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

The Former Steep Rock iron mine is host to numerous piles of mine waste and tailings impoundments of varying mineralogy and complexity. It is located approximately 6 km north-northwest of Atikokan, Ontario. The two tailings areas studied at the Former Steep Rock iron mine imparted separate and unique chemical signatures on both groundwater and surface water. The reason for the chemical difference lies within the mineralogy at each site, as the mineralogy of the tailings directly controls the chemistry of both groundwater and surface waters. Iron oxide rich tailings produced sulphate-rich groundwaters with near neutral pH; however, these levels sulphate dramatically decreased in adjacent surface water. Pyritic tailings produced acidic groundwaters and surface water elevated in sulphate, major cations, metals (Al, Fe and Mn). Key parameters are elevated in groundwater relative to downgradient surface water receptors.  This difference is a result of either precipitation of various mineral phases or dilution from groundwater.

Chris is currently working as Project Manager with True Grit Consulting Ltd. in Thunder Bay

For more details about this thesis contact Dr. Andrew Conly

The Bruce Formation is adiamictite succession located in the lower-most portion of the Paleoproterozoic Quirke Lake Group, of the Huronian Supergroup.  The Formation is exposed on the north shore of Lake Huron, and covers an area east of Sault Ste. Marie to east of Sudbury, Ontario, Canada.  This assemblage of rocks represents deposition on a passive margin after initial rifting and volcanism at approximately 2450 Ma (Fralick and Miall, 1989).  The passive margin succession is composed of three glaciogenic cycles beginning with outwash sandstones, which are overlain by glacial diamictites and capped by marine deposits.  The Bruce Formation is situated above the Mississagi Formation, which commonly shows evidence of extensive soft sediment deformation of its cross-stratified sandstones (Fig. A).  These are also more rarely intruded by clastic dykes (Fig. B), orientated perpendicular to bedding and filled with diamictite.  The upper contact with the Espanola Formation is sharp and conformable. The Espanola represents the oldest cap carbonate known in the worldwide geologic record and may be evidence of a snowball Earth event.  The Bruce Formation was studied in detail in an attempt to understand the ambient conditions that were present at the time of its deposition.  The study included measuring and describing 16 detailed sections in the field, plus petrological and geochemical analysis of samples collected from the field areas. 

Glaciogenic deposits can be either terrestrial or marine and marine deposits can be further divided into three lithofacies zones: 1) the grounding ice line zone, 2) the floating ice-shelf zone, and 3) the proximal iceberg zone.  Deposits in each of these environments have distinctive characteristics that, where present, can be used to identify the depositional setting.  Most outcrop areas in the sections studied consisted of massive diamictite that contained considerable quantities of sand and only scattered pebbles and cobbles.  The thickness of the assemblage of diamictites making up the Formation varied drastically from section to section,with three less than 10 meters thick and others hundreds of meters in thickness.  Within these massive diamictites are areas with more distinctive features.  Lenses and layers of moderately well-sorted sandstone are not uncommon.  In other portions of the section mud layers and mud wisps highlight layering in the diamictite, and at one location a fine-grained succession within the diamictite contained a dropstone (Fig. C).  If other dropstones exist in areas of the diamictite they are commonly impossible to recognize without layering to deform. However, where clay-rich layers and wisps are present in the diamictite they can be seen to bend under and be terminated by penetration of dropstones.  Layers of pebbles and cobbles in clast support were more rarely present (Fig. D).  These represent deflation lags produced by current activity removing the fine-grained material.  Rarest of all were flat bottomed and convex-up mounds of pebbles and cobbles in clast-support approximately one meter across, although a larger deposit of this type may also have been present in one section.  Similar features are produced in modern environments by uneven melting of icebergs causing flipping and dumping of melt-out debris on their surface.  In Pleistocene successions diamictite deposited near the grounding ice line commonly contains subaqueous outwash sand layers and lenses.  The diamictite deposited below floating ice shelves is generally massive but has features, such as mud-rich layers and sand-rich layers, which indicate current activity.  Dropstones and deflation lag layers can also develop in this zone. The proximal iceberg zone can also be dominated by massive diamictite, which has a lower clast concentration, and also contains dropstones.  The most conclusive evidence of the iceberg zone is the presence of mound shaped iceberg dumps, which are created when an iceberg overturns.  This implies that large segments of the glaciogenic succession were deposited under floating ice with open water present in the basin. The open water is necessary to develop current activity.  Although this data does not negate the development of a snowball earth at some point during this glacial period it does not support it.

