The 1108 Ma Thunder mafic to ultramafic intrusion is a small, 800 x 100 x 500 m, Cu- PGE (platinum group element) mineralized body, located on the outskirts of Thunder Bay, Ontario, and associated with the early magmatic stages of the Midcontinent Rift (MCR) based on geochemical similarities to mafic and ultramafic rocks of the Nipigon Embayment and an unpublished ²⁰⁷Pb/²⁰⁶Pb zircon age of 1108.0 ± 1.0 Ma.  The Thunder intrusion is similar to the other known mineralized early-rift MCR intrusions; however, it is the only known occurrence hosted by the metavolcanic and metasedimentary assemblages of the Archean Shebandowan greenstone belt.  Major textural and geochemical differences can be used to subdivide the intrusion into a lower mafic to ultramafic basal unit and an upper gabbroic unit; the similar trace and rare earth element ratios of the two units suggest a single magmatic pulse that has undergone subsequent fractional crystallization and related cumulate phase layering.  The estimated parental composition of the Thunder intrusion has a mg# (MgO/(MgO + 0.9*FeO^T)) of 57 which represents a more evolved magma than other early-rift mafic to ultramafic  intrusions.  This may indicate the involvement of multiple staging chambers during the accent of the parent magma.

Trace and rare earth element patterns are consistent with an ocean island basalt source but with indications of contamination such as high Th concentrations and the presence of a negative Nb anomaly.  The ԐNd_T values from the intrusion range between - 0.7 and + 1.0, with no trends indicative of wall rock participation, whereas the ⁸⁷Sr/⁸⁶Sr_i ratios range from 0.70288 to 0.70611 and trend towards wall rock values of 0.70712 and 0.70873.  The weak correlation between ԐNd_T and ⁸⁷Sr/⁸⁶Sr_i is also a feature of the Nipigon Sills where it has been interpreted to be due to shallow-level crustal contamination whereas plots of MgO and SiO₂ versus ԐNd_T indicate contamination at depth by an older crustal source. 

Ni-Cu-PGE sulphide mineralization (20 m of 0.22 wt. % Cu, 0.06 wt. % Ni, 0.25 ppm Pt and 0.29 ppm Pd) is hosted by feldspathic peridotite in the lower mafic to ultramafic unit adjacent to the footwall of the Thunder intrusion.  Sulphides typically occur from 1 - 5 modal %, rarely up to 30 modal %, with textures ranging from medium- to fine-grained disseminated, globular and rarely net-textured.  Pyrrhotite, chalcopyrite and rare pentlandite with common secondary marcasite-pyrite replacement occur along with trace michenerite, kotulskite, merenskyite, sperrylite, hessite, electrum and argentian pentlandite.  Whole rock geochemical data displays fractionated Ni-Cu-PGE patterns with depletion of iridium-platinum group elements (IPGE) relative to platinum-platinum group elements (PPGE). 

Sulphide δ³⁴S values from the Thunder intrusion range from -2.0 to +3.8 ‰ and are similar to values for the metavolcanic host rock that range from -3.1 to +2.3 ‰.  Two samples from the basal mineralization zone sulphides yield Δ³³S values of 0.066 and 0.122 ‰ and one sample from the metavolcanic wall rock yields 0.149 ‰.  The δ³⁴S and Δ³³S values for the Thunder intrusion fall within range of typical upper mantle.  The sulphur source appears to be of mantle origin, however, the assimilation of crustal sulphur is a possibility but hard to distinguish as the wall rock S isotope and S/Se^T signature is similar to that of upper mantle. 

A copy of the thesis can be downloaded here

Paleosecular magnetic changes through a 1.5m section of post-glacial lacustrine deposits are strongly influenced by mineralogy and differential compaction.  The sediments chiefly comprise clay and, in the lower one third part of the section, rhythmites which vary from ~2mm to ~5cm in thickness. 125 paleomagnetic specimens were collected in total from the 1.5m section. Anisotropy of magnetic susceptibility and anisotropy of anhysteretic remanent magnetization identify a magnetic fabric with maximum susceptibility parallel to the bedding plane of the sediments and with a preferred northwest-southeast axis, probably indicating paleo-current alignment. Minimum susceptibility represents the pole to bedding, due to grain alignment.  

