The following document is a pre-print version of:
Ross P-S, McNicoll VJ, Debreil JA, Carr P (2014) Precise U-Pb geochronology of the Matagami mining camp, Abitibi Greenstone Belt, Quebec: stratigraphic constraints and implications for volcanogenic massive sulfide exploration. Econ. Geol. 109:89-101
Precise U-Pb geochronology of the Matagami mining camp, Abitibi Greenstone Belt, Quebec: stratigraphic constraints and implications for VMS exploration
Ross, P.-S.*1, McNicoll, V.J. 2, Debreil, J.-A. 1, Carr, P.3
1. INRS-ETE, 490 rue de la Couronne, Québec (QC), G1K 9A9, Canada 2. Geological Survey of Canada, 601 Booth Street, Ottawa (ON), K1A 0E8, Canada 3. Xstrata Zinc Canada, Bureau d'exploration Matagami, C.P. 819, Matagami (QC), J0Y 2A0, Canada * Corresponding author ([email protected] )
Abstract from 1963 to 1988, of 25.64 Mt of ore at average grades The Matagami mining camp in the northern of 8.2% Zn, 0.56% Cu, 20.9 g/t Ag and 0.4 g/t Au Abitibi greenstone belt of Canada contains 19 known (Adair, 2009). The Persévérance mine opened in July Archean volcanogenic massive sulfide (VMS) deposits, 2008 with resources of 5.12 Mt of ore at average grades eleven of which have collectively produced 46.5 Mt of of 15.8% Zn, 1.2% Cu, 29 g/t Ag and 0.4 g/t Au (Xstrata zinc-rich ore to date. The VMS deposits occur in three plc, 2008). Renewed interest in the area and associated NW-SE to WNW-ESE oriented trends called the North intense exploration resulted in the recent discovery and Flank, the South Flank, and the West Camp which are delineation of the Bracemac and McLeod deposits, which composed of a felsic to mafic volcanic sequence cut by are currently being prepared for mining by Xstrata Zinc mafic to intermediate, synvolcanic sills and dikes. In and Donner Metals..Production is expected to start in order to clarify stratigraphic relationships between the 2013 at Bracemac-McLeod (Xstrata plc, 2010). South Flank and the West Camp, and to constrain the The VMS deposits in the Matagami mining camp temporal evolution of volcanic activity, six new high- occur in three NW-SE to WNW-ESE oriented trends precision U-Pb zircon ages have been obtained. These called the North Flank, the South Flank, and the West data show that the total duration of felsic volcanism in Camp (Fig. 2). Each trend is generally composed of a the South Flank was no more than 2.5 m.y., with the felsic to mafic volcanic sequence intruded by mafic to rhyolites extruded in the following order: Watson intermediate, synvolcanic sills and dikes. The geology of Rhyolite (2725.9 ± 0.8 Ma), Bracemac Rhyolite the Matagami mining camp is most clearly understood in (2725.8 ± 0.7 Ma), Dumagami Rhyolite at the the South Flank, where the majority of VMS deposits Persévérance Mine (2725.4 ± 0.7 Ma), Dumagami have been found to date, principally but not exclusively Rhyolite in the Orchan West VMS deposit area along a stratigraphic marker horizon known as the Key (2724.9 ± 0.7 Ma). A hiatus in effusive volcanism is Tuffite. The Key Tuffite is located just above a very represented by the Key Tuffite, an important marker thick and laterally extensive submarine rhyolite. Despite horizon in the camp. The hiatus probably lasted on the the presence of the Key Tuffite, or its interpreted order of 0.5 m.y. Significantly, the rhyolite from the equivalent, throughout the Matagami mining camp, footwall of the Caber VMS deposit in the West Camp has extending the South Flank stratigraphy to other areas, an age of 2725.9 ± 1.2 Ma, identical to that of the Watson notably to the “West Camp” (Fig. 2), has proven to be Rhyolite on the South Flank. problematic, because such areas are less well known, and in some cases more intensely deformed. Therefore, Introduction relationships and correlations between the different parts Since October 1963, the Matagami mining camp of the Matagami mining camp require clarification. in the Archean Abitibi greenstone belt in Canada has One strategy to better understand the temporal produced 46.5 Mt of ore at average grades of 9.1% Zn, evolution of volcanism and to correlate volcanic units 0.9% Cu, 28 g/t Ag and 0.5g/t Au (figures current as of between the different areas is to examine the combined 31 December 2010), making it an important contributor geochemistry and high-precision geochronology of felsic to the total production of base metals from the Abitibi volcanic rocks. Prior to our study, the U-Pb ages of (Fig. 1). The largest deposit mined in the camp was the volcanism and intrusions in the Matagami area were Mattagami Lake deposit (Fig. 2), with a total production, determined by Mortensen (1993) as part of an Abitibi- wide geochronology study, but the age of several key groups contain several felsic volcanic units (Table 1) felsic units remained unknown, with the actual time- which can be differentiated from each other based on stratigraphic context of the Matagami mining camp itself their stratigraphic position and geochemical signature being poorly constrained. (e.g., Table 2). Details and discussion of the geochemical In this paper, we present six new high-precision variations in the felsic rocks from the Matagami mining U-Pb dates from various felsic volcanic units from the camp will be published elsewhere. South Flank and West Camp at Matagami. At a regional scale, this allows us to demonstrate a stratigraphic Watson Group correlation between the productive South Flank and the In the South Flank, the Watson Dacite, which prospective West Camp. Within the South Flank, we consists of lobate and massive lavas in outcrop, occurs at show that the sampled felsic volcanism was of short the base of the Watson Group. The dacite forms at least duration. The volcanic hiatus during which the Key half of the volume of the group. This is overlain by the Tuffite was emplaced, and most of the VMS deposits Watson Rhyolite, which mainly consists of coherent formed, was even shorter. lavas. The rhyolite is typically quartz-phyric and spherulitic, with variable proportions of amygdules. In Geologic setting outcrop, this rhyolite displays lobes with very thin The Matagami mining camp is located in the hyaloclastite margins. The rhyolite, which is up to 500 m northern part of the Abitibi greenstone belt (Fig. 1), thick, is found everywhere on the South Flank (over a which is part of the Archean Superior Province in lateral distance of at least 19 km), indicating that the Quebec, Canada. Some 19 Zn-rich volcanogenic massive volcanic event that produced the Watson Rhyolite had a sulfide (VMS) deposits are currently known in the camp large volume. Submarine rhyolites of this volume are (Fig. 2), of which ten have been mined out, one is uncommon, but examples of Miocene subaerial rhyolite currently in production (Persévérance), and another will flows of this magnitude have been documented for begin production soon (Bracemac-McLeod). The VMS example in the Snake River Plain, USA (Branney et al., deposits are hosted by mafic to felsic, subalkaline 2008). Voluminous rhyolite flows are generally less volcanic rocks emplaced in a submarine environment. viscous than other rhyolites, and may be emplaced at Many VMS deposits consist of concordant sulfide lenses high temperatures (e.g., Barrie, 1995). Another possible underlain by sulfide stringers and a discordant chlorite explanation for the inferred low viscosities of some ±talc-magnetite alteration pipe (Lavallières et al., 1994). rhyolites in the Abitibi greenstone belt is the suggested The felsic volcanic rocks and the spatially associated presence of dissolved depolymerizing agents in the melt VMS deposits occur in three trends, orientated NW-SE to (e.g., Moulton et al., 2008, 2011), although the presence WNW-ESE, that subcrop below significant glacial till. of abundant amygdules in the Watson Rhyolite