K.E. Witherly Utah Mines Ltd., Toronto, Ontario

Transcription

1 32. GEOPHYSCAL AND GEOCHEMCAL METHODS USED N THE DSCOVERY OF THE SLAND COPPER DEPOST, VANCOUVER SLAND, BRTSH COLUMBA K.E. Witherly Utah Mines Ltd., Trnt, Ontari Witherly, K.E., Gephysical and gechemical methds used in the discvery f the sland Cpper Depsit, Vancuver sland, British Clumbia; in Gephysics and Gechemistry in the Search fr Metallic Ores; Peter J. Hd, editr; GelgicQl Survey f Canada, Ecnmic Gelgy Reprt 31, p , Abstract The sland Cpper Mine f Utah Mines Ltd. is a large, lw-grade cpper-mlybdenum depsit lcated 354 km nrthwest f Vancuver, B.C. The depsit lies in the Bnanza Vlcanic frmatin f lwer t mid-jurassic age. The re znes are in andesitic, pyrclastic rcks in the hanging wall and ftwall f a quartz-feldspar prphyry dyke. At the cmmencement f prductin, re reserves ttalled 257 millin tnnes averaging 0.52 per cent cpper and per cent mlybdenum. Explratin wrk n the depsit began in early 1966 when Utah Cnstructin and Mining C. (nw Utah Mines Ltd.) ptined apprximately 175 claims lcated n the nrth side f Rupert nlet. nitial wrk cnsisted f gelgical mapping, sil gechemistry, grund magnetic and P surveying. Cnsiderable dependence was placed n the latter three tls due t the extensive verburden cver n the prperty. The gechemical and gephysical surveys prduced an abundance f anmalies ver the prperty. During the first year f explratin, testing f gechemical and gephysical anmalies was dne with a small cmpany-wned diamnd drill which culd penetrate depths f up t 75 m under favurable cnditins. Althugh cpper and magnetite had a knwn assciatin in the area, initial direct testing f the best magnetic anmalies lcated nly subecnmic cpper mineralizatin. The P anmalies tested intersected sme lw-grade cpper with pyrite, but mre ften just barren pyrite. t was bserved frm the initial testing that the ttal sulphide cntent f the anmalies tested was fairly cnstant, i.e. when the chalcpyrite picked up, the pyrite cntent drpped. This made anmaly discriminatin based n amplitudes quite difficult. n view f the pr reslutin the gephysical anmalies prvided, it was decided t test the cpper sil gechemical anmalies befre any mre gephysical wrk wuld be dne. The rebdy was discvered as a result f testing ne such gechemical anmaly with several shallw drillhles. Deeper drilling f the depsit was initiated sn after and the rebdy was delineated a little mre than tw years later in the Spring f A VLF-EM survey ver the depsit did nt respnd t the re mineralizatin itself but did shw up a number f significant structural features. Althugh gephysics did nt assist directly in the discvery f the sland Cpper depsit, its cntributins t the develpment f gelgical thinking in the area have been valuable. A large part f the recent interest in the nrthern part f Vancuver sland stemmed frm a jint British Clumbia Department f Mines/Gelgical Survey f Canada aermagnetic survey flwn in Examinatin f the gephysical data made subsequent t the discvery f sland Cpper shw that the gephysical results supprt and enhance infrmatin n structure, alteratin and mineralizatin bth in and arund the rebdy. Such infrmatin is nt nly f interest in its wn right but as well prvides a valuable data base t draw upn fr explratin in similar gelgical envirnments. Resume La mine de cuivre sland de l'utah Mines Ltd. est frmee d'un imprtant gisement pauvre de cuivre-mlybdeme. 354 km au nrd-uest de Vancuver. en Clmbie-Britannique. Le gisement repse dans la frmatin vlcanique Bnanza du Jurassique inferieur et myen. Les znes de minerai se truvent dans des rches pyrclastiques a andesite dans la levre superieure et la levre inferieure d'un dyke prphyrique de quartz-feldspath. Au debut de la prductin, les reserves de minerai atteignaient 257 millins de tnnes d'une teneur en cuivre d'envirn 0,52 pur cent et d'une teneur en mlybdene d'envirn 0,017 pur cent. Les travaux d'explratin du gisement nt cmmence au debut de 1966, lrsque l'utah Cnstructin and Mining C. (aujurd'hui l'utah Mines Ltd.) a chisi envirn 175 claims sur la rive nrd de l'inlet Rupert. Les travaux preliminaires cmprenaient la cartgraphie gelgique, l'etude gechimique des sls, des leves magnetiques et des leves par methde PP. On avait beaucup mise sur les tris dernieres methdes, etant dnnee la cuche imprtante du terrain de cuverture. Au curs de la premiere annee d'explratin, des verificatins d'anmalies gechimiques et gephysiques nt ete effectuees a l'aide d'un petit fret au diamant que pssedait la sciete; cet util de frage puvait atteindre des prfndeurs de 75 m dans des cnditins favrables.

