The 2310 Ma Kona Dolomite of Marquette, MI lies within the Chocolay Group of the Marquette Range Supergroup and has previously been correlated to the Cobalt Group of the Huronian Supergroup. The dolomitic units of the Gordon Lake Formation, Cobalt Group, are equivalent to the Kona Dolomite in Marquette and this study refers to the two dolomite units as a whole. These formations, termed the Kona Dolomite (KD) were deposited on what was a passive continental margin after the last Huronian glaciation and the Great Oxidation Event, making the KD an interesting suspect for analysis.

In order to better understand how free oxygen entered our atmosphere, sedimentological, geochemical, and isotopic techniques were utilized. It’s important to have a good understanding of the sedimentology and lithofacies before looking at the geochemistry in order to see localized depositional trends with the ocean chemistry. Thus, nine lithofacies associations (LA) have been identified in the KD based on their morphological and mineralogical differences. Each LA is indicative of its own depositional setting on a tidal flat.

The Ripples and Low Domes LA is composed of soft, centimetric, irregular, and wavy laminations of varying pink and gray carbonates- representing climbing ripples, wave ripples, and low-domal stromatolites. Lenticular and wavy bedding show bi-directional cross-stratification, a feature common in intertidal flat settings. Small Domal to Stratiform Stromatolite LA (<4cm tall) are low pustular stromatolites that have laterally continuous lamination and tend to gradually change upwards into stratiform stromatolites. These likely formed in an intertidal flat setting as they are associated with the bi-directional ripples.

Smooth to crinkly, millimetric, and relatively isopachous laminations comprise the Parallel Laminated LA. Laminations are wispy in places and contain low domes that are indicative of microbial activity and were likely situated within a pond on the intertidal flat.

Hummocky Cross-stratified (HCS) LA is composed of gray carbonate sands that have low-angle truncation surfaces and likely formed in a tidal channel environment that feed the tidal flat system. The stunning outcrop of Large Columnar to Domal Stromatolites (LCDS) stands 5 to 6m tall, and are composed of laterally continuous columnar lamination joined by cuspate depressions that gradually shift into domal stromatolites. The LCDS grew on top of the sandy HCS within the tidal channels.

Fenestral Microbialite LA show good, fairly isopachous banding with dark reddish elongated fenestrae that are discontinuous on the microscale but show low domes on a macroscale. The fenestral microbialite is similar in colour to the Bedded Siltstone and Mudstone LA as they are both composed of similar reddish-brown siliciclastics and carbonate. The latter is composed of intercalated siliciclastics, iron-rich, and iron-poor carbonate mud, and contain sub-euhedral rectangular carbonate clasts. The clasts were deposited by storm events that ripped up the fenestral microbialite in the upper intertidal flat, flooded the supratidal flat and deposited them on a sabkha.

The Subaqueous Gypsum Pseudomorph LA is composed of laterally continuous chevron textured carbonates replacing vertical gypsum crystals, while the Subaerial Gypsum Pseudomorph LA is composed of euhedral, diamond shaped pseudomorphs that lie within a very fine-grained dark purplish siliciclastic- and carbonate-rich groundmass. The former would have formed in an open water supersaturated environment, such as a pond on the sabkha, whereas the latter would have formed within the sediment in the sabkha itself.

Geochemically, these LAs are enriched in middle rare earth elements (REEs), but do not have pronounced Eu anomalies. Prior to the 2310 Ma KD, ocean chemistry was controlled by hydrothermal activity that created Eu enrichment compared to the other REEs. This contrasts with today’s oceans that are controlled by continental inflow. The absent Eu anomaly is illustrated in the REE concentrations of the LCDS and HCS LAs and represents what seems to be a turnover event from an ancient ocean system to a modern system.

Carbon isotopic ratios show an interesting trend when compared to their respective lithofacies. The δ¹³C increases from lower tidal flat to sabkha environments. This probably represents increasing evaporative loss of light CO_2. This local trend is superimposed on the beginning of the Lomagundi Event which is known as the most prolonged and largest period of carbon-13 enrichment in Earth’s history.

