Earth Sciences / Sciences de la Terre - Master's Theses

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The nature of the Cadillac – Larder Lake Fault: Implications for gold mineralization along the KerrAddison-Cheminis segment
(2020-05-29) St-Jean, Nadia
The Cadillac-Larder Lake Fault (CLLF) is a major fault system that controls the location of gold deposits in the southern Abitibi greenstone belt. Over a distance of 250 km from Matachewan in Ontario to Val d’Or in Quebec, it marks the contact between mafic-ultramafic volcanic rocks of the Piché/Larder Lake group and younger metasedimentary rocks of the Hearst, Timiskaming and Cadillac sedimentary assemblages. In the Larder Lake area, the contact between sedimentary rocks of the Timiskaming assemblage to the north and volcanic rocks of the Larder Lake group to the south defines the CLLF. This contact is typically sheared and deformed by two generations of folds but locally, in areas of low strain, an unconformity is preserved, expressed by a pebbly sandstone which youngs away from the underlying ultramafic rocks and contains detrital clasts of the ultramafic rocks. The sandstone stratigraphically overlies older volcanic rocks of the Larder Lake group suggesting that the unconformable contact between the Timiskaming assemblage and Larder Lake group is a primary feature that was later structurally modified. The structural history of the CLLF and surrounding rocks began prior to the deposition of the Timiskaming assemblage with the juxtaposition of the Larder Lake and Blake River groups during an early thrusting and imbricating D1 deformation event. Both the Larder Lake group and the Timiskaming assemblage were then deformed during a D2 deformation / mineralizing event, which produced regional F2 folds, a regional S2 cleavage, and ductile shearing along the contact between the Larder Lake group and the Timiskaming assemblage. Reactivation of this contact during and post the D2 event localized the distribution of gold deposits and formed the present day manifestation of the CLLF.
Assessing the extent of local assimilation within the Platreef, Northern Limb of the Bushveld Igneous Complex, using sulfur isotopes and trace element geochemistry
(2019-04-15) Keir-Sage, Evan
The proximity to metasedimentary footwall units in the Northern Limb of the Bushveld Igneous Complex (BIC) has resulted in a complex local contamination of in this maficultramafic intrusive body, including the units containing platinum group element (PGE) mineralization. To assess the extent of incorporation of non-magmatic material and its effects on PGE mineralization, geochemical and isotopic data were collected from drill core UMT094 on the Turfspruit project, where core logging has shown a clear macroscopic division between mineralization and local footwall contamination. The S isotopic data combined with whole rock geochemistry data (including CaO/Al2O3, V/Ti, Ni/Cr, S/Se, LOI) present substantial evidence to assess the range of incorporation of local footwall material. A δ34SVCDT profile shows a steady decrease from the footwall assimilation zone (δ34S = +8 ‰) to near constant δ34S values (δ34S < +4 ‰) below mineralization. Through PGE mineralization, the δ34S data converge to the range that has been documented for the Merensky Reef in the Eastern and Western Limbs of the BIC (δ34S: ~ 0 to +3 ‰). Other geochemical parameters through mineralization, such as S/Se and CaO/Al2O3, also match the ranges documented for the Merensky Reef. In addition, parameters such as whole rock V/Ti are shown to be useful indicators of the type of contaminant (e.g. V/Ti > 2 for intervals assimilating shales and V/Ti < 1 for intervals assimilating carbonates; 1 < V/Ti < 2 for uncontaminated magmatic units). The results indicate that there is negligible local contamination through mineralization and that the primary mechanism of PGE mineralization in the Platreef was no different than the mechanism that generated the Merensky Reef in the Eastern and Western limbs of the BIC.
