A three to four meter thick limestone assemblage (Ardness Formation) contained within a thick redbed succession (Lismore Formation) was deposited in a semiarid climatic setting during an expansion of the Windsorian Sea (Late Vis©an).  Schenk's (1969) generalized facies model for the Windsor Group described eight depositional environments.  However, alluvial fans associated with an uplifted horst, mudcracks and authigenic sulphate minerals found in the salt flat, and algal mats of the intertidal zone are all absent in the Ardness and proximal Lismore Formations.  Shallow marine depositional systems controlled sedimentation in the offshore but a fluvial depositional system dominated the nearshore and terrestrial environments.  From the offshore landward the depositional environments in the Ardness Formation are:  1) oolitic shoal;  2) lagoon (subtidal);  3) nearshore; and  4) fluvial floodplains. 

A network of small meandering channels, represented by channel, point bar, and floodplain lithofacies, transported by siliclastics through the fluvial floodplain environment.  These high-sinuosity channels emptied into a restricted brackish lagoonal system dominated by siliciclastics on the landward side and carbonates on the seaward side.  During storm events ooids and shell debris were washed into the lagoon from the offshore.  An ooid shoal complex marked maximum transgression into the basin.  Decreasing water depth led to the stabilization of the oolitic shoals and to the development of minor amounts of evaporate minerals and algal stromatolites.  Fluvial channels cut into the top of the carbonate assemblage and mark progradation of the fluvial depositional system into the area.

Numerous gold bearing quartz vein systems are found in oxide facies banded iron formations of the Beardmore-Geraldton area.  They exhibit a spatial relationship with zones of dilated cleavage and fracture networks that transect the limbs and hinges of asymmetric folds.  Many of the gold deposits in the region are located in close proximity to east-west trending fault zones that may have acted as plumbing systems for the auriferous hydrothermal fluids.

In this thesis the geological setting of the gold mineralization is discussed with particular emphasis on mineralogy, alteration and structural control of the vein systems.  Several gold bearing veins were studied from a select number of mine sites and gold occurrences to obtain information on the mineralization processes.

The mineralogy of the quartz veins and spatially associated sulphidation and carbonatization alteration zones were examined in detail.  The results suggest the precipitation of gold from hydrothermal solutions was concomitant with the replacement of the iron formations by pyrite and arsenopyrite.

Gold may have been transported as reduced sulphur complexes in CO₂ rich fluids of low salinity derived by the metamorphic devolitization of a greenstone terrain at the transition between greenschist and amphibolite facies.  The emplacement of the veins is predominantly a late stage event although evidence suggests some veining may have occurred concomitant with a regional episode of deformation.

The iron formations in the study area were important as both chemical and structural traps for gold precipitation.  The competency of the units allowed for ductile and brittle deformation providing low pressure zones for the hydrothermal fluids.  They also supplied abundant Fe for sulphidation processes initiating the reduction of gold in solution to elemental gold following the reaction:

  2Fe₃O₄    +    6Au(HS)₂- +  6H +         6FeS_{2 +} 8H₂O  +  6Au
(magnetite)     (bisulphide gold complex)      (pyrite)           (gold)

Ivanhoe Lake is located 220km east of Wawa, Ontario, Canada. The Ivanhoe Lake structure strikes northeast to southwest and is the boundary between the high grade metamorphism of the Kapuskasing structural zone and the low grade metamorphism of the Abitibi subprovince. This difference in grade of metamorphism is what makes the Ivanhoe Lake structure so interesting to study. Through analysis of the microstructures seen in thin section a long deformation history was revealed. Ductile deformation, characteristic of deep burial, as well as deformation at or near the brittle-ductile transition zone were evident. This affects a wide area that extends to either side of the structure. This was followed by brittle fracturing at a shallower depth of burial. The brittle deformation is confined to a narrow zone found along Ivanhoe Lake. Examples of ductile deformation within the thin sections include: undulatory extinction in quartz, subgrains in quartz and feldspars, deformation twins in plagioclase and microcline, as well as irregular grain boundaries for all grains. The brittle-ductile transition zone is documented by the existence of pseudotachylites. These glassy rocks are characteristic of large faults. The brittle history is documented by quartz or calcite filled fractures found at both the outcrop and microscopic scale. These brittle structures always crosscut the ductile features. This crosscutting relationship suggests that the structure has had a long history which began with ductile deformation and progressed into brittle deformation.

The Zenith zinc deposit, near Schreiber, Ontario, is a small massive sulphide deposit yielding sphalerite, chalcopyrite, and pyrrhotite.  It is hosted by a metadiorite sill.  The country rocks are metasediments and metapyroclastic rocks in the foot wall in the western part of the map area, while a mafic metavolcanic unit forms the hanging wall in the northeast part of the area.  The entire series is bounded on the west and south by granite.  Metamorphic grades vary from high-grade (Winkler, 1974), indicated by migmatites at the contacts with the granite, to amphibolite and greenschist facies (medium and low-grade) in the country rocks.

