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

Fro. 3. Feldspathic gneiss complex with blocks of Frc. 4. Levack breccia veining feldspathic gneiss, pyroxene hornfels, 2625 tevel, gf1affugorumins. 2625 level. Stratlcona mine. section, blocky grains ef ctinepyroxene and pale pyroxene, euhedral grains of fresh orthopyrox- brown hornblende are interspersed with fresh ene and patches of clinopyroxene, amphibole stubby laths of andesine. Other primary minerals and biotite. A prominent feature of the matrix include orthopyroxene, biotite, titaniferous mag- is the development of coarse brown bioti,te por- netite and ilmenite. Partial or complete altera- phyroblasts. They occur with very fine-grained tion of the hornblende to a mixture of granular plagioclase of indeterminate composition, gran- magnetite and biotite is characteristic; ortho- ular clinopyroxene and variable amounts of pyroxene is commonly altered to talc, carbonate chlorite, carbonate, quafrz, magnetite and il- and chlorite. menite. Minute grains of suffides are widely Mafic pyroxene hornfels is the term app,lied disseminated throughout the brecsia. to blocks that are much darker and lack the Numerous aplite veinlets and irregular uniform texture of the equigranular pyroxene patches and dykes of coarse-grained red peg- hornfels. These have a glasy appearance on a matite are present within the feldspathic gneiss fractured surface and contain feldspathic complex., Joint planes commonly contain epidote patches. In thin section, horyever, texture is and pyrite; these are flanked by a zone up to almost identical to that of the equigranular 10 cm wide of epidotized, pink-stained country variety. Coarse-grained anhedral clinopyroxene rosk. and fresh granoblastic andesine laths form mosr TABLE2. COI4POSITTOI{S of the rock. Patches of original hornblende have OFI.IAJN ROCK TYPES IN FELOSPATHICGNETSS COIIPLEX broken dorrn to a granular mixture Feldspathlc Equigranular Haftc of biotire Gneiss pmxene Hornfels pII9I9!S]9!lqI and magnetite. The quite latter is abundant and sr02 invariably 61.8 48.8 48.5 carries exsolved blades of ilmenite. Ar203 2t.5 14.8 15.3 Levack brecsia is erratically distributed as l,fSo 1.5 7.0 5.9 veins, dykes and irregularly shaped masses with Cao 5.9 10.7 11 .8 sha4r contacts in .the feldspathic gneiss Feo 2.2 7.5 6.9 com- Fe203 1.0 4.3 5.3 plex 1Fig. 4). As pointed out in previous de- NaZo 5.0 2.9 3.1 scriptions of this unit (Speers 1957, Mitchell & u0 l.l 0.8 0.5 Mutch 1956, Cowan 1968), it consists of small f102 0.50 0.86 0.95 fragments llno 0.05 0.18 0.20 of host rock set in a very fine-grained Nr 0.01 0.01 o.ol dark matrix. Both fragments and matrix vary in Cu 0.01 o.Ot 0.Ol composition according to the local host rock; Z! 0.006 0.009 0.007 hence in the sections examined the Levack Pzot 0.17 0.14 0..t6 1.0.I. 0.56 0.34 0.25 breccia varies considerably in mineralogy. Frag- ments noted in tle breccia consist of pyroxene Total: 101.31 98.35 98.79 hornfels, quartz Analyses mosaic with or n'ithout re- : Falconbri dge t4etalI urgldl- Loboratorles, Tlonhl I l, Ont. crystallized pyroxene, granular mosaic clino, Constttuents reported ln Ft. t. CU IN FOOTWALL COMPLEX, SUDBURY 279

