In the Bousquet mining district, metamorphosed volcanic rocks of the Blake River Group (BRG) exhibit discrete strain features resulting from three generations of structures—D1, D2, and D3. Deformation D1 formed an east–west-trending, subvertical, penetrative schistosity that is coplanar with the axial plane of associated folds. This foliation contains a linear fabric plunging steeply westward, and mineral lineations are subparallel to fold axes and to intersection lineations.Defomations D2 and D3 formed a crenulation cleavage and a set of conjugate kink bands, respectively. The cleavage is oriented east–northeast, and the kink bands are oriented northeast–southwest and northwest–southeast. Both deformations distorted earlier-formed structures to a minor extent. A conjugate set of minor strike-slip faults with orientations similar to the kinks are the youngest structures found in BRG rocks.The volcanic sequence is composed of two lithotectonic domains juxtaposed along fault-related contacts. Each domain exhibits distinctive strain features attributed mainly to a broad network of anastomosing faults. This network of faults disrupted strata and destroyed many internal stratigraphic features, especially in domain 2; it relates to late stages of D1.Domain 1, occupying the northern half of the BRG in the mine area, represents a zone of weakly sheared tholeiitic basalts 750 m thick and is overlain by 150 m of felsic volcaniclastic rocks. Primary textures and structures indicate that this domain forms a south-facing homoclinal succession.Domain 2 is characterized by a strongly strained, 500 m wide belt of anastomosing faults adjacent to the southern margin of domain 1. Narrow bands of schist, mylonite, and phyllonite straddle fault zones and surround less-deformed, lozenge-shaped blocks of metamorphosed volcanic and (or) volcaniclastic rocks.The lack of syngenetic structures and textures, together with intense faulting and transposition, restricts stratigraphic correlations throughout the BRG as well as correlations between this volcanic succession and the adjacent sedimentary units. Structural evidence presented here complicates the original stratigraphic scheme commonly applied to volcano-sedimentary assemblages in the Rouyn–Val D'Or area. It is proposed that faulting is responsible for the spatial distribution of lithologies previously interpreted as resulting from folding phenomena in the Bousquet mining district. Gold mineralization is concentrated in bands of deformed rocks in the fault zones of domain 2 at the Bousquet mine.

The composite Mooshla stock displays clear evidence of variations in style and intensity of strain that are closely related to its internal lithological heterogeneity. Gabbro-diorite, quartz diorite, and tonalite rocks are weakly foliated and characterized by brittle and brittle-ductile small-scale shear zones, whereas leucotonalitic rocks are strongly foliated and transected by numerous wide and extensive ductile shear zones. Increasing degrees of penetrative deformation and marked changes of strain style in the pluton, from the more mafic rocks to the more felsic ones, are interpreted to reflect metamorphism-related rheological contrasts, rather than differences in the physical conditions of deformation. Metamorphism of the stock is characterized by an intensive hydration of the igneous rocks that has greatly enhanced their original heterogeneities. Petrographic, microstructural, and chemical studies show that the least deformed rocks are characterized by abundant albite-oligoclase (65-80%) with a matrix of minor quartz (5-10%) and actinolitic amphibole. The resistant plagioclase laths, although altered and replaced, form a stress-supporting framework that has protected the interstitial weak minerals, such as quartz, chlorite, and biotite, from deformation. However, the least deformed leucotonalites are characterized by low albite (35-45%) and high quartz contents (up to 65%). Extensive metamorphic hydration of these rocks produces quartz and phyllitic minerals that had enhanced significantly the ductility of the leucotonalites. Characterization of the chemical changes and the thermochemical conditions of the fluid, using microstructure and measurement of stable isotopes, indicates that fluid-rock interactions during metamorphism and syntectonic hydrothermal alteration have played an important role in creating the contrasting deformation of the composite granitoid.

