp. 59-76, June 1980. Cairnes, C.E. (1924): Coquihalla Area, British Columbia, -01. Surv., Canada, Mem. 139, 187 pp...... (1929): The Serpentine Belt of CoquihallaRegion, Yale District, British Columbia, Geol. Surv.,Canada, Summ. Rept., 1929, Part A. Cardinal, D.G. (1981): Unpublished Assessment Roport on Mpe Group Prop- erty (Emancipation Mine), AquariusResources Ltd. Coates, J.A. (1974): Geology of the Manning Park Area, Geol. Surv., Canada, Bull. 238, 177 pp. Cochrane, D.R., Griffiths, D., and Montgomery, J.T. (1974): Unpublis'hed AssessmentReport 4852, Aurum-Idaho-Pipestem project. Daly, R.A. (1912): Geologyof theNorth American Cordillera at the Forty-ninthParallel, Geol. Surv.,Canada, Mem. 38. Griffiths, D. (1975): LadnerCreek Project - Surface Geology Map, Scale 1: 6000, unpublished. Kayira, G.K. (1975): A Mineralographic and Petrographic Study of the Gold Deposit of the Upper Idaho Zone, Hope, B.C., unpubl. B.Sc. Thesis, University of British Columbia. McTaggart, K.C. and Thompson, R.M. (1967): Geology of Part of theNorth- ern Cascades in SouthernBritish Columbia, Cnd. Jour.Earth Sci., VOl. 4, pp. 1199-1228. Monger, J.W.H. (1970): Hope Map-Area, West Half (92H W1/2), British Columbia, Geol. Surv., Canada, Paper 69-47, 75 pp...... (1975): Correlation of mgeosynclinal Tectono-stratigraphic Belts in the North American Cordillera, Geoscience Can,sda, Vol. 2, pp. 4-10.

101 AGE OF THE COLDWATER STOCK AND NICOLA BATHOLITH, NEAR MERRITT (92H)

By W.J. McMillan British Columbia Ministry of hergy, Minesand PetroleumResources and R.L. Armstrong and J. Harakal, Department of GeologialSciences, University of British Columbia

The Coldwaterstock intrudes Late Triassic Nicola Group volcanicrocks (Figure 1). A previousattempt to datethe stock by K-Ar methodsgave discordant results of 215 to 234and 267 Ma (Preto, et a1 ., 1979). Stratigraphically, this apparentage was difficult to reconcile. Consequently, a series of samples was collected(Table 1; Figure 1) and subsequentlyanalysed by K-Ar and %-Sr methods (Table 2; Figure 1).

Figure 1. Generalizedgeological setting and location of age dating sample suite, Coldwaterstock.

102 dd ,I ,, dd

mm CL

" tttC 0000 mmmm

103 K-Ar analysis of biotite from sample RA 1 gave an apparent age of 208f7 Ma; hornblende from the same sample gave 21 2+7 Ma. Rb-Sr resultsare summarized in Table 1. Samples 1, 3, 4, and RA 1 gave an isochron of 194fl0, whereas Rb-Sr in biotite from RA 1 gaveage 219f10 Ma atinitial strontium ratio 0.7035 (Figure 2). The smallrange of rubidium and strontiumconcentrations limits theprecision of theseresults.

0.705 I

0.703

1t I I I I I 0 0.I 0.2 0.3 0.V 0.5 0.6 e7Rb/e6~r

Flgure 2. Plot of rubldlm-strontlm lsotoplc analyses, Coldwater stock.

In summary, isotopicdating indicates an age of approximately 210 Ma forthe Coldwaterstock. Ihe age accords well with those from otherintrusive bodies that cutNicola Group rocks and thestock is notanomalously old as suggested by earlier data.

NICOLR BATHOLITH

New Rb-Sr isotopicdata from theNicola Batholith are intriguing.Earlier K-Ar mrk (Preto, etal., 1979) gavea range of agesfor biotites from 37.3 to 59.8 Ma and forhornblendes from 60.2 to 70.6 Ma. Among thesamples were two biotite-hornblendepairs that gave nearlyconcordant results of 56.9 and 63.6 Ma and suggestthat the batholith is of Paleoceneage. Biotite from a satellitic stock at Fey Lake gave a latestCretaceous age of 68.9f2.5 Ma (McMillan, 1974).

Thenew datasuggest that at least some of thedeformed graniticor gneissic rocks in theNicola Batholith are Eirly Jllrassic or older (minimum 185 Ma). The younger datesprobably represent new magmatic materialthat intruded the olderpluton, although it could be remobilizedolder material.

104 REFERENCES

McMillan, W.J. (1974): Rey, 92I/SE-160, B.C. Ministry of Energy, Mines & Pet. Res., GFM, 1973, pp. 181-184. Preto, V.A.G., Osatenko, M.J., McMillan, W.J., and Armstrong, R.L. (1!379): Isotopic mtes and Strontium Isotopic Ratios for Plutonic and Volcanic Rocks in the plesnel Troughand NicolaBelt, South CentralBritish Columbia, Cnd. Jour. Farth Sei., MI. 16, pp. 1658-1672.

105 THE BLACK DOME MOUNTAIN GOLD-SILVER PROSPECT (920/73, 8W)

By B.N. Church

Thisreport is an update of an earlier reviewof exploration for gold and silver in the Black Dome llbuntainarea, 70 kilometresnorthwest of Clinton(Geological Fieldwork, 1979, Paper 1980-1. pp. 52-54).

Recentgeological studies shed light on the age relationships of the main lithologicalunits. A remnantvolcanic vent deposit considered to be youngerthan the vein mineralization forma the summit of Black Dome Mountain.This consists of basaltlava and agglomerate (No. 1, Table 1)

TAELE 1. CHEMICALANALYSES OF VOLCANIC ROCKS FRCM THE BLACK OCME MJUNTAIN AREA

1 2 3 4 5 6 Oxidesrecalculated to 100-

si02 50.96 53.92 62.77 64.43 75.46 72.72 Ti02 3.26 1.79 1.29 1.11 0.38 0.43 A1203 14.97 18.43 17.09 16.90 14.83 15.12 Fe203 4.65 4.1 I 5.46 2.37 1.08 1.65 FeO 5.88 3.15 I .05 2.72 0.51 0.33 MnO 0.14 0.11 0.11 0.08 0.01 0.02 MgO 7.41 4.86 2.33 1.78 0.14 0.18 CaO 8.60 7.65 3.96 3.90 0.16 I .38 Na2O 3.25 4.03 3.56 4.10 2.96 4.18 K20 0.88 1.95 2.37 2.61 4.52 3.99 100.00 100.00 100.00 100.00 100.00 100.00

Oxidesand elements as determined- H20+ 0.13 0.13 I .69 1.63 1.02 0.27 H20- 0.27 0.53 0.77 0.25 0.40 0.67 co2 0.07 0.07 0.26 0.480.07 0.07 S 0.01 0.01 0.01 0.01 0.01 0.01 '2'5 0.87 0.97 0.50 0.57 0.08 0.32 SrO 0.13 0.11 0.04 0.02 0.02 0.02 Ba O 0.04 0.13 0.04 BaO 0.13 0.13 0.14 0.16

R.I. 1.590 1.570 1.534 1.534 1.490 1.498

Key to Analyses

1 - Basaltlava, Black Dome Mountain(peak) (BKM-16). 2 - Basalticandesite lava, Flapjack Peak(summit) (BKM-287). 3 - Hornblendedacitic andesite, west shoulder of sack Dome Mountain. 4 - Daciticlava 'dome,'on main ridge south of Black Dane Mountain. 5 - Porcupine Creek rhyolite,south of Black Dome Mountain. 6 - Churn Creek rhyolite,above Churn Creek to theeast.

106 having an apparent K/Ar age of 20.5 Ma similar to rocks on Flapjack E'eak, 9 kilometresto the southwest, 24 Ma (Table 2).

TABLE 2. RMICMETRIC AGE OCTERMINATIONS No. Locat Ion Materlal K Ar Apparent Age percent M3

BKM-16 Black OmMountaln (smmlt) rockwhole 0.697 0.6552 x Ig-6cc/gm 24.W.8 BKM-287 FlapJack Peak (summlt)whole rock 1.49 1.91 x 10- cc/gm 20.5k0.8 (Argon determlnatlon andage calculatlon by J.E. Harakal,Unlverslty of kltlsh Columbia).

The principalunits hosting the gold-silver veins are hornblende daci.tic andesite and rhyolite which are exposed on the lower slopes and thesouth ridge of Black Dome Mountain. A series of dacitic 'domes' disconfornlably overlyingthe rhyolite on thesouth ridge are now correlatedwith the! hornblendedacitic andesite on thebasis of petrographic andchemical. similarities (Nos. 3 and 4, Table 1).

Inthe past year an intensivediamond-drill program has beencompleted by Blackdome ExplorationLtd. totalling 8 700 metres in 106 holes. The resultingreserve estimate forthe No. 1 veinsystem (MDI Kto. 0920/0!53) is 284 000 tonnesaveraging 12 ppm gold and 110 ppm silver. Also, a crosscuttunnel has been driven intersecting the 'Ridge Zone' of No. 1 vein 143 metres westerly from a portal at the 1 960-metre].eve1 on the east flank of the main ridgesouth of Black D~meMountain (Figure l).. Examinationof the crosscut shows thatthe mineralization continues below therhyolite. The rhyolitedips 15 degreeseasterly andhits been tra- versed by thetunnel through to underlying fine-grained dacite at a point about 50 metres west of theportal.

Currentplans by Blackdome ExplorationLtd. require 600 metres of drifting and raisingto confirm and furtherdelineate an estimated 103 000 tonnes of ore in the 'Ridge Zone' averaging 17.5 pp gold an(3 114.5 ppm silver according to the diamond-drillresults.

107 Figure 1. Geology In the vicinity of the Ridge zone of No. 1 veln, Black Dane Mounta 1 n prospect.

108 GEOLOGY AND LITHOGEOCHEMISTRY OF THE CAPOOSE SILVER PROSPECT (93F/3, 6)

By B.N. Church and L. Diakow

This description is based on recent investigationsof the Capoose silver prospect of Granges Exploration (AB) in the Fawnie Range110 kilometras southeast of Burns Lake. The propertyis centred on a geochemical anomaly discovered by Rio Tinto Canadian Exploration Ltd. Rio worked on the property from1969 until 1971.

GEOLOGICAL SETTING AND MINERALJXY

The area is underlain mainly by Jurassic lava8 of rhyolitet.0 dacite composition with minor amounts of interlayered argillite. Mineralized areas form conspicuous gossans throughout the Fawnie Range. Recent trenching and drilling has focused on garnetiferous rhyolite! lava and breccia on the ridge immediately north and northwestof the Granges campsite (Figure 1). Highest silver values coincide with the oc:currence,of galena and sphalerite.

LITHOGECCHEMISTRY

In the course ofa geological survey of the Fawnie Range, hand specimens were collected randomly from bedrock exposures. These were subsequently analysed, courtesy of Granges Exploration, fora selection of path- finding elements. The results on 45 samples are as follows,:

GeanetrlcMaan"Deviation Ppn ppm

Ag 0.6 0.2-5.5 CU 16 4-90 Pb 16 7-200 Zn 134 40-500 AS 9.6 2-75 S 0.162 0.3-1.3W *Owing to a range in values through several magnitudes It Is necessary to use i0!3 transforms to calculate meansand standard devlatlons.

The behaviour of element pairs is demonstrated as follows:

" " . . Pb 0.460.69 Zn 0.65 0.51 0.93 As 0.02 -0.010.14 0.07 S 0.05 0.01 0.12 0.11 -0.04

109 GEOLOGY AND LITHOGEOCHEMISTRY OF THE CAPOOSE SILVER PROSPECT (93F/3, 6)

By B.N. Church and L. Diakow

GEOLOGICAL SETTING AND MINERALJXY

LITHOGECCHEMISTRY

GeanetrlcMaan"Deviation Ppn ppm

The behaviour of element pairs is demonstrated as follows:

" " . . Pb 0.460.69 Zn 0.65 0.51 0.93 As 0.02 -0.010.14 0.07 S 0.05 0.01 0.12 0.11 -0.04

109 There is excellentpositive correlation for the Pb-Zn pair, good correlation comparing Aq with Pb and Zn, but only fair comparing Cu with Pb, Zn andAg. Little correlation is seen comparing thesemetals and sulphur or arsenic.

Element concentrations(Figure 1) were contouredaccording to the procedure outlinedin Geological Fieldwork, 1980 (Paper 1981-1, p. 27).

Figure 1. Llthogeochenlcal contours forsllver and sulphur In the vlclnlty of the Capoose prospect.

110 Sulphur at the0.25 per cent level and higher coincides with the gossans and the areaof pyritization on the north and west sideof the ridqr north of Fawnie Nose; sulphur abundance rises toward Green Lake.Si:I:rer contours crosscut sulphur contours and define a northeast-trending anomaly with concentrations in excessof 2 ppm in vicinity of the Grrnges campsite and to the north and west. The patternsfor copper, lead, cnd zinc are similar to thatof silver.

DISCUSSION

A broad silver lithogeochemical anomaly has been delineated.in the vicinity of current diamond drilling by Granges Exploration 'near Capoose Lake. This coincides with locally high values for lead, revsaled by Rio Tinto Canadian Exploration Ltd. (1970).

The predominantly felsic composition (Figure2) and subarea1 and submarine setting of the volcanic rocks give wide scope afor volcanogenic interpretation of the origin of mineralization. However, in the opinion of the senior author, detailed evidence points to the Capc'ose granitic intrusion, located just westof the map-area, as the ultimate source. As in mny porphyry-type deposits, widespread disseminated

NE sw

FREQUENT 0 INFREQUENT

Figure 2. Cmpositlonfrequency of Capoose prospect.

111 39 ANALYSES

RHYOLITE 1 DACITE 1 ANDESITE I BASALT

Refractive Index Glassof

Flgure 3. Fracture frequency plot for the areanear the Capoose prospect. pyrite near Green Lake and in the area to the south is peripheral to the granite. The mineralizing solutions were apparently channelled along southwesterly dipping beds (Figure1) and a set of strong east- northeasterly to northeasterly trending cross-fractures (Figure3). This mineralizing event is superimposed on the pyritic halo around the granite.

Dispersed, low-grade mineralization combined with the remoteness of the area has hampered exploration of the prospect.

ACKNOWLEDGMENTS

The geochemical data was supplied through cooperation with Granges Exploration (AB). Special thanks are extended to Granges program director Mr. G.W. Zbitnoff and Mr. H. Shear and MI. W. Lumley who assisted in the field.

REFERENCES

B.C. Ministry of Energy, Mines and Pet. Res., Geological Fieldwork, Paper 1980-1, p. 123; 1980, Paper 1981-1, pp. 27, 120-123; Assessment Report 2780.

112 AN INVESTIGATION OF THE PALYNOLOGY OF THE PEACE RIVER COALFIELD, NORTHEASTERN BRITISH COLUMBIA

By JaneBroatch Department of GeologicalSciences University of British Columbia

INTRODUCTION

Attentionhas been focussed on thePeace River Coalfield of northeastern British Columbia (Figure 1) as a result of an agreement to sell 115 milliontonnes of thermal and cokingcoal to Japanover the next 15 years. Miningand explorationactivities have been acceleratedbut are hamperedby the complex structure and poorlyunderstood stratigraphy cNf the foothillsregion.

The 1981 fieldseason was spent sampling Upper Jurassic-LowerCretaceous coal-bearingstrata in the southernhalf of the coalfield to determine whether fossilpollen, spores, and dinocysts can be used to generate a type-section of microfossils to aidin solving structural an43 stratigraphic problemsand assist in seam correlations.

Rapid evolution of bothflora andfauna during the Cretaceous, as well as theappearance of floweringplants (angiosperms) toward the end of the Lower Cretaceous,resulted in diverse species with restricted stratigraphicranges. Pollen and sporesproduced by land plants and cysts produced by marine dinoflagellates are extremelydurable and their relative abundance infiner grained sediments creates thepotential for a fairly complete microfossilrecord. Marine-influenced coal :neasures are particularlysuited to studies in palynologybecause of theirhigh plant content, their relatively high proportion of muds and clays, and because marineand continentally derived microfossils overlap as a rtzsult of wind transport of pollen and spores.This overlap allows direct correlation between non-marine facies and laterallyequivalent marinefat-ies.

PREVIOUS WORK

Studies of Upper Jurassic and Lower Cretaceous macroflora and microflora ofthe PeaceRiver district havebeen carried out by Zeigler and Pocock ( 1960) in the Minnes Group, by Singh ( 1971 ), andby McGregor forthe GethingFormation as reported byRaghes (1964) and Stott (1968). Studies of theadjacent Plains region havebeen published by Pocock (19621, Singh (19641, and Norris (1967). Much of thisprevious work has bsen concerned with establishing age and regionalcorrelation of strata, not stratigraphy.

113 AREA OF STUDY

Flgvre 1. Peace River coal district.

114 STRATIGRAPHY

The general stratigraphy of the Peace River Coalfield is outlinedon Figure 2. In the southeast, coal occurs in economic amounts in the non- marine Gates Member, in the central part in the Gething Form.stion, and in the northwest in Hughes' Brenot Formation. Non-marine strat,% have been identified on a gross scale and there are a number ofmarine incursions which my in part be responsible for the disappearance of co,sl in some areas (R.D. Gilchrist, pers. corn.). Detailed descriptions ,of the lithologies and structure may be found in Hughes(1964, 1967) and Stott (1968, 1973). They will only be discussed here in relation to specific stratigraphic problems.

Two sets of terminology (Figure2) are currently in use in exploration as a result of a number of unresolved problems which include:

A lack of identifiable stratigraphic horizons both locally and regionally. The one exception is the Bluesky Formation. It occurs as a thin (less than0.5 metre) glauconitic sandstone h,>rizon at the top of the Gething Formation in the eastern part of the coalfield. The Cadomin conglomerate is used as a stratigraphic horizon but varied thickness, rapid fining to the northwest, chse and resemblence to the Gething conglomerates, bothon surfaze and in drill holes, make it extremely difficult to identify in many cases. Only its log character appears consistent (R.D. Gilchrist, pers. corn.).

Certain members and formations are difficult to distinguish, for example, the Hulcross Member andmosebar Formation, the Gates Member and Gething Formation, the Gething and Cadomin conglomerates.

Lateral variations in certain units over the length of the coalfield, specifically the Cadomin/Dresser Formations ,and the formations that comprise the Minnes Group.

The difficulty of recognizing marine incursions in non-marine sequences because marine macrofossils are scarce.

Determination of the paleoshorelines. Studies in progress reveal that many are not oriented along the strike of the coa1,Eield as was previously believed.

Determination of the nature and significance of the 'unconformity' at the base of the Cadomin Formation (see Stott,1968).

Until recently workers in the Peace River Coalfield, with the exception of Stott and Hughes, have concentratedon locating economic (coal deposits. Attention is now being focussed on stratigraphic problems. New information should eliminate the need for a dual termino:togy and facilitate future exploration, mine planning, and reserve estimates.

115 116 FIELD AND LABORATORYWORK

A sampling program was carried out in the coal-bearing Upper Minnes through Gates section between the Narraway River in the southeast and Burnt River in the northwest. Very fine clastic rocks in seven surface sections and thirteen drill holes were sampled (Figure3).

Complete, undisturbed surface sections were difficult to find.. Extens:tve thrust faulting and poor outcrop exposure resulted in gaps in. surface coverage. Where relatively complete sections are available, steep dips and the recessive nature of themdstones and shales frequently made it difficult to obtain fresh samples at the desired 30-metre int,ervals.

Drill holes were selected to compliment the surface sections and were 'pieced together' to obtain a complete sequence of strata. Core samples were obtained from core storage facilities of the British Columbia Ministry of hergy, Mines and Petroleum Resources at Charlie Lake, British Columbia. It is expected that the core samples, which were taken at 15-metre intervals, will provide more complete and reliable results than surface samples. A total of 238 core samples and89 surface samp:tes was taken.

Processing of the samples is currently underway in a laboratory at the University of British Columbia. The rockmst be completely dissolved in acid to release the palynomorphs which are then treated as necessaryto concentrate and bleach them for mounting and identification. The general procedures employed are described in the Appendix. To date one complete section of core from the Mount Belcourt area has been processed and mounted.

PRELIMINARY RESULTS

Of the 60 samples processed todate, approximately 85 per cent contain palynormorphs. menty samples were examined by Dr. Glenn muse: half of the Minnes and Gething samples contain diagnostic spores and/or dinocysts; fewer Moosebarand Gates samples appear to contain diagnostic palynomorphs but exact statistics are not yet available. However, Gates samples apparently contain angiosperm pollen. There has not been time yet to attempt to identify them.

The Minnes samples contain: the diagnostic fern spores Cicatricosisporites dorogensis andC. mohrioides; the conifer pollen Podocarpidites multesimus; and one sample contains the dinocysts Gonyaulacysta cf. exilicristata, G. cf. cretacea and Cyclonephelium distinctum. Correlation with assemblages found in the Quartz Sand-Upper Develle Members of the Mannville Group (Pocock, 1962; Zeigler and Pocock, 1960) suggests a Valanginian to Early Barremian age for the upper 340 metres of the Minnes Group.

The Gethiny samples contain the diagnostic fern spores Appendicisporites tricornitatus, A. cf. problematicus, Cicatricosisporites australis, and

1'17 54

8 20 40 "- 1 Mil- l."'. t Km 0 2F 70

Figure 3. Surfacesectlons and drlll hole locations,Narraway Rlver-Burnt Rlver.

118 Trilobosporites apicerructus. Although the assemblage appears to be dominantly terrestrial the presence of dinocysts in one sample suggest!; occasional marine incursions. This assemblage correlates with the Calcareous Member of the Lower Mannville Group (Pocock,1962) and in the Gething and Calcareous Member (zeigler and Pocock,1960) sugqesting a Late Barremian age.

The presence of dinocysts in several of the Gates samples and one of the Gething samples supports the proposalby Gilchrist that marine incursions have occurred in the non-marine sequences. Macrofossils found in core by P. McL. D. Duff should provide a useful check of the relative ages of the palynomorph assemblages described above.

These preliminary results suggest that the unconformity at tb.e base of the Cadomin Formation does not represent a significant time qap in deposition. Mudstone samples from a coal-bearing lens in the Cadominto the north may provide a better indication of the temporal relationship of this unit to those above and below.

Only one section has been processed to date and it is not yet possible to recognize palynological or stratigraphic horizons. However, the presence of marine beds in non-marine sequences, and the abrupt appearance of species or assemblages holds much promise for the existencectf such horizons.

SUMMARY

Until recently work in the northeast coal block has been concerned primarily with locating economic coal deposits. Complex structure and a poor understanding of the stratigraphy have hampered the search and attention is now being turned to solving these problems. Initial resu1.t~ of a study of the palynology indicatea potential for determining age relationships, locating stratigraphic horizons and laterally correlating strata. Distinct assemblages in the Upper Minnes Group and Gething For- nation, and marine unitsin non-marine sequences have been identified. It is hoped that as processingof samples continues a microfossil typesection will be generated which will serve as a useful intool its own right and add support to other stratigraphic studies currently in progress.

ACKNOWLEDGMENTS

I would like to thank Dr. G.E. Rouse for his assistance in identifying the assemblages noted in the preliminary results and for his ongoing support, R.D. Gilchrist for providing stratigraphic information basedon studies carried out in conjunction with P. McL.D. Duff, and the companies that generously offered informationon surface section locations and their time to discuss and examine geology the and stratigraphy of their respective properties, most notably PetroCanada, Denison Mines, BP Exploration, and Gulf Canada Ltd. I am especially

1.19 grateful to the British Columbia Ministry of Energy, Mines and Petroleum Resources for their support of this project.

REFERENCES

Hughes, J.E. (1964): Jurassic and Cretaceous Strata of the Bullhead Succession in the Peace and Pine River Foothills, B.C. Ministry of Energy, Mines & Pet. Res., Bull. 51, 73 pp...... (1967): Geology of the Pine Valley, B.C. Ministry of Wergy, Mines & Pet. Res., Bull. 52, 137 pp. Norris, G. (1967): spores and Pollen from the Lower Colorado Group (Albian?-Cenomanian) of Central Alberta, Palaeontographica, Series B, Vole 120, pp. 71-115. Pocock, S.A.J. (1962): Microflora Analysis and Age Determination of Strata of the Jurassic-Cretaceous Boundary in the Western Canada Plains, Palaeontographics, Series B, Vol. 111, pp. 1-95. Sinqh, C. (1964): Microflora of the Lower Cretaceous Mannville Group, East-Central Alberta, Research Council of Alta., Bull. 15, 238 pp...... ( 1971 ) : Lower Cretaceous Microfloras of the Peace River Area, Northwestern Alberta, Research Council of Alta., 51111. 28, VOl. 1, 299 pp. Stott, D.F. (1968): Lower Cretaceous Bullhead and Fort st. John Groups, Between Smoky and Peace Rivers, Rocky Mountain Foothills, Alberta and British Columbia, -01. Surv., Canada, Bull. 152, 279 pp...... (1973): Lower Cretaceous Bullhead Group Between Bullmoose Mountain and Tetsa River, Rocky Mountain Foothills,Northeastern British Columbia, Geol. Surv., Canada, Bull. 219, 228 pp. Zeigler, W.H. and Pocock, S.A.J. (1960): The Minnes Formation, Field Meeting Guide, Edmonton Geol. Soc., June 1960, pp. 43-71.

120 APPENDIX

Extractlng Palynmrphs Wash approxlmately 50 grams of sample, crush to pea slze, and placeIn plastlc beaker; rlnse twlce to remove clay anddanaged palynonorphs. Test fa carbonatesuslng a IO-per-cent solution of HCI; whenno more flzzlng Is evldent rlnse sanple three times wlth water. Place beaker wlth sample In a water bathIn a fumehoodand add fullstrength HF acld Inmall lncrments (to prevent 'bolllng over') untll the volume ofacid Is approxlmately IO tlmesthat of sample; place on magnetlc stlrrer, add spln bar, and leave 24 to 48 hours (Insldethe funehood).

Remove fran stlrrer and allowto settle untll acld Is almostclear; pour spentacld Into waste bottle;rlnse sanple three tlmes In water allowlng to settle between eac:h wash sa thatvery flne clay remalnlng In suspenslon may be siphonedof!. Rinsethrough 210 steve to remove coarsefragments retalnlngthe Ilquld fractlon; pour through 20 yn sleve retalnlng sediment trappedIn sieve; rlnseInto centrlfuget tube.

Examlne by placlnga drop of sample on a glass slide to determlnedegree of carbonlzatlonof palynonorphs (If present) and mountof mlneral matter stlll present.

Bleachblack and dark brown palynonorphs to reduce thelr speclflc gravlty (before carrylng out heavy llquld separatlon) or to llghten to pale to golden yella, for easlerldentlflcatlon; rlnse three tlmes to remove bleach. Concentratlonof bleach and lengthof bleachlng vary for each sanple - startwlth low concentrations (5-10 percent) for short perlods of time (2-5 mlnutes) and Increase as necessary.

Remove unwanted mlneral matter by neutrallzlngIn IO percent %I acld and centrlfqlng In ZnBr2 wlth a speclflcgravlty of 3.4; plpetteorganlcr; ('float' materlal)Into a cleantest tube, neutralize agaln wlth 10 percent HCI and rlnse three times wlth water.

Bleachlng may break down unwanted organlcspermlttlng thelr removal by a second 20 slevlng.

Staln semple wlthSafrlnln (red); make flne. medlun and coarse mount placlnga dropof elvanol on acoverslip wlth 1 or 2 drops of sanple; stlr to dlstrltute evenly and dryslowly on hotplate cf Indesslcator; place a blob of gelva on R glasssllda and Invertthe coverslip wlth sanple onto It; press to spreadgelva; label.

1121 TOODOGGONE RIVER (94E)

BY T.G. Schroeter

INTRODUCTION

The Toodoggone River area is situated approximately 300 kilometres north of Smithers. Access is by aircraft because there areno roads into the area. During the 1981 season, a great variety of aircraft were used for supply and freight services to and from the Sturdee strip; these included a Cessna 180, Cessna 206, Beech-18, Otter, Beaver, Goose, Islander,Dc-3, and Hercules. All were routed through Smithers. The strip has a useable length of 620 metres and is equpped with landing lights.Du Pont of Canada Exploration Ltd. maintain the strip and have a traffic controller on duty during daylight hours. The area discussed in this report forms a northwesterly trending belt 80 kilometres in length,35 kilometres in width, and approximately centred on the Baker mine (Figure1). The area of economic interest may continue several more kilometres to the west- northwest.

During July and August1981, the writer commenced geologic field mapping with the aid of an especially contracted topographic base map at scale 125 000. The area covered by this base map is shownon Figure 1. Property investigations, ongoing since 1974, were continued. Much of the writer's effort was concentrated in the area bounded by the Finlay River on the southeast and Abesti Creek on the northwest. In addition, Andrejs Panteleyev with the British Columbia Ministry of Energy, Mines and Petroleum Resources and rarry Diakow, a graduate student at the University of Western Ontario, joined the project in August and expanded the area of mapping south of the Finlay River (see Panteleyev, this report) and Mount Graves. A preliminary geological map of the Toodoggone area should be availableby the spring of 1983.

During 1979-80, approximately 2000 mineral claim units were staked in the area. In 1981, approximately 1 300 more units were staked. In addition, after part of the area was opened to placer staking in November 1980, a placer staking rush occurred during the winter of 1980-81 (see Figure 1). The reader is referred to Geological Fieldwork, 1980 (Paper 1981-1) for a descriptionof the history of the camp.

GEOLOGY

Typical epithermal mineralization in the camp is related to a periodof Early Jurassic intermediate to acidic volcanism. Mineralization occurs both within Late Triassic alkaline andesitic rocks (Takla Group) and Early Jurassic calc-alkaline volcanic rocks (Hazelton Group). The host

122 volcanicrocks were deposited in an islandarc environment during the transitionperiod from submarine to subaerialvolcanism.

The regional geology is covered in Paper 1981-1 and onlyminor additions are offeredhere. The Toodoggone volcanicsequence consists of a pile of complexly intercalated and varicolouredsubaerial andesitic, dacitic, and trachytictuffs, ashflow sheets, and minor epiclasticrocks that is 1 000 metresor more in thickness. They aretentatively correlated with veryEarly Jurassic rocks of theHazelton Group. K-Ar and Sh-Sr dates obtainedfran whole rock and mineralsamples, including alunite from Alberts Hump (which is believed to be contemporaneous with the major pulse of epithermalmineralization), range between 179 and 1510f7 Ma. Thisrelatively old age compared tosimilar deposits in Nevada, Colorado, and Mexico may be a particularlyimportant factor in thefuture discovery of similarepithermal deposits in British Columbia (for example, Premier).

It is worth re-statingthat the Toodoggone volcanicrocks and intrusions areprobably coeval with associated Ckni-neca Intrusions. It is also significantthat porphyry deposits associated with the Omineca Intrusions haveanomalous gold and silvercontents (Paper 1981-1, p. 128). Quartz feldsparporphyry dykes may in fact be feeders to the Toodogqone volcanic sequence.

Regionally,the lower volcanicdivision consists dominantly of pyroclastic maroon agglomerate and grey to green to maroon andesitic and dacitictuffs. It is overlain by themiddle volcanic division consisting mainly of rhyolites,dacites, and an intermediateto acidic assemblage of orangecrystal to lithic tuffs, minorwelded tuffs, and quartzfeldspar porphyries. A young,upper volcanic-sedimentarydivision is locally present. In areas,major structural breaks and mineralizingevents (for example,Lawyers) coincide with thecontact betweenthe lower and midd:le volcanicdivisions.

STRUCTURE

The structuralsetting was probablythe most significantfact.or in allowingmineralizing solutions and vapours tomigrate through the thick volcanicpile in the Toodoggone area. Major fault systems withattendant splaysextend tens of kilometres(for example,McClair, Lawyers - Cliff Creek). Some arepostulated to be relatedto volcanic centres, particularlycollapsed ones (for example, Kodah, Alberts Hump).