Composition ol rock types in leldspathic gtuiss SrnerncoNe CoPPen ZoNs complex Compositions of the feldspathic gneiss and Copper mineralization in the feldspathic two varieties of pyroxene hornfels in tle foot- gneiss complex occurs as a series of fracture- wall complex are listed in Table 2. Feldspathic filing veins that can be arbitrarily confined gneiss, previously referred to as tonalitic gueiss within a block having horizontal dimensions of (Langford 1960) and quartz-plagioclase'augite 250 x 150 m and a di'p-slopelength of 215 m. gneiss (Naldrett & Kullerud 1967) have a com- The block strikes N68oW and dips to the south- position close to that of the average tonalite west at 45o. This attitude reflects the principal (Nockolds 1954). The composition of both strike direction of the veins within the block, pyroxene hornfels units are essentially the same but only represent$ an overall average dip 9f and probably have been derived from varieties the vein syitem. Available information at the of the same rock type. Pyroxene'rich inclusions present time indicates two principal veio_ sets in feldspathic gneisses of tle footwall complex witlin the system, one dipping at 35o and the have been termed mafic granulite (Mitchell & second at 6Oo, but both having an approximately Mutch 1956), mafic peiss (Langford 1960), identical strike of N68"W. The vein system is metagabbro (Greenrnan 1'970), or simply re- shown as it occurs in plan view on the 2625 crystallized gabbro by other Sudbury workers. level in Figure 5. If the plane of the vein system The analyses show that the inclusions are indeed is projected through the Strathsona Deep Zone, close to the average gabbro in composition. Re- its-apparent position on section 22200E wottld crystallization has taken trilace at a grade of appear as thai indicated in Figure 2. The relative metamorphism in the pyroxene-granulite fasies. poiition of the Copper Zone to the Main Ore

Frc. 5. Level plan 265, Strathconamine. 280 THB CANADIAN MINBRALOGIST

Ftg. 6. Geological cross-section21800q Strathcona mine (looking Er. Line of section is located in Figure 5.

