Revista Brasileira de Geociências 12(1·3): 510·521, Marc-Set., 1982 . Silo Paulo

LEAD ISOTOPE EVIDENCE REGARDING ARCHEAN ANO PROTEROZOIC METALLOGENY lN CANADA

RALPH I. THORPE*

AB8TRACT A new lead evolution model (Ao = 10.242, 80 = 11.9556, Co - 30.37 and To = 4,060 Ma) has been derived, in part, from a steep linear pattern defined by lead isotope . data for deposits from the Superior Province of the Canadian Shield. Application ef this model in Superior Province provides evidence that: a) supports widespread formationofmassive sulphtde deposits at 2,700 to 2,750 Ma; b) some deposits in northwestern Ontario may have formed at 2,Soo to 2,S50 Ma; c) deposition was synvolcanic or nearly so for a few gold deposits; and d) many gold deposits were probably formed, and a few massive sulphide deposits remobilized, at 2,656 to 2,700 Ma, a period of major deformation and emplacement of syntectonic to post-tectonic plutons in the greenstone belts containing the depcsits. The pattern for Slave Province deposits is similar, but massive sulphide deposits are generally 30w60 Ma younger. Modellead ages for Pro­ terozoic massive sulphide deposits in the Churchill, Southern, Grenville and Cordilleran provinces are generally in good accord with other geochronological evidence. The sarne also appears to be true for silver-arsenide veins at Great Bear Lake, Bear Province, and in the Cobalt area, Southern Province. and for certain other epigenetic deposits. Lead isotope data help define a I ,200~1 ,400 Ma metallogenic epoch in the central Yukon, northern Canadian Cordtllera.

INTRODUCTION Prior lo 1966 lead ísotope data for deposits in lhe Canadian Shield had been published by Russell and Farquhar (1960), Kanasewich and Farquhar (1965) and Roscoe (1965), and by a few other workers. Howev,er, more analyses have been accumulated in lhe subsequenl 17 years, many of them by lhe Geological Survey of Canada. Although some of these have been pub­ lished in various papers and two major data sets are contained in papers now in press (Franklin et al., in press; Franklin and Thorpe, in press), a significant proportion have not yet been published. This paper attempts lo presenl some of lhe general geochronological and melallogenetic conclusions and interpretations that can be reached on lhe basis of ali these data. Reference is also made to analyses available for deposits in Precambrian rocks within lhe Cordilleran Province.

GENERAL GEOLOGV AND METALLOGENV OF THE CANADIAN 8HIELD A reviewofCanadian Shield metallogeny has recently been prepared by Franklin and Thorpe (in press), who summarized lhe pertinent geology as well as inforrnation on deposits of iron, nickel, gold and volcanic-associated massive sulphide deposits for lhe main geological provinces. Therefore, only a brief'sketch ofShield geology and melallogeny will be presented here. The small Nutak Province, along lhe coast of Labrador Figure I - Index map showing geological provinces o/lhe Canadian (Fig. I), contains some of lhe oldesl rocks of lhe Canadian Shield. Ruled areas represem Phanerozoic cover Shield. These are mainly gneissic rocks and are of both plutonic and supracruslal origins, Superior and Slave provinces, lhe main Archean blocks belts, sedimentary rccks predominale in lhe belts of south­ of lhe Canadian Shield (Fig. I), contain greenslone belts em Slave Province. Rocks in greenstone belts are com­ and intervening granitic-gneissic belts similar lo those in monly at greenschist facies, whereas those in gneiss belIs, other Archean cratons. Although volcanic rocks generally in many cases including abundanl metasedimentary supra­ predominate over sedirnentary rocks in these greenstone crustal rocks, are aI higher metamorphic grades.

"Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario KIA OES, Canada R~lI ista Brasileira ae Geoci ências, Volume 12 (1.3). 1982 511

