Neepawa Island, located within the Sioux Lookout greenstone belt of the Western Wabigoon subprovince has been an area of several historical gold occurrences over the past century.  In this study, structural controls of gold mineralization are assessed with an emphasis on microstructural analysis.  The study area on west Neepawa Island is situated at the southern edge of the central volcanic belt, approximately 12km southeast of Sioux Lookout, Ontario near the center of Minnitaki Lake.  Locally, the study area hosts intermediate pyroclastic and mafic volcanic flow units displaying brittle and ductile deformation, pervasive hydrothermal alteration, and metamorphism to the greenschist facies.  Microstructural analysis concluded that gold mineralization is related to non-coaxial deformation of north-south striking, steeply dipping vein set 1, the oldest vein set at the study area.  Gold is concentrate where deformation is greatest in the quartz-carbonate vein and adjacent pyritic halo, approximately parallel to the regional foliation.  Gold mineralization is hosted in microstructures such as subgrain ribbons and microfractures in the quartz veins, as well as microfractures and pressure shadows associated with pyrite.  These brittle and ductile microstructures were produced from competency contrasts during deformation between the mesothermal quartz-carbonate veins, metavolcanic host rock, and syn-deformational pyrite.  Gold-hosting microstructures may be controlled by deformation caused by the sinistral-reverse displacement related to the regional Ruby Island Fault system.

St. Andrew Goldfield’s Holloway mine is located along the dextral transpressional steeply south dipping, east to west striking Porcupine Destor Deformation zone. Heterogeneous brittle-ductile deformation characterizes the structural environments that host economical gold mineralization within the Smoke Deep ore zone.  Gold mineralization is associated with three different microstructural settings all of which accompany pyrite mineralization.  Favorable depositional sites include synkinematic veins, rheological boundaries and felsic lithologies.  These settings occur locally within medium-grained to coarse-grained spherulitic felsic lithologies that create competency contrast with the neighbouring southern and northern schistose units.  The ore units are interpreted as hypabyssal intrusions of albitite composition, with associated aplite pods. Constituent phenocrysts of the albitites retained their relict shape evident of competency contrast between itself and neighbouring volcanic lithologies.  During deformation the formation of microfractures in competent pyrite porphyroblasts aided in the development of low-pressure structural localities conducive to the accumulation of gold from auriferous-carbonate-rich metamorphic fluids.  The neighboring schistose units effectively envelope the ore lithologies and are characterized as mylonitized mafic volcanics and metasediments.  Metamorphic temperatures within the zone reached lower amphibolite facies conditions indicated by amphibolite textures including kink banding of feldspars, specifically of albite, and the development of subgrains from relict albite and potassium feldspar phenocrysts.

A lamproitic igneous occurrence was recently discovered by a prospector working in the area to the north of Marathon, Ontario.  It occurs near a large number of features related to the 1.1 Ga Midcontinent Rift such as the Coldwell Complex and the Trans-Superior Tectonic Zone, but no radiometric dating has been completed on this particular unit of rock.

At outcrop level, the unit appears as a collection of metre-scale mafic sills within granitic country rock.  These sills appear on all sides of a large lake, marking the lake as the likely location of the main body of the lamproitic rock.

The rock is composed of a variety of minerals, including forsteritic olivine, diopside pyroxene, sanidine feldspar, and a variety of spinels. Later periods of magmatism contributed secondary apatite and phlogopite.  At the same time, the volatile-rich fluids produced by the magma created a variety of alterations, such as serpentine, chlorite, and carbonate, and heavily disrupted the primary minerals in the rock.

This rock retains a classification as a paralamproite, with a mineral assemblage that cannot fulfill the defined composition of lamproite due to geochemical differences between definition and observed samples.

