The Gunflint Formation near Thunder Bay, Ontario has undergone very low grades of metamorphism. In this study, two outcrops of the Gunflint Formation near Thunder Bay were analyzed for their deformation microstructures, which are used to constrain temperature conditions of the Gunflint Formation during deformation.  Common deformation microstructures within this Formation are pressure-solution stylolites, deformed calcite veins, deformed quartz veins and kinked illite-mica laths.  All processes that formed these microstructures operate at temperatures between 150°C to 300°C, providing a temperature constraint of the system during deformation. In addition to deformation microstructures, semi-quantitative x-ray diffraction (XRD) phase analysis was completed on one sample from a hanging wall ramp of the Gunflint Formation.  XRD analysis shows likely minor interlayered illite-smectite, as well as the ordered illite-muscovite 2M1 polytype.  These phases are interpreted to represent metamorphic temperatures between 200°C and 300°C.  Combining this with the deformation microstructures, all structures and phases present are satisfied by a temperature range between 200°C and 300°C, corresponding to the anchizone of metamorphism (sub-greenschist facies metamorphism, specifically the prehnite-pumpellyite facies).

Given this temperature range, and assuming an average geothermal gradient of 30°C/km, the depth of the Gunflint Formation during deformation and metamorphism is shown to be anywhere between 6 km and 10 km.  This depth is consistent with tectonic loading, due to bed-parallel thrust faults.  Based on the findings of this thesis, the Gunflint Formation near Thunder Bay is interpreted to represent an eroded foreland thrust and fold belt.

The Hemlo gold deposit is located 41 km east of the town of Marathon in northern Ontario, Canada.  The deposit was discovered in 1980 and active mining in the camp was initiated in 1985.  The different lithologies hosting gold mineralization at this deposit were classified and assigned names that were acceptable at the time of its discovery and development.  This study revisits and re-interprets the classification and nomenclature of the rocks cropping out west of the C-zone open pit.  This lithological classification is reinterpreted using a modern comprehension of plate tectonic dynamics, in conjunction with, the effects of brittle and crystal plastic deformation mechanisms observed in recent material science studies.  Microstructural investigations of the samples collected suggest that the rocks are a mylonitized coarse-grained quartzo-feldspathic plutonic rock.  Microstructural analyses of the samples under transmitted and reflected light indicate that strain has been preferentially accommodated at different rates and that brittle-ductile deformation was progressive and occurred as numerous incremental events.  Such deformation resulted in rocks exhibiting different textures in hand samples but having homogeneous features when observed microscopically.  A weak schistosity results in abundant and relatively coarse-grained quartz and feldspar porphyroclasts, whereas a strong schistosity results in a low abundance and finer-grained quartz and feldspars porphyroclasts.  The magnitude of strain can be approximated using the porphyroclast size and their abundance.  This study also observed that gold mineralization in the Hemlo gold camp occurs at or near strain gradients and that gold mineralization has an affinity for competency contrast.

The western Lake St. Joseph area in Northwestern Ontario is underlain by Archean metavolcanic and metasedimentary rocks.  The strata, referred to as the Lake St. Joseph Group comprise three formations representative of mafic to felsic volcanic cyclicity.  The Blackstone Formation, stratigraphically the lowest, contains a lower member composed of predominantly high-Mg, low-K tholeiitic pillowed basalts and an upper member composed of rhyliticflows and pyroclastic rocks.  The overlying Western Lake St. Joseph Formation contains a lower member composed of predominantly calc-alkaline massive and pillowed basalts and an upper member composed of dacitic pyroclastic and epiclastic rocks.  The overlying Carling Formation contains a volcanic member and a sedimentary member.  The volcanic member is composed predominantly of high-Fe, low-K tholeiitic pillow breccias and dacitic to rhyolitic epiclastic and pyroclastic rocks.  The sedimentary member consists of basal grewacke turbidites and laminated iron formation of economic potential overlain by chloritic classical turbidites.  These sedimentary rocks are overlain by massive and cross-bedded arkosic greywackes which are in turn overlain by conglomerate and pebbly sandstone.

The deformation of the rocks is expressed by isoclinal folding, most evident on Eagle Island, and development of the regional Lake St. Joseph Fault.  Contact and regional metamorphism (lower to middle greenschist facies) have also affected the rocks.

