A geoarchaeological investigation was north of Highway 11/17, 34km east of Thunder Bay, Ontario.  Five archaeological sites (Mackenzie 1, Mackenzie 2, RLF, Woodpecker 1, and Woodpecker 2) and seven additional sediment exposures were examined for stratigraphic analysis to accompany the archaeological excavations.  River-mouth sediments at 268m asl and a series of deltas indicate that the study area was subaqueous while placement of the Superior lobe prevented drainage to the Superior basin.  This elevation is consistent with Lake Beaver Bay, an ice-contact lake that received glacial meltwater from the north (the Hudson Bay lobe) as well as the south (the Superior lobe).  This is demonstrated by southward and northward prograding deltaic sequences within the study area.  

As the Superior lobe made its final retreat, Lake Beaver Bay dissipated into the Superior basin marking the beginning of the Minong phase, likely around 9,900 ¹⁴C yrs BP.  Additional sequences representing river-mouth, beach shoreface, and deltaic depositional environments indicate that a series of shorelines within the study area represent subsequent Minong lake levels.  The highest, and likely oldest of these strandlines is an erosional feature at 256m asl, consistent with wave-cut terraces previously identified in the Thunder Bay region.

Relative lake level drops occurred, likely due to a combination of gradual erosion of the Nadoway Point sill and isostatic rebound of the recently deglaciated land.  Beach and river-mouth sequences representing subsequent shorelines are located at 249m, 243m, and 240m asl.  Artifacts on each of these beach terraces suggest they were occupied by Paleoindian groups.

The occupation layer(s) at the Mackenzie 1 site are strongly bioturbated, although the sediment matrix is consistent with underlying beach sediments in the north and river-mouth sequences in the south.  The site is about 10,000 m², and 378 Paleoindian projectile points were recovered along with additional bifaces, other formal and expedient tools, as well as lithic debitage.  The frequency of artifacts and site size likely indicate that Mackenzie 1 was successively occupied over an extended time period of time.  However, absence of an unconformity separating the visible stratigraphy from the massive occupation layer(s) may indicate that the site was inhabited soon after deposition ceased.  This likely places site occupation within the Minong phase (dating to ~10,500 to 9,000 cal BP). 

Artifacts recovered from the RLF archaeological site are also within a bioturbated sediment matrix consistent with underlying stratigraphy.  Lithofacies indicate that soon after the beach shoreface sediments were deposited, the beach terrace was utilized by mobile Paleoindian groups.

A shoreline at 240m asl is evidenced by a wave-cut feature and beach sediments at the Woodpecker sites, river-mouth sequences at the Mackenzie 2 site, and beach shoreface deposits at a roadcut exposure.  Presence of artifacts and charcoal within beach sediments at the Woodpecker 2 site provides evidence that occupation was contemporaneous with active beach formation.  However, the majority of recovered artifacts at Woodpecker 1 and Woodpecker 2 are associated with bioturbated sediments consistent with underlying stratigraphy.  Most likely, the Woodpecker sites were occupied along an active Lake Minong margin, and subsequently inhabited soon after the relative lake level dropped again.  The artifact matrix at the Mackenzie 2 site similarly suggests that occupation occurred soon after deposition of the underlying river-mouth sequences

Two additional exposures revealing a deltaic sequence and beach sediments suggest that the relative lake level lowered to 233m, and subsequently to 224m asl.  This lowest shoreline identified within the study area likely represents the beginning of the Post-Minong phase.

All five archaeological sites are strategically placed on beach terraces, which is consistent with most presently known Paleoindian habitations in Northwestern Ontario.  As well, The Mackenzie and Woodpecker sites likely had access to a river, making them ideal for fishing as well as hunting at the river crossings.  The study area provides additional evidence that lake margins and river-mouths were highly attractive campsites for mobile Paleoindian groups.  In addition, artifacts recovered from within beach sediments at Woodpecker 2 suggest that the Thunder Bay region was first occupied soon after deglaciation.  The Mackenzie, RLF, and Woodpecker sites were likely inhabited between about 9,900 and 9,000 ¹⁴C yrs BP. 