MINERALIZATION

Styles of mineralizationare discussed in Paper 1981-1, pages, 128 and 129. The precious and basemetal epithermal type are the ml.n explorationtargets. Preliminary chemical data (Tables 2 and 3) suggest thefollowing:

123 Figure I. Toodoggone map-area.

124 'I 25 TABLE 2. SELECTED CHMICAL

"2'3 Lab. No. Fleld No. FleldLocatlo" DBSCrlptlon S102 A I 203 Tota I

24233 La 80-6-21 I Upper crystal tuff Lawyers 60.21 15.27 5.29 24234 La80-13-21.8 m Orange crystal tuff Layers 57.58 14.89 5.29 withoutquartz ayes 24235 La 80-13-94 rn Chocolate brmn dust tuff Lawyers 68.02 13.13 3.17 24236 La80-14-116.5 m Green fwtwall crystal Lawyers 56.06 15.06 6.01 t"f f 24237 La80-4-81.7 m 62.93 14.78 3.34 24238 La80-4-104.5 m 64.86 12.91 5.48

24239 La 80-1 1-1 I 111 L?.VWS 72.85 12.00 2.65 24240 K 74-3-48.5 m Lawyers 58.94 12.65 6.05 24241 La 80-6-105.4 m LII*"BTS 80.97 6.21 2.29 24242 La80-5-113.4 m Lawyers 46.03 16.68 9.62 24243 X 2-80-4 Northeast of CIlff Creek 59.76 15.39 5.53 24244 JC 6-80-24 NOrthwst of Mamot Lake 60.40 14.88 5.70

24245 Met 80-9 Metsantan 56.38 15.65 6.02

24246 AH 80-2 Rlberts Hump 55.58 17.43 0.46 24247 PI 11-80-1 PIIlar West (Nub Creek) 62.15 15.96 3.99 24248 T 80-6 Above tm ponds, crest 58.20 15.42 5.62 between Lawyers and Baker 24249 La 80-7 Northeast dO*nSlOpe of 49.76 17-43 10.36 Layers Knob 24250 JC 4-80-4 Duke's Oemlse - southeast 61.03 16.92 5.53 end 24251 JC 7-80-13 600 metres rest of Marmt 59.42 14.61 5.69 Lake 24252 X 7-80-15 Green to purple crystel 1 2% metresnorthwest of 61.79 15.14 5.58 t"f f Mamot Lake 24253 X 9-80-6 Flw-banded andesite Kodah Lake 57.77 17.72 5.97

Rock Nae* Cu Pb zn k4 A" Ppn Ppn Ppn Ppn Ppn Ppn Ppn Trachyte 5 14 0.02982 0.4 Trachyte I1 15 71 0.8 co.02 Trachyte 48.0 27167 41 0.027 Trachyandeslte 8 18 113 4.2 0.022 Trachyte 11.0 35118 44 0.042 Norma I daclts 41 40 214 29.0 0.092 Norm1Ite rhyol 13 19 61 5.3 0.056 Nom1 andeslte 37 30 82 4.4 0.031 """ 69 93 233 34.0 3.36 Sub-alkaline mflc phonolite 90 12 133 1.0 <0.02 Norm1andeslte 17 <0.43 78 (0.02 Nom01 andesite 16 10<0.4 77 <0.02 Trachyte 19215 10 <0.4 <0.02 Sub-alkallne trachyte 4 26 100 <0.4 (0.02 Trachyte 420 7 <0.4 138 (0.02 Noma1 andeslte 7 17<0.4 77 <0.02 Basalt-andesite 33106 11 <0.4 <0.02 Trachyte 8 9 85 (0.4 <0.02 Normal andesite 15 IO 68 <0.4 0.068 Trachyte 16 10 85 0.6 (0.02 Normal andesite111 19 4 <0.4 <0.02

126 ANALYSES, TCOOOGGONEAREA

MnO S H20-H20+ P205 GO2 2.18 3.07 3.375 5.602 0.562 0.13 0.22 2.42 tO.008 0.79 1.83 1.04 99.36 1.67 3.24 1.593 8.782 0.550 0.085 CO.08 5.10 0.02 0.55 0.85 0.30 99.10 1.50 0.37 0.191 9.026 0.483 0.075 0.11 2.62 0.04 0.14 1.28 1.14 99.88 2.84 1.94 0.878 9.588 0.520 0.142 tO.08 4.88 0.37 t0.1 1.54 1.44 99.73 1.50 0.76 0.848 9.498 0.532 0.073 0.18 3.59 0.042 0.18 1.7 1.52 99.59 2.00 0.68 0.931 6.616 0.435 0.104 0.15 3.30 0.008 0.44 1.26 0.82 98.29 0.23 1.17 0.987 6.683 0.326 0.092 0.15 0.81 a.008 0.80 1.04 0.24 98.19 3.17 4.30 0.128 4.293 0.459 0.143 0.13 6.34 0.012 1.33 1.0s -0.30 96.91 1.64 0.51 0.060 2.934 0.156 0.072tO.08 2.86 0.04 0.15 0.19 0.0497.74 5.91 2.30 4.533 2.041 1.151 0.257 0.13 7.37 0.014 1.84 3.31 1.47 97.49 2.80 4.30 2.971 3.514 0.617 0.158 0.23 1.39 0.008 1.38 3.00 1.62 98.28 2.66 2.68 3.476 3.523 0.566 0.133 0.23 0.95 0.008 1.88 5.04 3.16 98.36 1.56 2.001.56 0.210 10.64 0.610 0.274 0.18 4.81 0.016 0.34 0.66 0.32 98.68 <0.08 t0.22 0.335 3.832 0.139 t0.002 0.09 0.18 6.19 0.17 7.13 6.96 91.50 1.32 2.181.32 3.823 6.266 0.437 0.132 0.18 I .43 CO.008 0.29 0.97 0.68 98.58 1.92 5.34 3.4575.343.0961.920.579 0.141 0.22 2.57 0.0140.962.38 1.4297.98

3.93 7.87 3.025 3.688 1.040 0.182 0.30 to. 10 0.012 0.73 1.5s 0.86 98..43 1.99 2.85 4.841 3.318 0.518 0.152 0.13 0.99 0.008 0.53 1.82. 1.30 99..56 1.33 4.44 4.155 3.367 0.572 0.146 0.23 3.28 t0.008 1.21 1.29 0.08 97-32 2.82 1.56 2.242 6.608 0.561 0.142 0.19 0.70 0.04 0.50 1.94 0.44 97..82

2.19 5.24 3.536 4.039 0.562 0.158 0.15 to. 10 0.008 0.33 1.55 0.22 97..54

Hg sro Ea0 AS S" Se w Th U PPb per cent per cent Ppn Ppn Ppn Ppn Ppn Ppn 40 0.02 0.15 I8 2.0 8 6 5 8 3 45 0.02 0.18 28 1.8 3 6 5 9 5 47 0.02 0.18 26 (1.0 3 3 14 <7 6

t10 0.02 0.19~. ~ 24 1.8 5 d 6 tl 7 67 0.02 0.13 30 tl.O 5 4 6 t7 6 37 0.02 0.13 20 1;8 3 8 9 C3 45 0.02 0.19

25 0.05 0.19~. ~ 18 3.7 3 <2 I1.. 3 47 0.02 0.19 20 2.2 5 <2 8 4

127 TABLE 3. GEOCHEMICALRANGE OF SELECTEDHIGH-GRADE SPECIMENS FRCM TOODOGGONE PITHERMAL PROSPECTS (All values in ppm unless othenrise indicated.)

As 40 to 30 Ga <3 to io Se <5 'to 272 8 <2 Ge 6 S"

*Excluding one high-grade sample at Baker mine with 0.235 Mo.

There arethree main classes of rocks:varicoloured, andesitic, and daciticpyroclastic tuffs overlain by trachyticpyroclastic tuffs.

The ratio ~~o/t?a~Oincreases toward mineralization.

Sulphurvalues are very low - average <0.04 per cent S.

Traceelements are not enhanced near mineralization (Table 2). However, there is some hope for mercury as a pathfinder element.

The overall Ag:Au ratio is approximately 20:l.

There arethree stages of of veining. A pre-orestage consists of thin bands of amethyst and adularia with very minor mounts of calcite. This was followed by theore-bearing stage consisting of open space fillings, and post-oredeposition of coarselycrystalline calcite and minoramounts of zeolites.

ALTERATION

Typicallateral and verticalalteration patterns for epithermal deposits exist. There is an outerpropylite zone, consisting of chlorite, epidote,calcite, and pyritethat grades inward to an argillic-phyllic zone consisting of sericite, montmorillonite,illite, and silica and finallythere is a silicifiedcore zone that is adjacent to the vein system and consists of silica,adularia, and/or albite. Hematite is ubiquitousbut appears to bo especiallyabundant in mineralizedzones, as does manganese oxide.Locally there are zones of intense kaolinite+silicafalunitefsulphate alteration(for example, Alberts Hump area).Similar zonesoccur at theupper, low pH regions of other epithermalsystems. Native gold, hematite, and minor pyrite havebeen observed in thesesilica-rich rocks. When theyare mappedon a regional scale,they occupya crude concentric fracture system and areindicative ofa major collapsestructure.

I28 Bleachingappears to be more common in thehangingwall; chlorite is more common in thefootwall. Epidote, pyrite, and laumontiteare abundant in regionallyaltered zones.

GEOCHEMICAL SIGNATURES

Regional and detail& follow-up silt, soil, and rockgeochemical surv~9Y have been key tools i.n exploringfor and delineating mineral. deposits. They ranksecond only to good prospecting.Analyses for gold and Si1 I:.'- alone haveproven successfulbut lead, zinc, and copper are alsousff';, . values of anomalous clold in silts range from 20 ppb to 1 500 I?pb, a94 silver from 3 pyn to 400 ppm. Silification is accompanied by anomalous values in rockgeochemistry.

As mentioned earlier,these mineralized systems appear to be' relativ.-!: free of contamini!ntssuch asarsenic and antimony. On a det.ailed t";~::, the writer helievesthat mercurymight be a usefulpathfinder, espe"? 3iiy if theanalyses ere properly done in the field.

PROPERTIES

BAKER MINE (previous1,yChappelle) (MDI No. 0943/026)

The Baker gold-silver mi ne, formerlyChappelle, is currently operd: ; na3 at a rate of 100 tons per day. Publishedmineable reserves arc 100.3FO shorttons containing 0.92 troy ounce of gold and 18.7 troyounces of silverper ton. Puring the fall of 1980. surfacecut mininq down to about 6 metres was carriedout. Since thenunderground minihg hiis be'en in progress from the 5500 level anddevelopment work has proceeded on the 5400 level.

Seven quartz.vein systems, mostly occupying fault zones,have been identified in the area of the mine. The mainvein (Vein A) actually consists of tw or more subparallelveins that havebeen tr;iceJ more than 435 metres, have a width of 10 to 70 metres, and have a verl-ical depfh of atleast 150 metres. Individualveins within the system Val:) from 0.5 metre to greaterthan 9 m+?tresin width. A variety of quarj-' :rein textures and crosscutting relationships indicate a complex !,I::tory of mineralizationwith multip2.e stages of deposition.Fine-gra;ned acanthite, pyrite, el.ectrur;., chalcopyrite, bornite, native ']"id, sphalerite,galena, chi1?c? te,covellite, polybasite, and .itromeyerite occur in thishighly Tracti!.-rd and brecciatedquartz system i I Takla Group andesite and dacite(see Barr, 1980 fordetailed descr:,ption). Highergrade mineralization is most obviouslyassociated wii::i grey quartz, some of which contai.nsvisible acanthite. Alteration minerals includepervasivn laumcntite, chlorite, pyrite, anhydrite, and silica. It is interesting to note tha'. one sample of high-gradeore assayed 0.23 per cent molybdenum. During '981, dorebullion with a 95-pt:r-cent precious metal content thatcmtained approximately 950 oun(:es per ton silver and 50 ouncesper ton "'Id, with minor copper,lead, .and zinc, was

5 129 shippeddirectly from theminesite by air to Vancouver. Results from an additionalsurface diamond-drilling program totallingover 1 500 metres on surroundingquartz vein systems were discouraging.

LAWYERS

The Lawyers gold-silver deposit is located approximately 15 kilometres north ofBaker mine and is now connected by a four-wheel-drive access road. lb date some 40 surfacediamond-drill holes on a three-tiersystem havebeen completed and the Amethystgold breccia zone has been traced over a north-southlength of 610 metres, a width of 60 to 75 metres, and a vertical depth of 75 metres. Recently Serem Ltd. completed an undergroundprogram consisting of approximately 730 metres of adit,five crosscuts, andminor drifting from the 1750 levelapproximately 110 metres below thehighest surface expression.

Thispreliminary underground work hasoutlined mineralization along a length of 200 metres with a maximum widthin any single silicified system of 20 metres. Underground drilling is plannedfor next season.

Fine-grainedacanthite, electrum, and nativesilver, with minor pyrite, chalcopyrite,galena, and sphalerite,occur in a gangueof amethystine to whitequartz and adulariawith minoramounts of calcite. Secondary minerals includemalachite, chalcocite, and cerussite. The structurally controlled,steeply dipping, brecciated, silicified, and mineralized zones are located in a sequenceconsisting of greenquartz-eye footwall andesitictuff overlain by aphaniticchocolate brown tuff, welded tuff, andorange trachyte. The orangetrachyte generally occurs at stratigraphically and topographicallyhigh elevations within the Toodoggone area. Younger alteredmafic phonolite dykes cut the entire sequence.Specular hematite andmanganese oxide are common alteration products.Typical open-spaced epithermal textures occur within the fissure zone.Grades of mineralization are erratic but some assays exceed 20 ounces per tongold and 700 ounces per tonsilver.

The geologicenvironment at Lawyers inparticular has many similarities toepithermal deposits in Nevada, Colorado, andMexico.

The Cliff Creek breccia zone is locatedapproximately 2 kilometres west of the Amethyst goldbreccia zone. It has been tracedfor several kilometres on surface. Assay results are goodand this zone represents aninteresting target for drilling. To dateonly a few holeshave been drilled. The geologicsetting is identical to that at Lawyers.

JD (McClair) (MDI No. 0943/032)

The Schmitt and CarbonateBreccia showings on theTexasgulf (Kidd Creek Mines Ltd.) JD claim arelocated on a ridgeimmediately south of McClair Creek and north of Kodah Lake. Fissure zonesof rebrecciated, mineralizedrock occur within a sequence of massive,varicoloured green,

130 grey, brown, and maroon feldspar and hornblendeporphyritic andesite, trachyte, and latitetuffs of themiddle volcanic division cd the Toodoggone volcanic series. Locally,tuffaceous agglomerate and volcanic brecciaexist. Attendant alteration zones include kaolinite, gypsum,and pyritewith conspicuous manganese oxide and jasperyhematite. Rounded to subangularfragments of quartz,chert, jasper, and sulphides(including galena,sphalerite, chalcopyrite, and pyrite) occur in a fine-grained matrix of brecciated and silicifiedtuff. Assays are erraticwith some ashigh as 9.5 ounces per tongold and severalhundred ounces per ton silver. Gangue mineralsinclude amethystine to whitequartz, calcite, and minoramounts of barite. To date,only limited surface blasting has been carriedout; a muchmore aggressive program including diamond drilling is plannedfor next year.

ALBERTSHUMP, GOLDDI FURLONG, RIDGE

The Alberts Hump areaincludes an area bounded by Alberts Hump - Tuff Peak and the Metsantanpospect. It may be underlain by a collapsed structure(for example,volcanic core) which is now expressed on the surface by a roughlyconcentric broken ring ofmassive silica?kaolinitefsulphate-bearing rocks. These may be examplesof ancienthot springs indicative of theuppermost part or'cap' of an epithermalor high-level hydrothermal system. Hematitic fracturing witherratically distributed native gold exists. me hostrocks includetypical hornblende-feldspar andesitic tuffs of themiddle volcanicdivision of the Tbodoggone volcanic series. Significantzones containingalunite (especially Alberts Hump) occurwithin this area. A K-Ar agedate on alunite from Alberts Hump yielded 190+7 Ma. This dat.e foralteration is compatiblewith other age datesobtained for Toodoggone volcanicrocks in the area. Consequently, these deposits are Early Jurassic, significantlyolder than most otherepithermal deposits. Erratic gold and silvervalues havebeen obtained from altered zonesbut muchmore detailed work is required to fully understandthis area.

METSANTAN

The Metsantanprospect is located on thesoutheast flank of ,a mountain immediately east of the abandoned Indianvillage of Metsantan. During. 1980-81 LacanaMining Corporationidentified six zones of mineralization. They havean overallnorthwesterly trend, having been. tracedover 1 100 metres in length and 300 metres in width and may have a verticalrange of 200 metres. Zones of highergrade miner,alization range from 4 to 7 metres in width. Presentindications are that higher gold values at surfacegive way to highersilver values at d'epth. Rase metal mineralization, which includeschalcopyrite, galena, and sphalerite, is associatedwith orange trachytic tuff and appars to be more abundant at Metsantanthan elsewhere in the Toodoggone. Goldand silvervalues are associatedwith pyrite, specular hematite, and sericite. The largest zone,the Metsantan gold breccia zone, has been

'I 31 traced andsampled by hand-dugand blastedtrenches along a length of 600 metres and across a width of 120 metres. Diamond drilling is planned for nextyear. Gangue mineralsinclude amethystine to white quartz,kaolinite, and barite.

MOOSEHOREl

The Moosehorn prospect of Great Western PetroleumCorp. is in Moosehorn gulley,approximately 2 kilometresupstream from thejunction with the Toodoggone River.Amethystine to whitequartz and pyriteoccur in two silicified zones thatare 450 metres in length and 1 to 5 metres in width. The veinsare in typical Toodoggone hornblende-feldsparandesitic tuffs.

OTHER PROSPECTS

Otherepithermal prospects in the belt with surface showings include:

Mount Graves - a quartz-amethyststockwork in Toodoggone and Hazeltonvolcanic rocks.

Silver Pond - a largealtered zonewhich may represent a leachedcap zone.

Mess - a massivebarite-galena vein.

Kem (Attycelly) - a galena,sphalerite, and barite‘vein.’

Shas - gold-silvermineralization in a stockwork.

Saunders - a gold anomalyand chalcopyrite,pyrite, sphalerite, and molybdenite in quartzveins in Tbodoggone volcani-rocks.

Pillar West - gold-silvermineralization in a silicified zone in Toodoggone volcanicrocks.

PLACER GOLD

Tamarik Ltd. conductedpreliminary studies tnat i:lclurled shallcwblasting andoverburden drilling onmany ulacerlease4 covicing the W(1:3ir and .~ Toodoggone Rivers. ‘a1:i found is very fi?e. ii. I-. is sche3ule.i to continuenext year.

ACKNOWLEDGMENTS

The writer acknowledgesthe kind and generoushospitality and logistical supportoffered in the field by thef:>llowinq compa-..ies: Serem =tcl., Texasgulf(Kidd Creek Mines Ltd.), Du Pont of Cana.?a Exploratior Srest

I32 WesternPetroleum Corp., LacanaMining Corp., TransProvincial Rirlines, and Bema IndustriesLtd.

REFERENCES

Barr, D.A. (1978):Chappelle Gold-Silver Deposit, British Columbia, C.I.M., Bull., Val. 72, No. 790, pp. 66-79. .. , ...... (1980): Gold in the Canadian Cordillera, C.I.M., , Bull., Val. 73, No. 818, pp. 59-76. Cann, R.M. andGodwin, C.I. (1980): Geology and Age of the Kemess Porphyry Copper-Molybdenum Deposit,North-Central British Columbia, C.I.M., Bull., Val. 73, No. 832, pp. 94-99. Carter, N.C. (1971 ): Toodoggone River Area, B.C. Ministry of Energy, Mines L Pet. Res., GEM, 1971, pp. 63-70. Gabrielse, H., Dodds, C.J., Mansy, J.L., and Eisbacher, G.M. (1977): Geology of Toodoggone River(94E) and Ware West Half 1:94F), GeoL. Surv.,Canada, Open File 483. Schroeter, T.G. (1976): B.C. Ministry of hergy, Mines L I?&. Res., GeologicalFieldwork, 1975,Paper 1976-1, pp. 68-70; '1976, Paper 1977-6, pp. 66, 67; 1978,Paper 1979-1, p. 103;1980, Paper 1981-1, pp. 124-1 31. TOODOGGONE MLCANICS SOUTH OF FINLAY RIVER

By A. Panteleyev

Systematicgeologic mapping was started in August in the Tc,odoggone map- area, 94E. inorder to describe lithologies, stratigraphy, structure,, and mineralization of the 'Toodoggone volcanics' (Carter, 1971). A major objective of this program was to determinethe extent of thevolcanic beltsouth of FinlayRiver. Work inthe area was done in c!onjunction with T.G. Schroeter, District Geologist,Smithers (see accntpanying report, this volume) and L.J. Diakow, currently a graduatestudent ai: the University of WesternOntario. In 1982 thiscooperative mapping will be concentratedin the area north of FinlayRiver and extend t:oward the northern boundary of the Toodoggone volcanicsnear the Chukachida River.

GEOLOGY

TheToodoggone volcanics form a distinctregional map unitconsisting mainlyof airfall ash tuffswith subordinate ashflows, coarse pyroclastics,lava flows, and lenses of epiclasticsedimentary rocks. Thisassemblage forms a northwesterlytrending belt at least 90 kilo~ne- tres long and 25 kilometres wide alongthe northeastern margin of the Sustutbasin. From FinlayRiver Toodoggone rocks were traced as a continuous map unitfor 27 kilometressouthward. They extend beyond the boundary of map-area 94E and continuefor about 2 kilometresinto McConnell Creekmap-area, 94D (see Figure 1).

At its southern and southwesternboundary, rocks of the Toodoggone volcanic belt appear to be structurally conformablewith Tinkla rocks. Alternatively,they may overlie them with gentleangular unconformity. Elsewhere Toodoggone volcanics are generallyin fault cont,%ctwith bedded Takla, bedded Hazeltonor Omineca intrusiverocks. At lealstlocally, Omineca granitic rocksintrude Toodoggone volcanics. Alont3 its southeast boundary the Toodoggone volcanicbelt is overlapped by PahozoicAsitka and Triassic Taklarocks. The contactarea is a series of stackedt.hrust plates.In this region Toodoggone rocksdip steeply and 2-shaped northerlytrending Eolds withamplitudes of at least 20 metres occur. This is in marked contrastto the area further north in thts volcanicbelt where gentlydipping beds in tilted fault blocks or broad open foldswith horizontalaxes are the norm.

Indetail, six stratigraphic subdivisions of Toodoggone vblcanicrocks were =de south of FinlayRiver. These are based on generaloutcrop appearance,rock mineralogy, texture, and mode of deposition. The geologicsection there is probablythe most completesection exposed anywhere in the Toodoggone volcanicbelt. The basalunit (unit 1) is

135 -57-10’

57-00

136 r

137 exposed southeast of Kemess Creek; successively younger map units crop out to the north. The section is as follows:

Unit 1: Andesite - purple to brown and maroon, fine-grained hornblende feldspar porphyry flows. Closer to the southern boundary flows are interfingered with recessive mauve to pink airfall crystal ash tuff. Along the southern contact crystal ash tuff forms a thin veneer on Takla 'basement.'

Unit 2: Dacite - grey to pale green lithic ashto lapilli tuff and crystal-lithic ash tuff. Outcrops are resistant, dark grey in colour, and massive in appearance. There is no obvious bedding. Some indication of layering is givenby alignment of lapilli and breccia-sized clasts. Characteristically this unit has clasts of Takla rock; rarely it carries Asitka clasts.

Unit 3: Dacite - the rock is variably brown to orange or grey, biotite (chloritized) quartz feldspar crystal-lithic ash and lapilli tuff. The orange clasts consist of medium-grained feldspar phenocrysts set in a vitrophyric matrix. In thin section, the vitrophyre consists of radiating spherules of quartz-adularia- stilbite. The unit also includes crystal ash tuff, lapilli tuff, and rare lahar lenses.

Unit 4: Basalt - dark green to maroon, amygdaloidal feldspar porphyry flows that are up to50 metres in total thickness. These cap up to 10 metres of flaw or coarse pyroclastic breccia. Mafic phenocrysts are pervasively chloritized.

Unit 5: Andesite (Dacite, Trachyte) - grey, purple, and pink, predominantly hornblende-biotite-quartz-bearing feldspar crystal ash and crystal-lithic ash tuffs withsome lapilli tuff and lahar deposits and rare agglomerates. Immature sandstone and conglomerate, that is in part fanglomerate, form epiclastic lenses up to 50 metres in thickness but of local extent. Deposition of tuffs wasmainly from airfall deposits.Outcrops are stratified, poorly consolidated, and recessive. Despite their recessive nature, rocks of map unit5 form the thickest and mst extensive unit in the lbodoggone area; its total thickness apparently exceeds600 metres.

Unit 6: Dacite - grey to grey-green rocks that weather dark grey to brown. The rocks form resistant outcrops that commonly give rise to blocky jointed scarps. The rocks are relatively homogeneous with biotite-hornblende-quartz-feldspar-dacite porphyry clasts set in crystal-ash tuff matrix of similar composition. The clasts are oriented so they impart a faint foliation to the rock. Compaction is locally evident, but there is no evidence of welding in this unit. The unit apparently represents a subaerial ash flaw sheet that was up 150 to metres in thickness.

138 Map units 3, 4, and 5 are largely penecontemporaneous. Each was depositedfran separate, adjoining volcanic vents. Map units 3 and 4 are verylocalized but unit 5 is widespread.

Two smallvolcanic centres were recognized and are shown on Figure 1 as solidblack dots. The smaller centrein map unit 3 is appraximately 35 metres indiameter and consists of finely comminuted dark brown powdery dust and ashvent filling with bombsup to 60 centimetres in size. The largervolcanic centre near sample site AXT 3 has a 100-metre-wide feldsparporphyry intrusive neckemplaced alongthe margin ofan eruptive vent ofabout the same size.This centre is surrounded in a l-kilometre- sized area by agglomerate and breccia. Outward from thecoarse pyroclasticrocks are flankingaprons of lithiclapilli tuff grading to ashtuff. In bothvolcanic centres solfataric alteration rims up to 10 metres wide mark theperiphery of thevolcanic vent.

Map units 5 and 6 are known to occurnorth of FinlayRiver. Both units are found east and northeast of Baker mine and map unit 5 Eorms the countryrock in thearea of the Lawyers deposit.Lacustrine epiclastic sedimentaryrocks (unit 7) are found in a few localitiesnorth of Finlay River. Map units 5, 6, and 7 as describedhere correspond to map units 1 to 4 asdescribed by Schroeter(Geological Fieldwork, 1980, Paper 1981-1, p. 125). The correspondence is asfollows:

Map unit(this study, Figures 1 and 2) Map unit(Schroeter, 1980) 5a 1 Lower Volcanic Div. 5b 2 Middle Volcanic Div. 6 3 Upper Volcanic-1:ntrusive 'Div. 7 4 Volcanic-Sedimentary Div.

DISCUSSION - MAP UNIT 5

Preliminarychemical data for Toodoggone volcanicrocks (see Schroeter, thisreport) show thatthe majority are andesitic. However, the amount of quartz, commonly as quartzcrystals in ashtuff, varies from negligible toas much as 15 per cent. Therefore, when modal quartz was conspicuous in a series of outcrops,the rocks were mapped as 'dacite. ' Forexample, the area dominated by purplishquartz-bearing volcanic rocks was distinguishedas map unit 5a (Figure 1). Elsewhere, and probably overlying map unit 5a,quartz-poor rocks are andesitic (map unit5b). Withinthese rocks Schroeter has found areas containing more than 10 per cent K20. The 'andesites,'therefore, of map unit 5b are, at least in part,trachyte.

The geologic map (Figure1) is generalized and simplified. The northern part(unit 5b) is predominantlyandesitic crystal tuff and thesouthern part(unit 5a) quartz-bearing lithic-crystal tuff and, therefore, 'dacitic.' In realitythere are significantvertical and lateral variations in map unit 5. Quartz-bearing and quartz-poorrocks interfinger because slightly different rocktypes were erupting penecontemporane-

139 ously from adjoining eruptive centres. In the southernmost part of the map-area much of the basal part of unit 5a is crystal-lithic tuff. The matrix is quartz-rich crystal ash tuff which carries numerous granitic clasts.

ALTERATION AND MINERALIZATION

Hydrothermal alteration in the mapped area is fracture controlled and consists mainly of the zeolites laumontite and stilbite with calcite; it may be deuteric. Calcite, natrolite, and thompsonite fill arnygdales in dyke rocks but, overall, are rare. Intergranular calcite is pervasive in the epiclastic rocks. Throughout the district large areas of tuffs contain epidote clots and feldspars are alteredto a pink colour.

Zones in which fine-grained pyrite accompanies the epidote are of more economic interest. One such area occurs ina strongly faulted zone in map-unit 5b between Attycelley Creek and Finlay River.A large area of pervasive clay alteration is developed in the most westerly fault bounded block in this vicinity. Clay minerals identified by X-ray diffraction. include kaolinite and pyrophyllite. A composite sample of rock chips grabbed from a tenuous quartz stockwork-veinlet systemin the clay- altered zone yielded 676 ppb gold (sample AXT 5). Other composite grab samples cmprised of chips of quartz-veined material from silicified volcanic rocks contain trace amounts of gold. Values are shown in Table1 (see Figure 1 for locations).

TABLE 1. COMPOSITEGRAB SAM'LES FRCM SILICIFIED ZONES

Sample ALl Ag ppb ppm

AXT 1 26

Two occurrences of vein or breccia mineralization are known in the map- area. One is at sample site 3 (AXT 3) where green fluorite and barite accompanies hematitic chalcedony and calcite ina fault zone. The fault may be a radial structure related to the larger of the malltwo volcanic centres described previously. The second occurrence (shown on Figure 1 as Pb, Zn, Ea) is a quartz-calcite vein with base metal-barite mineralization. It occurs along the faulted contact between Toodoggone rocks and Takla rocks containinga porphyritic syenite dyke.

CONCLUSIONS

The 'Toodoggone volcanics' fonn a distinctive sequence of subaerial volcanic rocks that can be readily subdivided intoa number of lithologically similar map units. Some map units are distributed throughout the volcanic belt, others are very localized.

140 Publishedradiometric dates vary from 179 to 189 Ma (Gabrielse, et al,,, 1980).These, as well as a new date on hydrothermalalunite of 190 Ma (see Schroeter,this volume), suggest an EarlyJurassic age of deposition and relatedmineralization. Theseage data are compatiblewith the observationthat Toodoggone volcanics rest directly on Triassic Takla rocks andcan be correlatedin age witholder parts of theHazelton Group.

The regionsouth of FinlayRiver has similar lithologies,fault zones, and evidence of hydrothermalactivity as themineralized terrane of the Toodoggone epithermalgold-silver camp north of FinlayRiver. The area shownon Figure 1 appears to offerbountiful opportunities for additional epithermaldeposits. Close attention should be paid to lar$fer fracture/fault zoneswith associated hydrothermal alteration, particularly if there is silicification. Attention shouldalso be paidto bleached clay or alunite-bearing zones that might represent low-pH cappingsover buried precious metal deposits. All silicified zones, includingbreccias and weaklydeveloped chalcedonic veinlet systems and stockworks,should be sampled for gold.

ACKNOWLEDGMENTS

Bema IndustriesLimited provided expert expediting services from Smithers and Serem Limitedoffered logistic support in the Sturdee a.lrstrip vicinity. MitchMihalynuk ablyassisted the writer throughoutthis program.

REFERENCES

Carter, N.C. (1971): Toodoggone River Area, B.C. Ministry of Energy, Mines L Pet. Res., GEM, 1971, pp. 63-70. Gabrielse, H., Dodds, C.J., Mansy, J.L., and Eisbacher, G.H. (1977): Geologyof Toodoggone River(94E) and Ware West Half (94F), Geol.. Sum., Canada, Open File 483. Gabrielse, H., Wanless, R.K., Armstrong, R.L., and Erdman, L.R. (1980): IsotopicDating of Early Jurassic Volcanism and Plutonism in North CentralBritish Columbia, Geol. SUrv., Canada, Paper EO-lA, pp. 27- 32. Schroeter, T.G. (1981): Toodoggone River(94E), B.C. Ministry of hergy, Mines & Pet. Res., GeologicalFieldwork, 1980, Paper 1981-1, pp,. 124-131.

141 AKIE RIVER PROJECT

( 94F )

BY D.G. MacIntyre

The mapping project, which was initiatedin the Driftpile Creek-Akie River Ba-Zn-Pb district in 1979, was continued during the1981 field season. This year the project involved two helicopter-supported mapping crews operating froma base camp at Pretzel Lake. The following work was completed:

(1) Detailed mapping and measurement of stratigraphic sectionsin the vicinity of the Kwadacha barite deposit(94F) (see separate report, this publication). (2) Continuation of regional 1:50 000-scale mapping south of the Akie River’ (94F/lW, ZE; Figure 1). (3) Sampling of strategic Devonian sectionsfor a lithogeochemical study by J. Lowey at the Universityof Calgary. (4) Examination of ESSO Resources Reb prospect (94C/16W).

LEGEND

MIDDLE TO UPPER DEVONIAN

mUD Shale, Silty shale.minor siltstone, sandstone, conglmrate, limestone; chert.SlllCeWs arglllite, pyritic and bariticshale LOWER TO MIDDLEDEVONIAN

ImD FOsSi IlferWs i Imestone; minorcalcarenite, calcareous 51 itstone, and quartzite.

ORDOVICIAN TO SILURIAN ROAD RIVER FORMATION os Dolanltlcsiltstone, graptolitic black shale, calcareoussiltstone; mlnor Ilmestone,quartz, chert

KECH I KA FORMAT ION CO Nodular phyllltlc mudstone, Wavy banded, llmestone, platycalcareous siI tstone

symbols

High-anglefault; bail on darnthrarnside ...... Thrustfault ...... Antifon; synform ...... 9 Mineral occurrence ...... x550 Exhalitehorlzon ......

*To be released as a Preliminary Map, Spring 1982.

142 124-45' 94FAW.2E

A 0

1 KM 0

5 0 10 20 " . 1 KM

Figure 1. Generalized geology of 92F/IW, E.

143 In addition, L. Diakarspent 10 daysmapping and samplingthe Kwadacha baritedeposit (see separatereport, this publication).Tentative plans forthe 1982 fieldseason are to continueregional mapping in thearea between Kwadacha Park and theDriftpile Creek occurrence.Geochemical, paleontological, and petrographicstudies are currently in progress on samplescollected to date and results will be published when all wrk is completed.

STRATIGRAPHIC AND STRUCTURAL SETTING

The Devonian stratigraphy and structure of the Akie Riverarea havebeen discussed in two previousreports (MacIntyre, 1980,1981). In general, the Devonian consists of a lowersuccession of quartzose and calcareous turbidites and shallowwater carbonates that typically grade basinward intofiner grained reduced silty shales and siltstones. These rocks, which on interbasin rises have been removed by aMiddle Devonian erosionalevent, range in age from Earlyto MiddleDevonian and are unconformablyoverlain by a distinctive unit of rhythmically beddedblack chert,siliceous argillite, carbonaceous black shale, and minor limestone. Theserocks in part correlate with MiddleDevonian shelf carbonates of the MacDonald Platform and carbonates of the Akie and PesikaReefs. These reefs, which apparently grew on theuplifted edges of westward tilted fault blocks, divided the Devonian basin into parallel troughsduring Early and Middle Devonian time(MacIntyre, 19811, thus profoundlyinfluencing Devonian sedimentation.

The Devonian stratigraphy in thecurrent map-area (Figure 2) is a continuation of thatobserved to thenorth (MacIntyre, 1981). The lower part of thesuccession locally includes a unit ofmedium to thick-bedded quartzsiltstone, sandstone, and conglomerateturbidites (unit 1) that unconformably overliesgrey, pink, and redweathering platy siltstones and blackcherts at the top of theSilurian section. The quartzose unit grades up sectioninto interbedded calcarenites, limestone debris flows, and graptolitic(Pragian) black shale (unit 2). These turbidites presumablygrade into the Lower Devonian limestone unit (unit 2a) found atthe base of boththe Akie and PesikaReefs (Figure 3). Basinward the calcareousturbidites grade into black silty shales that have minor black chert and pelagiclimestone intercalations (unit 3). The vertical succession of rockssuggests progressively deeper water conditions with time,perhaps due to an EarlyDevonian episode of crustalsubsidence.

Where it hasnot been removed by erosion,the Lower Devonian transgressivecycle (units 1, 2 and 3) is overlain by a unit ofmedium to thick-beddedshallow water limestone that varies in thickness from over 200 metres in thecore of thePesika and Akie Reefs toless than ametre in adjacenttroughs. Bioclastic beds rich in crinoidossicles with doubleaxial canals ('2 holers')typically occurnear the top of the unit. The abundance of such ossiclesindicates a probableearly Middle Devonianage (Taylor and MacKenzie, 1970).

144 pq"_ "_ "

"_ .. mD

Figure 2. Idealizedstratigraphic column forthe Peslka Creekarea showing apparentposition of siIIceousexhalites (black bands) and barlte mineralization(cross hatched).

145 146 In contrastto the succession north of the Akie River,the Middle Devonian limestonein the current map-area is overlain by a relatively resistantunit of blackrusty weathering shale thatlocally exceeds 100 metres inthickness (unit 5). The siliceousargillite, chert and shale unit(unit 6), which hostthe bedded barite and massivesulphide deposiits ofthe Akie River district, lies stratigraphically above therusty sha.le unit in theeastern part of the map-area butappears to be discontinuous in thewesternmost shale belts. Where present,the siliceous unit is overlain by bluishgrey to brownish grey-weathering banded silty shales of probableLate Devonian toMississippian age (unit7). In the westernmostexposures of the Devonian sectionthin units of sandstone and siltstoneturbidites (unit 8) occurstratigraphically above thesiliceous unitin the Late Devonian transgressiveshale sequence. In the same area a 1-metre-thickgreenish grey to orange-weathering pyritic tuff bed occurswithin unit 5, a few metres above the MiddleDevonian limestone. Units 4 and 5 may represent a short-livedtransgressive cycle that preceded a period of tectonic and exhalitiveactivity that h.eralded the beginning of a majorepisode of progressive,eastward advancing crustal subsidence in Middle to Late Devonian time. Concomitantcrustal uplift andvolcanism occurred tothe west but shiftedeastward during Mississippian time. Thisuplift may be relatedto the beginning of accretion of oceanic terranesfurther west at theleading edge of the continental plate.

