The upper sands of the discontinous Halfway Formation to the northeast of Fort St. John were formed as barrier islands deposited perpendicular, or nearly perpendicular to the dip of the paleoslope of the Western Canadian Sedimentary Basin.  These upper sands of the area of study were deposited during a transgressive phase of the Triassic sea to the northeast, and formed the basal unit of an onlapping sequence comprising the Halfway and the Charlie Lake Formations that disconformably overstepped the erosional surface on the silty dolomite of the Doig Formation.  The Weasel sand body was deposited during a pause in the transgression, and then was submerged by a rapid rise in sea level.  The Wildmint to Beatton barrier islands trend was deposited during a second pause in the transgression.  These barrier islands would appear to have been deposited under arid conditions resulting in restricted lagoonal environments.  The lower sands of the discontinuous Halfway Formation which only occur at a few locations in southern Willow and Wildmint, would appear to have resulted from tidal inlet action that eroded channels into the Doig Formation below the base of the upper sands forming the barrier island complex.  These later were filled with sand.  Then this barrier island trend was submerged by renewed transgression of the Triassic sea.  The source of the sediments comprising the discontinous Halfway Formation probably was to the north and northeast of the area of study. 

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The Quetico fault is a major transcurrent fault in the southern Superior Province of the Canadian Shield.  Along part of its length the fault forms the boundary between the Quetico and Wabigoon subprovinces.  Dextral motion on the fault is indicated by dextral microfaults and approximately asymmetrical quartz c-axis petrofabrics.

The fault comprises a zone of dynamically metamorphosed rocks - primarily mylonitic rocks with some cataclastic rocks and pseudotachylite.  A transition from predominantly ductile deformation to brittle deformation occurred during the time the fault was active.

The ductile deformation of quartz within the fault zone is the result of crystal-plastic processes, predominantly slip on prism planes in the a-direction and slip on rhomb planes in the a-direction, accompanied by dynamic recovery and syntectonic recrystallization.  Feldspar grains are commonly deformed in a brittle manner by fracture processes.  Particulate flow appears to have made a significant contribution to deformation in the fault zone.

The harmonic mean of deformed grain axial-ratios and strain determinations by the all object-object separations method indicate that flattening strain is predominant within the fault zone.  The magnetic susceptibility anistropy ellipsoid is also flat-shaped and coaxial with the strain ellipsoids.  The characteristics of microfaults and folds within the fault zone indicate that flattening may have been accompanied by or followed by shearing.  The harmonic mean of deformed quartz grain axial ratios yields a minimum strain estimate of 130% extensions in X, 58% extension in Y, and 71% shortening in the Z direction.

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Detailed mapping was carried out in the Shebandowan Lakes area and eastward to the Kaministiquia River to study the structural and stratigraphic relationships between the Keewatin and Timiskaming rocks (herein referred to as Keewatin-type and Shebandowan-type, respectively, to avoid connotations of time-stratigraphic equivalence with type areas) of the region.

It is believed that the Shebandowan-type rocks are younger than the Keewatin-type rocks.  Although no actual contact between the two has been seen in outcrop in the study area, the trend of their contact is discordant with the trend of cleavage in the Shebandowan-type rocks.  This, along with the less recrystallized appearance of the Shebandowan-type rocks, and the presence of clasts of jasper in conglomerates of the Shebandowan-type sequence similar in appearance to the jaspilitic iron formation interbedded with the Keewatin-type mafic volcanics, leads to the conclusion that an unconformity separates the two groups of rocks.  Recent geochronological work on some of the rocks in the region, carried out by the Ontario Geological Survey, supports this theory.

The macroscopic, microscopic and sub-microscopic structure of both groups of rocks was examined in detail.  The minor structures seen in outcrop, the examination of thin sections, scanning electron microscope work, and the determination of the magnetic fabric of the rocks all show that the rocks in the present study area contain a single, penetrative, primary cleavage, which has a consistent trend across the whole area.  The regional structural picture which emerges from the data is characterized by close-spaced, isoclinal folding with sub-vertical fold axial traces trending roughly east-west.  Local variations exist in the eastern portion of the study area where more widely-spaced and open folding is more common.  No evidence of a second, significant period of deformation in the present study area has been found.