The primary structures, vertical and lateral variations in the felsic volcanic rocks of the Blackstone and Western Lake St. Joseph Formations indicate deposition on a subaqueous paleoslope.  Similarly the felsic volcanic rocks of the Carling Formation indicate subaqueous deposition on a different paleoslope.

The lithologies, primary structures, vertical and lateral variations of the units in the sedimentary member of the Carling Formation indicate deposition on a prograding submarine fan.  Meyn and Palonen (1980) support this interpretation.

Reconstruction of the paleoenvironment envisages three stages of evolution.  In stage 1 the Blackstone and Western St. Joseph Formations are extruded and deposited on the flank of a volcanic edifice.  In stage 2 the volcanic member of the Carling Formation is extruded from a separate vent and in part deposited upon the degradation products of stage 1.  In stage 3 laminated iron formation is deposited with clastic sediments in a submarine fan-basin plain system to form the sedimentary member of the Carling Formation.

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One or possibly two overlapping periods of deformation are responsible for the structures observed in the rocks in the Seine River area.  This deformation has resulted in the formation of tight to isoclinical, non-plane approximately F₁ folds with steeply dipping E-W striking axial surfaces.  A late stage deformation has resulted in the formation of a crenulation cleavage, kink bands and minor faulting.  There is also limited evidence of a possible pre-F₁ folding event.

Two major litholigical groups are present in the study area: shallow water metasedimentary rocks of the Seine Group and metavolcanic rocks.  The Seine Group metasedimentary rocks are younger than the metavolcanic rocks in the western part of the area but may be older than similar metavolcanic rocks in the eastern part of the area.  Two ages of metavolcanic rocks therefore appear to be present: older metavolcanic rocks in the west which underlie the Seine Group, and younger metavolcanic rocks in the east which overlie the Seine Group.

Regional metamorphism to the chlorite to biotite zone greenschist facies was synkienematic with the deformation of the rocks but may have outlasted the folding in places.

Strain analysis from the metasedimentary rocks reveals that the conglomerate units are more intensely strained than arenite units, although all the stain ellipsoids are of the flattened (K < 1) type.

Average shortening in Z ranges from 52% for arenite units to 75% for conglomerate units.  A new empirical approach suggested  by the writer and Dr. Borradaile for assessing competence contrasts between strain markers and matrix is outlined.  This method uses the effects of competent markers on cleavage traces in the matrix of conglomerates.

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A gravity survey in an area involving portions of the Quetico and Shebandowan subprovinces of the Superior structural province resulted in the establishment of 350 new gravity stations in addition to 50 previously established stations.

For the purposes of this study the bedrock was divided into 4 major units including the metavolcanic rocks, metasedimentary rocks, assorted gneissic rocks and a group of intrusive igenous bodies.

Based on gravity modeling of these principal units, the following subsurface structure results.  The metavolcanic rocks vary in depth extent from 6 km to 12 km and typically occupy a trough-shaped structure flanked by a domical feature of granitoid gneisses to the south.  To the north of the metavolcanic unit, the metasedimentary rocks form a basin-like structure of variable depth extent.  The contact between these two units is modeled as dipping steeply southward.

The Quetico granitoid gneisses to the north of the metasedimentary unit form a southward dipping wedge which extends to depths of 10 km in the model structure profiles.  These gneisses are modeled as being underlain by a denser substratum representative of more basic gneiss and amphibolite.  The basal surface of this unit is gently convex upward, and the unit as a whole thickens toward the north and dips toward the south in a tapered wedge extending to a depth of 10 km.  This unit is inclined slightly from east to west, and is exposed at the present erosion surface in the eastern portion of the study area only.

A number of quartz monzonite plutons have been emplaced near the northern portion of the metasedimentary unit and outcrops above the southern most edge of the dense substratum underlying the Quetico gneisses.

A tectonic model put forward synthesizes the available information regarding Archean crustal evolution and the data from this study.  The proposed model consists of a basin-like structure (Quetico subprovince) which received sedimentary and volcanic debris from a mature volcanoplutonic terrane to the north (Wabigoon subprovince).  Additional sedimentation into the basin was provided from the less mature volcanoplutonic terrane to the south (Shebandowan subprovince).  Subsequent deformation accompanied by high grade metamorphism resulted in a general upwarping of the basin, producing the structures now observed in this part of the Quetico subprovince.