MINERAL OCCURRENCES

The widespreadLate Devonian baritic and/or pyritic siliceous exhalite unit, which is ubiquitousnorth o€ the Akie River,appears to be only locallypresent in the current map-area. Thisunit is exposed on Cyprus Anvil's Gin claims and Cominco'sPesika claims butsurface mineralization is restrictedto thin beds and laminae of nodular andmassive barite. Theseoccurrences (Nos. 1 and 3 on Figure 1) are on strikewith a long belt of barite-sulphideoccurrences that extends northward t:o the Driftpilecreek district. The depositsappear to have formed in a linear structurallycontrolled trough bounded by the Akieand Pesika reefs.

Two other showings arealso located within or near the 1981 map-area. Cominco's Ern showing (No. 2, Figure 1) comprisesstratabound massive pyrite in a brecciatedquartzite host. The quartzite is int:erbeddedwith darkgrey calcareous siltstones, black chert, and limestone.,Similar rockshave been observed elsewhere in the map-area;typical!.y theyoc'cur near thetop of theSilurian section, immediately below the Lower Devonian quartzite unit (unit 1, Figure 2). A similarstratigraphic position is suggestedfor the Ern showing.

ESSO'S Reb prospect (No. 4, Figure1) is locatedslightly south of thearea mapped in 1981. The showing is located in a small creek valley and consists of severalfinely laminated pyrite bands in a sequence of interbeddedblack shale,chert and siltstone.Graptolites collected froman outcrop of shale upstream from the showing indicate an Ordovician age forthe mineralization. The Ordoviciansection on the Reh property appears to be anomalouslythick

147 relative to those to thenorth, suggesting the presence of a localsedimentary basin or trough.

ACKNOWLEDGMENTS

The author would like to thankRiocanex Exploration and Dick Woods ofVernon Helicoptersfor providing logistical support for the mapping project. In addition, Alf Stewart of ESSO Resourcesprovided a veryinformative tour of the Reb property. Mike Fournier, Karen Downing, and Jennifer Lowey ably assisted in the mapping project and their work is gratefully acknowledged.

REFERENCES

MacIntyre, D.G. (1980): Driftpile Creek-AkieRiver Project, B.C. Ministryof Energy, Mines 6 Pet. Res., GeologicalFieldwork, 1979, Paper 1980-1. pp. 55-67...... (1981): AkieRiver Project, B.C. Ministry of Energy, Mines E, Pet. Res., GeologicalFieldwork, 1980, Paper 1981-1, pp. 33-47...... (1981): Geologyof the Akie River Ba-Pb-Zn District, B.C. Ministry of Energy, Mines 6 Pet.Res., Prelim. Map 44. Taylor, G. and MacKenzie, W.S. (1970): Devonian Stratigraphy of Northeastern British Columbia,Geol. Sum., Canada,Bull. 186, 62 pp.

148 KWADACHA BARITE DEPOSIT (94F/10W)

By D. MacIntyre and L. Diakow

INTRODUCTION

Duringthe 1981 field seasonthe Kwadacha baritedeposit, which is locatedimmediately north of theconfluence of the Kwadacha andNorth Kwadacha Riverswithin Kwadacha WildernessPark, was thesubject of de-. tailedregional and property scale mapping. Thismrk was done over a 10-day periodin late June and involvedthree two-person field crews. The deposit, which is well exposed in a series of fault and foldrepeat.s alongthe crest of a north-trendingridge, is accessibleonly by helicopter.

REGIONAL GEOLOGY

The geology in thevicinity of the Kwadacha baritedeposit is shown on Figure 1. This part of the Rocky Mountain Fold and Thrust Belt is underlain by Cambrian to Late Devonian clastic and carbonaterocks (MacIntyre, 1981). Northeast of thedeposit, shelfcarbonates of the MacOonald Platform predominate and thesegrade westward into time equivalent clastic facies. The rocks havebeen foldedinto a series of northwest-trendingasymmetric, overturned antiforms and synformst,hat have bothsouthwest and northeast-dippingaxial surfaces. The latterare somewhat enigmatic in that structuraltransport is generallyto the northeast with mst of the thrust mvementoccurring along the southwent- dippingaxial surfaces of major foldstructures. Folds with northeast- dippingaxial surfaces are interpreted to result from gravity back- sliding of an incompetentthrust plate as it moved upward along a southwest-dippingfault surface rooted in competentshale units. Some of thehigh-angle normal faults, which typically have downthrown blocks to the west, may also be related to back-sliding and break up of the overthrust plate.

STRATIGRAPHICSETTING

The stratigraphic setting of the Kwadacha baritedeposit is dmilar to that of otherbarite-sulphide deposits in theDriftpile Creek-Akie River District (see MacIntyre, 1981). In general,the baritic zone occurs near thetop of a resistantunit of rhythmically bedded blackchert, siliceous argillite,silty shale andminor limestone.This unit is overlain by a thicksection of monotonous blackshale and underlain by shallowwater medium to thin-beddedgrey fossiliferouslimestones and calcamenites. Several beds withinthis limestone unit are rich in crinoid ossicles, 125'15'

57'30'

0 5 10 IS 20 25 t . L KM

2 1 0

Flgure 1. Generalized geology In the vlclnlty of the Kwadacha barite deposlt.

150 LEGEND

DEVONIAN D Shale,siltstone, chert, siliceousargillite; minorlimestone LOWER TO MIDDLE DEVONIAN ImD Fossiliferous limestone, calcarenite; quartz sandstone, quartz slitstone, conglanerate; minor shale. ORDOVICIAN TO SILURIAN os Dolanltic siltstone, graptoiltic black shale, calcareous siltstone, limestone, dolostone; minor chert, maficvolcanic rocks CAMBRIAN TO ORDOVICIAN co Nodular phyllitic mudstone, calcareous siltstone; minw shale, limestone, calcarenlte

Symbols

Geologic contact ...... Thrust fault ...... Normal fault (ball on downthrown side) ...... 5 Antictine; syncline ...... Known surface trace of barltic and/or pyritic exhalite horizon 56 Stratigraphlc section location ...... A Barite-sulphide deposit, 1 .Kwadacha; 2 .Cirque ...... Boundary of Kwadacha Wilderness Park...... some withdouble axial canals ('2 holers')indicating a probable Middle Devonianage (Taylor and MacKenzie, 1969).

The basalpart of the Devonian successionconsists ofgraded beds of quartzsandstone and siltstone which are locallycrosslaminated and containangular shale rip-up clasts. These quartz-richrocks; unconforrnably overlie a unit of pink,grey, and red platy weathering laminatedsiltstone with minor limestone and chert intercalat.ions that is apparentlythe uppermost part of theSilurian section. The quartzose unit is less than 10 metres thick in thevicinity of the Kwadacha barite deposit(section a, Figure 2) but is mre than 50 metres thick on the ridgeimmediately east of thedeposit (section b, Figure 2). A similar westward thinning is noted€or the limestone unit; overlying siliceous rocks, on theother hand, apparentlythicken westward. Westward thinn.ing and finingare characteristic of mst of the Lower Devonian unitsthat occuralong the shelf margin, suggesting these sediments were! deposited by turbiditycurrents moving down a westward dippingslope. Basinward thickening of thesiliceous unit, on theother hand,suggestti accumulation of silica-richsediments was favoured in thedeeper water, more euxinicenvironment. Some of thesilica may havebeen introduced by submarineexhalitive activity that preceded andaccompanied formation of

151 rloo

I-

Figure 2. Stratlgraphlc fence dlagrarns shalng thlckness variations In Devonlan unlts and stratlgraphlc posltlon of the Kwadacha barlte deposlt: l- dolornltlc slltstone, rnlnor chert, and Ilmestone; 2 - quartz sandstone, slltstone, and conglowrate; 3 - thin-bedded limestone, calcarenlte, and calcarerns slltstone; 4 - Interbedded black chert, slilceous arglllite, and shale; 5 - msslve bedded barlte, nodular barlte; 6 - black shale (sea Flgure 1 for locatlon of sections).

152 the Kwadacha baritedeposit. Overall, the vertical stratigraphic succession from nearshore high energy quartz-rich sandstones upward into reducedbl.ack shale and progressiveonlapping of theseunits eastward with timeare evidence for a major marine transgressionthat kegan in Early Devoniantime. This transgression was probablythe result of eastwarrl advanci.19 crustalsubsidence.

BARITE MINERALIZATION

Bedded barite is repeated by imbricatethrust faults and foldingalong the cr-:st of a north-trendingridge (Figure 3). The barite is resistant and outcrops a; a series of jagged,low-amplitude, southwest-dipping hog backs. ‘I110 barite zonesare present separated by a 10 to 15-metre-thick interval of recessiveblack shale with a thingrey weathering limestone interbed. The lower zone consists of several 10 to 15-centi.metre-thick intervals of laminated and nodularbarite that occur in the upper 10 to 15 metres of theinterbedded chert, siliceous argillite and shaleunit. ?he upperzone, which varies from 1 to 10 metres in thickness,,consists (of massive,finely laminated barite withthin argillaceous partings. A colour gradation from lightgrey-white barite at the base to Clark grey barite at thetop of the zone was noted and is attributedto $an increase in admixed argillaceousmaterial up-section.

The upper barite zone contains no visiblesulphide mineralization but thin laminae of veryfinely disseminated pyrite were found in the underlyingsiliceous shale unit. Outcrops of barite were sampledalong the entire length of theridge from stratigraphic bottom tostratigraphic top and arebeing analysed to determinevariations in majorand trace elementcontent tl~roughout the unit. Results will be published when the anaLytica1 work is completed.

Thin,discontinuous beds of discrete and coalescingbarite nodules in a blackshale host occur close to the base of thesiliceous unit and in blackshales immediai?ly overlying the upper massive barite zone. Thes:e beds probably oriyina+>d from the precipitation of Bas04 from meteoric solutionsliberaten during diagenesis.

DEFORMATION

Deformationrelated to northeast-directedsupracrustal shortening is readilyapparent in the vicinity of the Kwadacha baritedeposit. Sil.urian and Lower nevcnianfine clastic and chemicalsedimentary rocks: have hen foldedinto major upright and overturnedsoutheast-plunging anticline-syncline pairs. In contrast,the less competentshale-rich Middle andUpper Devonian unitsare characterized by tightlyappressed or isoclinal folds with a penetrativeaxial planar cleavage. The upper massive barite unit, which is underlain and overlain by shale, behaved plasticallyduring deformation and internalfolding and thickening in the hinge area of folds is commonplace.

