New expansion along Highway 11/17 east of Thunder Bay, Ontario exposes faults and damage zones that cut through and displace the Gunflint Formation of the Animikie Group, the underlying Archean basement rock, and the basal unconformity between them.  Observations and stereographic projections were used to characterize outcrop-scale deformation along a curved road-cut on a hill approximately 1km long and covering an increase in elevation from west to east (where the unconformity is exposed) of about 65m.  The Highway 11/17 road-cut exposes a fault zone network that has accommodated a minimum of 60m of vertical displacement and unknown horizontal displacement.  Two sets of well-preserved slickenlines record normal oblique sense movement on the fault zone.  A void-filling calcite vein system is exposed in conjunction with the fault systems and is associated with brecciation.

Calcite crystals reach up to 10cm in diameter where larger voids are filled.  At least two major fault zones with damage zones at least 1m wide are exposed at the study site and are seen at the far east and far west of the road-cut.  The Eastern Fault Zone (EFZ) has an average strike and dip of 071°/72° cutting through both Archean basement rock and Gunflint Formation.  The Western Fault Zone (WFZ) average strike and dip is 067°/65° and cuts through Gunflint Formation rocks.  Two relatively minor reverse faults strike 345° and dipping 48° to 58° cut through the Gunflint Formation about 80m southwest of where the WFZ first appears.  The relationship between EFZ and WFZ is obscured by an oblique fault cutting through Archean rock between them with an average strike and dip of 040° and 60°.

The site is a potentially important study location for understanding fault/fluid interactions and how extensional faulting can accommodate fluid transportation.  All major extensional features in the study area have a roughly northeast strike which aligns well with the orientation of the Mid-Continent Rift to the southeast suggesting that this fault zone is associated with extension ca.  1Ga. 

The Paint Lake Deformation Zone is an east-west trending lineament that extends approximately 40 km east of Lake Nipigon, in theWabigoonSubprovincein the Superior Province of Ontario.  Sage Gold Inc. owns thePaintLakeproperty, host to a shear zone hosted gold occurrence at a major lithological contact.  This lithological contact occurs between the Northern Sedimentary Unit (NSU) and Northern Volcanic Unit (NVU) of the Beardmore-Geraldton Greenstone Belt, from north to south respectively.  Mapping of the property, combined with transmitted light microscopy and geochemical analyses revealed the Northern Sedimentary Unit to be represented by polymictic metaconglomerate, and the Northern Volcanic unit to consists of steeply-dipping pillowed to massive tholeiitic basaltic flows and interleaved lenses of intrusive high-Fe tholeiites, with one occurrence of a calc-alkaline dacite tuff.  A total of four rock suites were identified on the property and later confirmed using geochemical data.  An arc/back-arc environment was characterized as the tectonic environment, within which the volcanic units were deposited.

The contrast between competent and incompetent rock units, and their associations with ductile and brittle structures is integral to the presence of alteration and mineralization.  Gold associated with pyrite occurred most often at or adjacent to lithological contacts between rocks differing competencies.  This idea can be examined on various scales, from the regional scale of thePaintLakedeformation zone and its relation to the contact between the NSU and NVU, to the outcrop scale in which mineralized quartz veins occur within contacts of differing lithons of rock.  Significant contrasts between the rock units are important, otherwise there might not be enough opportunity for considerable gold mineralization to occur.

Microstructural analysis provides evidence of significant ductile deformation concentrated along the Main Break, in Kirkland Lake, ON.  The Main Break is an east-west striking mineralized fault system that has sustained multiple gold mines since its discovery in 1911.  It is found in the southern Abitibi gold belt on Kirkland Lake Gold Inc.’s Lakeshore Mine property, which is a structurally controlled orogenic gold deposit.

Oriented samples for microstructural analysis were collected from two new 1-meter long channels across the Main Break spaced eight meters apart.  Samples were examined in transmitted and reflected light microscopy.  Evidence of ductile deformation by dislocation creep to produce mylonite, inclues porphyroclasts of potassium feldspar in an extremely fine-grained matrix, mineral alignment, and undulatory extinction and subgrains in potassium feldspar; as well as lenticular aggregates of feldspar and muscovite showing dextral shear sense.  Dislocation creep occurs in feldspar during ductile deformation at temperatures in the amphibolite facies of metamorphism or higher, which puts deformation of the Main Break at temperatures above 400°C.

Sericite aggregates replacing potassium feldspar likely enhanced grain softening during this ductile deformation process.  Sericite as well as evidence of pressure solution along grain boundaries indicate the presence of a hydrous fluid during deformation.