2 686 K.E. Witherly Les leves gechimiques et gephysiques nt revele un grand nmbre d'anmalies sur tute l'etendue du terrain. Bien que 'n ait su que, dans cette regin, e cuivre et la magnetite etaient asscies, la verificatin directe initiale des meilleures anmalies magnetiques n'a indique qu'une mineralisatin de cuivre nn susceptible d'etre explitee de famn rentable. Les anmalies verifiees par la methde PPnt livre un peu de cuivre pauvre cntenant de la pyrite, mais surtut de la pyrite sterile. On a remarque lrs de la verificatin initiale que e cntenu ttal en sulfure des anmalies verifiees etait a peu pres cnstant, c'est-a-dire que lrsque la chalcpyrite augmentait, la pyrite diminuait. Cette cnstatin a rendu assez difficile la distinctin des anmalies en fnctin des amplitudes. Cmpte tenu du faible puvir de reslutin qu'avaient furni les anmalies gephysiques, il fut decide de verifier les anmalies gechimiques des sls cntenant du cuivre avant que d'autres travaux gephysiques ne sient entrepris. Le gisement en amas fut decuvert a la suite de la verificatin d'une tele anmalie gechimique au myen de plusieurs trus de frage peu prfnds. Le frage du gisement a plus grande prfndeur fut entrepris peu de temps apres, et e gisement en amas fut delimite un peu plus de deux ans plus tard, au printemps de Un leve electrmagnetique a tres basse frequence efrectue sur l'ensemble du gisement n'a pas reagi a la mineralisatin elle-meme, mais a revele un nmbre imprtant de particularites structurales. Bien que la gephysique n'ait pas cntribue directement a la decuverte du gisement de cuivre sland, elle a influe grandement sur l'pinin que se fnt les gelgues de la structure de la regin. Une grande partie de l'interet manifeste dernierement a ce sujet dans la partie nrd de 'ile Vancuver fait suite a un leve aermagnetique effectue en 1962 par e ministere des Mines de la Clmbie-Britannique et la Cmmissin gelgique du Canada. L'analyse des dnnees gephysiques effectuees a la suite de la decuverte de la mine de cuivre sland indique que les resultats d'rdre gephysique crrbrent des renseignements sur la structure, l'alteratin et la mineralisatin tant ij. l'interieur qu'autw' du gisement en amas. De tels renseignements ne snt pas seulement interessants en eux-memes, mais ils furnissent egalement une base de dnnees de valeur pur decider de travaux d'explratin dans des milieux gelgiques semblables. NTRODUCTON The sland Cpper (SCU) depsit, cntrlled and perated by Utah Mines Ltd. (frmerly Utah Cnstructin and Mining), is lcated n the nrth shre f Rupert nlet ( 'N, 'W) apprximately 16 km suth f Prt Hardy n nrthern Vancuver sland (Fig. 32.1). The twn f Prt Hardy is 354 km nrthwest f Vancuver, B.C. and is serviced daily by scheduled flights frm Vancuver. Prt Hardy and the nrthern prtin f Vancuver sland can als be reached by surface transprtatin using either public rads r a cmbinatin f prvincial ferries and rads. Elevatins n the prperty range frm sea level t 150 m. The area arund the depsit is heavily timbered with spruce, hemlck and cedar. Glacial depsits with thicknesses f up t 75 m cver mst f the area. Average annual precipitatin at Prt Hardy is 1900 mm, which includes an average f 600 mm f snw. The yearly temperature range is frm -7 C minimum t 27 C maximum, with an annual mean f 8 C. The rebdy was discvered after mre than fur years f explratin activity that stemmed frm the release f results f an aermagnetic survey flwn frm July t September 1962 ver the whle nrthern prtin f Vancuver sland. This survey was a jint effrt between the BritiSh Clumbia Department f Mines and the Gelgical Survey f Canada. Release f the aermagnetic survey results in 1963 stimulated cnsiderable explratin interest in the area, with bth cmpanies and individuals participating in the fllw-up. As part f their prgrams, a number f majr mining cmpanies, including Utah Mines Ltd., recnnitered the Rupert nlet area (Fig. 32.2), but fund n encuraging evidence f ecnmic mineralizatin. A small island, called Red sland, lcated slightly less than 2 km t the sutheast f the present pit, was knwn t have gd cpper grades assciated with abundant magnetite in vlcanics. Prspectrs at the time hwever, felt that the ccurrence was nly a high-grade pd and nt part f a larger, mineralized system. Sn aftcr the release f the aermagnetic data, Grdn Milburne, a lcal prspectr, ran a dip-needle survey ver a lcalized magnetic high, situated just nrth f Rupert nlet. Tw years later, Milburne returned t the area and lcated flat and utcrps cntaining native cpper and chalcpyrite, just west f Frances Lake (Fig. 32.2). Subsequent trenching revealed high-grade chalcpyrite in vlcanic rcks. Utah Mines Ltd., examined Milburne's grund in Octber 1965, and cncluded that the prperty warranted fllw-up. After sme preliminary explratin wrk in the Fall f 1965, Utah signed an agreement with Milburne in January] 966. Because utcrps n the prperty were very sparse, due t an extensive cver f glacial verburden, it was decided that an integrated gelgical, gechemical and gephysical apprach shuld be used in evaluating the prperty. T facili tate this evaluatin, a survey grid ttalling 160 line km was established ver the prperty. The lines were spaced 152 m apart with survey statins every 30.5 m. The lines were riented N22 E, but lcal magnetic disturbances ccasinally caused significant deflectins in a surveyed line. The chice f gechemical and gephysical parameters t be measured was based largely upn the initial test surveys dne in ] 965. Since nly cpper had been fund in any significant amunts n the prperty, cpper was the nly element fr which the sil samples were analyzed. Magnetic surveys were cnsidered an imprtant tl, due t the knwn affinity cpper 8nd magnetite shwed in the area. nduced plarizatin was als felt t be useful, since cnsiderable pyrite was fund in assciatin with the knwn cpper mineralizatin. Shallw drilling, with a cmpany-wned X-ray machine, began early in 1966 t evaluate the mineralized area at the suthwest end f Frances Lake. As gechemical and gephysical surveys prgressed, the X-ray drill was used t test anmalies lcated elsewhere n the prperty. The initial criterin fr drilling was that the anmalies be cincident