153 metres

~~~~ ~

Flgure 3. Geology of the Kradacha barltedeposit (mapplng by L. Dlakar).

154 Numerous subparallel, southwest-dipping thrust faults along the hinges of shear folds produced a stacked succession of single-limb half folds. lhe frequency of faulting is greatest in the shale-rich sections and at the base of a thin limestone bed underlying the upper massive barite unit. In this stress regime, limestone acts rigid and detaches easily from the underlying shales.

Structural thickening of incompetent shale sections and dragging of beds adjacent to fault planes is widespread.

ACKNOWLEDGMENTS

The writers would like to thank John Mawdsley, Mike Fournier, Karen Downing, and Jennifer Lowey for their very capable and cheerful assistance in the field.

REFERENCES

MacIntyre, D.G. (1981): Akie River Project, B.C. Ministry of Energy, Mines & Pet. Res., Geological Fieldwork, 1980, Paper 1981-1, pp. 32-45. Taylor, G. and MacKenzie, W.S. (1970): Devonian Stratigraphy of Northeast- ern British Columbia, Geol. Surv., Canada, Bull. 186,62 pp.

1!55 CASSIAR GOLD DEPOSITS McDAME MAP-AREA (104P/4, 5)

By A. Panteleyev and L.J. Diakow

INTRODUCTION

A study of theCassiar gold deposits initiated in 1980 was continued duringJuly of 1981. Additionalfill-in geological mapping at scale 1: 10 000 was done west of QuartzrockCreek and north of TroutlineCreek, alongFinlayson Creek, to thesouth of WDame Creek,and along the northernboundary o€ the 1980 map-area (seeFigure 1, thisreport and Figure 18, GeologicalFieldwork, 1980,Paper 1981-1, p. 56).

Particularattention was paid to delineating major quartzvein systems. A number of northeasterlyto east-northeasterly trending fracture zones containingquartz veins are outlined on Figure 1.Within these zones, mineralizedareas and individualveins ofeconomic interest were mapped at 1:lOOO scale.

Mining and explorationactivity in the Cassiar gold belt was brisker during 1981 than in previousyears. For the third consecutive year miningand exploration were conducted on TableMountain by Erickson Gold MiningCorporation (Jennie vein MDI No. 104P/029). 'lWo new mills were commissioned in August. On August 14ththe United Hearne - Taurus ResourcesLimited's plant turned over at the Hanna gold mine (Cornucopia, Benroy, Copco) (MDI No. 104P/012), 8 kilometres east of Cassiar. On August17th Plaza Mining Corporation started milling at theirplant that adjoinsthe Cassiar road 3 kilometressoutheast of Hanna mine. Mill feed forstart-up of both new mills came from stockpiledore. At Hannamine (Cornucopia),ore was provided by undergrounddevelopment work whereas at plaza it came from a small open pit locatedat the eastern extension of

SYLVESTER GROUP IMlSSlSSlPPlAN TO ? PERMIAN1

11""""" 2 GREENSTONE-CHERT ASSEMBLAGE: MASSIVE ~~t~~~~ 4 BASALT: WIDESPREAD PILLONS. SOME BRECCIA. "11.1.. PALE TO DARK GREEN ANDESITE FLOWS. TUFF, n".""""" TUFF, AN0 MINOR ARGILLITE;IN SOUTHEAST, IN PARTFINE-GRAINED DYKES AN0 SILLS. ABUNDANT BRECCIA. TUFF. AN0SMALL LIME- SOME CHERT, INCLUDES PORPHYRITIC FEU- STONE PODS SPATHIC ANDESITE FLOWS (AND 7 SILLS) . .<'..,,.. 3 SILTSTONE, ARGILLITE, GREYWACKE. PEBBLE 28 CHERT, TUFFACEOUS CHERT, INCLUDES SOME .. '...... ; CONGLOMERATE, QUARTZ ARENITE. TALCAR- ARGILLITE; IN NORTHEAST WELL-LAYERED EOUS SILTSTONE. LIMESTONE CHERT-PHYLLITE. TUFFACEOUS CHERT, RIB- BONNED CHERT, ANDARGILLITE VEIN SYSTEM 1 ARGILLITE. SILTSTONE, CHERT, QUARTZITE. LIMESTONE. PEBBLE CONGLOMERATE, TUFF: INCLUDES NUMEROUS OIABASE AND ANDESITE SILLS LEGEND TO ACmMPANY FIGLRE 1.

156 alsooccur (Bruce Spencer, pers. corn.). These suspected thrust faults areseen in new undergroundmrkings and diamond-drillcores. If these structures arepart of the same faultthat is present in outcropssouth and west of Snowy Creek,then a major flat fault or series of faults underliethe lower reaches of Troutline and QuartzrockCreeks:.

QUARTZ VEIN SYSTEMS

Auriferousquartz veins and placerdeposits in theCassiar region have beendescribed in considerabledetail by mndy (1931, 1935, 1937). These

157 the Vollauq vein (MDI No. 104P/019) on Table Mountain. All three of the operating mills in the Cassiar gold belt have rated capacity of100 to 150 tonnes per day.

GEOLOGY

Fill-in mapping affirmed the stratigraphic and structural interpretations presented in Geological Fieldwork 1980 (Paper 1981-1). During current mapping map units described in 1980 were extended; chert and tuffaceous chert of map unit2A was found to underlie the northeastern part of Table Mountain along Pinlayson and McDarne Creeks, and greenstones, clastic rocks, and basalt of map units2, 3, and 4 were noted to the north of the previously mapped area.

The presence of at least one major, westward dipping thrust wasfault confirmed by mapping ridges north ofSnowy (Snow) Creek and east of Quartzrock Creek. Other flat-lying to locally eastward dipping faults reports provide a historical record of exploration as well as sound descriptive and assay data.

Few new veins, with possible exceptions of the Cusac,ESSO, and Berube vein systems, have been foundas a result of recent work. However, much information has been gained fran new exposures of known veins.A geologic IMP (Figure 1) shows the locations and current namesof the main quartz vein systems.

In this study veins were divided into two fundamental types. Type1 veins are hostedby 'greenstone' and Type 2 veins occur at bedding contacts between greenstone and argillite.

TYPE 1 VEINS

The host rocks for Type1 veins are mainly metamorphosed andesitic flows or tuffs, pillowed basaltic flows, and rarely diabasic dykes, sills,or flows. These rocks are now greenstones as a result of greenschist metamorphism or propylitic alteration. Type 1 quartz veins consist of fine to coarse granular milky white quartz with small amountsof erratically distributed ferroan carbonate and rare vugs with clear, terminated quartz crystals. The veins occupy sets of steeply dipping, generally northeast to east-northeasterly trending, subparallel fractures or en echelon gashes. Type 1 veins are generally short and narrow. Even those in the larger shear zones tend to pinch and swell along strike. Many veins are arcuate or cymoid (sigmoidal) and terminate either by pinching out, by splaying into 'horsetails,' or locally by forming bulbous quartz 'knots' that are generally less than1 metre in diameter. Where a vein terminates in quartz 'knots,' it is common to see another quartz vein developed in the hangingwall of the first vein. These hangingwall veins are wispy and thin near the quartz 'knots' but increase in thickness along strike. A typical Type 1 quartz vein wouldbe up to 1 metre wide and asmch as 60 metres in length; rare veins are up 5 to metres wide and persist for hundreds of metres (for example, the Elan

158 veinsystem). En echelonveins and ladderveins which common1.yshow preference for certainbeds are generally short, rarely more t.han 10 metresin length.

Type 1 veinshave characteristic bleached wallrock alteration envelopes. The alterationenvelopes are commonly 5 to 10 times as wide as: thequartz veinsthat they surround and mostlyhave sharp, knife-edged margins. In some casesalteration zones up to 100 metres wide surround small discontinuousquartz veinlets, such as inthe Hanna mine (Cornucopia)- QuartzrockCreek area.

The alteration zonesserve as excellent exploration guides because they give rise to distinctive orange-brown soilsover buried vein 13ystems. The bleachedaltered greenstone consists of albite,carbonate,, clay minerals,pyrite crystals and rarechlorite and epidote. The quartz veins in the most highly altered zonescontain sericite and tourmalinein addition to ankeriticcarbonate.

Type 1 veins occur in four main zones as shown on Figure 1. From south tonorth these include:

Zone 1: Callison - McDame Lakessystem (MDI No. 104P/017, 018): The veinsystem includes the ESSO, Gold Hill, andDavis (Nora) veins in azone thattrends at 055 degrees for at least 2 500 metres. Most veinshave a shortstrike length and are controLled by 040 to 050 degreestrending joint sets. The recentlydiscovered ESSO vein is one of the few veinsthat follows shear joints; it trends 020 degrees. The Davis(Nora) vein strikes at 070 to 085 degrees,the most common trend of thelarger veins in the McDame map-area.

Zone 2: Quartz Centre - WingsCanyon - Snowy CreekSystem (MDI No. 104P/013, 014, 015): l%is is the most persistent of thevein systems. It gives rise to amineralized belt approximately 5 kilometreslong and 150 metres wide. This systemincludes the Reo, Blueberry Hill, Wings Canyon (Red Rock),and Snowy Creek veinsincluding the Rlch vein, Snow Creek, andBerube veins. TheReo veinsare unusual in this district in that two ages of quartz are evident.Older veins are massive and trend 090 to 115 degrees;younger veins trend at 045 degrees and truncate t.he olderveins. zone 3: QuartzCity - Upper Snowy CreekSystem (MDI No. 104P/Oll, 012): This belt is marked by a wide alteration zone witha large number of smallquartz veins. The largerveins include the QuartzrockCreek (Mack, Mac) veins, and the Hannamine (Cornucopia)vein system.

Zone 4: Elan veinsystem: A number of largequartz lenses up to 8 metres wideoccupy a shear zone that trendseast-westerly over a strike length of 3 kilometres.

1 !59 TYPE 2 VEINS

This second type of quartz vein occurs at bedding contacts of greenstone and argillite. Invariably greenstone is in the footwall and argillitein the hangingwall. Most Type 2 veins occupy the bedding plane contact; locally the veins are entirely in greenstone or splay into strands, some of which pass in and out of greenstone. Where the quartz veins pass into argillite, they become ribboned with abundant graphitic lamellae and commonly pinch or feather out. In some workings, the quartz veins are split by basic dykes about 1 metre wide. Within the veins the dykes are pervasively bleached and carbonate altered and become 'felsite.'

Movement took place along many of the bedding plane contacts before and after emplacement of Type 2 veins. For example, on Table Mountain blocks of dyke rock and dismembered limestone beds are contained in contorted argillites that overlie the plane of decollement. Mandy(1937) considered this setting tobe a major thrust fault in which the Vollaug vein was developed.

The Vollaug vein, a graphitic, ribboned quartz vein, is a good exampleof a Type 2 vein. It is an east-westerly trending, gently northward dipping, vein up to2 metres in width that has been traced nearly2 kilometres as a semi-continuous structure. The east-northeast-trending, more steeply Jennie vein is another example. The Cusac veins occur at the same major greenstone-argillite contact but consist a ofnumber of small quartz veins that are confined mainlyto steep fractures in the footwall greenstone. Other Type 2 veins are found individually or in groups along the contact of map units 2 and 3 on Troutline Creek, or near map unit 2A and 3 contacts with unit 4 in the Snowy Creek area.

Alteration in the footwall greenstones associated with Type2 veins is similar to that in Type1 veins, though less intense. In hangingwall argillites, there is little alteration evident other than a thin zone of carbonate veining and a slight increase in pyrite content.

MINERALOGY

Both vein types contain free gold, small amounts of pyrite, tetrahedrite, chalcopyrite, and arsenopyrite, and traces of sphalerite and galena. Covellite, azurite, and malachite occur in weathered zones.In some veins, for example theReo, Elan, and West Hope (Hopeful), tetrahedrite is the main ore mineral. Tetrahedrite is erratic in its distributionbut locally can be so abundant that it produces spectacular silver grades. Gold in Type 1 veins is associated with pyrite, ankeritic carbonate, and arsenopyrite. In weathered specimens free gold occurs as grains in cellular boxworks or plates cavity walls. In Type 2 veins, gold accompanies tetrahedrite or occurs with graphite. The average gold/silver ratio in Type2 veins is 1: 1.

160 QUARTZ-CARBONATE-MARIPOSITE ROCK (LISTWANITE)

Numerous bodies of listwanitethat vary from a few metresto 700 metres in length havebeen noted. They appearto beendemic tothe gold-bearing regionbut have no directspatial relationship to auriferous quartz veins.Listwanites are metasomatized zonesformed alongfaults and beddingcontacts. Boundaries are sharp or gradational. The;;e peculiar rocksare derived mainly from basicflows but also from tuff13 and tuffaceoussediments. Locally they accompany serpentinebodles. In the area mapped thesesmall serpentine bodies constitute lenses that also appear to be derived from thebasic volcanic wallrocks.

The relationship of quartzveins, listwanite bodies, and ran?serpentine lensesappears to be largely a structural one - theyoccupy the same fracture zones.

AGE OF GOLD MINERALIZATION

Hydrothermalwhite mica from a tourmaline-bearingauriferous vein from Snowy Creek yielded apotassium-argon age date of131*5 Ma. In view of the73”a Late Cretaceous dates reported for the closest raniti tic intrusions west of theCassiar gold belt (Panteleyev,1980), the gold mineralizationappears to be related to structure-metamorphicevents that pre-date and areindependent of major granitic emplacement.

ACKNOWLEDGMENTS

The cooperation and logistic support offered by Cassiar Asbelstos CorporationLimited is acknowledged. We thankthe following gentlemen foraccess to properties and forthe information they provided: A1 Beaton,Camille Berube, Chris Bloomer, Tim Riordan,Bruce *(?mer, and Bill Storie.

REFERENCES

Diakow, L.J. and Panteleyev, A. (1981):Cassiar Gold Deposits, McDame Map-Area (104P/4, 5), B.C. Ministry of Energy, Mines & ]?et. Res., GeologicalFieldwork, 1980, Paper 1981-1, pp. 55-62. Mandy, J.T. (1931):Placer-Gold Deposits of McDame CreekArea, B.C. Ministry ofEnergy, Mines & Pet.Res., Minister of Mines, B.C., Ann. Rept., 1931,pp. A54-A61...... (1935): McDame CreekArea, Dease River, B.C. Min:.stry of Energy, Mines & Pet.Res., Minister of Mines, B.C., Ann,, Rept.. 1935,pp. BIZ-822...... (1937): McDame CreekArea, B.C. Ministry ofEnergy, Mines & Pet.Res., Minister of Mines, B.C., Ann. Rept., 1937,pp. B24-B37. Panteleyev, A. (1980):Cassiar Map-Area, B.C. Ministry ofEhergy, Mines & Pet. Res., GeologicalFieldwork, 1979, Paper 1980-1, pp. 80-88.

6 161 MIDWAY OCCURRENCE (1040/16W)

By D.G. MacIntyre

INTRODUCTION

The Midway stratabound massive sulphide discovery which is located approximately 96 kilometres west of Watson Lake, Yukon Territory, was examined on September 9 and 10. The property comprises 240 Yukon claims

LEGEND CRETACEOUS CASS IAR BATHOLITH Kqm Quartz monzonlte, granodiorite

MISSISSIPPIAN AN0LATER Mu Serpentlnlte,dunite, peridotite

UPPERDEVONIAN TO MlSSlSSiPPlAN SYLVESTERGROUP (UPPER) OMV Greenstone, agglomerate; dacltlctr Iff; minorchert, metadior 'Ite

MIDDLETO UPPER DEVONIAN SYLVESTER GROUP (LCWER) uo Slate,argl I I Ite, chert.siltstone, chert-arenite, greywacke, chert pebble conglowrate, mlnor I lmestone

MIDOLE DEVON I AN McDAME GROUP mD Oolanlte,fossiliferous limestone

CAMBRIAN, ORDOVICIAN, AND SILLRIAN €OS Dolomite,dolomltlc sandstone and slltstone,graptolltlc black shale, platy si Itstone, calcarews phyl I lte, phyl I itlc i imestone skarn, hornfels,limestone, quartzite

symbols High-angle fault;ball on donnthrown block ...... J Antiform ...... d Contact:deflned; assumed ...... k Road ...... Stratabound barite ...... 0 Strataboundmasslve sulphlde ...... + Mineral occurrenceIn carbonate rocks ...... Exhalltehorizon ......

162 €05

0 25 b 4 KM

Figure 1. Generallzed geology In vlclnlty of the Mldway shalng, Jen:llngs Rlver map-area; geology and legend modlfled fra Gabrlelse 11969).

163 and 881 British Columbia claim units accessible via a rough four-wheel- drive road that connects with the Alaska Highway near Rancheria (Milepost 702). The property was acquiredby Cordilleran Engineering on behalf of Regional Resources Ltd. during 1980 and is currently under option to Amax of Canada Ltd.

STRUCTURAL SETTING

The Midway showing is located within a north-trending belt of Middleto Late Devonian basinal facies sedimentary rocks (Figure1). These rocks are preserved within the core of a major synclinorium that is bounded and intruded by the Cretaceous Cassiar Batholith(Kqm) to the west and the Lower Cambrian carbonatesof the Atan Group to the east (Gabrielse,1969). Unlike areas east of the Rocky Mountain Trench, deformation within the synclinorium is relatively minor and broad open folding is the predominant structrual style. The stratigraphic succession is locally offset by high angle normal and reverse faults.

STRATIGRAPHIC SETTING

The host rocks for the Midway showing are black silty shales and siliceous argillites of the lower partof the Sylvester Group. These rocks conformably overlie Middle Devonian McDame limestone (mD) (Gabrielse,1969) and therefore are probably late Middle to Early Late Devonian in age. Detailed mapping and measurement of stratigraphic sectionsby Cordilleran Engineering and Amax Exploration geologists has defined three major coarsening upward sedimentary cycles (units 1, 2, and 3, Figure 2) in the lower part of the Sylvester Group (uD) (Figure 2). These cycles, that typically begin with a relatively thin sequenceof interbedded shale, silty shale and baritic and/or pyritic exhalite, grade up section into progressively coarser, thicker, and more calcareous turbidites. These coarsening upward cycles suggest an increasing proximity to a source area with time, perhaps as a resultof eastward advancing crustal uplift. Coarse clastic rocks of unit3 are overlain by mafic to felsic volcanics of the upper partof the Sylvester Group (DMv). These volcanic rocks appear to be largely subaerial in origin.

MINERAL OCCURRENCES

Trenching on the property hasexposed a zone of stratabound recrystallized massive pyrite that averages2 metres in thickness over a strike length of approximately 40 metres. High-grade concentrations of zinc mainly as diffuse bands of blonde-coloured sphalerite occur locally within the massive pyrite. Minor amounts of galena are also present. Elsewhere on the property several baritic and pyritic exhalite horizons have been discovered that canbe traced for considerable distances north and south of the showing. A 4-metre-thick bedded barite Occurrence (Ewen barite)was

164 DMv

Y A- Lower *U U Sylvester UD WJ, 2 _""...... 1: 1: 100 1

McDame mD

-!. Idealized column for the Midway shcwlng stratigraphic property location of exhall te zones (cross hatched) and sulphlde and barite mlneralizatlon (black Ilnes). 1 - Ilmestone; 2 - shale, silty shale; 3 - siliceous exhalite, chert; 4 - siltstone, sandstone; 5 - conglomerate, sandstone; 6 - mflc to feislc volcanlc rocks.

165 discovered in thenortheast corner of theproperty near the British Columbia-Yukon boundary.

Six diamond-drillholes, totalling 853 metres, were completed late in the yearin the vicinity of the Discoveryshowing (see RegionalResources News Release, November 23, 1981). Results of this work indicatethe presence of threesoutheast-dipping mineralized wnes. The Lower Zone which is locallyabsent overlies MiddleDevonian dolostone,varies from 1 to 2.5 metres inthickness, and has combined zinc-leadgrades ranging from 2.65 to 23.39 percent and silvervalues ranging from 1.24 to 22.59 ounces per ton.This zone is locallylead-rich.

TheLower Zone is overlain by 70 metres of argillites and sandstones which arethe footwall rocks of the Middle orDiscovery Zone. Drill intersectionsindicate that this zone varies from 4.6 to 11.2 metresin thickness and has combined zinc-leadgrades ranging from 4.56 to 13.36 per cent and silvergrades ranging from 1.26 to 5.03 ouncesper ton. Ten to 12 metres above theDiscovery Zone is the UpperZone which ranges from 0.43 to 3.2 metres thick and has combined lead-zincgrades ranging from 2.62 to 13.15 per cent and silvergrades ranging from 0.63 to 6.52 ouncesper ton. Both theDiscovery and Upper Zones are predominantly zinc-rich.Interbedded argillites andsandstones overlie the Upper Zone.

ACKNOWLEDGMENTS

The author would like to thankCordilleran Engineering and Amax Explorationfor the opportunity to visit the Midway occurrence and for their generoushospitality and logisticalsupport during the examination of theproperty. Discussions with Mr. S.E. Parry were particularlyvalu- ableas an introduction to theregional stratigraphic setting of the mineraloccurrence. Mr. M. Fournierably assisted in the field.

REFERENCE

Gabrielse, H. (1969): Geology of the JenninqsRiver Map-Area, British Columbia (1040), Geol. Surv.,Canada, Paper 68-55, 37 pp.

166 OTHER INVESTIGATIONS

MULTIVARIATE MODELS FOR RELATIVE MINERAL POTENT'IAL SLOCAN SILVER-LEAD-ZINC-GOLD CAMP (82F)

By A.J. Sinclair Departmentof Geological Sciences University of British Columbia

ABSTRACT

One hundredand thirty-eightvein deposits forming the wes,tern partof Slocan camp are used to develop statistical modelsbased on known ore production and averagegrades of production.Relative siz,e of depo!rits asestimated by thebiased variable 'production' (short tons of ore) is used as a relativevalue measure to (a) serve as a dependentvariab:te for multipleregression models, and (b) form thebasis for subdividing data into low, medium, and high-tonnagegroups for discriminant, analysis models.Both types of models appearuseful judging by their abilit!y to forecast known productionfor a targetproduction of depos,its from-the eastern part of Slocan camp. Resultssuggest that multiple regression is more usefulthan is discriminantanalysis in classifyingdeposits with respect to potentialsize.

INTRODUCTION

Statistical methodshave been appliedover a wide range of scales in attempts to develop a rigorousapproach to measuringabsolute or relative resourcepotential (Kelly and Sheriff, 1969; Sinclair and Woodsworth, 1970; Orr and Sinclair, 1971; Godwin and Sinclair, 1979). Comparable approaches are used widely in evaluating oil and gas potential (for example,Harhaugh, et al., 1977). Little effort hasbeen expended on the application of statistical models to theevaluation of specific polymetallicmineral deposits in terms of grades of economically importantmetals, particularly in vein camps.

Such modelshave two importantapplications viz:

(11 Newly locateddeposits can be sampled and theaverage grades used to estimate potentialsize and therebyprovide an evalua.tion of the usefulness of additionalexploration.

(2) A statistical model may identify known depositswith low productivitythat havegrade characteristics of largedeposits,, thus indicatingspecific known depositsthat appear to warrant more detailedexamination.

167 Orr and Sinclair (1971 ) attempted to usemultiple regression in Slocan Cityvein camp as a means of estimatingrelative value of a deposit. Averageproduction grades for silver, gold, lead, and zinc here used as theindependent variables and recordedproduction tonnage was the relativevalue indicator (dependent variable). Statistically significant models were describedbut no dataexisted by which the geological validity of a model could be tested.Furthermore, their models were of little practical interest becausethey pertained to a camp in which deposits were verysmall and of little generalinterest.

More than 200 veindeposits in Slocan camp haveproduced from 1 to 700,000 tons of orefor which averagegrades of total recordedproduction are more or less completely known (Orr and Sinclair, 1971 ). These data provide an unusuallycomprehensive information base fortesting the validity of variousstatistical approaches to theestimation of 'value' of a deposit, and thepotential of suchmodels as anexploration tool.

PROCEDURE

Deposits in Slocan camp were divided into tw groupsfor the purposeof thisstudy. One hundredand thirty-eightdeposits forming the western two-thirds of the camp were taken as a training set forthe development of statisticalnodels to determinerelative 'value' of individual deposits. The eastern part of the camp contains 65, more dispersed depositsthat form a targetpopulation. Averge productiongrades and tonnagesare known forthese 65 deposits so real valuescan be compared withvalues calculated according to various models, and a rigorous test of thepredictive capability of a model can be conducted.

RELATIVE VALUE MEASURE

Sinclair(1979) has discussed the problem of relativevalue measures for multi-commodity deposits. Metal content is an idealvalue estimator for single commodity depositsbut where severalcommodities contribute significantly to total value of a vein deposit,for example, size is commonly a more meaningfulrelative value measure. Production ore tonnage,despite obvious limitations, can be used as an adequate estimator of relativedeposit size, and therefore of relativevalue.

We never know thetrue size (volume ortonnage) of a depositbecause we arenever sure that it hasbeen completely worked outor had all the reservesoutlined. Consequently, ore production tonnage is a biased estimator of size and of relativevalue that is always low relative to thetrue value. Furthermore, the bias may not be the same for all sizes because of selective mining, hand sorting, and so on. Nevertheless, as a relative measure,production tonnage is still adequate except for:

168 (1) many pairs of depositswith identical or nearly similar prcductj.on tonnages (a trivialcase), and (2) some depositsthat really are large despite the fact they have producedonly small amounts of ore to date.

thislatter case is not a problem,rather it is a situationthat we hope exists so that such deposits can be recognizedeventually by our predictive models.

In thepresent case, production tonnage is accepted as an adequate relativevalue measure. A probabilityqraph for production tonnage,s shownon Figure 1 forboth the training set and thetarget population, indicatesclose similarity of statisticaldensity functions between the tw areas. Tm populations are presentin identical proportionsin each area,although theaverage size is somewhat lower in thetiwget populationthan in thetraining set. The probabilitygraph for the training set has been partitionedinto two populations with mean sizes thatdiffer by severalorders of magnitude.This fact empllasizes the desirability of a numerical model that muld allow distinction between hightonnage deposits of economic interests and the low tonnage population of little economic interest.

L 12 10 30 50 70 90 E CUM %

Figure 1. Probabllitygraphs of ore productlon tonnage forthe tralning seIt lfilledclrcles) and thetarget populatlon (fllled tr1,angies). Tu, stralght llnes arethe two interpreted lognormal populatlonsdra nn throughconstructim polnts (open clrcles)derived fran thetrat nlng servecurve.

169 The principal metal contributor to value in Slocan camp is silver, which is plottedversus production tonnage on Figure 2. From this diagram it is difficult to ascertain whether two distinctivepopulations exist, each with its own averagegrade and dispersion of averagegrades, or whether, on averagethere is a continuousvariation in metal content and size (productiontonnage). Both possibilities will be tested,the continuous case using multipleregression and thediscontinous case using discriminant analysis.

2.5 I

a* .a a a 0 0 a a a a e a 8 -e a e e .* e me e 8* a 1.0 - a a a a a a

I I 0 1 .o 2.0 3.0 4.0 5.0 Log (tons) Figure 2. Scatterdlagran of average Ag gradeversus ore production (tonnage for trainingset). MULTIPLE REGRESSION MODELS

Multipleregression modelshave theform V = 6, + BIX1 + p2X2 ----- 6nXn + e, where v is a dependentvariable (value measure in our case), 6's are constants, e is thestandard error, and X's are independent(geological) variables. We haveexamined a variety of potential models and quote two here to illustratethe variation in results. Model 1 relates ore productiontonnage to thefour metal grades(silver, gold, lead, zinc);

170 model 2 relates oreproduction tonnage to three metals (silver,lead, zinc), and thepercentage of veinsulphides.

Model 1

Log (tons) - 1.6853 - 0.4222 log (Ag) - 0.0146 (Pb) - 0.2607 log (Zn) - 1.0429 10'3 (Au) R2 = 0.6565 S2 = 0.9770

Model 2 (omitting Au)

Log (tons) - 3.836 - 1.1784 log (Ag) - 0.0140 (Pb) - 0.4518 log (Zn) + 1.151 log (% sulphides) R2 = 0.3467 S2 = 1.1489

In bothmodels log transformations were used where dictated by the form of thedensity function. Statistically the results are significant. However, we want to know ifthe modelshave practicalapplication over theirentire range.

The fivehighest calculated and observedore tonnages for the training set are shown as a scatter diagram(Figure 3) for model 1. The fit j.s / CONTROL / 6r /

171 w I m. v-0 a 0 MODEL 1 -I

I I 0 1 2 3 4 5 6 Loglo (obs. tons)

Flglre 4. Observed versus calculatedore productlon tonnages for 19 deposltsIn the targetarea, Slocan canp. reasonably good visually and Figure 3 provides a quantitative appreciation of theinternal consistency of the model for largetonnage potential. However, a proper test of the model involvesapplication to thetarget population, a set of datanot used in developingthe model. Such a comparison is shown on Figure 4 for the 19 depositsin the training set for which averagegrades were availablefor all silver, gold,lead, and zinc. It is apparentthat the model is a relatively good forecaster1Other multiple regression models (for example, model 2) were not so successful and results will not be discussedhere, although high values for model 2 areplotted on Figure 3.

The model has been shown to be an adequateforecaster of relativevalue (oreproduction tons) of individualveins in Slocan camp. Unfortunately application of the model is limitedbecause average grades of thefour metals incorporated in the model are availableonly for about one-third of the deposits in the camp. It was forthis reason that we attempted to develop models omitting gold (for example, model 2). It is unfortunate thatgold grades are notavailable for more of thedeposits because this work has shown that gold is by farthe most importantsingle component in our models. Gold assays,along with silver, lead, and zinc, should be an integral part of evaluating anyvein deposit in Slocan camp.

172 DISCRIMINANT ANALYSIS

Discriminantanalysis is a method by which k clusters of datain n- dimensionalspace are separated as efficiently as possible by (k-1) n- dimensionallines. These 'discrimination'lines are arranqed between pairs of clusters such thatthe two clustersproject onto the line with a minimum overlap(Figure 5, from Klovan and Billings, 1967),.

Slocandata were divided into high-tonnage, medium-tonnage, and low- tonnagegroups based on thresholds of 1,000 tons and 16,000 tonsselected usingthe probability graph of Figure 1. The tm groups of average productiongrades corresponding to high and low-tonnagegroups =re transformed as in themultiple regression study and linear'discriminant'

2 4 b .I 1.0 10. 1W. PERCENTPOROSITY HORIZONTALPERMEABRITY Imd I A B

I PERCENT POROSITI

0246810 PERCENT SOPOSlTI D C Flgure 5. Conceptual model ofdlscrlmlnant functlon analysts as a mare efflclent means ofseparattng clusters In two-dimensionalspace than eitherof the varlablesalone; frm Klovan and BlIIlng (1967).

173 functions were calculated between adjoining data clusters.These functions were then used to classify deposits into high-tonnage low- and tonnage categories. Results for both the training set and the target population showed very high proportions of apparently correct classifications (that is,>EO per cent correct) when the discriminant classifications were compared with the corresponding known ore production tonnages.

The misclassifications of particular interest are those thought to be small based on low ore production tonnages, but which appear to be high tonnage according to the discriminant classification. Such deposits are listed in Table 1 for the training set. Of course, these results must be interpreted in light of the validity of the model. Consequently, the model has been applied to the same subset 19of deposits that formed the basis of a test of the multiple regression model. Results are summarized in Table 2 where it is apparent that more ambiguity exists than is apparent in the multiple regression model. Consequently, results of the discriminant analysis mst be viewed cautiously and further validation is desirable.

TABLE 1

Deposltswith lbl know productlonclassed as havlnghlgh-tonnage potential, by discrlmlnant function analysls of tralnlng setdeposits, Slocan canp.

Deposit Name ProductionProbabl I Ity'

lver RidgeSI lver 395 0.99 GreyCopper 66 0.86 Freddy0.91 Lee 817 Deadman 616 0.73 Leadsmith-Noonday 383 0.72 Echo and Echo Graphic 896 0.69

'The probability that a deposlt falls wlthin the hlgh-tonnagecategory according to a discrlmlnant modelbased on averagegrades of Ag,Pb, Zn, and Au.

TABLE 2

La-tonnage (<1,000 tons) and medium-tonnage (1.000-1.600 tons)deposits in target productionclassed as havlnghlgh-tonnage potential (>16,000 tons) by dlscrlminant model, S I ocan camp

Recorded Depos It Name ProductionProbabil lty* (short tons)

Ooherty 6.097 1.00 Black Fox 1.577 1-00 HighlandSurprlse 3; 027 0.96 Jackson 6,314 0.98 Glbson-Daybreak 676 0.92 F I lnt FI 351 0.85 We1 I lngton 0.74 1,961

'Probabilitythat the deposit falls In thehlgh-tonnage category according to the discrlmlnant model.

174 CONCLUSIONS

Statistical modelling of relative value of veindeposits appears an attainable goalproviding data of adequate quality are available. The studyreported here is only a smallpart of much more extensiveresearch intoexploration modelling. The principalapplication of statistical. models is in(1) identifying deposits with high tonnage potential which, todate, haveproduced only small tonnages, and (2) evaluating newly founddeposits in the camp to which a model applies. Multipleregression appears a more appropriateapproach to explorationmodelling in Slocan camp thandoes discriminant analysis. Gold assaysshould form an integral part inthe evolution of all deposits in theSlocan camp.

ACKNOWLEDGMENTS

Funds for this work were obtained from PrismResources Ltd., the British Columbia Ministry of hergy, Minesand PetroleumKesources, and the GeologicalSurvey of Canada. Technical assistance has been provided at various times by J.F.W. Orr (deceased) and A. Bentzen.

REFERENCES

Godwin, C.I. and Sinclair, A.J. (1979):Application of Mul.tiple RegressionAnalysis to Drill TargetSelection, Casino Porphyry Copper-Molybdenum Deposit, Yukon Territory, C.I.M., Transactions, Vol. 88, pp. B93-Bl06. Harbaugh, J.W., Doveton, J.H., and Davis, J.C. (1977):Prclbability Methods in Oil Exploration, John Wiley and Sons, New >!ork, 269 pp. Kelly, A.M. and Sheriff, W.J. (1969): A StatisticalMamination of the MetallicMineral Resources of British Columbia, Symposiumon Decision-making in Mineral Exploration, 11, ExtensionDept., University of British Columbia, pp. 221-243. Klovan, J.E. and. Billings, G.K. (1967):Classification of Geo1ogica:L Samples by Discriminant-functionAnalysis, Bull., Cnd. Pet.Soc., Vol. 15, No. 3, pp. 313-330. Orr, J.F.W. and Sinclair, A.J. (1971): A Computer-processi.ble file for Mineral Depositsin the Slocan and SlocanCity Areas of British Columbia, Western Miner, Vol. 44, pp. 22-34. Sinclair, A.J. (1974):Probability Graphs of Ore Tonnages j.n Mining ICamps - A Guide to Exploration, C.I.M., Bull., Vol. 67, pp. 71-75...... ( 1979): Preliminary Evaluation of Summary Production Statistics and location Data for Vein Deposits, Slocan,Ainsworth and SlocanCity Camps, SouthernBritish Columbia, Geo!.. Surv., Canada,Current Research, Part E, Paper 79-1B. pp. 173-178. Sinclair, A.J. and Woodsworth, G.J. (1970):Multiple Regression as Method of EstimatingExploration Potential in an Area near Terr.sce, B.C., Econ. Geol., Vol. 68, pp. 998-1003.

175 RAPID ANOMALY RECOGNITION AND RANKING FOR MULTI-ELEMENT REGIONAL STREAM SEDIMENT SURVEYS

By P. Matysek, A. J. Sinclair, and W. K. Fletcher Department of Geological Sciences University of British Columbia

INTRODUCTION

As part of our continuing study of rapid, thorouqh evaluation procedures for multi-element stream sediment data (for example, Sinclair and Fletcher, 1979; Matysek, et al., 1980), we have developed a systematic, computer-oriented method of recognizing and ranking anomalous samples. Our detailed procedure utilizes the type and quality of data incorporated in various regional programs undertakenby the British Columbia Ministry of Energy, Mines and Petroleum Resources but becan adapted easily for data for other programs.

Regional multi-element stream sediment surveys of the type carried out in British Columbia under termsof the Uranium Reconnaissance Program contain coded informationon the principal rock unit forming the provenance region of each sample. Consequently, the following procedure for determining multi-element background modelsis intended to be applied to sample subsets based on provenance (rock type). Rock-type coding for this purpose is never perfect: some basins may be underlain by two or more important rock types, other drainage basinsmy be miscoded, perhaps because of the scale of geological base maps available. In any case it is apparent that some apparently anomalous metal concentrations arise from incorrect assignment of the dominant rock type or from mixing of sediments derived from several rock types.

GENERAL METHODOLOGY

Our general approach to recognition and ranking of anomalous samples is summarized on Figure 1. In brief the method involves the following steps:

(1) Sorting of data into provenance groups, that is, predominant rock type in drainage basin above the sample.

(2) Evaluation of simple statistics and probability graphs for each element in each provenance group.

(3) Threshold selection using the methodof Sinclair (1976) to isolate anomalous samples from background samples.

(4) Selection of one or more elements to serve as the focus of the study (for example, zinc).

176 .nomalous rod.. I Iluroui

Figure 1. Sequential approach to anomaly recognltlon and rankllg.

(5) Backward stepwise regression of each provenance group to develop background models for zinc in terms of other elements.

(6) Ranking individual samples in terms of (a) their contamination code and (b) the regression model and threshold.

(7) Output of sample information in a manner convenient for practical use in follow-up examination.

SORTING INTO PROVENANCE GROUPS

Data for each provenance group shouldbe dealt with separately. Means and standard deviationsof all raw and log-transformed metal abundances provide insight into levels of abundance, dispersion, and general aspect of population densities (histogram). Correlation coefficienss indicate metal associations of geological importance (for example, Si:nclair and Tessari, 1980). If only background values are considered, these associations commonly reflect differences in background environments and are not related directly to anomaious samples.

THRESHOLD SELECTION

Separation of background and anomalous samples is essential'to our method because it leads directly to statistical models for backgrou~ld metal abundances. Consequently, the method of thresholdrecogniti'm is important. We have adopted the probability graph approachOE Sinclair (1976) because this procedure is systematic and has been shorn by numerous examples to provide effective thresholds for many types of geochemical data.

177 ELEMENT SELECTION

We must decide which elementor elements are of directconcern to our search problem. Are we interestedin silver-lead-zinc, copper- molybdenum, tungsten-uranium, or others? Of course, we may want to investigate many associations of thesort listed, but in our approach eachassociation would be dealtwith separately. Within a particular metal association it my not be necessary todeal thoroughly with all elementsbecause some may be redundant,others may not show adequate geochemical contrast, and still othersmy present limitations resulting from analyticalproblems. In our case we will usezinc data as a basis for evaluatingregional silt samples interms of silver-lead-zinc and lead-zincassociations typical of our studyarea (map-area 82F).