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Zn-Pb-Ag mineralization at Nanisivik, northwest Baffin Island, is hosted by Proterozoic, laminated dolostone of the Society Cliffs Formation.  Mineralization of the Main Orebody is highly variable in terms of texture and mineralogy exhibiting both replacement and open space filling textures.  Sulfides are generally coarsely crystalline and banding, consisting of interlayered pyrite, sphalerite, galena and sparry dolomite, is common along the margins of the Upper Lens of the Main Orebody.  The eastern and central portions of the Upper Lens are characterized by laterally extensive mine units, which are distinguished on the basis of texture and mineralogy.  Contacts between units are generally sharp.

The physical and chemical parameters responsible for the textural and mineralogical variations have been evaluated through a study of fluid inclusions, sulfur isotopes and ore mineralogy.  Fluid inclusion homogenization temperatures from simple, two-phase primary and pseudo-secondary inclusions in sphalerite and sparry dolomite gangue indicate initial temperatures of ore formation from 150-210°C in the eastern Upper Lens when the estimated pressure of ore formation is taken into consideration.  The temperature of ore formation decreased to 100-150°C in the western portion of the Upper Lens.  Freezing studies indicate that the ore-forming fluid was a brine containing 20-37 equivalent weight percent CaCl₂.  The sulfur isotopic compositions of late and main stage pyrite crystals range from δ³⁴s = +27.4€ to + 28.0€, suggesting relatively constant temperature, fluid source and dominant sulfur species in the ore fluid during ore formation, providing there has been no subsequent re-equilibriation of sulfur isotopes.  The iron content of sphalerite varies from 14 mole % to 0 mole % from crystal centers to rims respectively, corresponding to well developed colour zonation.  Sphalerite iron contents constrain the oxygen activity of the ore fluid from 10^-46 to 10^-41 at 200°C during sphalerite precipitation.  The best developed zoning and, thus, the highest oxygen activities occur within sphalerite adjacent to carbonate wall rock.  Under high oxygen activities, conditions were favorable for the generation of sulfanes considered necessary for precipitation of marcasite.  X-ray diffraction studies indicate that primary marcasite has inverted completely to pyrite.  The stability of the simplest sulfane, H₂S₂, constrains the maximum allowable pH of the ore fluid at the time of marcasite precipitation to 5.0.  The presence of interbanded marcasite pseudomorphs and sparry dolomite indicate that the ore fluid fluctuated around pH = 5.0.

Comparison of solid organics extracted from the Society Cliffs dolostone to bitumen associated with mineralization suggests that organics within the host formation have played a role in sulfate reduction.  The model of ore formation therefore proposed involves the in situ reduction of a hot, saline, metal-bearing ore fluid by hydrocarbons liberated by the replacement and dissolution of wall rock.  Sulfate reduction was probably concentrated at the wall rock orebody interface along a replacement front that migrated away from the orebody.  Banding was likely the result of repetitive sulfate reduction, metal precipitation and wall rock dissolution in response to the pulsatory influx of ore fluid.  Gross textural and mineralogical variations are probably a result of slight variations in the oxidation state of the ore fluid, the availability of H₂S and, to a lesser extent, temperature.

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The Quetico metasedimentary rocks are the metamorphosed equivalents of a turbidite sequence, comprised of a repetitive interstratification of sandstones and mudstones.  The rocks are metamorphosed to lower greenschist facies, but metamorphic grade increases progressively from north to south.  Anchimetamorphosed phyllites and slates in the north part of the present study area grade progressively into biotite schists in the south part.

Interpretation of structural features in the study area, mainly bedding (S₀) - cleavage (S₁) relationships and structural facing directions, has led to the delineation of a number of major F₁ folds.