Deformation in the Animikie Group near Thunder Bay is characterized by intense, localized fold-and-thrust belt deformation within units that are otherwise relatively undeformed and flat-lying.  This deformation is interpreted to be the result of regional stress during Proterozoic tectonism.  Stereographic analyses of structural measurements and outcrop observations are used to determine beta-axes (mean fold axes) for fold populations, as well as to determine structural relationships within the region.  Two main fold populations are observable in the data.  The primary population exhibits a north-south trending beta-axis, indicating east-west compressive stress.  The secondary population exhibits an east-west trending beta-axis, indicating either north-south compressive stress or the presence of lateral ramps.  Slickenlines are also observed to trend north-south and east-west, depending on outcrop location.  East-west trending slickenlines tend to be in areas of more intense folding, indicating they may be older than the north-south trending slickenlines.   Older slickenlines may have been destroyed when fault surfaces were reactivated in areas of less intense folding replaced by the slickenlines associated with the most recent deformation.  Additional observations include the presence of fold-hinge breccia associated with non-cylindrical folding, which may indicate lateral ramp formation, as well as the presence of a possible cleavage duplex structure, which may indicate repetitive east-verging thrusting.
These observations suggest that the deformation of the Animikie Group began with regional east-west compression resulting in the development of an east-verging thrust belt.  Stresses associated with this thrust belt are interpreted to have resulted in fault-bend folding on frontal and lateral ramps in the region.  Most of these folds are included in the population with north-south trending axes, although lateral ramps on this thrust sheet likely resulted in the development of folds with east-west trending axes, as well as non-cylindrical folds and fold-hinge breccia.  East-west trending slickenlines on thrust faults were also developed during this compressive deformation.  Subsequently, north-south compression may have overprinted this deformation, developing folds with east-west trending axes and north-south trending slickenlines on fault surfaces, though not in areas of intense folding (indicated by preservation of east-west trending slickenlines).  Finally, north-south directed extensional deformation deformed the area, resulting in normal faulting and the reactivation of fault surfaces in areas not intensely folded.  This caused the development of north-south trending slickenlines on new and reactivated fault surfaces.  A specific tectonic history for the Animikie Group is suggested based on these observations and interpretations.  It is proposed here that primary east-verging thrusting was associated with the Trans-Hudson orogeny in the Paleoproterozoic.  Following this, there may or may not have been a secondary compressional phase due to the Yavapai-Mazatzal orogenies during the early to middle Proterozoic; the effects of these orogenies remain unclear.  Deformation likely culminated in the late Proterozoic with north-south extension related to the Mid-Continent Rift.

The world-class Hemlo gold deposit is representative of an atypical mesozonal shear-hosted lode-gold deposit that is comprised of numerous lithologies.   A contemporary classification scheme for the categorization of dyke lithologies that occur in the immediate Hemlo deposit is utilized by the mine geologists of Williams Operating Corporation at Barrick Gold’s Williams Mine.  Although the deposit area has been studied extensively by myriad researchers, the physical and chemical properties of an intermediate intrusive lithology, designated as unit (11) in accordance with the Hemlo Geology Legend, are not well described.  Nineteen samples representative of the (11) Intermediate Intrusive unit were obtained from varying localities throughout the Williams “C Zone” and “B Zone” sites, specific to the Hemlo deposit, within the Williams mine.  Petrographic and geochemical analysis of these samples suggests that they are representative of a calc-alkalic magma series that evolved via the process of fractional crystallization in an island arc setting.

The Badwater Gabbro south of Armstrong, Ontario is a Proterozoic mafic intrusion.  It is cut through by thin dikes of the Badwater Syenite and overlain by the Pillar Lake volcanics.  Through petrographic work, the intrusion was subdivided into six lithologies: altered mafic rocks, syenite, norite, gabbronorite, olivine gabbro/olivine gabbronorite, and gabbro.  The altered mafic rocks consist of metagabbro, metagabbronorite, serpentine-actinolite gneiss as well as talc-magnetite schist.  Much of the alteration is present in the form of hydrous alteration minerals.  This section is heavily altered and overprinted, likely the result of surficial weathering as well as hydrothermal alteration from extrusion of the Pillar Lake volcanics on top of the Badwater Gabbro.  The alteration minerals and textures seen throughout the intrusion could be the result of localized contact metamorphism caused by emplacement of the Nipigon sills at ~1.1 Ma.  Geochemically the Badwater Gabbro are similar to rocks derived from a mantel plume.  The Badwater Gabbro is characterized by high Gd/Yb ratios (2-7), indicating that the melt is sourced from within the garnet stability field.  The Badwater Gabbro was possibly emplaced along the lithospheric scale weakness of the Black Sturgeon fault zone.  The intrusion was likely affected by crustal contamination during emplacement; as suggested by the depletion of the HFSE on the trace element plots, indicating assimilation and enrichment of LREE relative to HFSE.

the Hemlo gold mine is located along the Hemlo shear zone within the Hemlo-Schreiber greenstone belt, within the Wawa subprovince of the Superior Province.  Geographically, the mine is located 350 km east of Thunder Bay, Ontario, Canada.  The C-zone has a mineralization style distinct from the well-studied B-zone.  Detailed mapping, oriented sampling, drill core observations, and a microstructural analysis were completed to determine the role brittle deformation plays in gold mineralization.  Ductile deformation of feldspar grains indicates amphibolite facies temperatures during deformation, consistent with historical work on metamorphism.  Annealed grains are evidence for lingering high temperatures.  The area is characterized by mutually overprinting brittle and ductile deformation within all lithological units.  The degree of deformation within each lithological unit indicates competency contrast during brittle-ductile deformation and the competency contrast plays a key role in the mineralization of gold in the C-zone at Hemlo.  Gold occurs within deformed quartz veins in more competent rock bodies.  Gold is also found along quartz veins within the less competent rock and within the more competent rock as fine-grained disseminated gold.