A unit of mafic rock inDevonTownship, south ofThunder Bay, was mapped by Tanton (1931) and was termed Rove Formation Basalts.  Geul (1970) mapped this unit as aLogandiabase sill.  The primary objective of this study was to characterize the unit and test whether it is of intrusive or volcanic origin.  This was achieved by mapping the unit at a scale of 1:20 000, and through petrographic and geochemical analysis.

The unit is exposed on a plateau 7 km long and 0.8 to 1.0 km wide.  The unit is 4 to 6 m thick and is in apparent conformable contact with the underlying shales of the Paleoproterozoic Rove Formation, where a pronounced chilled margin consists of variolitic material up to 20 cm thick.  The flow-top also exhibits a variolitic texture ~15 cm thick.  The presence of ropy flow top and amygdules as well as quench textures, support a volcanic origin. 

Major element chemistry reveals a tholeiitic, intermediate composition with samples plotting in the basaltic andesite to andesite fields as well as in the basaltic trachy-andesite to trachy-andesite fields on a TAS diagram.  The unit typically has an intergranular texture consisting of randomly oriented plagioclase laths with interstitial chlorite, an alteration product of primary augite.  Most samples contain minor serpentine (after olivine), opaque minerals, secondary quartz, oxides, pyrite and calcite.  Amygdules are present in most samples and are infilled with some combination of calcite, quartz, chlorite and pyrite. Lower flow contacts and flow-tops are typically glassy with abundant spherulites that sometimes coalesce into bands.

Rare-earth element geochemistry shows the unit to be relatively enriched in both HREEs and LREEs, similar to the ultramafic sills of the Nipigon Embayment as well as the Riverdale Sill (Hollings et al., 2007, 2009).  A primitive mantle-normalized REE plot shows that the volcanic unit  is characteristic of an Ocean-Island Basalt, but with a negative Nb anomaly, most likely the result of lower crustal contamination.  This evidence is further supported by an ∊_Nd(t=1100Ma) of -3.48, which also suggests contamination of the unit by a lower crustal source.  The trace element characteristics of the volcanic unit suggest an origin in Keweenawan time as they are geochemically similar to volcanic units of the MCR (Hollings et al., 2007) rather than Paleoproterozoic volcanic units of the Gunflint Formation.

Field, petrographical and geochemical analysis suggests that the unit is of volcanic origin with evidence towards emplacement during Keweenawan Midcontinent rifting.  Thus, we are proposing that the unit be renamed the Devon Volcanics.

Rob is currently working on his MSc thesis at Lakehead University

For more information about this thesis contact Dr Pete Hollings

The Riverdale Sill is located within the southern city limits ofThunder Bay. Although the sill consists mainly of gabbronorite, olivine gabbro can be found in a number of localities. The intrusive contact between the sill and the Paleoproterozoic Rove Shale is sharp and the chilled margins are only a few centimetres thick. The sill is exposed over an area approximately 6 km long and 2 km wide but the true thickness is unknown because the upper contact is not visible.

In comparison to other Midcontinent Rift-related intrusions, the Riverdale Sill is geochemically similar to ultramafic intrusions such as Hele and Disraeli (Hollings et al. 2007). Although it is found south ofThunder Bayit most closely resemble the Jackfish Sill of the Nipigon Embayment rather than the Logan and Nipigon Sills which surround it.

The Riverdale Sill crops out in a quarry on West Riverdale Road where it has an exposed thickness of 10 m.  Detailed sampling was carried out every metre up through the sill to investigate geochemical variations within it.  There is no geochemical evidence for fractionation within the sill which is supported by the absence of cumulate textures.

On a primitive mantle-normalised plot, a number of samples of the Riverdale Sill broadly resemble Ocean Island Basalts. However, some samples within the sill have negative niobium anomalies though geochemical evidence for contamination of the sill is localized to within less than 1m of the contact with Rove Shale. Therefore, this contamination is best interpreted to be the result of crustal contamination at depth. The less-contaminated samples are typically found towards the center of the sill. The geochemistry of the center of the sill varies slightly from that near the sill margins. Samples of gabbronorite taken adjacent to a shale xenolith within the sill do not display a negative Nb anomaly.  The lack of this anomaly, combined with the lack of contamination above the contacts in the sill at the quarry, supports a model in which contamination is occurring at depth rather than during emplacement.

Geochemical variations within the sill can be interpreted as the result of two pulses of magma, with the first more-contaminated pulse intruded by the second, less-contaminated magma shortly after the emplacement within the shale. The less-contaminated magma may have pushed the contaminated magma to the edges of the sill, leaving a less-contaminated core.