Three granitic dike swarms of peraluminous composition within the southern North Caribou Terrane display both compositional and textural zoning.  Two distinct mineralogical phases can be recognized within each swarm: a granodiorite and tonalite phase at 6k Ridge and Lake 282 drill core, and a monzogranite and granodiorite phase at Cigar Lake.  In addition to mineralogical zoning, textual zoning is also present within the dikes at each of the locations.  A fine-grained border zone next to the contact with the host rock consists predominantly of albite and quartz.  Secondly a medium-grained wall zone with albite, quartz, microcline ± tourmaline that extends inward from the border zone and into the dike.  Finally, a coarse-grained quartz, albite, microcline, muscovite ± biotite ± garnet zone extends inward from the wall zone into the core of the dikes.  Structures such as internal foliation parallel to the adjacent host rock, as well as pinch and swell structures, suggest that the dikes and host rocks were still ductile when they were emplaced and that timing of emplacement was syn-orogenic.  Trace element geochemistry shows significant alteration within the dikes, as well minor assimilation of the adjacent host rock.  ɛNd values of -0.9 to -6.0 suggest enrichment of the magma from a crustal source through partial melting prior to emplacement.

The Steepledge Intrusion is an irregularly shaped mafic to ultramafic layered intrusion located north of Thunder Bay, Ontario.  It is recognized as part of the early intrusive phase of the 1.1 Ga Midcontinent Rift.  Light rare earth element enrichment and fractionation of the heavy rare earth elements is consistent with other early Midcontinent Rift-related intrusions and is interpreted to indicate a primitive mantle source.

The stratigraphy of the Steepledge Intrusion can be divided into seven zones on the basis of internal variations in petrology and geochemistry.  The Hybrid Zone is a quartz leucogabbro containing quartz rich inclusions assimilated from the Quetico Basin country rocks.  The Upper Layered Zone is a weakly layered sequence comprised of cm-scale layers of alternating troctolite and olivine gabbro.  A gradational contact exists between the Upper Layered Zone and the underlying Upper Gabbroic Zone.  The Upper Gabbroic Zone comprises a sequence of unlayered olivine gabbro containing oikocrystic clinopyroxene which poikilitically encloses fine-grained cumulate olivine.  The Middle and Lower Layered Zones comprise a 70m thick unit of olivine gabbro to olivine melagabbro with increasing olivine content at depth.  Centimetre-scale layering within the Middle and Lower Layered Zones are composed of alternating bands of olivine-cumulate peridotite and pyroxene-cumulate-pyroxenites. A transition from fine-grained olivine melagabbro to coarse-grained lherzolite marks the upper contact of the Coarse Peridotite Zone.  The Coarse Peridotite Zone is characterized by coarse-grained cumulate olivine, intercumulate plagioclase and megacrystic orthopyroxene that enclose the cumulate olivine.  The Basal Peridotite Zone is an approximately 130m thick zone of monotonous, very-fine grained to fine-grained peridotite.  Geochemical analysis has identified the presence of cryptic layering throughout the entirety of the intrusion and is interpreted to be the resulted of multiple pulses of more primitive magma causing cyclic variations in the magma composition within the intrusion.

Sulphur isotope values for the Steepledge Intrusion range from -3.0 to -0.8 and are consistent with a mantle-derived magma with no external input of sulphur.  Localized contamination by the host Quetico metasiltstones is concentrated in the Hybrid Zone, however, the overall negative Nb anomaly observed may represent an earlier, more pervasive contamination of the parent magma at depth.

The Nipigon Embayment encompasses ~10,000 km³ of magmatism in an area of 200,000 km² that stretches from Lake Nipigon to the southwestern side of Thunder Bay. The majority of the intrusive units within the embayment have been classified as Nipigon Sills. Diabase sills at Hele, Tease Lake and two at Thread Lake exhibit textures typical of Nipigon sills. All four sills contained three distinct textures throughout; a chill zone at contacts, a medium-grained to coarse-grained subophitic zone, and a coarse-grained ophitic texture, with Hele and Tease Lake also displaying of a fourth type of texture in the form of a megacrystic ophitic zone. The crude layering that is seen throughout the sills is evidence of a multiple pulse system. All sills maintained consistent mineral modal abundances down hole; Hele averaged 55% plagioclase and 45% pyroxene; Thread Lake 60% plagioclase and 40% pyroxene; and Tease Lake 55% plagioclase and 45% pyroxene.