Ductile deformation will produce porphyroclasts with penetrative foliations wrapping around them.  Such porphyroclasts would normally be explained by a difference in rheology, however, even in monomineralic rocks it is possible to have adjacent grains deforming by different mechanisms.  These different responses could be controlled by variations in crystallographic orientation of the grains where the slip planes are favorably oriented for slip in one grain but in a hard orientation for surrounding grains or simply different sized grains of the same mineral accommodating deformation by different mechanisms.  The most significant evidence of simultaneous brittle-ductile deformation is a potassium feldspar porphyroclast with strong undulatory extinction and subgrains in one half of the grain and microfractures in the other half.

It is concluded that the Main Break is a narrow ductile shear zone with minor brittle deformation.

The McKenzie granite is an approximately 18 km igneous intrusion within the Quetico Subprovince, located 20 km northeast of Thunder Bay, Ontario. Petrologic and geochemical data has been used to classify the McKenzie granite as dominantly S-type. The intrusion is classified as a quartz monzonite with assemblages characterized by muscovite+biotite±sphene±hornblende. The McKenzie granite contains a peraluminous geochemistry with SiO₂ contents ranging from 63.8-68.2% along with enrichment in light rare earth elements, fractionated heavy rare earth elements, decreasing trends of major oxides, transition metals and high field strength elements and scattered large ion lithophile elements due to remobilization during chlorite, sericite, and carbonate alteration. Formation of the McKenzie granite was likely similar to the model proposed for the later stages of the genesis of the Dog Lake Granite Chain, which involved partial melting of the mantle wedge beneath the Wawa-Abitibi island arc. The mafic melt produced from the subducting oceanic lithosphere would underplate the Quetico Subprovince leading to formation of granitic I-type melts via fractionation. These melts would then rise through structural conduits at the Quetico-Abitibi border. The majority of the underplated melt would contribute to the production of the S-type granites that are normally seen in Quetico Subprovince. These S-type melts formed from the partial melting of the overlying metamorphosed sedimentary rock and may have been allowed to interact with I-type melts. This would allow for variations in geochemical and petrological data that is not common for standard S-type granites.

The Sibley Peninsula is an approximately 300km² land mass that projects southwest into Lake Superior, approximately 30km east of Thunder Bay, Ontario, Canada.  The geology of the peninsula consists of Southern Province assemblages, including intrusive rocks of the ~ 1.1Ga Midcontinent Rift.  Due to their location within Sleeping Giant Provincial Park, the Sleeping Giant Sill (SGS) and numerous dikes on the Sibley Peninsula have not been geochemically classified.  With permission from Ontario Parks, this study was undertaken to 1) classify the SGS and dikes of the Sibley Peninsula based on their geochemistry and 2) determine relative ages of the SGS and dikes of various orientations.

Thirty-four dike samples and five SGS samples were collected and analyzed for whole rock geochemistry at the Geoscience Laboratories.  Dikes with three different orientations were sampled: 1) ~70˚ striking dikes, which represent the majority of the dikes on the peninsula, 2) two 110˚ striking dikes and 3) two 29˚ striking dikes. The ~70˚ striking dikes were classified as Pigeon River Dikes based on Mg# versus TiO₂and Gd/Yb_n versus La/Sm_n discrimination diagrams. The 110˚ striking dikes plotted near or within fields defined by Hollings et al. (2007a) for ultramafic intrusions of the MCR.  Despite geochemical similarities, the 110˚ strike directions of these dikes make them spatially unsuitable as feeders to any of the ultramafic assemblages found in the Nipigon Embayment, northeast of the study area.  The 29˚ striking dikes plotted in the field defined for mafic / ultramafic sills and intrusions on the Mg# versus TiO₂ plot and in the field defined for Nipigon Sills on the Gd/Yb_n versus La/Sm_n diagram. Although these dikes were geochemically similar to Osler volcanic rocks of the neighbouring Black Bay Peninsula, they were just 18 and 20 cm wide and tapered eastward, making them unlikely candidates as feeders to Osler volcanic rocks.  Using Mg# versus TiO₂ and Gd/Yb_n versus La/Sm_n discrimination diagrams, the SGS was determined to be of Logan affinity and now represents the easternmost recognized Logan Sill.  The thickness of the SGS was found to be 194 metres, thicker than any other previously recognized Logan Sill.