Characterization of metamorphic assemblages and assessment of Cu-Pb-Ag-Au-Zn mobility at the Lalor deposit, Snow Lake, Manitoba
(2018-12-21) Lam, Judy
The Lalor VMS deposit is located within the Snow Lake arc assemblage at the easternmost end of the Paleoproterozoic Flin Flon belt. A regional metamorphic event at 1.81 Ga, up to middle amphibolite facies (550˚C, 5kbar), recrystallized the mineral assemblages in the massive sulfide and hydrothermally altered rocks that are associated with the formation of VMS deposits in the area. The Lalor deposit differs from most VMS deposits in the area in that it contains low-sulfide Au rich zones that are proximal to but separate from the massive sulfide lenses. Gold mineralization primarily occurs in three rock types at the Lalor deposit: massive sulfides, and calc-silicates to carbonate silicates, and Fe-Mg altered rocks. Electrum is the dominant form of gold, but gold also occurs in sulfosalt phases such as aurostibite (AuSb2) and in tellurides such as petzite (Ag3AuTe2). It is often associated with hessite (Ag2Te), altaite (PbTe), chalcopyrite (CuFeS2), and galena (PbS). Gold mineralization occurs along fractures, grain boundaries, cleavage planes, and as discrete inclusions in metamorphic minerals. There are two dominant metal associations with gold: Cu-Au and Pb-Au. The Cu-Au association is more common and occurs in a variety of rock types (including massive sulfides and Fe-Mg altered rocks), whereas the Pb-Au association is restricted to calc-silicate to carbonate silicate altered rocks. In the massive sulfides, gold content and distribution are a function of primary VMS zone refining processes; however, Au has been locally remobilized during metamorphism and deformation. In the Fe-Mg altered rocks proximal to massive sulfide, the distribution and tenor of Au reflects primary zone refining and local remobilization due to metamorphism and deformation, whereas in Fe-Mg altered rocks distal to massive sulfide, gold distribution is largely a product of pre-peak to peak metamorphic remobilization of primary VMS gold via fluid-dominated transportation. In the calc-silicate to carbonate silicate rocks, which contained or contain carbonate, Au distribution reflects metamorphic remobilization. Metamorphic devolatilization of primary carbonate bearing rocks is responsible for adding components such as H2O, CO2 and S2 into a fluid phase that remobilized Au and some metals (e.g. Cu, Pb) in the deposit, and in altered rocks located proximal and distal to the massive sulfide lenses. Gold was mobilized and transported as a sulfur complex, with CO2 acting as a buffer for a low salinity fluid phase such that it could maintain an elevated gold content for transport and deposition. The result of this mobilization is responsible for the Pb-Au in calc-silicate to carbonate silicate altered rocks
A textural and mineralogical study of the footwall rocks to the Sudbury Igneous Complex (North and East ranges)
(2019-03-18) Enright, Jeffrey Michael
In the North and East range footwall rocks of the 1.85 Ga Sudbury Igneous Complex (SIC), quartz and plagioclase (An20-30), plastically deformed prior to the emplacement of the SIC, were thermally annealed, resulting in their replacement by aggregates of strain-free grains that coarsen towards the SIC footwall contact due to radiant heat. In the Victor footwall deposit, SIC East Range, granoblastic polygonal quartz was overprinted by dynamically recrystallized quartz, with microstructures indicative of bulging (BLG) recrystallization. Incipient melting at quartz-plagioclase interfaces in Victor footwall rocks is recorded as interstitial plagioclase seams in quartz with quartz-quartz-plagioclase dihedral angles that peak at ~40 ⁰, characteristic of wetting angles. Subsequent fluid-mediated modification of least-altered plagioclase (An20-30) generated porous albite (An0-10) through a coupled dissolutionprecipitation (CDP) mechanism, which was likely contemporaneous with the crystallization of secondary epidote-group minerals. In the Victor footwall, textures and mineral chemistry of plagioclase, epidote- and chlorite-group minerals support the notion that a relatively oxidized, acidic, Fe-bearing fluid with a temperature of ~310 – 385 ⁰C favoured quartz-plagioclase interfaces as grain-scale fluid pathways, preferentially dissolving the anorthite component of plagioclase and creating void space prior to formation of disseminated chalcopyrite proximal to massive Cu-rich sulfide veins in the footwall setting.