Incremental acquisition and demagnetization of isothermal and anhysteretic magnetizations and the orthogonal three-axis test indicate that the sediments contain two magnetic phases with different coercivities. Magnetic hysteresis measurements (clays n=226; silts n=37) show that clay is dominated by single domain magnetite and hematite (means of M_s=58.47±9.22Am², M_rs=17.12±27.22Am², H_c=21.09±7.69mT, H_cr=62.04±4.09mT) whereas silt is dominated by pseudo-single domain and single domain magnetite (means of M_s=681.0±395.9Am², M_rs=163.2±84.75Am², H_c=26.07±2.94mT, H_cr=56.08±3.17mT). The silt is dominated by magnetite, whereas the clay carries both hematite and magnetite.

Incremental alternating field demagnetization of clay, in 10 to 17 stages, successfully isolated three distinct remanence components, with different directions. A weak and spurious component that is due to handling magnetization, for example, was removed in early demagnetization steps. The two remaining components, isolated by further demagnetization, have geological significance. Mineral magnetic properties as well as differential compaction are responsible for the different directions of the two geologically significant magnetizations in the clay. One has intermediate coercivities (20 - 40mT) with a Fisher mean declination = 357.4° and Fisher mean inclination = 62.0°, approaching the present Earth's magnetic field (declination=356.7° and inclination=74.7°). The other has harder coercivities (>40mT) and represents a stable geological magnetization. The silt has a single component of magnetization carried by magnetite. Laboratory re-deposition of clay in large (125cm³) cubes accurately records the direction of the laboratory magnetic field; thus major inclination shallowing in natural sediments occurred subsequent to acquisition of original DRM.

A magnetostratigraphic record of the hard coercivity component over the 1.5 meter section reveals paleosecular variation of the Earth's magnetic field, with some complications due to compaction. A single westward drifting loop is recorded in the sediments, representing a time-period of circa 600 - 2400 years, with declinations varying from 199.8° to 119.9° (Fisher mean=005.2°) and inclinations varying from -2.4° to 77.4° (Fisher mean=50.9°). In comparison the inclination of the geocentric axial dipole (GAD) for the study location is +66°.

The Coldwell Alkaline Complex was emplaced as a Midcontinent Rift-related intrusion into Archean-aged rocks of the Schreiber-Hemlo Greenstone belt, centered around the town of Marathon, Ontario. Although the complex consists of predominantly alkaline rocks, numerous PGE-(Cu) mineralized gabbroic intrusions also comprise a substantial portion of the complex and are of considerable economic interest. The PGE-(Cu) mineralized sub-ophitic to ophitic gabbros within the Marathon deposit of the Eastern Gabbro Suite have been studied in detail by numerous workers, leading to many interpretations of genetic models for the emplacement of the gabbros and subsequent mineralization.

This study focuses on characterizing two trenches in the Boyer Lake district, located along the northeastern border of the complex that consist of predominantly PGE-(Cu) mineralized coarse-grained to pegmatitic sub-ophitic olivine gabbros as well as many smaller ultramafic intrusions and pyroxenites that are in contact with Archean footwall rocks. Of particular interest, is an area located on Trench 2 that consists of olivine- and plagioclase-rich olivine gabbros, and does not exhibit the typical sub-ophitic texture of olivine gabbros elsewhere on the trenches as well as in the Marathon deposit, rather poikilitic olivines that commonly contain thin partial rims of pyroxene. Additionally, this zone is characterized by enriched PGE mineralization, a chalcopyrite  bornite sulphide assemblage and geochemical signatures that are all characteristic features of the W-Horizon, which is a known lens of high-grade PGE mineralization within the Marathon deposit. Mineral chemistry data in conjunction with Sm-Nd and Sr isotope analyses suggest that the PGE-enriched olivine- and plagioclase-rich zone consists of very primitive intrusions, and likely represents some of the earliest, if not earliest emplaced rocks comprising the study area in contrast to more pyroxene-rich and less mineralized sub-ophitic gabbros. The chaotic nature of the intrusions, variable geochemistry, PGE grades and mineralization styles suggests that the genesis of the Boyer Showing may best fit with a previously hypothesized dynamic magma conduit model that has been postulated for the genesis of the gabbros of the Marathon deposit.