argues The first two trends are called the North Flank and the against the latter idea. South Flank (Piché et al., 1993), and they are located on The Watson Rhyolite is stratigraphically overlain the sides of the Bell River Complex, a layered mafic by a 0.3 m to 12 m thick volcaniclastic-exhalative intrusion which is considered to be synvolcanic (e.g., horizon known as the Key Tuffite (Jenney, 1961; Mortensen, 1993; Maier et al., 1996). The third trend is Davidson, 1977; Liaghat and MacLean, 1992) which is known as the “West Camp” and contains the Phelps present throughout the South Flank. The vast majority of Dodge, Caber and Caber North deposits, plus other the VMS lenses of the South Flank are located at the occurrences (e.g. Masson, 2000; Fig. 2). Volcanic rocks stratigraphic level of the Key Tuffite, which therefore generally dip at medium to high angles toward the SW in serves as an important exploration guide (Lavallière et the South Flank (Fig. 3), and are subvertical in the other al., 1994). The discordant portion of these mineralized two trends. The stratigraphic facing direction is to the bodies is located within the uppermost part of the Watson northeast in the West Camp, to the north in the North Rhyolite. Flank and toward the southwest in the South Flank. An exception is the Persévérance Mine area where the strata Wabassee Group are nearly subhorizontal (Fig. 3). Stratigraphic The Wabassee Group on the South Flank consists relationships between these three areas require mostly of basalts and andesites, with volumetrically clarification and this is among the objectives of the minor felsic rocks and a number of volcaniclastic- current geochronological study. exhalative intervals that are less laterally continuous than the Key Tuffite. Some of these horizons are nevertheless South Flank geology associated with VMS lenses, for example in the The largest portion of the ore tonnage extracted to Bracemac-McLeod area, which has been intensely date has been from the South Flank, principally from the explored recently (Adair, 2009). In this area, the base of Mattagami Lake mine. Historically, Sharpe (1968) the Wabassee Group consists of the Bracemac Rhyolite, assigned the volcanic rocks of the South Flank (and the a relatively thin (up to 70 m thick), quartz-phyric, and larger Matagami area) to two stratigraphic units: the mostly coherent (massive) rhyolite sitting directly felsic-dominated Watson Group at the base and the upsection from the Key Tuffite (Fig. 3A, B). Both the mafic-dominated Wabassee Group at the top. These Watson Rhyolite and the Bracemac Rhyolite were 2 sampled for U-Pb geochronology in cross-section rhyolites for U-Pb geochronology: one at the Caber VMS 13300E through the McLeod VMS deposit, to constrain deposit and one to the SE of the McIvor Pluton (Fig. 5). the time interval between the two rhyolites (Fig. 3A, B; The Caber deposit consists of a relatively small, Table 1). During this volcanic hiatus, the Key Tuffite and but Zn-rich massive sulfide lens (0.48 Mt at 11.7% Zn, some massive sulfides were deposited on the sea floor. 0.97% Cu, 14.4 g/t Ag and 0.23 g/t Au; Masson, 2000) Mineralization in this area is also present along two other that occurs at the top of a Watson-like rhyolite (Fig. 5A, stratigraphic horizons above the Key Tuffite, all linked B, Table 2: see the first three geochemical ratios). by a semi-continuous alteration zone. This provides Laterally, the Caber mineralization grades into an evidence that the hydrothermal system that produced interval containing chert-pyrite ±sphalerite (a “tuffite”) sulfide mineralization in the three horizons at Bracemac- which has been proposed to be correlative with the Key McLeod was active through volcanic activity over time Tuffite (Masson, 2000). The footwall rhyolite at Caber is in this area. typically quartz-phyric, spherulitic, and commonly To the northwest of Bracemac, the Bracemac amygdule-rich. Chlorite alteration is present, increasing Rhyolite thins and the base of the Wabassee Group in intensity with proximity to mineralization. The VMS consists of mafic to intermediate volcanic rocks. Higher lens is overlain by mafic to intermediate volcanic rocks, up in the sequence however, the Dumagami Rhyolite and semi-concordant mafic to intermediate dikes have occurs, forming a lens-shaped unit that is up to 400 m extensively inflated the volcanic sequence and invaded thick. The Dumagami Rhyolite was sampled for U-Pb the mineralized zone. Towards the NE, the McIvor geochronology in the Orchan West area (Fig. 4, Table 1). Pluton occurs on the other side of an important fault zone At this locality, the rhyolite is quartz-phyric, highly named McIvor Fault Zone. spherulitic, and lobate to massive. The second U-Pb sample from the West Camp Still further to the northwest, in the Persévérance comes from a Watson-like rhyolite located near the Mine area, the Dumagami Rhyolite directly overlies the McIvor Pluton, 7 km southeast of Caber (Figs. 2, 5C, D, Key Tuffite, without intercalated mafic or intermediate Table 2). Based upon map patterns and geochemistry, volcanic rocks (Fig. 3C, D). Three distinct ore lenses are this appears to be the same rhyolite as that at Caber, but mined at Persévérance: Persévérance-main, the new U-Pb dating suggests otherwise (see below). In Persévérance-West and Equinox. These ore lenses are this area, the stratigraphy is subvertical, and mafic to present within chlorite pipes, with little concordant lens- intermediate intrusions again thicken the volcanic type mineralization (Arnold, 2006). The Dumagami succession. The rhyolite is a weakly spherulitic, quartz- Rhyolite in the Persévérance area (informally called phyric, mostly coherent rock. “Dumagami-P” Rhyolite herein) is quartz-phyric and often strongly spherulitic. Relative to other known U-Pb geochronology thicknesses of the Dumagami Rhyolite in the South Previous U-Pb dating Flank, it is unusually thick and may be filling a local In his regional eastern Abitibi geochronological graben (Arnold, 2006). Geochemical data (e.g., Table 2: study, Mortensen (1993) obtained an age of Ti/Zr ratio) indicates that the Dumagami-P is different 2724.5 ± 1.8 Ma for the Watson Rhyolite from an from the Dumagami Rhyolite elsewhere in the Matagami outcrop location on the South Flank (Fig. 2). A rhyolite mining camp, including on the North Flank. This from the North Flank was dated at 2723.1 +0.8/-0.7 Ma geochemical difference, combined with the position of by the same author; however, it is unclear exactly which the Dumagami-P directly overlying the Key Tuffite rhyolite was dated on the North Flank, as no geochemical (without intervening mafic to intermediate volcanic analysis is available for the dated sample (Fig. 2). On the rocks), suggests that the Dumagami-P may be a distinct basis of the 2 σ age envelope, Mortensen (1993) therefore stratigraphic unit, possibly older than the Dumagami concluded that volcanism in the Magatami area occurred Rhyolite present elsewhere. The Dumagami-P Rhyolite between 2726.3 and 2722.4 Ma. In the same study, a was sampled for U-Pb geochronology just above the Key granophyre from the Bell River Complex gave a Tuffite in cross-section 29725E, above the Equinox lens crystallization age of 2724.6 +2.5/-1.9 Ma (Fig. 2), and (Fig. 3C, D; Table 1). the complex was interpreted to be a synvolcanic intrusion. West Camp geology The stratigraphy of the West Camp is not well Samples selected for this study established due to the following factors: fewer drill holes, Drill core samples for the current U-Pb less outcrop, a greater degree of deformation, and a larger geochronology study were collected from geological proportion of intrusive rocks in many areas relative to the cross-sections typically containing the Key Tuffite and/or South Flank. Watson-like rhyolites and dacites can be VMS deposits, so that the relationship between the dated identified in the West Camp on a geochemical basis; rocks and mineralization is unambiguous. In each other rhyolites with different geochemical signatures also selected cross-section, several drill holes were examined occur. To compare the West Camp with the South Flank in order to select the least altered rocks based on visual volcanic stratigraphy, we have sampled two Watson-like examination of the cores. High Ishikawa alteration index