Volcanic cyc1es in lhe greensto ne belts consist, in many de formed , and in part highl y metamorphosed , sedirnenta ry cases; of basal ultramafic (kornatiitic) lavas, overlain by rocks that grade westward into deeper water fades. an extensive and thick " plate" of pillowed basaltic lavas Rocks o f the Southern Province are dorn inated by an and capped by areally restricted felsic volca nic rocks. ea rly Aphebian (Hur onian) sedi rnenta ry succession co n­ Most major greenstone belts contain two to five volcaníc sisting o f conglomerate, sands to ne, argillite, mudstone, and cyc1es. ln greenston e belt s in lhe Slave Province, however , mino r limestone. Early sedimentatio n was confined to ba­ relatively few ultramafic rocks are known, no ult ramafic sins, troughs an d valleys, but later spread lo blanket large lavas have beco documented, and o nly in a few cases is areas of Archea n roc ks of lhe Superior Pro vince. Th e there more than Doe volcanic .cycle. Volcanic-derived Gowganda Fo rrna tio n in lhe eastern part of So uthern epiclastic rocks, greywacke and finer-grained turbidites Province has been interpreted lo be of glaeial origino Sedi­ co nstitute lhe maio sedimentary rocks in greensto ne belts, mentation was probably confined lo lhe period 2,500 lo whereas iro n-fo rrnation and carbonate units are less com­ 2,300 Ma . ln lhe Sudbury lo Cobalt region thick undula­ mo no lron-forrnation is locally ab"u nda nt ln the Superio r ting sheets of gabbro (Nipissing diabase), yielding a Rb-Sr Province and within Archea n terranes in lhe Churc hill isochron age of abo ul 2,120 Ma (Fairbairn et al., (969) , Province, Nort hwest Territories, but it forros o nly minor have int ruded lhe Aphebian seq uence and older basement occurrences in Slave Province. Carbonate units are locally rocks. Relatively littl e deforrned clastic and chemica l sedi ­ present in Superior Province belts (F ra nklin and T horpe, mentary rocks of the Gunflint and Rove lormatio ns form a in press), but are co mparative ly common in SIave Province homoelinal seq uence in lhe Thunder Bay area. T he White­ belt s. water Group o f tufTs, carbonaceous and pyriti c siltstones The bulk of lhe volcanic rocks in Superior Province were an d greywacke is confined lo lhe Sudbury Basin , extruded between 2,700 and 2,750 Ma ago (Krogh (' I al., The Grenville Province is similar in many respects to the 1982a ; Nunes and Pykc , 1980 ; Nunes a nd Jcnsen, 1980 ) Churchill Province. The rocks are, in many places, gneissic according to zirco n U-Pb data. However, some greenstone a nd inelud e highl y deformed and rneta mo rphosed sedi­ belts in no rthwestern Ontario also contai n sequences 3,015 mentary rocks. Volcanic rocks are abundant in some parts lo 2.9 15 Ma and abo ut 2.776 to 2,794 Ma old (Nu nes of the Province arid marble is abundant in oth ers, Granitic, and T hurs to n, 1980 ; Nunes and Wood, 1980 ; Dav is et al., and in sorne areas anorthositic, pluton s are relatively com­ 1982). A V· Pb zirco n age of 2,670 ±4 Ma was recently mo n. Supracrustal rocks are in part known and /or presumed obtained for volcanic rocks in the Back River area , eastern lo have ·been deposited in lhe intcrval 1.400 to 1.200 Ma . SIave Province (La mbert and Henderson, 1980 ). Th is date but some older rocks hav e been identified, pa rticular ly is in cxccllent agreernent with a date of about 2,666 lo in lhe Grenv ille Tectonic Zo ne flânking Superior Province. 2,669 Ma fo r a subvolcanic intrusion in lhe Hackett River Rocks in lhe G renville Province were generally highly area a Iittle farthcr no rth, and with prior zircon data for de forrned and metamorphosed during lhe Grenville oro- so uthem Slave Province (F rith and Loveridge, 1982). geny at about 1,050 lo 1,000 Ma (Stockwell, 1973). . Volcanic rock s are similar in age, about 2,680 Ma , in lhe T he differenl structural-geologica l provinces of lhe Ca na­ Po inl Lake area , north western Slave Provi nce (Krogh, dian Shield have distinctive metallogenetic characteristics. pers. co rnmun.], where olde r basement rocks, 2,870 lo Superior and Slave prov inces both co ntain irnportant Cu-Zn 3,155 Ma , are kno wn (Krogh and Gi bbons, 1978 ). Zircon massive sulphide an d gold deposits, However, while Suo ages of about 2,677 ànd 2,953 Ma have been reported. res­ perior Province co ntains importam iron and nickel deposits, pec tively, fo r volcanic roc ks in lhe Rankin -Enn adai belt, these are lackin g in Slave Province. The absence of nickel Churchill Province and for paragneiss associated with Prince deposits in SIave Pro vince is no doubt related lo the pa ucity Albert Group supracrusta l rocks on Melvi lle Peninsula , o f ultramafic rocks. The Bear Province is characterized by District of Franklin (Wanless, 1979 ). deposits of uranium, copper and silver-a rsenide veins, and by lhe striking laek of signifi cant go ld o r massive sulphide Churchill Provínce co ntains Proterozoi c volcanic-sedi­ deposits. Churchill Province co ntains abundant volcanic­ menta ry sequences, belts of shelf-facies sedimenlary rocks, -associated massive sulphide deposits, similar to those of gneissic rocks o f various co mpos itio ns and of varied sour­ Superior Province, in Aphebian terrane in lhe circum­ ce lith ologies und ages. and also, as noted abov e, so me -Kisseynew (Flin Flon, Snow Lake) region , and oec urrences major belts o f Archean rocks. The latter are in part Inter­ ofthis type in Archean terranes in the Northwest Territories. folded with Proterozoic strata, and are also in part ai low Major iron deposit s and a few rnassive sulphide depo sits are metamorphic grade. However , rocks ove r large areas of presem in lhe Labrad or Trough, and impo rla nl nickel Churchill Province were highl y deformed and rnetarnor­ deposits in lhe Lynn Lake and Th ompson a reas , Manitoba, phosed lo mod crat e lo high grades du ring lhe Hudsonian and lhe Ca pe Smith-Wakeham Bay belt , Southern Province orogeny, which peaked at roughl y 1,780 Ma . The Cape co ntains major quartz-pebb le-conglomerate uranium depos­ Smilh·Wakeha m Bay beh eo nsisls dominantly of ko ma· ils near lhe base of lhe Huronian (Ap hebian) sedi mentary tiitic to tholeiitic basalt, some assodated sedimentary rocks. succession in the Elliotl Lake dislricl , and the major Sudbury and lalerally persislent mafi c lo uhramafic sills lhal have nickel deposils associated wilh lhe differenlialed Sudb ur y intruded these strata. Nickel Irruptive. Silver-bearing carbo nate-Ouo rite veins in Rocks in Bear Province have also been subjected to the the Thunder Bay arca are associa ted with olivine dia base Hudsonian orogeny. The Echo Bay group in western Bear sills and silver-arsenide veins in the Co balt area with a Province consists of a widespread sequence o f intermediate majo r sill of N ipissing diabase. The Errington-Vermilio n to felsic, do minantly subaerial. lavas and pyroclastic rocks, massive sulphide deposits occ ur in Whitewater Group and some assodated sedimentary rocks. Other rocks include SI'rala ' wilhin lhe Sudbury basin . The Grenv ille Province a yo unger sequence of sedimentary rocks. and granitoid co ntains zinc depo sits assoeiated with highly metamorph o­ .plulo ns of various Iypes. The easlem parI of lhe Bear sed carbona le strala in the Balmal districl , New York slate, Provi nce ineludes a predomina nt1y shelf seq uence of highly V .S.A. and aI Long Lake, Onla rio, urani um deposils in 512 RevistD Brasileira de Oeocéncías, Volume 12 (l~3). 1982 pegmatites in the Bancroft area, several massive sulphide 1972). More recent data (Franklin and Thorpe, in press; deposits associated with volcanic rocks, and numerous, other unpublished analyses) have confirmed this paleo­ mostly minor, deposits of vein, skarn and pegmatite types. isochron (Fig. 2) and established a slope of 0.804±0.OO5. Assuming an age of about 2,672 Ma, established for some greenstone belts in the Slave Province (Lambert and Hen­ LEAD ISOTOPE DATA fOR ARCHEAN DEPOSITS derson, 1980; Frith and Loveridge, 1982), is applicable to Although some rock lead analyses are available for rocks ali deposits defining the paleoisochron (i.e., that ali the of the Nutak Province (Fig. I), along the coast of Labra­ leads analyzed represent syngenetic, or at least syn-volcanic, dor (Davis, 1978), no ore lead data have been reported. mineralization rather than subsequent intrusive or meta­ The rock lead data suggest multiple stages of evolution of morphic events), two-stage calculations yield a source age the rocks, but do not directly confirm ages as great as of approximately 4,045 Ma. 3,760 Ma obtained for some of the gneissic rocks in this province (Baadsgaard et ai., 1979; Wanless et ai., 1979). Superior Paleolsoehron Model The fact that analyses for The SuperiorProvince is the main Archean province of Superior Province deposits also define a paleoisochron has the Shield in terms of knowledge of its geology and mineral only recently been established, although older data did deposits, and in terms of amount of lead isotope data establish a general steep trend (Franklin et ai., in press). available. Galenas and other lead minerais associated A slope of 0.822 ± 0.005 has been obtained for the Superior with volcanic-hosted massive sulphide, gold and iron de­ paleoisochron (Fig. 2). Assuming an average age of2,718 Ma posits, and a fewdeposits of other types, have been analysed. for syngenetic and syn-volcanic deposits (Krogh et al., The SIave Province, also Archean, has many isotopic and 1982'; Nunes and Pyke, 1980; Nunes and Jensen, 1980) geological similarities, although there are lead isotopic this indicates a source age of approximately 4,060 Ma for difTerences. A few lead isotope values are available for the these deposits. Rankin-Ennadai block, Northwest Territories, that forms The Slave and Superior paleoisochrons indicate that, for a major Archean outlier within the Churchill Province. the Canadian Shield at least, a lead evolution model is required that starts at a time intermediate between that Slave Peleoisoehron Lead isotope data for base metal of 4,509 Ma for the Cumming-Richards (1975) model and deposits, largely of volcanogenic massive sulphide type, in that of 3,700 Ma for the Stacey-Kramers (1975) mode!. the Slave Province have established a steep paleoisochron The Superior Province paleoisochron in conjunction with (Robertson and Cumming, 1968; Robertson, 1970;Thorpe, (a) isotopic data for the Big Stubby and Lennon Find deposits, Pilbara Block, Australia (Richards et al., 1981) and a, zircon U-Pb age of 3,452 ± 16 Ma (Pidgeon, 1978) 15.2 that can be applied to these deposits, and (b) the most :'lo I primitive lead isotope data for galenas from the Isua supra­ crustal sequence, Greenland (Appel et ai., 1978) and an 15.1 • ./ age of 3,770 Ma established for this sequence by whole rock Pb-Pb (Moorbath et ai., 1973), zircon 207Pb(206Pb Point Lake ""'. 1-•/ 15.0 (Baadsgaard, 1976), zircon U-Pb (Michard-Vitrac et ai., • 1977), and Sm-Nd techniques (Hamilton et ai., 1978), allows selection of a plausible initial lead isotope cornposi­ .a 14.9 tion at 4,060 Ma. This composition is Ao = 10.242, Bo = o. = 11.9556,and Co = 30.37. Use of this initial composition o.. permits calculation of model ages for Canadian Shield -s, 14.8 .a leads both older and younger than the assumed average ....0. 2,718 Ma age of deposits defining the Superior paleoiso­ o 14.7 chron. This model, termed here the Superior model, will be N presented in more detail elsewhere.