Geochemistry and isotopic composition of sediment cores to understand the lithological and anthropogenic controls on eutrophication in the New River Estuary, Southland, New Zealand
(2019-03-22) Brown, Danielle J.
The New River Estuary (NRE) in Southland, New Zealand is highly eutrophic and has rapidly declining ecosystem health. Historic estuarine reclamation, extensive catchment drainage, and waterway modification have increased the susceptibility of the estuary to degradation. In addition, more recent (post-1984) agricultural intensification and a shift in primary land use from sheep to dairy farming have increased the fine-sediment and associated pollutant loss to the catchment. Extensive macroalgae cover in the NRE reflects the ecosystem's response to eutrophication, where opportunistic species outcompete native plants in the nutrientenriched environment. Three sediment cores from the primary depositional areas in the NRE, the Waihopai Arm and Daffodil Bay, were geochemically characterized, including stable and radiogenic isotopes, to assess changes in the rate of sediment, nutrient, and heavy metal accumulation. The sedimentation rate in the upper Waihopai Arm has increased from 7.3-13 mm yr-1 before 1935 to a very high rate of 20-22 mm yr-1 from 2009-2017. The lower Waihopai Arm and Daffodil Bay have increased to a high rate of sedimentation in the last decade from 5.9 to 17.5 mm yr-1 and 5.5-7 to 10.3 mm yr-1 , respectively. Phosphorus and trace metal concentrations in the bioavailable sediment fraction, which includes Fe- and Mn-oxides, sulfide, organic, or surface-adsorbed phases, have increased up to three and eight times higher than geogenic levels, respectively, which heightens their vulnerability to mobilization in response to changes in salinity and redox state. Increasing heavy metals and decreasing calcium loads, coupled with carbon- and nitrogen-isotopic values trending toward a terrestrial signature (𝛿 13C = -28‰, 𝛿 15N = 8‰), delineates a transition in sediment source from marine-dominated (pre-1935) to terrestrial-dominated (post-1985). The composition of fallout radionuclides also indicates a change in the delivery of terrestrial sediment from channel bank collapse and subsoil erosion (pre-1965) to sheet erosion of surface, likely pasture, soils (post-1997). This study highlights the importance of differentiating the natural sediment signatures from the anthropogenic sources of pollutants to assess the proportion of low-quality sediment (i.e., high nutrient and/or metal concentration) for which a targeted mitigation approach should be applied.
Constraining alteration in the footwall of the Sudbury igneous complex: a case study of the alteration footprint to the Podolsky, Cu(-Ni)-PGE deposit, Sudbury
(2018-11-19) MacInnis, Linette
The footwall environment of the Sudbury Igneous Complex (SIC) host high-grade Cu-(Ni)-PGE deposits that have become a prime exploration target due to increases in metal prices and depletion of traditionally mined contact-style deposits that are high-grade Ni-Cu rich deposits. Understanding and constraining footwall deposits has been underway for some time, still, several aspects of these deposits that need to be constrained. With respect to alteration the nature, origin, relevance, and significance of these hydrothermal minerals have not yet been constrained. A detailed study of the homogeneous grey gabbro unit that is hosted in the Podolsky 2000 deposit host’s sharp-walled sulfide veins, rich in copper and PGEs was an ideal study area to look at alteration leading up to sharp-walled sulfide veins and its association to mineralization as the vein is approached. The initial step is to define and understand what the composition of the least altered grey gabbro with respect to its petrogenetic, spatial, and chronological relationship. Once the least altered grey gabbro is characterized alteration associated to these veins can be explored in detail. Alteration assemblages associated to these sharp-walled veins could potentially be implemented into an exploration tool for mining companies local to the area in search of such footwall deposits. The least altered grey gabbro unit was not as homogenous as previously thought, after careful review of petrography, SEM-DES, geochemical bulk-rock data, isotope work, and U-Pb age dating; a suitable petrographic summary of the grey gabbro was achieved. Once a least altered summary was achieved, comparing this data to transects leading up to these sharp-walled sulfide veins and various samples of most altered grey gabbro were petrographically, geochemically, isotopically, compared to the least altered samples available. Generally, understanding footwall deposits and unravelling the relevance and significance of these hydrothermal minerals was summarized in this thesis, unfortunately, these alteration trends are rather small and can only be observed <30 cm away from the vein, and are most obvious against the vein. This indicated that alteration signatures are not very strong outside of these sharp-walled sulfide veins, despite these veins ~1 m thick.