The Malartic Composite Block of the southern Abitibi belt underwent at least two phases of ductile deformation over a period of 25 Ma during the late Archean. It is divided into seven tectono-stratigraphic domains on the basis of their lithologicai content, structural styles, and geochemical affinities of the volcanic and plutonic rocks. The Malartic Composite Block is bounded to the south by the sedimentary rocks of the Kewagama Group that have been also affected by deformation. The crosscutting relationships between the structural elements, along with precise geochronological data, provide a basis for evaluation of the evolution of the deformation in this part of the southern Abitibi. The D1 tectonic event produced ductile thrust faults and folds in the mafic and ultramafic domains of the Malartic Composite Block. The calc-alkalic rocks of the Val-d'Or Domain (2705 Ma) were erupted on top of these deformed domains, thus establishing the minimum age for D1. The D2 event is divided into three increments that are linked to the same progressive deformation. D2.1 produced northwest-trending folds in the rocks of the Kewagama Group, but did not affect the rocks of the Malartic Composite Block. The age of the youngest detrital zircon in the Kewagama indicates that D2.1 was active after 2687 Ma. D2.2 developed a consistent east–west regional foliation that overprints all the rocks of the area. Radiometric data on related metamorphic minerals indicate an age of 2680 Ma for this event. Locally, S2.2 is modified by Fo2.3 folds of asymmetric Z shape associated with a late dextral transcurrent shearing. A minor D3 event produced small, local conjugate kink folds recording an east–west shortening.

Thirty-one audiomagnetotelluric (AMT) soundings have been collected along a N-S profile across the northern Abitibi greenstone belt. The recording frequency ranges of 10 000-1 Hz for 25 stations and 10 000-0.001 Hz for the other six stations were appropriate for defining the near-surface geoelectric structures and for imaging major faults and shear zones down to approximately 10 km along the profile. Six time-domain electromagnetic (TEM) soundings were also collected near the southern end of the profile, to provide a correction for static shift. Extensive static distortion analysis reveals that most of the AMT data are not distorted by localized near-surface structures; however, they are affected by static shift. In order to remove this static shift, a spatial filter was designed and applied to the data, effectively reducing static shift as verified by TEM soundings at the same sites. Extensive 2-D inversions of the filtered data were carried out. The results suggest the presence of a thin overburden with both conductive and resistive blocks overlying a very resistive basement. Among the four geological deformation zones crossed by the profile, only two zones are imaged as subvertical conductive crustal structures extending to the limit of resolution of AMT. These correspond to major breaks (Porcupine-Destor Fault and Casa Berardi Tectonic Zone) as evidenced by the seismic reflection data collected over the same area.

Shear-zone-related gold–quartz veins in granitoid intrusions are commonly intimately associated with mafic dikes, which may have a profound influence on the localization, orientation, and kinematics of auriferous shear zones. The Bourlamaque pluton of the Val-d'Or district contains several economic auriferous shear zones, most of which follow and overprint diorite dikes. Mineralization in all deposits consists of quartz–tourmaline–pyrite veins in reverse- oblique orientation with a significant range of strike, dip, and slip direction. The geometry and kinematics of shear zone and vein array within the pluton is more complex than the simple conjugate pattern predicted for a deforming homogeneous intrusion. The stress tensor determined from the auriferous shear zones within the pluton indicates the same northerly-directed compression recorded by similar shear zones outside the pluton. This indicates that the complex shear zone and vein pattern within the pluton reflects the influence of diorite dikes, which acted as weak layers that were activated during subsequent deformation, showing the importance of layer anisotropy in auriferous shear zone development.The plunges of orebodies bear simple geometric relationships to the slip direction along a host shear zone: these are generally perpendicular to, or in some cases parallel to, the slip direction. Knowledge of the slip directions along activated dikes would therefore allow prediction of the possible plunge(s) of orebodies at early stages of exploration programs. Slip direction along an activated layer is controlled by the orientation of the layer with respect to the stress field and by the relative magnitudes of the three principal stresses. Using techniques developed for analysis of fault slip data, both parameters can be determined, provided there is a sufficient database, and slip direction can be predicted for activated layers of any orientations.

Reprocessing of part of a Lithoprobe high-resolution seismic reflection line across the southern part of the Abitibi Belt has improved the imaging of shallow reflections and allowed correlation of the data with surface geology. Enhancement of early reflections was accomplished by focusing on the high-frequency content of the data. This improved resolution of reflections at two-way traveltime as early as 0.3 s and attenuated noise such as shear waves. The shallow reflections are interpreted as impedance contrasts at the contact between a metadiabase–diorite body and metavolcanics rocks. Offsets of the reflectors correlate with faults mapped at the surface and indicate a downdropped block, which may be of interest for mineral exploration.

Abstract The Cadillac fault is generally thought to be coincident with a highly schistose zone, a few tens of meters thick, composed of chlorite-carbonate and talc-chlorite-carbonate schists (Gunning and Ambrose, 1940; Norman, 1946). However, outcrops on the Orenada zone noo2 property indicate that deformation related to the Cadillac fault has affected different rock types over a width of more than 200 m. It is therefore more appropriate to refer to the Cadi11ac tectonic zone (CTZ) than to the Cadi11ac fau1t. This outcrop zone exposes a lithological succession that can be extended using outcrops and drill hole data for more than 10 km. This succession differs from the one presented on the available compilation maps and has important implications for the regional “stratigraphy”.