14.6 Leads older then the Superior Peleolsoehron ln contrast to ore leads from the Pilbara Block, Australia and from 14.5 Zimbabwe, relatively few in Canada have model ages sig­ nificantly greater than 2,720 Ma when the model presented above is applied. One specimen of galena from Point Lake, 14.4 Slave Province and 8 specimens from 6 deposits in north­ western Ontario in the Superior Province yield older model ages (Fig. 3; Table I). Model ages for the latter deposits 14.3 . are mostly in the range 2,800 to 2,847 Ma.

13,0 13.5 14.0 Sleve Provinee Areheen deta: bese metei deposlts Base 206 .1. metal deposits, largely of volcanic-associated massive sul­ Pb/2 04Pb phide type, in Slave Province (Fig. 4) define the Slave paleoisochron that lies nearly parallel to the Superior Figure 2 - Superior Provínce and Slave Provínce paleoísochrons paleoisochron and suggests a slightly younger age. Only the as deftned by massive suíphide deposits (e Superior Pro\'ince;'. minor Point Lake occurrence of massive sulphide type Slave Provinceí, .a few go/d deposite (e) and a few ga/ena veins appears, as noted above, to be significantly older (model (.Â.l. The o/der Point Lake deposit in Slave Province is índicated, age 2,768 Ma, Fig. 2). Most base metal mineralization in RevistaBrasileira de Oeociénctas, Volume 12 (1-3),1982 513

16.0

15.8

15.6

15.4

r§

13.0 " 14.0 15.D 16.0 17.0 18.0

Figure 3 - Leal! isotope data for setected, Superior Pmvince deposits. Tlw evotution CIII'l'{'S shown are based on .a model deríved for Superior Provínce deposits as explaíned ín lhe text

Tabíe J - Mode/ ages of the oldest Canadían Shield leads using a model presented ín this paper

Geological 20hPbj 207Pbj 208Pbj Model Locality Latitude Longitude Province 204Pb 204pb 204Pb agc(Ma)

Point Lake Slave 65'16'10" 113'06'00" 13.881 14.995 33.766 2.768 Berens River Superior 52'50' 93'37'30" 13.183 14.486 32.983 2,744 Berens River Superior 52'50' 93'37'30" 13.333 14.517 33.070 2.862 Severn Mines Ltd. Superior 52'49'26" 93'37'00" 13,154 14.445 32.907 2,844 North Spirit Lake Superior 52'27'50" 92'44'00" 13.608 14.799 33.767 2.806 Trout Bay Superior 51'00'32" 94'12'51 " 13.25 14.49 32,95 2.798 Dickenson Superior 51'04'00" 94'03'45" 13.120 14.419 32.924 2,846 Onaman (Headvue) Superior 50'01 '14" 87'39'38" 13.464 14.705 33.292 2.836 Onaman (Headvue] Superior 50'01 '14" 87'39'38" 13.497 14.743 33.338 2.847

Slave Province thus appears lo have taken place ai approxi­ are from Cumming and Tsong (1975). The other available mately 2,670 Ma. Much of lhe lead isotope data.has been data, ali for galena, are listed in Table 2. Most of lhe galena given by Franklin and Thorpe (in press). The general geolo­ analyses til closely lhe steep Slave paleoisochron. They gical characteristics of many of lhe deposits are given by show a range aiong lhe paleoisochron of about 60'/;, of its these authors and in other publications (Money and Heslop, length. The galenas yield model ages of 2,597 lo 2,705 Ma. 1976; Rockingham, 1979; Frilh and Roscoe, 1980; Eco­ While some of lhe galena analyses, especially those by nomic Geology Division, 1980). Cumming and Tsong (1975), plot systernatically on lhe Some leads from lhe Indian Mountain Lake, Takiyuak older side of lhe Slave paleoisochron and yield model ages (Zone 3) and Hood River No. 10 volcanic-associated mas­ of 2,690 lo 2,705 Ma, this could be due lo differences in sive sulphide deposits show isotopic and physical evidence analytical procedures. The validity of this pattern requires of having been subjected lo rernobilization (Fig. 5). The further testing, Four of tive analyses for gold deposits near secondary isochron defined by these dala, and some pyrites lhe northern and northeastern extremities of lhe Slave from gold deposits, suggests that remobilization occurred Province, at Coronation Gulf (Tree River) and in lhe at 1,730 Ma. Hope Bay area, have model ages of 2,516 lo 2,542 Ma.