Proximal braided-river morphodynamics reconstructed through groundpenetrating radar and multi-temporal remote sensing: Kicking Horse River, British Columbia, Canada
(2018-12-07) Cyples, Natasha Nicole
Located in southeastern British Columbia, the Kicking Horse River is a gravel-bed braided river that flows westward through the Canadian Rocky Mountains. Prior studies focused on using ground observations to describe processes of bar formation and sediment distribution patterns; however, a complete model of planform evolution and related stratigraphic signature is lacking. The river was re-examined combining ground observations, multi-temporal remote sensing, discharge data, and ground-penetrating radar to develop three-dimensional models of bar geometry and to highlight changes in alluvial morphology. Remote sensing indicates extensive lateral channel migration over an eight-year period and demonstrates how varying flood stages are associated with episodes of channel braiding. Ground-penetrating radar imaging and analysis identified the distribution of sedimentary facies in the subsurface, which were used to understand the river’s depositional history. The Kicking Horse River’s sedimentary signature is compared to those of both proximal, coarse-grained and more distal, mixed sandy-gravel fluvial systems where similarities in sedimentary architecture and fluvial processes are observed.
Volcanic, structural, and hydrothermal controls on coincident Archean Low and High Sulfidation VMS Systems within the Onaman Assemblage, Onaman-Tashota Greenstone Belt, Northern Ontario, Canada
(2018-11-05) Strongman, Keaton Reid
High sulfidation volcanogenic massive sulfide (VMS) deposits show characteristics of VMS and high sulfidation epithermal deposits and are suggested to have formed through magmatic fluid contribution to an evolved seawater hydrothermal system. Two superimposed systems within the Neoarchean Onaman assemblage in Northwestern Ontario present an opportunity to assess the association between high sulfidation and traditional “low sulfidation” VMS systems. The stratigraphy of the Onaman assemblage consists of pillowed mafic volcanic flows, volcaniclastic rocks, and felsic flows and domes. The assemblage hosts a metamorphosed alteration system defined by kyanite and chloritoid-bearing mineral associations that overprint more traditional VMS associations of calcite, chlorite, and sericite. The sequence is consistent with subaqueous volcanism followed by uplift and erosion, which subsequently subsides to marine conditions. We postulate that the reactivation of synvolcanic structures, during uplift and subsidence, allowed for a direct magmatic volatile input into an evolved seawater dominated, VMS hydrothermal system.
Strontium isotope stratigraphy of the platreef at Turfspruit, Northern Limb, Bushveld Igneous Complex
(2018-10-25) Mayer, Cedric
The origin of the Platreef in the Northern Limb of the Bushveld Igneous Complex (BIC) and its correlation as the stratigraphic equivalent of the Merensky Reef in the Eastern and Western limbs has been long debated. Strontium isotope stratigraphy across the Platreef was completed on drillcore from the Turfspruit farm to test a possible correlation with the Merensky Reef. The results show a significant 87Sr/86Sri shift from ~0.7060 to 0.7090 through the mineralized section of the Upper Platreef, which decreases to 0.7074 and then increases again and stabilize at ~0.708 in the Main Zone. This matches the isotopic shift previously documented through the Merensky and Bastard Cyclic units in the Eastern and Western limbs of the BIC. This coincident shift in 87Sr/86Sri is substantive evidence to confirm that the mineralized intervals in the Upper Platreef are the stratigraphic equivalent to the Merensky and Bastard Cyclic units. This thesis also documents the presence of micro-cycles within magmatic units (up to 350 cycles identified through 215 meters). Working hypotheses linking the micro-cycles to thickness of mineralization are suggested. Testing those hypotheses are outside of the main scope of this study and are suggested for future work.