A potential kimberlite target known as “Target #6” has been identified 40km northwest of Marathon, ON, within the Wawa-Abitibi sub-province of the Superior Province.  Ground prospecting revealed a botanical anomaly that consists of a large semi-circular grassy area surrounded by a boreal mixed-wood forest.  A grassroots exploration program began in 2013, which has included diagnostic testing such as Soil Gas Hydrocarbon (SGH) analysis and an aeromagnetic survey, both of which showed positive indicators for the presence of a kimberlite (or related rock type).  This study utilized investigative techniques focusing on the surficial geology above this potential target to try and explain the botanical anomaly, and to further explore the geologic setting in order to better understand the occurrence.  Vegetation has been identified as Calamagrostis Stricta and Carex Utriculata, The species present in the anomaly are generally found in wet environments such as lake shores and margins of streams.  It has been shown that pH is not a control on the vegetation above the anomaly.  Grain size analysis of the soils was completed and shows indicator mineral chemistry was completed for any potential kimberlite indicator minerals, and results indicate that kimberlitic indicator minerals are not present.  It is possible that the vegetation above Target No. 6 is being directly influenced by an anomalous deposit below the sediment but the data collected in this study was unable to explain the vegetation anomaly.  The target appears to be a depression that has been filled in by sediment from a stream mouth bar, and the sediment may be acting as a vent for the deposit beneath it allowing the Soil Gas Hydrocarbons to be measured at surface.  The minerals in the surficial deposit above the target were not indicative of a kimberlite as they were likely derived from the previous glaciation event and not from weathering of the kimberlite (or other deposit) itself.

The Copper Bar Prospect, located southwest of Thunder Bay, Ontario is of interest for Ni-Cu-PGE exploration. Five historic trenches are found along the dike though there are no records of any results from them. The Copper Bar dike is a tholeiitic diabase intrusion, dominated by a sub-ophitic texture of plagioclase and pyroxene (primarily orthopyroxene). Sulphide mineralization is fairly consistent along the dike forming blebby fine- to medium-grained blebs. Fine-grained disseminations of chalcopyrite, pyrite and sphalerite are found throughout the dike. Secondary chalcopyrite mineralization is found in fractures in the more heavily altered samples. Three groupings can be distinguished petrographically and geochemically, Group one corresponding to more altered portions of the dike where complex mineralization is observed with galena, pyrrhotite, pyrite, magnetite, sphalerite, bornite, chalcopyrite, covellite, chalcocite and pentlandite with other trace sulphide mineralization. Group two represents relatively unaltered samples dominated by sub-ophitic texture. Mineralization in these samples is minimal, usually occurring as fine-grained disseminations of chalcopyrite, sphalerite and pyrite. Group three occurs as a more coarse-grained sample with overprinting blebby magnetite, pyrolusite and ilmenite phases. Generally, group three is similar to group one. Secondary pulses of magma seem to have effected the more altered samples with chalcopyrite rimming some sulphide grains and filling fractures. Overprinting sulphides and coarse- grained zones also indicate possible secondary magma pulses during emplacement of the dike. Though the dike presents favorable mineralization, low grade values were seen for Cu, Ni, Pt, Pd, Rh, Ir and Co. Partial melting and fractionation as well as failure to reach sulphide saturation sufficient to assimilate crustal sulfur are considered probable causes for the low grades observed. Positive Th and negative Nb anomalies typical of MCR-related intrusions indicate deep crustal contamination. Geochemical results also showed a strong vanadium depletion and slight titanium depletion. Group one samples showed more crustal contamination then group two, and group three had a distinct enrichment of heavy rare earth element not seen in group one or two.

The EBL 10-027 drill hole goes through the 2.94 Ga top of the Ball assemblage of the Red Lake greenstone belt, northwestern Ontario.  It reveals a succession of chemical sediments and siliciclastics that shows, for the most part, a progression from a hydrothermal signature with the formation of sulphides close to the bottom of the sequence to chemical sediments reflecting the influence of seawater at the top.  The stratigraphy is dominated by sulphides, i.e. pyrite and pyrrhotite, carbonaceous slate, magnetite iron formation and chert.  The chert varies from units roughly mixed up with siliciclastics and sulphides to chert that is nicely layered with sulphides and contorted to finely layered carbonate with dolomite crystals.

The drill hole has a true thickness of about 280 metres which allows the bottom sediments to reflect the geochemistry of deeper water hydrothermal activity with fluids rich in iron and manganese while the top is composed of carbonates that reflect the chemistry of a shallow, continental shelf environment.

The evident europium (Eu) anomaly present in the sample signifies the effect of the leaching of basalt which is interlayered with carbonate iron formation at the lowest point of the sequence.

The Wabigoon and Quetico subprovinces are east-west trending belts of metasedimentary and metavolcanic rocks located within the Superior province, the world’s largest preserved Archean craton.  The Wabigoon-Quetico subprovince boundary in the Decourcey Lake area is complex and several kilometres wide.  The 130m-long roadcut on Hwy 527 near Decourcey Lake is composed of a garnet-biotite to biotite schist with three intrusions, a pegmatitic intrusion, a felsic intrusion and a mafic dyke.  There are also several quartz-carbonate veins that have been folded and boudinaged; the folded veins crosscut the boudinaged veins that are parallel to foliation. 