Slave Province Archean data: 901d daposits Gold deposits Superior Province Archean data: massive sulphida deposita that have been isotopically studied are shown in Fig, 6 Lead isolope data for volcanic-associated massive sulphide and lhe isotopic data are presented in Fig. 5. The data for deposits in Superior Provinee extend only about 25~; of lhe sulphides other than galena, and some galena analyses, length of lhe Superior paleoisochron. The upper end of lhe 514 Revista Brasileira de Geocíêncías, Volume 12 (J·3), 1982

/)0 IIi" '-"'_'.r--'-;''.

.'

BASE METAL OEPOSITS 1. HIGH LAKE Za. HOOO RIVER 10 Zb. HOOO RIVER 41 ~ 3. 120K LAKE (f 4. POINT LAKE . ~~ 5. HACKETT RIVER 6. CLEAVER LAKE cf 7. OUCK LAKE ~ VOUNGER COVER B. VAVA ~ SEQUENCES 9. MUSK 10. PAIL GROUP VOLCANIC 11. INDIAN Mtn. LAKE ROCKS 12. TURNBACK LAKE 13. VICTORV LAKE 14. ROSS LAKE 100 I\m SEOIMENTARY 15. HOMER LAKE ROCKS ." ..~..•.

Figure 4 - Generalized geological map of Slave Provínce showing the locaüons o] isotopícallv anaívzcd base metal deposits tcourtesy of S.M. Rosooe; Geological Survey of Canada) paleoisochron is defined by galena veins cutting siderite from the country rocks ar introduced from elsewhere dur­ iron formation at Michipicoten, and galenas from gold ing the subsequent event. While the model ages obtained deposits provide intermediate data points. for these leads may in some cases provide meaningful dates Most of the analyses for Superior massive sulphide de­ for ore remobilization ar metamorphism, they are likely posits plot on or near the Superior paleoisochron. Analyses to be highly in errar in cases where the host rocks were for certain deposits, however, plot slightly to the right of highly depleted in uranium at the time of initial ore deposi­ the paleoisochron. These deposits include the Selbaie and tion. Lemoíne, Quebec for which the isotopic results yield model Some galenas associated with massive sulphide deposits ages of 2,674 to 2,704 Ma, including, significantly, three of have highly anomalous compositions. The e1assic case five values for Selbaie galenas at 2,689, 2,689 and 2,690 Ma. involves galenas from the Quemont deposit, Quebec (Cum­ The analyses most probably indicate addition, at some time ming and Gudjurgis, 1973; Franklin et ai., in press), for subsequent to ore deposition, of a radiogenic lead campo­ which very recent forrnation ar continuous addition of nent to lead that formed an integral part ofthe ore. ln sorne­ radiogenic lead due to an intimate association with uranium cases, however, the lead may have been totally scavenged seems to be indicated. Hayles (1973) obtained a similar Revista Brasileira de Geocténctas, Volume 12 (lw3), 1982 515

16.6

16.0 o

15.5

• REMOBILlZED GALENA, MASSIVE SULPHIDE DEPOSITS 15.0 • GALENAS, GOLO DEPOSITS ... OTHER SULPHIDES, GOLO DEPOSITS o WESTERN ORANODIORITE IROCK '" SOUTHEA8TERN ORANODIORITE LEAD 14.5 o OH08T LAKE GNEISSES, ORANITES DAT'"

, , !, , .13.2 14 15 16 17 18 19 20 21 22 22.6 206Pb/204Pb Figure 5 - Slave Province /ead isotope data for remobílízed íead in base meta/ deposits, for gatenas and other sulphldes from gold deposíts and, fá!' rejerence, rock anelfetdspar lead datafrom Robertson and Folínsbee (1974), ond Cumming mui Tsong (1975) for some gneisses and granites

Table 2 - Lead ísotope data for archean goíd deposíts ln Slave Province

N." (Fig. 5) Properly 206Pbj204Pb 207Pbj204Pb 208Pbj204Pb Lob. & Dole

I Hope Bay 13.791 14.706 33.601 Geospec Cons. 1982 I Hope Bay (CAR cls.) 13.905 14.70 33.65 Teledyne, '1974 2 Cannuck, Tree R. 13.937 14.810 33.757 Geospec Cons. 1982 2 Cannuck, Tree R. 13.917 14.817 33.732 Geospec Cons. 1982 2 Tree River 13.86 14.75 33.68 Teledyne 1974 3 W.T. 13.908 14.887 33.689 U. or Toronto 1979 4 Dome 13.870 14.838 33.680 U. ar Alberta 1979 5 Hidden Lake 13.64 14.64 33.22 Teledyne 1974 5 Hidden Lake 13.819 14.811 33.613 G.S.c. 1976 6 Ruth Mine 13.70 14.74 33.45 Teledyne 1974 7 Ptarmigan veín 13.89 14.92 33.89 Teledyne 1974 8 Con Mine 13.95 14.96 33.78 Teledyne 1974 8 Cón Mine 13.76 14.79 33.35 Te1edyne 1974 9 Giant Mine 14.05 15.06 33.99 Te1edyne 1974 10 Clan Lake 13.80 14.82 33.67 Teledyne 1974 10 Clan Lake 13.80 14.86 33.63 Teledyne 1974 II Jchnston Lake 14.19 15.14 34.19 Teledyne 1974 II Johnston Lake 14.032 14.964 33.821 Teledyne 1975 pattern for galenas from lhe Fox Creek fault where it cuts Superior Province Archean data: gold deposlts A number the Geco massive su1phide orebody, Manitouwadge, On­ of Superior Province gold deposits plot on, and help define, tario. Three galena analyses from the Kam Kotia deposit, the Superior paleoisochron (Fig. 2). These include the Timmins area, Ontario (Franklin et aI., in press) appear to Bousquet (Valliant, 1981) and Camilo deposits, Quebec fit a very steep secondary isochron. The Geneva Lake depo­ and the Ross Mine and Goldlund deposits, Ontario. Other sit, Ontario. probab1y a highly metamorphosed and remobi­ gold deposits plot slightly off the paleoisochron (Fig. 3), lized massive sulphide deposit, and the similar Stralak depo­ and some show a wide range of values. Plotting slightly sit yield analysis that define a secondary isochron witha off the paleoisochron are values for galena from the Smith­ slope of approximately 0.336. This slope can be interpreted, -Thorne, Pamour, Sullivan, Kerr Addison and Rainville assuming initial ore formation at 2,710 Ma, to indicate that deposits (Franklin et ai., in press), and also for lhe Opawica, remobilization occurred at 2,040 Ma. A specimen of claus­ Michipicoten, New Rouyn, Ursa Major, Norbeau, Upper thalite from a selenide-bearing copper-rich zone at the Kidd Canada, Ashley, Kerr Addison, McFinley Red Lake and Creek deposit, Ontario is anomalous, although galena from Rengold .(Stover Twp., Ont.} deposits and occurrences elsewhere in the deposit falis on the Superior paleoisochron (unpublished data). Data for ali these deposits result in (Franklin and Thorpe, in press; Bugnon et al., 1979). Inter­ calculated model ages of 2,584 to 2,709 Ma, with a cluster pretation of lhe clausthalite composition is uncertain, but of values at 2,656 to 2,700 Ma. the calculated I' and Th/U values corresponding to the One of the best defined secondary isochrons for Superior model age of 1,353 Ma are so close to those for galenas Province gold deposits is that established for deposits and falling on the Superior paleoisochron thal this model age occurrences in the Matachewan area, Ontario {Sinclair, must be considered close to the true age. 1982). This line (Fig. 3) has a slope of 0.384 ± 0.009 and 516 Revista Brasileira de Oeocünctas, Volume 12 (1-3), 1982