These are tight to isoclinal, asymmetric sheath folds, with axial planes arranged en echelon and slightly oblique to the dominant east-west, vertically-dipping, structural trend.  The orientation, geometry and disposition of the F₁ fold suggest the Quetico rocks of the present study area have experienced a regional dextral transpressional tectonic evolution, with components of north-south regional shortening and east-west regional dextral shear, with a possible component of vertical (south side up) displacement.

The Quetico metasedimentary rocks have a polyminerallic magnetic mineralogy comprised of significant proportions of a ferromagnetic (magnetite and pyrrhotite) and a paramagnetic (chlorite, biotite, muscovite) component.  The rocks possess a predominantly tectonic magnetic fabric, which consists of a deformational, and a metamorphic, magnetic fabric.  In some rocks (especially coarse-grained sandstones with wide-spaced cleavage planes) a depositional magnetic fabric is partially preserved.  The complexities involved in having component deformational, metamorphic and depositional magnetic fabrics indicate that the principal magnetic susceptibility directions of the rock's magnetic susceptibility anisotropy cannot be considered reliable indicators of principal finite strain directions in the Quetico metasedimentary rocks.  Great care must be taken in interpreting the significance of principal magnetic susceptibility directions.

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Various aspects of the geochemistry of Ga in upper mantle-derived garnet lherzolite xenoliths (from the Bultfontein Floors mine dump in Kimberly, South Africa), spinel lherzolite xenoliths (from Mount Pordnon, Australia), and continental alkaline volcanic rocks (from the Freemans Cove, Balcones, Urach and Hegau suites of Canada, the U.S.A., and Germany, respectively) have been investigated.  Ga abundances were determined by RNAA.  The feasibility of using epithermal INAA to generate accurate Ga data was investigated.  Analysis of U.S.G.S. standard granite G-2 suggests that epithermal INAA utilizing 630.1 KeV⁷²Ga data has the potential to produce geologically useful Ga data.

The abundance of Ga in the lherzolite xenoliths varies by a factor of approximately 10 from 0.52 ± 0.14 ppm to 5.23 ± 0.44 ppm.  The spinel lherzolite xenoliths contain appreciably more Ga (2.78 ± 0.26 ppm to 5.23 ± 0.44 ppm) than the garnet lherzolite xenoliths (0.52 ± 0.14 ppm to 1.44 ± 0.18 ppm).  The sequence of enrichment of Ga in the minerals comprising the lherzolites is, from lowest to highest Ga content, olivine (0.20 ± 0.04 ppm to 0.72 ± 0.11 ppm), clinopyroxene (1.31 ± 0.13 ppm to 4.92 ± 0.32 ppm), garnet, if present (3.17 ± 0.16 ppm to 6.03 ± 0.48 ppm) phlogopite, if present (7.65 ± 0.21 ppm), and spinel, if present (43.49 ± 0.91 ppm to 65.91 ± 2.10 ppm).  Ga mineral/mineral distribution coefficients have been calculated.  Preliminary results suggest the distribution of Ga between certain mineral pairs (e.g., D_Ga^opx/pcx) is temperature dependent and might be profitably utilized as a geothermometer.

The abundance of Ga in the continental alkaline volcanic rocks varies by a factor of approximately 3.5 from 12:14 ± 0.32 ppm to 41.97 ± 1.20 ppm.  Ga behaved as an incompatible trace element during the genesis of these rocks.  Model-derived constraints for Ga bulk-solid/melt distribution coefficients vary from 0.16 (Balcones suite) to 0.28 (Hegau suite).  Intrasuite variations in the Ga/Al ratios of the mafic continental alkaline volcanic rocks range from approximately 14% (Hegau and Urach suites) to approximately 20% (Freemans Cove suite).  Ga/Al ratios of primary melts from the Freemans Cove and Balcones suites decrease slightly (from 2.86 ± 0.16 top 2.28 ± 0.13, and from 4.12 ± 0.24 to 3.35 ± 0.19 respectively) with increasing degrees of partial melting.