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The lithology of the Late Quaternary lacustrine sequences of five lakes in the North Bay area differs from one lake to another.  However, chronostratigraphically equivalent sections of cores taken from the same lake do show similarities in mean grain size, sand percentage and organic and carbonate carbons.  The lithology of the Late Quaternary fiord sedimentary sequence of McBeth Fiord, Baffin Island exhibits a slightly higher sand content and lower organic carbon content than the North Bay lacustrine sediments.

The magnetic mineral grains deposited on the bottom of lakes and fiords tend to align in the direction of the earth's magnetic field at the time of deposition creating a remanent magnetic field in the sediments.  The sedimentary sequences of lakes in the North Bay and McBeth Fiord, Baffin Island areas provides a record of the direction and intensity of the earth's magnetic field for these regions during the Late Quaternary.  The declination and inclination values of oriented samples taken from soft-sediment cores of the Late Quaternary lacustrine sequences of the North Bay area and the fiord sequences of McBeth Fiord can be compiled into paleodeclination and paleoinclination logs.  The oscillations of the relative paleodeclination logs show a similar character for cores taken from the five lakes and the fiord as do the paleoinclination logs.  Marker horizons picked on the character of either the paleodeclination or paleoinclination logs provide a method for chronostratigraphic correlation from one core to another within the North Bay area and also for the McBeth Fiord area.

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The upper sands of the discontinous Halfway Formation to the northeast of Fort St. John were formed as barrier islands deposited perpendicular, or nearly perpendicular to the dip of the paleoslope of the Western Canadian Sedimentary Basin.  These upper sands of the area of study were deposited during a transgressive phase of the Triassic sea to the northeast, and formed the basal unit of an onlapping sequence comprising the Halfway and the Charlie Lake Formations that disconformably overstepped the erosional surface on the silty dolomite of the Doig Formation.  The Weasel sand body was deposited during a pause in the transgression, and then was submerged by a rapid rise in sea level.  The Wildmint to Beatton barrier islands trend was deposited during a second pause in the transgression.  These barrier islands would appear to have been deposited under arid conditions resulting in restricted lagoonal environments.  The lower sands of the discontinuous Halfway Formation which only occur at a few locations in southern Willow and Wildmint, would appear to have resulted from tidal inlet action that eroded channels into the Doig Formation below the base of the upper sands forming the barrier island complex.  These later were filled with sand.  Then this barrier island trend was submerged by renewed transgression of the Triassic sea.  The source of the sediments comprising the discontinous Halfway Formation probably was to the north and northeast of the area of study. 

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The Quetico fault is a major transcurrent fault in the southern Superior Province of the Canadian Shield.  Along part of its length the fault forms the boundary between the Quetico and Wabigoon subprovinces.  Dextral motion on the fault is indicated by dextral microfaults and approximately asymmetrical quartz c-axis petrofabrics.

The fault comprises a zone of dynamically metamorphosed rocks - primarily mylonitic rocks with some cataclastic rocks and pseudotachylite.  A transition from predominantly ductile deformation to brittle deformation occurred during the time the fault was active.

The ductile deformation of quartz within the fault zone is the result of crystal-plastic processes, predominantly slip on prism planes in the a-direction and slip on rhomb planes in the a-direction, accompanied by dynamic recovery and syntectonic recrystallization.  Feldspar grains are commonly deformed in a brittle manner by fracture processes.  Particulate flow appears to have made a significant contribution to deformation in the fault zone.

The harmonic mean of deformed grain axial-ratios and strain determinations by the all object-object separations method indicate that flattening strain is predominant within the fault zone.  The magnetic susceptibility anistropy ellipsoid is also flat-shaped and coaxial with the strain ellipsoids.  The characteristics of microfaults and folds within the fault zone indicate that flattening may have been accompanied by or followed by shearing.  The harmonic mean of deformed quartz grain axial ratios yields a minimum strain estimate of 130% extensions in X, 58% extension in Y, and 71% shortening in the Z direction.

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Detailed mapping was carried out in the Shebandowan Lakes area and eastward to the Kaministiquia River to study the structural and stratigraphic relationships between the Keewatin and Timiskaming rocks (herein referred to as Keewatin-type and Shebandowan-type, respectively, to avoid connotations of time-stratigraphic equivalence with type areas) of the region.