----_..-

'v ~ d? GOLO DEPOSITS ~ 1. HOPE BAV CJ 2. TREE RIVER 3. W.T. 4. DOME Mafkenzie 5. HIDDEN LAKE Riv 6. RUTH MINF. 7. PTARMIGAN VEIN VO l C ANIC 8. CON MINE _ ROCKS 9. GIANT MINE D 10. CLAN LAKE 11. JOHNSTON LAKE 100 km f~ ':,': :j SEDIMENTARY :.. :::. ROCKS .'t...

Figureô - Locatíons oj'gold deposits in Slave Provínce for whích lead ísotope data huve been obtaíned appears to indicate the leads were formed or subjected to Ao anomalous value of some interest is one for the Ross addition of a radiogenic component at about 2,400 Ma, Mine (206Pb/204Pb = 16.286, 207Pb/204Pb = 15.209 and assuming the lead was derived from source rocks 2,710 208Pb/204Pb = 36.324) which gives a model age of 1,075 to 2,720 Ma old. Data for gold vein occurrences in the Ma. This cornposition gives calculated J1 and Th/U values Atikokan-Mine Centre-Rainy Lakes region, western On­ essentially identical to those for three samples of common tario, follow the Matachewan pattern reasonably well, lead from the deposit with model ages 2,726 to 2,738 Ma. with five of nine data points falling very near the line and This suggests that I ,075 Ma may be a reasonably reliable two others plotting only a Iittle farther away. age for the anomalous galena, Lead isotope data for altaite specimens from gold-telluride assernblages in the syenite-hosted gold deposits at Kirkland Lake (Fig. 3) define a secondary isochron with a slope of 0.165 ± 0.090 for four of five data points. Unless the line Churchill Province Archean Data Lead isotope data have has been generated by mixing of leads that evolved in envi­ been obtained for three occurrences of massive sulphide ronments very different in U/Pb ratios, this suggests a maxi­ type within the Rankin-Ennadai belt, Keewatin District, mum age of about 2,510 Ma for ore formation, Alternative Northwest Territories (Franklin and Thorpe, in press). interpretations, which appear unlikely, would involve rela­ These data plot on the Superior paleoisochron and between tively recent mineralization, probably early Paleozoic ar it and the Slave paleoisochron, and yield model ages of youngcr, from source rocks younger than 2,510 Ma. 2,642 to 2,728 Ma. Revista Brasileira de Geocíências, Volume 12 (1-3),1982 517

LEAD ISOTOPE DATA fOR PROTEROZOIC to 1,533 Ma, are a little younger than for the Great Bear DEPOSITS Bear Province Protero.ole Data Lead isotope Lakesilver-arsenide veins. The data for these veins however, data have been presented by Jory (1964)and Thorpe (1974) appear to lie on a short secondary isochron with a slope for the silver-arsenide vein deposits in the Great Bear Lake of about 0.454. area. These analyses defined what appear to be two popula­ Galena-bearing quartz veins cutting coarse granite at tions of cornmon lead (Fig. 7). By the Superior Province Galena Point, Bathurst Inlet contain moderately radiogenic model the model ages for these are about 1,550 to 1,593Ma lead with 206Pb/204Pb ratios between 18.55 and 19.80. The and 1,700 to 1,725Ma. These model ages are greater than a six available anatyses define a line with a slope of approx­ pitchblende U-Pb age of 1,424 ± 8 Ma (Miller, in press) imately 0.096. The meaning of a line with such a shallow for the Echo Bay veins, although Miller also obtained an slope is not clear, although origin of the leads and/or their age of 1,500 ± 10 Ma for pitchblende veins elsewhere in the source rocks by a mixíng process may be a possibility. area. ln addition to the two common lead clusters, many Galena from a small veinlet associated with nickel arsenide ofthe analyses are anomalous. There is some scatter in these mineralization along the contact of a gabbro dike at Itchen anomalous leads but the best interpretation may be that Lake is anomalous (Table 3). Assuming this lead evolved they were derived from the general Bear Province country from some position on the Slave paleoisochron, it is possible rocks, with some ditTerences in source rock ages and initial that, if it evolved from the upper end of this line, it may lead isotope compositions, The galenas may have been have done so by continuous addition of radiogenic lead. deposited during or shortly after the main stage of silver- If it evolved from the lower end, however, mineralization . -arsenide vein formation, and have subsequently been sub­ may have occurred as much as 1,460 Ma age. jected to continuous addition of radiogenic lead. Very few other analyses of galena specimens from the Bear Province are available. A very imprecise analysis for Churehill Province Protero.oie Data EAST ARM AREA, the lead-rich gold-bearing veins at Norris Lake, near the GREAT SLA VE LAKE. Base metal mineralization of Slave Province-Bear Province boundary, yields a model age skarn and probable syngenetic types at Thubun Lake, south of roughly 1,440 to 1,770 Ma. Galena from a quartz vein at of the East Arrn, is isotopically homogeneous (Table 3) the former Rayrock uranium mine yields a model age of and yields a model age of 2,000 Ma. Galena from a vein about 550 Ma (Table 3). This young age is in good agree­ at Thekulthili Lake has a model age of about 2,100 Ma. rnent with a pitchblende U-Pb age of 517 ±80 Ma for An analysis for lead from a vein at Salkeld Lake (model the deposit (Miller, in press). age 1,603 Ma) is similar to those for the main cluster of values for the Great Bear Lake silver-arsenide veins. Galena associated with minor native silver on the ED ciaims, near Slave Provinee Protero.oie Data Silver-bearing carbonate the LaLoche River, has a composition comparable to that veins, with minor associated arsenides, in the Hope Bay from the Hope Bay silver veins. area on the Arctic coast and lead-rich quartz veins cutting The isotopic composition of galena from a vein at gneissic granitic rocks on an island in Bathurst Inlet (Wolf MacInnis Lake (W.A. Padgham, personal communication) claims) have lead isotope compositions (Table 3) suggesting may be the result ofcontinuous addition of uranogenic lead. they represent a Proterozoic mineralization evento The If this is so and if the lead was initially similar to that at position of these veins near the margins of the Slave Prov­ Thubun Lake, an age of 2,165 Ma, very close to the model ince may be significant. Model ages for these veins, 1,475 age of the Thubun lead, is indicated.