MULTIVARIATE MODELLING OF BACKGROUND VALUES

Multipleregression has been shownby many to be an effective method of demonstratingempirical relationships between a particularelement (dependentvariable) and a group of otherelements (independent variables).In many cases a highproportion of the variability of the dependentvariable is explainedin terms of variationsin the independent variables(Sinclair and Fletcher, 1980). Where such methods are applied to backgroundsamples only, the abundance of a dependentvariable (for example, zinc) can be expressed as a linear combination of theabundances (orlogarithms of abundances) of many otherelements to provide a multivariate background model.

We have experimentedwith two approaches to the selection of samples used toestablish a multipleregression model. Inour firstattempts sample selection was based on the dependentvariable for a singleprovenance groupwith only those values below thethreshold (based on probability graphs)being selected. In a later refinement we edited the database for a single provenancegroup by omittingsamples that were also obviously anomalous withrespect to any of theindependent variables.

The specific method we use for multivariate backgroundmodelling is backward, stepwise regression which starts with all independentvariables inthe data base and sequentiallydrops those that make no statistically significantcontribution to explaining the variability of the dependent variable.Eventually a point is reached where all remainingvariables arestatistically significant (at the 0.05 level,for example) and an equation is obtained of the form Log (zn) = Bo t 6, log (X,) + 6, log (x,) + f19 log (x,) etc. where 6's are constant and Xi's are abundances of metal i.

RECOGNITION AND RANKING OF ANOMALOUS SAMPLES

For each sample we determine a series of ranks from 0 to 3 by comparing theobserved value of thedependent variable with the valuescalculated

178 by each of the provenancegroup multivariate models. Significance of the rank numbers is shownon Figure 2. We thencalculate a 4-digitranking code foreach sample where the first digit is the number ofrock types for which rank 3 was obtained,the second digit is the number of rock typesfor which rank 2 was obtained, and so on. If there are sevenrock types all withvery high zinc values (rank 3) theranking code muld be 7000; inanother case rankmight be (3) for two rocktypes, (:!) for three rocktypes, (1 ) for two rocktypes, and (0) for one rock. type to give a ranking code of 2321.

The main advantage of thisprocedure is as a refinement in theselection of anomalousvalues relating to theprobability graph procedure and the assigning of relativepriorities to anomaloussamples. Values above tl (Figure 2) arerecognized as being anomalous without the aid of multip1,e

METAL (log ppm obs.)

Flgure 2. Sample ranklng In relatlmto flelds on a plot of observed value versus a value calculated from a multivariate model.

regression. In addition, however,values below tl that depart substantially from theexpectation according to a multiple regression model (1 and 2 on Figure 2) arealso out of the ordinary and warrant examination. In particular, w are interested in thosevalues below t.l thatare much higherthan the correspondingcalculated values. Such samplesare anomalous in one element,relative to a linear combination of other elements. On Figure 2 thesuggestion is made graphicallythat samples are anomalous if observedvalues are more than two standard errorsgreater than values calculated according to the multiple regression model.

'1 79 OUTPUTPROCEDURES

We havedesigned an outputsystem by whichsamples can be ordered in terms of decreasingpriority for follow-up exploration. All anomalous samplesrecognized by theforegoing procedures are ranked according to theestimated likelihood of sample contamination from such factors as known mines, man-made metallicfeatures, or fertilizer, on a scale of 0 to 3. Our first rank of anomaloussamples is based on this coded parameter,zero contamination being of most interest. Within this group we code a sample foreach background model as 3, 2, 1, or 0 as described previously and a 4-digitranking code is used to list sampleswithin each contaminationgroup in order of decreasingranking code. Mcationsfor eachsample are listed as is the observedabundance of the dependent variable and the sample number. These items are arrangedin such a manner as to promote efficiency of evaluation of eachsample. In addition, he useplot locations ofanomalous samples with their identification number and rankingcode.

CASEHISTORY (MAP-AREA 82F)

Multi-elementdata are available for sample sites in map-area 82F at an approximatesample density of one sample per 12 squarekilometres. Samples areanalysed for zinc, lead, nickel, cobalt, manganese, copper, mercury,tungsten, and molybdenum. Samples here grouped initially on the basis of coding as to dominantrock type inthe provenance region. Data foreach element in each provenance group were examined as a probability graphand a thresholdselected separating two populations(presumably anomalousand background) using the method of Sinclair (1976). We chose to examine zinc as the dependentvariable described here because of the associationsilver-lead-zinc in known veindeposits in the area. Background multivariate models forzinc in terms of other elements were obtainedfor each of theseven provenance groups for which we have adequatesamples. Three of these models are summarized in Table 1 to illustratethe type of results obtained.Statistics for all seven provenancegroup models for zincare given in Table 2 to illustrate the statistical quality of the background models.

All samplescoded in one of the sevenprovenance groups for which we couldcalculate background models were treated by each of thebackground equationsseparately. me calculatedzinc background according to a given model was then compared withexpectations for that model so that foreach background model a sample received a ranking from 0 to 3 inclusive(compare Figure 2). In our caseeach sample was rankedseven times, once foreach model. Theserankings were accumulated into a singleranking code. Samples recognized as anomalous orpotentially anomalous were dividedinto three contaminationclasses with priority decreasingas certainty of contaminationincreases. For each contaminationcategory samples are ranked according to decreasing numeric value of theranking code. An example is shown inTable 3, where a small part of the0-contamination category is listed.

I80 GRANITE

LOX (zn) 0.4726 0.0713 log (.Cu) + 0.2420 log (Pb) f 0.0529 log (Ni) + 0.3994 log ("I) + 0.4189 log (Fe) - 0.2334 log (Co) R2 = 0.62 Se = 0.1277 n = 393

QUARTZITE

log (Zn) = 1.1020 + 0.2721 log (Pb) + 0.1316 log (Ni) + 0.4891 log (Fe) i-0.1412 log (Mo) + 0.0399 log (Hg) R2 - 0.74 se = 0.0915 n = 287

SCHIST

log (Zn) = 0.8392 + 0.4100 log (Pb) + 0.2244 log (Nil + 0.560:; log (Fe) + 0.2412 log (W) R2 = 0.76 Se = 0.1008 n = 27

TABLE 1. EXAMPLES OFMULTIVARIATE REGRESSION BACKGROUND MODELS FOR ZINC MAP-AREA 82F

PROVENANCE GROW

GRNT QRTZ SLTE ANDs ARGL GNSS SCST

n 287 393100 57 56 53 21

R .86 .79 .84 .84 .92 35 .87 R2 .62 -74 .70 .70 .as .71 .76 s, .1271 .1184 .0915 .0812 .lo31.0940 .loo8 - d

TABLE 2. SUMMARY STATISTICS FORMULTIVARIATE BACKGROUND ZINC MODELS SEVEN PROVENANCEGROUPS MAP-AREA 82F

181 17 53610 5457758 7000 354 ORTZ 0 773118

28 507056 55t8881 7000 359 SCST 0 777314

29 476055 5450823 7000 345 ANOS 0 77 1076

30 482531 5461913 7m 314 AM)S 0 719 I26

31 501599 9526605 7000 309 SLtE 0 7772?4

31 4896015443717 7000 304 SLTE 0 713056

33 4848075518468 7000 199 GPNT 0 77 I I98

34 4874963456218 7000 195 SLTE 0 173086

35 416166 5487364 7000 199 GRNT 0 777198

36 4805075487605 TWO 199 GRNT 0 777136

37 476597 5458197 7000 174 ANOS 0 77 I103

38 4750755488439 7000 119 GIINT 0 777302

39 502653 5508315 7000 279 SL7E 0 777159

40 1796465495841 7000 164 ARGL 0 771100

41 4949635528151 7000 155 SLTE 0 771306

41 4747925451528 70W 144 ANOS 0 771077

43 4899165458581 70W 239 SLTE 0 7751 I6

.4 509423 5500800 6iW 114 SCST 0 773237

45 5149145447471 61W 114 OR12 0 775100

46 4481855533845 GI00 214 SCST 0 779163

47 4621645538222 6103 109 GRN7 0 775328

48 487885 5451555 6 100 191 GRNT 0 777112

49 4894435499169 6 100 198 GPNT 0 777212

50 549914 ssla2& GWI I91 ORTI 0 777 182 SI 481276 5463771 43w IO6 APGL 0 771094 52 4844875484729 4300 181 CRNT 0 771203

53 1417795442706 4W3 186 GNSS 0 77501s

TABLE 3. PART of A TABLE LISTING ANMALOUS SAMPLES IN ORDER OF DECREASED RANKING CODE”

From a total of1 259 samples, this procedure produced115 anomalous samples in the 0-contamination category. Our procedure is to list these samples in tabular form in Table3 and to produce computer-drawn plots of anomalous sample locations as illustratedon Figure 3.

In addition to ranking information, original raw data, and coordinates, the output table contains a simple consecutive numeric identifier used for clarity on the map output and permitting easy combined use of the tabulated data and the output map. The output map is of particular use because it identifies the most obvious anomalous samples(for example, 7000) from those that might escape detection (for example,0520). The scale of the location plot shouldbe identical to geological base maps of the area so the two can be studied together without ambiguity. We tested sensitivity of the regression procedure for determininga multivariate background for zincby establishing such models basedon two training

182 .6100 6 100 (44) (49) 0403 (61) *O 106 0403 (83) (67) 7000 (3.8) 7000 (36) .0204 a7000 (36) (72) (33) 117O00' W 0403e a 4300 (66) (52) 49'30' N

.060 1 + (63)

0601 (60)

0106 (86)

0502

Flgure 3. Plot of an area of anomalous samples redraftedfran computer output. sets: (1) all samplesindicated as having background zincvalues, and (2) the same data set minus any samples that appearedto be anomalous in any elementother than zinc. Tables 1 and 2 arebased entirely on thesecond training set. Figures 4 and 5 illustratethe contrasting results obtained in backgrounddefinition. It is clearthat the 'cleaner' data set (number 2 previously)leads to a bettermultiple regression relationship,that is, withless scatter of calculated and observed values. The problemwith using the second training set is that more work is requiredto set it up and more samples will be included in the anomalouscategory.

183 , I

2.2 -

m 2.0 - 0 Y

Log Zn (obs.) Figure 4. Observed versuscalculated zinc values for provenance group, 'ARGL.' map-area 82F; calculatedvalues based on a mdel determined fran all saples wlth background zlnc va 1 ues.

JISCUSSION

The methodology described here would appear to have a wide range of applications to geochemical data evaluation, perhaps withminor modifications to suit particular data sets. For example, many geochemical surveys my not record the likelihood that a sample is contaminated, and this level of ranking might have to be omitted.The precise limits tothe coding regions illustrated on Figure 2 can be changed to suit particulara bias to anomaly selection, resulting in a slightly different listing of anomalous samples.

One of the serious problems is the question of initial grouping of data on the basis of dominant rock type that underlies the drainage basin of each sample, a classification which is fundamental to our procedure.A substantial amount of effort is required to code this rock-type information even if the data are available. If rock type has not been coded it may be necessary to use some less satisfactory methodof grouping data, such as the use of factor analysis to provide an approximation of background geology for each sample. In some environments, of course, some other parametermy be more useful than rock type for grouping data.

184 Log Zn (ob4

Flgure 5. Observedversus calculatedzlnc values for provenancegroup, 'ARGL,' wp-area 82F; calculatedvalues based on a model detenlned from thosesanples wlth zlnc background valuesthat also are not anomalous In any otherelement (that is, a 'cleaner'subset of the data used forFigure 4).

CONCLUSIONS

A method of anomaly selection and rankingfor multi-element regional stream sediment data has been described. The procedure offers the following advantages:

(1) The method is rigorous in making useof established statistical methods for treating geochemical data such as a probability graph analysis and backward stepwise regression.

(2) The procedure is computer based and is rapid and thorough.

(3) The methodology ensures that some anomalous values which are not obvious (that is, are not higher than a simple threshole,) will be recognized. (4) A novel ranking procedure is described that assigns relative priorities to samples for further investigation. Details of the ranking procedure are subjective but a system of ranking codes clearly describes the manner in which a sample is anomalous.

(5) Because samples are tested against every rock type, the procedure incorporates an evaluation as to whether other rock types might be contributing to the provenance area of a particular sample. Possible additional rock types are identified and can be compared with available geological maps.

ACKNOWLEDGMENTS

This project has been funded by the British Columbia Ministry of Energy, Mines and Petroleum &sources.

REFERENCES

Matysek, P., Fletcher, W.K., Sinclair, A.J., and Bentzen, A. (1980): A Preliminary Evaluation of Categorical Field Observations for Regional Stream Sediment Samples, B.C. Ministry of mergy, Mines & Pet. Res., Geological Fieldwork, 1980, Paper 1981-1, pp. 148-158. Sinclair, A.J. (1976): Applications of Probability Graphs in Mineral Exploration, ASSOC. Explor. Geochem., Special Vol. No. 4, 95 pp. Sinclair, A.J. and Fletcher, W.K. (1979): Evaluation Procedure for Geochemical Data, Uranium Reconnaissance Program,B.C. Ministry of Energy, Mines & Pet. Res., Geological Fieldwork, 1979, Paper 1980-1, pp. 130-141. Sinclair, A.J. and Tessari, O.J. (1981): Vein Geochemistry, An Exploration Tool in Keno Hill Camp, Yukon Territory, Canada, Jour. Geochem. Expl., Vol. 14, pp. 1-14.

186 STRUCTURAL SETTING ALONG THE NORTHWEST FLANK OF FRENCHMAN CAP DOME MONASHEECOMPLEX

(82M/7)

~y J. Murray Journeay Department of GeologicalSciences, pleen's University

INTRODUCTION

The MonasheeComplex of southeasternBritish Columiba is one o:E many metamorphiccore complexes in theinternal zoneof the western Cordillera (see Crittenden, Coney, and Davis, 1980). The MonasheeComplex consists of Aphebian basement gneiss and mantlingmetasedimentary racks which are exposed in an elongatefenster within Proterozoic to MiddleMesozoic coversequences of theSelkirk Allochthon (as defined byRead and Brown, 1981; and shown here on Figure 1 ).

Frenchman Capdome, the northernmost of fourstructural culminations with the MonasheeComplex, records an extensivehistory of complex folding, overthrusting (Dl, D2, and D3) and late-stagearching (D3/Dq) believed to be associated with Jurassic to Late Cretaceous/EarlyTertiary (?) periods of crustalshortening (Read and Brown, 1987 ). Superposed on this structural setting is a prominent set of northerlytrending fractures, dyke swarms, and normal faults (Dq) related to a regional, more brittle episode of EarlyTertiary crustal extension(Price, et al., 1981 1.

Middle to upperamphibolite facies regional metamorphism is associated withsecond generation folding in thenorth-central Frenchman Capdome (Dz) and is believed to be correlativewith Middle Jurassicregional metamorphism developed in structurallyoverlying rocks of theSelkirk Allochthon(for further discussion, see Read andWheeler, 1976; Pigage, 1977; Read and Brown, 1981 ).

Coherentlithostratigraphic successions (Brown and Psutka, 1979; Hay and Brown, 1981) andmajor structural and tectonic elements(wheel,er, 1965; HOy, 1979; Brown, 1980) havebeen successfully tracedaround the northern margin of Frenchman Capdome from the Columbia River fault zone tothe Cottonbeltregion north of RatchfordCreek (Figure 2). A similar lithostratigraphicsuccession has been tracedaround the soutklern umrgin of the dome from theplydeformed Jordan River area (Fyles, 15170; Brown andPsutka, 1979) to theheadwaters of PerryRiver and Myoff Creek (Hoy,, 1980; Hoy and McMillan, 1979; McMillan, 1973). These studieshave demonstratedboth stratigraphic and structuralcontrol on theoccurrence of stratiformlead-zinc mineralization within mantling metaseclimentsof Frenchman Capdome.

The purpose of thisstudy is to complete stratigraphic and structural correlationsalong the west flank of Frenchman Capdome as shownon

187 FI gure the

ned

188 Flgure 2. Regionalgeologlc map of the Frenchman Cap dmdellneating sources of detalled mapplng data, and major I Ithostratlgraphic,structural, and tectonic elements; modlfled frm a recentregional +?eologlc compilatlon map of theeastern margin of the Shuswap Complex (Hoy and Wan, 1981). Mp unltsare referenced on Flgure 3. The results of Journtpay (this report)are not Included for the north-central Frenchnan Cap done.

Figure 2. Specificobjectives are: (1) to map theminera1i:zed 'Cottonbeltsequence' frm its typelocality on GraceMountain (Hoy, 1979) tothe headwaters oE PerryRiver; (2) totrace the KirSyville-Grace Mountain syncline(Wheeler, 1965; HOy, 1979) intorefolded structures of thePerry River-Myoff Creek region (McMillan, 1973) : (3) to extend mapping of the Monashee d&collement (Brown, 1980a,1980b) as Ear southas, possible; and (4) to present preliminary interpretations of the deformation and structural evolution of thenorthwest Frenchman Capdome.

189 This report is basedon the results of detailed mappingin the Cottonbelt (Hoy, 1979). Perry Fiver (McMillan, 1973), and Fatchford-Myff Creek regions (Journeay, this study) combined with three-dimensional structural modelling by the author during the 1980/81 seasons (Figure 2). The results of this study are partof an M.Sc. thesis on the structural evolution of the north-central Frenchman Cap dome in progressween' at s University under the joint supervision ofJohn M. Dixon, Dugald M. Carmichael, and Richard L. Brown (Geotex Consultants Ltd.).

STRATIGRAPHY

Three main lithostratigraphic subdivisions are recognized along the west flank of Frenchman Cap dome (Brown and Psutka, 1979; Hoy and McMillan, 1979; Hoy and Brown, 1981; and Figures2 and 3). Exposed in the deepest structural levels of the dome ais sequence of intercalated orthogneiss and paragneiss yielding Fb-Sr whole rock ages of 2.17Ga (Armstrong and Brown, in prep.). Unconfomably overlying this basement complex isa mantling sequence of platform-type metasedimentary rocks locally intruded by a suite of alkalic gneiss tentatively dated at 773Ma (Okulitch, et al., 1981). These data suggest possible time-stratigraphic correlation of mantling metasediments with the Furcell Supergroup (Okulitch,al., et 1981). The Monashee d6collement separates mantling metasedimentsfrom an allochthonous sequence of pegmatite-laced feldspathic paragneiss and amphibolite that maybe correlative with Hadrynian sequences of the Horsethief Creek Group (Brown, 1980).

APHERIAN CORE GNEISS

Aphehian core gneiss canbe subdivided into lower paragneiss, intermediate orthogneiss, and upper paragneiss in the Patchford-Bourne Creek region (Journeay, in prep.). The structurally lowest exposed unit (In) consists of intercalated biotite-quartz-feldspar paragneiss, pelitic and semi-pelitic schist, and quartzofeldspathic gneiss of unknown thickness, and is overlain and locally intrudedby alkali-feldspar augen gneiss (1B). Feldspar augen gneiss grades upward into intercalated garnet-hornblende-clinopyroxene gneiss and alaskitic gneiss (le), banded and migmatitic biotite-hornblende leucoqneiss (lD), and homogeneous biotite- quartz-feldspar gneiss (1E). The upper paragneiss (2) unit consists of a heterogeneous sequence of semi-pelitic schist, quartzofeldspathic gneiss, amphibolite, biotite-feldspar augen schist, and some quartzite. Biotite- feldspar augen schist is locallyabsent due to erosion priorto deposition of overlying autochthonouscover rocks.

AUTOCHTHONOUS COVER (HELIKIAN 7)

Mantling metasedimentary rocks along the west flank of Frenchman Cap dome attain a stratigraphic thickness of nearly 2 kilometres. The succession consists predominantly of quartzite, quartz-mica schist, semi-pelitic and pelitic schist, biotite-quartz-feldspar paragneiss, calc-silicate, and thin but laterally continuous marble horizons. Within this sequence,

190 Figure 3. Geologiccompllatlon map of thenorthwest flank of Frenchman Cap dm; geofogy afterMcMIIlan (1973), f6y (19791, and Journeay (thlsreport). Sources of dataare referenced on Flgure 2. basalquartzite (3q) and marblelayers (Wheeler, 1965; E'yles, 1970; McMillan, 1973) and locallycarbonatite and mineralizedlayexs (McMillan, 1973; Hay, 1979) are usedas marker unitsto delineate major structural elements.Detailed sections of particularlyuseful markerhorizons, and theirposition in a stratigraphicsuccession due south of Rat.chford Creek, arepresented on Figure 4. Locallydefined stratigraphic sections in remaining portions of the platformsequence exhibit lateral facies variationsthat prohibit detailed regional correlation.

191 1 1 \ + ul .-fn al C 0 m

I -0 m E 0 .-

* m

192 An instructive example of lateral facies changesoccurs alon'3 the upper limb of theKirbyville-Grace Mountain syncline between Grace Mountain and Ratchford Creek (Figure 3). Calc-silicate and micaceous schistnear GraceWuntain grade laterally into fine-grained biotite-quartz-feldspar paragneiss and biotiteschist to thesouth. It is unlikelythat these! are structurallyinduced lithologic variations because of the perseverance of both a marble-carbonatitemarker to the east and marb1.e- quartzitehorizons to the west. Primarysedimentary structures indicatingstratigraphic top directionsare poorly preserved in complexly deformedzones throughout the fieldarea. Crossbedding has been locally observed in basal quartzite units above thebasement-cover contact andl confirmsthe structural interpretation.

ALLOCHTHONOUS COVER (HADRYNIAN 7)

Allochthonouscover sequences have not yet been mapped in detail but consistprimarily of feldspathic grits, amphibolite,hornblende gneiss, micaceous schist, and calc-silicate,abundantly laced with both concordant and discordantpegmatite. This distinctive sequenceforms the hanging wall of the Monashee d6collementalong the west flank of Frenchman Cap dome and is apparentlytraceable into known exposures of Horsethief Creek Group alongthe northern margin of the dome (Brown, 1980).

DEFORMATION

Structuralanalysis in thenorth-central Frenchman Capdome hasoutlined threegenerations of penetrativedeformation that are believedto be associatedwith Jurassic to Late Cretaceous/EarlyTertiary (?) periods of crustalshortening (Read and Brown, 1981). Each generation(Dl, D2, and D3) represents a period of progressivedeformation which can be recognized in thefield by therelationship ofminor structu.resto regional metamorphic mineral assemblages, and by consistentoverprinting relationships on bothmacroscopic and mesoscopic scales. The oldest recognizable structures in the north-central menchman Cap dome deform both Aphebian basement gneiss and autochthonousmetasediment,ary rocks that unconformably overlie them. Thissuggests that pre-Helikian (7) deformationhas either been pervasivelyoverprinted by younqer orogenesis or is non-existent.Structures related to all three generations of deformationare superposed and modified by a prominent set c8f northerly trendingfractures, dyke swarms, andnormal faultsassociated with a. younqerepisode (Dq) of regional crustal extension (Price, et al., 1981). A similar hierarchy of deformation is manifestin afljacent parts of Frenchman Cap dome and has been previouslydescribed by Wheeler (1965),Fyles (19701, McMillan (19731,PSutka (19781, Brown and Psutka (1978), Hoy (1979), Brown (1980a.1980b), and Read and Klepacki(1981 I.

Serialcross-sections and sequentialdeformation diagrams presented in Figures 5 and 6 summarize boththe geometryand interpretedstructural evolution of thenorthwest Frenchman Cap dome.

7 193 L mc -0

194 Dl STRUCTURES

First generation megascopic folds are characterizedby easterly verging, shallow plunging isoclines that have been variably reorienta?dby subsequent deformation. Two orders of first generation iso8:linal folds are recognized in the field area and can be tracedadjxent into parts of the north-central Frenchman Cap dome (Journeay, in prep.).

The Kirbyville-Grace Mountain syncline (Hoy, 1979; Brown, 1'380) has exposed limb lengths in excess of7 kilometres and dominateis the structural setting of the northwest flank of Frenchman SomeCap (Figu.res 3 and 5). This structure is definedby stratigraphic facin'g directions in lower quartzites of unit 3, and by the repetition of a distinctive marble-carbonatite marker in unit 4 (Hoy, 1979). The axial surface trace of the Kirbyville-Grace Mountain syncline extends from the southern headwaters of Kirbyville Creek (Hoy, 1979; Brown, 1980a), through the Cottonbelt region (Hoy, 1979), and has been projected south of Fatchford Creek by Hoy and McMillan (1979). Both limbs of the Kirbyville-Grace Mountain syncline havenow been traced to the west branch headwaters of Myoff Creek and Perry River where they are refoldedby mcroscopic second generation folds (Figures 3 and 5). The closure of the Kirbyville-Grace Mountain syncline is correlated with the westernmost isoclinal fold closure of McMillan (1973).

Second order, first generation isoclines are well exposed in the hinge of a major second generation fold near the headwaters of Perry RLverand Myoff Creek (Figures 3 and5). Basal quartzite of unit 3 delineatesa refolded anticline-syncline pair (McMillan, 1973) with limb lengths of 3 to 4 kilometres. These first generation isoclines structurally underlie the southern extension of the Kirbyville-Grace Mountain syncline. Ar:ial surfaces of these second orderDq structures can be traced around the hinges of major second generation foldsin the Perry River-Myoff Creek area (McMillan, 1973; and FigureS), and extend into the north-centra.1 Frenchman Cap dome where they become periclinal in character (Journeay, in prep. 1. The apparent vergence and limb length of this first generation anticline-syncline pair suggests that it may be either a second order structureon the lower limbof the Kirbyville-Grace Mountain syncline, or related toan episode of Dl deformation prior to or synchronous with emplacementof the Kirbyville-Grace Mountain syncline (Figure 6).

A homotaxial northwest-facing sequence of lower quartzite (3q), calc-. silicate (3c), interlayered pelite-quartzite (4p,q) and marble-carbonatite (4% ct) is exposed on adjacent limbs of two first generation isoclinal folds near the western headwaters of Perry River (Figure 3). The repetition of this distinctive sequence strongly suggests that the Kirbyville-Grace muntain syncline may have been displaced northeastward along a low-angle thrust fault relative to underlying Dl isoclinal folds (Figures 5 and 6). Displacement along this fault clearly pre-dates D2 deformation and Middle Jurassic regional metamorphism. The lateral extent and timing of this fault with respect to the developmentof second order Dl isoclinal folds have not yet been determined.

195 ...I 0

01 0

196 On a mesoscopic scale,first generation folds generally contain an axial planar fabricthat i.s subparallel to compositionallayering along attenuatedfold limbs. This axial planar fabric is defined by the flattening of quartz and feldspar, and by thepreferred orientation ,of platy metamorphic minerals.This suggests that first generation folds weredeveloped eitherduring initial stages ofEarly-Middle Jurassic regional metamorphism or an olderepisode oflow-grade metimorphism. The possibility of multi-episodic first generationfolding is recognized,but hasnot yet beendocumented.

D2 STRUCTURES

The notabletransition from first and second order Dl isocl.ina1folds alongthe northwest flank of Frenchman Capdome to the complexly refolded structuressouth of Fatchford Creek reflectsthe spatial distribution of macroscopicsecond generation folds below the Monashee d6collement. Basalquartzite of the mantling platform sequence (3q) outlines two broad reclined,second generation fold closures which form a distinctive Z- shaped structureadjacent to the headwaters of PerryRiver and Myoff Creek (Figures 3 and 5). Thisreclined fold structure (McMillan,1973) is characterized by west-southwestdipping axial surfaces and west- southwest-plungingfold axes that are subparallel to a prorninent southwest-northeast-stretchinglineation in all units below the Monashee d6collement. A nearlyidentical fold style is observed on a mesoscqpic scale and is well developedthroughout the northern Frenchman Cap dolae.

Axial surface traces ofmegascopic ~2 foldsare truncated along the western margin of Frenchman Capdome by the Monashee d6collement and: associatedsecondary shear zones. Second order D2 asymmetricfolds can be tracedover the culmination of north-central Frenchman Zapdome where theyreverse their plunge direction and are overprinted by northerly trendingthird generation folds (Journeay, in prep. ). A verySimi1a.r Set ofsecond generationreclined folds are documented by Read and Klepacki (1981) in thestructural depression between Frenchman Capdome and I'hor- Odin nappe.

Consistentoverprinting relationships on bothmacroscopic and mesosoopic scales indicatethat D2 folds were developedduring Middle Jurassic syn-metamorphic deformation(Figure 6). Thisinterpretation is Supported by thewidespread occurrence of medium grademetamorphic minerals such as kyanite and sillimanitethat are orientedwith their long axes subparallel to second generationfold axes and prominentsouthwest- northeast-stretchinglineations.

The Monashee d6collement (Brown, 1980a,1980b; Read and Brown, 1981) is definedalong the western margin of Frenchman Capdome by a widezone of mylonitizedfeldspathic grits and semi-pelitic metasedimentaryrocks:. The fault zone appearsto be a major structural discontinuitysepara.ting platform-typemetasediments in the footwall from rocksthat may be correlativewith the Horsethief Creek Group in thehangingwall (for furtherdetails see Read and Brown, 1981).Preliminary fabric analyses

197 of fault zone mylonites from severalalpine localities south of Ratchford Creeksuggest an easterlysense of displacement of hangingwallwith respect to footwallrocks. This interpretation is based on the asymmetry of minor folds, and theangular relationship of flatteningfabrics with respect tonylonitic foliations in thefault zone.

D3 and Dq STRUCTURES

Thirdgeneration folds are easterly verging, post-metamorphic structures withnorthwest-trending axial surfaces(Figure 6). Inthe north-central Frenchman Capdome, thirdgeneration fold axes are refolded by broad, westerlytrending open foldsthat are believed to be associatedwith subsequentarching events. Along thewestern margin of Frenchman Cap dome, thirdgeneration folds are well developednorth of mtchford Creek butdecrease in amplitude and intensity towardthe polydeformed Myoff Creek-PerryRiver region. Fold styles vary fromasymmetric kink folds and crenulationsin well layeredmetasedimentary rocks to broad open folds andwarps in massivequartzofeldspathic gneiss of the basement complex. Thisvariation in fold style may reflect a competency contrast between a rigid basement and a thinlylayered metasedimentary cover that was accentuatedduring waning stages of regional metamorphism. On a mesoscopic scale, third generation folds crenulate medium grade metamor- phicminerals anddeform prominent southwest-northeast stretching linea- tionsindicating a late to post-metamorphic age of deformation(believed to be youngerthan Late Jurassic and olderthan Eocene).

Late stagearching, whichproduced theoverall domal character of the northern Monashee Complex, apparentlypost-dates third generation deformation(Figure 6). No minor structuresassociated with this arching event are recognized in thefield area (Fiqure 3) west of Myoff Creek or theheadwaters of RatchfordCreek.

Overprinting all earlierstructures in thenorthern Frenchman Cap dome is a prominent set of northerlytrending brittle extension fractures and associatedbimodal dyke swarms. These fracturesrarely exceed 3 to 5 metres in width and are commonly filled by undeformedlamprophyre dykes and/orgranitic pegmatites. Overprintingrelationships in one alpine localityindicate that the emplacementof lamprophyre dykes (Eocene ?) post-datesthe intrusion of granitic pegmatites.

The PerryRiver fault (Figures 3 and 5) is theonly major normal fault exposed inthe field area, and clearlypost-dates earlier generations of deformation.Displacement of second generation macroscopic fold axes in thePerry River-Myoff Creek regionindicates several hundred metres of relative west-side-downnormal movement acrossthe westerly dipping fault surface.

Similarbrittle extension features havebeen describedthroughout the Frenchman Cap dome (Wheeler, 1965; Fyles, 1970; McMillan, 1973; Psutka, 1978; Brown and Psutka, 1978; Read and Klepacki, 1981) and apparently record a transition from periods of crustal shortening (Dl, D2, and

198 D3) to periods of crustal extension (Dq). The nature of thh transition and its tectonic implications for the Early Tertiary evolution of Frenchman Cap dome are not yet fully understood.

MINERALIZATION

A sphalerite-galena-magnetite layer occurs as part of the stratigraphic success ('Cottonbelt sequence') in both limbs of the Kirbyville-Grace Mountain syncline north of Ratchford Creek (Hoy, 1979). In tracing t.his marble-carbonatite-bearing sequence (unit 4m, ct) south of Ratchford Creek, two additional exposures of disseminated oxide-sulphide mineralization were discovered. The first showing cccurs on the upper limb of the Kirbyville-Grace Mountain synclineand consists mainly of disseminated molybdenite, pyrite, chalcopyrite, and hematite immediat.ely adjacent to a thin marble unit of the 'Cottonbelt sequence.' This showing is located near the hinge of a first order D2 fold near the western headwaters of Perry River, and is markedby an 'x' on Figures 3 and 5.

Oxide-sulphide mineralization also occurs in a sequence of calcareous skarns near the hinge zone of the Grace mountain syncline, approximat.ely 1.75 kilometres south of Ratchford Creek(MJ-720, Figures 3 and 5). Mineralization appears to be zoned and consists primarily of glomeroblastic magnetite, pyrite and minor sphaleritein the centre, and grades outward into disseminated pyrite-molybdenite along its margins.

Assay values for two grab samples within this mineralized zone are presented below.

Sarnp I e Au Ag Pb cu Zn Mo wo3 NO. oz./tonoz./ton percentper cent per cent percent percent ore ore

MJ-720 A trace 0.25 0.02 trace 0.04 trace 0.04 MJ-720 B trace 0.10 0.02 trace 0.03 trace trace

ACKNOWLEDGMENTS

The author gratefully acknowledges funding fran theNSEE (Grant #A-'3146) and a grant from the British Columbia Ministry of Energy, Mines and Petroleum Resources awardedto John Dixon of Queen's University. Discussions with hyqve Hoy and Bill McMillan (British Colclmhia Ministry of Energy, Mines and Petroleum Resources) andJohn M. Dixor, and DugaSdM. Carmichael (Queen's University) have been very helpful. I would also like to thank Richard L. Brown (Geotex Consultants Ltd. and formerly of Carleton University) for his continuing interest and generous supervision. Huqh Davis, Alain Leclair, Don Murphy, and Cimol Newel'l provided very helpful and inquisitive field assistance for periodsoE time during the 1980/81 field seasons. In particular, I would like to thank Bryan B. Dean and family of Revelstoke, British Colunbia,for their friendship and logistic support.

199 Thismanuscript was greatly improved by thethoughtful and constructive criticisms of Bill McMillan, Trygve HOy, Richard L. Brown, andJohn M. Dixon. Any remaininginconsistencies in theideas or presentation of this paper are entirelythe responsibility of theauthor.

REFERENCES

Brown, R.L. (1980a): Frenchman Cap Dome, ShuswapComplex, British Columbia: A ProgressReport, in CurrentResearch, Part A, Geol. Sum.. Canada, Paper 80-1A, pp. 47-51...... (1980b): Metamorphic Complex of SoutheasternCanadian Cor dillera and Relationship to ForelandThrusting, in Thrust and Nappe Symposium, Geol. Soc. London. Brown, R.L. and Psutka, J.F. (1979):Stratigraphy of the East Flankof Frenchman CapDome, ShuswapComplex, British Columiba, inCurrent Research,Part A, Geol. Surv., Canada,Paper 79-1A, pp. 35-36. Crittenden, M.D., Coney, P.J.and Davis, G.H. (1980):Cordilleran Meta- morphic Core Complexes, Geol. Soc. Amer., Mem. 153. Fyles, J.T. (1970): The JordanRiver Area nearRevelstoke, British Columbia, B.C. Ministry ofEnergy, Mines & Pet. Res., Bull. 57. HOy, T. (1979):Cottonbelt Lead-Zinc Deposit, B.C. Ministty of Energy, Mines 6 Pet. Pes., Geological Fieldwork, 1978, Paper 1979-1, pp. 18-23...... (1980): Geology in the Eews Creek Area, Southwestern Margin of Frenchman Cap Dome, B.C. Ministry of Energy, Mines & Pet. Res., GeologicalFieldwork, 1979,Paper 1980-1,pp. 17-22. HOy, T. andBrown, R.L. (1981): Geology of Eastern Margin of Shuswap Complex,Frenchman Cap Area, B.C. Ministry ofEhergy, Mines & Pet. Res., Prelim. Map 43. HOy, T. andWMillan, W.J. (1979): The Geology in the Vicinity of Frenchman Cap Gneiss Dome, B.C. Ministry of Energy, Mines & Pet. Res., GeologicalFieldwork, 1978,Paper 1979-1,pp. 24-30. McMillan, W.J. (1973):Petrology and Structure of the West Flank, Frenchman Cap Dome, nearRevelstoke, British Columbia, Geol. Surv., Canada, Paper 71-29. Murphy, D. (1980):Mylonitic Gneiss: ColumbiaRiver Fault Zone, British Columbia, M.Sc. Thesis,Stanford University, Stanford, California. Okulitch, A.V., Loveridge, W.D., and Sullivan, R.W. (1981):Preliminary RadiometricAnalyses of Zircons from the Mount CopelandSyenite Gneiss,in Current Research, Part A, Geol. SUrv., Canada,Paper 81- lA, pp. 33-36. Pigage, L.C. (1977): Rb-Sr Datesfor Granodiorite Intrusions on the Northeast Marginof the Shuswap Metamorphic Complex, Cariboo Mountains, British Columbia, Cdn. Jour.Earth Sci., Vol.14, pp. 1690-1695. Price, R., Archibald, D., and Farrar, E. (1981): Eocene Stretching and Necking of theCrust and TectonicUnroofing of theCordilleran Metamorphic Infrastructure,Southeastern British Columbia and AdjacentWashington and Idaho,Geol. ASSOC. Canada,Programs and Abstracts, Vol. 6, p. 47.

200 Read, P.B. and Brown, R.L. (1981): Columbia RiverFault Zme: South- eastern Marginof the Shuswapand Monashee Complexes, Southern British Columbia, Cdn. Jour.Earth Sci., Vol. 18, No. 7, pp. 11.27- 1145. Read, P.B. and Klepacki, D. (1981): Stratigraphy and Struc!ture: No:rth- em Half of Thor-Odin Nappe, Vernon East Half Map-Area, Souther:n British Columbia, in CurrentResearch, Part A, Geol. !jurv., Can.sda, Paper 81-1A, pp. 169-173. Read, P.B. and Wheeler, J.O. (1976): Geology, Lardeau West: Half, British Columbia, Geol. SUN., Canada, Open File 432. Wheeler, J.O. (1965): Big-Bend Map Area, British Columbia,. Geol. Surv., Canada, Paper 64-32.

201 PRELIMINARYMAMINATION OF GOLD METALLOGENY IN THE INSULAR BELT OF THE CANADIAN CORDILLERA USING GALENA-LEAD ISOTOPE ANALYSES

By A. Andrew, C.I. Godwin, and A.J. Sinclair Department of Gzological Sciences University of British Columbia

ABSTRACT