Zone is .more evident on section 213008 (Fig. a system of fractures in a zone of dilatancy in 6), where it can be seen to lie between 15b the feldspathic peiss complex. The fractures and 350 ,m below the dark norite-late granite postdate the brecciation and recrystallization of breccia contact. the comtrrlex. Individual veins within the system range in width from a few mm to approximately 6 m. TABLE3. ELEcTR0NMIcRopRoBt nMLvsrsi oF sEtEcTEDsrJLFIoEs The multiplicity of veins sreates a problem in SAIIPLE SULFIDE Cu NI Fe Co 5 TOTAL extrapolation and interpretation of diamond- 5817 ChalcopyrJto 34.6 0.l6 30,4 35.02'I 100.2 drill hole results. A complete structural analysis Aton. Prup.r 0.499 0.002 0.498 of the vein system must await the availability of 5817 Cubanlte 23.4 0.13 40.9 34,8 99,2 Atm. Prcp.* 0.339 0.002 0.675 I mine epsnings at some point in the future. 5086 Pentl.ndlte 31,2 34.0 0.44 33.4 99,0 Veins consist alrnost entirely of massive sul- Atm. Prcp., 0.510 0.584 0.@7 I fides and have extremely shary contacts with 58t7 ilacklno{lte 2.14 s.80 54.9 35.5 98.3 Aton. Prcp.r 0.030 0.089 0.888 1 the host rocks. Some veins are straight and maintain a consistent width for manv metres. Zn cd te TOIAL whereas others are more irregular anO exhibii 5817 Sphalerlte 54.9 1.43 ir, ,*, 99.0 Atom. Prc!.r 0.805 0.012 0.153 ""0.004 I marginal apophyses extending short distances 'Anolyses into the wall rock. The latter type gives the reported ln rt. Z.i analJEt: c, Springer, Falconbridge 'Atom. appeariance of having fragments of ryall rock prop.: atonJc prcportions r".[T]t;:l;;1"':H:t*t*' enclosed withrn the vein. Minor disseminated "" sulfides in the wall rock are restricted to within MnrsRALoGy oF THB Coppsn M.TNSRALIZATToN a few cm of tle veins. Sulfide migration seems to have been restricted during emplace- Sulfide veins consist essentially of chalcopyrite ment of tle massive vein system. Some offset and cubanite with an average ratio of about is. commonly apparent between intersecting 3.7:1. Accssory vein ,rnineralsinclude coarsely veins, and Darrow veins may terminate against crystalline pentlandite, blocky pyrrhotite com- wider veins. The vein sulfides evidently oecupy monly replaced by cubanite, sphalerite, niskel- CU IN FOOTWALL COMPLB& SUDBI'RY 281 iferous mackinawite, primary and secondary rite. Some sphalerite is inclusion-free, but the mapetite, and traces of assorted sulfides, tellu- majority contains numerous blebs of exsolved (Table rides and native metals. chalcopyrite. An analysis of sphalerite Chalcopyrite comprises approximately 67Vo 3) shows a Cd content of. L.43qo and 15.7 of the total mineral assemblage.It is invariably mol 7o FeS. as coarse-grained mosaic Mackinawite is a minor constihrent of these twinned and occurs 'in patches averaging more than 1.5 mm in dia- ores, occurring as narrow spindly grains heter; these enclose all of the other sulfide and chalcopyrite (Fig. 10). Their development is oxide phases. A microprobe analysis of cfSl- controlled by grain boundaries and crystallo- copyrite (Table 3) shows it to be nearly stoichio' graphic direitions in the ohalcopyrite. 