16.0

16.6

15.6 ERRIN(lTOH

15.4 FREDERICI';SON l.

15.0

14.8 o CO~ALT AREA SILVER VEINS o THUBUN LAKE 00 14.6 .,..' ... GREAT BEAR LAKE 'SllVER VEINS • HOPE 8AY AREA SILVER VEINS • PROTEROZOIC DEPOSITS, YUKON 14.4 @ SULLIVAN MINE, 8.C.

13.0 14.0 15.0 16.0 17.0 18.0

Figure 7 - Lead ísatope data for selected Proterozotc deposíts discussed in the text 518 Revista Brasileira de Geociêncías, Volume 12 (1-3), 1982

Table 3 - Lead ísotope data for some proterozotc deposits díscussed tn lhe" text

Locality Latitude Longitude 206Pbj204Pb 207Pbj204Pb 208Pbj204Pb Lab, & Date

Rayrock 63"27'10" 116"32'20" 17.835 15.645 35.977 G.S.c.' 1972 Hope Bay Ag Veio 68"14'09" 106"31 '30" 15.955 15.345 35.882 V.T.' 1981 Hope Bay Ag Vein 68"14'09" 106"31 '30" 16.038 15.408 35.991 V.T. 1981 Wolf Claims 67"05'41 " 107"22'10" 16.197 15.454 35.768 V.T. 1981 Galena Point 67"53'42" 109"53'00" 19.773 15.984 38.851 G.S.c. 1980 Galena Point 67"53'42" 109"53'00" 18.760 15.894 37.644 G.S.c. 1980 Galena Point 67"53'42" 109"53'00" 18.556 15.874 37.664 G.S.c. 1980 Galena Point 67"53'42" 109"53'00" 19.461 15.966 37.903 G.S.c. 1980 Galena Point 67"53'42" 109"53'00" 19.406 15.949 37.829 T.I.' 1978 Galena Point 67"53'42" 109"53'00" 18.637 15.863 37.600 T.I. 1978 Itchen Lake 65"33'06" 112"50'54" 19.156 16.071 38.245 V.T 1981 Boylen 57"39'42" 69"27'00" 15.222 15.245 35.143 T.I. 1978 Boylen 57"39'42" 69"27'00" 15.251 15.265 35.151 TI. 1978 Boylen 57"39'42" 69"27'00" 15.151 15.186 34.975 T.I. 1978 Frederickson L. 55"03'12" 66"15'54" 15.298 15.222 35.222 V.S.G.s.' 1980 Frederickson L. 55"03'12" 66"15'54" 15.004 15.197 35.256 V.S.G.S. 1980 Thubun Lake 61"32'50" 111"48'40" 15.094 15.202 34.635 G.S.c. 1980 Thubun Lake 61"32'50" 111"48'40" 15.099 15.205 34.671 G.S.c. 1980 Thubun Lake 61"32'50" 111"48'40" 15.101 15.212 34.660 G.S.c. 1980 Thubun Lake 61"32'50" 111"48'40" 15.115 15.196 34.641 G.S.C. 1980 Thekulthiü L. 60"58' llO"15'lu" 14.711 15.034 34.971 G.S.c. 1979 Salkeld Lake 61"26'30" 109"47' 15.915 15.391 35.542 Geospec Cons. 1981 Maclnnis L. 61°18' 110"13' 18.318 15.639 35.375 V.B.C.' 1978 Fax River SiIl 55'48'10" 94"04'50" 15.705 15.385 35.24) Geospec Cons. 1981 Fox River SilI 55"48'10" 94"04'50" 15.710 15.382 35:238 Geospec Cons. 1981 Fox River Sill 55"48'10" 94"04'50" 15.705 15.407 35.406 G.S.c. 1979 Fox River Sill 55"48'10" 94"04'50" 15.797 15.413 35.369 V.T. 1979 Errington 46'32'15" 81"15'24" 15.363 15.316 35.534 G.S.c. 1979 Errington 46"32'15" 81"15'24" 15.342 15.280 35.427 V.S.G.S. 1979 Errington 46'32'15" 81'15'24" 15.345 15.278 35.439 V.S.G.S. 1979 New Calumet 45"42'10" 76"40'25" 16.465 15.346 36.051 V.B.C. 1972 New Calumet 45'42'10" 76"40'25" 16.403 15.267 35.832 G.S.c. 1972 Long Lake 44'41'23" 77"46'20" 16.774 15.376 36.264 G.S.c. 1972 Hart River 64"38' 136"51 ' 16.574 15.459 36.219 TI. 1978 Hart River 64"38' 136"51 ' 16.538 15.467 36.197 V.T. 1979 Hart River 64"38' 136"51 ' 16.538 15.478 36.214 G.S.c. 1979 LWR-2(SH) 65"05' 135"40' 16.833 15.478 36.442 V.T. 1979 GiJlespie Creek 64"4ó' 133"56' 16.533 15.402 36.318 V.B.c. 1979 Tart 64"50' . 139"53' 16.557 15.524 36.584 V.B.C. 1979 OG 64"50' 140"00' 16.862 15.488 36.606 V.B.C. 1979

"The analyticallaboratories are Geological Survey of Canada (O.S.c.), University of Toronto (V.T.), TeJedyne Isotopes (T.l.), United States Geological Survey (V.S.O.S.), Geospec Consultants. and University of British Columbia (V.a.c.)