Boreal forest soils represent globally significant stores of carbon, and to a lesser degree nitrogen, yet there is little consensus about how they are altered by natural and anthropogenic disturbances. Disturbance by wildfire and forest harvesting is widespread, yet there are few investigations comparing the impacts of these disturbances on soil nutrient cycling, and even fewer on compound disturbance, such as salvage logging. A chronosequence approach was used to investigate the impacts of full-tree harvesting, wildfire, and compound disturbance i.e. post-fire salvage logging on soil carbon and nitrogen stores, pH and carbon to nitrogen ratios overtime. Stable carbon and nitrogen depth profiles were examined to identify the dominant mechanisms driving the observed trends following disturbance. The findings suggest that full-tree harvesting and wildfire impact carbon and nitrogen stores in fundamentally different ways, with stores being reduced after wildfire and increased after harvest. However, the differences observed were confined primarily to the organic and upper mineral soil, and the changes diminished with time. Results from this study suggest that impacts of post-fire salvage logging on carbon and nitrogen stores resembles that of fire, but that recovery is much slower making the practice potentially more harmful than harvesting and wildfire alone. Additional exploration into the long-term effects of compound disturbance on carbon and nitrogen stores is needed if salvage logging is to continue to become a justifiable practice. The driving mechanism of ¹³C enrichment with depth was inconclusive, with both mixing and kinetic fractionation during humification appearing to be equally dominant at these sites. Rayleigh distillation analysis indicated no differences in overall depth enrichment among the sites. Similarly, examining ¹⁵N enrichment profiles did not contribute to developing a process-based understanding of nitrogen cycling in these soils. This research demonstrates a need for further investigation into the usefulness of stable isotope depth profiles to indicate mechanisms responsible for storage change on a variety of soil types and textures following disturbance.

A kimberlite indicator minerals suite from above the DO18 kimberlite has been analyzed both texturally and chemically resulting in identified kimberlitic olivine, garnet, clinopyroxene, spinel, and ilmenite. Through a detailed glacial analysis of the Lac de Gras region containing DO18, the indicator suite is not limited to an origin from DO18. Northern kimberlite pipes have indications of kimberlite indicator trains following a southward ice flow direction, towards DO18. Textural evidence from the grains supports kimberlitic material that underwent minimal transport, as the grains are dominantly euhedral. Through major element chemical analysis, all minerals indicate an origin from a diamondiferous kimberlitic grains source. This suite is likely derived from a single kimberlite as the total chemical variation is limited for each mineral phase and along compositional trends. All indicators are a reflection of source from within the subcontinental lithospheric mantle beneath the Lac de Gras region, defined by both peridotitic and eclogitic compositions. Of the suite, garnet and olivine strongly indicate metasomatism to the subcontinental lithospheric mantle through increased titanium content and average forsterite value of 92, this corresponds to the rapid low angle Farallon plate subduction, dehydration, and partial melting. 

Musselwhite mine is situated in the North Caribou Lake greenstone belt within the North Caribou Terrane of the Superior Province, located approximately 500 kilometers north of Thunder Bay, Ontario.

The focus of this study was to classify the biotite at Musselwhite mine between the different economic zones of interest. Biotite from ten sampleswas chosen to be examined using petrography and quantitative mineral analysis with the scanning electron microscope (SEM). The biotite from Musselwhite mine is hosted in mafic metavolcanic rocks, classified as schists. The majority of the samples are comprised of biotite, hornblende, plagioclase, chlorite and calcite with minor amounts of tourmaline, apatite and quartz. Ilmenite is also present with minor amounts of pyrite, pyrrhotite, pentlandite and arsenopyrite. The biotite in the zones of interest show variation in iron content, with biotite plotting in the biotite and phlogopite zones on a metamorphic biotite graph that compare Fe/Fe+Mg and Al_Tot values.  