11 this metric. lsvilsnment, mackinawite is believed to be the Cubanite is the next most abundant sulfide product of unmixing of solid solutions that mineral in the Copper Zane, comprising about iontained nickel or iron in excess of that which on lSVo of. the total sulfides. It occurs in chalco- can be held by chalcopyrite (or cubanite) pyrite either as massive round patches tlat cooling (Hawley 1962). An electron-probe (Table it to invariabty enclose relict grains of pyrrhotite or analysis of mackinawite 3) shows pentlandite, or as coarse laths up to 5 mm long contain 2.l4%o Cu and 5.8OVo Ni. Additional ore oriented parallel to the (112) planes of the minel sad rare minerals identified in the chal- host chalcopyrite (Fig. 7). Interpenetrating tex- include galena, violarite, pyrite, bornite, tures of cubanite blades following three (112) cocite, millerite, altaite (PbTe), native silver, directions in chalcopyrite are not uncommon. native bismuth, empressite(AgTe), and hauche' These textures seem sirnilar in occurrence to cornite NL(Bi,Sb,Te) sS8. those in the cubanite-rich zone at the Frood- Magnetite constitutes approximately 5Vo of. Stobie mine (Zarbigg et al. 1957, Hawley the vein material and is present in two distinctive L962). The texture results from unmixing in an relationships. Prominent subrounded to euhedral FeS-saturatedCuFeSg solid solution at approxi' grains up to several mm in diameter occur mately 59OoC (Yund & Kullerud 1966). An throughout the sulfide assemblage. A cell'edge electrbn microprobe analysis of cubanite shows measrirementof 8.3985(15) A for this mag- it to have a composition of Cur.oaFes,osSs(Iable netite compares closely wi,th the lattice dimen' 3). sion of 8.396 A for pltre magnetite (Deer rdacement of Pyrrhotite constitutes about 3.5Vo of the sul- et al. 1962). Marginal and cubanite fides in the vein system. It is a nonmagnetic magnetite crystals by chalcopyrite preserves of variety and occurs as very coarse-grained is a common feature that "ghosts" (Fig. 11). patches with diameters commonly exceeding 1 the original euhedral crystal outline consistsof bladed im. Extensive replacement by chalcopyrite and The secondtyrye of occurrence of late 'formation that cubanite is observed in most samples. to vein-like magnetite in chalcopy- Although abundant in some narro* stringers follows crystallographic directions other sulfides and forming nickel-rich zones in some of the rite and occasionally cross-cuts larger massive sulfide veins, pentlandite consti- (Fig. 12). the total sul- tutes only an estimated I.5% of. Sutfide zoning and distibution ol metals fide assemblage. It is present as large blo{Y development of the crystals up to 10 cm across' readily visible in Although underground yet the stage hand specimen, and as fine-grained crysbls Copper Zone has not reached about sulfide resulting from exsolution. The larger grains are wheie meaningful conclusions it is evident invariably replaced by chalcopyrite and cubanite zoning within the veins san be made, pattern of sulfide along cleavage planes and shatter cracks (Fig. that ihere is an irregular 'oflame" across the widths 8). Exsolution pentlandite occurs along distribution and metal content the copper and the basal planes of pyrrhotite and at the junction of some veins. In Figure 13, 'massive inter- of cubaniie laths and chalcopyrite (Fie; 9). The nickEl contents of two sulfide drill hole are electron-probe analysis of 'massive pentlandite sections from the same diamond with the listed in Table 3 shows it to have a lowet presented-percentages in histogram form, together phases,pre- nickel content than pentlandite ,from the Main of the principal sulfide of chem- Ore Znne, where it reaches 35.97o. sent, as calculated from a combination diffraction method' Sphalerite is evenly distributed throughout the ical assays and an X-ray proportions of the vein sulfides to a total estimated content of The lattei determines relative and cuba- O.SVo.It occurs as irregular patches up to 0.35 copper-bearing sulfides, chalcopyrite m,m in dia.meter, usually enclosed in chalcopy' nite. 282 THB CANADIAN MINERALOGIST