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The northern and central metasedimentary belts (NMB, CMB) are east-trending, regional (formation- to group-scale) lithostratigraphic units within the Beardmore-Geraldton Archean terrane of northern Ontario's Superior Province.

Gravelly braided rivers deposited the lithofacies assemblage of clast-supported polymict conglomerate and interbedded sandstone that comprises most of the NMB.  Felsic volcanic pebbles and cobbles are the most abundant clast lithology.

The CMB contains several east-trending lithofacies assemblages that together form a generally northward-coarsening sequence.  The southern CMB is composed of mudstone, iron formation and sandstone with common graded beds.  This fine-grained assemblage is paralleled to the north by a horizon of rhythmically bedded and cross-bedded sandstone units, and a heterogeneous, conglomerate-rich assemblage.  The northern CMB strata are mostly a conglomeratic assemblage similar in form (lithofacies) and composition (provenance) to the NMB.  Some fine-grained units (mudstone, iron formation, graded sandstone) of relatively minor regional extent are present near the north margin of the CMB.

The CMB's southern (lower) fine-grained subaqueous facies are apparently capped at different sites by:  1) rhythmic delta front couplets;  2) sandy braided river deposits with very rare associated intertidal strata;  and 3) a conglomerate submarine fan or fan-delta front resedimented assemblage.  The northern (upper) CMB is a gravelly braided river deposit, with minor aquabasinal facies.

The CMB is probably a 1 - 2 km thick structurally modified homoclinal sequence.  Relative positions of its depositional paleoenvironments, as deduced from lithofacies assemblages, suggest that the epiclastic portion of the CMB is the record of a dominantly coarsening-upward, subaqueous to subaerial trend that was produced by a prograding clastic system(s), likely a number of fan-deltas.

The extreme eastern part of the CMB is composed of generally oligomict, coarse (conglomerate) felsic pyroclastic and/or reworked volcaniclastic facies which are probably subaerial deposits.

Similar clast compositions and several sedimentological criteria, including average maximum deformed clast size, strongly suggest that highly proximal fluvial facies in the NMB and more distal fluvial and aquabasinal facies in the CMB were originally part of a continuous coarse clastic wedge or sheet.

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Consideration of the existing thermodynamic theory of pressure solution (PS) shows that this theory is applicable to the development of PS structures as well as to local grain-scale diffusive transfer.  Local precipitation of pressure solved material ceases when pores are reduced to equilibrium size, if not before by kinetic considerations.  Longer range diffusion may then occur if a site of non-equilibrium porosity is available.  Such porosity may be generated by particulate flow or by hydraulic fracturing.  Long range diffusion may also depend on greater ease of diffusion, as may occur along stylolites.

Measurement of PS strain rates was attempted by stress relaxation tests (SRTs) at room temperature of both Carrara marble and compacted aggregates of calcite and quartz sands.  Neither material gave results indicative of PS although strain rates as low as 10^-8.5s^-1 were obtained.  Work hardening during loading resulted in alternating increase and decrease of strain rate concomitant with steadily declining differential stress during the SRTs.  The variation in strain rate, termed cycling, was interpreted to be the result of non-steady state flow during loading.  Thermal expansion and contraction were shown to be the cause of pressure fluctuation in a long term quantitative experiment on PS begun during this study.  Such expansion and contraction should be avoided in quantitative studies, particularly at low strain rates.

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Triaxial compression tests were preformed such that changes in the magnetic susceptibility anisotropy with strain would be represented by experimental approximations of simple shear and pure shear.  Both types of tests were performed on artificial materials of high magnetic susceptibility at room temperature and atmospheric pore fluid pressure.  Experimental displacement-rates and strain-rates were computer controlled during testing.