3 values and low sodium contents suggest that some of the zircons contain abundant fractures and inclusions (Table selected rocks have nevertheless suffered significant 3). Six single grains were analyzed from the rhyolite. VMS-related hydrothermal alteration (Table 2). The Three of the grains were physically (air) abraded, rhyolites sampled in drill cores are massive rocks which yielding results that are 1.6 to 0.5 percent discordant, preserve, at least in part, pre-alteration volcanic textures while three were annealed and chemically leached for six such as spherules and phenocrysts and were verified to hours, and gave results that are concordant to only 0.5 have the typical geochemical signatures of each targeted percent discordant. A linear regression with lower felsic unit using ratios of immobile elements (Table 2). intercept at the origin and containing all of the analyses When present, dikes were excluded from the sampled has an upper intercept at 2725.8 ± 0.7 Ma core intervals, and the samples did not contain inclusions (MSWD = 0.91; probability of fit = 46%; Fig. 6B). The of other rock types. date of 2725.8 ± 0.7 Ma is taken to be the crystallization age of the Bracemac Rhyolite. Analytical techniques U-Pb ID-TIMS (isotope dilution thermal Dumagami-P Rhyolite; EQ-00-41 (z9625): The ionization mass spectrometry) was performed at the Dumagami Rhyolite sample from the Perséverance mine Geological Survey of Canada in Ottawa. Analytical (Dumagami-P) contains a small number of fair to good methods utilized in this study are modified after Parrish quality zircons. Six single grains were analyzed, each et al. (1987). Heavy mineral concentrates were prepared showing very low U contents, ranging from 40 – 12 ppm by standard crushing, grinding, Wilfley table, and heavy (Table 3). All of the analyses overlap and range between liquid techniques. Mineral separates were sorted by only 0.7 to 0.2 percent discordant (Fig. 6C). The magnetic susceptibility using a Frantz TM isodynamic chemically abraded analysis A6-1 overlaps the others but separator and were handpicked using a binocular is slightly more concordant. A weighted average of the microscope. All of the analyses are of single zircons, 207 Pb/ 206 Pb ages of all of these near-concordant analyses unless otherwise noted, which have been very strongly is 2725.4 ± 0.7 Ma (MSWD = 0.62; probability of air abraded using the method of Krogh (1982) or fit = 64%), which is taken to be the age of the chemically abraded following the techniques of Dumagami-P Rhyolite. Mattinson (2005). Chemically abraded grains were annealed for 48 hours at 1000 °C, followed by leaching Dumagami Rhyolite; OR-01-32 (z9913): The with HF for varying lengths of time as noted in Table 3. Dumagami Rhyolite from the Orchan West area contains Details of zircon morphology, quality, and abrasion a small number of fair quality zircons. Analyses for five technique are summarized in Table 3. Procedural Pb single grains overlap and are nearly concordant (Fig. blanks for analyses in this study are generally 1 pg or 6D). A weighted average of the 207 Pb/ 206 Pb ages of these less. Treatment of analytical errors follows Roddick analyses is 2724.9 ± 0.7 Ma (MSWD = 0.95; probability (1987). U-Pb ID-TIMS analytical results are presented in of fit = 44%). A sixth analysis, A2, is slightly older at ca. Table 3, where errors on the ages are reported at the 2 σ 2734 Ma and is interpreted to be an inherited grain. The level, and displayed in the concordia plots (Fig. 6). Errors date of 2724.9 ± 0.7 Ma is taken to be the crystallization calculated for ages presented in the text are also reported age of the Dumagami Rhyolite at Orchan West. at the 2 σ level of uncertainty. Results and interpretation: West Camp Results and interpretation: South Flank Watson-like rhyolite; NCB-98-38 (z9912): The Watson Rhyolite; MC-08-37 (Geological Survey sample of quartz-phyric, massive rhyolite collected from of Canada geochronological laboratory number z9627): the Caber area contains high quality, well faceted The Watson Rhyolite from the McLeod area contains zircons. The grains that were analyzed contained low U abundant high quality zircons. Those that were selected (<35 ppm). Three single-grain analyses overlap each for analysis contained low U (all analyses but one are other and concordia, and a fourth analysis is more <26 ppm U). Six single-grain analyses overlap each other discordant (1.3%) (Fig. 6E). A weighted average of the 207 206 and range from 0.8-0.3 percent discordant (Table 3, Fig. Pb/ Pb ages of all four analyses is 2726.2 ± 1.2 Ma 6A). A weighted average of the 207 Pb/ 206 Pb ages of all of (MSWD = 1.1; probability of fit = 33%). A weighted these near concordant analyses is 2725.9 ± 0.8 Ma (mean average including only the three most concordant standard of weighted deviates, MSWD = 0.90; analyses (0.4-0.3% discordant) is 2725.9 ± 1.2 Ma probability of fit = 48%). This age of 2725.9 ± 0.8 Ma is (MSWD = 0.86; probability of fit = 42%). This age of taken to be the crystallization age of the Watson Rhyolite 2725.9 ± 1.2 Ma is taken to be the best interpretation for in the McLeod area and, by extension, on the entire the crystallization age of the rhyolite and is the same as South Flank. that presented above for the Watson Rhyolite on the South Flank (Fig. 7). Bracemac Rhyolite; MC-08-43 (z9624):The sample from the Bracemac Rhyolite contains a fair Watson-like rhyolite; 1214-98-2 (z9626): The number of small, well faceted zircons. Many of the Watson-like rhyolite sample taken south-east of the McIvor Pluton contains abundant euhedral zircons 4 ranging in morphology from stubby prismatic to The Dumagami-P Rhyolite at Persévérance and elongate. Six zircon analyses range from being 0.5 to 0.1 the Dumagami Rhyolite in the Orchan West area are percent discordant. Chemically abraded analyses A12-1 different chemically and are in different stratigraphic and C16-1 overlap the other analyses but are slightly positions, as explained above. The U-Pb ages and more concordant (Fig. 6F, Table 3). A weighted average associated errors for these felsic units overlap, but the of all six analyses is 2723.4 ± 0.7 Ma (MSWD = 0.70; Orchan West rocks may be slightly younger. This probability of fit = 62%), which is taken to represent the supports the idea that the Dumagami-P Rhyolite could be crystallization age of this rhyolite. a distinct stratigraphic unit. While there is an intimate association between Discussion sulfide mineralization and the Key Tuffite, evidence from South Flank the South Flank VMS deposits show that mineralizing On the South Flank, the four ages and their hydrothermal activity occurred both contemporaneously associated errors overlap significantly. However, the with the Key Tuffite and following its deposition. At progression of ages (represented by the squares on Fig. 7) Persévérance for example, the Key Tuffite is mostly yields a temporal evolutionary sequence for the South devoid of mineralization (Arnold, 2006) and tuffite Flank volcanism that corresponds to that observed from fragments are included in the massive sulfides, stratigraphic relationships: the Watson Rhyolite is the suggesting that at least a part of the mineralization here