3 sland Cpper Depsit, B.C. 687 with gechemical, magnetic and P highs. On this premise, after sme initial drilling nrth f Frances Lake, sme interesting bservatins were made. Firstly, testing f the best magnetic anmalies encuntered nly lw-grade cpper mineralizatin; secndly, pyrite seemed ubiquitus in the area, with its distributin n a lcal scale being apparently unrelated t ecnmic cpper mineralizatin. Thus, primarily fr these reasns, it was decided early in 1966 t give the gechemical anmalies the highest pririty in the drilling prgram. Later that year, in the curse f testing ne such gechemical high lcated several kilmetres t the sutheast f the riginal prspect area, re-grade mineralizatin was encuntered in three f fur X-ray hles. Sn after these first shallw intercepts were cnfirmed with deeper drilling, the explratin temp gradually built up, and by 1968 there were fur large diamnd-drill rigs wrking n the prperty. When drilling f the depsit was cmpleted in May 1969, a ttal f 128 hles had been drilled fr an aggregate length f ver m. The results f the drilling prgram utlined a depsit cntaining 240 millin tnnes f cpper and mlybdenum re, grading 0.52 per cent cpper and per cent mlybdenum, extending frm surface t a depth f 300 m, alng a strike length f abut 1700 m. Mill cnstructin began in late 1969 and the first shipment f cncentrates was made in December The current prductin frm the mill is apprximately tnnes per day, and the current reserves (1976) are abut 230 millin tnnes. GEOLOGY OF NORTHERN VANCOUVER SLAND AND THE SLAND COPPER DEPOST Reginal Gelgy The rcks f Vancuver sland, nrth f Rupert and Hlberg nlets, are primarily vlcanic and sedimentary units ranging in age frm Upper Triassic t Lwer Cretaceus (Muller et a., 1974). ntrusive rcks f early t middle Jurassic age intrude the central and upper prtins f the Nrth sland sequence and lcally are assciated with cppermlybdenum mineralizatin. The Karmutsen Frmatin is the ldest rck unit in the area and cnstitutes the largest vlume f the varius units. Rcks f the Karmutsen are predminantly prphyritic and amygdalidal basalt flws. The next ldest unit is the Quatsin Frmatin, which is generally a massive limestne with rare interbeds f tuffaceus material. Fllwing the Quatsin Frmatin is the Parsn Bay Frmatin. This is a transitinal unit that separates the Quatsin Frmatin frm the Bnanza Frmatin. The Parsn Bay Frmatin is cmprised f black calcareus siltstnes, shales and limestnes with shaly interbeds. The Bnanza Frmatin is mid t lwer Jurassic in age. The vlcanic unit cnsists f bedded and massive tuffs, frmatinal breccias and rare amygdalidal and prphyritic flws. Prphyritic dykes and sills intrude the lwer part f the unit. Uncnfrmably ver the Bnanza lie rcks f Lwer Cretaceus age, cnsisting primarily f cnglmerates, siltstnes, sandstnes and greywackes. YUKON N.W.T. PACFC OCEAN -- -' B.C. SLAND COPPER MNE 300 kms t "_._ 1 "-.-. \ _.-._.-._.~._._. U.S.A. 300 miles Figure Lcatin map - sland Cpper Mine, nrthern Vancuver sland, British Clumbia.

4 688 K.E. Witherly LEGEND CRETACEOUS NTRUSVES QUARTZ FELO-.SPAR PORPHYRY fhll/llu BONANZA VOLCANCS ~ 1:,:«,\ PAltSON BAY FOtMATON QUAT$NO FORMATON KARllUTSEN LAVAS MLES METERS SLAND COPPER PROPERTY lo~k: 0 J.L"'b lp Figure Reginal gelgy f sland Cpper Mine (after Cargill et a., 1976). A nrthwest-trending zne f intrusive stcks extends frm the east end f Rupert nlet t the Queen Charltte Sund in a zne abut 56 km lng and up t 6.5 km wide. The stcks range in cmpsitin frm dirite t quartz mnznite. Quartz-feldspar prphyry dykes ccur alng the suthern edge f the zne f stcks. These dykes tend t be quite small, usually less than 30 m wide and 150 m lng. Felsic dykes and sills Dccur arund the margins f sme Df the intrusive stcks. They are generally a few metres wide and less than 100 m lng and cut thrugh rcks Df the Karmutsen, QuatsinD and Bnanza frmatins. Andesite dykes which cut the Karmutserl, QuaLsin and Parsn Bay frmatins are apparently feeders t Bnanza-age vlcanism. Gelgy and Mineralgy f the sland Cpper Depsit The gelgy n the nrth side f Rupert nlet is a representative sectin f the rcks just discussed in the reginal setting. The rcks increase in age ging nrtheasterly frm the shreline and dip at apprximately 30 t the suth. The reginal strike is abut N700W, with several Dther prminent nrthwesterly and nrtheasterly trends superimpsed n the reginal strike. A small grandirite stdck lies at the east end f Rupert nlet (Fig. 32.2). The mineralized quartz-feldspar-prphyry dyke at SCU is 4 km t the nrthwest frm this stck alng a N700W bearing. the SCU dyke lies in the upper part f the Bnanza Frmatin and dips t the nrtheast apprximately nrmal t the bedding f the Bnanza rcks. Several kilmetres t the nrthwest f the SCU dyke lies anther grandirite bdy f larger prprtins than the ne at the east end f Rupert nlet. This intrusive bdy utcrps lwer in the gelgical sectin and lies predminantly in the Karmutsen Frmatin. The SCU depsit lies in the upper prtin f the Bnanza Vlcanic Frmatin. The depsit is lcalized in and adjacent t a quartz-feldspar-prphyry dyke that striks at N700W, and dips at abut 60 t the nrtheast (Fig. 32.3). The dyke at the pre-mining bedrck surface has a strike

