Canadian Mineralogist Vol. 17, W.275-?A5 Q%9) GOPPERMINERALIZATION IN THE FOOTWALLGOMPLEX, STRATHCONAMINE, SUDBURV, ONTARIO M.K. ABELI, R. BUCHAN2, C.J.A. @ATS8 AND M.E. PENSTONE1 tFalconbrige Nickel Mines Ltd., Falconbridge, Ontario POM 150 sFalconbridgeMetallurgical Laboratories, Thornhill, Ontario L3T 4A8 sFalconbridgeNickel Mines Ltd,, Winniryg, Manitoba R3l AMI Arsrnecr suivantes: galdne, violarite, pyrite, bornitg chalco- cite, mill6rite, altaite, empressite,bismuth et atrgent High-grade copper mineralization has been fouud natifs et hauchecornite.Ia plupart des filons mon- in the footwall feldspathic gneiss complex at trent une zonation en sulfures, avec utr enrichis- Stathcona -ine, on the North Range of the sement en pentlandite et pyrrhotine du c6t6 de Sudbury Basin. The mineralization occupies a sys- f6ponte inf6rieure. L'alt6ration de la roche encais- tem of fractures that strike N68oW and dip to sante le long des filons s€ limfue e une lisi0re, the southwest at 45". This zone, containing an large de quelques mm, d€ hornblende, 6pidote, estimated 910,000 metric tons with a grade of chlorite, magn6tite et erenat. La min6ralisation 9.O9Vo C\t, 0.52% Ni and 34.3e/t Ag, is located r6sulte probablement de I'introduction, i tem.p€ra- from 150 to 350 m beneath the Imrptive contact, ture 6lev6e, dans un systdme de cassuresb6antes The fracture-filled veins range in tlicknes$ from a d'une zone en dilatation, d'un liquide cuprifdre few mm to 6 m and are essentially massive sulfides charg6 de pyrrhotine nickelifdre. composed of chalcopyrite and cubanite with lesser (Traduit par la R6daction) amounts of pentlandite and pyrrhotite. Minor com- ponents are magnetite and sphalerite; more rarely encountered galena, in the ore are violarite, pyrite, INTRODUCTION bomite, chalcocite, millqrils, altaite, empressite, native bismuth, native silver and hauchecornite. Sulfide zonation is evident in most veins, with The Strathcona mine, o\ryned and operated pentlandite and pyrrhotite concentrated on the foot- by Falconbridge Nickel Mines Limited, is lo- waU side. Wall-rock alteration adjacent to veins is cated in Levack Township on the northwest rim restricted to selvages a few mm wide composed of the Sudbury basin (Fig. 1). It is one of a of hornblende, epidote, chlorite, maguetite and group of nickel-copper sulfide ore deposits garnet. The introduction of a high-temperature, present alqng an 8.2 km section of the North copper-rich liquid containing a crystallizing nickel- Range of the Sudbury Irnrptive. In the mines rich pymhotite phase into a system of open fractures of the North Range, subunits of the Imrptive, in a dilatant zone is considered tle most likelv going from hangtng wall. to footwall, includb mode of genesis. felsic norite, dark norite and dark norite breccia, The footwall complex at Strath- Sonruernn cona includes the late granite breccia, which hosts a large proportion of the nickel- On a d6couvertune min6ralisationriche en copper ores, and a compositionally variable cuivre dans le complexe de gneissfeldspathique qui group of brecciated and migmatized rocks, herein constitue l'Qnnte inf6rieure i, la mine Strathcona, referred to as the feldspathic gneiss complex. au flanc septentrionaldu bassin de Sudbury. La It is within this latter group of rocks that the min6ralisation est localis6e dans un systdme de vein system of the Copper Zone occurs. cassuresorient6es N68oW, b pendagede 45o vers The Copper Zone was discoveredby diamond lo sud-ouest.Cette zone se trouve 150 i 350 m drilling in 1976, by tracing the upward extension audessous du contact avec les eabbros du massif of narrow, subeconomic stringers of chalcopy- .tonnes irnrptif; elle contient environ 910,000 m6tri- rite and millerite" which had been intersected quesde minerai A"9.09Vo Ca, 0,52VoNi et 34.3 e/t in mine openings on the 305O level. Diamond Ag. Les filons, d0s au remplissage des cassures, drilling to date indicates probable ore reserves varient de quelquesmm i 6 m de largeur, consis- teot surtout en sulfures massifs, chalcopyrite et of 910,000 t grading 9.O97o Cu, 0.527o Ni cubanite, mais aussi en pentlandite, pyrrhotine et, and almost 34.3 g/t Ag. The Copper Zone is accessoirement,magn6tite et sphal6rite. Le minerai presently being developed for production, contient aussi, en quantit6s minimes, les espbces scheduled to commence late in 1978. n5 276 TIIE CANADIAN 1VTINERALOGIST l.EEEilD S Olivin diobd |rrupfir. rr++t+t K illil*tt'" >Nict.r r t t + a a + a t+ El Clnln ftd roddo|r g orolln tbi. El Oiofan! torrEtlon E oioii. od gmhr g Arftito - 6.arrach. cid A Ll u6votolomrr ' -.Folt! o.tu'lnc Fro. 1. Geological map of the Sudbury basin, showing the location of Strathsona mine. Gsolocy oF THE STRATHcoNAMr.rE The major sulfide minerals in these