Other lead isotope data for veins in the area are older and Sasaki (1980) and Gale et ai. (1980). There is some sugges­ less precise (Robertson and Cumming, 1964). ln general tion inthe data that rnodel ages may fali into two clusters, the data follow a trend that may retlect vein formation at but the data are not sufficiently precise to demonstrate roughly 2,000 Ma with Archean rocks serving as the source this is clearly the case. The model lead ages are in good of the lead. agreement with other geochronological data. A secondary isochron based on a single specimen of LABRADOR TROUGH. Very few lead isotope analyses anomalous galena from the Flin Flon mine, led Slawson are available for mineral deposits in the Labrador Trough and Russell(1973) to suggest the orebody had evolved by (Franklin et ai., in press; Franklin and Thorpe, in press). a two-stage processo Analyses for the Sherridon and WilI Analyses for volcanic-associated massive sulphide deposits Group deposits, and for galena from a scheelite-bearing indicate model ages of 1,939 to 1,953 Ma for the .Boylen vein in the Flin Flon area, also lie ou this secondary iso­ deposit and 1.&67-2,066 Ma for the Frederickson Lake chron, which has a slope of about 0.298. Although initial deposito deposition of the orebodies was prior to the Hudsonian orogeny, this suggests a source age of about 2,650 Ma for FLIN FLON-SNOW LAKE AREA. MANITOBA Mo­ these galenas if they formed during the Hudsonian orogeny dellead ages ofabout 1,750-1,950 Ma for volcanic-associat­ at approximately 1,780 Ma. This source age agrees closely ed massive sulphide deposits in this area, termed the cir­ with the known ages of Archean supracrustal rocks in the cum-Kisseynew belt, have been reported by Sinha (1970) Slave Province, and the fact that the secondary isochron and Sangster (1972, 1978). A few additional analyses have does project into the cluster of data at the lower end of the been presented by Slawson and Russell (1973), Sato and Slave paleoisochron indicates this interpretation may have Revista Brasileira de Geociências, Volume 12 (1·3), 1982 519