Plots of Th/Yb_pm versus Nb/Th_pm subdivide the sills into distinct subclasses. Hele, Thread Lake 2 and Tease Lake all plot within the Nipigon 1 suite whereas Thread Lake 1 represents a Nipigon 2 Suite. This classification is based on the emplacement and contamination history of the sills. Hele, Thread Lake 2, and Tease Lake represent a more primitive magma, whereas Thread Lake 1 is derived from a less primitive magma. Thus giving evidence of differing contamination histories.

The occurrence of red granite and quartz diabase along the Jarvis Bay Road, in the Jarvis District of Thunder Bay, Ontario was found to be a tholeiitic Logan intrusion, formed primarily by the processes of fractional crystallization and associated assimilation. This is observed in the identification of fractionated plagioclase clusters, possessing a relative Sr, and Eu enrichment, as well as plagioclase compositions  and other mafic phases in disequilibrium  relative to the surrounding rock  (more An-rich, allowing greater substitution of Sr²⁺ for Ca²⁺).  Assimilation of upper crustal rocks in conjunction with fractionation processes can be shown on a primitive mantle normalized multi element diagram, where a relative Nb trough, and a consistent enrichment in LREE is found in all samples of the red granite and quartz diabase.

The mechanism that produced the granophyric intergrowths is observed to involve the interaction of a late stage volatile phase. This is shown through the pervasive iron oxide alteration, forming irregular patches, staining feldspar phenocrysts (in the red granite most notably), as well as replacing and rimming anhydrous mafic phases. The presence of abundant volatile phases such as hornblende, and biotite in all samples collected also support this interpretation. 

It is important to be aware of fluoride concentrations in drinking water and to ensure levels are adjusted to acceptable levels because if the levels are not within the suggested range as stated by the Ontario Drinking Water Standards, serious health complications may arise.  Water from ten private homeowner wells was sampled for fluoride concentrations (amongst other parameters) and data was also used from the Provincial Groundwater Monitoring Network.  These samples were all taken in different types of bedrock in Thunder Bay and the surrounding area which included: the Rove Formation, the Gunflint Formation, metasedimentary, diabase, massive granite, intermediate intrusive, mafic metavolcanic, and the Sibley Goup.  There were four characteristics of the bedrock which were believed to have the biggest influence of fluoride concentration which were calcium concentration, pH levels, presence of fluorite, and depth of the well.  Based on interpretation of my data and the available geological information, out of these four influences on the concentration of fluoride, it is likely that wells which are most susceptible to having high levels of fluoride are those which encounter fluorite mineralized vein systems.  These systems are most common in areas underlain by the Rove and Gunflint Formations as well as diabase.  However, this is a small data set and although it does seem like the Rove and Gunflint Formations as well as diabase most commonly have higher fluoride levels, it is still suggested that homeowners who use well water for drinking have it tested for regularly as reliable data should be based on a larger scale and during a longer time frame.

The Grassy Pond sill lies in the Caribou Lake greenstone belt of the Wabigoon subprovince of the Superior province. It was exposed in a Landore Resources Ltd. mineral exploration trench about twelve kilometres east of Armstrong, Ontario. It is composed of a megracrystic plagioclase (individual crystals 1-15 cm across) anorthosite intruding mafic pillowed to massive volcanic rocks; this occurrence provides an excellent opportunity to add to the limited research into Archean megacrystic anorthosites. The Grassy Pond sill is c omposed of primarily plagioclase megacrysts of high anorthite content (An₆₅ to An₈₅) with associated mafic matrix composed of replacement minerals, chiefly amphibole, with calcite and epidote group minerals. A cogenetic relationship between all three units is suggested as the spatially associated mafic volcanic rocks and gabbros share similar mineral assemblages and chemical signatures. Detailed field mapping at outcrop scale and petrographical and geochemical work was performed in order to accurately determine the relationships between the units. The contact between the anorthosite and gabbro is often gradational (decreasing concentration of plagioclase megacrysts and increasing coarse grained mafic matrix). The gabbro and volcanic rocks have a much different relationship. The gabbro has intruded the volcanic rocks along selveges and through more massive sections and lacks well defined chill margins. This relationship suggests that the volcanic rocks might have been warm at the time of intrusion. This could imply that gabbros and anorthosites have intruded their own volcanic pile. These relationships coupled with the similar trend in geochemical signature suggest that the anorthosites and gabbro served as the subvolcanic source for the associated volcanic rocks. The previously unclassified Grassy Pond sill shares similar lithologies and geochemical pattern with the Bad Vermilion Lake calcic megacrystic anorthosite complex, as well as other Archean anorthosites and therefore is recognised as an Archean calcic megacrystic anorthosite.