5 sland Cpper Depsit, B.C. 689 length f slightly ver a kilmetre and an irregular width that varies frm 180 m t less than 20 m. The dyke is grandirite in cmpsitin, the same as the stck at the east end f Rupert nlet. These tw bdies are believed t be genetically f the same rigin. Several perids and directins f faulting are apparent in the vicinity f the depsit. The mst prminent structure adjacent t the depsit is the End Creek fault (Fig. 32.3), which dips steeply t the suth n the suthwest side f the dyke. This fault is believed t be pst-mineralizatin and has an unknwn magnitude and directin f ffset. The End Creek fault has a width f apprximately 60 m and has a strike that has been mapped and inferred fr a length f several kilmetres. A secnd majr fault zne strikes N65 E, rughly thrugh the centre f the depsit (Fig. 32.3). As with the End Creek fault, this structure has a steep dip and pssesses an unknwn amunt f ffset. Tw majr stages f metamrphism have been recgnized at SCU (Cargill et a., 1976). The first stage is called the cntact metamrphic stage, which ccurred when the dyke initially intruded the vlcanic pile. The majr alteratin minerals frmed in the hst rcks at this time were bitite, chlrite and epidte, in a directin mving away frm the dyke. After this initial alteratin ccurred, the hydrthermal system arund the dyke changed as the dyke cled. As a result f further heating, a secnd stage f alteratin - the wall rck stage, tk place. The characteristic. minerals frmed during this stage were chlrite, sericite, pyrphyllite, dumrtierite and a rusty-range dlmite. This last alteratin sequence affected bth the quartz-feldspar-prphyry dyke as well as the surrunding vlcanic rcks. There are three assciated breccia phases identified with the depsit: (1) pyrphyllite; (2) marginal; and (3) Yellw Dg breccia. The pyrphyllite breccia lies ver the tp f the dyke in a hd-like fashin at the nrthwest end f the depsit and extends ver 1100 m in a nrthwesterly directin. The breccia fragments riginate bth frm the dyke and frm highly altered vlcanic rcks. The marginal breccias lie n bth sides f the dyke in a sheet-like fashin and extend dwn-dip t a cnsiderable depth. Cmpsitin varies frm predminantly vlcanic fragments, away frm the dyke, t almst ttally quartz-feldspar-prphyry fragments, adjacent t the dyke. The Yellw Dg breccia derives its name frm the rusty-brwn clur f veinlets f ferrandlmite. The Yellw Dg breccia cuts thrugh the middle f the depsit and has nrth and nrtheast trends. The fragments are primarily highly altered vlcanic rcks with quartz and carbnate vein fillings. The re minerals at sland Cpper are chalcpyrite and mlybdenite. The rebdy is cmpsed f a hanging wall zne and a ftwall zne arund the quartz-feldspar prphyry dyke. The re zne, n bth sides f the dyke, is abut 60 m t 180 m wide and 1700 m lng, extending t ver 300 m belw the surface. The bulk f the re is fund in the vlcanic rcks adjacent t the dyke, althugh sme parts f the dyke are mineralized. Mst f the chalcpyrite ccurs in veinlets n slip surfaces and ccasinally as disseminatins. Mlybdenite ccurs primarily n slip surfaces, but ccasinally in quartz veinlets. Other prminent minerals are pyrite and magnetite. Pyrite is tw t three times mre abundant than chalcpyrite in the re zne and is als lcally abundant in the alteratin hal arund the dyke. The mde f ccurrence fr pyrite is disseminatins and fracture fillings. Magnetite ccurs in bth the vlcanic rcks and in the dyke. n the vlcanic rcks the magnetite is fund as small disseminatins and with chlrite pseudmrphs f mafic minerals. There appears t be very little primary magnetite in the Bnanza vlcanics themselves; therefre, the bulk f the magnetite is believed either t have been intrduced, r mre likely, altered frm riginal irn-rich minerals. Recent magnetic susceptibility studies cnfirm in a qualitative way, the affinity between magnetite and chalcpyrite in the area (J. Flemming, pel's. cmm., 1977). GEOPHYSCAL SURVEYS OF THE SLAND COPPER DEPOST Aermagnetic Survey The Federal/Prvincial aermagnetic survey was flwn n nrth-suth lines with a nminal 800 m (0.5 mile) line spacing. The ttal magnetic field was recrded at a mean elevatin f 305 m abve the grund surface. Results were diurnally crrected and cmpiled n 1: scale tpgraphic maps (Annymus, 1964) with a 10 gamma minimum cntur interval. The majr feature f the aermagnetic survey cnturs nrth f Hlberg and Rupert nlets (see Fig. 32.4) is a nrthwesterly-trending magnetic high which crrelates clsely with the line f Jurassic stcks discussed in the Reginal Gelgy prtin f this reprt. The strngest magnetic respnses ccur alng the edges f the stcks in cntact with the Karmutsen rcks. Sme skarn highs als appear ver the Quatsin Limestne Frmatin, but these are generally small. The smaller stcks are generally hmgeneus, lw amplitude highs n the airbrne data. Sme f the larger stcks hwever, shw cnsiderable magnetic zning inside their bundaries. At the far sutheasterly end f the majr axis f the magnetic high and ffset slightly t the suthwest, lies a small, islated high. The SCU depsit underlies the suthern part f this magnetic anmaly. The aermagnetic cnturs arund the SCU depsit (Fig. 32.4) shw a prminent anmaly centred just nrthwest f the pit. The anmaly as defined by the 4000 gamma cntur is shaped like a lpsided arrw head, with the suthern side drped dwn ver the tp f the depsit. The peak values f the zne lie rughly parallel t the nrth shre f Frances Lake and extend sme distance t the west and east. The cmplete anmaly is apprximately 6 km lng, striking N65 W, with a width varying frm 1 km t 1.5 km. A smaller high dminates the sutheast prtin f the verall feature and is situated at the edge f Rupert nlet. Several kilmetres nrth f the SCU high lies a larger but smewhat less intense anmaly. This crrelates with a grandirite stck that straddles the Karmutsen and Quatsin frmatins. A third and much weaker high ccurs at the east end f Rupert nlet and crrelates with the sutheast edge f the grandirite stck mapped in the area. OM g ~... Figure SCALE ~~... s,--_-i0'o EET 150 loo lters -----j , l,500n rmi;~1 ::~::: POPrUY f Pit gelgy... T3J = OM ~ YlO DOC BCCA PfOPlYLT nlcc