Lead isotopedata from quartz-goldvein deposits and volcanogenicand relateddeposits in the Insular Belt group fall in fourdistinct clusters on Pb-W plots. Each clustercorresponds to a specific deposittype and host rockcategory. Two parallelevolutionary trends in the lead isotopiccomposition exist: (1) Sicker-hostedvolcanogenic deposits to Sicker-hostedveins, and (2) Karmutsen and Bonanza-hostedvolcanogenic or paramagmaticdeposits to Karmutsen and Bonanza-hosted veins. The trends indicate a geneticrelationship between hostrock and isotopic composition. These observationsfavour a hostrock source for the lead in vein deposits and, by association, a comparable source for gold. Plutonicor abyssal direct sources of metalsare not consistent with the lead isotopic data.

We suggestthat the gold was extracted from thecountry rock, concentrated as veins by hydrothermalactivity related to Tbrtiary plutons. Vein deposits are isotopicallydistinct from volcanogenic and relateddeposits, providing a model fordistinguishing syngenetic from epigeneticdeposits in a general way. Karmutsen and Bonanza-hosted deposits are more depletedin 207Pb than similar depositsin Sicker Q-oup rocks,indicating significantly different sources for volcanic components ofthese two important rockunits.

INTRODUCTION

Galena-leadisotope data from mineral depositsin British Columbia have beencompiled at the University of British Columbia since 1978 as part of a systematicstudy of galena-leadisotopes applied to metallogenyin the CanadianCordillera. One aspect of thatdata considered here concerns isotopiccompositions of lead from volcanogenic and relateddeposits and quartz-goldveins in the Insular Belt, as they relate to the metallogeny of gold-bearingdeposits.

All thedata used in this study are listed in Table 1. Information regarding the geologicalsetting, mineral associations, and deposittype was extracted from MINDEP and MINFILE computer files of mineraldeposits, annualreports of theBritish Columbia Ministry of hergy, Minesand PetroleumResources, and assessmentreports submitted to theBritish Columbiagovernment. Ihe appendixdescribes the 18 deposits used in this

202 TABLE 1. LEADISOTOPE ANALYSES ON GALENA FRO\I MINERAL DEPOSITS InsularBelt, B.C.

Lead Isotooe Data (relative :. S ~ITOTas 5) zo7Pb/204Pb 208pb,20dpb

G79CL Cowichan CL 124.348.7 18.646(.03) 15.581(.05) 38.276(.10) -001 Lake G79CL Cowichan CL 124.348.7 18.666(.02) 15.589(.07) 38.396(.10) -002 Lake G79CL Cowichan CL 124.348.7 18.702(.07) 15.546(.10) 38.086(.30) -003 Lake-003 *average for CowichanLake 18.671(.04) 15.572(.07) 38.252(.16)

*G79IC Iron Clad IC 48.85123.68 18.682(.08) 15.581(.07) 38.304(.12) -001 G79LN Lenora LN 48.87123.78 18.534(.04) 15.538(.09) 38.216(.04) -001 G79LN Lenora LN 48.87123.78 18.562(.08) 15.572(.08) 38.23(.09) -002 *average for Lenora 18.548(.06) 15.555(.08) 38.223(.06)

*G79TY -001 Tyee -001 "Y123.78 48.87 18.558(.08) 15.577(.07) 38.123(.11)

G79W Western: WM 49.57125.59 18.506(.06) 15.579(.04) 38.186(.07) -001 Nyra 679W Western: UM 125.5949.57 18.488(.07) 15.554(.07) 38.089(.06) -002 Myra 2 G79!i?l Western !+W 125.5949.57 18.484(.06) 15.551(.09) 38.115(.03)

18.493(.06) 15.561(.07) 38.130(.05) [18.595(.06)1 [15.569(.07)1 [38.206(.10)1 Standarddeviation = S 0.081 0.011 0.079 Standard error = SGk 0.036 0.005 0.035 Cluster 2: Upper Triassic-Jurassic *30335 Nutcracker49.75124.59335 18.609(.07) 15.521(.09) 38.048(.10) -001 *30366 Ban 36650.26 126.67 18.587(.06) 15.526t.04) 38.086(.10) -001 30314 Starlight 314 49.02124.71 18.592(.07) 15.562(.09) 38.196(.05) -001 Average for Cluster 2 (n=2) D8.598(.07U n5.524(..07fl p8.067( .08)] Standarddeviation = S 0.016 0.004 0.027 Standard error = Sn4 0.011 0.003 0.019 cluster3: Tertiary 30317 Lone Star 317 50.02126.79 18.940(.08) 15.569(.03) 38.445(.07) -001 -ReyOro 30317 Lone Scar 317 50.02 126.79 18.950(.10) 15.571(.06) 38.378(.03) -001 -ReyOro er age for one Star-ReyOro 18.945(.09) 15.57 (.OS) 38.4111 .as)

*30318White Star 31LI 50.03126.81 18.867(.10) 15.499(.04) 38.245(,05) -001 "30320 Peerless 32050.04 126.84 18.9w.06) 15.56 (.IO) 38.4531.08) -001 *30334Lucky Strike 334 50.06126.84 18.827(.05) 15.532(.03) 38.405(.09) -001 *30349 Privateer 341 50.03 126.81 19.011(.08) 15.581(.09) 38.505i.06) -001 G79AB Alphaand AB 48.73124.09 18.882(.03) 15.581(.05) 38.406:.07) -001 Beta-001 ~~eragefor Cluster 3 (n=5) p8.926(.07)1 D5.548(.06fl p8.411:.05)1 Standarddeviation = S , 0.078 0.033 0.099 Standard error mean = Sn-* 0.035 0.015 0.044 * Asterisk denotes analysis used in calcualtion of averages

203 TABLE 1 (Continued)

Sillple ~apLato Long' Lead IsotopeData (relative 1 S error as I) Ncmber Deposit Name Name North West 206Pb/zo4Pb207Pb/204Pbzo8Pb/204Pb

Cluster 4: Tertiarx? *30313 Golden 313 Golden *30313 19.007(.08)15.621(.07)124.5938.577(.12) 49.11 -001 Eagle *30315 Victoria 18.828(.04)31515.646(.04)124.6638.733(.04) 49.18 -001 30323 Fandora 32349.25 125.68 18.856(.07) 15.526(.04) 38.290(.04) -001 *30355 Cream Lake 35549.49 125.54 19.171(.04) 15.585(.04) 38.796C.07) -001 Average for Cluster 4 (n=3) @9.002(.05)]p5.617(.05)l[r38.702(.08)1 Standarddeviation = S 0.172 0.031 0.133 Standard error mean = Sn4 0.099 0.018 0.065

* Asteriskdenotes analysis used in calculation of averages.

study and lists thechief sources of informationfor each. Locations of the deposits are shownon Figure 1.

ANALYTIC&TECHNIQUES

Lead in galena from the samples was dissolvedusing HC1. Purifiedlead was obtainedusing anion columns and anodicelectro-deposition. Samples were analysedusing single-filament silica geltechniques on a 90-degree, 12-inch,solid source mass spectrometer.In-run precision, reported in thetables as per centstandard deviation within the brackets following mean isotopicratios, is generally better than 0.1 per cent at one standarddeviation. Multiple analyses ofBroken Hill No. 1 standald shows that the reproducibility of sample analyses is about 0.1 per cent at one standarddeviation. All datain the tables havebeen normalized to the Broken Hill No. 1 standard;normalizing procedures assumed the followingcomposition for this standard: 207Pb/204W = 15.389, 206W/204Pb = 16.003,208Pb/204Pb = 35.657. All analyses were done in theGeology-Geophysics Laboratory, the University of British Columbia.

DATA

Galena-leadisotope data from Table 1 faLl into fourdistinct clusters on the W-Pb plots of Figures 2 and 3. Qch clustercorresponds to a deposittype and hostrock group. Vein depositsare consistently more enriched in 206E% thanare volcanogenic and relateddeposits. Sicker- hosteddeposits are generally more enriched in 207Pbthan the Karmutsen and Bonanza-hosted deposits. ?he clusters, numbered 1 to 4 (Figures 2 and 3), are described in more detail below.

204 205 15.f

n f 2L ::c

15.:

18.3 18.5 18.7 18.9 19.1 18.9 18.7 18.511 18.3 19.3 206?b/204?b Figure 2. Galena-ledplot of 207Pb/20%'b versus 20%'b/204Pb (Table 1).Open symbols are used for velns; circles denotedeposlts related to Karmutsen or BonanzaGroup rocks;square symbols aretor deposits related to Sicker Group rocks.Unreasonable analyses are crossed and arenot used In our Interpretation. Bars mark standarderror of the mean and lines extends to standarddevlatlon. Lines 1 and 2 representthe evolutlon ot lead from tl to t2for varying values of )I; t2 for Cluster 4 is not known withcertainty (see text). The average grarthcurve shown is Stacey and Kramars (1975) curve for average crustallead growth.

CLUSTER 1: SICKER GROUP VOJXANOGENIC AND RELATED DEPOSITS

The Sicker Group is made upof dominantlyandesitic volcanic rocks and interbeddedsedimentary and limestone units ofCarboniferous-Permian age (Northcote, et dl., 1972). On thebasis of paleontologicalevidence (Muller andCarson, 1969), an age of 270 Ma has beenassigned in this study to the deposits which make up this cluster.

Severalvolcanogenic massive sulphidedeposits (and related showings) are containedin the Sicker Group, the best known being Western Mines (Figure 1 ). Lead isotopedata from thesedeposits form a tight cluster in the pb-Pb plots(Cluster 1, Figures 2 and 3) centred belowthe Stacey and Kramers (1975)curve for average crustal lead growth, but within the field of'ocean volcanics'described by be and artman(1979). me compositions are tooenriched in 206~and toodepleted in 207F?J to plot on any 270-Ma isochron of the Stacey and Kramers (19751, Cumming and Richards ( 1975).or Doe and Zartman ( 1979)lead evolution models.

206 38.75 -

N \ n

N 38.25-

-2 18.1 18.3 18.5 18.7 18.5 18.3 18.1 18.0 10.1 19.3 20sPb/204pb

Flgure 3. Galena-leadplot of 20$b/20+b versus 206pb/204Pb (Table 1); for symbol descrltplon see Figure 2. Llnes 3 and 4 represent the evcNlutlon of lesad frm tl to t2 forvarylng values of w If K Is 3.3 and 3.9 respectlvely (Table 2).

The IronClad deposit (Appendix) has not been classifiedpreviously as volcanogenic. We note that the composition of thelead is the same am othervolcanogenic deposits in the Sicker Group. Consequently, we believethis deposit to be cogeneticwith volcanogenic deposits within theSicker Group.

CLUSTER 2: KARMUTSEN AND BONANZA GROUP VOLCANOGENIC AND RELATED DEE’OSITS

Karmutsen Group volcanicrocks form a thicksequence of Triassic (circa 200 Ma) tholeiiticpillow basalts, flows, and breccias, which are similar inchemistry to those of mid-ocean ridges (Monger, et al., 1972). Muller ( 1971 ) and souther (1977) suggestedthat they arevolcanogenic arcrocks which formed close to a trench. They overlie theSicker Group island arc assemblages and lackgabbro, chert, and ultramaficrocks which usually are associatedwith ocean basalts. In other words,they probably represent volcanicrocks generated above a Bnioff zone duringearly stages of subduction.

BonanzaGroup volcanicrocks are flows and pyroclastic layers ranging in composition from basalt to rhyolite. ‘Ibey overliethe Karmutsen Group and are dated as Middle Jurassic(circa 160 Ma) on thebasis of radiometric ages from coevalgranitic plutons (Muller and Carson, 1969).

207 "vn depositsdefine Cluster 2; both are enclosed by Karmutsen volcanic rocks;consequently, anage of 200 Pa was assigned to hoth depositsfor our purposes in interpretinglead isotopic data, Cluster 2 plots below thegrowth curve of Stacey and Kramers (1 975)for average crustal lead (Figure 2) and is more depletedin 207Pb thanCluster 1. If the age difference between Clusters 1 and 2 is takeninto account, the difference in isotopiccomposition would be more pronounced,since Cluster 2 would have been even less radiogenic at 270 Pa. The twu deposits which definethis cluster are not demonstrably volcanogenic and the term paramagmatic (White, et al.,1971) may be more suitable. Paramagmatic is the name given to epigeneticdeposits which can beshown to be an integralpart of a magmatic event. The lead isotopiccomposition of such a depositprobably reflects the composition of leadin the magma at its time of formation. We thinkthat the relativelynon-radiogenic Pb-isotope character of Cluster 2 reflectsthe isotopiccharacteristics of theenclosing Karmutsen volcanic rocks. "ne Starlightdeposit (Table 1, Appendix)might belong to thiscluster, but no mention is mdein the literature of its host rockgroup, although the lead-isotopiccomposition plots within an areaunderlain by the Karmusten Group on regionalgeological maps (Muller,1963). We excludethis depositin our calculations but inclusion of this datum wuuld make little difference to the mean position of Cluster 2.

CLUSTER 3: TERTIARY VEINS IN KARMUTSaJ OR BONANZA GROUP VOICANIC ROCKS

Bonanzaand Karmutsen Group volcanicrocks are host to severalquartz- goldveins from which,galena-lead isotope data wre obtained. "nese veinsvary in width. They are predominantly of quartzwith minor carbonate and generallycontain pyrite, sphalerite,chalcopyrite, galena, arsenopyrite, and gold.Spatially they are closely related to Tertiary quartzdiorite stocks (Northcote and bbller, 1972). "nree of the wins are within the Eocene Zeballospluton (Appendix). Consequently, an age of 30 Ma was assigned to thiscluster (Bancroft, 1940; Stevenson, 1950; Wanless, et al., 1967).

Galena from the veins which make up Cluster 3 has a uniformlead composition,the average of which is depletedin 207Pb relative to Cluster 1, but is enriched in 206Pb, 207Pb,and 208Fb relative to Cluster 2. The dataplot beneath the Stacey and Kramers (1975)curve for average crustallead and the averagehas a future model age.

Alpha and Beta deposit(Table 1, Appendix)belongs with Cluster 3 on geologicalevidence, but was excluded from calculationsbecause of a highly anomalous207Pb/204Fb value (Figure 2). It plotswith Cluster 3 on Figure 3 butwith Cluster 4 on Figure 2. Its highvalue in 207Pb possiblyresults from analyticalerror which is greaterfor 207Fb than for 206~and 208Pb.

208 CLIJSTER 4: TERTIARY VEINS IN SICKER GROUP ROCKS

Quartz-goldveins inSicker Group rocksthat form Cluster 4 on Figures 2 and 3 have the same generalappearance and mineralogy as those of Cluster 3 (Muller and Carson,1969).

Although Cluster 4 forms a distinctly different group relative to Cluster 3, thereare only three data points which are quitewidely scattered on the Pb-Fb plots. The averagecomposition of thecluster is more radiogenicthan the average for any of theother clusters. Althoughthe age of thoseveins is not known with certainty anage of 30 Ma was assigned on the basis of thesimilarity in 206Pbcontent with (Cluster 3, and theassumption that they are related to the same phase of :intrusive activity.victoria showing(Table 1, Pppendix) may be an o1de:c deposit related to the JurassicIsland Intrusions. The age t2 of Cluster 4, however, is not crucial to thehypothesis proposed in thisstudy. Fandora deposit(Table 1, Appendix)belongs to this group on geological grounds,but was notincluded in the discussionbecause of its anomalously low radiogeniclead contents; the sample is to be re- analysed.

LEAD ISOTOPEMODELS

Distribution of the four clusters on Figure 2 givesthe appearance of two paralleltrends. One is from Sicker-hosted volcanogenic to veindeposits (line 1,Clusters 1 and 4), the other from Karmutsen and Bonanza-hosted volcanogenic and relateddeposits to veindeposits (line 2, Cl.usters 2 and 3).

Four possibleexplanations for these groupings are:

(1) veinlead is unrelated to the volcanogeniclead, (2) veinlead lies on an isochronwith the volcanogenic lead, (3) veinlead lies on a growthcurve with volcanogenic lead, and (4) veinlead lies close to a growthcurve with volcanogenic lead but is preferentiallyenriched in radiogenic lead.

The firsthypothesis appears unlikely on thegeneral grounds that the relativeplot positions of the two 'volcanic'clusters are identicalwith the relative plot positions ofthe tm younger vein clusters. One 'volcanic' and one vein cluster have evolved in environmentswith low uranium/leadratios (Clusters 2 and 3) compared with theother volcanic- veinpair of clusters. %is seems an unreasonablecoincidence. It is more likelythat volcanic-vein pairs of clusters are somehow genetically related. The relationship was tested by calculating the slopes of the linesthat pass through Clusters 1 and 2 (Figure 2, Lines 1 and 2), wi-th pairs of ages 270 and 30 Ma, and 200 and 30 Ma respectively,using Equation 3 (Table 2). In bothcases the lines passthrough their respective vein clusters butnot through theaverages ofthe vein clusters (Figure 2). This result shows thatthe parallel trend is significant and thereforehypothesis one can be eliminated. Equation 1: [%] = + u(ehltl - eht2) '04Pb t2 '04Pb tl

Equation 3: M207-206 = 1 207Pb/204Pb1f2- - [ 137.88 206Pb/204Pb]t2 - [

238 204pb P= u/ k=232Th/w8U W = ku

X1 = 0.155125 x lo-' (Jaffey &., 1971)

X2 - 0.98485 x lo-' (Jaffey "et al., 1971) X3 = 0.049475 x lo-' (LeRouxand Glendenin, 1963)

areslopes of isochrons on the Pb-Pb plots. M207-206 and M208-2Q6

TABLE 2. EQUATIONS USED IN LEAD ISOTOPE MODEL CALCULATIONS

Hypothesis two can be dismissed on geologicalgrounds since there is clearly a large agedifference betweenthe syngenetic wlcanogenic deposits and epigeneticveins. The distinction betweenvein and volcanogeniclead in z06Pb/204Pb ratio is markedand provides a method fordistinguishing epigenetic versus syngenetic deposits in the Insular Belt. All theepigenetic deposits have206Pb/204Pb ratios greater than 18.8, and thesyngenetic deposits have ratios less than 18.7. Iron Clad is anexample of oneshowing which was thought to be epigeneticbut which is likelysyngenetic on thebasis of its isotopiccomposition.

Hypothesisthree can be tested by calculatingthe apparent 238U/204F% (p) value which would be required to producethe vein leadcompositions from the volcanogeniclead compositions in the time intervals 270 to 30 Ma and 200 to 30 Ma, usingequations 1 and 2 (Table 2). lhis method is based on the assumptionthat the volcanogeniclead is representative of the composition of thelead in the volcanic hostrocks at their time of

210 formation (t,)to the time of veinmineralization (t2). The amount Of change in the ratiosover any time interval depends on the va.lue Of 238~/204pb (p) and 232~h/204pb (w). Apparent p values were clalculated andfound to be highrelative to expectedvalues (Fame, 1977; Coe and Zartman,1979). %us, the veins are mre enrichedin radiogenic lead than would be expected if they fell on growthcurves with the volcanogeniclead. mis causes us to reject hypothesis three. %e apparenthigh p valuesnoted above, however, might be becauseradiogenic lead is mre easily removedfrom sourcerocks than is common lead (because of its unstableposition in minerallattices). An ore-forminq fluidwuld therefore be able to scavenge more radiogenic 1ea.d than common lead and so would give rise to a leaddeposit with an artifical'ly highapparent u. This process of radiogenicenrichment has been observed at Beaverdell(Watson, et al., in preparation) and inthe Mississippi valley(Heyl, et dl., 1974) and supports hypothesisfour.

Strongsupport for hypothesis four comes from the observatiorlsthat lines 3 and 4 (Figure 3), which pass through the centres of both pairs of clusters, have slopes which givegeologically reasonable 232Tph/238U (k) values. k values were calculatedusing equation 4 (Table 2) and found to be 3.9 for line 3 and 3.3 for line 4. These valuesare close to those listedfor volcanic rocks by Faure(1977).

SOURCEOF GOLD

The Source of gold invein deposits is controversial. Boyle 1:1979) summarized threepossibilities:

(1 ) gold comes from an abyssalsource such as themantle, (2) gold comes from a plutonicsource, and (3) gold comes from thehost rocks by processessuch as metilmorphic secretion OK hydrothermalextraction and deposition.

Each of thesehypotheses is discussed with respect to thelead isotope data, based on the assumptionthat the origin of the lead is the same as that of the associatedgold.

Lead from an abyssal source would have a depletedisotopic composition due to the absence of uranium and thorium-richminerals in tho mantle (Faure,1977). Galena in the Bonanza and Karmutsen-hostedveins (Cluster 3, Figures 2 and 3) is notablydepleted in 207Pb and must therefore have a source which is less radiogenicthan the Sicker volcanic rocks (Cluster 1, Figures 2 and 3). Ifthis source was the rmntle, then all the quartz- goldveins of the sa.= age and within a limitedgeographical area, would have a uniformlead composition irrespective of hostrock group. Recognition of two groups of veins with different isotopiccompositions, corresponding to different host rock groups,tends to negatethis hypothesis. The unradiogenicnature of the KdKmUtSen andBonanza volcanicrocks (Cluster 2, Figures 2 and 3) provides anadeqlmte source forthe lead without appealing to an ahyssalsource.

;!1 1 Cluster 3 (Figures 2 and 3) deposits(Privateer, White Star,an3 Lone Star) are all spatiallyrelated to theZeballos pluton, the latter two occurwithin the pluton itself (Appendix).If the source of the metals in eachvein was plutonic,then one might expect to see either a uniform composition of leadin the veins,unrelated to hostrock, or variations in the veinlead compositions corresponding to differentplutons. The closecorrelation betweenvein composition and hostrock group is too persuasive to allowfor all of the metal to havebeen introduced from plutons.

Closespatial association of the quartz-goldveins to Tertiaryquartz dioriteintrusions suggests that the plutonsplay a rolein the mineralizingprocess. We suggestthat the plutonsprovided a heatsource thatcirculated hydrothermal fluids through the host rocks; these fluids extractedradiogenic lead and gold from thevolcanic terrane and precipitatedthese metals inquartz veins. This model is inaccord with Boyle’sthird proposition, namely that the hostrocks provided the metals which were mobilized and concentrated by igneous,hydrothermal activity. Consequently,the isotopic composition of the leadin the veins is a reflection of its hostrock.

CONCLUSIONS

Lead isotopedata from volcanogenic and quartz-goldvein deposits in the Insular Belt suggest that the gold inveins was derived from theirhost rocks.Extraction, concentration, and deposition were probablyby hydrothermalfluids mobilized in geothermal cells generatedadjacent to Tertiaryplutonic centres.

Lead isotopiccompositions for quartz-gold veins of thesouthern Insular Belt are depleted in 207Pb relative to silver-bearingveins in the Yukon Tertiary (Godwin, et a1., in press ), reflecting the more primitive volcanicsource terrane of the Insular Belt. The uniformity of the vein leadcompositions of Cluster 3 contrastswith the linearpatterns of data forvein deposits elsewhere in theCordillera (Doe and Zartman, 1979; Godwin, et al., in press). There is alsoevidence that radiogenic ewichment of lead in veins,noted in the Insular Belt quartz-goldveins, occurredin other silver-gold veins, for example, in the Beaverdell camp insouth-central British Columbia (Watson, et al., inpreparation).

From a practical paint ofview, isotopicanalyses of galenaappears usefulin distinguishing young epigeneticvein deposits from older volcanogenicdeposits (parhaps with related veins).This distinction will have an effect on theapproach to detailedexploration within the Insular Belt.

ACKNOWLEDGMENTS

Ourwork hasbeen supported financially by the British Columbia Ministry of hergy, Minesand PetroleumResources, Cominco Ltd., Cyprus Anvil Mining Corporation, and Rio Tinto CanadianExploration Limited. The lead

212 mass spectrometryfacility was supported by a NSERC coregrant and was housed in theDepartment of Geophysicsand Astronomy at theUniversity of British Columbia. Analyticaldata was obtained by B.D. Ryan.

REFERENCES

Bancroft, M.F. (1940):Zeballos Mining District and Vicinity, B.C., Geol.Surv., Canada, Paper 40-12, 38 pp. British Columbia Ministry of Energy, Mines andPetroleum Resources, p. 253; AssessmentReports 19, 1821, 1884, 4914; GEM, 1970;1971; MINFILE. Boyle, R.W. (1979): me Geochemistry of Goldand Its Deposits, Geol. Surv., Canada, Bull. 280, pp. 390-428. Cumming, G.L. and Richards, J.R. (1975): Ore Lead IsotopeRati,os in a Continuously Changing Earth,Earth Planet. Sci. Lett., 155-171, 28 PP . Doe, B.R. and Grtman, R.E. (1979):Plumbotectonics, in Geochemistry of Hydrothermal Ore Deposits,edited by H. L. Barrres. Faure, G. (1977) : Principles of Isotope Geology,Smith-Wyllie,. International series. Fyles, James T. (1 955) : Geology of the CowichanLake Area, Vancouver Island,British Columbia, B.C. Ministry of Energy, Mines E; Pet. Res., wI11. 37, p. 16. Godwin, C.I., Sinclair, A.J., andRyan, B.D. (1981): Lead Isotope Models forthe Genesis of Carbonate-hosted Zn-Pb, Shale-hosted @a-Zn-Pb and Ag-richDeposits inthe Northern Canadian Cordillera, %on. Geol., in press. Godwin, C.I. and Sinclair, A.J. (1981):Preliminary Interpretations of Lead Isotopesin Galena-lead from Shale-hostedDeposits in British Columbia and the Yukon Territory, B.C. Ministry of hergy, Mines L Pet. Res., GeologicalFieldwork, 1980, Paper 1981-1, pp. 179-194. Heyl, A.V., Landis, G.P., and Zartman, R.E. (1974):Isotopic Evidence forthe Origin of MississippiValley-type Mineral Deposits: A Review, &on.Geol., Vol. 69, pp. 992-1006. Jaffey, A.H., Flynn, K.F., Glendenin, L.E., Bentley, W.C., and Essling, A.M. (1971): Precision Measurements of Half-lives and Specific Activities of 235~and 23*u, Phys. Rev. c., 4,pp. 1889-1906. LeRoux, L.J. and Glendenin, L.E. (1963): Half-life of 232Th, Proceedings of NationalMeeting on NuclearEnergy, Pretoria, South Africa, p. 78. Mathews, W.H. and McCammon, J.W. (1957):Calcareous Deposits of SouthwesternBritish Columbia, B.C. Ministry of Energy, Mines 6 Pet. Res., wlll. 40, p. 46. Minister of Mines, B.C. (1904): Ann. Rept.,1904, p.253. Monger, J.W.H., Souther, J.G., and Gabrielse, M. (1972):Evol.ution of the Canadian Cordillera: A PlateTectonic Model, Amer. Jour. Sci., Val. 272, pp. 577-602. Muller, J.E. (1963) : Alberni Area 92F/SE, Geol. Surv., Canada., Map49- 1963.

213 ...... (1971): Chemistry and Petrology of Some Mesozoic Volcanic Rocks ofVancouver Island,British Columbia,Geol. Surv., Canada, Paper 71-1, Part B, pp. 5-10. Muller, J.E. and Carson, D.J.T. (1969): Geology and Mineral Deposits of Alberni Map-Area, B.C., Geol. Surv.,Canada, Paper 68-50,52 pp. Northcote, K.E. and Muller, J.E. (1972): Volcanism,Plutonism and Mineralisation: Vancouver Island, C.I.M., Bull.,October 1972, pp. 49-57. Souther, J.G. (1977): Volcanism and Tectonichvironments in the CanadianCordillera - A Second Look, inVolcanic Regimes in Canada, edited by Baragar, W.R.A., Coleman, L.C., and Hall, J.M., Geol. ASSOC. Can., SpecialPaper 16, pp. 3-24. Stacey, J.S. and Kramers, J.D. (1975): Approximation of Terrestrial Lead IsotopeEvolution by aTwo-stage Model, EarthPlanet. Sci. Lett., 26, pp. 207-221. Stevenson, J.S. (1950): Geology and MineralDeposits of theZeballos Mining Camp, B.C., B.C. Ministry of Energy, Mines & Pet. Res., Bull. 27. University of British Columbia: MINDEP (computer-file of mineraldeposit information. Watson, P.H., rdwin, C. I., and Christopher, P.A. (1981 ) : General Geologyand Genesis of Silver and Gold Veins inthe Beaverdell Area, South-Central British Columbia, inpreparation. White, W.H., Harakal, J.E., and Carter, N.C. ( 1971 ) : K-Ar Ages of Some Ore Deposits in British Columbia, C.I.M., Bull., 1968. Wanless, R.K. (1967): Age Determination and GeologicalStudies, K-AT Isotopic Ages, Geol. Surv.,Canada, Rept. 7, Paper 66-17.

214 APPENDIX

Western Mlnes:Lat. 49.57';Long. 125.59'; 92F/12E Samp I e Nos. : G79WM-001, 002. and 003. Description: It Is a kuroko-typemasslve sulphlde deposit. Lenses, velns. and mDDLses ofpyrlte, chalcopyrlte, sphalerlte. and galenaoccur InSicker GroUF' rhplltic volcanlc rocks. Metals Recovered:Copper, zlnc, lead,gold, sllver, cadmium,and barlte. Reference: MDI No. 092/071.

Lenora: Lat.92B/13W123.78.; Long. 48-87.; Sample Nos. : G79LN-001and 002. Description: Thls is descrlbedas a 'replacement' ore, but Is probably a volcanogenic masslve sulphideIn Slcker Group foldedtuffs. Two oretypes occur: barite ore Is a flne-gralnedmixture of pyrite, chalcopyrlte, sphalerlte, and galena In a barlte,calcite, and quartz gangue;and quartz ore Is malnlyquartz and chalcopyrite. Metals Recovered:Zlnc, copper, sllver,barlte, andlead. Reference: M)i No. 092F/O01.

Tyee: Lat.Tyee: 92B/13W123.78.; Long. 48-87.; Sample No.: G79TY-001. Description: Thls Is descrlbed as a 'replacement'ore, but Is probably a voIcanogenlc masslve sulphldeIn Slcker Group foldedtuffs. Two oretypes occur: barlte ore Is a flne-gralnedmlxture of pyrite, chalcopyrlte, sphalerlte. and galenaIn a barite,calclte. and quartz gangue;and quartzore is mainlyquartz and chalcopyrite.

CowlchanLake: Lat. 48-7.;Long. 124.78.; 92C/16W Samples Nos. : G79CL-001. 002, and 003. Descrlptlon:Penno-Carbonlferws Buttle Lake Fonnatlonlimestone (Sicker Group) I!; underialn by Slcker Group cherts,tuffs, and brecclas and overlaln by Karmutsen Formationbasalt and dlabase. References: B.C. Mlnlstryof Energy, Mines 6 Pet. Res., Bull. 46;p. 40, Bull. 31. p. 16.p.

Iron Clad:Lat. 48-85.;Long.123.68';92B/13E Sampls No.: G791C-001. Description: Sphalerite,pyrrhotlte, and chalcopyrite mineralizatlon occurs In a shear zone ofquartz-serlclte schlst of Slcker Group. Metals Recovered: Zlnc and copper. References: Ministerof Mines, Ann.B.C., Rept.1904, p. 253; Assess%entReport 19.

Bon : Lat.126.67.; Long. 50.27.; 92L/7E Samp Ie No. : 30366-001. Descrlptlon: The Em mlneralOccurrences are In predmlnantly volcank rocks of the KannutsenFormation Inthe type area (GEM, 1970,pp. 274-278). Prlnclpal showlngs arereplacements of certain volcanic layers by jkarnwlth elther magneticor pyrrhotlte. he confilctingreport sagest5 that Ebn Is In BonanzaGroup rocks (Assessment Report 1821). Metals Recovered: Iron and copper. References: B.C. Mlnlstryof Energy, Mlnes d Pet. Res., GEM, 1970,pp. 274-278; Assessment Report 1821.

2 15 Nutcracker: Lat. 49.75';Long. 124.59.; 92F/IC€ Sample Nos. : 30335-001. Description: Brown porphrite (Karmutsen ?) istraversed by several fisswe zones3 to 4 feet wide, rarelycapletely filled with quartz.Usually narrow veinlets occupy the zones. A contactwith the Marble Bay Llmestone occurs tothe southeast. Galena and chalcopyrite occur inthe quartz. References: MDI No. 092/359; Assessment Report 6414.

Starlight: Lat. 49-06.;Long. 125.54.; 92F/3E Samp Ie Nos. : 30314-001. Description: Fine-grainedfree gold Is associatedwlth galena that Is finely disseminatedthrough extensively altered diabase. Metal Recovered : t%ld. References: M)I No. 092/216; Geol. Surv.,Canada, Nap 49-1963.

Cream Lake: Lat. 49-49.;Long. 125.54'; 92F/5E Samp Ie No. : 30355-001. Description: Velns of quartz with lesser slderlte and calcite contaln values In silver, gold,zinc, andcopper. They areunderlain by volcanicrocks and lessersedimentary rocks of Permian ageand overlain by Karmutsen volcanic rocks. A distinct band of Permian limestone occurs between the two. The Western Mines' orebodies lie to thenorth within this belt. Metals Recovered: Gold, sliver, copper, and zinc. Reference: Assessment Report 1884.

GoldenEagle: Lat. 49.11.; Long.124-59'; 92F/2E Sample No.: 30313-001. Description: Gold occursIn a vein of ribbonquartz and'pyrite with other minor sulphidesin a small Intrusionof feldspar porphyry. Metal Recovered: Gold. References: MlI No. 092F/080; Geol. Surv.,Canada, Paper 68-50.

Victoria: Lat. 49-18.;Long. 124.66'; 92F/2E Samp Ie No. : 30315-001. Description: Gold and pyrite are associated with quartz veins In sheared sections of andesiticflows and tuffs. The rockgroups observed were placed tentatively In the Sicker Group, though goverment geologists left them inthe Island serles. The depositis adJacent to a stockrelated to the Coast Range Batholith (that Is. this vein Is probably an oldervein than the. .._ other<>- . .. -. - . - Metals Recovered: Gold, silver, and copper. References: MDI No. 092F/079; Geol. Surv.,Canada, Paper 68-50; Assessnent Report 4914.

Fandora: Lat.125.68'; Long. 49.25.; 92F/5E Sampl e No. : 30323-001. Description: Gold and silver-bearingveins of quartzwith sane carbonate, finely crystalline pyrite, and rarely lerlte cut altered volcanic rocks near andesltlc dykes In one workingciow, to a small mass oflntruslve quartz diorite. Metals Recovered: Gold, silver, copper,lead, and zinc. References: MDI No. 092F/040; Geol. Surv..Canada, Paper 68-50.

216 WhlteStar: Lat. 50.30';Long.126.81.;92L/2W Sample No.: 30318-001. Description: Quartz dlorlte of Eocene Zeballospluton is cut by feldsparporphyry dykes and subsequently jointed In threedirections. puartz veins wlth pyrlte, galena, arsenopyrlte,sphalerlte, and gold occur In gangueand breccia zones along which faultmovmnt has takenplace. lhe sulphlder; areusually concentrated In bands alongthe wal Is of the velns. Metals Recovered: Gold, silver, lead, and zinc. References: MDI No. 092L/010;Geol. Surv.,Canada, Paper 40-12.

Lone Star-Rey-Oro:Lat. 50.02';Long. 126.79.; 9W2W Sample No.: 30317-001. Descrlption: Quartz diorite of Zeballos pluton Is cut by aplite and ande:;ltic and feldspar porphyry. Fbny quartzveins with galena, arsenopyrite, gold, chalcopyrite, and sphalerite occur In shears Injolnted quartz dlorite and the dykes. Metals Recovered: Gold, sllver, zinc, lead, and copper. References: M)I No. 09W015; MINDEP 05841.

Peer less: Lat. 50.04.; Long. 125.84.;92L/ZW Sample No. : 30320-001. Descrlptlon: A quartzvein 5 centimetres wide follows a contact between 23 feldspar porphyry dyke and feldspathlzedandeslte of Lower Jurassiclbnanza Group. Quartzcontalns abundant calcite and small amounts (of sphalerite and chal copyr I te. Metals Recovered: Gold. zlnc, and copper, References: MDi No. 092L/025; MINDEP05851.

Privateer: Lat. Long.50.03.; 126.81'; 9K/2W Sample No.: 30349-001. Description:puartz veins wlth pyrite, sphalerlte. galena, arsenopyrite,pyrrhotite, and nativegold cut massive BonanzaGroup volcanlc rocks, lime sllicates, and smallbodies of JuraSSlC lntruslvequartz diorite. Metals Recovered: Silver, gold,copper, and lead. References: M)i No. 092L/008; Geol. Surv.,Canada, Paper 1940-12.

Alpha, Beta: Lat. 48.73';Long.124.09'; 92C/9E Sample M.: G79AB-001. Descrlptlon: Frank1 in Creek(Karmutsen Formation)andesite and lenses of Quatslno limestoneare cut by dykes ofgranodlorlte. granlte porphyry, and diorite porphyry. Llmestone, andeslte, and granodlorlteare partly alteredto garnet-epldote-pyroxeneskarn with chalcopyrite, magnetite, and pyritelocally. References: M)I No. 09'E/039; B.C. Ministry of Energy, Mines h Pet. Res., GEM, 1970, p. 291; 1971, 226.p.

Lucky Strlke: Lat. 50.06';Long. 126.84.; 92L/2W Sample No.: 30334-001. Description: The Vancarver4 1 shear, whlch folicus a feldsparporphyry dyke In diorite and granodlorltebreccia, contalns lenses of quartz 5 to 7.5 centimetres wide withpyrite and free gold. Metals Recovered: l.01 No. 092L/030; MINDEP 05856; Geol. Surv.,Canada, Mem. 272, p. 59.

2 17' PLATINOIDS IN THE TIJLAMEEN ULTRAMAFIC COMPLEX (92H)

By Robert M. St. Louis Department of Geology, University of Alberta

INTRODUCTION

The Tulameen Ultramafic Complex is approximately22 kilometres west of Princeton, and 48 kilometres north of the Canada-United States border. The complex has a surface of about57 square kilometres and is largely concordant with the regional northwest-southeast structural grain. It has been tentatively dated as Late Triassic (Findlay,1969).

The Tulameen River area has been knownto be a gold and platinum producer for mnre than one hundred years. Essentially all of the precious metal production has been from placers in the Tulameen River and its tributaries. No hard-rock mining of platinum has been attempted, mainly because information about the platinum distribution within the complex is lacking. The purpose of this project is to establish the distribution of the platinum group elements (PGE) and determine if they have any mineralogical associations. This research is being conducted as part of the requirements for an M.Sc. degree at the University of Alberta.

REGIONAL GEOLOGY

The Tulameen Complex intruded Late Triassic NicOla Group metavolcanic and metasedimentary rocks. The intrusion took place at the same time as major folding was in progress in the Nicola Group (Findlay,1963). The Eagle granodiorite lies just westof the mrgin of the complex. This acidic intrusion is slightly younger than the Tulameen, and may contact the ultramafics at depth (Findlay, 1963).

The Tertiary Princeton Group, which consists of terrestrial coal-bearing sedimentary rocks, volcanic rocks, and basalt flows, unconformably overlies the eastern margin of the Complex (Findlay,1963). In addition, glacial deposits cover much of the ultramafic, making outcrops scarce, especially in the southern half of the area.

GEOLOGY OF THE COMPLEX

As shown on Figure 1, the Tulameen Complex is oval with long axis trending northwest. It is imperfectly concentrically zoned. The general pattern of zonation, from core to margin is: dunite, (peridotite), olivine clinopyroxenite, hornblende clinopyroxenite, syenogabbro, and syenodiorite (Findlay, 1963,1969). Because they are common along the southeastern coast of Alaska ultramafics with this type of zoning are

218 Flgure 1. Generalized geology of the Tulaeen Complex.

219 called Alaskan peridotites. The Alaskan peridotites are a special variety of alpineperidotites but they differ in zoning and chemistry. Both are found ingeosynclinal orogenic zones (Wyllie, 1967). In addition to thezoning, Alaskan intrusions characteristically lack orthopyroxene and feldspars, and containhighly magnesian olivine, on the order of Fo75-93 (Wyllie, 1967). Inthe 'hlameen Complex the bulk Fe ratioincreases from core to margin,feldspars are only present in thegabbroic units, and no orthopyroxene has beenfound (Findlay, 1963).

The ,duniteunit occurs at the northwest end of the complex and is also elongated to the northwest. It containschromite in variablequantities, generallyranging from 2 to 20 volume per cent.Serpentine and magnetite are common. Serpentinegenerally constitutes less than 50 percent of therock and is commonly in zones of deformation and atcontacts.

Peridotite is volumetricallyinsignificant and doesnot constitute a mappable unit.Olivine/serpentine and diopsidecomprise 45 to 90 per cent of therock. The peridotite is generallylocated at the dunite-olivineclinopyroxenite contact, butalso occurs within the olivineclinopyroxenite (Findlay, 1963).

Olivineclinopyroxenite partly envelopes the dunite unit on the south and extendssouthward as a single zone. It consists of 70 to 80 per cent diopside, 10 to 25 per cent olivine and serpentine, some magnetite,and local chromite .

Hornblende clinopyroxenitecomprises the outerunit around most of the complex. It contains 30 to 75 per cent diopside, 5 to 70 percent hornblende, 5 to 25 percent magnetite, and accessorybiotite.

Gabbroicrocks comprise a large mass alongthe eastern part of the complex. The syenogahbrogenerally contains 30 to 50 percent diopside, 25 to 35 per centplagioclase, 15 to 20 per centK-feldspar, andminor biotite and magnetite.Syenodiorite contains 10 to 25 percent diopside andhornblende, 35 to 55 percent andesine plagioclase (An40), 15 to 35 per centK-feldspar, and accessorybiotite, magnetite, and apatite (Findlay, 1963). These two unitsare typically saussuritized, and alteredareas resemble one anotherin outcrop.

Contact3between gabbroic and ultramaficrocks are sharp. However, the ultramaficrocks grade into one another(Findlay, 1963). In general, contacts between ultramaficunits are markedby xenoliths of one type in theother. Near contacts,hybrid mixtures of the two contactingunits are common (Findlay, 1963).

The Tulameen Complex is geologicallyinteresting for a number of reasons. It is oneof thevery few Alaskan peridotites found in Canada (one of the othersbeing the Turnagain Complex, northernBritish Columbia). Also, it is unusual in that the mlameen gabbroicrocks are potassic, whereas those of otherAlaskan peridotites are tholeiitic. In addition, both ultramafic and gabbroicrocks of the 'hlameen suiteare undersaturated in

220 silica (Findlay,1969). Finally, platinum in Tulameen placers is partof a special class; it occurs as nuggets. Other placers of this typeare found in theUral Mountains and in Alaska.

PLATINM GROUP ELEMENTS

Findlay(1963) performed some analysesfor platinum and palladiumin tht? Tulameen Complex.However, he didnot analyse for the other platinoids,, and didnot develop a detailedpicture of the PGE distribution.Raicevic andCabri (1976), Cabri, mens, and LaFlamme (1973), and Cabri and Hey (1974) examined PGE from Tulameen placers. They recognized one newPGE mineral(tulameenite) and helpedestablish some of the platinoid chemistry and mineralogy.

Alaskan peridotitesare characterized by high Pt/(PttOstIr) ratios and highPt/Pd ratios, relative to largelayered ultramafic intrunions (Raicevic and Cabri,1976). It should be notedthat Fd is rare inthe Tulameen mterial(Raicevic and Cabri, 1976; Findlay,1963).