 Cross-cutting relationships indicate that the ~70˚ striking dikes are younger than both the SGS and the 29˚ striking dikes.  The SGS and the 29˚ striking dikes had lower silica and higher magnesium weight percentages than the ~70˚ striking dikes, which may suggest that more primitive magmas were locally emplaced earlier. The ~70˚ striking dikes displayed the largest negative niobium anomalies which could indicate an increase in contamination of magma sources over time, since these dikes were the youngest intrusions observed in this study.

The SGS was exclusively observed on the Sibley Peninsula's southern tip where it has a lowermost contact with Rove Formation shale.  The SGS is unexpectedly absent in drill core taken from the peninsula's northeastern shoreline from which the thickness of the Rove Formation was determined to be ~ 610 metres.  This can be explained by the timing of the Silver Islet Fault and the glacial erosion that removed the SGS from the northern portion of the peninsula and shaped the Sleeping Giant landform on the peninsula's southern terminus.

The Georgia Lake pegmatite field is located in the Quetico Gneiss Belt of the Superior Province.  Spodumene-bearing and subordinate beryl-bearing pegmatites of the Georgia Lake area are flanked to the south and east by an extensive granitoid terrain, which previously has not been subdivided.  Granitoids of the immediate Georgia Lake area were investigated in conjunction with rare-element pegmatites to determine the character of the granitoids as parental intrusions to rare-element pegmatites.  The granitoids include two-mica leucogranites occurring as a large plutonic mass south of the pegmatite field and as smaller satellitic intrusions, the Kilgour Lake Group granitoids centered on a small gabbroic-metagabbroic unit near Kilgour Lake tonalitic sills dispersed throughout the pegmatite field.  The distinction of the three types of granitoids was made on the basis of field observations, petrography and analytical geochemistry.  Two-mica leucogranites and tonalitic sills were derived as partial melts of pelitic metasediments and metagreywacke, respectively.  The Kilgour Lake Group granitoids were presumed to be the products of fractional crystallization of a mafic melt generated in the upper mantle or lower crust.

Mineralogical studies were carried out on perthitic microcline, tantalite-columbite and Sn oxide minerals from rare-element pegmatites.  Results indicate that perthitic microcline in all pegmatites is of the maximum microcline structural state, tantalite-columbite minerals occur in a partly to completely disordered structural state and the dominant Sn oxide mineral is staringite.

Division of spodumene-bearing rare-element pegmatites into Southern, Central and Northern Groups was made on the basis of internal textural variations, mineralogy and differences in geochemistry of perthitic microcline and muscovite.  The Southern Group consists of one pegmatite which is unique to the Georgia Lake pegmatite field with respect to development of mineralogical zones and strong internal fractionation of Rb and Cs.  Central Group pegmatites are linked by a fractionation trend, with respect to Rb and Cs, across the group.  A similar fractionation trend is not observed across the Northern Group pegmatites.  The pegmatite groupings reflect different modes of source fluid derivation, although all pegmatites of the Georgia Lake area originated as the result of a common anatectic event responsible for the intrusion of two-mica leucogranites.  Central and Southern Group pegmatites were derived from low viscosity fluids differentiated from granitic melts, while Northern Group pegmatites are presumed to be the products of fluids generated by direct anatexis of metasediments.

An occurrence of corona structures, resulting from a reaction between olivine and plagioclase to form a distinct, mineralogically zoned reaction rim between those two phases, was observed near Killala Lake in Northwestern Ontario.  These corona structures were seen to occur in a large ultramafic body, composed primarily of olivine, located in the midst of a terrain comprising granite gneiss and migmatite.  This body was veined by quartzo-feldspathic material that provided the plagioclase necessary for the reaction to occur.

A petrographic study was undertaken to determine the mineralogy of the coronite.  As a result of this, four distinct zones were defined - a core zone, comprising the original ultramafic material; an inner reaction zone, consisting mainly of orthopyroxene with a bronzitic composition; an outer reaction zone, consisting of biotite, which fills the role of an aluminous phase, and the amphiboles hornblende and cummingstonite; and a zoine of plagioclase, primarily, representing the original quartzo-feldspathic material.

The coronite was analyzed by zone by x-ray diffraction methods to confirm the above mineralogy, and by atomic absorption to determine elemental distribution.  In this manner, Fe, Mg, Ca, Al were found to be the major elements present; Na and Mn are minor elements and Ni, As and Ba trace elements.  Since the Fe and Mg are assumed to have originated in the olivine and Ca and Al in the plagioclase, the distribution of these elements amongst the four zones suggests that some form of diffusion took place.