The samples examined have experienced amphibolite facies metamorphism and retrograde metamorphism due to the presence hornblende and chlorite, respectively.

The formation of sand bars located on a deltaic sand shelf was investigated.  The sand bars are oriented in three separate directions, one set forms parallel to the shelf edge, one set forms lengthwise in a north to south orientation, and the last set forms lengthwise in an east to west orientation.  All three sets form in a relatively small area.  The transition from deep water to the shelf occurs quickly, and the shelf edge to the shoreline remains relatively flat.  The profiles for the sand bars show that the ones that form along the edge of the sand shelf are asymmetrical.  Thus, they are probably formed by breaking waves, while the bars that form in the interior of the shelf are symmetrical and form after the breaking waves have reformed.  Examining wind direction and speed data shows that the dominant wind direction is from the west and would support the formation of waves travelling in the directions needed for the bar formation.  The grainsize distribution for the transition from deep-water to the shoreline and beach indicates a coarsening trend as the water becomes shallower.  There is a high percentage of a suspension population in the deep-water samples, while the samples obtained across the sand shelf and the beach are dominantly a saltation population.

Goldcorp’s Musselwhite mine is one of the largest gold deposits in Canada producing over 4 million ounces.  The mine consists of a variety of lithologies that are geochemically and structurally unique.  Musselwhite mine is situated within the North Caribou Greenstone Belt of the Superior Province.  The North Caribou Greenstone Belt is composed of eight metavolcanic and metasedimentary assemblages.  Musselwhite mine is located in the Opapimiskan Lake assemblage, which consists of wide range of mafic to ultramafic metavolcanic rocks. Interposed banded iron formation are found within the Opapimiskan Lake assemblage.  The mine geology is divided into five packages.  Packages consist of the Lower Basalts, South Iron Formation, Basement Basalts, Northern Iron Formation and the Upper Volcanics.  Musselwhite is an epigenetic structurally gold deposit.  Majority of gold mineralization is found in the iron formation, with two main styles of mineralization.  A quartz pyrrhotite flooding and sulphide replacement. 

The purpose of this project was to characterize pyrite and other associated sulphide minerals by examining their textural and mineralogical relationship to gold mineralization.  A total of fifteen core samples were collected by Musselwhite geologists.  The samples were prepared for petrography and SEM analysis.  Eleven of the fifteen samples were chosen for detailed analysis by the SEM.  A total of eight different lithologies were looked at in the study.  Petrographic descriptions were done for each sample.  It was found that all samples contained pyrrhotite displaying a variety of textures.  Five sample included pyrite with a range of textures.  Trace sulphides included chalcopyrite and arsenopyrite.  It was determined that gold was only correlated with pyrrhotite and quartz in this study.  There was no visible gold correlation with the pyrite.

The Paleoproterozoic (1.83 ± 0.01 Ga) Rove Formation forms the upper sedimentary unit within the Animikie Basin of the Superior Province. The Rove Formation is underlain by the Paleoproterozoic Gunflint Formation (1.878 ± 1 Ga), which contains the Sudbury Ejecta Layer near its upper contact. The ejecta layer is composed of debris from the Sudbury impact (1850 ± 1 Ma) and fragments of the Gunflint Formation.

The Rove Formation is a turbidite succession with characteristics of both turbidite system end-member models: submarine fans and ramps. Sediment input to the submarine system was from the north-north-west, with the likely source being the Trans-Hudson Orogen. The Rove Formation was deposited within a basin created by crustal subsidence associated with the Trans-Hudson Orogen, which was forming at the time of Rove Formation deposition.