A copy of the thesis can be downloaded here

Musselwhite Mine and Hammond Reef are shear-zone-hosted gold deposits located in Northwestern Ontario, in the Western Superior Province of the Canadian Shield. A detailed microscopic investigation of three gold-hosting lithologies from Musselwhite Mine and Hammond Reef demonstrate close similarities in the microstructures which host gold and the relative timing of gold mineralization. The gold deposit at Musselwhite Mine is hosted by metamorphosed banded iron formation, while Hammond Reef is hosted by metamorphosed tonalite. Despite the difference in rock types, Musselwhite Mine and Hammond Reef are similar in that that they are located proximal to regional shear zones, have undergone regional metamorphism and are dominated by ductile deformation. Although these two deposits are hosted by completely different lithologies the microstructures which host gold are very similar, indicating structural control on mineralization at a microscopic scale.

The most common gold-hosting microstructures in these gold deposits result from heterogeneous deformation. Gold mineralization commonly occurs in fractures in competent minerals such as garnet and pyrite in every lithology in this study. These gold-hosting fractures do not extend throughout the matrix but are restricted to the competent minerals because the competent minerals are resistant to the ductile deformation around them. Gold mineralization is also associated with other deformation-induced microstructures, such as strain shadows. Gold mineralization is hosted by metamorphic minerals at both Musselwhite Mine and Hammond Reef. Gold inclusions occur at Musselwhite Mine in such metamorphic minerals as grunerite and garnet and at Hammond Reef gold inclusions occur in metamorphic muscovite. Also gold mineralization commonly occurs on plane defects, for example on grain boundaries.

Relative timing of gold mineralization is shown to have occurred during ongoing metamorphism and deformation. Inclusions within metamorphic minerals indicate that gold mineralization must have occurred before or during metamorphism, while gold mineralization associated with deformational features indicate gold mineralization to have occurred during or after deformation. This thesis demonstrates close similarities between the relative timing of gold mineralization as well as the microstructures which host gold at Musselwhite Mine and Hammond Reef.

Maura is currently working as a geologist for Fladgate Exploration Consulting Corporation in Thunder Bay.

A copy of the thesis can be downloaded here

Banded iron - and manganese - rich precipitates were collected from the lake bottoms of Lake Charlotte (Nova Scotia), Lake Shebandowan (Ontario) and Sowden Lake (Ontario). Investigations of study areas at the macro, meso and micro scale were conducted to understand the iron-manganese rich- nodules in their natural environment. The nodules appear as circular precipitate bands which alternate between high concentrations of iron and manganese.  Analysis of precipitates revealed that those from Lake Charlotte are highly concentrated in arsenic. Lake Shebadowan and Sowden Lake samples are highly concentrated in phosphorous.

Correlation between iron, arsenic and phosphorous suggests oxidation and precipitation of these elements in the same bands of the nodule. Iron relies on the Eh and pH of an environment to precipitate from solution. At a redox boundary in a near neutral environment, iron is able to oxidize as a sediment coating and co-precipitate arsenic and phosphorous from the water.  An affiliation between manganese, barium and cobalt suggests precipitation of these elements in the alternate bands present in the nodule. Barium and cobalt are able to co-precipitate with manganese by either penetrating a manganese oxide by means of protonation, or oxidize and become interchangeable with Mn⁴⁺. 

The growth of the nodules at Shebandowan and the majority of Lake Charlotte sites were probably affected by a redox boundary created by the diffuse upward flow of groundwater with lower Eh than the oxidized lake water. It is likely that photosynthetic and iron and manganese oxidizing microorganisms are present in a bacterial mat covering the nodules and probably played a role in their precipitation. Analysis of the growth mechanisms of precipitates revealed in Sowden Lake and the Granite Islands site of Lake Charlotte were inconclusive.

Research involving iron and manganese rich precipitates may be used for environmental implications involving heavy metals and arsenic. Examples of remediation areas that would benefit from precipitate research include drinking and waste water filtration and reducing the environmental footprint of mine tailing waste sites.