oldest, followed by the Bracemac, the Dumagami-P, and postdated the Key Tuffite, but predated the deposition of the Dumagami rhyolites. the Dumagami-P Rhyolite. In another example, the More interesting is the duration of volcanism. The Bracemac-McLeod VMS deposit exhibits the maximum duration of felsic volcanism in the South Flank development of sulfide mineralization in lenses both at was from 2726.7 Ma (maximum age of the Watson the Key Tuffite level and at two horizons upsection Rhyolite) to 2724.2 Ma (minimum age of the Dumagami within the Wabassee Group. All three horizons can be Rhyolite at Orchan West), i.e. a maximum duration of linked by relatively continuous footwall alteration, 2.5 m.y. Since all known VMS deposits in this area were suggesting that hydrothermal activity persisted over a likely formed between the eruption of the Watson period of time that exceeded the deposition of the Key Rhyolite and the Dumagami Rhyolite, the mineralization Tuffite and the Bracemac Rhyolite in this area. therefore occurred, together with the deposition of associated tuffites, within 2.5 m.y. or less. West Camp The Key Tuffite represents a period of quiescence Correlations between the South Flank and the in the effusive volcanism, during which most of the VMS West Camp have been based on the occurrence of deposits of the South Flank were formed. The period of geochemically similar rhyolites (e.g., Watson Rhyolite in deposition of the Key Tuffite, and the more or less the South Flank and a Watson-like rhyolite in the West contemporaneous VMS deposits, is constrained by the Camp) overlain by tuffite intervals. The high-precision ages of three rhyolites: the Watson (directly below the age determinations presented herein for the Watson tuffite), the Bracemac (directly above) and the Rhyolite, just below the McLeod massive sulfide lens in Dumagami-P (also directly above). Assuming the age of the South Flank, and a Watson-like rhyolite, just below the Watson Rhyolite at McLeod applies throughout the the Caber sulfide lens in the West Camp, yield identical South Flank, at Persévérance, the Key Tuffite deposition ages (Fig. 7). This supports the South Flank-West Camp period lasted a maximum of 2.0 m.y. (this value is correlation and reinforces the exploration potential of the obtained by taking the difference between the maximum West Camp. In addition, this correlation increases the age for the Watson Rhyolite, 2726.7 Ma and the total extent and volume of the Watson Rhyolite in the minimum age for the Dumagami-P Rhyolite, 2724.7 Ma). Matagami area. These results demonstrate the high It is more likely, however, that the period of time for the potential for unraveling stratigraphic relationships within Key Tuffite deposition was on the order of 0.5 m.y. or a study area using high-precision U-Pb ages. less (between 2725.9 Ma for the Watson Rhyolite and At the 2σ level of uncertainty, the 2725.4 Ma for the Dumagami-P Rhyolite). Clearly, the geochronological results suggest that the Watson-like volcanic hiatus between the Watson Group and the rhyolite near the McIvor pluton is younger than the Wabassee Group was brief. For comparison, Barrie et al. Watson-like rhyolite at the Caber VMS deposit by at (1999) calculated based on a numerical model that the least 0.6 m.y. (minimum age of 2724.7 Ma for Caber giant Kidd Creek VMS deposit was formed within about minus maximum age of 2724.1 Ma for McIvor). So, 0.65 m.y. Based on their numerical modeling work on the although the two Watson-like rhyolites dated in the West synvolcanic Bell River Complex at Matagami, Carr et al. Camp share the same geochemistry, they have distinct (2008) found that hydrothermal venting lasted about ages. There are two possible explanations for this result: 135 000 years. Elsewhere in the Abitibi greenstone belt, (1) two temporally distinct Watson-type effusive events Thurston et al. (2008) have identified depositional gaps occurred at Matagami; or (2) the dated sample represents marked by sedimentary interface zones lasting between 2 not an extrusive rhyolite but instead a small tonalitic and 27 m.y., i.e. longer than the estimated depositional intrusion (or endogenous dome) with a rhyolitic texture gap for the Matagami mining camp. 5 and a Watson-like chemistry. More work will be needed geochemically identical rhyolite in the footwall of to identify the correct hypothesis. the Caber VMS deposit in the West Camp (2725.9 ± 1.2 Ma). This correlation confirms a Link between Archean volcanism, magmatism and VMS strong exploration potential for the West Camp. deposits at Matagami Most VMS deposits in the Matagami mining camp Acknowledgements are situated stratigraphically on top or near the top of the Funding for the U-Pb work presented here came Watson Rhyolite, and geographically not far from the from the Geological Survey of Canada, Targeted synvolcanic Bell River Complex. This is clearly not a Geoscience Initiative 3 program, Abitibi project, led by coincidence, since a similar pattern is also visible at B. Dubé, whom we thank for support. Current research at Chibougamau about 250 km to the East, where the VMS Matagami is also funded by the Natural Sciences and deposits also occur at the top of a tholeiitic rhyolite along Engineering Research Council of Canada (NSERC), the flanks of a large mafic synvolcanic intrusion Consortium de recherche en exploration minérale (Daigneault and Allard, 1990). The Watson Rhyolite is a (CONSOREM), the DIVEX network, Breakwater large-volume effusive felsic unit, which we presume was Resources Ltd., Donner Metals Ltd, SOQUEM, and emplaced rapidly. This unit may have erupted in Xstrata Zinc Canada. We thank the four companies for response to the arrival of the Bell River Complex in the permission to publish this paper. We acknowledge useful upper crust: either the Watson magma was derived discussions with M. Allard, G. Bouchard, Y. Bussières, directly from the then-melted Bell River Complex during M. Chouteau, R. Daigneault, M. Dessureault, B. Dubé, its early stages of emplacement (Maier et al., 1996), or D. Gaboury, D. Genna, S. Lacroix, M. Malo, M. Masson, the Watson magma could represent the high-temperature P. Mercier-Langevin, P. Pilote, P. Rhéaume, Y. Trudeau, low-pressure partial melting of hypothetical older basalts and especially G. Roy. C. Beausoleil and G. Roy updated (e.g. Hart et al., 2004). In any case, there was substantial the cumulative production figures for the Matagami heat flow available due to Bell River Complex mining camp. V. McNicoll would like to thank J. emplacement to drive hydrothermal circulation within Peressini, L. Cataldo and C. Lafontaine for their volcanic rocks, and perhaps within the complex itself too assistance in the generation of the U-Pb data. M. (Ioannou et al., 2007; Carr et al., 2008). This Hannington, P. Mercier-Langevin, R. Adair and O. van hydrothermal circulation was responsible for VMS Breemen reviewed a draft of the manuscript and made generation at and below the sea floor. many helpful suggestions. M. Hamilton and T. Barrie reviewed the submitted version and are thanked for their Conclusions input. Special Issue Guest Editor P. Mercier-Langevin This paper presents six new high-precision U-Pb reviewed the revised version and made further useful ages for the Matagami mining camp, allowing a better suggestions. GSC contribution number 20110053. understanding of the temporal evolution of volcanic activity and more confident stratigraphic correlations References between different parts of the camp. Specifically, this Adair, R., 2009, Technical report on the resource calculation for study has shown or confirmed that: the Bracemac-McLeod discoveries, Matagami (1) Geochronological data supports a distinction Project, Québec: Donner Metals Ltd., National between the “typical” Dumagami Rhyolite, found Instrument 43-101 Report, filed on April 3, 2009 at http://www.sedar.com , 194 p. above a package of mafic to intermediate volcanic Arnold, G., 2006, Perseverance deposit geology: Falconbridge rocks, and a slightly older Dumagami-P Rhyolite in Ltd. (now Xstrata Zinc Canada), internal report, 101 the Persévérance mine area, in direct contact with p. the Key Tuffite. Barrie, C.T., 1995, Zircon thermometry of high temperature (2) The duration of felsic volcanism in the South Flank rhyolites near volcanic-associated massive sulfide was no more than 2.5 m.y., with the rhyolites deposits, Abitibi Subprovince, Canada: Geology, v. extruded in the following order: Watson, Bracemac, 23, p. 169-172. Dumagami-P, and Dumagami. Barrie, C.T., Cathles, L.M., and Erensi, A., 1999, Finite (3) The Key Tuffite and the VMS deposits emplaced element heat and fluid-flow computer simulation of a deep ultramafic sill model for the giant Kidd Creek along this marker interval by exhalative processes volcanic-associated massive sulfide deposit, Abitibi were formed within a time period shorter than 2.0 Subprovince, Canada: Economic Geology Monograph m.y. – possibly on the order of 0.5 m.y. or less – i.e. 10, p. 529-540. between the crystallization of the Watson Rhyolite Branney, M.J., Bonnichsen, B., Andrews, G.D.M., Ellis, B., and that of the Dumagami-P Rhyolite. The volcanic Barry, T.L., and McCurry, M., 2008, 'Snake River hiatus and hydrothermal activity therefore lasted a (SR)-type' volcanism at the Yellowstone hotspot relatively short period of geological time. track: distinctive products from unusual, high- (4) The West Camp and the South Flank can now be temperature silicic super-eruptions: Bulletin of more confidently correlated based on the fact that the Volcanology, v. 70, p. 293-314 . Carr, P.M., Cathles, L.M., and Barrie, C.T. 2008, On the size same age was obtained for the Watson Rhyolite on and spacing of volcanogenic massive sulfide deposits the South Flank (2725.9 ± 0.8 Ma) and a 6 within a district with application to the Matagami Mattinson, J.M., 2005, Zircon U–Pb chemical abrasion (“CA- District, Quebec: Economic Geology, v. 103, p. 1395- TIMS”) method: combined annealing and multi-step 1409. partial dissolution analysis for improved precision Daigneault, R., and Allard, G.O., 1990, Le Complexe du lac and accuracy of zircon ages: Chemical Geology, v. Doré et son environnement géologique: Ministère de 220, p. 47-66. l'Énergie, des Mines et des Ressources du Québec, Mortensen, J.K., 1993, U-Pb geochronology of the eastern report MM 89-03, 275 p. Abitibi Subprovince. Part 1: Chibougamau- Davidson, A.J., 1977, Petrography and chemistry of the Key Matagami-Joutel region: Canadian Journal of Earth tuffite at Bell Allard, Matagami, Quebec: Sciences, v. 30, p. 11-28. Unpublished MSc thesis, McGill University, Moulton, B.J.A., Fowler, A.D., Ayer, J.A., Berger, B.R., and Montreal, Canada, 131 p. Mercier-Langevin, P., 2011, Archean subqueous Hart, T.R., Gibson, H.L., and Lesher, C.M., 2004, Trace high-silica rhyolite coulees: Examples from the Kidd- element geochemistry and petrogenesis of felsic Munro Assemblage in the Abitibi Subprovince: volcanic rocks associated with volcanogenic masive Precambrian Research, v. 189, p. 389-403. Cu-Zn-Pb sulfide deposits: Economic Geology, v. 99, Moulton, B.J.A., Fowler, A.D., Mercier-Langevin, P., Proulx, p. 1003-1013. N., and Berger, B., 2008, Volcanology of the felsic Ioannou, S.E., Spooner, E.T.C., and Barrie, C.T., 2007, Fluid volcanic rocks of the Kidd-Munro assemblage in temperature and salinity characteristics of the Prosser and Munro townships and preliminary Matagami volcanogenic massive sulfide district, correlations with the Kidd Creek deposit, Abitibi Quebec: Economic Geology, v. 102, p. 691-715. greenstone belt, Ontario: Geological Survey of Ishikawa, Y., Sawaguchi, T., Iwaya, S., and Horiuchi, M., Canada, Current Research, v. 2008-18, p. 1-21. 1976, Delineation of prospecting targets for Kuroko Parrish, R.R., Roddick, J.C., Loveridge, W.D., and Sullivan, deposits based on modes of volcanism of underlying R.W., 1987, Uranium-lead analytical techniques at dacite and alteration halos (in Japanese with English the Geochronology Laboratory, Geological Survey of abstract): Mining Geology, v. 26, p. 105-117. Canada; in Radiogenic age and isotopic studies, Jenney, C.P., 1961, Geology and ore deposits of the Mattagami Report 1: Geological Survey of Canada Paper 87-2, p. area, Quebec: Economic Geology, v. 56, p. 740-757. 3-7. Krogh, T.E., 1982, Improved accuracy of U-Pb ages by creation Piché, M., Guha, J., and Daigneault, R., 1993, Stratigraphic and of more concordant systems using an air abrasion structural aspects of the volcanic rocks of the technique: Geochimica et Cosmochimica Acta, v. 46, Matagami mining camp, Quebec; implications for the p. 637-649. Norita ore deposit: Economic Geology, v. 88, p. Large, R.R., Gemmell, J.B., Paulick, H., and Huston, D.L., 1542-1558. 2001, The alteration box plot: a simple approach to Roddick, J.C., 1987, Generalized numerical error analysis with understanding the relationship between alteration applications to geochronology and thermodynamics: mineralogy and lithogeochemistry associated with Geochimica et Cosmochimica Acta, v. 51, p. 2129- volcanic-hosted massive sulfide deposits: Economic 2135. Geology, v. 96, p. 957-971. Roy, G. and Allard, M., 2006, Matagami, une approche ciblée Lavallières, G., Guha, J., Daigneault, R., and Bonenfant, A., sur de nouveaux concepts: Résumé des conferences et 1994, Cheminées de sulfures massifs atypiques du des photoprésentations, Québec Exploration 2006, gisement de l'Isle-Dieu, Matagami, Québec: Ministère des Ressources naturelles et de la Faune implications pour l'exploration: Exploration and (Québec), report DV 2006-03, p. 13 Mining Geology, v. 3, p. 109-129. Sharpe, J.I., 1968, Geology and sulfide deposits of the Liaghat, S., and MacLean, W.H., 1992, The Key Tuffite, Matagami area, Abitibi-East County, Ministère des Matagami mining district: origin of the tuff Richesses Naturelles du Québec, report RG-137(A), component and mass changes: Exploration and p. 1-130. Mining Geology, v. 1, p. 197-207. Thurston, P.C., Ayer, J.A., Goutier, J., and Hamilton, M.A., Maier, W.D., Barnes, S.-J., and Pellet, T., 1996, The economic 2008, Depositional gaps in Abitibi Greenstone Belt significance of the Bell River Complex, Abitibi stratigraphy: a key to exploration for syngenetic subprovince, Quebec: Canadian Journal of Earth mineralization: Economic Geology, v. 103, p. 1097- Sciences, v. 33, p. 967-980. 1134. Masson, M., 2000, Option Caber, rapport de sondages 1998- Xstrata plc, 2008, Annual Report 2008, downloaded from 1999: Mining exploration file, Ministère des www.xstrata.com on May 3, 2010, 210 p. Ressources naturelles et de la Faune (Québec), Xstrata plc, 2010, Annual Report 2010, downloaded from document GM 58074, 3699 p. www.xstrata.com on March 25, 2011, 228 p.
7 TABLES
Table 1. Location, context and results for the new U-Pb samples.
Stratigraphic unit Area Diamond drill Sampled GSC lab U-Pb age hole interval number (Ma) South Flank Watson Rhyolite McLeod deposit MC-08-37 870.5-877.0 m z9627 2725.9 ± 0.8
Bracemac Rhyolite McLeod deposit MC-08-43 718.2-728.7 m z9624 2725.8 ± 0.8
Dumagami Rhyolite Orchan West deposit OR-01-32 756.0-768.8 m z9913 2724.9 ± 0.7
Dumagami-P Rhyolite Persévérance mine, EQ-00-41 117.9-130.5 m z9625 2725.4 ± 0.7 Équinoxe lens
West Camp Watson-like rhyolite Caber deposit NCB-98-38 287-292.2 m z9912 2725.9 ± 1.2
Watson-like rhyolite or SE of McIvor pluton 1214-98-02 244-268.9 m* z9626 2723.4 ± 0.7 tonalite
* Minus one dike and some more altered sections
Table 2. Geochemical analyses of the geochronological samples, performed at INRS-ETE.