Geological characterisation guided by fuzzy k-means clustering of physical properties measured from core samples from the Victoria property, Sudbury Ontario
(2018-08-14) Huggins, Jacqueline
Core logging is a subjective practice done by geologists, which documents the mineralogy, textures, alteration, mineralisation and other features to give core a rock name. Pattern recognition techniques are able to characterise the rocks and link the geophysical and geological data quantitatively. The fuzzy-k means algorithm is an unsupervised pattern recognition technique, which groups data into clusters based on properties measured. This study will use the fuzzy-k means algorithm to characterise core samples from 2 drillholes from the Victoria property in Sudbury with thin section examination to identify how mineralogical changes can affect the measurements. Four different physical properties (density, gamma ray, conductivity and magnetic susceptibility) were measured from a total of 203 core samples of quartz diorite, metagabbro, metabasalt, pyroxenite, olivine diabase and metasedimentary rocks. The samples were classified into 4 different physical units, with additional confusion index values that indicate how well the data was classified. Quartz diorite, metagabbro and metabasalt have the highest confusion index values while the olivine diabase and metasedimentary rocks have the lowest confusion index values. Combining the fuzzy k- means results and thin section examination proved to be successful because heterogeneities in sulphide minerals, ore mineralisation and variation in rock forming minerals cause an overlap in physical properties with other rock samples, increasing the confusion index while homogeneity in mineralogy results in a low confusion index.
Evaluating mineralogical, geochemical and microbial relationships within sulfur-bearing mine wastes; a multianalytical and multivariate statistical approach
(2018-03-27) Principe, Emilia
Mine tailings harbour a dense population of extremophiles that play key roles in metal and mineral transformations. While microbially mediated mineral oxidation and reduction within sulfurbearing mine waste has been widely reported, linkages and statistical significance between environmental parameters and geochemical and mineralogical compositions with microbial community diversity has not yet been documented. A combined geochemistry, mineralogy, and genomics approach has been used in this study to better understand the biogeochemical processes occurring within a gradient of tailings dam materials both at surface and down a depth profile. Complex microbial diversity patterns across sample types, environmental conditions, spatial locations, and geochemical and mineralogical compositions, are addressed using multivariate statistical analysis. Additionally, scanning electron microscopy (SEM) and transmission electron micrscopy (TEM) are used to analyze the compositional and morphological features of microbemineral assemblages. A total of 40 sulfur-bearing tailings samples have been collected aseptically from five constructed tailing dam structures, in Sudbury, Ontario. Samples have been grouped into three zones including oxidized, transition, and unoxidized, which are distinguished by pH, munsell colour and mineralogical composition. Oxidized material is composed of silicates and ironhydroxides (goethite) and iron-hydroxy sulfate minerals (jarosite, schwertmannite), with contact pH ranging from 2.6 - 4.5. Material from the unoxidized zone consists mainly of silicates and sulfides (pyrite, pyrrhotite, chalcopyrite and greigite), with a higher contact pH ranging from 4.14 - 5.71. Transitional material is dominantly composed of silicates, but contains both sulfides and secondary iron and sulfate minerals, with pH ranging from 3.6 - 5.31. Microbial community composition and structures are often attributed to their surrounding geochemical environments. However, no significant correlations are observed between total metal content and microbial community compositions across the analyzed samples. However, community compositions and structures exhibit significant changes based on the contact pH ranges and mineralogical iv compositions of the analyzed tailings material. Oxidized, transition, and unoxidized material exhibit similar taxa, however, relative abundance of taxa exhibits extensive variability across the identified zones. Key indicator species are statistically tested across the three alteration zones, with microorganisms whose metabolic functions underpin iron and/or S oxidation and/or reduction identified as microorganisms characterizing alteration zones. Microbial-mineral assemblages analyzed at the nano-scale exhibit minerals that were not identified by routine whole sample analysis (XRD), thereby indicating the importance of performing both SEM and TEM to fully understand microbial-mineral interactions. The microbial-mineral relationships observed in this study both at the micro- and nano-meter scale have resulted in furthering understanding of biogeochemical processes occurring within the analyzed sulfur-bearing tailings material.