some validity. It is not clear, however, whether Archean Province model. This may be considered in reasonable rocks equivalent to those in the Slave Province contributed agreement with the Rb-Sr isochron age of about 2,120 Ma direct1y to formation of the circum-Kisseynew volcanic for the Nipissing Diabase sill, with which the silver-arsenide rocks associated with the deposits and oceurrences defining veins, at least, are commonly considered to be genetically this secondary isochron. related (Jambor, 1971). The difTerence in these ages may indicate either that the lrue emplacement age of the sill is FOX RIVER BELT, MANITOBA. The Fox River belt greater than indicated by the Rb-Sr method, or that some contains a sequence, approximately 7 km thick, of predom­ adjustments to the Superior Province model used here may inant1y pelitic metasedimentary rocks, and an overlying be required. sequence, 5 km thick, of pillowed basaltic and komatiitic lavas (Scoates, 1981). This volcanic sequence is separated GrenvUie Province Proterozoic Date The New Calumet into two units by a central metasedimentary unit, The Fox and Tetreault massive sulphide deposits, Quebec have mod­ River Sill, a zoned ultramafic to mafic body 2 km thick, el ages of 1,124 to 1,134 Ma and 1,219 to 1,237 Ma, re­ has intruded the latter unit. Lead isotope analyses for minor spectively (Fletcher and Farquhar, 1982 and Table 3). The galena veinlets cutting the sill give model ages of about Long Lake carbonate-hosted zinc deposit, Ontario gives a 1,715 and 1,747Ma. These probably indicate a minimum model age of about 930 Ma and other similar zinc occur­ age for the sill. rences in Ontario and Quebec give comparable ages (895 to 1,244 Ma; Fletcher and Farquhar, 1982). Galenas from lhe URANIUM'CITY AREA,SASKATCHEWAN. Thelead major Balmat-Edwards carbonate-hosted zinc deposits in isotope compositions of specimens M galena and claus­ New York state, U.S.A. have, for comparison, model ages thalite from uranium deposits in the Uranium City area of 1,005 to 1,115 Ma (Fletcher, 1979l. . were studied by Koeppel (1968). The data indicated that the main periods of pitchblende deposition (redeposition) Cordilieran Province Proterozolc Date The only deposits were at 1,750 and 1,090 Ma. The least radiogenic galenas in the Canadian Cordillera yielding Prolerozoic lead isotope yield model ages ofabout 2,340 Ma, with normal calculated compositions are the Sullivan Mine, other less imporlant Th/U ratios of 4.0 to 4.2, suggesting they have not been deposits and occurrences in the surrounding region ofsouth­ subjected to addition of uranogenic lead. em British Columbia, and the Hart River massive sulphide deposit and small carbonate-hosted Pb-Zn occurrences in central Yukon. Data for the Sullivan Mine (LeCouteur, Superior Province Proterozoic Date Lead isotope data 1973) gives model ages of 1,260 to 1,299 Ma, in reasonable for galenas from Cu-Au deposits in lhe Chibougamau dis­ accord with a previously assumed 1,300 lo 1,400 Ma age trict, Quebec indicate that they apparent1y formed at about for lhe hosting well-bedded lurbiditic sedimentary rocks of 2,200 Ma (Thorpe et al., 1981). The Chibougamau Cu-Au deposits occur along major altered and sheared zones as the Aldridge Formation. The Hart River volcanic-associated much as 2,000 m long and 500 m wide, or along subsidiary deposit has model ages of 1,206 to 1,257 Ma, whereas the veio and breccia Pb-Zn occurrences in the sarne region fractures to these zones, in anorthosite of lhe Dore Lake (Godwin et al., 1982 and LWR, Gillespie, Tart and OG in complexo Galena forms a minor component ofthe orebodies Table 3) give model ages of 1,024 lo 1,378 Ma. and the ages indicated are thus perhaps to be interpreted as times ofore remobilization. Using lhe Superior model, ages of 2,011 lo 2,091 Ma are obtained for lhe main cluster of METALLOGENETIC SUMMARV A lead isotope analyses, an three analyses for galenas from lhe Copper model based on data for many Superior Province deposits, Rand deposit give model ages of 1,890 to 1,930 Ma. and a few U-Pb zircon dates of 2,700 to 2,750' Ma for host volcanic sequences, helps confirm widespread volcanism Southem Province Proterozoic Date SUDBUR Y BA SIN, and formation of massive sulphide deposits during this ONTARIO. Lead isotope data for a few galenas in vein­ period. ln addition, model ages for small massive sulphide lets associated with the nickel orebodies, and for other sul­ deposits and a few veios jn northwestem Superior Province phides from lhe Errington and Vermilion massive sulphide are generally 2,800 to 2,847 Ma. Volcaníe' sequences older deposits within lhe Sudbury basin were given by Ulrych and than the prevalent 2,700to 2,750 Ma span forvo1canism have Russell (1964). Data subsequently obtained for galena from been established in this region, but no ages yet obtained. fali the Errington deposit yield model ages of I,896to 1,928Ma. in the 2,800 to 2,847 range. Deposition that was synvolcanic Galena from the Frood nickel mine has a comparable model or essentially so is indicated for a few gold deposits. Remo­ age, but other galenas associated with the nickel orebodies bilization ofthe Selbaie massive sulphide orebody at approx­ appear to have been formed at roughly 1,710 Ma, perhaps irnately 2,689 Ma appears to be indicated. Many gold' de­ during a subsequent metamorphic or deformation event. posits contain galenas yielding model ages of 2,656 to The zircon U-Pb age for the Sudbury Irruptive is 1,849.5 ± 2,700 Ma. This is the general span of time for major defor­ b ± 3 Ma (Krogh et al., 1982 ). mation .and syntectonic to post-tectonic plutonic em­ placement in the Abitibi and Wabigoon belts, where most COBALT AREA, ONTARIO. Data for galenas from the lead isotope data are available, For example, many Abitibi silver-arsenide veios associated with the NipissingDiabase belt granitic plutons are 2,675 to 2,697 Ma in age, although sill, from mineralized interflow horizons in the Archean a few in and near the Kapuskasing zone are younger, about volcanic sequence and from layers containing disseminated 2,615 to 2,627 Ma (Krogh et 01., 1982'). Metamorphism, galena in the Aphebian (Huronian) sedirnentary rocks have structural deformation, especially the formation of major been published (Kanasewich and Farquhar, 1965; Thorpe, transcurrent faults, and the emplacement of granitoid plu­ 1974; Franklin et al., in press). The main cluster ofgalenas tons may ali be processes important in the formation ofgold yields model ages at about 2,180 Ma using the Superior deposits. Data for gold deposits in the Matachewan (Sin- 520 Revista Brasileira de Oeocuncías, Volume 12 (1.3), 1982 elair, 1982) and Rainy Lakes regions apparently indicate and assocíated lead mineralization in the Cobalt area, ore formation or remobilization at approxirnately 2,400 Ma. Ontario (Cobalt Plate of the Southern Province) yield a If a model involving subsequent continuous addition of main eluster of analyses with model ages of approximately radiogenic lead is correct, data for Kirkland Lake tellurides 2,180 Ma. Similar veins in the Great Bear Lake area, NWT' may indicate an age of about 2,510 Ma for the important (Bear Province) define two elusters of common leads with syenite-hosted gold-telluride ores. model ages of 1,550 to 1,593 Ma and 1,700 to 1,725 Ma. Lead isotope data for Slave Province deposits have esta­ Compositionally simpler silver veins at Hope Bay (Slave blished patterns similar to those for Superior Province. Province) and on the EO elaims, south of the East Arm of Massive sulphide deposits define a line approximately paral­ Great Slave Lake (Churchill Province) have model ages of lei to the Superior paleoisochron, indicating lower model about 1,475 to 1,533 Ma. Galenas assocíated with the pitch­ ages as would be expected from zircon U-Pb dates of about blende veins in the Uranium City area, Saskatchewan, 2,670 Ma for Slave volcanism (Lambert and Henderson, also in Churchill Province, give model ages of about 1980; Frith and Loveridge, 1982). However, model ages 2,340 Ma, in contrast to U-Pb pitchblende ages of I ,750 ± 20 using the Superior Province model would appear to be and 1,090±50Ma (Koeppel, 1968). The lead isotope data approximately 20 Ma too old. Model ages (Superior model) for galenas associated with the most important of the for galenas from gold deposits in southern Slave Province Grenville carbonate-hosted zinc deposits, Long Lake in are 2,597 to 2,705 Ma, in reasonable agreement with the Ontario and deposits at Balmat-Edwards, New York yield 2,570 to 2,670 Ma ages of many plutonic bodies. Gold model ages of 926 to 1,059 Ma. These are significantly deposits near the northern extremities of the Slave Province lower than the model ages of massive sulphide deposits in appear to be younger, 2,516 to 2,542 Ma. Data for galena Grenville Province and may indicate the galenas formed veins associated with massive sulphide deposits and for when the carbonate-hosted deposits were highly deformed some pyrites associated with gold deposits suggest lead during the Grenville orogeny. ln the Cordilleran Province remobilization has occurred -in association with the Hudso­ data for both carbonate-hosted Pb-Zn occurrences and the nian orogeny. Hart River deposit in the central Yukon, north ofthe major Proterozoic lead isotope data indicate model ages for Tintina fault, help define a Proterozoic metallogenic epoch massive sulphide deposits as follows: in the northern Canadian Cordillera.

Model age Provlnce Reglon Deposlt Acknowledgements The encouragement of J.M. (m.y.) Franklin, O.F. Sangster and other colleagues is gratefully Churchill East Arm, Great Stave L" NWT 2.000 Thubun acknowledged. Many colleagues contributed significant1y to Churchill Labrador Trough, Que. 1,939-1,953 Boylen this paper by providing specimens and lead isotope data. Churchill Labrador Trough, Nfld. 1,867-2,066 Frederickson L. Southem Sudbury Besin, OnL 1,896-1 .928 Errington High quality analyses by the Geochronology Laboratory Churchill Flin Flon-Snow Lake. Man. 1.750-1,950 numerous of the Geological Survey of Canada and by Geospec Cordilleran Sullivan, R.C. 1,260-1,299 Sullivan Consultants, Alberta, have been essential for many of the Cordilleran Hart River. Yukon 1,206-1,257 Hart River conclusions presented here, R.O. Lancaster, O.F. Garson Grenville Ottawa Valley, Om-Que, [,124-1,134 New Calumet Orenville Trois Riviere. Que. 1,219-1,231 Tetreault and J. Shaw assisted in the establishment of a computer file of lead isotope data. R.O. Lancaster also assisted in data compilation, in computer manipulation of data and It should be noted that Thubun and Hart River are not in many other detailed aspects of this study. The figures typical massive sulphide deposits, aIthough both are consi­ were drafted by K.K. Nguyen. The paper was critically dered to be syngenetic in parto Silver-arsenide vein deposits read by O. F. Sangster.

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