Stratigraphic unit Watson Bracemac Dumagami-P Dumagami Watson-like Watson-like Site McLeod McLeod Persévérance Orchan West Caber McIvor area DDH MC-08-37 MC-08-43 EQ-00-41 OR-01-32 NCB-98-38 1214-98-02 Major oxydes by fusion ICP-AES (%) SiO 2 78.0 74.8 68.4 70.7 70.0 77.2 TiO 2 0.26 0.23 0.70 0.73 0.31 0.27 Al 2O3 10.13 9.89 10.70 11.5 10.4 9.59 T Fe 2O3 4.29 7.15 6.18 7.12 8.26 5.46 MnO 0.03 0.07 0.04 0.14 0.09 0.02 MgO 4.76 0.91 9.20 1.05 7.01 4.51 CaO 0.12 0.64 0.12 3.78 0.15 < 0.09 Na 2O 0.59 4.09 < 0.07 3.78 0.05 < 0.07 K2O 1.59 0.29 0.26 0.06 0.81 1.36 P2O5 < 0.02 0.01 0.10 0.15 0.03 0.02 LOI 2.9 1.5 4.5 1.8 3.8 2.8 Total 103 99 100 101 101 101 Ratios* and alteration indices Ti/Zr (ppm/ppm) 2.7 3.3 9.0 14.5 2.9 2.9 Al 2O3/TiO 2 (%/%) 40 43 15 16 34 36 Zr/Y (ppm/ppm) 4.1 2.6 3.6 2.7 3.4 3.9 La/Lu (ppm/ppm) 12 18 20 19 17 12 La/Sm (ppm/ppm) 2.1 2.2 2.2 2.6 2.0 1.9 Gd/Lu (ppm/ppm) 7.9 10.9 10.8 8.1 9.5 8.3 Ishikawa AI** (0-100) 90 20 99 13 97 100 CCPI*** (0-100) 77 59 94 62 90 83
* Trace elements by fusion ICP-MS. ** Alteration index from Ishikawa (1976). *** Chlorite-carbonate-pyrite index (Large et al., 2001).
8 Table 3. Geochronology results: U-Pb ID-TIMS analytical data.
Table 3. Geochronology results: U-Pb ID-TIMS analytical data Isotopic Ratios 6 Ages (Ma) 8 Fract. 1 Description 2 Wt. U Pb 3 206Pb 4 Pb 5 208Pb 207Pb ±1SE 206Pb ±1SE Corr. 7 207Pb ±1SE 206Pb ±2SE 207Pb ±2SE 207Pb ug ppm ppm 204Pb pg 206Pb 235U Abs 238U Abs Coeff. 206Pb Abs 238U 235U 206Pb
(a) MC-08-37 (Z9627): Watson Rhyolite (drill hole MC-08-37; depth 870.5-877.0 m) A1 (Z; 1) Co,Clr,Eu,Pr,fIn,rFr 2.5 23 14 1491 1.3 0.18 13.53607 0.02075 0.52194 0.00072 0.918 0.18809 0.00011 2707.4 6.1 2717.8 2.9 2725.6 A3 (Z; 1) Co,Clr,Eu,Pr,fIn,rFr 1.7 20 12 755 1.5 0.15 13.56606 0.02826 0.52278 0.00103 0.898 0.18821 0.00017 2711.0 8.7 2719.9 3.9 2726.6 B1 (Z; 1) Co,Clr,Eu,St,fIn,rFr,Osc 6.8 14 9 2615 1.2 0.15 13.56866 0.01804 0.52310 0.00060 0.919 0.18813 0.00010 2712.3 5.1 2720.1 2.5 2725.8 B2 (Z; 1) Co,Clr,Eu,St,fIn,rFr,Osc 2.6 26 16 2313 0.9 0.17 13.54954 0.02126 0.52287 0.00079 0.879 0.18795 0.00014 2711.3 6.7 2718.7 3.0 2724.3 B3 (Z; 1) Co,Clr,Eu,St,fIn,rFr 3.7 11 7 1899 0.7 0.18 13.55329 0.02225 0.52237 0.00076 0.910 0.18817 0.00013 2709.2 6.5 2719.0 3.1 2726.3 B4 (Z; 1) Co,Clr,Eu,St,fIn,rFr,Osc 1.4 54 33 3001 0.8 0.18 13.63189 0.02982 0.52523 0.00110 0.968 0.18824 0.00010 2721.3 9.3 2724.5 4.1 2726.8
(b) MC-08-43 (Z9624): Bracemac Rhyolite (drill hole MC-08-43; depth 718.2-728.7 m) A6-1 (Z; 1,CA) Co,Clr,Eu,Tip,Fr,CA6 2.6 29 18 1422 1.7 0.16 13.55914 0.02846 0.52343 0.00103 0.941 0.18788 0.00013 2713.7 8.7 2719.4 4.0 2723.7 A6-2 (Z; 1,CA) Co,Clr,Eu,Pr,Fr,fIn,CA6 1.8 75 47 5612 0.8 0.18 13.65845 0.01643 0.52643 0.00051 0.936 0.18817 0.00008 2726.4 4.3 2726.3 2.3 2726.3 A6-3 (Z; 1,CA) Co,Clr,Eu,Pr,Fr,fIn,CA6 2.7 43 27 1253 3.0 0.19 13.64011 0.01918 0.52600 0.00058 0.886 0.18808 0.00013 2724.6 4.9 2725.0 2.7 2725.4 B1 (Z; 1) Br,Clr,Eu,Pr,fIn,rFr,Osc 0.9 51 31 1020 1.4 0.17 13.58695 0.02405 0.52376 0.00085 0.903 0.18814 0.00014 2715.1 7.2 2721.4 3.3 2726.0 B2 (Z; 1) Br,Clr.fOm.rFr,Osc 1.0 93 58 2579 1.2 0.20 13.44203 0.01869 0.51802 0.00062 0.930 0.18820 0.00010 2690.8 5.3 2711.2 2.6 2726.5 B4 (Z; 1) Br,Clr,Eu,St,fIn,Osc 0.9 87 54 2835 0.9 0.20 13.53107 0.01921 0.52171 0.00064 0.939 0.18811 0.00009 2706.4 5.4 2717.5 2.7 2725.7
(c) EQ-00-41 (Z9625): Dumagami-P Rhyolite (drill hole EQ-00-41; depth 117.9-130.5 m) A1 (Z; 1) Co,Clr,Eu,Pr,rFr,Osc 7.6 12 8 2424 1.3 0.16 13.59523 0.01825 0.52426 0.00060 0.931 0.18808 0.00009 2717.2 5.1 2721.9 2.5 2725.4 A2 (Z; 1) Co,Clr,Eu,Pr,rFr,Osc 3.6 14 9 1372 1.2 0.16 13.57315 0.02590 0.52336 0.00094 0.930 0.18809 0.00013 2713.4 8.0 2720.4 3.6 2725.6 A3 (Z; 1) Co,Clr,Eu,St,fIn 3.7 13 8 1388 1.1 0.14 13.57956 0.02232 0.52401 0.00080 0.908 0.18795 0.00013 2716.1 6.7 2720.8 3.1 2724.3 A4 (Z; 1) Co,Clr,Eu,St,fIn 2.0 40 24 3484 0.8 0.16 13.59712 0.01813 0.52395 0.00061 0.915 0.18821 0.00010 2715.9 5.2 2722.1 2.5 2726.6 A6 (Z; 1) Co,Clr,Eu,Pr,fIn,Osc 1.1 40 24 1454 1.0 0.16 13.54960 0.02199 0.52260 0.00078 0.911 0.18804 0.00013 2710.2 6.6 2718.8 3.1 2725.1 A6-1 (Z; 1,CA) Co,Clr,Eu,St,fIn,fFr,CA6 12.7 21 13 9101 0.9 0.16 13.61106 0.01592 0.52500 0.00049 0.945 0.18803 0.00008 2720.3 4.1 2723.0 2.2 2725.0
(d) OR-01-32 (Z9913): Dumagami Rhyolite (drill hole OR-01-32, depth 756.0-768 m) A1 (Z; 1) Co,Clr,Eu,St,Osc 4.5 142 95 14156 1.5 0.28 13.66741 0.01566 0.52726 0.00048 0.943 0.18800 0.00008 2729.9 4.0 2726.9 2.2 2724.8 A2 (Z; 1) Co,Clr,Eu,St,fFr,Osc 2.2 81 49 3082 1.9 0.13 13.70969 0.02088 0.52608 0.00075 0.869 0.18900 0.00014 2724.9 6.3 2729.9 2.9 2733.5 A3 (Z; 1) Co.Clr,Eu,St,Osc 1.4 30 18 1006 1.4 0.10 13.67467 0.02543 0.52717 0.00092 0.893 0.18813 0.00016 2729.5 7.7 2727.4 3.5 2725.9 A4 (Z; 1) Co,Clr,Eu,St,fFr,Osc 1.7 87 55 2359 2.1 0.22 13.58855 0.01688 0.52431 0.00052 0.919 0.18797 0.00010 2717.4 4.4 2721.5 2.4 2724.5 A5 (Z; 1) Co,Clr,Eu,Tip,Osc 11.6 46 29 8535 2.1 0.21 13.65130 0.02698 0.52681 0.00097 0.977 0.18794 0.00008 2728.0 8.2 2725.8 3.7 2724.2 C2 (Z; 1) Co,Clr,Frag,Osc 2.5 64 41 5024 1.0 0.21 13.62776 0.01732 0.52530 0.00057 0.918 0.18815 0.00010 2721.6 4.8 2724.2 2.4 2726.1
