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.

The Morley Pyrite Occurrence is an Algoma Type sulfide-facies iron formation, located southeast of the town of Schreiber, in the Abitibi-Wawa Subprovince of the Superior Structural Province.  The iron formation consists of colloform pyritic structures, horizontally laminated pyrite, veins and massive pyrite in a chert/carbonaceous slate assemblage.  This is overlain by fine grained metasediments and mafic volcanics, and underlain by intermediate volcanics.

Colloform structures, up to 5.2 centimeters in diameter, are comprised of alternating, millimeter thick laminae consisting of pyrite or chert/carbonaceous slate.  The colloform structures have distinctive morphologies and display variable angular relationships with underlying strata.  Where several structures have developed adjacent to one another, the resulting structure appears stromatolitic.

Carbon, while present in pyritic laminae, was a major constituent in the siliceous bands, with magnetite, hematite, greenalite and stilpnomelane also being identified.  Magnetite and hematite, present at the upper chert and lower pyritic laminae contacts, indicate cyclical variations in Eh conditions during the formation of the laminae.  Stilpnomelane, indicative of greenschist metamorphism, is also associated with brecciated fragments of colloform structures.  Pyrite rims have developed on these fragments, which in turn are locally mantled by sphalerite.  Stilpnomelane is associated as rinds on the sphalerite.  Stilpnomelane is associated as rinds on the sphalerite, indicating post breccia development and possible association with higher temperature hydrothermal fluids.

The geochemistry of the occurrence, the fine grained nature of the sediment, the abundance of pyrite and the presence of tuffaceous material incorporated into the laminae, suggests a distal, anoxic basin in which reducing conditions dominated and episodic, low temperature hydrothermal input played a significant role.  The presence of carbon in the laminae and the regular morphology of the colloform structures suggests an at least partial biogenic origin in which Archean organic mats accumulated sulfidic and siliceous sediment.

The study area is located approximately 55 km west of the city of Thunder Bay, at the intersection of Highwasy 11 and 17.

Two outcrops were studied; one being a coarse lithic greywacke and the other a polymict conglomerate, both of Archean age.

R_f/φ analysis was used to determine the shape and orientation of five strain ellipsoids from oriented samples of greywacke, and one strain ellipsoid from the conglomerate.  An averaged strain ellipsoid was calculated using averaged strain components.

Analysis showed that original pebbles had cross-sections ranging from circular (R_o = 1.0) to elliptical (R_o = 6.0).  The strain ellipsoid is a flattened type ellipsoid with k = 0.19, and the X_tY_t plane lying parallel to the plane of bedding in the greywackes.

The close approximation of the averaged strain ellipsoid to a uniaxial pancake type ellipsoid allows discussion to be simplified to the X_tZ_t plane (ie. the maximum strain ellipse) of the strain ellipsoid.  The plane of the maximum strain ellipse lies perpendicular to the plane of bedding and defines a maximum shear strain of 4.5, a maximum angular shear of 77° with 80% shortening in the Z_t direction versus 83% lengthening in the X_t direction.

A simple model involving progressive deformation of an infinity long bed is proposed to explain the shape and orientation of the strain ellipsoid, as well as the closely spaced opposing facing directions which occur in the study area.

The area of investigation is located at the interface of the Quetico and Wabigoon Subprovince of the Superior Province of the Canadian Shield, in Northwestern Ontario, about 235 kilometers west of Thunder Bay.

The Quetico Subprovince comprises a monotonous series of thin- to medium-based, metamorphosed mudstones, wackes and sandstones that display many of the primary sedimentary features attributed to turbidites.  To the north, a highly sheared polymictic conglomerate grades conformably into a mafic to intermediate tuff.  This shear zone, believed to represent rocks of the Quetico Fault zone, accentuates the boundary of the Quetico and Wabigoon Subprovinces at this point.

Greenschist facies metamorphic grade increases from chlorite zone in the north to biotite zone in the south. 

A single, dominant deformation event resulted in the development of two isoclinal folds with ENE striking axial surfaces accompanied by a discrete, penetrative and, probably axial planar cleavage.  These folds are identified as an antiformal syncline closing to the west and a synformal anticline closing to the east.  The folds have moderate to steeply plunging, curved hinge lines.   The structural facing of the folds of the Quetico metasediments varies from vertically downward- facing to eastward- facing

The bedrock underlying Burnt Island and portions of the East Bay of Dog Lake is typical of the lithologies commonly associated with those of the Quetico Gneiss Belt.

Investigation of this area has revealed five distinct rock units, many of which are comprised of more than one rock type.  Two of these units represent metamorphic equivalents of pre-existing rocks of pelitic and basic compositions.  These units have undergone polyphase deformation and metamorphism.

The first deformational episode produced folding about east-west axial surfaces and was associated with amphibolite grade metamorphism.  Partial melting of the host rocks during this metamorphism gave rise to two distinctive rock units.  The last of the five rock units recognized is incorporated in crystallized partial melt products as exotic blocks.

A second deformational event affected the rocks producing folds with north-south striking axial surfaces.

All rocks in this area are variably affected by a later retrogressive metamorphic event.