In the southern portion of the outcrop, mats of fibrolite in the schist indicate peak metamorphism at amphibolite facies or higher.  However, some parts of the outcrop show evidence of overprinting retrograde metamorphism.  The amount of retrograde metamorphism increases from south to north in the outcrop.  In the southern part of the outcrop there are minimal amounts of chlorite (~1%) and the amount increases to about 30% in the north.  The chlorite replaces biotite, the main mica in the southern portion of the roadcut.  Chlorite replacing biotite is indicative of retrograde metamorphism.

Other evidence for this retrograde metamorphism is the presence of stable garnet in the southern portion of the outcrop and metastable garnet in the northern portion, indicated by euhedral unfractured crystals in the south and anhedral, fractured and separated grains in the north.

Throughout the schist, quartz with undulose extinction, irregular grain boundaries and subgrains provides evidence for deformation by dislocation creep.  In the southern portion of the outcrop, undulose extinction in feldspar indicates deformation at amphibolite facies temperatures or higher.  This higher temperature deformation of feldspar is not evident in the northern portion of the outcrop where retrograde metamorphism is more pervasive.  The pegmatite and felsic intrusions preserve evidence of deformation at the amphibolite facies or higher, including undulose extinction in feldspar and bent mica grains.

The preservation of evidence for amphibolite facies metamorphism and high temperature deformation in schist in the southern portion of the outcrop as well as in the pegmatite and felsic intrusions suggests that the Decourcey Lake roadcut is composed of metamorphosed Quetico lithologies.  Therefore, the Quetico-Wabigoon subprovince boundary lies to the north of this roadcut.  The increase in retrograde metamorphism toward the northern portion of the outcrop (in the direction of the subprovince boundary) suggests that this lower temperature metamorphism may be associated with the boundary.

The Hemlo gold deposit, Ontario, Canada is located in the Archean Schreiber-Hemlo greenstone belt, Wawa subprovince, of the Superior Province.  The deposit has been subjected to a complex history of deformation and intense hydrothermal alteration.

The host lithology to most of the gold at Hemlo is the Moose Lake Prophyry Complex (MLPC), a felsic orthogneiss, characterized by the occurrence of quartz “eyes”.  These quartz “eyes” are deformed quartz porphyroclasts.  The matrix of the MLPC is mylonitic, composed of quartz, microcline, minor biotite and white mica.  The micas define the weak to strong foliation.  Other minerals present are calcite, plagioclase, and pyrite, with trace gold, titanite and tourmaline.  The porphyroclasts of quartz range in size from 1mm to 5mm, are typically elongated to form the characteristic eye shape and rarely appear together to with feldspar porphyroclasts.

Although common in association with gold deposits, quartz “eyes” are generally rare.  An objective of this thesis is to explain the occurrence of quartz porphyroclasts in a mylonite, quartzo-feldspathic matrix.  Microscopic observations reveal the brittle deformation and alteration of feldspar porphyroclasts in spatial association with ductile deformation of quartz porphyroclasts.  Although debatable, the protolith of MLPC is generally thought to be volcanic.  After detailed examination of samples collected from the MLPC, this study concludes a plutonic origin for the quartz porphyroclasts can not be ruled out.

The purpose of this study was to use leaching test experiments to help explain the lithological controls on the groundwater geochemistry of different geologic formations in the Thunder Bay area.  A secondary goal of this project was to test the effectiveness of the 15 minute USGS Field Leach Test for this purpose relative to more conventional 30-day deionized water and acetic acid tests.

Samples were taken from different sedimentary units of the Gunflint and Rove as well as from the Sudbury Impact layer, diabase, and granite formations of the Thunder Bay area.  Some of the samples used in this study were collected from previously logged drill core from the MNDM library.  Each sample was crushed into a fine powder.  The fine powders were bottled and labeled, with half the bottles being shipped to the Geoscience Labs in Sudbury for whole rock geochemical analysis and the other half remaining in Thunder Bay to be used for leach test analysis.

Three types of leach tests were performed in this study.  These included the USGS Field Leach Test, a 30-day double deionized water leach test, and a 30-day leach test using a 5% acetic acid solution.  All three of the leach test types used a 20:1 leachate to sample ratio, using 2.5 grams of sample and 50 mL of leaching agent.  The USGS Field Leach Test is a relatively new method developed for testing the leaching potential of different geologic and environmental materials.  This testing method requires the use of the 20:1 sample to leachate ratio, and that the sample be added to deionized water, shaken for a period of five minutes, and then allowed to settle for ten minutes before being filtered and submitted for geochemical analysis.  The effectiveness of this method as a way of determining the leaching potential of rocks in groundwater basins was in question because it did not seem logical that such a short-term test could provide any accurate insight into the water rock reactions that occur over long-periods of time in groundwater basins.

Whole rock and leach test geochemical data were used to produce two types of graphs.  The first graph type showed a comparison of whole rock and leach attest concentrations for each element analyzed.  The second graph showed the percentage of whole rock elemental content that was leached into solution for each of the three leach tests.  Through analysis of each graph it was determined that calcium, magnesium, sodium, and potassium are the elements most readily leached into solution from the rock samples analyzed.