It is believed that the Shebandowan-type rocks are younger than the Keewatin-type rocks.  Although no actual contact between the two has been seen in outcrop in the study area, the trend of their contact is discordant with the trend of cleavage in the Shebandowan-type rocks.  This, along with the less recrystallized appearance of the Shebandowan-type rocks, and the presence of clasts of jasper in conglomerates of the Shebandowan-type sequence similar in appearance to the jaspilitic iron formation interbedded with the Keewatin-type mafic volcanics, leads to the conclusion that an unconformity separates the two groups of rocks.  Recent geochronological work on some of the rocks in the region, carried out by the Ontario Geological Survey, supports this theory.

The macroscopic, microscopic and sub-microscopic structure of both groups of rocks was examined in detail.  The minor structures seen in outcrop, the examination of thin sections, scanning electron microscope work, and the determination of the magnetic fabric of the rocks all show that the rocks in the present study area contain a single, penetrative, primary cleavage, which has a consistent trend across the whole area.  The regional structural picture which emerges from the data is characterized by close-spaced, isoclinal folding with sub-vertical fold axial traces trending roughly east-west.  Local variations exist in the eastern portion of the study area where more widely-spaced and open folding is more common.  No evidence of a second, significant period of deformation in the present study area has been found.

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Zn-Pb-Ag mineralization at Nanisivik, northwest Baffin Island, is hosted by Proterozoic, laminated dolostone of the Society Cliffs Formation.  Mineralization of the Main Orebody is highly variable in terms of texture and mineralogy exhibiting both replacement and open space filling textures.  Sulfides are generally coarsely crystalline and banding, consisting of interlayered pyrite, sphalerite, galena and sparry dolomite, is common along the margins of the Upper Lens of the Main Orebody.  The eastern and central portions of the Upper Lens are characterized by laterally extensive mine units, which are distinguished on the basis of texture and mineralogy.  Contacts between units are generally sharp.

The physical and chemical parameters responsible for the textural and mineralogical variations have been evaluated through a study of fluid inclusions, sulfur isotopes and ore mineralogy.  Fluid inclusion homogenization temperatures from simple, two-phase primary and pseudo-secondary inclusions in sphalerite and sparry dolomite gangue indicate initial temperatures of ore formation from 150-210°C in the eastern Upper Lens when the estimated pressure of ore formation is taken into consideration.  The temperature of ore formation decreased to 100-150°C in the western portion of the Upper Lens.  Freezing studies indicate that the ore-forming fluid was a brine containing 20-37 equivalent weight percent CaCl₂.  The sulfur isotopic compositions of late and main stage pyrite crystals range from δ³⁴s = +27.4€ to + 28.0€, suggesting relatively constant temperature, fluid source and dominant sulfur species in the ore fluid during ore formation, providing there has been no subsequent re-equilibriation of sulfur isotopes.  The iron content of sphalerite varies from 14 mole % to 0 mole % from crystal centers to rims respectively, corresponding to well developed colour zonation.  Sphalerite iron contents constrain the oxygen activity of the ore fluid from 10^-46 to 10^-41 at 200°C during sphalerite precipitation.  The best developed zoning and, thus, the highest oxygen activities occur within sphalerite adjacent to carbonate wall rock.  Under high oxygen activities, conditions were favorable for the generation of sulfanes considered necessary for precipitation of marcasite.  X-ray diffraction studies indicate that primary marcasite has inverted completely to pyrite.  The stability of the simplest sulfane, H₂S₂, constrains the maximum allowable pH of the ore fluid at the time of marcasite precipitation to 5.0.  The presence of interbanded marcasite pseudomorphs and sparry dolomite indicate that the ore fluid fluctuated around pH = 5.0.

Comparison of solid organics extracted from the Society Cliffs dolostone to bitumen associated with mineralization suggests that organics within the host formation have played a role in sulfate reduction.  The model of ore formation therefore proposed involves the in situ reduction of a hot, saline, metal-bearing ore fluid by hydrocarbons liberated by the replacement and dissolution of wall rock.  Sulfate reduction was probably concentrated at the wall rock orebody interface along a replacement front that migrated away from the orebody.  Banding was likely the result of repetitive sulfate reduction, metal precipitation and wall rock dissolution in response to the pulsatory influx of ore fluid.  Gross textural and mineralogical variations are probably a result of slight variations in the oxidation state of the ore fluid, the availability of H₂S and, to a lesser extent, temperature.

A copy of the thesis can be downloaded here