6 690 K.E. Witherly Figure Aermagnetic survey ver the sland Cpper (frm Aermagnetic Map 1734G, Ge!. Surv. Can.). Grund Magnetic &Lrveys The grund magnetic surveys were carried ut alng the 160 km f survey grid by several tw-man crews wh tk bth mgnetic readings and btined sil samples. T extend the survey data, 50 statins were bserved ver Frances Lake using an aluminum bat, s as t better define the anmaly immedi3tely nrth f the lake. The instruments used were a Jalander fiuxgate and an Askania Gfz trsin magnetmeterbth are vertical field instruments with repeatable sensitivities f abut ± 20 gammas and ± 5 gammas respectively. The nrmal diurnal crrectins were applied t the readings and the results pltted and cntured n 1:2400 scale bse maps. A backgrund lcvel f 1000 gammas was selected t reference the lcal magnetic variatins against. The grund magnetic survey reslved the aermagnetic anmaly bserved ver thc SCU depsit int tw distinct znes f psitive magnetic anmalies (Fig. 32.5). The largest and mst cntinuus f the tw znes lies several kilmetres t the nrthwest f the rebdy. This zne is called the Frances Lake Zne, having a strike f N73 W, a length f 2.8 km and an irregular width that averages abut 300 m inside the 2500 gamma cntur. The magnetic relief alng the Frances Lake Zne is lcally 4000 gammas abve backgrund, with the mst intense prtin just nrthwest f the lake. This is the area that Milburne riginally investigated with a dip-needle instrument. The ther zne f psitive magnetic anmalies is ciled the Pit Zne. This zne is rughly parallel t the Frances Lake Zne, but is ffset KLOMETERS, 2«3 abut 700 m t the suthwest with an verlapping stagger f 1400 m. The Pit Zne strikes at N65 W and has an bserved length f 3.3 km. Observed length is a significant qualificatin since the sutheast end f the zne ends at the shreline. Red sland is lcated n the same sutheast trend at a distance f 1.2 km frm the shreline (Fig. 32.2). On the aermagnetic map (Fig. 32.4) the extensin f the Pit Zne t include Red sland is apparent s the ttal length f the zne, bth n land and underwater, is almst 5 km. The Pit Zne's width as defined by the 2500 gamma cntur is variable but is generally slightly less than 700 m (Fig. 32.6). Fur majr anmalies stand ut in the zne, f which the tw central highs are lcated directly ver the rebdy. A third high lies ff the nrthwest end f the depsi t and the furth high is a partially defined zne lying alng HOD m f shreline. Even thugh the Frances Lake and Pit Znes are spatially quite clse t each ther, there are several differences in their magnetic expressins. n a semi-quantitative sense, the differences can be listed as: 1. The Frances Lake Zne is quite cntinuus in appearance; it is nt brken-up like the Pit Zne. 2. An examinatin f the anmaly frequencies ver the tw znes shws the magnetic surces in the Frances Lake Zne are very near surface, while in the Pit Zne, particularly at its nrthwest end, the bulk f the causative magnetic bdy is lcated at 0 substanmine area tial depth. The anmaly ver the nrthwest end f the pit has a surce depth based n the half-width rule (Riddell, 1966) f abut 215 m. With regard t the first pint f differe~ce, crrbrating infrmtin was btained frm a detaled magnetic susceptibili ty mapping prgram n cre and utcrp in the pit at varius bench levels. The instrument used was a small, hand prtable magnetic susceptibili ty meter mdel PP 2A, manufactured by F:llit Gephysical Cmpany, Tucsn. The survey results in general substantiated the interpretatln f the surface magnetic data in that the distributin f magnetite arund the rebdy was fund t be quite irregular. Drilling f the Frnces Lake and Pit Znes bth befre and after the explratin phase substantited the secnd bscrvatin - early testing f the Frances Lake Zne encuntered magnetite at a shallw depth, while mre recent drilling at the nrthwest end f the pit fund the percentage f magnetite t increase sharply 240 m belw the pre-mining surface (vs 215 m based n the half-width rule). Althugh there are apparent differences between the Frances Lake and the Pit Znes, there is als evidence frm the magnetic data suggesting that the tw znes are clsely related in rigin and may at ne time, have been a mre r less cntinuus feature. Supprt fr this hypthesis cmes in part frm the gemetrical relatinships between the magnetic highs and lws arund the depsit. The lws f particular interest are tw magnetic trughs that trend N15 E; ne cmmences frm the sutheast end f the Frances Lake Zne and strikes t the nrtheast and the ther cmmences 1400 m t the nrthwest f the Pit Zne nd extends t the suthwest (Fig. 32.5). The sepamtin between

7 sland Cpper Depsit, B.C !... l n... Figure Reginal grund magnetic survey. the trughs n a nrthwest-sutheast line is abut.1400 m and the displacement n a nrtheast-suthwest lne S abut 730 m. These figures are almst identical t the displacement and ffset values between the Frances Lake Zne and the Pit Zne. The cnclusin then is that the tw znes f magnetic high might well have riginally frmed tgether alng the same structural trend but that pst-mineralizatin faulting has displaced the znes in a right lateral sense t the present psitins. The rigin f the magnetic lws is nt certain, but they are prbably due t the presence f a majr fault that was nce active, resulting in the lcal destructin r rembilizatin f magnetite. One ther prminent N15 E magnetic trend is a line nrmal t the sutheast end f the Frances Lake Zne. f this lineament is carried t the suthwest, it lines up with the Yellw Dg breccia in the pit, which, in turn separates the tw magnetic