Located in the western area of the Uchi subprovince of Superior Province Mesoarchean carbonates and iron formation that extend from western Red Lake to Wallace Lake are the remnants of a large carbonate platform that formed at some time between 2940Ma and 2925Ma.  The platform is dominated by peritidal depositional structures overlain by basin transitional lithofacies which give the impression that the platform had a flat topped and relatively steep sided geometry.  The peritidal lithofacies assemblage consists of tidal flat to subtidal structures that are common in the Archean (i.e. laterally linked and unlinked domal stromatolites, crystal fans, and herring bone calcite), and has REE characteristics of carbonate precipitated from water with near neutral pH, high pCO₂, and an oceanic REE reservoir dominated by hydrothermal input.  The peritidal lithofacies assemblage has δ¹³C_PDB=0.42‰ +/- 0.53‰ which is consistent with other shallow water carbonates of the Meso- and Neoarchean.  The basin transitional lithofacies assemblage consists of slump structures and carbonate associated oxide facies iron formation (IF).  The REE characteristics and depositional structures are the result of down-welling water from a saline, semi-restricted, peritidal depositional environment and mixing with basin waters.  The carbon isotopes of the carbonate associated oxide facies IF show basin transitional values  δ¹³C_PDB  as low as -3.07‰ reflecting the mixing of shallow water with positive δ¹³C_PDB  values and basin water with more negative δ¹³C_PDB values.  More distal lithofacies consist of chert-oxide facies IF.  The chert-oxide facies IF shows positively sloping shale normalized FEE patterns and strong positive Eu anomalies characteristic of the precipitation of iron hydroxides from ocean waters with a pH~5 and REE characteristics that are strongly influence by hydrothermal alteration of oceanic crust.

Negative Ce anomalies in the peritidal carbonates occur consistently in the crystal fans and rarely in other facies suggesting precipitation from water that was relatively oxic.  The fans also contain consistently elevated basin derived elements such as P, Fe, Sr, and Ba.  Storm events and/or small scale transgressive-regressive cycles probably episodically added open ocean water to the semi-restricted platform providing nutrients for photosynthesising organisms.  Blooms of photosynthesising organisms would remove CO₂ from the platform water and cause an increase in pH resulting in the precipitation of fans.  The Red Lake-Wallace Lake carbonate platform is the oldest known carbonate platform in a series of geographically scattered platforms contributing to a gradual change in oceanic processes in the Mesoarchean and Neoarchean including the gradual oxidation of the atmosphere by the initial production of oxygen in these semi-restricted, shallow water settings.  The evidence for oxygenic photosynthesis presented here predates the Great Oxidation Event by 400 my.

The central Gulf of California coast region of the Baja Peninsula records the transition from arc to rift tectonics.  As a consequence of the changing tectonic regime, magmatic activity in the area changed from arc-related andesites to rift-related basalt-andesite-rhyolite pyroclastics.  Associated with rifting was the development of the Santa Rosalia basin, one of several proto-Gulf basins to develop, and the Boléo Cu-Co-Zn-Mn district.  The aim of this study was to utilize remote sensing techniques in order to see if it is possible to map the arc and rift lithologies of the Santa Rosalia basin and its border lands.  A key goal was to assess if remote sensing techniques could be used to differentiate between arc- and rift-related igneous units, that make up the central peninsular arch (Sierra Santa Lucia) and form the western boundary of the Santa Rosalia basin; as various studies over the past decade have shown that Sierra Santa Lucia is not comprised entirely of arc-related andesite.  An additional objective of the work is to assess the plausibility for the existence of a collapse caldera that lies along the west-south western margin of the Santa Rosalia basin.  Confirmation of a rift-related caldera would establish a key genetic link between early Gulf magmatism, incipient basin sedimentation and hydrothermal activity of the Boleo district.

To answer these questions, remote sensing techniques were utilized to analyze a 30m resolution Landsat 8 satellite imagery.  Based on the spectral bands of the Landsat 8 imagery and remote sensing techniques, such as band ratios and combinations, principal components analysis, and classification, some of the rock types present were separated based on their differing mineralogy and a geological map was created.  By taking advantage of specific spectral bands such as 2/4:6/7:4/6, 4/2, and 7/6, arc to rift volcanic rocks could be differentiated from unlithified alluvium and carbonates and sulphates.  However, it was not possible to separate arc volcanic rocks from rift volcanic rocks because their mineralogical differences were too subtle to produce different spectral responses.