ore zones are pyrrhotite, pentlandite, chalcopyrite and pyrite. Magnetite is an important acces- The geology of the Strathcona ore deposit lesser sory mineral. Differences in quantities of sul' has been documented by Cowan (1968). Prin- fide minerals and variations in metal ratios cipal geological features of the mine are illus- are important features of the ore zones. There trated on cross-section 222.0OE (Fig. 2). The is a pronounced zoning in the ratio of pent- orebody, associated with an embayment in the landite to pyrrhotite. The Ni content in Fe-Ni footwall of the Sudbury Imrptive, has a strike sulfides is loqrest in the Hangrng Wall Zone length of about 800 m and a dip of 20-60" and highest in the Deep Zone. The average south. Some mineralization occurs as irregular Cu:Ni ratio in the orebodies also changes zones in dark norite and dark norite breccia steadily:Hangrng Wall Zane l:3,Main7.one l:2, and constitutes ,what is termed the Hanging Deep Zone 1:1. The Cu-Ni ratio increases Wall Ore Zones. Most of the Strathcona miner- markedly at the base of both the Main and alization is present in the Main Zone, Ore which Deep Zones, where stringers consisting almost occurs in a zone of late granite breccia, between wholly of chalcopyrite are common. the knrptive and the underlying feldspathic gneiss complex. This breccia varies from 10 to Feldspathic gneiss complex 60 m in thickness and is composed of fragments The footwall rocks of the mines on the North derived from both the Imrptive and gneiss Range consist of a brecciated volcanic and complex in a quartz-rich breccia matrix (Cowan sedimentary sequence intruded by tonalite dur' 1968, Hewins 1971). Mineralization of the ing regional metamorphism (I-angford 196O, Main Ore Zone consists of sulfide stringers and Greenman 197U. Commonly referred to as the disseminations in the breccia matrix. Lenses Levack complex, this 3-5 km wide z'ote of and stringers of massive sulfides form the Deep brecciated rocks has a highly variable content Ore Zone, Iocated up to 200 m below the base of fragments in tonalite matrfi ranging between of the Imrptive in a system of dilation fractures 2-O and 8OVo. An increase in the content of in the footwall gneissic rocks. fra8rnents is evident towards the contact with CU IN FOOTWALL COMPLEX, SUDBI'RY n7 . -: J.ECE!!- " El LAIEoRANIE rREccra Nl FEL8rcxoRrrE mo^* ro fiE ff, rrlmnrrmc etEnc cqPLEl I cu- ir lulFto! otr! Frc. 2. Geological cross-section 22200E,,Strathcona miue 0ooking E). Line of section is located in Figure 5. the Irruptive. At Strathcona, the principal rock Occasionally the titaniferous mapetite is partly types in tle complex are feldspathic gneiss of or wholly replaced by chlorite, leaving only toualitic composition, equigranular pyroxene the exsolved blades of ilmenite unaltered. hornfels, mafic pyroxene hornfels and Levack Equigranular pyroxene hornfels occurs asr breccia. As tle main component of this hetero- large blocks, bancis or small inchrsions in tte geneous footwall assemblage is a medium- feldspathic gneiss. In drill-core intersections grained grey feldspathic gneiss, the preferred it is quite distinctive, appearing as a medium- to term for the whole unit is feldspathic gneiss fine-grained equigranular gabbroic 1esft. In thin complex. Modal compositions (in vol. Vo) for TASLEI. IIIIIIEM! ASSEI,IBLAGESIN ROCK TYPES OF TlE FELDSPAIHICEilEISS OIiIPLTX each rock tytrle within the complex are given Equigtanular l'hflc LevockBrelia. in Table 1. Feldspatilc Pyroxene Pyroxene - ktrlx. lncluslons Hbrnfels Hornfels (varlable) (vflablei Feldspathic p.eiss has a welldeveloped llineral Greiss 3{)-50 Pldoiocllse-(An) 55-60 35-45 4s-50 50-60 goeissosity that commonly is intricately folded An:s toqo-s4 An4o togo-qo brecciation (Fig. 3). and disnrpted by local Al bl te Aggregates of subhedral to euhedral andesine quartz m-25 5-10 25-40 laths about 0.1H.15 mm long are predominant ortiopyrcrene 6-10 4-6 2-5 0-10 10-20 in this leucosratic rock. Gneissosity is defined Cllnopyrcrene l-4 15-25 40-45 Anphlbole Tt to-m 1-2 0-2 0-2 by coarser-grained mosaic qruartz and blocky Blotlte l-z 6-10 5-8 2-10 2-5 subhedral grains of or'thopyroxene for'ming light ilagnetlte l-2 3-6 8-10 0-3 0-3 Tr and dark layers wifh plagioclase. Other primary Ilmnlte l-2 <l <l 0-l Chlorlte Tf Tr . Tr 0-10 l'2 'I'2 tninerals include clinopyroxene, euhedral apa- Carlonat€ Tr tr <1 0-4 tite, traces of zircon, blocky subhedral grains Apatlte Tr - of titaniferous magnetite and ilmenite. The rock Zlr@n Tr tr Talc Tr Ir - is very fresh, with only minor alteration of Epldote the ferromagnesian minerals to for,m traces of sulfldes (Tr) Cp,PY cp,polpnt,py cp,;o,Py Po,cp:Pnt,8n,sp;;l biotitg amphibole, chlorite, talc and oarbonate. 278 THE CANADIAN MINERALOCIST Fro.