highs in the depsit. Other magnetic features f interest include the End Creek fault which lies n the suthern flank f the Pit Zne. This structure appears in prfile frm n a number f lines as a psitive peak with a distinctive negative n the s~th side. The amplitudes f the psitive and negative varies cnsiderably frm line t line but the pattern indicates lcal remval f magnetite alng the fault zne with sme rembilizatin t the ftwall side. This signature lies n the suth side f the larger magnetic highs caused by deeper surces frm within the depsit. Anther area f interest is arund the tw highs lcated in the nrthern and nrthwestern prtin f the survey area. The anmaly in the nrthwest part f the grid appears t be an extensin f the west end f the Frances Lake Zne. nterestingly, the nrthwest zne cmmences with a dg-leg frm the Frances Lake Zne at a bearing f N29 W. The nrthern part f the utlined anmaly lies adjacent t a grandirite stck mapped ff the nrthwestern crner f the survey grid. The nrthern anmaly crrelates with a mapped dirite stck and the magnetic respnse seems t be due t the presence f riginal magnetite in the rck. 20PO HET i--!l!.!-...:,6~o _mil Figure nduced Plarizatin SJ.rvey.> ~ GAMMAS Pit area grund magnetic survey. The eguipment used fr all the induced plarizatin (P) explratin wrk carried ut n the!scu. prperty.was a Hewitt 100 time-dmain P system. ThiS Unit S a physlcallylinked transmitter-receiver system with a rated utput f 800 watts. The receiver integratin perids are similar t the Newmnt standard (Dlan, 1967) and in cmparisn field tests, the cnversin factr between the tw systems was abut 1:1. The Wenner electrde array was used except fr the last survey ver the rebdy when the ple-diple array was utilized. A reginal survey alng the lgging rads used diples f 152 m and 183 m spacing while the ple-diple wrk used a ptential electrde spacing f 61 m with N=l and N=2 separatins. The extremely damp cnditins n the pr~perty, especially during the winter mnths, caused the P equipment t malfunctin a number f times which was partly the reasn why the P methd was nt utilized mre in the initial explratin stage... ~... O,OlON 5,OOON

8 6_9_2 ~K~.E. Wit_h_e..:.r..-'y:...- _ g.n...!... C C :;} j20,ooon 111>80 m60-80 S40-60 rnrm MVV ,001 N t J ;5 i 1;0 MLE 5 scale SC DEPDS' l _._5 _1_,0 _1:_5 K lo_e_'_er_s-'-- -' Figure Reginal P survey. The induced plarizatin technique was used initially t investigate specific areas f gelgical and gechemical interest arund the west end f Frances Lake. Numerus anmalies were btained and it was fund by subsequent drilling that the best P highs were due mstly t pyrite. Althugh this infrmatin was useful in an indirect manner, in that it culd help utline znes f alteratin, the magnetic and gechemical survey results prvided much less expensive and mre diagnstic means by which t lcate cpper mineralizatin. Largely fr this reasn, little P wrk was dne during 1966 and nce the depsit was fund, nly the immediate area f the depsit was surveyed using P. n 1968, as part f a prgram t evaluate the remaining grund held by Utah Mines Ltd. arund the depsit, a reginal P survey was cnducted utilizing the extensive system f lgging rads n the prperty. The results f this survey (Fig. 32.7) shws a large zne f clrjmalus chargeability as utlined by the 40 ms cntur trending at N700W acrss the prperty. The zne has an bserved length f 6.4 km and a width f abut 2 km. The anmaly ends 1500 m past the sutheast end f the pit and is pen t the nrthwest. There are several clusters f intense highs (>80 mv/v) within the verall zne. These clusters vary in size, but there appear t be at least fur pairs with the members aligned at abut N500E ± 10. nterestingly, these pairs f P highs all straddle anmalus magnetic znes. The Frances Lake Zne is straddled by tw such pairs and the magnetic high in the nrthwestern crner f the prperty is almst encircled by an P high, pen nly t the nrthwest. The resistivity results prvide little in the way f unique diagnstic infrmatin, either n the structure r mineralizatin in a reginal cntext. The dminant feature is a nrthwesterly-trending break running rughly acrss the prperty, as indicated by the 500 hm-metre cntur. Nrtheast f the break, resistivities are generally greater than 500 hm-metres, while t the suthwest f the cntur, they tend t be less than 500 hm-metres. This crrespnds rughly t the cntact between the Bnanza-Parsn's Bay frmatins t the suthwest and the Quatsin-Karmutsen frmatins t the nrthwest. The results shwn in Figure 32.8 (chargeability) and Figure 32.9 (resistivity) are the N=1 data frm the detailed ple-diple survey ver the depsit. The chnrgeability results arund the depsit shw tw bands f high straddling the dyke and the pyrphyllite breccia cap n a mre r less cntinuus basis, with the high n the nrth side f the dyke being much mre intense and extensive than the zne n the suth side. This difference is felt t be prbably due in part t vertical mvement alng the End Creek Fault which has remved mst f the pyritized wall rck n the suthwest side f the dyke. t is apparent frm Figure 32.8 that there are several pairs f charqeability highs straddling the rebdy and the pyrphyllite cap in a similar fashin t thse already nted in the reginal results. The pairs f anmalies arund the depsit are nticeably smaller in area and smewhat less in amplitude than the pairs arund Frances Lake and in the nrthwest crner f the prperty, but they shw the same nrtheasterly alignment and similar straddling f magnetic highs. Besides the majr zne f anmalus P, a secnd anmalus zne is nted in Figure 32.7 at the far sutheastern crner f the survey. This anmaly is adjacent t the grandirite stck at the east end f the nlet, and culd be cnsidered a cntinuatin f the main chargeability zne, interrupted by Rupert nlet.