(e) NCB-98-38 (Z9912): Watson-like rhyolite at Caber (drill hole NCB-98-38, depth 287.0-292.8 m) A1A (Z; 1) Co,Clr,Eu,St 2.1 34 21 2212 1.1 0.21 13.60485 0.01917 0.52446 0.00064 0.928 0.18814 0.00010 2718.1 5.5 2722.6 2.7 2726.0 A2A (Z; 1) Co,Clr,Eu,St,fIn 4.4 18 11 1057 2.4 0.17 13.63298 0.02127 0.52520 0.00068 0.867 0.18826 0.00015 2721.2 5.8 2724.6 3.0 2727.0 A4A (Z; 1) Co,Clr,Eu,St,Osc 3.0 18 11 1362 1.3 0.16 13.59993 0.02676 0.52466 0.00095 0.939 0.18800 0.00013 2718.9 8.0 2722.3 3.7 2724.8 A5A (Z; 1) Co,Clr,Eu,St,fIn,Osc 2.0 31 19 1132 1.8 0.18 13.49441 0.02408 0.51968 0.00082 0.913 0.18833 0.00014 2697.8 7.0 2714.9 3.4 2727.6
(f) 1214-98-2 (Z9626): Watson-like rhyolite (drill hole 1214-98-2; depth 244-268.9 m) A12-1 (Z; 1,CA) Co,Clr,Eu,St,Fr,CA12 3.5 77 47 4626 1.9 0.15 13.59035 0.01592 0.52494 0.00048 0.935 0.18777 0.00008 2720.1 4.1 2721.6 2.2 2722.7 A3 (Z; 1) Co,Clr,Eu,El,rIn,rFr,Osc 1.2 119 70 2511 1.9 0.12 13.53041 0.01800 0.52269 0.00060 0.885 0.18775 0.00012 2710.6 5.1 2717.4 2.5 2722.5 A5 (Z; 2) Co,Clr,Eu,Pr,fIn,Osc 3.6 65 37 5819 1.3 0.09 13.55243 0.01617 0.52319 0.00051 0.930 0.18787 0.00009 2712.7 4.3 2719.0 2.3 2723.6 A6 (Z; 2) Co,Clr,Eu,Pr,fIn 2.3 75 44 6067 0.9 0.10 13.55266 0.01625 0.52343 0.00053 0.899 0.18779 0.00010 2713.7 4.5 2719.0 2.3 2722.9 B2 (Z; 1) Co,Clr,Eu,Pr,rIn 1.4 65 37 2857 1.0 0.09 13.55685 0.01872 0.52321 0.00063 0.928 0.18792 0.00010 2712.8 5.3 2719.3 2.6 2724.1 C16-1 (Z; 1,CA) Co,Clr,Eu,St,In,Fr,CA16 3.0 77 48 7438 1.0 0.18 13.58775 0.01602 0.52442 0.00049 0.942 0.18792 0.00008 2717.9 4.2 2721.4 2.2 2724.0 Notes: 1Z=zircon. Number in bracket refers to the number of grains in the analysis. CA = chemically abraded following the method of Mattinson (2005); all other grains were physically abraded (Krogh, 1982). 2Fraction descriptions: Co=Colourless, Br=light brown, Clr=Clear, Eu=Euhedral, Pr=Prismatic, St=Stubby prismatic, El=Elongate, Tip=Tip, Frag=Fragment, rFr=Rare Fractures, fFr=Few Fractures, Fr=Abundant Fractures, rFr=Rare Inclusions, fIn=Few Inclusions, In=Abundant Inclusions, Osc=Oscillatory zoning, CA#=Chemically Abraded for # hours. 3Radiogenic Pb 4Measured ratio, corrected for spike and fractionation 5Total common Pb in analysis corrected for fractionation and spike 6Corrected for blank Pb and U and common Pb, errors quoted are 1 sigma absolute; procedural blank values for this study ranged from <0.1- 0.1 pg for U and 0.5-2 pg for Pb; Pb blank isotopic composition is based on the analysis of procedural blanks; corrections for common Pb were made using Stacey-Kramers compositions 7Correlation Coefficient 8Corrected for blank and common Pb, errors quoted are 2 sigma in Ma
9 FIGURES Figure 1. (a) Location of the Abitibi greenstone belt in eastern Canada. (b) Simplified geological map of the Abitibi greenstone belt showing the location of Matagami.
Figure 2. Simplified geological map of the Matagami area, modified from Roy and Allard (2006), with locations of the VMS deposits (square symbols). The location of samples dated by U-Pb methods reported by Mortensen (1993) are shown (circles) according to the reported longitude/latitude coordinates. However, the sample from the Bell River Complex was placed north-east of Matagami rather than at the reported coordinate (which is not in the Bell River Complex). The location of more detailed maps is illustrated except for Figure 5A which was too small to display (refer to the Caber deposit symbol for location). Grid on all maps is UTM Nad 83, zone 18.
Figure 3. Location of U-Pb geochronological samples from the South Flank. A and B. Surface geology and vertical cross- section at the McLeod VMS deposit, where the Watson and Bracemac rhyolites have been sampled. C and D. Surface geology and vertical cross-section through the Equinox lens at the Persévérance mine, where the Dumagami-P Rhyolite has been sampled just above the Key Tuffite. At McLeod, the Bracemac Rhyolite is capped by the Bracemac Tuffite and the rest of the Wabassee Group consists of mafic to intermediate lava flows. The volcanic rocks are cut by numerous mafic to felsic intrusions. In the Persévérance area, note the lack of mafic to intermediate lavas between the Watson Rhyolite and the Dumagami-P Rhyolite. Drill holes shown on both sections are projected horizontally by up to 50 m.
Figure 4. Geological map (a) and vertical cross-section (b) through the Orchan West area of the South Flank, showing the location of the U-Pb sample in the Dumagami Rhyolite. Drill holes on the section are projected horizontally by up to 50 m.
