The area is underlain by Archean sedimentary and volcanic successions and forms part of the Shebandowan-Wawa volcano-plutonic belt.  In the area the rocks have been subjected to three distinctive episodes of deformation.  Two phases of folding were followed by development of kink bands and a crenulation cleavage.  The first folding consisted of tight, recumbent folds with east-west trending axial traces.  The second phase of folding consisted of smaller, more open folds with northeast trending, steeply dipping axial traces.  The later kink bands formed only in rocks possessing a strong planar anisotropy.

The most abundant rock type present in the study area are greywackes.  These greywackes exhibit features characteristic of turbidites.  Framework minerals of these rocks consist primarily of felsic volcanic rock fragments.

The presence of coarse pyroclastic rocks interbedded with these sedimentary rocks is the result of contribution of detritus from multiple sources.

The metasedimentary unit at Little Dog Lake consists of schists and gneisses.  These rocks formed a layered regionally metamorphosed sequence with minor folds and late intrusions.

Parts of the metasedimentary unit are composed of angular to sub-angular clasts set in a medium grained matrix.  The clasts show a strong preferred orientation which parallels the structural foliation.

Chemical analyses show the clasts and matrix to be quite similar.  Geochemical data indicates the rocks to be pelitic in compositon.

Assemblages characteristic of the amphibolite facies were found.  These rocks constitute a medium to high pressure facies.  Field evidence suggests the granitic gneiss to be the oldest unit.  The dioritic intrusion which bounds the southern extent of the metasedimentary unit is relatively unmetamorphosed.  Petrographic data indicates this to be the last event to occur.

Well exposed, glacially polished iron formation outcrops near the town of Mellen, Wisconsin.  There, units form a portion o the western Gogebic iron range which strikes east-west through the area.  Iron formation exposure of this calibre is unusual in the Lake-Superior region and provides an opportunity to investigate physical and chemical sedimentary controls on accumulation of this type of sediment.

A 40 x 40 m section of iron formation composed of trough cross-stratified chert grainstones and parallel laminated slaty iron formation was mapped in detail.  The sequence is composed of three distinct stratigraphic units.  The first comprises 12 m of parallel laminated slaty iron formation with small chert lenses appearing at the bottom of the section.  The second is a 15 m thick succession of large trough cross-stratified grainstone lenses, some extending laterally 10-15 m.  The third unit lies immediately above the grainstone succession and is composed of 8 m of slaty iron formation.  Paleocurrent data is dominantly unidirectional from the north.

Slaty iron formation is dominated by parallel laminated beds 2-5 mm in thickness.  In regions where slaty iron formation coexists with small grainstone lenses the characteristic parallel lamination gives rise to wavy bedding.  Ripple lamination is present in the lowest stratigraphic unit.  Many beds are both physically and chemically graded.  Variations in the distribution of Al, Mn, Fe and Mg are seen within individual beds and throughout the entire span of the section.  Mineralogically, the dominant phases are hematite, magnetite and chert with minor amounts of greenalite, apatite and manganese oxide.  A few of the largest magnetite grains possess cores composed of ilmenite.

The trough cross-stratified chert grainstone lenses are composed of rounded chert and hematite grains ranging in size from 0.1 to 2 mm.  Many chert grains are coated with hematite, suggesting rolling by bottom currents through iron-rich muds.  The matrix is dominantly chert & calcite with traces of stilpnomelane.  Lenses range from 2 to 40 cm thick and may extend laterally 0.70 to 15 m.  The smallest grainstone lenses appear at the base of the section within slaty iron formation.  The largest lenses are found in the succession of trough cross-stratified grainstones.  Rip-ups of slaty iron formation, 1-3 cm in length, are common at the base of the largest lenses (30 cm thick, 8-11 m wide) at the top of the succession.

The section is characterized by a coarsening then fining upwards sequence in which muddy shelf deposits pass through ripple laminated fine sand into a succession of cross-stratified dunes, then back into muddy shelf deposits.  Both offshore bar complexes and tidally influenced, storm enhanced shelf deposits possess sedimentary structures similar to those described.  The thin ripple lamination in slaty iron formation in the lowermost slaty unit may represent sands moved by storm produced currents.  The dominantly unidirectional paleocurrent pattern is also indicative of storm enhanced currents.  Slumping is suggested throughout the sequence by the presence of extensive convolute bedded slaty iron formation.