Sedimentology, stratigraphy, and U-Pb detrital-zircon geochronology of the Meall Dearg Formation, Stoer Group, Torridonian succession, north-western Scotland
(2018-09-12) Lebeau, Lorraine Elizabeth
The Meall Dearg Formation is a c.1.2 billion year old sandstone, and represents the uppermost unit of the Stoer Group (Torridonian succession, north-western Scotland). Originally described as purely fluvial, the Meall Dearg Formation is here reappraised to represent coeval fluvial-channelised, floodbasin, and aeolian erg environments by facies analysis and petrographic methods. Evidence from palaeoclimate indicators points to humid conditions at time of deposition — inferred from clastic rather than evaporitic floodbasin strata. U-Pb detrital-zircon geochronology resolved provenance from the underlying Lewisian Gneiss Complex (comprising several juxtaposed terranes). Erosion from the Assynt, Gruinard, and Gairloch terranes provided most sediment supply. A statistical comparison of ages from the fluvial and aeolian deposits revealed that both underwent sediment transfer and/or were supplied from comparable terranes. The Meall Dearg Formation, a post-rift fill, is largely comparable to the coeval, pre-Rodinian Gardar-Rift sequence of Greenland.
Spatial and temporal relationship between intrusive rocks and gold mineralisation in the Miller Dyke Complex, Abitibi greenstone belt, Ontario, Canada
(2018-04-23) Arteaga Melo, Luis Alfonso
The Miller Dyke Complex (MDC) is located 15 km south of the Kirkland Lake gold camp. It consists of a series of narrow, structurally controlled dykes, that range from felsic to mafic in composition, and are spatially associated with Au, ± Cu, ± Mo mineralisation. The MDC provides an excellent locality for a careful study of the igneous petrology and the different alteration assemblages associated with the mineralisation. The study is focused on the metasomatic processes related with alkali elements. It is shown that strong sodic alteration has a strong influence on the textural, mineralogical, and geochemical features of these rocks. Previously undescribed textures and mineralisation styles are documented, as well as the existence of a Paleoproterozoic hydrothermal reactivation event with metal deposition or remobilisation. The relationship between the alkali metasomatism and gold mineralisation is discussed within the regional context of the Abitibi greenstone belt.
Ground electromagnetic experiments to investigate the possibility of using an airborne electromagnetic system to detect nuclear magnetic resonance associated with unbound water in the subsurface
(2017-05-31) Gazo, Nikolas
Ground-based geophysical experiments were undertaken to test the possibility of de- tecting groundwater using nuclear magnetic resonance from an airborne electromagnetic prospecting system. Two experimental surveys were conducted: One over an ice-covered lake, containing a large volume of freshwater, and the other over an equal volume of land, with little to no freshwater in the subsurface. If exposed to a radio-frequency pulse at the Larmor frequency, protons in water molecules create a magnetic eld oscillating at the Larmor frequency. Both surveys used a 120-second long frequency sweep from 2300 to 2400 Hz. It was initially hypothesized that as the frequency passed over the Larmor frequency, 2348 Hz, there would be phase shift between the transmitter and receiver signals. Phase measurements, using the heterodyne method, between the lake and land data proved to be inconclusive, although the lake data showed an oscillatory decay in the o -time, not equal to the Larmor frequency.