9 w sland Cpper Depsit, B.C. 693 w! i O,OOON!! -c-1 1 ẉ.. SCALE ~ r qOO feet ~ loo 6h m.s L -~ ~~ ,000 N H <250 1f--'----!!i-->SO.60-S0 :m f ~40-60 ~ » ~ MVV O'M-M ~ i 1 L - ---f "., 5,OOON SCALE ~_~19'~'_~2g.. felt '".l ",.S Figure Pit area P survey. Figure Pit area resistivit.y survey. n assessing the P results, cnsideratin must be given t the unknwn dilutin effects caused by the large variatins in verburden thickness arund the depsit. The chargeability anmalies n the SCU prperty are felt t be due t a cmbinatin f sulphide and nn-sulphide respnses. Pyrite is present bth in the re and in the adjacent rcks as nted earlier. Tgether with chalcpyrite, sulphides in the pit ttal abut 5 per cent cmbined, whereas pyrite reaches 15 per cent lcally nrth f the depsit. Alteratin clays arund thc depsit als appear t make a significant cntributin t the bserved chargeability respnse. nterestingly, the pyrphyllite breccia cntains a small but significant amunt f finely disseminated pyrite. On the P results, hwever, the breccia cap stands ut as a prnunced chargeability lw. Sme graphitic material is fund in sediments nrth f Frances Lake, hwever the sediments are spatially quite restricted and are nt believed t have cntributed significantly t the verall P picture. The reginal sulphide zning as indicated by the P results with respect t the magnetite in and arund the depsit, appears t be an interesting variatin f the pyriteshell-p-dnut pattern smetimes suggested fr the Suthwest United States-type prphyry cpper depsits. Gelgically, the mineralizatin at SCU appears t have been emplaced when an extensive zne f sulphides was first intrduced alng a nrthwesterly grain. This was fllwed by the alteratin f sme f the sulphide irn t magnetite. At abut the same time, faulting (prbably) disrupted the riginal nrthwesterly zne f weakness and sme sulphides were selectively redistributed alng nrtheasterly structures. Later, pst-mineral faulting then further dislcated the sulphide distributins t their present psitin. Arund the pit area, the resistivity results (Fig. 32.9) were a little mre diagnstic than thse btained in the reginal survey. A prtin f the End Creek Fault crrelated with a resistivity lw n its hanging wall side. Nrthwest and slightly suthwest f this lw, 8 prnunced zne f high resistivity shws up with a lw n its nrtheastern side. The pyrphyllite breccia cap extending frm the nrthwestern end f the dyke is lcated between the resistivity ridge and trugh and where the cap apparently ends, s des the ridgetrugh resistivity feature. The character ver the depsit itself is quite unifrm, with the resistivity values ranging frm 200 t 300 hm-m. A typical crss-sectin thrugh the depsit is shwn in Figure This figure presents the magnetic, gechemical, chargeability and resistivity prfiles acrss the rebdy and quartz feldspar prphyry dyke, and illustrates the spatial relatinship f the re with the gephysical and gechemical data. VLF-EM Survey n the early drilling arund the suthwestern crner f Frances Lake, sme massive cpper mineralizatin was fund in a near-surface vein system. T try t assist in the detectin f such mineralizatin, a limited VLF -EM survey was run ver the area. A Genics EM-16 receiver was emplyed with the Jim Creek (Seattle), Washingtn statin (48 12'N, 'W) being used as the transmitter. This transmitter prvided a gd alignment with respect t the reginal gelgical strike n the prperty. After sme initial psitive results ver mineralizatin arund Frances Lake, it was decided t cnduct a survey ver the newly fund rebdy using the EM-16. Althugh the verburden generally had a fairly high resistivity, there were many pr surface cnductrs (swamps, beaver pnds, etc.) where the EM-16 culd be expected t respnd. The VLF-EM results 8re presented in Figure and because f their lw amplitude char8cter, little in the way f quantitative infrmatin was gained frm the results at the time f the survey. Subsequent examinatin f the data shwed that several sets f cnductrs axes culd be crrelated with legitimate structural and lithlgical features. Three f the mst distinct sets f crssvers were adjacent t magnetic highs and tw f the three cnductr axes straddled the rebdy. One ther majr cnductr axis picked ut the edge f the Bnanza vlcanic-cretaceus sediment cnt8ct west f the pit. This cntact can be traced fr a distance f almst 2 km, based n the EM-16 results. Mst f the survey was carried ut alng grid lines 152 m apart with survey statins every 30.5 m. This type f cverage althugh likely t carse fr massive SUlphide detectin, gave satisfactry results in mapping majr structures. GEOCHEMCAL SURVEY OF THE SLAND COPPER DEPOST The gechemical survey f the SCU prperty was carried ut in cnjunctin with the grund magnetic survey during the first half f Sil samples were taken every 30.5 m alng lines that were 152 m apart (the same distance used in the magnetic survey). A ttal f 4203 samples were cllected lng 160 km f grid. The area arund the SCU depsit has a variable cver f glacial till, peat and mss which ranges in thickness frm less than ne metre t ver 75 m. The sil samples were taken with a mattck in areas where the rganic cver was thin and with a 1.2 m lng auger where the cver was thicker. The B sil hrizn was sampled wherever pssible. n all, hwever, 22 per cent f the statins culd nt be sampled due t excessive rganic cver, lakes r lck f sil develpment ver bedrck.

10 694 K.E. Witherly ~ ~ ~, Magnetics ~1500E 1000 ~ ~ ~~~~==:?v~ --L----:=:: E " >... > ~ slew -- BEDDNG N PYROCLASTC VOLCANC ROCK ~:;~ ';;..,~~~~~~~trffmllmmeeb;~[""~_:_ ~~ ~ / N 18E SEA LEVEL /7 r ,-!.~ ' / / ~~t...:..;~~~ ~~~t ' LMB OF ORE ' OVERBURDEN ( SCALE HORZONTAL a VERTCAL) 460 FEET QUARTZ FELDSPAR PORPHYRY SECTON 115 (LOOKNG NW) METERS BONANZA VOLCANCS Figure Crss-sectin 175; shwing gechemical, grund magnetic, P and resistivity prfiles. The sil samples were first dried, grund and then sieved thrugh an 80 mesh screen. Thc residues were then analyzed spectrgraphically fr ttal cpper cntent in parts per millin (ppm). n rder t assist in interpreting the gechemiccd results, sme statistical treatment f the data was applied. A semilgarithmic frequency distributin histgram f the gechemical data is presented in Figure Based partly n the statistical analysis f the gechemical, but mre n empirical results derived frm the drilling, an anmalus threshld f 100 ppm was decided upn. Values between 100 t 200 ppm were cnsidered slightly anmalus, betwcen 200 t 500 ppm were anmalus and abve 500 ppm were cnsidered significantly anmalus. Several large anmalus znes were identified inside the survey blck (Fig ), the largest being a N75 W trending zne lcated rughly in the west central prtin f the prperty (apprximately 10 OOOW t 15 OOON, 10 OOOE, t 25 OOOE). The zne is cmpsed f a number f discrete anmalies linked tgether by an envelp f abve-backgrund values. The zne terminates quite abruptly t the east but splits int a number f small parallel-trending znes in the west. Several relatively discrete gechemical anmalies with apprximately N700W trends were fund t lie suth f Frances Lake (Fig. 32.2), ne at the suthwest end f the lake centred at 9460N, E and the ther several kilmetres t the sutheast centred at 6720N, E.