Frc. 7. Multiple lamellae of cubanite (dark) in chalcopyrite (light). The rectangular white grain is altaite (PbTe). Scale bar 0.01 rnm. Fro. 8. Coarse grain of porous penflandite (light) extensively replaced along cleavagesand cracks by chalcopyrite and cubani,te.Minof retct py.rrhotite occurs in tle cubanite. Scale bar 0.1 --. Fro. 9. Exsolution blades and patchesof pentlandite within and along the sharp- boudary of cubani.te laths in chalcopyrite. The chabolyrite is etched with Agl.{Os. Scale bar 0.1 mm. Fro.- 10. lvrnltiple lamellae and irregular massivepatches of cubanite (dark) with-chalcopyrite (lieht grey). pentlandite (white) pres€nr afoig thi interface of chalcopyrite and subanite is mostly

2

I 5

F

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E t

I* Ilrrql Prots tloE (6lG)

FIc. 13. Histogram plot of copper and nickel content of two massive sul- fide veins interseCtedby DH 23--239 on 2375 level, Stratlcona mine. Mineral proportions are calculated for chalcopyrite (cpy), cubanite (cub), pyrrhotite (po) and pentlandite (pn) from chemical analyses and X-ray diffraction results.

Although the sample lengths along the core adjacent to sul'fide veins (Fig. 14). These a-re are not uniform, the relations illustrated by principally composed of green . horn'blende, Figure 13 seem to be valid. Nickel content of epidote and chlorite. Euhedral grains of horn- the sulfides incteases substantially towards the blende and porous anhedral epidote ate also loryer or footwall side of each vein, and is ac- usually enclosed ip and partly replaced by the companied by a corresponding decrease in adjacent sulfides.' Chlorite com:nonly forms copper content. This is reflected in the calculated narrow veinlets parallel to the sulfide/host rock proporlions of pentlandite and chalcopyrite contact. Coarse p-atches of reerystallized albite present in the massive sul'fides' The proportions enclose stubby laths of andesine, and round of pyrrhotite and cubanite vary sympathetically sieve-textured magnetite grains with bntrained with each other and an increase in these two feldspar laths are also generally present in this sulfides .is accompanied by a decreasein chal- zone. Of more restricted occurrence are round copyrite content. Stated another way, an inverse garnets in which Mn, Ca and A1 are fhe domi- relationship exists between the amount of pyr- nant components, i'e', a spessartine-grossularite rhotite present and the chalcopyrite/cubanite fire. These are porous in texture and generally ratio. This is in agreementwith the replacement contain abundant sulfide disseminations. Rarely textures observed in polished section, which in- associatedwith garnet is tle mineral pyrosmalite dicate that the granular variety of cubanite has (Mn,Fe) eSieOs(OH,CI)ro. formed from the breakdown of chalcopyrite and pyrrhotite. Sphalerite is not plotted in Figure 13, but is very evenly distributed throughout each DrscussroN AND CoNcLUsroNs sulfide intersection, occurring in the same ab- solute amounts (OSVo). Massive stringer ores consisting almost solely Wall-rock alleration of chalcopyrite are commoo to many of the Narrow selvages of dark alteration up to 5 ore deposits of. the Sudbury basin, particufarly mm in width are observed in the wall rock along their margins and in areas remote from 284 THB CANADIAN MINERALOGIST