Overall,Findlay (1963) found the highestconcentrations of Pi: indunite and peridotite.In rock samples, he foundthe highest Pt content to be 0.225 gram per shortton in dunite on OlivineMountain. The background Pt content in the dunite is 0.08 to 0.09 gram per short ton (:Findlay, 1963).Chromite segregations within the ultramafic rocks retllrned the highestvalue of 7.34 grams pershort ton Pt. Findlay(1963) also found that pt is enriched in themagnetic fraction of chromitesamples relative tothe non-magnetic fraction.

AlthoughFindlay (1963) gives a briefsketch of the distributionof platinumwithin the "hlameen Complex, he has notsystematically determined the overall PGE distributionor mineralogical/chemical associationsfor the PGE. The authorhopes to establishboth of these.,

Duringthe 1981 fieldseason some 300 rocksamples from the Complex were collected(Figure 2). Most weighed 4 or 5 kilograms. The samples represent all the major units of the complex, although the greatest samplingdensity was in theOlivine-Grasshopper Nountain area. The samplingdistribution is largely a function of access and outcrop availability.

Analysisfor all six PGE and gold will be carriedout on theUniversity of Alberta slowpoke reactor. A selectivegroup separation scheme for radiochemicalneutron activation, described by Nadkarni and Morrison (1977), will be used.This technique allows for precise precious meta:ls determinations to less than 20 ppb levels of concentration. About 150 samples will be analysed in this manner.

Once the PGE concentrationin the samples is known, reflectedlight and transmittedlight microscopy will be used to determinemineralogical associations.Electron microprobe analysis will be used to supplement

221 this work. These observations will be of interestnot only with respect to the TdlameenComplex, butalso to thoseseeking PGE inother Alaskan ultramafic complexes.

ACKNOWLEDGMENTS

I would like to thank Drs. Roger Morton and Bruce Nesbitt, Department of Geology, University of Alberta, fortheir help and supervision of this research. The author was ablyassisted by Mr. HarryNelson and Mr. Donald Dingwellduring parts of the 1981 fieldseason. Thanks arealso extended to claimholders in the study area for their assistance during thefield work, including Mr. David Javorsky, Mr. Bill Halliday, and Mr. Richard Davies. Special thanks to Mr. Ernie North who has been extremely helpful in thefield and in discussion. The support of theBritish Columbia Ministry of Energy, Mines and PetroleumResources is gratefully acknowledged.

REFERENCES

Cabri, L.J., Owens, D.R. andLaFlamme, J.H.G. ( 1973) : Tulameenite, a New platinum-Iron-CopperMineral from Placersin the Tblameen Fiver Area, British Columbia, Cdn. Mineral., Vol. 12,pp. 21-25. Cabri, L.J. and Hey, M.H. (1974):Platiniridium - Confirmation as a validMineral Species, Cdn. Mineral., Vol. 12, pp. 299-303. Findlay, D.C. (1963):Petrology of thelblameen Ultramafic-Gabbro Complex, Yale District, British Columbia, unpub. Ph.D. Thesis, Queen'sUniversity, 407 pp. plusreferences and appendix...... (1969):Origin of the Tulameen Ultramafic-Gabbro Complex, SouthernBritish Columbia, Cdn. Jour. Earth Sci., Vol. 6, pp. 399- 425. Nadkarni, R.A. and Wrrison, G.H. (1977):Neutron Activation Determination of Noble MetalsUsing a Selective Group Separation Scheme, Jour.Radioanalytical Chem., Vol. 38, pp. 435-449. Raicevic, D. and Cabri, L.J. (1976):Mineralogy and Concentration of Au- andPt-Bearing Placers from the TUlameen Fiver mea inBritish Columbia, C.I.Y., Bull., vol. 69, No. 770, pp. 111-1 19. Wyllie,P.J. (1967): Ultramafic and Related Rocks, Wiley and Sons, New York, 464 pp.

222 MANTLEPROCESSES AS DEDUCED FROMALPINE ULTRAMAFIC3

By John V. Ross and MartinEngi Departmentof Geological Sciences University of British Columbia

INTRODUCTION

This study of mantle processes, as deduced from alpineultramafics, has been initiated in the hope that some positive statements may be made concerningthe predictability and conditions of occurrences of chromite depositswithin British., Columbia. Severalwell-exposed alpine ultramafic bodieshave been chosen forstudy. They are allwithin Upper Paleozoic rocks and thus may be slices of the same original mantle material that have since beenwelded to thecraton.

Interpretation of conditions of equilibrium and deformationprocesses depend upon accuratedetermination ofgeothermometry and geobarometry of theconstituent phases. Methods €orcalculation of theseconditions are based upon calibrated exchange equilibria among olivine,pyrox.ene(s), and spinel. These require accurate probe analyses of fresh materi.al. Thus,. we have examined threealpine ultramafic bodies whose rock typedistribution hasbeen mapped previouslyin some detail. These are theBridge River ultramafic(Wright, 1974), thenorthern end of theShulaps ult.ramafic complex (Leech, 19531, and theBlue River ultramafic (Wolfe, ‘1965) north of Cassiar .

GENERAL DESCRIPTION

TheseultramaEics were chosenbecause they reportedly lack or have only a moderatedegree of serpentinization. Complete structuralsections were mapped across each of the bodies and samples collected for thh section and probeanalysis.

At this time, preliminaryexamination o€ thinsections indicates that the BridgeRiver and Shulapsultramafics are remarkably similar. Both are composed essentially of harzburgitewith interlaminated dunite and very minorwebsterite and wehrlite. Where they are interdigitated,dunite and harzburgite are present in almostequal proportions and individuallayers varyin thickness from a few centimetres to several metres. Macroscopia layeringdefined by complex interdigitations of harzburgite and dunite is theearliest recognizable structure, and in some instances it is possible to inferthe original facing direction of crystallization. AI: several localitiesthis layering is involvedin tight folds, some nearisoclinal. These foldsare on theoutcrop scale (Figure 1) and in many instances elongateorthopyroxenes outline a foliation that is locally parallel to theiraxial surfaces.

223 2 24 On a regionalscale, the layering and orthopyroxenefoliation are folded into broad open structureswith angles between their limbs ofapproxima.tely 60 degrees andwhose axes appear to be coaxialwith those of theearlier tightfolds. Near thecore regions of these open foldselongate orthopyroxenesare very well aligned parallel withthe axial surfaces clf theselater folds.

It is frequentlyobserved that small stringers of orthopyroxe:%eand dunite alsoparallel the axial surfaces of the two fold sets, wherea:~chromite, where present in any concentration,appears aligned only with the earliest foldset elements.

The generalpetrographic and earlystructural character of theBlue River ultramaficappears to be similar to thatjust described. owing to subsequentintrusion of theCassiar Batholith (Wolfe, 1965), however, thereare notable differences in later development. The northernportion of thisultramafic body, aswell as adjacentsedimentary rock3 and andesites, are thoroughlycontact-metamorphosed by thebatholith and locally display a series of clearlydefined isograds. Thesehave been mapped along severalstructural traverses. Within the contact aureole pervasive recrys- tallizationpartly destroyed mesoscopic structuralelements and obliterated microscopicfeatures. The southern part of the body,however,, provides some materialthat can be directly compared to specimens from theother two bodies. However, serpentinization is muchmore intensehere and outcrop conditionsare generally poorer.

OUTLINE OF LABORATORY INVESTIGATIONS

The sample materialcollected this summer is presentlybeing examined petrographically,specifically with the aim of identifyingsections most suitablefor geothermometric and -barometric work and formic~:ostructur,al characterization. The extent and detail of thesefurther studies will depend to a largedegree on the consistency of thepicture emerging. Particularquestions we hope to answerinclude the following:

(1) what were the physico-chemical and rheologicconditions of (de-) formation of the mntle assemblages and mineralfabric? (2) How didthe crustal emplacement affectthese conditions 2nd what conditionsprevailed during and after emplacement? (3) what controlsthe occurrence, abundance, and composition of chromi.te (as pods,stringers, or in disseminatedform) in theseul.tramafics?

ACKNOWLEDGMENTS

Peter van der Heydenand MichielDronkert provided able and cheerful assistance.Brian Cranston prepared the thinsections. JohnWatkins and Doug Whalen (CanadianSuperior Exploration Ltd.) offeredfree helicopter support at Blue River.

225 REFERENCES

Leech, G.B. (1953): Geologyand Mineral Deposits of theShulaps Range, SouthwesternBritish Columbia, B.C. Ministry ofEnergy, Mines & Pet. Res., Bull. 32. Wolfe, W.J. (1965): The Blue River UltramaficIntrusion, Cassiar District, British Columbia,Geol. Sum., Canada,Paper 64-48. Wright, R.L. (1974): Geologyof thePioneer Ultramafics, Bralorne, British Columbia, unpuh. M.Sc. Thesis,University of British Columbia.

226 BOWRON RIVERPROGRESS REPORT

By R.K. Linds University of British Columbia

Thisstudy of the Bowron River coaldeposit, supported by grants from thle British Columbia Ministry of hergy, Mines and PetroleumResources and contributing to an M.Sc. degree, is now inthe final stages. It includes two and a half seasons of mrk in the Bowron Rivervalley under I. Borovic inassociation with Norco ResourcesLtd. andcombines a compilation of previous work and presentdrill results. The most recent. resultsincluded were obtainedduring the spring and summer of 1981. Prior to this drill program there was insufficientinformation to conduclt a meaningfulstudy of thestratigraphy and lithologies of thecoal deposit. Data collection time was lengthy due to spacing of the drill programs and adversedrilling conditions.

Duringthe two seasons of drilling 22 holes were attempted(l0rotary and 12 diamond-drillholes). Also duringthis period limited seismic and geomagneticsurveys were conducted.Further drilling is requiredto accuratelydelineate the fault contact between thesedimentary rocks and the underlyingvolcanic rocks, and to resolveproblems regarding faulting versuslithofacies changes. Norco ResourcesLtd. plans to continue drilling late thisfall.

Between drilling programs, the lithologies and stratigraphy of the sediments ware analysed at theUniversity of British Columbia. These studiesincluded definition of thelithologies and associatedsedimentary structures, analysis and mapping of thelithofacies, determination of the lithofacies,determination of thesubsurface structure, maceral and reflectivityanalysis of thecoals, X-ray diffractionanalysis of some of the shales, and petrology of theconglomerates and sandstones. Some of the resultsobtained from these studies are as follows:

Thirteendistinct lithologies exist withinthe Bowron River basin. The lithologies may occursingly, or in combinations of several types. TWJ lithologies of the Mountain Group Slide crop outin the basin. These are greenstones of theAntler Formation and two differentlimestones which havebeen assigned to theGreenberry Limestone Member of themyet Formation.

Sediments inthe Bowron Riverbasin can be broadlysepara.ted into threefacies groups. These are a lacustrinefacies, anadluvial fan to plan facies, and a transitionalfacies which contains elements of bothlacustrine, and alluvialfacies.

A predictablestratigraphy is best developed in the lacustrine facies, and most poorlydeveloped in thealluvial fan to plan facies.

227 (4) Subsurfacestructure involves little foldingexcept locally along faultcontacts. The structure is dominated by high-angleblock faults. 'Itro patterns of faultingexist: one set of faultsparallel to thetrend of thebasin. The othertrends northeastward across thebasin. The general form of thebasin appears to be a faulted, asymmetricalsyncline.

(5) The coalhas sub-hituainous rank. Maceral and reflectivityanalysis are in generalagreement with previous work by Donaldsonof the GeologicalSurvey of Canada. The coalconsists of vitrinite, vitriniteprecursors (telinite and collinite), and variousexinites of which resisite and cutinite were the most abundant.Reflectivity values were variablebut generally agreed with those obtained by Donaldson.There was no apparentincrease in reflectivity with depth of burial.

(6) Examinationof some ofthe shales, particularly those with swelling properties, showed thatthey consist of quartzchlorite, illite, and micas. Despitethe swelling or disaggregating nature of theseshales on exposure torain water, only onesample contained abundant smectites.

(7) Shales from thelacustrine facies were tested for palynomorph content. Most possessed an abundantpalynomorph assemblage that correlateswith Middle to LatePaleocene assemblages. The flora represents a warm to temperate, wet paleoclimate.This is the first documented Paleoceneassemblage described in British Columbia.

(8) Conglomerates and sandstones were sampled andexamined under a petrologicmicroscope. They consist of quartz of varioustypes, argillitic and phylliticclasts, limestone clasts, and carbonaceous materials. On the basis of compositionthe most likelysources for the Bowron Riversediments are the Guyet Formation and theupper Cariboo Group.

228 PRELIMINARYRESULTS OF A FLUID INCLUSION STUDY OF SAM GOOSLY DEPOSIT EQUITY MINES LTD., HOUSTON

By K. Shen and A.J. Sinclair Department of Geological Sciences University of British Columbia

INTRODUCTION

Sam Goosly copper-silverdeposit (MDI No. 093L/001) of Equity Mines Ltd. is 35 kilometressoutheast ofHouston. The deposit was puti.nto productionin 1980 withabout 35 milliontonnes of reservesqrading 0.33 per cent copper, 87 grams silver per tonne, and small but significant amountsof gold and antimony.Recent studies(Wetherell, 1979; Wetherell, et al., 1979; Wodjak, 1974; and Ney, etal., 1972) have ledto proposal of severalgenetic models. Our fluidinclusion work hasbeen undertaken to obtaininformation concerning the ore-forming process as a means o€ establishing a genetic model €or the deposit. Samp1.e~used in ourstudy were obtained from a collection made originally by Wetherell (1979) representingall principal stages of theparagenetic sequence that hedescribed. It alsoincludes samples from allthe principa.1 centres of mineralization knownon theproperty.

Four mineralized zones are located on theproperty. The Main. and Southern Tail zones are the most importantdeposits; present production is entirely frcm theSouthern Tail zone. The Tourmaline Brec!ciazone .and a smallporphyry-type copper-molybdenum wne inthe quartz nmnzonite stock are of special interest becausethey may be geneticallyrelated to ore(Wetherell, 1979).

Sulphidesin both ore zones consist mainly of pyrite,tetrahedrite and chalcopyritewith less abundantarsenopyrite, galena, sphalexite, pyrrhotite, and varioussulphosalts. Theseminerals occur mostly as stockworks,veins, and disseminations.Locally they form rnarlsive wne:;. Dominant gangue minerals are quartz and sericite with lesser amounts OE chlorite,tourmaline, corundum, andalusite, calcite, and pyrophyllite. The two ore zones are part of a single,larger mineralized zone that i:3 apparentlyepigenetic and crosscutsstratigraphy.

METHOD OF STUDY

Twelve samples were selectedfor detailed fluid inclusion study, seven from theSouthern Tail zone, onefrom the Main zone, two from the Tourmaline Breccia zone, one from a vein at thecontact of thequartz monzonitestock, andone from theporphyry-type Occurrence within the quartz monzonitestock. Doubly polished plates were preparedfor each sample tolocate fluid inclusions and severalchips containing fluid inclusions were selected from eachdoubly polished plate for heating and freezingexperiments. Filling and lastmelting temperatures were determined using a Chaixmeca stage. Temperature measurements ere producible to about 0.1 degrees C with the freezing stage and to less than 5 degrees C with the heating stage. Inclusions in quartz were studied most commonly because of the ease with whichthey could be examined and the presence ofquartz in most stages ofthe paragenetic sequence. Associated minerals and indications of any stagesof deposition were noted. Several samples of sphalerite and calcite and one of vein andalusite were also examined.

RESULTS

Three types of inclusions are recognized based on phase relations at room temperature.

Type I: Two-phase inclusions consisting of liquid anda small gas bubble generally comprising 10 to 20 volume per centof the inclusion.

Type 11: Two-phase inclusions consistingof a large bubble and a condensed liquid. The bubble generally occupies more than 60 volume per cent of the inclusion.

Type 111: Multi-phase inclusions consisting of liquid,a small bubble (about 15 volume per cent of the inclusion), and one or more (up to four) solid phases. Solid phases are most commonly halite although hematite has been identified and sylvite is suspected in some cases.

Primary inclusions are recognized in all paragenetic stages examined, largely by relations to crystal growth zones. In many cases, however, individual inclusions cannotbe proved with certaintyto be primary or secondary. Many inclusions are clearly secondary relative to their host mineral, although it seem likely that manyof these may represent younger stages in the primary paragenetic sequence.

A histogram of filling temperatures is shown on Figure1 where peaks correspond to specific stages in the paragenetic sequence. The filling temperatures are not corrected for pressure, but indicatea regular decrease in filling temperature (and therefore temperature of deposition) with increasingly young stages of mineralization. Most of the filling temperatures represented on Figure 2 are for quartz from various paragenetic stages. However, it is of interest to note that calcite is late in the paragenetic sequence and filling temperatures in it allare relatively low. Similarily, inclusions in pale sphalerite have relatively low filling temperatures, comparableto those in calcite, but witha more restricted range. A single inclusion fran vein andalusite hasa filling temperature of about 305 degrees C.

Freezing temperatures (Figure 2) indicate a wide range of salinities. In general, the lower temperature stages of mineralization have higher

230 .

FILLING TEMP ("C) Flgure 1. Fillingtanperatwes for 147 incluslons, Sam Goosly deposit. Most are for quartz(blank); other symbols aredeflned on Figure 2. Numbered peaks relatedto speclflc mlneral assenblages as follows: 1 - porphyry-typemlneralizatlon, 2 - Tourmlin~s Breccla zone, 3 to 5 - %in and Southern Tall zones. meltingtemperatures and therefore lower salinities. Highest salinities are indicatedfor fluid inclusions €ran theporphyry-type occurrence €or which halitecrystals dissolved between 360 degrees C and 425 degrees C.

Intermediatesalinities were obtained€or fluid inclusions frcm the TourmalineBreccia, and a range of low salinities is indicated€or most of the stages of mineralization in the Main and Southern Tail zones.

DISCUSSION

The temperature of filling of primaryinclusions decreased with time, as shown by therelationship with paragenetic sequence illustrated on Figure 2. In addition,there is a spatial component to variations in filling temperatures.Highest temperatures are €or porphyry-typemineralization directlyassociated with a quartzmonzonite stock. Somewhat 'lower fillingtemperatures relate to a TourmalineBreccia zone north of theore zones and a wide range of filling temperatures closelyrelated to paragenetic sequence existswithin the Main and Southern Tail zones.

These dataare consistent with the model proposed by Wetherell(1979) in which thequartz monzonite stock just west o€ theprincipal ore zones providedthe energy to drive a circulatinggeothermal system. Periodic fracturingduring mineralization combined with a generallyde(:reasing temperatureregim led to a clearly deEinedparagenetic sequence of veining.

231 LAST MELTING TEMP ("C)

Figure 2. Freezing(last neltlng) temperatures for 115 fluid Incluslons. Sam Goosly deposit.

Freezing data indicate high salinity for mineraliztion within the quartz monzonite stock, moderate salinityfor mineralizing fluids of the Tourmaline Breccia zone anda range of lower salinities for the Main and Southern Tail zones. In the Wetherell model, the quartz monzonite is the centre of the mineralizing system. These salinity data indicate that high salinity fluids came from within the quartz monzonite stock, whereas a substantially more meteoric water component was involved elsewherein the hydrothermal system.

CONCLUSIONS

A preliminary evaluation of fluid inclusion data for theSam Goosly deposit suggests that all of the principal mineralized zones formed during a single episode of mineralization. The hydrothermal system was

232 apparentlycentred on and driven by thequartz monzonitestock which 1.i.e~ just west of the two principalore zones. Mineralizationproceeded underconditions of gradually decreasing temperature and intermittent fracturing so a well-defined sequence of veiningresulted. High salinity fluidinclusions that contain halite as a daughterproduct suggest that a very small proportion of theore fluid had an igneousorigin. Most of theore fluid, however, was of relatively low cutvariable salinity indi- catingthat meteoric water was the dominant component in the hydrothenma1 system.

REFERENCES

Ney,C.S., Anderson, J.M. and Panteleyev, A. (1972): Discov

233 CHROMITE OCCURRENCES IN MITCHELL RANGE ULTRAMAFIC ROCKS OF THE STUART LAKE BELT CACHE CREEK GROUP (93N)

by Peter J. Whittaker Department of Geology, CarletonUniversity

INTRODUCTION

The Mitchell Range map-area, located 240 kilometresnorthwest of Prince George, is withinthe Stuart Lake Belt of the Cache Creek Group (Permian). The Cache Creek Group consistspredominantly of massively bedded carbonate rockswith minoramounts of laminatedchert-siltstone and shalysiltstone. The carbonatesuccession extends from theMitchell Range 120 kilometres southeastward to theFort St. James area where it attains a thickness of 8 kilometres(Armstrong, 1949).

The southeast-strikingcarbonate succession is foldedinto an open anticline-syncline pair immediatelysouth of theMitchell Range ultramafic rocks. The open foldshave subhorizontal east-southeast-trending fold axes suggestingcompression from the south-southwestassociated with thrust faulting and obduction of theMitchell Range allochthonousrocks.

Chromiteoccurrences inthe Mitchell Rangewere documented inArmstrong's 1949 memoir. Little (1947) describedultrabasic and associatedrocks of the MiddleRiver Range, approximately 70 kilometressouthwest of the Mitchell Range ultramaficrocks. Since then various companies and individuals have shown an interestin the chromite and nephrite('British Columbia jade')potential in the area.

PREVIOUS WORK

Previousgeological work was of a reconnaissancenature, primarily by geologists of theGeological Survey of Canada.Selwyn (1872) examined the area betweenQuesnel and PeaceRiver, followed a few yearslater by Dawson (1878, 1881 1. McConne11 (1896) reported on the areasdrained by theFinlay and Omineca Rivers and alsovisited the placer gold fields at Germansen Landing and Manson Creek,northeast of theMitchell Range ultramaficrocks. Camsell ( 1916) reported on thenorthern interior of British Columbia, Hanson (1925) on thearea from PrinceRupert to BurnsLake, and Lay (1 926- 19391, of theBritish Columbia Department ofMines, examined numerous mineral deposits and placerfields in thenortheastern mineral survey district.In 1934 Kerr examined placerdeposits at Manson and Slate Creeks.Regional mappingof the Fort St. James area began in 1936 and ended in 1944; it was coordinated by J.E. Armstrong (1949).

234 GENERAL GEOLOGY

MITCHELL RANGE ALLOCHTHON

Allochthonousrocks within the Mitchell Range consistprimarily of harzburyitewith minor dunite(Figure 1); they are everywhereserpen- tinized.Sparse pre-tectonic orthopyroxenite veins and gabhrodykes are deformed and reflect internal deformationpresumably developed during obduction.Alteration dykes o€ albitite-rodingite are simi1.arily deformed. Chromititelayers and layerswith disseminated chromite exhibit variable degrees of deformationwithin the harzburgite, from isoclinailfolds to brittle segmented planarlayers.

Xenoliths of Cache Creek Group rocks up to severalsquare kilometres .in areathat occur in the serpentinized ultramafic rocks (Fiqure 1) appear to havebeen rotatedduring transport. Contacts between harzburgiteand xenolithsregularly exhibit a 0.5-metre-thick,highly fissile zone; rarely, a 1 to 2-metre-thickamphibole-rich alteration zone is deve1o:ped in theharzburgite.

Laterintrusions are now seen as meta-gabbro (Figure 1) and meta-diorite dykes.Clinopyroxene in the dykes has been alteredto amphibolebut primarysub-ophitic and equigranular medium-grained texturesare preserved. Thesedykes may be derived from thedioritic-granodioritic Hitchell Range Batholith(Armstrong, 1949) which occurs 2.5 kilometres west of the ultramafic body.

STRUCTURE

The Mitchell Range ultramaficallochthon is bounded by north-northeastand east-trendinglineaments (Figure 1). Rocks of the Cache Cnsek Group occur tothe south and east,Takla Group volcanicrocks (Upper Triassic to Upper Jurassic)crop out to the north, and theMitchell Batholith (Upper Ju.rassic to Lower Cretaceous;Armstrong, 1949) hasintruded to thewest.

Serpentinizedharzburyite of the Mitchell Ranye allochthon exhibits a stronglydeveloped penetrative north-northeast-trending ductile shear foliation(Figure 2). Dip of thefoliation changes Eran westerly in the western part of the area toeasterly in the east. The contour maxima. on Figure 2 indicate a preferrednorth-northeast foliation but they are centredabout an east-southeast great circlegirdle, indicative of a broad north-northeast-trendingantiform. Internal breccia zonesoccur in the harzburyitewith well-rounded, randomly oriented,pebble to cobble-sized fragments set in a finely comminuted serpentinized matrix. The northeast and east-centralareas of theultramafic massif are underlain by tect.onic breccia(Figure 1). The brecciahas sub-angular fragments up to 2 metres in size that are predominantly of harzburgitewith minoramounts of dunite. Thiscoarse tectonic breccia appears to representthe sole of the allochthonousultramafic rocks.

235 I

2 36 N

Figure 2. Contoured stereo-proJection of poles to fol latltm planes, Mitchell Range (135 poles); contour Interval, 2 per cent per 1-per-cent area.

TECTONIZED HARZBURGITE

Tectonized and serpentinized harzburgite comprise approximately90 pe!r cent of outcrop in the Mitchell Range allochthon. Its mottled, foliated weathered surface is deep brown with pale silvery brown talcose patches. On fresh surfaces it is mottled black-green to black-brown. Talcose patches are 0.5 to 1.5 centimetres in size and are pseudomorphicaftw sheared orthopyroxene. Intense shearing in some outcrops has resulted in mechanical segregation of orthopyroxene and olivine into granular, 1.0 to 1.5-centimetre-thick, discontinuous layers. A braided, rippled weathered surface results because orthopyroxene-rich layersare more resistant than olivine-rich layers. More extensive shearing led to development of well rounded 2 to 10-centimetre augen-shaped clots of coarse-grained orthopyroxene pseudomorphed by talc. Orthopyroxene augen in fine-grained olivine-rich harzburgite usually exhibit length to width ratios3: 1.of

Less intensely foliated harzburgite showing pre-tectonic cumulate texture crops out discontinuously in a narrow zone along the east-centralof part the ultramafic massif. It is variably medium to coarse-grained with subhedral orthopyroxene and anhedral olivine. On the northeast ridge, very coarse-grained harzburgite exhibits primary magmatic olivine poikilitically enclosed in orthopyroxene; both are anhedral.

Harzburgite hosts all but one of the layered and nodular aggregate and massive chromitite Occurrences. Disseminated accessory chromite occurs throughout the ultramafic rocks and varies fran a trace2 perto cent of the rock.

237 6x3 It.

H. H. H. H.

H. x.

". D.

lSS/L*I" H. H. H. H.

H. H. H. H. H.

Host Rock

H. lbreccial

H. H. H. H. H.

238 DUNITE

Duniteoccurs in approximately 1 to 2 per cent of theoutcrqp area as contorted,irregularly shapedpatches that reflect the internal deformation in theultramafic body. A planardunite layer, 15 metreslong and 30 centimetresthick is one exception.Dunite weathers with a smooth,orange- brown surface and is waxy brownishgreen on freshsurfaces. It consists of fine to medium-grained anhedralolivine. It is foliated so is finely fissile on weatheredsurfaces. Accessory chromite is fineto medium grained and subhedral. With theexception of one chromititelayer (Table 1, location X5) no other anomalous concentrations of chromite were observed inthe dunite.

PRE-EMPLACEMEW GABBRO

Segmented and deformedgabbro dykes occur primarily in thecentral and southwesternparts of theMitchell Range allochthon. They are fine grained,serpentinized, and vary in thickness from 5 centimetresto 1,.5 metres. Dyke segments orboudins are up to 3 metres long andform open to isoclinalfolds. The dykeshave associateddyke-like alteration zoneswith planar or 'pinch and swell' to boundinaged structures. These alteration zonesconsist of rodingite and arevery fine grained to aphanitic and equiqranular. Colour varies from bone white to pastel shadesof brown, green, and pink.Contacts between harzburgite and thealteration zones are sharplydefined with a 1 to 3-centimetreaphanitic black-green selvage.

POST-EMPLACEMEW GABBRO

Generallynorth-south-trending gabbro dykes (Figure 1) up to 15 metres thickintrude the harzburgite in thenorth, central, and southern parts of themassif. This gabbro is fine to medium grainedwith sub-ophitic tsD equigranulartexture and is notserpentinized. In placesclino-pyrox,ene hasbeen altered to amphibole, and palegreen plagioclase was saussuritized.

CACHE CREFXGROUP

Xenoliths of thecache Creek Group (Figure1) up to 1 squarekilometre in area,occur in thesouthern part of themassif. Smaller xenoliths of 10 to 300 square metres are distributedthrough the northern part. The xenoliths consist oflimestone and dolostone,siltstone with chert laminae, and shalysiltstone.

Limestonexenoliths are thickly beddedand fine grained with equigranular texture.Small, 2 to 10-centimetre,chert nodules in the carbonate blocks are contortedwith thin, 1 to 3-millimetre,quartz veins originating from them.Black siltstonexenoliths havegrey 0.5 to 2-millimetre chert laminae which are highlycontorted and brecciated.

239 CHROMITE OCCURRENCES

Chromite occurrences (Figure 1, Table 1) are concentrated in the central and southwestern parts of the Mitchell Range allochthon, although several occurrences are scattered on the northeast ridge. The Bob and Simpson deposits described by Armstrong (1949) were examined and sampled.

Chromite occurs in disseminated and layered form, as aggregate and massive chromitite in layers, and as discrete nodules (Figure3). Chromite nodules exhibit both aggregate and massive chromitite textures.

Accessory chromite is widely disseminated throughout the ultramafic rocks and varies from a trace to2 per cent. In this form it is very fine to fine-grained and subhedral to euhedral. Medium-grained, disseminated chromite occurs rarely and is either anhedral or forms aggregates of two to four grains.

Layered chromite (Table 1; XS,.,: 9, 16, 17) consists of massive chromitite and aggregate chromltlte; as well as concentrations of disseminated chromite.

Outcrops of massive chromitite arewooth textured and freshly broken surfaces display coarse hackly fracture and sub-metallic black-blue lustre. These layers range in thickness from 2 (Table 1; X,) to 75 centimetres (Table 1; X8, 9) and are truncated by joints (Figure 3c) or breccia zones in host harzburgite. Layer contacts with harzburgite are sharply defined and they are usually parallelto the foliation.

Aggregate chromitite and disseminated chromite layers consist of disseminated fine to medium-grained chromite. Aggregate chromitite layers (Table 1; X16, 17) contain greater than 75 per cent chromite and exhibit sharply defined contacts with harzburgite. Internally they display a fine to medium-grained subhedral to anhedral texture. Layers are plastically deformed into open and isoclinal folds and display pinch and swell structures. Granular, fine to medium-grained chromite fragment trains extend from the ends of deformed layers. Brittle deformation has resulted in some layers being faulted into angular2 to 5-centimetre fragments with displacements of 10 to 20 centimetres.

Disseminated chromite layers,2 to 25 centimetres thick, responded to deformation in a ductile fashion because silicate minerals between chromite grains absorbed most of the strain. Contacts between disseminated chromite layers and harzburgite are gradational Over2 to 3 millimetres and are gently undulatory. Pinch and swell structures are developed as well as both open and isoclinal folds. Along strike from the ends of disseminated chromite layers, detached chromite augen may occur.

Thicker massive chromitite layers (Table 1; X8, 9) contain irregularly shaped 3 to 10 centimetre coarse-grained patches of aggregate chromitite. These consist of anhedral 1-centimetre chromite grains in an open framework separated by approximately 10 per cent interstitial blue-grey aphanitic serpentine. The coarse-grained patches are highly irregular.

240 Chromiteand aggregate chromite to massive chromitite nodules display fine to medium-grained subhedralto anhedral textures. Nodulesrange in size from 1 centimetreto 1.3 metres and are rounded to augen-like. Some appear to be thin (0.5 centimetre)selvages on shearsurfaces whereas most extend to depths of at least severalcentimetres. Chromitite nodules exhibit massive,aggregate, and disseminatedtextures. Brittle fracturing is rmre evidentin increasingly massive chromitite. Larger nodules (Table 1; X7, 11, 14) usually have a massivechromitite core with discontinuous ]rims of disseminatedchromite. Rims pinch and swell from 0.5 to 5 centimetres and mst are offset by late jointing and small-scalefaulting. All the texturesobserved in layered occurrences also occurin chromite nodules.

The progressionfran open isoclinalfolding in chromite layers, to pinch and swell structures, and finally to detachedsegments of chromitelayers (Figure 3a. b)strongly suggests that chromite-chromitite nodules resu:it from theshearing of primarychromite-chrornitite layers. Abundant nodules,the largest being 1.3 metresin size (Figure 3d). an.d remnant chromititelayers up to 75 centimetresthick (Table 1) suggest that extensiveprimary chromite-chromitite layering existed. This has since? been disrupted and redistributed by ductileshearing during tectonic emplacement of theMitchell Range allochthon.

d 30cm tom

Flgure 3. Sketches frm photographs of chromite occurrences: (a) deformed nodule, (b) deforned layer wlth ’pull-apart’ structure, (c) planar layered couplet wlth angular truncations, and(dl deformed masslve chromltlte nodule.

SUMMARY

Extensivebrecciation and penetrativeductile shear foliation within the Mitchell Range allochthonsuggests extensive transport of theserocks while in a solid,but perhaps still hotplastic state. Final movement

9 241 resulted in brecciationalong the sole of theultramafic massif. Similar emplacement breccias at thesoles of allochthonousultramafic bodies occur inthe TableMountain and St. Anthony Complex ophiolites (R. Talkington, pers.corn., 1981).

The proximity of theMitchell Range ultramaficrocks to a thrust zone,the predominanceof massive harzburgite with only minor patches of dunite, and thesuggestion of primarychromite-chromitite layers indicate that the Mitchell Range allochthonconsists of rocks from below thecumulate dunite-layered zone asobserved at MurrayRidge (Whittaker and Watkinson, 1981) and represent a low stratigraphiclevel in theophiolite succession.

RECOMMENDATIONS

Detailed mapping of theMitchell Range allochthonrevealed additional chromiteoccurrences not previously noted. Additional workon chromite occurrences in otherlarge ultramafic massifs, such as Mt. Sydney-Williams and Bitsutl Mountain to thesouthwest, should therefore he considered. Inaddition this would aid in reconstructingthe ultramafic part of the now fault-dissectedophiolitic rocks of the Stuart Lake Belt of the Cache Creek Group.

ACKNOWLEDGMENTS

The author would like to express histhanks and appreciation to H. Kukal forcapable and cheerfulfield assistance and to R. Talkington and Dr. D.H. Watkinson forhelpful discussions. Financial support for field work from theBritish Columbia Ministry of hergy, Mines andPetroleum Resources and from theGeological Survey of Canada (Grant 203/4/81) to Dr. D.H. Watkinson is acknowledgedwith thanks.

REFERENCES

Armstrong, J.E. (1949): FortSt. James Map-Area, Cassiar and Coast Districts, British Columbia, Geol. Surv.,Canada, Mem. 252, 210 pp. Camsell, C. (1916): Explorationin the Northern Interior of British Columbia, Geol. Surv.,Canada, Summ. Rept. 1915, pp. 70-75. Dawson, G.M. (1878): Report on Explorationsin British Columbia, Chiefly inthe Basins of theBlackwater, Salmon and Nechako Rivers, andon Francois Lake, Geol. Surv.,Canada, Rept. of Progress, 1876-77, Part 111, pp. 17-94...... (1881 ) : Report on an Exploration from Port Simpsonon the PacificCoast to Edmontonon theSaskatchewan, Embracing a Portionof theNorthern Part of British Columbia and the Peace RiverCountry, Geol. Surv.,Canada, Rept. of Progress, 1879-80, Part B, pp. 1-142. Hanson, G. (1925): PrinceRupert to BurnsLake, Geol. Surv.,Canada, Sum. Rept., 1924, Part A, pp. 38-42.

242 Kerr, F.A. (1934): Manson River and Slate CreekPlacer Deposits, Mneca District, B.C., Geol. Surv.,Canada, Sum. Rept.,1933, Part A, pp. 9-29. Lay, D. (1929-1939):Northeastern Mineral Survey District No. 2, Minister of Mines, B.C., Ann. Rept., 1925, pp.A142-A145; 1926, pp. A1 44-A146; 1927, pp.C150-Cl53, C155-C160; 1928, pp. C177-Cl82; 1929, pp. C181- 182, C185-C187; 1930, pp. A143-A149; 1931, pp. A75-A76,A80; 1933, pp. A99-Al00; 1934, pp. C13-C15; 1936, pp. C3-Cl6; 1938, pp. C3-Cl4. Little, H.W. (1947): The Ultrabasic and Associated Rocks of theMiddle River Range, British Columbia, Ph.D. lhesis, University of Toronto. McConnell, R.G. ( 1896):Report on an Exploration of theFinlay and Oinineca Rivers, Geol. Surv., Canada, Ann. Rept. (new series), '1894, Vol. VII, Part C. Selwyn, A.R.C. (1872): Journal and Report of PreliminaryExploration:; in British Columbia, Geol. Surv.,Canada, Rept. of Progress, 1871-72, pp. 16-72. Whittaker, P. J. andWatkinson, D.H. (1981 ) : Chromite in Some Ultrama:Eic Rocks of the Cache Creek Group, British Columbia, in Current Research, -01. Surv., Canada, Part A. Paper El-lA, pp. 349-355.

243 DEPOSITIONAL ENVIRONMENTS AND PALEOCURRENT TRENDS IN THE GATES MEMBER NORTHEAST COALFIELD

By S.M.M. Carmichael Departmentof Geological Science University of British Columbia

INTRODUCTION

The Lower Cretaceous Gates Member is an importantcoal-bearing stratigraphicunit in the Rocky Mountain Foothills of northeasternBrit- ish Columbia.During the past two years,depositional environments in the Gates have been studied between the WolverineRiver and the Mount Belcourt area, usingoutcrop, core, and geophysical log data. In this paper, some of thepreliminary results of this study are presented.

LITHOSTRATIGRAPHIC NOMENCLATURE