A copy of the thesis can be downloaded here

The McFaulds Lake area (commonly known as the Ring of Fire), has been the site of much recent exploration within northern Ontario.  The area represents a recently discovered Archean greenstone belt which is host to world class chromite deposits along with significant Cu-Zn VMS, magmatic Ni-Cu-PGE and Fe-Ti-V occurrences.  Much emphasis has been placed on the chromite mineralized ultramafic intrusions with little attention focused on the Fe-Ti-V mineralized ferrogabbroic intrusions.

The Butler and Thunderbird intrusions represent the best described intrusions within the volumetrically significant ferrogabbroic suite within the McFaulds Lake area.  These intrusions are characterized by a suite of well layered magnetite-ilmenite rich rocks which are dominantly composed of gabbroic to anorthositic units with lesser stratigraphically conformable units composed of pure magnetite-ilmenite.  The Fe-Ti oxide rich layers contain variable vanadium mineralization and low chromium contents within magnetite (up to 2.45 V₂O₅ wt. %, 0.99 % Cr₂O₃ wt. %) and ilmenite (up to 0.57 V₂I₅ wt. %).  The massive and semi-massive oxide layers occur as basal members of repeated cycles characterized by sharp lower contacts which grade upwards into oxide-rich pyroxenite, followed by oxide-bearing leucogabbros and/or anorthosites.  The layers are believed to be cause dominantly by magmatic convection currents within a system which is at least partially open to oxygen.  No evidence has been found to suggest multiple pulses of magma.  Oxide-silicate liquid immiscibility is thought to only occur within the evolved, apatite-bearing margins of the Thunderbird intrusions; however, additional drilling may reveal further apatite mineralization.

The ferrogabbroic intrusions are thought to have originated from a shallow depleted mantle source, possibly related to a plume event.  The ferrogabbros have likely undergone a two stage differentiation to account for the extreme iron enrichments.  The first stage is characterized by an anhydrous, tholeiitic melt, within the upper mantle (above the garnet stability field, <110km) which underwent Fe-Ti enrichment due to the crystallization of Fe-poor phases (e.g., olivine, plagioclase, etc.) within a system closed to oxygen.  The second stage is considered to be a very shallow intrusion within the McFaulds Lake mafic-felsic volcanic rocks.  This final stage is characterized by a system which was at least partially open to oxygen from an originally reduced magma (<QFM buffer).  These magmas initially crystallized Cr-V-rich magnetite-ilmenite horizons and gradationally evolved into Cr-V-poor, apatite-bearing ferrogabbros.  These ferrogabbros likely share a parental magma with the coeval Cr-Ni-PGE-bearing ultramafic intrusions of the McFaulds Lake greenstone belt.  Additionally, spatial and geochronological evidence suggests that abundant VMS-style mineralization within the McFaulds Lake area may be a result of a thinned lithosphere during plume tectonics.

A copy of the thesis can be downloaded here

Glacial sedimentary rocks of the Huronian Supergroup crop out along the north shore of Lake Huron and were likely deposited on what is thought to have been a divergent continental margin (Fralick and Miall, 1981; 1989). The rocks of the Gowganda Formation record one of three glacial events preserved in the Supergroup and are therefore of interest for developing further glaciomarine models (Puffett, 1974) and furthering understanding of this early stage in Earth's history. Data has been collected in five main study areas in an attempt to cover as much of the ancient continental margin as possible.  The study areas include Espanola, Elliot Lake, Thessalon and Cobalt, Ontario and Marquette, Michigan. There are two glaciogenic formations in the Marquette area of Paleoproterozoic age, the Reany Creek Formation and the Enchantment Lake Formation.  The Enchantment Lake Formation has been chronostratigraphically correlated to the Huronian Supergroup based on U-Pb age determination on detrital zircon, 2317±6 Ma, and diagenetic xenotime, 2133±11 Ma (Vallini et al., 2006).  As these formations are present in such close proximity to each other, and there are no Archean glacial events recorded in the rest of the Canadian Shield, it is reasonable to correlate them with the Gowganda Formation, the thickest and most commonly preserved of the three Huronian glacial events.