With reference to earlier work, it is therefore postulated that the olivine reacted with water under conditions of middle to upper amphibolite facies metamorphism, that also caused the gneissification and migmatization of the surrounding rocks, to form the orthopyroxene of the inner zone and release Fe and Mg.  These elements diffused across the original olivine-plagioclase interface to react with plagioclase and water to form the amphiboles; biotite required an introduction of K into the system.  Incoming water brought this K into the system, along with As, which formed brandtite (Ca_2, Mn (AsO₄).2H₂0) in the core zone.  Water also acted as a catalyst for the reactions involved, by suppressing pressure requirements in an isothermal system, and as means of increasing P₀₂So that magnetite, a ubiquitous phase in the coronite, could be formed.  Extensive subsequent alteration by serpentinization is noted in the coronite.

Late Archean lamprophyre dikes are common throughout the Superior Province of the Canadian Shield, and are associated with the late stages of Archean deformation in the Canadian Shield.  Accurate age constraints on the timing of this late metamorphism would benefit both the economic and the academic fields of study in this area.  Limited geochronology suggests an approximate age of 2696"2Ma (Corfu and Stott, 1986), for the shoshonitic volcanism in the Superior Province.

Oriented samples taken from dikes outcropping between Thunder Bay and Atikokan were used to make 60 oriented core samples.  These samples underwent anisotropy of magnetic susceptibility measurements (AMS) to determine the origin of the internal fabric and define the cryptic metamorphic fabric.

Subsequently, the samples underwent low temperature demagnetization (LTD), to minimize domain-wall effects on the remnant magnetism contained within each sample.  The samples were then treated to ten steps of thermal demagnetization (100°C - 550°C) with the remnant magnetization measured between each step.  The data acquired from the thermal demagnetization was examined and A-and B-components of magnetization were isolated by Principal Component Analysis (PCA).  The principle components of magnetization were then used to determine the paleopole positions on a geographical map and compared with the best known apparent polar wander paths (APWP) for the Archean and the Proterozoic.  From this, the ages of magnetization may be estimated as 2500 Ma for the A-component and 2400-2300 Ma for the B-component.

An Archean sequence of rocks is exposed along Highway 527, approximately 90 kilometers north of Thunder Bay.  This sequence consists of metasedimentary and metavolcanic rocks which have been affected by lower greenschist facies metamorphism.

Structural elements in the area are S-surface and folds.  S-surface are designated S₀, S₁, S₂, and S₃, while folds are designated F₁, F₂, and F₃.

Cleavage-bedding relationships delineate the hinge lines of F₂ folds.  Younging information projected onto the axial planar cleavage (S₂) of F₂ folds, results in reversals in the structural facing directions.  These reversals indicate that the cleavage developed in previously deformed rocks.

The overprinting of structural elements indicates that three deformational events (D₁, D₂, D₃) can be defined.

D₁ produced nearly vertical and, in part, inverted F₁ folds.  D₂ produced a set of F₂ folds which resulted in refolding of the F₁ structures.  D₃ produced kink bands and crenulations that resulted in folding of the F₁ and F₂ structures.

The quartz-hematite laminations of Mink Mountain, Northwestern Ontario have become the subject of some considerable controversy with respect to the origin of these laminations.  To date, two schools of thought exist regarding the origin of these laminations.  The first concept is that these laminations are the result of hot spring activity producing geyserites or sinter (Walter, 1972).  The second view is that the laminations constitute biogenic results of the growth and preservation of stromatolites.  This thesis presents considerable evidence that indicates the quartz-hematite laminations of Mink Mountain are more likely the result of stromatolite activity and subsequent preservation by cementation and burial.

The quartz-hematite laminations occupy the Upper Algal Chert member of the Gunflint Formation.  A seventy-eight metre long section of the Upper Algal Chert member of Mink Mountain was extensively sampled and these samples were studied in detail by tracings of orthogonal cuts of individual samples and documentation of data into Hofmann's (1969b) stromatolite classification.  In addition, evidence was found to indicate biogenic activity had occurred and that these laminations were formed on a littoral margin.

Through Hofmann's (1969b) classification, it was found that Forms A, C, D, E and G stromatolites exist at Mink Mountain (Hofmann, 1969b).  Microfossils are fairly abundant as filamentous rods similar in appearance to Gunflintia, indicating a biogenic component of the laminations.  The characteristics and configuration of the bioherms suggests these stromatolites thrived in and around tidal pools of a tidal flat on a grainstone substrate.  It is possible that the stromatolite organisms originally secreted carbonate but during the early of late stages of diagenesis, almost total silicification of the bioherms by jaspilitic chert took place.