The Shrimp Lake intrusion is part of the suite of TTG-like granitoid intrusions found throughout the Superior Province.  Although originally classified as a trondhjemite, major element geochemistry of the Shrimp Lake intrusion, specifically SiO₂, Al₂O₃, MgO and Fe₂O₃ abundances paired with specific Yb and La/Yb values suggest a TTG rock suite.   

The Shrimp Lake intrusion is interpreted to be synvolcanic with the intermediate metavolcanics and the Hewitt Lake intrusion which has been dated at 2743±2 Ma and has been taken to be representative of all three synvolcanic intrusions in the North Spirit greenstone belt, and 2735±10 Ma for the Hewitt volcanic assemblage.  The three synvolcanic intrusions of the North Spirit Lake greenstone belt show similar compositions of porphyritic granodiorite-tonalite with abundant plagioclase phenocrysts in a fine-grained groundmass of quartz, plagioclase and K-feldspar.  The age of the Shrimp Lake intrusion is interpreted to be slightly younger relative to the other two intrusions because of the lack of deformation and alteration observed in the Hewitt Lake and Makataiamik Lake intrusions.

Mineralization within the Shrimp Lake intrusion is found in two outcrops: one containing massive sulphides of pyrite, pyrrhotite chalcopyrite and sphalerite.  The other is similar in composition, however alteration is less intense with the plagioclase phenocrysts preserved in the host rock indicating a granodiorite-tonalite host.  The host rock to the massive sulphides is interpreted to be the granodiorite-tonalite, however intense alteration and the presence of a mafic xenolith from an adjacent volcanic assemblage make it difficult to confirm this.  Geochemical analysis of the rock show a typical granitic trend comparable to the rest of the intrusion.   

The magmatic source for North Caribou superterrane TTG suites is typically derived from a depleted mantle with minor contamination from old remelted crust.  Formation of these TTG's is commonly associated with oceanic arc-type settings, however, the lack of necessary data for the Shrimp Lake intrusion prevents it being characterized in this way.

Avery is currently working for Fladgate Exploration in Thunder Bay

For more details about this thesis contact Dr. Peter Hollings

The Marshall Lake property is a copper-zinc-rich volcanic-hosted massive sulfide (VHMS) deposit located approximately 255km northeast of the city of Thunder Bay, Ontario.  The study area consists of a series of Archean rocks such as volcanics that range in composition from mafic to felsic, and sedimentary units, both clastic and chemical.  These are intruded by Archean intrusions like the Marshall Gabbro and the Summit Lake Pluton, and Proterozoic mafic dikes.

In the past, most work in the area has been concentrated on the northern part of the sequence where most of the mineralization is known to occur.  In 2006, East West Resource Corporation acquired the property, and since this time there has been an increased effort to understand the deposit as a whole; not only the area proximal to the mineralization, but also the distal rocks to the south. 

Mapping and sampling in the area near the southern boundary of the felsic volcanics can reveal patterns related to the distribution of the hydrothermal alteration.  It was noted during this study that the rocks from near the volcanic-sedimentary boundary are characterized by the assemblage garnet-amphibole and are anomalously rich in magnesium and potassium, while depleted in silica and sodium.  This is an important observation since this is a signature that one would expect to see only in certain places in the VHMS model.