The main sulphide ore, massive sphalerite, occurs in fracture fillings which form the matrix of a zone of fault breccia.  The mechanism of hydraulic fracture is proposed to explain the localization of the sulphide ore.  These sulphides are postulated to have been remobilized from sulphide rich xenoliths contained in the sill which originated as metasedimentary-metapyroclastic foot wall rocks.

The Pass Lake Formation forms the lowest portion of the Sibley Group sedimentary sequence.  It consists of a basal conglomerate overlain by upward thinning beds of quartz arenite which disconformably overly the Paleoproterozoic Rove Formation.  This study used both SEM-EDS analyses of zircon, as well as whole rock geochemical methods in determining possible source areas for the Pass Lake Formation.  The use of zircon analyses in provenance studies has been undertaken only once before by Owen (1987) in a stuffy which yielded promising results.

Zircon from the Pass Lake Formation, Redstone Point granite and two regional granite sources were analyzed for Zr, Hf, Y, Th, and U using SEM-EDS methods.  Three distinctive fields were defined by the granite:  Type I - Redstone Point granite field, Type II - Regional granite field, and Type III - Y, Th, U enriched field.  The majority of the Redstone Point sandstone and a significant portion of the Pass Lake sandstone plot within Type I and Type II fields.  Approximately 40 percent of Pass Lake sandstone zircons plot within the heavy element enriched field.

Whole rock geochemical data divide the Redstone Point, and Regional granites into three distinct fields.  Pass Lake and Redstone Point sandstones plot together in a separate field which lies between the Redstone Point granite (enriched) and a Regional granite (depleted) fields.  Ratio plots using Y and Zr vs Nb indicate a mixing trend in the sandstones between the Redstone Point and Regional granites.

The influence of the Redstone Point granite within the Pass Lake Formation appears to be spread throughout the sequence with a relatively constant mixing ratio between Redstone Point granitic material and other sources.  Whole rock geochemical data compiled over the course of this study was compared with additional geochemical data from both published and non-published sources.

Volcanic rocks in the area form part of an Archean volcano-sedimentary succession.  The rocks have been subjected to three episodes of deformation.  Minor folds in the area have formed on the southwest limb of a regional anticlinal structure.  The axial surface of the regional anticline strikes north-northwest and dips steeply to the northeast.  The minor folds were superimposed by small-scale folds and chevron folds of a later folding episode.  A prominent crenulation cleavage and kink banding accompanied this folding event.  The final deformation is expressed by the development of kink bands which are overprinting pre-existing structures.

Plutonic rocks were emplaced and their outcrop pattern is elongated parallel to the axial surface of the regional anticlinal structure.

In this study of the Gunflint Formation a two part approach was taken in the determination of the depositional environments and diagenesis of selected sections.

A depositional systems method was employed consisting of a progression of lithofacies, lithofacies associations and depositional environments.  The model derived is from a genetic interpretation of the conditions that prevailed during sedimentation. 

Sequencing of post depositional alteration produces a branching pattern of mineralogic and textural variation in a separate evaluation of diagenesis.

Segmenting into depositonal and diagenetic systems is made in recognizing that the environment of deposition and the conditions of diagenesis are unique in their physical and chemical characteristics.

Primary textural considerations suggest carbonate deposition in an arid environment.  Diagenetic textures indicate that deposition was followed by early silica cementation accompanied by iron compounds.  Subsequent replacement and alteration results in the progressive elimination of primary, sedimentary, mineralogy and structure.

The area of study was the UNESCO World Heritage site, Dinosaur Provincial Park, Alberta, Canada.  The sedimentary rocks that are exposed here are composed of medium-grained sandstone and mudstones.  They represent the upper 3^rd member of the Old Man Formation, the Dinosaur Park Formation, and the basal Bear Paw Formation.  This study focused on the sediments deposited at and near the Old Man Formation / Dinosaur Park Formation contact that were laid down seventy-five million years ago.

The various lithofacies found in the Dinosaur Provincial Park stratigraphy have been grouped into lithofacies associations, and because of Walther's Law, these associations can be traced across stratigraphic units, and can illustrate aspects of the overall palaeoenvironment.

The environment at this time was dominated by a fluvial-floodplain-lacustrine depositional system.  The lacustrine facies are mostly composed of parallel laminated silts and clays, with periodic interbedded massive or ripple-laminated sand lenses.  Sand layers and coarsening upwards sequences of clay, silt and sand were observed, from splays and delta outbuilding respectively.  The lakes were the most common mode of deposition on the floodplain especially in the Old Man Formation, though crevasse splays were observed near the active channels.  The fluvial sandstones exhibited epsilon x-stratification in some cases, and stacked channel sequences (espically in the Dinosaur Park Formation), and are also commonly errosively scoured into underlying units.  Also the sequence of bedforms and fining upward sequences observed in these sandstones are similar to those described in the classical point-bar model of Allen (1964).  This suggests that floodplain-lifetime was dictated by the amount of time it took for a meandering streams point-bar to cross it.