tures developed subsequpnt to &e deformation and high-grade metamorphism of the feldspathic i goei.r complex, but presumably prior io or i during the intrusion of the Imrptive. r A high-temperature copper-rich liquid and a r srysfallizing nickel-rich pyrrhotite phase seem , to have invaded the fraqtures of ihe dilatant , zoue. Whether by a flow nsgfoanism or gravita- r tional seffIing, the homogeneous pyrrhotite phase , became consentrated at the lower side of larger , veins. This welldeveloped zonation suggests a relatively unrestricted movement of crystalliz- l ing pyrrhotite in its surrounding liquid. As chal- i copyrite appears as..a phase on the liquidus at r about 97OoC, the temperature of the vein fluid , was probably at least lO0OoC. By analogy rwith r the experimen8 of Craig & Kullerud (1969), i the presence of. SVo magnetite in the system presumably Flo. 14. Hand sample showing the sharp contact lowered somewhat the initial melting of massive zulfide (lower half) and feldspathic temperature. The temperature at the contact of gneiss wallrock. The fracture occupied by the footwall rocks with the Imrptive during its sulfidesis essentiallynormal to the well-developed intrusion is estimatedto have been about 700'C peissosity of tle wall rock. A thin septum of (Naldrett & Kullerud 1967). As the Copper wall-rock alteration ic visible adjacent to the Zone mineralization extends to at least 350 rn sulfide vein. from the contact, the tlermal gradient between veins and wall rock must have been relativelv high. The coarse grain-size of the vein sulfides the Imrptive contact. This led Hawley (1962) indicates that this high gradient was maintained to postulate the separation of a highly mobile over a long period of time. Cu-rich liquid by fractionation of Ni4u-Fe a At lower temperatures, subsolidus transfor- sulfide magma and its introduction into fras- mations in the vein sulfides included the separa- tures and dilatant brecsia zones. Experimental tion of pentlandite from pyrr,hotite and the work on phase relations in the Cu-Fe-Ni-S breakdown of chalcopyrite solid solution to chal- system (Craig & Kullerud 1969) has verified copyrite and cubanite. The relatively large the coeilstence of a Cu-rich liquid with crystal- crystals (up to l0 cm) of pentlandite and pyr- lizing pyrrhotite above 85O'C. Separation of rhotite invariably display textures indicative of this liquid can result in the formation of chal- extensive replacement by chalcopyrite and cuba- copyrite-rich veins and segregations. nite. Feathery zones of exsolved pentlandite It is not known at tle present time qrhether commonly occur at the mutual boundary of there is a physical connection between the thesetwo minerals. The separationof mackinaw- Colper Zone and the mineralization of the ite in chalcopyrite occurred at some low, but Deep Zone (Fig. 5). As a unit, the latter ore indeterminate temperature. Magnetite crystal- deposit plunges S35oW at 48", which is c.lose lized as euhedral grains, evenly dispersed through- to the calculated dip of the Copper Zone S23.\il out the sulfides and as a second generation of a! 45", The two deposits most probably have fine veinlets. Although quantitatively minor, the same structural control, the-Coppei Zone such rninerals as galena, altaite, native silver, representing distal mineralization .for whioh the native bismuth, empressite and hauc.hecornite pngqy source must have been both the Deep indicate an enrichment of Ag, Bi, Pb and Te in and Main Zones of the Strathcona orebody. these ores. There is no accompanying enrich- ment in platinum-group elements. Many features of the Copper Zone are con- sistent with an interpreted origin by introduction of a copper-rich sulfideoxide iiquid. Sharp AcrNowr,sDcnIvrENTs contacts of veins with adjacent wall rock, uni- forrm vein widths for ionsiderable distances The geological staff thank the semor manage- a-nd- intersecting and offsetting veins indicate ment of Falconbridge Nickel Mines Limited for the infi[ing of a dilatant fracture system. Frac- permission to publish this paper. The authore cu IN F@TWALL COMPLB:(, SrrDBrrRY 285 receivedconsiderable a$sistance frm other me'm- LANcFoRD,F.F. (1960): Geologyof Levack Town- bers of the geologicalstaff at Falconbridgewith ship and the nortlern part of Dowling Township, Prelim, respect to geological observations,constructive District of Sudbury. Ont. Dep. Mines criticism and photography.Diagrams were pre- Rep. 6. paredby Miss Giselle Co€. MrrcuruL, G.P. & Murctt, A.D. (1955): Geology of tlo Hardy mine, Sudbury district Ontario. Can,Inst. Mining Met. Traw. 59,3743, REFBRBNCBS NALDRETT,AJ. & Kur-r-eRUD,G. (L967): A study of tbe Strathcona mine and its bearing on the (1968): ore Cowurt,I.C. Geologyof the Strathcona origin of the nickel-copper ores of the Sudbury deposit Can. Mining Met. Bull. 61, 38-54. district, Ontario. I. Petrologt 8, 453-53t, Cherc, I.R. & Kur.r.nnrm, G. (1969): Phase rela- (1954): compo- tions in the Crr-Fe-Ni-S system and their ap Nocror-os, S.R. Averagechemical Geol. Soc. Amer. plication to magmatic ore delnsits. Iz Magmatic sitions of some igneous tacks. Ore Deposits (H.D.B. Wilson, ed.), Econ. Geol, BulI.65, lW7-1032. Mon,4,34y',-358. Srrrns, EC. (1957): The age relation and origin DSER,W.A., HowrE, R*{. & Zussuex, J. (1962): of cornmon Sudbury breccia. I. Geol. 65' 497- Rock-Forming Minerals. 5. Non-siliaes. Long- 514. mans, London. Yuxo, R.A. & Kwr-nnuo, G. (1966): Thermal GRrnttrreN, L, (1970): The Petrology of the Foot- stability of assemblagesin the Cu-Fe-S system. wall Breccias in the Yicinity of the Strathcona J. Petrologt 7' 454488, Levack, Ontuio. Ph.D. tlesis, Univ. To- Mitu, Srerr (1957): The ronto. Zunmrcc, H.F. & GEoLocrcAL Frood-Stobie mins. ln Structural Geology of Can' HAwry, I.E. (1962): The Sudbury ores: their adian Ore Deposits, 2. Can, Iwt. Mining. Met.' mineralogy and origin. Can. Mineral. 7, b?n7. CongressVol.34t-350. Hrwr.rs, R.H. (1971): The Petologt of someluTar- ginal Malic ilocks along the Noiih ilange of tfu Received July 1978, revised manuscript accepted Sudbury Inaptive. Ph.D. thesis, Univ. Toronto. December 1978,