The southern volcanic zone (SVZ) of the Late Archean Abitibi belt of the Superior province of Canada is dominated by komatiitic to tholeiitic volcanic plateaus and large, bimodal, mafic-felsic volcanic centers. These volcanic rocks were erupted between about 2717 and 2700 Ma in a series of rift basins that formed as a result of wrench-fault tectonics. They overlie and juxtapose a volcano-plutonic assemblage characterized in the northern Abitibi belt. The age of the assemblage is about 2720 Ma or older, and it comprises basaltic to andesitic and dacitic subaqueous massive volcanics, cored by comagmatic sills and layered anorthositic complexes and overlain by felsic pyroclastic rocks that were comagmatic with the emplacement of tonalitic plutons at 2717 ± 2 Ma. A tectonic model is proposed in which the SVZ formed in a series of rift basins that dissected an earlier formed volcanic arc. Comparisons are made with rift environments that have been postulated for Phanerozoic areas such as the Hokuroko basin of Japan, the Taupo volcanic zone of New Zealand, and the Sumatra and Nicaragua arcs.

The effusive rocks of the Blake River Group in the Abitibi volcanic belt, Rouyn–Noranda region, belong to a bimodal sequence in which andesites and rhyolites clearly dominate. The identification of calc-alkaline and tholeiitic affinities is made upon examination of the major, trace, and rare earth element (REE) content. Thus, the andesites (58% normalized SiO2 value without volatiles) of the calc-alkaline units have average K (4800 ppm), Ba (160 ppm), and Rb (13 ppm) values that are greater than the average K (1800 ppm), Ba (130 ppm), and Rb (3 ppm) values for andésites (57% SiO2) that belong to associated tholeiitic units. Furthermore, tholeiitic andesites have distinctive average values of Ti (9600 ppm) and Y (40 ppm) that are higher than the average values of Ti (6700 ppm) and Y (25 ppm) of calc-alkaline andesites. An effective discrimination between the calc-alkaline and tholeiitic affinities is obtained using the Zr/Y and Ti/Zr ratios, which are, respectively, less than 4 and greater than 70 in andesites of the tholeiitic units.REE profiles of tholeiitic andesites are flat when compared with those of calc-alkaline andesites, which show an enrichment in light rare earths.The tholeiitic units of the Blake River Group are found in the proximity of the Porcupine-Destor and Larder Lake – Cadillac faults, the major faults of the region, and at the periphery of an ensemble of calc-alkaline units. Four of the five tholeiitic units are differentiated, showing an enrichment of iron passing from basalt to andesite. These units possess felsic variole-bearing flows, the result of an unmixing, which was probably responsible for the formation of minor associated quantities of porphyries and rhyolitic volcaniclastites.A progressive increase in the concentration of hygromagmatophile elements (REE, Zr, Nb) is observed in the tholeiitic units from the Pelletier unit beginning at the base and passing through the Trémoy, Destor, and Dufresnoy units, at the top of the Blake River Group. The calc-alkaline units are characterized by an alternation of rhyolitic complexes and calc-alkaline andesites. This cyclic repetition occurs without significant modification of the calc-alkaline andesite composition.It is proposed that the volcanism responsible for the formation of the Blake River Group was restricted to a concentric zone centring on a continental environment. Mafic magmas nourished the central reservoir where melting of the sialic crust took place. The rhyolitic magma occupying the upper part of this reservoir mixed with the basaltic magma, producing calc-alkaline andesites. Successive mantle melt products were also emplaced into subsidiary reservoirs peripheral to the central chamber. Injections of tholeiitic magma in the peripheral reservoirs underwent differentiation and unmixing during emplacement of a part of the magma at the surface.