Paleocurrents were measured during the logging of all sections.  One hundred and eighty-six paleocurrents were measured in total, seventy-four from the Old Man Formation, and one hundred and twelve from the Dinosaur Park Formation.  These were grouped into give metre intervals from 20m below the Old Man Formation / Dinosaur Park Formation contact, to 20m above.  The paleocurrents illustrate a gradual switch in flow direction from northeast to southeast as you move up section.  This is compatible with the change found by Eberth and Hamblin in 1993.

Accompanying the change in paleocurrent direction across the contact, there was considerable penecontemperaneous deformation, specifically, convoluted bedding and ball and pillow structures.  This suggests that there were earthquakes associated with the block rotation, which changed the slope of the land in the Upper Cretaceous area near Dinosaur Provincial Park.

Reconnaissance studies along a roughly north-south traverse across the Quetico gneiss belt, utilizing roadcuts in Ontario Highway 527, have been made in order to characterize uranium-bearing pegmatites I and adjacent to the Gneiss Belt.  Analyses of samples by the Geological Survey of Canada revealed uranium contents ranging from less than 10 ppm U to 36.3 ppm in the pegmatites.

The pegmatites are of three distinct types: a granitic pegmatite showing intrusive relationships to all other rocks in the area, a migmatitic pegmatite intimately related to the gneisses of the Quetico Belt, and, a pink syenitic pegmatite emplaced in the high grade gneiss.  The granitic pegmatites are located near the north and south margins of the Gneiss Belt and extend into the adjacent Wabigoon and Shebandowan Wawa Greenstone Belts.  The pegmatites occur as dykes or lensoidal bodies of plagioclase-perthite-quartz with varying amounts of biotite and muscovite.  Accessory minerals include zircon, garnet, tourmaline, and rare hematite.  Apatite occurs in the most uranium-rich sample.

The syenitic pegmatite occurs as a dyke in the middle of the Quetico belt and is bordered by the migmatitic pegmatites.  Feldspars constitute 75% of the rock, and quartz 20%, with biotite and zircons as the accessories.  Uranium in the syenitic pegmatites is the lowest at 2.3 ppm.

The migmatitic pegmatites occur as lenses and migmatite bands most strongly in the centre of the Quetico Belt.  The pegmatites are feldspar-rick (ca. 75%) consisting of oligoclase with microcline exsolutions, quartz, muscovite, and minor corroded biotite.  Accessories include zircon, cordierite, sillimanite, garnet, and chorite.  The latter suggest that these pegmatites have been metamorphosed.  Boudinage and ptygmatic folding of small dykes is also observed.

Uranium in the migmatitic pegmatites was fairly uniformly distributed in the range of 2-7 ppm, but ranges to highs of 36.3 ppm in the granitic pegmatites.  No uranium mineralization was identified, but zircon is the probable host in most rocks.  The high value was found in an apatite-bearing rock, and this mineral is a likely host for uranium, as well.  The pegmatites do not seem likely prospects for economic deposits of uranium, owing to a lack of identifiably mineralization and low concentrations.  They may, however, be the ultimate source of disseminated uranium in the Sibley Group sandstones and unconformity-vein type uranium deposits in the Greenwich Lake area.

A Paleomagnetic Study of the Logan Sills, Northwestern Ontario

David A. Baker - 2001

A total of 74 oriented samples were collected from the Proterozoic Logan Sills of Northwestern Ontario.  The anisotropy of magnetic susceptibility (AMS) of 207 cores drilled from the 74 oriented samples was measured.  The magnetic foliation which defines the average magmatic flow plane shows that the flow was subhorizontal with flow axes varying between sample locations; however a NE-SW flow axes dominates.  This is approximately perpendicular to the Nipigon Rift.

The natural remnant magnetism (NRM) was used to determine the Koningsberger ratio of all 74 samples.  The average value is 1.060 " 0.166, with a standard deviation of 13.856.  This advocates great caution in the interpretation of aeromagnetic or ground magnetic surveys, because remanent magnetization may mask the induced magnetization due to the present geomagnetic field.

Progressive thermal demagnetization of 74 oriented samples in 10 steps from 100°C to 560°C revealed stable components by principal Component Analysis (PCA).  These sample show both upward and downward primary remanence directions, as well as a downward secondary.  Some, but not all of the principal components correspond to the Proterozoic apparent polar wander path (APWP) for North America.  The anomalous principal components have yet to be explained.