This study involved the examination of approximately 1340 m of previously unexamined drill-core from five holes and reexamination of approximately 4840 m of previously examined drill-core from ten holes, totaling 6180 m of drill-core. The data from the drill-cores were used to create a series of stratigraphic diagrams in order to allow detailed architectural and sequence stratigraphic analysis of the Rove Formation to determine if the traditional submarine fan or ramp models match its stratigraphy. The drill-cores examined were drilled southwest of Thunder Bay, Ontario, in an area approximately 50 km wide between Thunder Bay and the United States Border. Architectural analysis of the Rove Formation indicated that the Rove is similar to submarine fan systems in that some well-structured depositional lobe and channel sequences are present. However, it also indicated that most of the system is more chaotic and relatively poorly structured, similar to submarine ramp systems. Furthermore, it was determined that the Rove Formation was fed by a delta coming of a braided river system and that there was not a singular point source of sediment input, as in submarine fans, but a linear sediment source and multiple feeder channels existed, similar to submarine ramp systems. Sequence stratigraphic analysis of the Rove Formation showed that there were a large number of transgressive sequences, represented by condensed shale intervals, within the Rove, indicating that relative sea-level was variable during its deposition.

While it was determined that the Rove Formation does have characteristics of both submarine fans and ramps, the architecture of the Rove does not fit either model well. This indicates that the traditional turbidite system models may be flawed and that these systems may need to be re-examined and re-interpreted using more extensive and complete data sets, similar to the data set used for this study.      

The Cerro la Mina Cu-Au-Mo porphyry-epithermal prospect is located in southern Mexico in the state of Chiapas. Discovered in 2004 as part of a larger project, referred to as the Ixhuatán Project, Cerro la Mina is one of five deposits owned and operated by joint venture partners Linear Gold Corp and Kinross Ltd. The state of Chiapas lies within a tectonically complex region marked by the triple junction of the North American, Caribbean, and Cocos plates.  It is comprised of a pre-Mesozoic metamorphic and sedimentary basement, a sequence of Mesozoic sedimentary rocks, and a sequence of volcanic and sedimentary Cenozoic rocks. Cerro la Mina is situated within a volcanic belt known as the Chiapanecan Volcanic Arc (CVA) in an area of major faulting and fracturing. Host rocks at Cerro la Mina are comprised of sequences of andesitic volcanic rocks ranging from tuff-lapilli-breccia-size fragments and coarser dacitic pyroclastic units including flows, lahars, and debris flows. The majority of these host rocks have been highly altered to the point where advanced argillic alteration has obscured any primary textures. Zircon in the host rock at Cerro la Mina has been dated at 1.01± 0.04 Ma which is younger than the surrounding rocks which generally range in age from 2.14±0.04 to 2.79±0.08 Ma.

While much work has been done on Cerro la Mina, very little has been done on the clay alteration which overprints everything. In order to better understand this alteration, a study was performed on 45 samples using x-ray diffraction, Reitvelds analysis, formamide intercalation, scanning electron microscope and acid etching. XRD revealed that the two major clays at Cerro la Mina were halloysite (7Å and 10Å) and kaolinite which were identified in 30 and 34 of the 45 samples respectively. Other clays included alunite in 12 samples, dickite in eight samples, illite in 15 samples, pyrophyllite in six samples and an unknown white clay in one sample. Halloysite (7Å and 10Å) and kaolinite were found together in 28 of the 45 samples. Twelve samples were then analyzed using the SEM and showed the presence of tubular and spheroidal halloysite as well as platy kaolinite throughout each sample. Acid etching of 21 samples revealed that feldspars at Cerro la Mina are secondary in origin.

The association of both halloysite 7Å and 10Å with minerals including quartz, alunite,
dickite, kaolinite, gypsum, and jarosite suggests a supergene overprinting of the primary mineralogy. However, the association of orthoclase, phlogopite, pyrite and molybdenite may indicate that some halloysite was formed as a result of hypogene processes.  The parent mineral subsequently altered to halloysite and kaolinite was most likely feldspar and not mica, with early formed halloysite later being converted to kaolinite. The Cerro la Mina prospect is interpreted to be a high-sulfidation epithermal deposit situated within a lithocap overtop a deeper porphyry copper system.