The lithostratigraphicnomenclature of the Lower Cretaceousin the Foothills and thestratigraphic equivalents in the subsurface to the east, is illustrated on Figure 1. In theFoothills, south of the Pine River, the Gates,together with the €kIlcrossand Boulder Creek, are members of the Commotion Formation.In the subsurface to the east the stratigraphicequivalents to the Gates are theFalher and the Notikewan Members.

In recentyears, two new terms have come intoinformal use: Transition Beds, to describean interval of thinly bedded sandstones and claystones between the underlying Moosebar Formation and the Gates; and the Torrens Member, for a thick, regionally extensive, marinesandstone inthe lower part of the Gates. Neither of theseunits hasbeen formally described.

TECTONIC SETTING AND REGIONAL PALEOGEOGRAPHY

During EarlyCretaceous time, northeasternBritish Columbia occupied part of the Rocky Mountain foredeep basin, a rapidlysubsiding sedimentary troughthat was bounded to thesouthwest by the Columbian Orogen and to thenortheast by theInterior Platform. A thicksequence of molasse was depositedin the foredeep; it was derivedmainly from thetectonically active area to thesouthwest. The sediments here depositedin both marineand non-marine environments.

During the EarlyCretaceous, a major embaymentof theBoreal Sea layto the north(Douglas, etal., 1976). A series of major transgressive/ regressivecycles show thatthis sea transgressed southward on several occasions. Wide areas of mrine muds and silts were depositedduring major transgressions whereasnon-marine deposition was more widespread duringregressions. The Gates Member, which mnsists of non-marineand

244 PINERIVER FOOTHILLS,BC. PLAINS,PEACE ALBERTA,IV1 ' I U BOULDERCREEK WL MBR.

-+u aa FALHERMBR. - MOOSEBARFM. u WILRICHMBR. - BLUESKY FM. uGETHINGFM. GETHINGFM. 1I CADOMINFM. CADOMINFM. I rFlgure 1. Llthostratlgraphlcnmnclature of the Lwer CretaceousIn the FOathlIIs and thestratlgritphlc equlvalentsIn the subsurface to the east; fra Stott, 1968. nearshoremarine sediments, was depositedduring a generalperiod of regression.

DUMB GOAT MOUNTAIN SECTION

Dumb GoatMountain* is locatedin the southern part of the area, approximately 3 kilometresnorthwest of Mount Belcourt.Outcrop is good and a fairly complete section was measured from thebase of the Moosebar Formation to the top of the Hulcross &&er (Figure 2). lPle interval:^ are described as follows:

(1) Moosebar Formation: Twenty-seven metres of grey,silty claystones, deposited in a marine environment. "ne lower contactwith the GethingFormation is abrupt and represented by a thin, 10 to 20- centimetre-thickconglomerate overlying 1 metre of bicmturbated sandstones.This conglomerate was depositedduring the marine transgression which occurred at the base of the Moosebar. *Dumb Goat Muntaln - an informal nme used by coalcapany geologists in the area. 245 L1

GATES MEMBER i

WF Orientation of Wood I Log Fragment:

Figure 2. Moosebar,Gates, and Hulcross section on Dumb GoatMountaln.

246 (2)Transition Bedsand Torrens Member: The Moosebar Formation is overlaingradationally by two major coarsening-upcycles in the Transition Bedsand Torrens Member.The lowermostcycle consists of thinly bedded,very fine-grained sandstones, and interbedded,silty claystones. The sandstonesoccur as individualunits 15 to 30 centimetres thick,or as composite units up to 2.5 metres thick. Contacts are generallyabrupt or slightly erosional, as indicated by thepresence of smallclay rip-up clasts. Bedding is predominantly hummocky crossstratification (HCS) butthere is some hclrizontal bedding.Symmetrical wave ripples areoccasionally present on the topsurfaces of thesandstones, as are burrows,tracks, and trail::.

The secondcoarsening-up cycle consists initially of thinly bedded HCS sandstones and siltstones like thosein the lower cycle,but they are overlain by a thickunit of fine to medium-grained sandstone. The thinly bedded sandstones and siltstones in thelower cycle and the lower part of the secondcycle are assigned to the Transition Beds; the thicksandstone at thetop of the !:econd cycle is assigned to theTorrens Member. On thebasis of sedimentary structures, three units are recognized in the Tbrrens. The lowermost is fine-grainedsandstone that is 4.6 metres .thick. It haslarge, shallowtroughs, horizontal to low-anglebedding, and occasionalplanar crossbedding similar to swaleycross stratification (Walker,1981). The overlying10.8-metr

The Wansition Beds and 'Ibrrens Member are interpreted to be marine deposits formed during a period of coastalregression. Thin-bedd.ed HCS sandstones in thelower pat are interpreted to be offshore storm-generateddeposits, whereas thick sands of theTorrens Member were deposited closer to shoreline.

(3) Non-Marine Part of the Gates: Themain part of theGates section. is a 259-metre-thicksequence of non-marine sandstones,siltstones, claystones, and occasionalcoal seam (mostlycovered), that includes three major conglomerateintervals.

The conglomerates occur as massive units 10 to 24 metresthick. Their lower contactsare erosional and impressions of largetree trunksare common near thebase. Up sectionthe conglomerates are interbeddedwith coarse, pebbly trough and planarcrossbedded sandstones which grade upward intofine-grained rippled to horizontally bedded sandstones and siltstones. A coal seam generallycaps these fining-up sequences.

The conglomeratesare mainly clast supported with coars,e sand in the matrix. Most of thepebbles are rounded andshow considerable variation in size. The largestclast measured was 16 by 7 by 7

247 centimetres; the averagepebble diameter is 1 to 3 centimetres. Bedding is uncommon butpebble imbrication zones are very common and locallyimpart a weak horizontal stratification.

Comparison with the Donjek verticalprofile model (Miall, 1977) suggeststhat these conglomerates were deposited in a braidedriver environment. In the Gates, theconglomerates are associated with fairlythick overbankdeposits. In braided river deposits,overbank deposits may result from lateralchannel restriction on the floodplain,coupled with rapid subsidence (Miall, 1977).

Inthe upper part of the Gates, there are severalfining-up sandstoneunits. Their vertical profile and sedimentary structures suggestthat they are channel deposits. However, theyrepresent a smaller andlower energy river system (? meandering) compared to the underlyingconglomerate channels.

Althoughthey are largely covered, coal seam in the section are inferred from coal bloom and occasionalpieces of coal in float. The thickestcoal zones are in the lower part of thesequence, above the TOrrensWmber. Above theupper conglomerate coals occur at the top of fining-upsequences. These coal seams appear to be thinner, but more numerous, than those in the lower part of the Gates.

(4) Hulcross Member: The marinetransgression at the top of the Gates is marked by a 30-centimetre-thick, clast supportedconglomerate. The conglomerate rests on a thincoal seam and is overlain by 2 recognized;the top cycle resulted in the development of a thick, fine to medium-grainedmarine sandstone (basal Boulder Creek unit).

The sandstonesin the Hulcross are 5 to 50 centimetresthick and predominantlymassive to horizontally bedded. They have abrupt bases and tops. Hummocky crossstratification is presentin 80me and symmetrical wave ripples are commonon thetop surfaces. Small loadstructures my be present on basal surfaces. Ihe thinly bedded sandstones are interpreted to be offshorestorm deposits and turbidites,while the thicker sandstone at the top represents relativelynearshore conditions.

REGIONAL CORRELATION OF THE MOOSEBARFORMATION, GATES AND HULCROSS MEMBERS

A regionalcorrelation of the Moosebar Formationand Gates andHulcross Members for a distance of 85 kilometres from Dumb Goat Mountain inthe south to the Murray area in the north is shown on Figure 3. Marineand non-marine intervalsin the Gates are shownon thissection together with the locations of major non-marineconglomerates and the major coal zones. This correlationillustrates the followingimportant points:

(1) The non-marine part of the Gates thickens to the south, whilethe marine Moosebar toTorrens and lblcrossintervals thin in that

248 direction. Also the number of coarsening-upmarine cycles in the TransitionBeds/Torrens Member increases from two on Ihmb Goat Mountain to fivein the Murray area.

?tlo majormarine transgressions are present within the Gates Member. Both come from a northerlydirection and extendedas far south .as the Monkman area. These transgressions are essential1.y nondepositional, most of themarine sediments were deposited dulring thefollowing phase of regression.

Threemajor non-marine conglomerates are recognized. All occur at consistentstratigraphic levels throughout the area. In thecase of conglomerates 1 and 3, deposition was followed by periods of marine transgression.

The marine unit in the upper part of the Gates hasnot previously been formallyrecognized or described. It is well developed inthe Babcock andMurray areas, where it consists of a laterallyextensive 25 to 40- metre-thickunit of sandstoneswith occasional conglomerates and thin claystones.These, together with the underlying non-marine conglomerate, form a distinctivelithological unit that DenisonMines' geologists (call the Babcock Member.

Marine bivalves were found in thesandstones. Subsequently they were identifiedas pectinid bivalves, probably htolium and Camptonectes 'by Dr. PaulSmith at theUniversity of British Columbia.Further evidence for a marine depositionalenvironment is provided by tracefossils, .which arefairly common and easilyrecognized in cores.These include several distinctivetypes of marineburrows. The base of themarine sands i:3 markedby a thinlayer of verycoarse conglomerate that is interpreted to be a marinelag deposit formed duringthe transgression. The overlying marinesandstones form a coarsening-upsequence, in which several lithofaciesare recognized. Detailed core studies suggest that them were depositedin marine shelf and tidallyinfluenced coastal environments.

COAL OCCURRENCES

Between the Monkman andMurray areas, four distinctcoal zones* are recognized. The location of thesezones is shown on Figurf! 3.

ZONE IA: This zone occurs between tw marine units in the lower part of theGates and contains one or two thincoals. The coal is generally less than 1 metre thick; seams thicken to the south and pinchout to thenorth. Coals in this interval were deposited at thetop of a regionallyextensive, coarsening-up marine sequenceduring a short-livedregressive phase.

ZONE 1B: This zone occurs abovethe next coarsening-up ma:sine Unit and representsthe beginning of the main phase of non-marine sedi- *Coal zones: refers to an Interval rlth one or more coal seans.

249 ...... >- a a a- 3 5

Y 0 0 0- m ma

v) k z 3 w z E a 8 5 008 .:.:.:.:.:.:...... c3 ...... :.:.:.:.:.: 4 ...... 0z 0 0

250 mentationin the Gates. In the Babcock area, up to three closelyspaced seams are present in this interval. Ihe thic'k- est of these, seam J, has an averagethickness of 6 metres.

ZONE 2: This zone occursabove zone 1B and below the marinl? unitin the upper part of the Gates. On Babcock, this zone contains four to five seams, each with an averagethickness of approximately 2.5 to 3.5 metres. Typically, these coalsare developed at the tops of fining-upcycles. On Babcock, two of the seams in tbis zone, seams E and G, wdgeout laterally and are r'zplaced by channeldeposits.

ZONE 3: This zone occursbetween the Upper Gatesmarine sands and the Hulcross Member. Coals in it arethin and noteconomically important. On Babcock there are three seams, A, B, and C, whi.ch rarely exceed 0.75 metre inthickness. Seam B, the middle seam, is thethickest and most persistent.

PALEOCURRENTS

Figures 4 to 7 show paleocurrentdata, plotted as a series of rose diagrams,for the following intervals:

Transition Beds:Measurements inthis interval were madeon axe3of symmetrical wave ripples, and flute and groove marks from thinly bedded sandstonesthat were depositedin the offshorearea as a result of stormactivity. The axes of symmetrical wave ripplesgive anapproximate guide to thetrend of thepaleocoastline, while flute andgroove marks indicate the direction of the paleoslope.This datasuggests an averageeast-northeast - west-southwestorientation forthe paleocoastline and a north-northwest - south-southeast paleoslope. The flute marks indicatethat sediment wazi derived from the southeast .

'Middle' Gates: Data is from fluvialsandstones and conglomerates in the non-marine part of the Gates between the Tvbrrens Member and theconglomerate in the Upper Gates. Measurements wen? made of troughcrossbedding, planar crossbedding, pebble imbri(:ation, and thealignment of logs from thebase of channels. The 'data indicates anaverage paleocurrent direction to the north-northea,stalthough therange includes directions betweennorthwest and east-northeast, Part of the spreadin paleocurrent directions is from using differentkinds of paleocurrectdata for differrent types of fluvial systemsin this interval.

'Upper' Gdtes Conglomerate:This map shows paleocurrent information fromthe conglomerate below the marine sandsin the upper part of the Gates and from conglomerate 3 onDumb Goat Mountain. Measurements are from pebbleimbrication, log orientation, and planarcross-bedding. Conglomerate 3 on Dumb GoatMountain show a

251 PALEOCURRENTDATA

TRANSITION BEDS

Figure 4. Paleocurrent data - Transltlon Beds.

252 PALEOCURRENTDATA MIDDLEGATES

Figure 5. Paleocurrent data - 'Mlddle' Gates.

253 Flgure 6. Paleocurrentdata - 'Upper'Gates conglmrate.

254 PALEOCURRENT DATA UPPER GATES MARINE UNIT AND HULCROSS MEMBER

Flgure 7. Palmcurrent data - 'Upper' Gates rrmrlne unlt and Hulcross Umber.

255 paleocurrentdirection to the north, while further to thenorth the averagedirection is to the northwest.Planar cross-bedding from sandstones near the top of theconglomerate suggest currents in the oppositedirection, towardthe east-southeast. This is interpreted torepresent deposition associated with the start of the marine destructivephase at theonset of marinetransgression which occurs at the top of theunit.

(4) Marine Units of the 'Upper'Gates/Hulcross: Paleocurrent measurements from theseintervals were madeon the axes of symmetrical wave ripples from thinly beddedmarine sandstones and conglomerates. The conglomeratesoccur at the base of the Upper Gates and Hulcrossmarine transgressions and are believed to !.E the result ofmarine processes. In addition, measurements were madeon thelong axis orientation of largepebbles in the 'lag'deposit at the base of the Upper Gatestransgression on Babcock.

In the Babcockand Murray areasthis data indicate an averageeast- west trendfor the paleocoastline. On Babcock, the datasuggest an east-southeast - west-northwestorientation for the upper Gates paleocoastline.

DISCUSSION

( 1 ) Gates Nomenclature

The last comprehensivedescription of Lower Cretaceousstratigraphy inthe Foothills was that by Stott (1968). Since then, muchnew informationhas become available as a result of drilling by coal companies.Consequently, there is a need for a review of the stratigraphicnomenclature. Some of theproblems with regard to the Gates nomenclature are as follows:

The typesection of the Gates (McLearn, 1923) is inthe-Peace River Canyon, east of Hudson Hope. The Gates there is predominantly marine and verydifferent in character from the Gates further to the southalong the length of thecoalfield.

The Gates inthe PeaceRiver area has formation status, but in the PinePass and the Foothills to the south, it is givenonly member statuswithin the Commotion Formation.

The Torrens Member is a name frequently used for a thick, relativelycontinuous marine sand in the lower part of the Gates. Thisunit, however, hasnot been formallydescribed and there is some ambiguityin deciding which marine sand it refers to. Forexample, inthe regional correlation section (Figure 3), does the Torrens Member refer to thesand above or below coal zone 1 A, orboth?

Eollowingsuggestions may be of valuein a futurerevision of nomenclature:

256 (a) The Gates is a sufficientlyimportant interval for it to be givenformation status alongthe length of the coalfield.

(b)Several marine units within the Gates can be recognized and correlatedover a fairlylarge area. (Trace fossils are particularlyuseful in identifying these marine units). These unitsincrease in number to thenorth and arereplaced by non- marine sediments to thesouth. It is proposed thatthese marine units be given member statuswithin the Gates Formation. The marine unitin the Upper Gates is particularly well developed in the Babcock area is referred to asthe Babcock Memberby Denison geologists.This unit is probablyequivalent to part of the Notikewan Wmber inthe subsurface to the east.

(2) Paleocurrents

Many of thepublished paleogeographic maps of the Lower Cretaceous show the main fluvial systemstrending to the east or northeast, ai: right angles to the tectonicstrike. These arefrequently hypotheticaldirections and theydiffer frommeasured paleocurrent directionspresented in this paper and those of Leckie ( 1981 ) for i:he Gates north of theWolverine River. Both studies show a more northerly component for thefluvial paleocurrents and a paleocoastlineoriented approximately east-west.

Measured paleocurrentdata indicates, therefore, that the main drainage patterns inthe Gates weke longitudinal,subpara.lle1 to the tectonicstrike. In the presentday Himalayan molasse basin,the direction of flow of themajor rivers is longitudinal,scibparallel tothe tectonic strike. It is notsurprising, therefore, that similar drainagepatterns are found inthe Gates, whichformed in a similartectonic setting.

3) Conglomerates,Tectonics, and Marine Transgressions

The interdependence of sedimentation and tectonics in mol.asse basi:ns has heen described in some detail by Miall (1978). In the Gates, three major conglomeratesare recognized at consistentstratigraphic levelsthroughout the area. These areinterpreted as indicating threeseparate phases of tectonicactivity in thesource area.

~nthe Gates, deposition of conglomerates 1 and 3 was followed by marine transgressions. It is postulatedthat these transgressions rwulted from isostatic adjustment and increasedsubsidence in the foredeep basin followingperiods of increasedtectonic activity. Other factors suchas sedimentsupply and eustaticsea level changes can alsocause a marine transgression. me relativeimportance of thesein the Gates has yet to be fullyevaluated.

257 ACKNOWLEDGMENTS

Thisstudy was supported by grants from Union Oil and the B.C. Ministry ofEnergy, Minesand PetroleumResources. I wish to thankDenison Mines, Petro Canada,Ranger oil, andCrows Nest Resourcesfor supplying data and assistance in thefield. Dr. R.M. Bustin and Dr. J.W. Murray reviewed thepaper and made useful criticisms.

REFERENCES

Douglas, R. J.W., Gabrielse, E., Wheeler, J.O., Stott, D.F., and Belyea, H.R. (1976): Geologyof Western Canada,Geology andFconomic Minerals of Canada, Part B, Geol. Surv.,Canada, Economic Geology Rept. NO. 1, Pp. 446-448. Leckie, D.A. (1981 ): Stormand TidallyInfluenced Shorelines in the Moosebar-Gates Members (Wilrich-FalherEquivalents ), Northeastern British Columbia, Geol. ASSOC. Can., Annual Meeting,Program with Abstracts, May 1981. McLearn, F.H. (1923): PeaceRiver Canyon Coal Area, British Columbia, Geol. Surv.,Canada, Sum. Rept., 1922, Part B, pp. 1-46. Miall, A.D. (1977): A review of theBraided River Depositional Environment,Earth Sci. Revs., Vol. 13, pp. 1-62...... (1978): TectonicSetting and SyndepositionalDeformation of Molasse and OtherNonmarine-Paralic Sedimentary Basins, Cdn. Jour. Earth Sci., Vol. 15, No. 10, pp. 1613-1632. Stott, D.F. (1968): Lower CretaceousBullhead and FortSt. JohnGroups Between Smoky andPeace Rivers, Rocky Mountain Foothills,Alberta and British Columbia, Geol. Surv.,Canada, Bull. 152. Walker, R.G. (1981): Wapiabi-BellyRiver Transition - Storm Influenced Sedimentswith North Oriented Paleoflow, Southern Alberta, Geol. ASSOC. Can., AnnualMeeting, Program with Abstracts, May 1981.

258 GEOLOGY OF THE MCDAME TUNGSTEN SKARN PROSPECT ( 104P/5)

Ey B.J. Cooke and C.I. Godwin Department of Geological Sciences University of British Columbia

INTRODUCTION

The McDame tungsten skarn prospect (MDI No. 104P/004) lies s.pproximately 6 kilometres north of Cassiar in northern British Columbia (Figure1). Road access is available from Cassiar via the Cassiar Asbestos mine road and a four-wheel-drive track. The property, consisting of 'IO claims .and 109 units, is presently under optionto Shell Canada Resources Ltd. Two main zones of economic interest have been identified: theA zone, on which the Kuhn tungsten-molybdenum skarn showing occurs,and the B zone, which includes the Dead Goat tungsten skarn and the Contact lead-silver vein occurrences (Figure 1).

LATE CRETACEOUS rn3.KA.N

259 TABLE 1. REGIONAL CORRELATION OF GEOLOGICAL UNITS -

TECTONIC ELEMENT, GABRIELSE PANTELFYEY MSY I'RITZ THIS REPORT AGE *No GROUP 1963 1979 1978 1980

260 Earlyprospecting in theCassiar area concentrated on goldplacer and asbestosvein deposits. The Contactvein was exploredin 1954 by the Harvest Queen Mill and Elevator Company (McDougall, 1954).Fort Reliance Mineralslater attempted to high-grade the vein (Minister of Mines, B.C., Ann. Rept.,1962) and in 1961 discoveredthe Lamb Mountain (MD:C No. 104P/003)tungsten-molybdenum skarn showing north of the McDamta property A zone(Cook, etal., 1979).Prospector B. Kuhn restaked the Lamb Mountain prospectin 1977 for Union Carbide and subsequentlydiscovered similarmineralization on strike tothe south (the Kuhn and Dead Goat showings on the McDame property).

REGIONAL GEOLOGY

The geologyof theCassiar area has been mapped on a regionalscale by Gabrielse(1963) and Panteleyev (1978, 1979). Three major lithotectonic! elements havebeen identified(Figure 1):

(1) Cassiarplatform, a miogeoclinalcontinental t-errace wedge developed alongthe eastern margin of the North American craton in Late Proterozoicto Early Paleozoic times (Monger, etal., 1979).

(2) Sylvesterallochthon, an oceanicbasin assemblage tectonically emplaced in MiddleMesozoic times (Monger, etal., 1979).

(3) Cassiar complex, a Late Mesozoic plutonic complex,probatlly related toanatexis of continentalcrust (Tempelman-Kluit,1979).

Gabrielse(1963) showed thatthe Cassiar complex lies inthe c!ore of a northwest-trendinganticlinorium flanked on theeast by theCa.ssiar platform, which forms the southeast-plunging McDame synclinorium. The Sylvesterallochthon now occupiesthe core of thesynclinorim! (Figure 1).

PROPERTY GEOLOGY

Rocks on the McDame property havebeen subdividedinto six main units (Table 1). Lower Hadrynian to Lower OrdovicianIngenika, Atan and Kechika Group metasedimentaryrocks (Units 1 to 3 respectively) are crosscut by minor Mesozoic mafic intrusions (Unit 4) and Idte Wsozoic felsicintrusions (Unit 5). Skarn (Unit 6) occursalong favourable stratigraphichorizons in the metasedimentary rocks near the iielsic intrusions.

The stratigraphy forms theupright and steeplyeast-dipping western limb of the WDame synclinorium. Minor folding was observedbut the main foliation,lineation, and fracturedirections correspond resptctively with the axial plane, foldaxis, and a-c joints of the WDame synclinorium. Only one fault with an apparentleft-hand strike offset of about 120 metres was mpped in the A zone (Figure 2).

261 Flgure 2. Geology of the A zone.

262 INGENIKA GROUP

Ingenika Group rocksunderlie the B zone and containthe Dead Goatand Contactshowings (Figure 1). These rocksrepresent the hesternmost exposures of stratifiedrocks on the McDame property and are dividedin.b threemetasedimentary units. From west to east these are:

(1)interbanded biotite hornfels, white marble, and garnet-pyroxene skarn;these form thecountry rocks in contactwith fe1si.c intrusive rocks of the Cassiar stock to the west.

(2) banded graphitemarble and massivegrey marble that makeup a carbonate band which containsrare patches of zebra-textured graphiticdolomite and pods of concentrically banded structures up to 20 centimetresacross (stromatoporoids 7).

(3) spottedcordierite hornfels (Unit li, Figure 2) that forms a thick unitwith minor biotite and muscovitehornfels bands and rarewhite marblebands.

These threerock bands correlate respectively with theredbed, carbonatre, and clasticlayers in the upper part of theStelkuz Formation mappedby Mansy (Mansy, et al., 1978; Mansy, 1979)elsewhere inthe Cassiar Mountains(Table 1 1.

ATAN GROUP

AtanGroup rocksunderlie the western part of the A zone and containthe Kuhn showing (Figure 1). The strataare conformable with theIngenika Groupand consist of two metasedimentaryunits. From west to eastthese are :

(1 ) interbandedhornfels that form a thick band which includesthe followinglithologies:

Banded biotitehornfels, Unit 2h, is rustyweathering, brown, and veryfine grained, with minor cordierite,quartz, or muscovitehornfels layers.

Spottedcordierite hornfels, Unit 2i, is rustyweatblering, brown to grey,foliated, very fine grained, and porphyroblastic,with minor biotiteor quartz hornfels; disseminatedpyrrhotite is common.

Foliatedmuscovite hornfels, Unit Zj, is bleachedweathering, tan, and aphanitic, and generally forms partingsin quartz hornfels.

Massive quartzhornfels, Unit 2k, is rustyweathering, white, andvery fine grained,with moderate muscovite hornfels bands and minor cordieriteor biotite hornfels bands; quartz- tourmalineveins and pods are common.

263 (2) interbandedmarble and dolomite form acarbonate band which includes the following lithologies :

Banded graphitemarble, Unit 2a, is greyweathering, black to white, and medium grained,with moderate grey or white marble bands and rare hornfelsbands.

Massive greymarble, Unit Zb, is greyweathering and medium grained and is almostpure calcite.

Massivewhite marble, Unit 2c, is greyweathering and coarse grained and occurs as bleachedfracture envelopes or bands within the othermarbles.

Zebra graphitedolomite, Unit 2d, is tan weathering,black to white,fine grained and sucrosic,with moderate grey or white dolomitebands, minor marble or hornfelsbands, and rare dolomitebreccias or nodular pods; thebreccias contain concentricallylayered structures (stromatoporoids ?) and the pods containelongate ovoid structures up to 5 centimetreslong (Archeocyathids ?); well-developedzebra texture is characteristic of this rock.

Mottledgrey dolomite, Unit Ze, is tan weathering,fine grained, and sucrosic and is almostpure dolomite.

Massive white dolomite, Unit 2f, is tan eathering,fine grained, and sucrosic and occurs as bleachedfracture envelopes or bands within the otherdolomite.

Banded graphitehornfels, Unit 29, is greyweathering, black, and aphanitic and forms rare bands within marble or dolomite; disseminatedpyrrhotite is common.

The tm metasedimentaryunits of the Atan Group are lithologically similar to clastic and carbonatesedimentary rocks of the Boya and RosellaFormations as mappedby Fritz (1978,1980) elsewherein the Cassiar Mountains (Table 1 ).

KECHIKA GROUP

Kechika Group rocksunderlie the eastern part of the A zone (Figure 1 ). The rocks are conformablewith the Atan Group and consist ofhanded hornfels,with minor marble,including the following lithologies:

Banded graphitichornfels, Unit 39, is similar to Unit 29.

Banded biotitehornfels, Unit 3h, is similar to Unit 2h.

Banded graphiticmarble, Unit 3a, is similar to Unit 2a.

Massivewhite marble, Unit 3c, is similar to Unit 2c.

264 Theserocks are lithologically comparable with clastic and carbonate rocks of the Kechika Group as mappedby Gabrielse(1963) and lanteleyev ( 1978,1979, 1980) nearCassiar (Table 1).

MAFIC INTRUSIONS

Mafic intrusionsoccur as dykes cutting the olderstratified rocks ( Figure 2 ) :

Massivelamprophyre dykes, Unit 4a, are green,very fine grained, and subophiticto porphyritic with biotite; chilled mrgi.ns; in places, there is a strongfoliation.

Fracturesin the lamprophyre occasionally contain skarn surrounded by bleachedenvelopes, suggesting that the mafic intrusions are olderthan skarn. They are probably of MiddleMesozoic age.

FELSIC INTRUSIONS

Felsic intrusionsoccur as fourdiscrete stocks on the McDame property (Figure1) and containthree different lithologies:

Biotitequartz monzonite, Unit 5-3, is pink,coarse grained, and porphyritic with K-feldsparmantled by Na-feldspar(rapalrivi texture). lhis unit is typical of the Cassiar and Contactstocks.

plartzfeldspar porphyry, Unit Sb, is grey,fine grained,. and stronglyjointed; biotite and hornblendeare accessory minerals in the Kuhn stock and quartz-muscovitepatches occur in the Windy stock.

Aplite and pegmatite sills, Unit Sc, arewhite, fine to coarse grained, and equigranular;they cut both the sedimentary and other plutonicrocks.

Units Sa and 5b and lithologically comparable with Panteleyev's(1978) Units B and C respectively as mapped in the Cassiar area (Table 1).

SKARN

Skarnforms several bands on the McDame property(Figure 2) and is classified into six main facies:

(1 ) Massive calc-silicateskarn occurs as semi-continuouszones up to 10 metresthick along the weste.rn contacts of thecarbonate bands in theIngenika and Atan Groups. Thisskarn type also forms; lenses alongthe eastern contacts of the two carbonatebands and withinthe carbonatesthemselves. The followinglithologies were olmerved:

265 Massive garnetskarn, Unit 6a, is red to brownand coarse grained,with a faint bandingoccasionally apparent from variationsin grain size andmineralogy. This unit is the most common massive calc-silicateskarn on theproperty.

Massivepyroxene skarn, Unit 6b, is green to white and coarse grained; it generallyoccurs in the A zone as narrowbands in garnetskarn or as bands separatinggarnet skarn from country rocks.

Massiveamphibole skarn, Unit 6c. is white and verycoarse grained and occurs as small pods in dolomitenear quartz feldsparporphyry dykes in the A zone.

Massive epidoteskarn, Unit 6d, is green and medium grainedand forms rare bands associatedwith garnet skarn and quartzskarn inthe A zone.

Spottedbiotite skarn, Unit 6e, is variablein colour and grain size; it occurs as rare bands in the A zone between Atan Group marble and hornfels where garnetskarn is absent.

Banded wllastoniteskarn, Unit6f, is white and verycoarse grained; it is foundonly in one outcrop of Kechika graphite hornfels and whitemarble at thenorth endof the A zone.

(2) Banded calc-silicateskarn forms tm majorbands on the McDame property:

Banded quartzskarn, Unit 6q, is lightcoloured and aphanitic tofine grained; textures in this unit reflect original features.Quartz skarn in Kechika Group hornfels formsnarrow, bleachedquartz and calc-silicate-richenvelopes on bedding plane and a-cjoint fractures. Where fracturedensity is high, theoriginal rock can be bleachedthroughout; near the Kuhn stock,the quartz skarn forms a distinctalteration halo and the Kechika Group rocks are generallybrecciated, with banded quartzskarn to biotitehornfels fragments enclosed in a siliceous matrix containingdisseminated sulphides; two other minor quartzskarn zones occur in AtanGroup hornfelsin the southern part of the A zoneand are associatedwith quartz feldsparporphyry dykes. Banded calc-silicateskarn within the Ingenika Group inthe B zone discretefine-grained calc- silicate bandswith bleached quartz-rich envelopes and remnant biotitehornfels and whitemarble bands.

(3) Vein sulphideskarn fills fracturesin AtanGroup dolomitesin the A zone north of the Kuhn showing and includes:vein chlorite skarn, and Unit 6h which is green and finegrained, with disseminated and vein pyrrhotite and pyrite.

(4) Massive sulphideskarn forms pods and veins up to 1 metre thickin massivegarnet or pyroxeneskarn. Tne followingunits are defined:

266 Massive pyrrhotiteskarn, Unit 6i, that is bronze and coarse grained,with minor disseminatedchalcopyrite; this is the most common typ of massivesulphide skarn.

Massive sphaleriteskarn, Unit 6j, which is black and coarse grained andcommonly intergrownwith pyrrhotite; sphalerite is most common south of the Kuhn and Dead Goat showings in the A and B zones.

(5) Vein oxideskarn forms a unique set of fracturefillings in Atan Group dolomites north of the Kuhn showing inthe A zone and includes banded magnetite skarn, Unit 6k, which is black to green and fine grained and commonly containssulphide and calc-silicate minerals. Thisfacies locally formsbands between dolomite and massivegarnet or pyroxeneskarn.

(6) Gossan oxideskarn is simplythe weathering product of massive and veinsulphide and oxideskarns and consists of thefollowing:

Goethiteskarn, Unit 6i, is yellow to brown, finegrained, and earthy.

Hematiteskarn, Unit 6m, is red to brown, fine grainctd,and earthy.

MINERALIZATION

Mineralogy and texturevary in boththe A and B zones. At the Kuhn showing, scheelite,powellite, and molybdenite,associated with minor pyrrhotite,pyrite, calcite, quartz, and fluorite, form coarse.-grained disseminations and veins in massivegarnet and pyroxeneskarn. North of the Kuhn showing, powellite and scheeliteoccur as fine-grained disseminations and veinswithin vein chlorite and magnetiteskarn. South of the Kuhn showing, significantdisseminated scheelite is foundwith massivepyrrhotite skarn, but only minor scheelite is found in the more sphalerite-richskarn toward the south end of the A zone. A similar change in mineralogyoccurs in the B zone. Significantdisseminated scheeliteoccurs in massive garnet, pyroxene, and pyrrhotiteskarns at the Dead Goat showing,but only minor scheelite is foundwith mmssive pyrrhotite and sphaleriteskarns toward thesouth end of the B zone.

CONCLUSIONS

Cn a regional scale (Figure 1) metamorphism, metasomatism,and mineralization in the Cassiar areaare all spatially related to felsic intrusions. These intrusiverocks are acidic, porphyritic, and jointed. They represent high-level,late differentiates of granitic magma. On propertyscale, skarn and oreminerals are concentratedalong favourable stratigraphichorizons (Figure 2). ?he countryrocks are interbedded clastic and carbonatebeds typical of continentalshelf sedimentary rocks in a cratonicenvironment.

2 67 Mineralizedzones containing tungsten-molybdenum, tungsten-copper,and tungsten-zinc occur withinmassive calc-silicate and sulphideskarn along majormarble-hornfels contacts in the Ingenika and Atan Groups. Banded calc-silicateskarn forms severalzones, normally barren of mineralization, in hornfels of theIngenika, Atan, and KechikaGroups adjacent to the Cassiar and Kuhn stocks. Minor amountsof tungsten mineralization are containedin vein sulphide and oxideskarns that fill fractureswithin Atan Group dolomites.

Detailedstudy of theseskarn deposits is inprogress. However, field mapping indicatesthe following to be significantexploration parameters :

Favourablecountry rocks are composed of interbeddedcarbonate and clastic sedimentaryrocks that contain major elementssuch as silica and calciumthat are necessaryfor skarn formation. Bleached hornfelszones are a potentialsource of iron, zinc, and sulphur and bleachedmarble and dolomite are potentialsources of sulphur.

Favourableintrusive rocks are felsicstocks of anatectic origin. These arecapable of supplyinglithophile and atmophileelements such as tungsten, molybdenum, fluorite, oxygen, and sulphur to the mineralizingfluids (Godwin, et al., 1980).

Extensiveskarn development inhornfels (for example quartzskarn) indicatesproximity to favourableintrusive rocks whereas skarn betweenmarble and hornfels(for example, garnetskarn) defines favourablestratigraphic horizons.

Minor tungsten-zincmineralization within massive skarn(for example, pyrrhotiteskarn) may mark thedistal end of a zoned hydrothermalsystem which containsproximal tungsten-molybdenum mineralization.

ACKNOWLEDGMENTS

Shell Canada Resources La. supportedfield workby the seniorauthor in 1980 and 1981. Financialassistance from theBritish Columbia Ministry of Energy, Mines and Petroleum ReSOUrCeS is gratefully acknowledged. Stimulatingdiscussions with G. Moffat of Shell Canada and A. Panteleyev of theBritish Columbia Ministry ofEnergy, Mines andPetroleum Resources were veryhelpful.

REFERENCES

British Columbia Ministry ofEnergy, Mines and PetroleumResources, Assessment Report 7242. Fritz, W.H. (1978): Upper (Carbonate)Part of Atdn Group, Lower Cambrian,North-Central British Columbia, Geol. Surv.,Canada, Paper 78-1A, pp. 3-16.

268 ...... (1980): Two New Formations inthe Lower Cambrian Atan Group, CassiarMountains, North-Central British Columbia,Geol. Surv., Canada,Paper 80-1B, pp. 217-225. Gabrielse, H. (1963): McDame Map-Area, Cassiar District, British Columbia, Geol. Surv., Canada, Mem. 319. Godwin, C.I., Armstrong, R.L., andTompson, K.M. ( 1980) : K-Ar and Rb-Sr Dating and theGenesis of lbngstenat the Clea mngsten Skarn Property, Selwyn Mountains, Yukon Territory, C.I.M., Bull., Vol. 173, No. 821, pp. 94-99. McDougall, J. J. (1954): The TelescopedSilver-Lead-Zinc Deposits of the Contact Group MineralClaims, ~c~ameMap-Area, British Columbia, M.Sc. mesis, University of British Columbia. Mansy, J.L. (1978):Stratigraphy and Structure of Proterozoic Rocks neem Good Hope Illke, McDame Map-Area, British Columbia, Geol. Surv., Canada,Paper 78-1A, pp. 5, 6. ManSY, J.L. and Gabrielse, H. (1977):Stratigraphy, Wrminology, and Correlation Of Upper Proterozoic Rocks in Ominecaand Cassiar Mountains,North-Central British Columbia, Geol. Surv.,Canada, Paper 77-19. Minister of Mines, B.C. (1962): Ann. Rept.,1962, p.6. Monger, J.W.H. and Price, R.A. (1979): Geodynamic Evolution of the CanadianCordillera - Progress and Problems, Cnd. Jour.Earth %is, VOl. 16, pp. 770-791- Panteleyev. A. (1978):Cassiar Map-Area, B.C. Ministry of hergy, fines & Pet. Res., GeologicalFieldwork, 1978, Paper 1979-1, pp. 51-60...... (1979):Cassiar Map-Area, B.C. Ministry of Energy, Mines & Pet. Res., GeologicalFieldwork, 1979, Paper 1980-1, pp. 80-88. Tempelman-Kluit, D. J. (1979):Transported Cataclasite, Cphiolite and Granodioritein Yukon: Evidence of Arc-ContinentCollision, -01. Surv.,Canada, Paper 79-14.

269 270 REGIONALGEOCHEMICAL SURVEY HOPE, ASHCROFT, AND PEMBERTONMAP-AREAS (92 H, I, and J)

By W.J. McMillan

The British Columbia Ministry of Energy, Minesand PetroleumResources conducted a regionalgeochemical survey of map-areas 92H, 921,and 92J duringthe 1981 fieldseason. It is anticipatedthat analytical work will becompleted and the data compiled in late May of 1982. Resu:Lts of the survey will be releasedin June or July, depending onsnow conditions,in the form of sample location maps and data sheetssimilar to those of previoussurveys.

Streamsediment and stream watersamples were collected in a .truck-supported groundphase where possible and withhelicopter support in more remote locations. Sample density was similar tothat for previous silrveys, about 1 per 15 squarekilometres.

The sampling crewand equipment for the program were provided by ROO1 EnterprisesLtd. Helicopter support was from QuasarAviation Ltd. Ministry supervision was supplied by W.J. McMillanand W.M. Johnson.

Sample preparation was done by Kamloops Research E, AssayLabo:ratory Ltd. The stream sediments were analysedfor all other elements by 'Chemex LaboratoriesLtd. Stream waters were analysed by Bondar-Clegq and Company Ltd .

The stream sediments were analysedfor zinc, copper, lead, nickel, cobalt, silver, manganese, iron,arsenic, molybdenum, tungsten, mercu:ry, uranium, andantimony. Stream waters were analysedfor uranium, fluorine, and pH. Data processing was performed by theGeological Survey of Canada data processinggroup.

Figure 1 shows map areascovered by previoussurveys and thosecovered by this survey. Results of the 1980 program in areas 93A and 933 were released May 26, 1981.

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