A Middle Devonian carbonate-hosted lead-zinc-flourite occurrence was studied in northern Saskatchewan.  Drill core was obtained from Canadian Occidental Petroleum Limited, Minerals Division.  Because fluid inclusion temperatures of about 100°C were obtained, it is likely that these temperatures could only be achieved by pore fluids originating from a large basin outside the study area.  Fluids transporting lead and zinc likely used the Cambro-Ordovician sandstone as an aquifer.  The reason for precipitation of the sulphides specifically in the grey argillaceous bed of the Smoothstone River Formation is obscure.  It was found that mineralization from the study area has many similarities to that found in most deposits located in the Mississippi Valley area of the United States.

The Coldwell Complex is a large Proterozoic alkaline igneous complex on the north shore of Lake Superior west of Marathon, Ontario.  From east to west across the complex, three distinct magmatic centres form an overlapping sequence; Center 2 is characterized by biotite-bearing alkaline gabbro and nepheline syenite (Mitchell and Platt, 1982).  Within Center 2, a fine-grained porcelaineous variety of nepheline syenite is recognized as being chemically eqivalent to the more typical coarse-grained nepheline syenite.  This porcelaineous nepheline syenite outcrops in a narrow arcuate zone along the western shore of Redsucker Cove.

Microstructural evidence for dislocation creep indicates that the porcelaineous syenite is a mylonite formed by localized solid-state deformation.  As the Coldwell Complex has not been subjected to regional metamorphism, the high temperature required for ductile solid-state deformation in the procelaineous syenite must be related to the magmatic activity.  Localized high-temperature ductile strain within this arcuate zone could have led to catastrophic brittle failure along ring faults culminating in caldera collapse.  This discovery may have implications for understanding the processes associated with caldera collapse in large alkaline igneous complexes.

The Rabbit Mountain Mine hosts silver-bearing quartz-carbonate veins that are representative of the veins encompassing the Mainland Belt Silver Region near Thunder Bay, Ontario.  These veins, which also contain base-metal sulphide mineralization, fill fractures within Rove Formation argillite and Logan diabase sills of the Proterozoic Southern Province of the Canadian Shield.

Silver and base-metals could have been derived from the diabase; however, a lack of differentiation within the sills and spatial relationships, which indicate that the veins occupy post-diabase faults, seem to preclude the diabase as the source of the metals.

The intruding diabase caused a contact metamorphic zone to be developed within the shale.  Metamorphic reactions released calcium, carbon, and water from the shales, and these products migrated to low pressure zones centered on faults to form the gangue minerals.

To determine if silver, base-metals and arsenic accompanied this lateral secretion of gangue constituents, an outcrop of altered argillite cut by a vein (located at the Rabbit Mountain Mine) was sampled on lines perpendicular to the vein.  The samples were analyzed by the Atomic Absorption method to determine the distribution pattern of silver, base-metals, arsenic and mercury in the argillite adjacent to the vein.  Copper, zinc, lead, silver and possibly nickel are all depleted below their background levels indicating they have been removed from the shale during the heating event instigate by the diabase, and, like the gangue minerals, were deposited as vein constituents.  Cobalt is elevated above background levels adjacent to the vein, indicating it was introduced to the argillite from the vein, ultimately being derived from the cooling diabase.  Arsenic shows a slight depletion towards the vein.  Mercury was above the lower detection limits only in samples taken immediately adjacent to the vein.

The Lac des Iles Complex appears as a linear zone of mafic plutons that trend east to northeast and extends from Lake Nipigon to Atikokan in northwestern Ontario (Sutcliffe, 1986).  The complex is situated in Archean granitoids that consist of gneissic tonalites, medium-grained hornblende diorites and quartz diorites.  The Lac des Iles Complex occurs in a circular outcrop fashion that is approximately 30 km in diameter and is the largest of a series of mafic to ultramafic intrusions (Sutcliffe, 1986).  The Roby Zone was the initial site of mining at the Lac des Iles Mine.  The North Roby Zone is its narrow northward extension.