Figure 5. Geological maps and vertical cross-sections of two sectors from the West Camp: A and B through the Caber VMS deposit, showing the location of the U-Pb sample in a Watson-like rhyolite; C and D through the volcanic rocks SE near the McIvor Pluton, showing the location of the other U-Pb sample in a Watson-like rhyolite. Drill holes shown on both sections are projected horizontally by up to 50 m.
Figure 6. U-Pb concordia diagrams for the six dated rhyolite samples. See text for discussion.
Figure 7. Compilation of new U-Pb results (squares) for the South Flank and the West Camp. Also shown is Mortensen’s (1993) U-Pb age for the Watson Rhyolite (circle). See text for discussion.
10 a b 80o 78o 76o 74o W
Matagami Chibougamau 50o Ontario 50 km Québec Fig. 2
49o
Timmins Rouyn-Noranda Québec Kirkland Lake Val d’Or N o Grenville Front ABITIBI 48 N Ontario PROTEROZOIC ARCHEAN Fault zones Sedimentary rocks Granitoids
ARCHEAN Stratiform intrusions Sedimentary rocks Volcanic rocks
Ross et al., Fig. 1 270 000m E 280 000 290 000 300 000 310 000 320 000
Matagami Lake Faults NORTH FLANK VMS deposit Mined VMS deposit Location of Mortensen’s (1993) U-Pb samples New Hosco 5 520 000m N Norita 2723.1 +0.8/-0.7 Ma PD-1 Garon Lake Caber North Persévérance Matagami 2724.6 +2.5/-1.9 Ma Allard River Fig. 3b Caber Radiore #2
2724.5 ± 1.8 Ma McIvor Pluton Bell River Complex Isle-Dieu Bell River Orchan Mattagami Lake West Fig. 4a Orchan Fig. 5c SOUTH FLANK Proterozoic diabase 5 510 000 Bell Allard Bell Allard Sud Sedimentary rocks WEST CAMP Cavelier Bracemac Intermediate to felsic intrusions PD-2 McLeod Mafic to intermediate intrusions Fig. 3a Mafic to intermediate Lynx volcanic rocks 0 2.5 5 Felsic volcanic rocks kilometres 5 500 000
Ross et al., Fig. 2 a 308 100m E 308 300 308 500 308 700 c Overburden Intrusive rocks 298 500mE 298 700 298 900 299 100 299 300 299 500 Faults Mafic to intermediate
5 505 600 Persévérance Geochronology sample Felsic to intermediate West
Volcanic rocks 5 515 800m N Tuffite, alteration and Wabassee Group mineralization
5 505 300 Mafic rocks Tuffite 5 515 600 Dumagami-P Rhyolite Équinox Massive sulfides 9725 E Bracemac Rhyolite Persévérance section 13300E (Fig. 3b) Intense chlorite 5 515 400 Main (Fig. 3d)
5 505 000 McLeod deposit alteration Watson Group Section 2 0 150 300 Watson Rhyolite metres 5 515 200 0 100 200 Watson Dacite
metres 5 504 700m N b d 206° 26° 198° 18°
0 m 0 m
Not Drilled DUMAGAMI-P 200 m
100 m
BRACE MAC 400m
EQ-00-41 WATSON 600 m WATSON McLeod VMS deposit Equinox lens 200 m
MC-08-43 50 m 800 m MC-08-37 50 m
Section 13300E Section 29725E 100 m McLeod deposit 300 m 100 m Persévérance Mine 1000 m
Ross et al., Fig. 3 a b 301 700m E 302 000 302 300 302 600 302 900 270° 90° 0 200 400 0 m metres 5 510 900m N 200 m Orchan West deposit 5 510 600 400 m
Section E-W (Fig. 4b)
5 510 300 600 m
Overburden 800 m
Geochronology sample DUMAGAMI
Massive sulfides 1000 m OR-01-32 Mafic to intermediate intrusions Wabassee Group WATSON 1200 m Mafic to intermediate volcanic rocks
Dumagami Rhyolite 200 m 1400 m Watson Group 200 m Watson Rhyolite Orchan West Section
Ross et al., Fig. 4 a c 282 100 m E 282 400 282 700 277 600 m E 277 700 277 800 277 900 278 000 Faults Geochronology sample McIvor Fault Zone Overburden Volcanic rocks Mafic 5 509 100 m N
5 514 000 m N Felsic Intrusive rocks
Mafic to intermediate Section 5 000S (Fig. 5d) Intermediate to felsic 5 513 900 Caber VMS deposit Sulfides and oxides
Section 11700 S (Fig. 5b) 5 508 800 0 150 300 0 50 100 Massive sulfides metres metres Magnetite 5 513 800 b d 228.5° 48.5° 225° 45°
0 m 0 m
100 m 100 m
200 m 200 m 50 m Caber VMS deposit 50 m 300 m 300 m
NCB-98-38 50 m Section 11700S 1214-98-02 Section 5 000S Caber sector 50 m McIvor sector
Ross et al., Fig. 5 South Flank
(a) Watson Rhyolite at McLeod (b) Bracemac Rhyolite at McLeod 0.529 0.529 MC-08-37 (z9627) 2730 MC-08-43 (z9624) 2730 0.527 2726 0.527 2726 A6-2 2722 2722 0.525 2718 A6-3 0.525 2718 B4 2714 2714 B2 0.523 2710 A6-1 B1 B1 0.523 Pb/ U A3 Pb/0.521 U 206 238 206 238 0.521 B4 B3 0.519 A1 2725.9 ± 0.8 Ma 2725.8 ± 0.7 Ma 0.519 0.517 B2
0.517 0.515 13.40 13.45 13.50 13.55 13.60 13.65 13.70 13.75 13.35 13.40 13.45 13.50 13.55 13.60 13.65 13.70 13.75 207Pb/ 235 U 207Pb/ 235 U
(c) Dumagami-P Rhyolite at Persévérance (d) Dumagami Rhyolite in Orchan West area 0.528 0.530 2730 2738 A3 EQ-00-41 (z9625) 2728 OR-01-32 (z9913) 2734 2726 A1 2724 0.528 0.526 2730 2722 A6-1 2720 A1 2726 A5 2718 0.526 2722 2716 A2 0.524 2714 A3 2718 Pb/ U Pb/ U C2 A4 0.524 206 238
206 238 2714 A4 0.522 A2 2725.4 ± 0.7 Ma 0.522 2724.9 ± 0.7 Ma A6
0.520 0.520 13.44 13.48 13.52 13.56 13.60 13.64 13.68 13.72 13.44 13.54 13.64 13.74 13.84 207Pb/ 235 U 207Pb/ 235 U
West Camp
(e) Watson-like rhyolite at Caber (f) Watson-like rhyolite in McIvor sector 0.529 0.528
NCB-98-38 (z9912) 2728 1214-98-2 (z9626) 2728 0.527 2724 2726 2724 2720 A2A 0.526 0.525 2722 2716 A12-1 2720 2712 2718 0.523 A1A C16-1 2716 A6 A4A 0.524 2714 B2 Pb/ U Pb/0.521 U 206 238 206 238
0.519 A5 A5A 2725.9 ± 1.2 Ma 0.522 2723.4 ± 0.7 Ma A3 0.517
0.515 0.520 13.40 13.44 13.48 13.52 13.56 13.60 13.64 13.68 13.72 13.44 13.49 13.54 13.59 13.64 13.69 207Pb/ 235 U 207Pb/ 235 U
Ross et al., Fig. 6 SOUTH FLANK WEST CAMP
2723 Ma Rhyolite Rhyolite 2724 Ma Dumagami at Orchan West hyolite Dumagami-P at Persévérance Watson-like rhyolite at Caber Bracemac R at McLeod
2725 Ma Watson Rhyolite at McLeod Watson-like rhyolite at McIvor
2726 Ma
2727 Ma (Mortensen) Watson Rhyolite
Ross et al., Fig. 7