Stratigraphic sections were compiled in each of the study areas and the sedimentary rocks were grouped into seven lithofacies associations (LA): 1) Planar Cross-Stratified Sandstone LA, 2) Basal Breccia LA, 3) Diamictite LA, 4) Interlayered Siltstone and Fine-Grained Sandstone LA, 5) Slump LA, 6) Heterogeneous Sandstone LA and 7) Quartz-Rich Sandstone LA.  These lithofacies associations likely represent a sequence of depositional environments on a shallow continental shelf.  Initially, the shelf was dominated by what were likely large-scale, low-angle sandwaves, interbedded with successions of wavy bedding and possible hummocky cross-stratification indicating an open-water setting with tidal and storm processes reworking the sediments.  The shelf then gradually evolved into an environment dominated by diamicite layers.  The diamictite layers have dropstones as well as evidence of current activity indicating outsized clasts were likely being introduced into the environment as ice-rafted debris.  Resedimentation events in the form of debris flows are thought to account for conglomeratic layers that are common in the Diamictite LA.  The Interlayered Siltstone and Fine-Grained Sandstone LA, along with the Slump LA, seem to indicate deposition from suspension in a prodelta setting where large slump events are common.  The gradual transition into a more sandstone dominated LA, with an abundance of current-related sedimentary structures, is indicative of the shallowing and coarsening upwards succession common to deltaic deposits.  A final transition into the Quartz-Rich Sandstone LA indicates a return to a sandy, current-dominated open continental shelf environment with abundant tidally generated sedimentary structures such as herringbone cross-stratification.  The Cobalt study area differs from this overall model in that evidence of grounded ice is present.  Less exposure in the Marquette study area makes it difficult to draw overall conclusions on the evolution of the continental shelf but deposition in a subaqueous glacial outwash fan is hypothesized.

A copy of the thesis can be downloaded here

Dyke rocks occurring in the Coldwell alkaline intrusive complex, N.W. Ontario, were studied by various petrographic and geochemical means.  The resulting observations indicate that 5 types of mafic alkaline lamprophyres, distinguished on the basis of chemistry and mineralogy according to the scheme of rock (1977), and 1 type of felsic tinguaite occur in the complex (in approximate order of abundance):

The Geordie Lake Intrusion (GLI) consists of alternating zones of layering-free troctolite and olivine gabbro outcropping in the north-central part of the Coldwell alkaline complex, northwestern Ontario.  The troctolite exhibits harrisitic texture in which dendritic olivine (Fo_44-56), plagioclase (An_48-57), and skeletal magnetite are the main constituents.  Small amounts of clinopyroxene (Di₃₆Hd₆₀Ae₄-Di₃₀Hd₆₆Ae₄) are present in the troctolite.  The ophitic olivine gabbro consists of clinopyroxene (Di₄₁Hd₅₄Ae₅-Di₂₉Hd₆₆Ae₅), plagioclase (An_46-54), altered olivine, and skeletal magnetite.  Some gabbros contain high-alumina clinopyroxenes (Ti-Px₄CATS₄₈Ae₄₈-Ti-Px₃CATS₄₂Ae₅₀).  Mineral chemistry and whole-rock geochemistry indicate that the troctolite and gabbro are note related by differentiation and their parent magma is a relatively evolved low-alumina tholeiite.  The GLI is characterized by high Sr, Rb, Ba, Th, Ta and light rare-earth element (LREE) content but low in Ni and Cr content.  Europium anomalies are absent.  Fe-Ti oxide geothermometry and geobarometry of the troctolite and olivine gabbro give an average equilibrium temperature of 603°± 35° and oxygen fugacity of 10^-17 bar. 