The North Roby Zone contains a narrow strip (<50 m) of anomalously high PGE and Au values associated with sparse sulfides called "Noseeum Ore".  Five stripped outcrops approximately 50 x 10 m were studied in the North Roby Zone.  Alteration of primary pyroxene to talc and pink coloration of recessively weathered plagioclase is strongly suggestive of hydrothermal alteration.

The five stripped outcrops reveal a northeasterly striking, steeply dipping sequence of leucogabbro, varitextured gabbro, pyroxenite and east gabbro.  A total of 32 hand samples were collected and studied in thin section.  From these 21 were selected for whole-rock and trace element analysis in order to compare chemistry of altered and unaltered samples.

Hydrothermal alteration appears to have affected the primary ortho-and clinopyroxenes of the host rocks, progressively converting them to talc.  Other petrographic indications are obscure, as regional metamorphism has overprinted the Lac des Iles Complex and its mineralized rocks.

The grade of metamorphism is the albite-epidote subfacies of greenschist facies as evidence by incipient breakdown of plagioclase to sericite and clinozoisite, chloritization of pyroxenes and formation of tremolite-actinolite, as well as minor metamorphic albite.  Chlorite coronas surround mafic minerals, and develops decussate assemblages of chlorite and tremolite-actinolite.  Minor penetrative deformation is evident in undulatory extinction in plagioclase and development of weak schistosity.

The development chlorite coronas and general overprinting of mafic minerals by chlorite and sericitization of plagioclase are significant in distinguishing hydrothermal alteration from subsequent regional metamorphism.

Analysis did not generally reveal striking compositional variations in the host rocks; however, more detailed analysis did show chemical effects of alteration.  Chondrite-normalized REE plots revealed that all REEs were depleted relative to unaltered rocks; however, in most altered leucogabbro and varitextured gabbro, minor to insignificant depletion of Eu relative to other REEs produced an apparent positive Eu anomaly in the plots.  Other chemical changes, because of their subtle expression and obscurity owing the problem of closure, were examined by use of Pearce Element Ratios.  Most notable was Na-depletion due to alteration, which can be distinguished from igneous fractionation effects in plagioclase.

The Sibley Group is an essentially unmetamorphosed, Mesoproterozoic sedimentary succession consisting of a mixture of siliciclastic and chemical sedimentary rocks.  This study examined the sedimentology and geochemistry of the Pass Lake and Rossport Formations, the lowermost lithostratigraphic units of the Sibley Group. 

Lithofacies analysis subdivided the sections studied into sixteen lithofacies associations corresponding to distinct allostratrigrahic units, roughly equivalent to previous lithostratigraphic subdivisions.  A lower clastic unit is comprised of the following lithofacies associations:  boulder conglomerate-sandstone-dolocrete (proximal ephemeral braided system), pebble to cobble conglomerate (ephemeral braided stream), massive cobble conglomerate (transgressive lag, reworking of braided stream deposits during transgression), trough cross-stratified sandstone (braided stream), green sandstone-siltstone (wave and storm influenced fluvial dominated delta), planar cross-stratified sandstone (nearshore migration of large sandwaves), and thinning-upward sandstone (beach and storm remobilized nearshore sandstone sheets).  The lower clastic unit is disconformably to conformably, depending on geographic location, overlain by a mixed siliciclastic-carbonate unit.  The mixed siliciclastic-carbonate unit is comprised of the red siltstone (non-saline lake), red siltstone-dolostone (perennial saline lake, distal from clastic source) and red siltstone-dolomitic sandstone (perennial saline lake, proximal to clastic source) lithofacies associations and is sharply overlain by an upper clastic unit.  The upper clastic unit consists of the sheet sandstone (ephemeral playa lake (?) or perennial lake with increased sand supply with respect to underlying units) and black chert-carbonate (microbial mats forming at restricted, shallow, subaqueous shoreline) lithofacies associations.   Subaerial exposure features are present at the top 0of the black-chert-carbonate lithofacies association and include the intraformational conglomerate lithofacies association (subaerial debris flows, intrusive and/or extrusive sedimentary breccias, terra rossa style soils, dissolution collapse breccias).  Subaerial exposure features at the top of the upper clastic unit are overlain by the massive dolostone (saline lake), red siltstone-sulfate (wet evaporate-rich mudflats around lake margins) and fine-grained sandstone (dry, evaporate-poor mud and sand flats around lake margins) lithofacies associations of the mixed siliciclastic-carbonate-evaporite unit.