The second method used to analyze data in this study was Piper plots.  Piper plots are commonly used for analyzing groundwater geochemistry.  A Piper plot classifies water samples into four different types based on its concentration of major cations (Ca²⁺, Mg²⁺,Na²⁺, and K⁺) and major anions (HCO₃^-, CO₃^-, CI^-, SO₄^2-).  Through analysis of each Piper plot, it was determined that samples collected from the Rove Formation tend to produce sodium bicarbonate type groundwater, whereas samples collected from the Gunflint Formation produce a variety of groundwater types.

Lastly, this study was conducted to evaluate the effectiveness of the USGS Field Leach Test as a method for determining the leaching potential of elements in groundwater analysis.  Due to the difficulty of filtering the leach test solutions performed in the method specified by the USGS Field Leach Test protocols and the poor geochemical data provided by these leach test solutions, it was determined that this is not the best method that can be used for groundwater analysis.

The Gold Creek prospect is hosted in a brittle-ductile shear zone within the eastern margin of the Peewatai pluton, a dioritic to monzodioritic intrusion in supracrustal rocks of the Greenwater and Shebandowan assemblages, within the Shebandowan greenstone belt of the southern Superior province.  The deformed plutonic host rock, a quartz-feldspar gneiss, is cross-cut by discrete east-northeast-to east-trending dextral shear zones.  Gold mineralization occurs in approximately north-trending extensional veins, which are hosted entirely within quartz-feldspar gneiss along the contact of ductile shear zones.  The emplacement of the auriferous extensional veins is interpreted to have taken place contemporaneously during dextral shearing.

The Chipman Lake carbonatite is located NW of Marathon, Ontario, within the Wabigoon Subprovince of the Superior Province.  The dikes are generally less than one meter thick and outcrop along the glaciated shores of Chipman Lake.  The spatial localization of multiple alkaline and carbonatite complexes along the Thiel Fault supports a relationship to Midcontinent rift related events.  Recent exploration in the area has revealed some new outcropping thin dikes, which had not been previously identified.  The focus of this study was to classify these new occurrences of Chipman Lake carbonatite dikes, based on their mineralogy and petrology, and compare with other previously investigated carbonatites.  Minerals identified include dolomite, calcite, ferroan dolomite, phlogopite, biotite, fluoromagnesio- arfvedsonite, apatite, albite, K-feldspar, aegirine, pyrochlore, pyrite, synchysite, cerrusite and burbankite.  The Chipman Lake dikes were determined to represent carbonatites without associated silicate rocks and are interpreted to be the late stage fluids derived from a nearby or buried carbonatitic parent.  The presence of Ca-bearing niobium pyrochlore and the REE-fluorocarbonate synchysite are strong indications of a primary carbonatite parent.  Detailed analysis of pyrochlore indicated that these pyrochlore were calcium-bearing niobium pyrochlore with enrichment in U and Ce.

The Coldwell Alkali Complex is a Proterozoic intrusion emplaced within the Archean Schreiber-Hemlo Greenstone belt in northern Ontario.  The rocks that comprise the greenstone belt include metavolcanic and metasedimentary rocks, as well as granitic intrusions.  Along the northwestern contact of the complex, the Archean host rocks have been altered in a manner not normally seen throughout the complex.  This study analyzed sandstones, felsic pyroclastic rocks, iron formation, lamprophyres and a gabbroic intrusion in order to characterize the mode of occurrence of alteration present and determine a potential origin.  The alteration types include silicification, sericitization, tourmaline alteration and hematite alteration.

Trenches were created in order to produce exposure of the units that host the alteration.  Hematite alteration has created a distinct reddening of the felsic pyroclastic units present, and displays great variability in its mode of occurrence and alteration intensity.  Although hematite alteration is most intense in the felsic units within the trench area, the alteration occurs throughout the area and affects all intrusive units present.  Distal sandstone samples taken as control units did not exhibit pervasive alteration.  The mode of occurrence of the hematite is consistently pervasive into the crystalline lattice of quartz and feldspar grains, and it is concentrated along quartz veins, within fractures, and forms as replacement of Fe-sulphides.  There is a weak correlation to iron concentration corresponding to areas of more intense hematite alteration.

The dominant lithology is a felsic tuff unit consisting of a quartz and feldspar dominated groundmass with varying intensity of pervasive hematite alteration.  There is a high incorporation of volcanic ash within the iron formation unit, and thus it has acquired the geochemical signature of the felsic tuff unit.  This felsic tuff is defined by U-Pb zircon geochronology that represents a Neoarchean zircon population that indicates an age of roughly 2708 ± 23Ma.