Disseminated chalcopyrite is the dominant style of Cu-sulphide mineralization in the GLI.  Massive chalcopyrite aggregates are rare.  Bornite exsolved from chalcopyrite.  The other sulphides present are pyrite, millerite, siegenite with exsolved pentlandite, galena, and supergene chalcocite.  The tellurides and PGM occur as small inclusions (5 – 10 mm) in, and as coarser sunhedral to anhedral grains on the margins of, the disseminated chalcopyrite.  Small amounts of tellurides and PGM are also present in the massive chalcopyrite and silicate minerals.  The tellurides are melonite, hessite, unnamed Ag₃Te₂, and altaite.  The PGM are kotulskite, merenskyite, michenerite, sopchiete, palladium bismuthotelluride, paolovite, palladium arsenide, guanglinite, and palladium antimonide.  Sperrylite is the only platinum mineral present in the GLI.  Electrum forms small discrete and replacement minerals.  Two probable new minerals are Pd_1.6As_1.5Ni and AgSb₄.  Textural evidence from the sulphides, tellurides, PGM, and host rock silicates favour a late stage magmatic origin.  Cu-sulphide mineralization was induced by precipitation of magnetite and other Fe-bearing minerals, and subsequent mineralization resulted from cycles of sulphide and magnetite deposition.  Conditions of deposition for the tellurides and PGM associated with the disseminated chalcopyrite have been estimated to be approximately from 550°C to between 450° and 400°C, and at log P(Te₂) from -2.4 ± 0.13 bar to between -6.4 and -9.7 bar, and at log P(S₂) from between -3.7 and -0.8 to between -4.2 and -2.3 bar.  The predominance of palladium over platinum minerals reflects the relatively evolved nature of the GLI.

A copy of the thesis can be downloaded here

This thesis describes the occurrence, mineralogy and assimilation of basic xenoliths hosted by Centre 3 syenites.  Field work was carried out in two locations, one in the vicinity of Neys/Ashburton and the other a large megaxenolith hosted by Centre 1 syenites in the vicinity of Wolf Camp Lake. 

Least altered xenoliths consist of plagioclase, pyroxene amphibole, biotite, apatite and opaque phases.  With increasing assimilation this changes to a combination of plagioclase, amphibole, biotite, apatite, opaque phases, alkali feldspar, calcite, fluorite, sphene, zircon, REE phases and quartz.

Plagioclase is replaced by alkali feldspar in the form of porphyroblasts and crystals in the groundmass.  Plagioclase is also decalcified to more albitic compositions along with recrystallization.  Amphibole compositions extend over the same range of amphibole compositions in the host ferro-edenite syenite.  The general effect of xenolith assimilation is the equilibrium of a xenolith's mineral assemblage to that of the host syenite.  Assimilation processes seen at Wolf Camp Lake are similar to those seen at Neys/Ashburton.

Bulk rock data along with mineralogical compositional variation in clinopyroxenes, suggest a tholeiitic basalt parentage for xenoliths in both areas.  Cr and Ni contents indicate an evolved nature to the parent volcanics.  Data also suggest the possible existence of a second undersaturated type of volcanic xenolith present at Neys/Ashburton.  Parental basalts are postulated to be coeval volcanics related to the formation of the Coldwell Complex.

Modelling by mass balance mixing calculations of contamination of host syenites indicates that contaminated ferro-edenite syenites are the result of direct assimilation of volcanic xenoliths by ferro-edenite syenite.  Quartz syenites are found to be unsuitable parents to contaminated ferro-edenite syenites.

A copy of the thesis can be downloaded here

The  Coldwell Alkaline Complex, situated on the north shore of Lake Superior, is of Neohelikian age.  It is intruded into Archean supracrustal rocks of the Superior Province,  near Marathon,  Ontario.  The complex has a diameter of 25 km and consists of three major magmatic centres.  Each centre represents the focus of a cauldron subsidence event.  From earliest to latest they are:  Centre I - saturated alkaline rocks with peralkaline oversaturated residua; Centre II - miaskitic undersaturated alkaline rocks; and Centre III - alkaline rocks with oversaturated residua.  This thesis documents the rocks of Centre III.