11 N PHASE QUADRATURE.. l c... sland Cpper Depsit, B.C n e Z " [ -ZO" SCALE loll Z, flt 311 '~ H ~ (/)600 w...j D- ::!: «(/) ::;400 0: w ::!: :::> z200 Figure VLF-EM survey. Figure RANGE OFGEOCHEMCAL VALUES ppm Histgram f cpper gechemical data. 0 g 0 0 ~ l ~ g~ n ft n... n -... C"... ~ qlftb )500 CD> Q lb \D ~ [[ll] ([] ppm 20,OOON 10,000N 0 f scale MLES, i i KLOMETERS 0 Figure Reginal gechemical survey.

12 696 K.E. Witherly The majr gechemical anmaly, just nrth f Frances Lake, was tested in a number f places alng strike and the underlying bedrck was fund t be mstly vlcanic rck cntaining subecnmic cpper (0.2% t 0.25% range) with a variable amunt f magnetite. The Frances Lakc magnetic zne is cincident with a large part f the gechemical zne and based n the bserved crrelatin between cpper and magnetite, it was felt that cnsiderablc lw-grade cpper might ccur alng the length f the magnetic anmaly. A limited amunt f drilling has tcnded t bear this hypthesis ut. The gechemical anmaly suthwcst f Frances Lake, cincides in part with the mre massive vein-type mineralizatin as was first lcated by Milburne and later cnfirmed frm drilling by Utah Mines Ltd. The anmaly sutheast f Frances Lake is centred ver a prtin f the SCU depsit. Subsequent drilling f this anmaly indicated the area f the anmaly abve the 200 ppm level crrespdnded fairly well with the part f the rebdy verlain by less than 9 m f verburden. Testing f ther gechemical anmalies n the prperty mst ften encuntered sme lw-grade cpper miof~ralizatin in the bedrck. This bservatin encuraged the reliance upn the gechemical anmalies as being a prime surce f drill targets, since, even thugh much f the glacial till had been transprted, a signi ficant amunt f the sil at a given site Wi-lS apparently lcally derived. Extensive drilling f the anmaly ver t.he depsit did shw, hwever, that mre than 15 m f the verburden culd inhibit the surface expressin f even subcrpping re-grade mineralizatin. CONCLUSONS Of all the survey techniques carried ut in the discvery f the sland Cpper (SCU) depsit, a sil gechemical survey was the mst successful due t its advantages f speed, cst and detectin f t.he specific element f interest. The prblem f thick verburden subduing the gechemical expressin was apparent n the prperty but did nt present a serius prblem. Magnetic surveys were the mst useful f the gephysical tls used at SCU; an aermagnetic anmaly ini tially fcused attentin n the area arund SCU, and later bth during and after the explratin phase, grund magnetic surveys prvided invaluable infrmatin cncerning the structure and mineralizatin arund the depsit. nduced plarizatin surveys did nt cmpare with qechemical and magnetic surveys in their effectiveness in directly lcating mineralized bedrck at SCU. Hwever, after a reginal perspective using P was bt.ained, it allwed mre det.ailed wrk t be put int an intelligible cntext, which in turn direct.ed attentin t sme unique structures and alteratin effects in the area f the depsit. A VLF-EM survey demnstrated its usefulness as an aid t tracing structures, even in the presence f thick verburd8n and numerus pr near-surface cnductrs. The authr wuld like t acknwledge permissin f Utah nternatinal nc., t publish and t thank the varius peple wh have assisted in the preparatin f this paper. REFERENCES Annymus 1964: Aermagnetic Map 1734G, Gel. Surv. Can., Aermagnet.ic Series, Scale 1: Cargill, D.G. 1975: Gelgy f th8 "sland Cpper" Mine, Prt Hardy, British Clumbia; unpubl. Ph.D. thesis, Univ. British Clumbia. Cargill, D.G., Lamb, J., Yung, M.J., and Rugg, E.S. 1976: sland Cpper; in Prphyry Depsits f the Canadian Crdillera; Can. nst. Min. Metall. Special Vl. 15, p Dlan, W. 1967: Cnsideratins cncerning measurement standards and design f pulsed P equipment; in Prceedings f a Sympsium n nduced PlariZatin, Univ. Califrnia, Berkeley. Hewitt, L. 1965: Hewitt 100.P. System Technical Manual. Muller, J.E. et al. 1974: Gelgy and mineral depsits f Alert Bay - Cape Sctt map area, Vancuver sland, B.C.; Gel. Surv. Can., Paper Riddell, P.A. 1966: Magnetic bs8rvatins at the Daytn irn depsit, Lyn Cunty, Nevada;.i.Q Mining Gephysics, v. 1, Case Histries, Sc. Explr. Gephys., p Yung, M.J. and Rugg, E.S. 1971: Gelgy and mineralizatin f the sland Cpper depsit;.i.q Western Miner, v. 44 (2), p