During deposition of the lower clastic unit paleocurrents and detrital zircon geochronology suggest a south- to southeast-down paleoslope.  A lack of major thickness changes in stratigraphic units or laterally extensive coarse-grained clastic deposits is consistent with a broad intracratonic sag architecture during initial basin subsidence.  Paleocurrents from the upper clastic unit suggest a change to northward oriented paleoslope during its deposition.  This corresponds with an apparent thickening of the upper two units towards the north and Black Surgeon Fault, consistent with the development of half-graben structure and increased evidence of tectonic activity (e.g. intrusive sedimentary breccias, synsedimentary faulting and debris flows).

Carbon, oxygen and sulfur stable isotope analyses, Sr isotope analyses and trace element analyses (in some cases analyses include rare earth elements) were preformed on a variety of distinct carbonate and sulfate lithologies.  Sulfur isotope compositions, strontium isotope compositions and rare earth element/yttrium ratios support a non-marine depositional setting.  Low *¹⁸O values appear to be a good indicator of diagenetically altered samples.  *¹³C values have typical marine values consistent with lacustrine carbonate precipitated in equilibrium with atmospheric CO₂.  Stratigraphic changes in C and O isotope compositions in the red siltstone-dolostone lithofacies association were likely driven by evaporations and residence time effects.  Stratigraphic variations in sulfur isotope compositions may reflect changes in the composition of sulfides weathering to supply sulfate to the basin.  Overall, both the interpretation of physical sedimentologic and various type of geochemical data strongly support a non-marine lacustrine setting for the deposition of the Pass Lake and Rossport Formations.

Riku is currently working for the Ontario Geological Survey

Black line faults tend to cut and displace various lithologies, dykes, and gold-bearing veins and are a common feature found in the Red Lake gold mines. They are characterized by their distinct black color and may have anomalous traces of gold but are usually barren. Black line faults along the Red Lake mine trend may vary in size, geometry, and significance, but they all share the same general composition of mostly tourmaline, chlorite, and interstitial quartz. They have previously been described as faults associated with brittle late stage deformation; however, some are overprinted by ductile deformation. Black line faults are significant in that they represent a time of brittle-ductile deformation and the presence of complex hydrothermal fluids, typically related to orogenic gold mineralization.

Bol©o is a low-grade, sediment-hosted stratiform Cu-Co-Zn-Mn deposit located midway along the eastern side of the Baja Peninsula. The deposit consists of multiple conformable, laterally extensive horizons of disseminated sulphide and oxide mineralization, which extends over 90 square kilometres.

All four mantos studied display similar mineralogy, but manto 3 contains a greater proportion of both Mn- and Fe-oxides.  Both the breccia and parallel laminated claystone lithofacies have nearly identical mineralogy, but are texturally different, while the massive claystone lithofacies is dominantly composed of chrysocolla and Mn-oxide altered smectite-group clays. The gangue mineralogy of the three alteration facies, sulphide, oxide and mixed sulphide/oxide, are largely similar, except that the oxide facies contains higher, albeit variable, abundances of Mn-and Fe-oxides.

There is no direct correlation between Co concentrations of the lithofacies and mantos, all of which display localized high and low cobalt concentrations. Based on the concentration of Co within the various alteration facies, the higher Co concentrations are associated the sulphide facies, which implies that Co is occurring as a sulphide. Locally, high cobalt grades appear to be associated with high copper grades. As no discernable Co-bearing minerals were identified by optical microscopy and XRD analysis, additional study using SEM-EDS and/or EMP analysis is required to determine the host mineral(s) for Co within the mantos.