Two different shear zone materials were employed for the "simple shear" testing, a sand-cement mixture and a calcite-cement mixture.   Three series of simple shear tests were conducted on the sand-cement material at various confining pressures; Series A, at 0.689 kbars, Series B at 1.0 kbar and Series C at 1.5 kbars.  Two series of simple shear tests were conducted on the calcite-cement material, Series 1, at 1.0 kbar confining pressure and Series 2 at 1.5 kbars P_c.  For both materials a constant axial displacement-rate of 5.0 x 10^-6 inches.  s^-1 (corresponding to a slip displacement-rate on the shear zone walls of 8.7 x 10^-6 inches. s^-1) was employed.  Final shear strain values ranged from 0.025(to 0.378(. 

One series of pure shear deformation was conducted on the calcite-cement material at 1.5 kbars confining pressure employing a constant natural strain-rate of 5.0 x 10^-6s^-1.  Final axial strain values ranged from 4.42% to 18.3% shortening.

The development of simulated "tectonic" magnetic fabrics in both pure and simple shear has been achieved.  Principal directions of susceptibility rotate sometimes in complex patterns toward 'tectonically' significant stable orientations.  Magnitudes of susceptibility show progressive changes consonant with the intensity of strain such that there appears to exist a consistent relation between the change in the degree of anisotropy of susceptibility ()P') and the bulk strain ratio (In X/Z) for both the pure and simple shear experiments.

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Placer accumulations are formed by the preferential sedimentation of heavy minerals from the general population of detritus being transported by a fluid.  The depth, velocity, and grain size conditions under which placers form on beaches, sand-dominated meandering, and braided fluvial systems is at present only partially understood.  Our knowledge of the controls on alluvial placer formation in gravel-dominated longitudinal bars of braided rivers is even more poorly developed despite their obvious economic importance.

The accumulation of heavy minerals in coarse-grained longitudinal gravel bars was studied by examining and sampling surficial and matrix sediments from modern, naturally occurring bars, and by simulating these bars under a variety of controlled flow conditions in a sediment-water recirculating flume.

Two processes dominated the deposition of sediments in both the natural and artificial systems studied:  1) suspension rain out; and 2) avalanche face progradation.  Sediments which were deposited as a result of avalanche face progradation were found to contain significantly higher concentrations of heavy minerals in both the naturally occurring and experimental longitudinal gravel bars.  Data also indicate that the difference in heavy mineral content amongst sediments deposited as a result of these two processes will increase substantially with increasing density of the detrital minerals present.  This suggests that denser heavy minerals are more likely to be deposited amongst less dense surficial sediments whereas less dense heavy minerals are more likely to be vertically distributed throughout the bar sequence.

In the natural systems studied, heavy mineral content was found to be much higher in poorly sorted, coarse-grained sediments deposited amongst pebble sized clasts.  Flume tank experimentation similarly revealed that detrital lead content was highest amongst pebble sized clasts during the fastest velocity runs.  In addition, an increase in clast size resulted in a decrease in the amount of heavy minerals accumulating in surficial sediments.

This study has also highlighted two processes which results in the formation of alluvial depositional placer accumulations in coarse-grained braided river systems.  The first process occurs as a result of heavy minerals in channel bottom sediments becoming progressively enriched through the winnowing of less dense sediments, resulting in the formation of an erosional placer deposit.  Flume experimentation revealed that when high concentrations of heavy minerals armouring the stream-bed were reached, this often resulted in the initiation of their movement downstream.  This process can also be triggered by catastrophic events such as large floods of regional tectonic uplift.  A sudden increase in energy typically associated with such events results in the flushing of erosional placers and their eventual deposition in areas of higher preservation potential.  Therefore, a catastrophic adjustment helps to flush out erosional placer deposits into the basin to form a depositional placer accumulation.  The second process of depositional placer formation results from heavy minerals travelling in bed load transport, while less dense sediments are kept mostly in suspension.  With a decrease in velocity, heavy minerals are sedimented with hydraulically equivalent sized, less dense sediments in open framework gravels.

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