Centre III magmatism of the Coldwell Alkaline Complex is represented by alkali feldspar syenites and alkali feldspar quartz syenites.  In order of intrusion from earliest to youngest these are (1) synneuritic magnesio-hornblende syenite,  (2) perthitic ferro-edenite syenite,  (3) contaminated ferro-edenite syenite and  (4) quartz syenite.  Amphiboles are the major mafic phase in all syenite types.  Their evolutionary compositional trend ranges from magnesian hastingsite in the magnesio-hornblende syenite to riebeckite in the quartz syenite.  Pyroxenes are Ti-Al rich in the earliest syenites, but evolve to Na-Fe rich members in the youngest.  The contaminated syenites result from the assimilation of xenoliths of oligoclase basalts which are interpreted to represent contemporaneous lavas.  Varying degrees of contamination lead to an apparent plethora of syenite types.

The Centre III syenites are miaskitic and metaluminous with normative quartz content increasing from the earliest to the latest varieties.  All of the syenites are enriched in U, Th, REE, and Zr, reflecting the presence of zircon, chevkinite, REE-carbonates, Nb-rutile and aeschylite.  Centre III syenites have petrological affinities with A-type granites and are interpreted to have been formed by partial melting of lower crustal material.

A copy of the thesis can be downloaded here

The Ham diatreme and dyke are post-late Silurian intrusions located in north-central Somerset Island and are the most northerly known kimberlites in theSomerset Islandkimberlite province.  The Ham diatreme, which consists of three petrographically distinct varieties of kimberlite, formed as a series of fluidized intrusions at the intersection of several regional fracture sets.  Type 1A kimberlite is petrographically similar to the Ham dyke (a single intrusion located 1.5 km to the east) and forms the flanks of the Ham diatreme. This dark, massive rock contains phenocrysts and xenocrysts of garnet,olivine, chrome-diopside, phlogopite, spinel and carbonate in aserpentine-carbonate groundmass containing carbonate and serpentine emulsion textures.  Type 1B kimberlite, which occupies the central portion of the Ham diatreme, is a highly altered, light green, seperentine-carbonate-rich rock formed by the prograde serpentinization and carbonatization of Type 1A kimberlite. This alteration occurred during the degassing of structurally lower portions of the Ham diatreme.  Type 2 kimberliteis a carbonate-rich mineralogical equivalent of Type 1A kimberlite and formed as a late stage dyke within the Ham diatreme.

Pre-fluidization phenocrysts include Mg-rich olivine (Fo_89-93), low Cr, (<3.5 wt.% Cr₂O₃), high Ti (>0.3 wt. % TiO₂) pyrope-garnet, Al-rich, Ti-poor (<2.00 wt % TiO₂) aluminous-magnesium chromite (Cr/Cr + Al = 0.18 - 0.85) and Ti-rich phlogopite(1.0 - 4.6 wt. % TiO₂). Post-fluidization microphenocrysts include Mg-rich olivine (Fo_89-93),Ti-rich phlogopite (2.5 - 4.0 wt. % TiO₂) and spinel which evolved from Ti-bearing (2.00 wt. % TiO₂), titan-magnesium-aluminous-chromiteto Fe³⁺- and Ti-rich (max. 17.0 wt. % TiO₂) magnesium-ulv_spinel - ulv_spinel-magnetite.  Atoll spinels, formed prior to the complete crystallization of the kimberlite groundmass are present in the Ham dyke but extensive resorption of magnesium-ulv_spinel-ulv_spinel-magnetite and titan-magnesium-aluminous-chromite in the Ham diatreme has precluded their persistence.

Xenocrysts formed by the disaggregation of garnet and spinel lherzolites include Cr-rich (3.5 - 10.0 wt. % Cr₂O₃), Ti-poor (<0.30 wt. % TiO₂) pyrope-garnet, Mg-rich olivine and chrome-diopside.  Pressure temperature estimates from garnet lherzolite xenoliths range from 36 to 37 kb and 1031 to 1146EC corresponding to a depth of origin of 110 to120 km.

Multiple discriminant analysis demonstrates that cluster analysis can only distinguish between garnets of grossly different chemistry and paragenesis and that major and minor element variation diagrams are required to separate statistically,chemically similar garnets within a paragenesis.

Geophysical studies may be used to delineate kimberlite subcrop patterns and structural elements which may have controlled the intrusion of the kimberlites.

A copy of the thesis can be downloaded here