Structural analysis of the Blake River Group volcanic rocks in the Rouyn–Noranda region shows the formations to be distributed largely in Z shapes, resulting from the interference of two early fold systems oriented west-northwest–east-southeast and east–west, respectively. The first of these two fold systems is probably related to the shortening associated with left-lateral movement along the two major fractures in the region, namely the Porcupine–Destor and Larder Lake – Cadillac faults. The second system appears to be the result of north–south compression perpendicular to the two major fractures.The two major faults, the first system of early folding, the normal and reverse faults, and the minor dextral and sinistral strike-slip faults that have been observed in the Blake River Group rocks can all be integrated into one tectonic system, that of wrench fault tectonics. The orientations of the principal structures recognized in the Abitibi Belt (major shear zones, folding, and faulting) suggest that the deformation mechanism for the rocks in the belt could be a large lateral movement controlled by megashears similar to those observed at present on the California coast (San Andreas Fault), in New Zealand (Alpine Fault), and in Sumatra (Semangko Fault).

At the present time, graptolites provide the only satisfactory biostratigraphical zonation of the Nicolet River Formation in Quebec. Five detailed sections of this formation show that it ranges in age from the Corynoides americanus or Orthograptus ruedemanni Zone to post-Climacograptus manitoulinensis Zone. Correlation of these strata with others in North America indicates that the bases of the Cobourgian (classical uppermost Champlainian) and Edenian (basal Cincinnatian) are not correlative, although these stages must be partially time equivalents; however, we have refrained from suggesting a new stadial term for these post-Shermanian but pre-Edenian strata. Our graptolite-based correlation of Berry's Zone 13 (Marathon region, Texas) with the eastern North American and western European successions differs from conodont-based correlations.

The composition of the detrital fraction of the Nicolet River Formation suggests that the rocks of the Autochtonous and the External Domains of the Quebec Appalachians were mostly derived from the sedimentary nappes of the External Domain. The contribution from the metamorphic nappes and ophiolites of the Internal Domain was minor but it indicates that the dynamothermal metamorphism had been completed by the end of the Middle Ordovician (C. spiniferus Zone). Piling up of the nappes, each one progressively richer in feldspar, produced a source of high relief subject to subaerial erosion. The vertical evolution observed in the flysch probably results from tectonic activity at the source area rather than from deep-sea fan progradation. The stratigraphic relationships evince that the deposit accumulated in basins controlled by a series of horsts and grabens.

Stromatoporoids are abundant in parts of the Sayabec, St. Leon, and Mont Wissick formations of Wenlock and Ludlow age in eastern Quebec, Canada. The fauna is a mixture of species from Wenlock strata of northern Europe, the Wenlock and Ludlow beds of Baie des Chaleurs, Quebec, and Niagaran rocks of the Great Lakes region. Clathrodictyon crickmayi and Stromatopora prima show the affinity of the fauna to that described by Parka from Baie des Chaleurs. Densastroma astroites indicates a close connection of the fauna with the rocks of Wenlock age in England and the Baltic area. Stromatopora antiqua shows the affinity of the fauna to that of central North America. Ecclimadictyon fastigiatum is a widespread species in all these regions. A new species of Actinodictyon (A. quebecense) is described. Two unnamed species of Stromatopora and Clathrodictyon cf. podolica make up the rest of the fauna.

The Archean Abitibi belt is one of the largest and most studied greenstone terranes in the world. This is due not only to its precious and base meta 1 production, but also to its excellent bedrock exposure which permits observation of many Archean geological features in the south part of the belt lying between Rouyn-Noranda and Val d'Or.The main objective of the regional field trips and the mine visits is to present the rna in stratigraphic, st ructura 1 and ore characteristics of the southern part of the Abitibi Belt. This regional field trip is scheduled to cover the Rouyn-Noranda and Cadi 11 ac-Bousquet mining camps. Operating mines will also be visited: Francoeur, Pierre-Beauchemin, Ansil, Mobrun, Doyon and Bousquet. The delegates will be able to examine the main volcanic, plutonic and sedimentary rocks as well as the various structural features in this part of the Abitibi. Ore deposits will include both massive sulphide and gold deposits. The various geological and structural environments of these deposits will also be examined.The southern part of the Abitibi Belt in Quebec is dominated by a prominent deformation corridor, the Cadillac-Larder Lake Fault Zone. This zone is oriented E-W and separates a volcanic domain in the north from an essentially sedimentary domain in the south. This sedimentary domain, comprising clastic rocks and various granitic complexes, belongs to the Pontiac Subprovince. The volcanic domain is composed of various "blocks" of volcanic assemblages intruded by granitic masses, separated from one another by fault zones, discordances and inear sedimentary units. On the regional scale, the imbricated volcanic "blocks" are lozenge-shaped, with E-W orientd long axes. In most cases, the relationships between these volcanic and sedimentary "blocks" remain ambiguous.