Nathan is currently working for East West Resources in Thunder Bay as a project geologist

For more details about this thesis contact Dr. Mary Louise Hill

Kooyak Island is small, kilometer-sized island located about 75 km off the northeastern coast of the Boothia Mainland, Nunavut.  The Boothia Mainland lies within the Rae Domain of the Western Churchill Province; a polymetamorphic, multiply-deformed Archean terrane flanked by Palaeoproterozoic orogenic belts.  Kooyak Island is dominated by granulite facies gneissic rocks of pelitic origin.  Peak metamorphism reached the second sillimanite zone with conditions of 750-850°C, 7-9 kbars.  Retrogression is characterized by a chlorite-sericite assemblage with conditions of 525-575°C, 3-5 kbars.  Within the granulites are numerous northeast-trending mylonite zones characterized by sinistral ductile shearing.  Shearing began during retrograde metamorphism and finished before the chlorite-sericite assemblage formed.  Two deformational events shaped the island's structure.  The first, shown by NNW-SSE-trending crenulating folds, is overprinted by the second, shown by northeast-trending large-scale folds which dominate the structural grain of the island.

The structure and metamorphic events of Kooyak Island correlate with that of the Boothia Mainland and Rae Domain described in literature.  Prograde metamorphism and the first deformational event correspond to the crustal thickening compressional event that affected the Rae Domain at 2.43-2.35 Ga.  This reflects thermal reworking during the Arrowsmith orogeny.  The second deformational event on Kooyak Island corresponds with the Rae Domain's compressional event related to the Trans-Hudson orogen at 1.82-1.80 Ga.  The mylonites also occur regionally with syn- to late-shear pegmatites of assumed Palaeoproterozoic age and are thought to represent the last stages of crustal stabilization.

Dan is currently working for Pacific Northwest Capital Corp. (PFN) as a project geologist

For more details about this thesis contact Dr. Mary Louise Hill

The Elora Property hosts to two past producing gold mines and is located roughly three kilometers from the historical town of Goldrock on the northeastern end of Upper Manitou Lake. The Elora Property lies in the western portion of the Wabigoon Subprovince in the Manitou-Stormy Lakes metavolcanic-metasedimentary belt. The property falls mostly within the tholeiitic to calc-alkaline, predominantly metavolcanic flows of the Pincher Lake Group rocks; except for the westernmost part of the claims, which lie within the stratigraphically lower calc-alkaline, predominantly pyroclastic metavolcanic rocks of the Upper Manitou Lake Group.

Transmitted light microscopy combined with whole-rock, trace-element, and rare earth element geochemical data were used to identify the principal rock units and associated hydrothermal alteration assemblages proximal to gold mineralization at the Jubilee Zone. Timing of gold mineralization was also characterized in the Jubilee Zone.

Mafic metavolcanic rocks were continuous into the section of drill core studied, whereas rocks logged as metasedimentary could not be conclusively identified as such. However, the presence of pyrrhotite, fine grained carbonaceous material, a lack of gold mineralization, and primitive mantle plots contrasting with those of mafic metavolcanic rocks all suggest that there is a lithological contrast of some sort with the mafic metavolcanic rocks. However, it is unclear what the protolith of these rocks was.

On the scale of the geochemical study there were no reliable vectors to gold mineralization. Na2O was the only element that displayed a noticeable and somewhat gradual increase towards the Jubilee Zone from both above and below. Other elements do not exhibit enrichment or depletion towards the Jubilee Zone, but this may be due to the short interval of core studied. Geochemical discrimination plots used to distinguish lithologies provided some insights into the tectonic setting, but were inconclusive due to key elements being below detection limit.

Based on the relationships observed in thin section, gold mineralization could have occurred during a either a single or multiple mineralizing events. Free gold is encapsulated in pyrite and may suggest a single pyrite-gold mineralizing event. An earlier pyrite-gold mineralizing event followed by a later gold-bearing quartz-carbonate fluid would also create the relationships observed in thin section. Lastly, partial assimilation of existing gold-bearing pyrite by a barren quartz-carbonate fluid would remobilize gold into fractures and boundaries of pyrite grains.

Steve is currently working for his MSc at Lakehead University

For more details about this thesis contact Dr. Peter Hollings