Exploring for copper–gold deposits with electromagnetic surveys at Opemiska, Canada
(2017-05-31) Gaucher, Frédéric E. S.
Finding and delineating new economic Cu-Au ore zones corresponding to poorly conductive disseminated mineralization and narrow massive chalcopyrite veins in the Chapais-Chibougamau mining district of Québec is a challenging exploration problem. The site of the former Opemiska underground mine was the location for conducting an experimental ground time-domain electromagnetics (EM) survey for mapping the conductivity, the anisotropy of the conductivity and the chargeability estimated from shape reversals. Measurements at fourteen different sites confirmed the variability of the EM response, and the difficulty of relying on a definite EM signature to locate the economic sulfides. The Cu-Au zones showed a variety of EM responses with a maximum conductance of 100 Siemens and 2 ms time constant. The trends, sizes, shapes and conductances of the relatively strong conductors were identified with success and modeled using thin plates in full space. The vein direction in the weakly conductive zones were quantified from the x-component data. In only one instance was a TDEM response associated with mineralization interpreted to be chargeable. Petrophysical measurements and microscopic observations suggest complex interrelations between the amount of ore, the fabric of the rock, texture, porosity, mineralogical associations and impurities. This explains a wide range of bulk conductivity values from ~0.01 S/m to 4000 S/m measured on rock samples, and suggests that chalcopyrite might be a semiconductor at some locations at Opemiska. The magnetic viscosity effects observed at time scales between 0.01 and 10 ms at Opemiska are associated with magnetic grains of variable size in rocks. Recent observations made during a ground time-domain electromagnetic (TDEM) survey at Opemiska are consistent with four aspects of the spatial and amplitude characteristics of a magnetic viscosity response: (1) the ∂Bz/∂𝑡𝑡 decay rate is roughly proportional to 1/𝑡𝑡1+ α, where -0.4 < α < 0.4; (2) the anomalies are mainly visible on the z-component when the EM receiver sensor is located inside or just outside the transmitter loop; (3) there is no obvious x- or y-component response; (4) the sites where magnetic viscosity effect are seen in the TDEM data are coincident with an airborne magnetic anomaly. Previous studies have demonstrated that the magnetic viscosity could be caused by (i) fine-grained particles of maghemite or magnetite in the overburden, regolith or soil that were formed through lateritic weathering processes; (ii) volcanic glass shards from tuff containing ~1% by weight magnetite, which occurs as grains ~0.002 to 0.01 μm in size precipitated in a spatially uniform way, or (iii) from Gallionella bacterium that precipitates ferrihydrite that oxidizes to nanocrystalline maghemite aggregates. The sites investigated at Opemiska are outcropping and well exposed with relatively little or no overburden, and are unfavorable to the formation of maghemite; hence, it is assumed that the source of magnetic viscosity seen at Opemiska cannot be the maghemite, or the other aforementioned causes. Hand samples were collected from Opemiska to identify the minerals present. Polished thin sections observed under an optical reflecting microscope identified the accessory minerals magnetite, ilmenite and pyrrhotite, all known for their relatively high magnetic susceptibility. The use of the scanning electron microscope confirmed fine grained magnetite grains as small as 0.667 μm. An electromagnetic induction spectrometer confirmed the viscous nature of the susceptibility of the Opemiska samples. This suggests that magnetic viscosity could originate not only from fine-grained magnetite and maghemite particles located in the weathered regolith, but also from other iron oxides and magnetic minerals embedded in the rock itself.
Geology and genesis of hybridized ultramafic rocks in the black label hybrid zone of the black thor intrusive complex, McFaulds Lake Greenstone Belt, Ontario, Canada
(2017-05-23) Spath III, Charles S.
The ca. 2.7 Ga Black Thor Intrusive Complex (BTIC) is a komatiitic elongate layered intrusion composed primarily of dunite, lherzolite, olivine websterite, websterite, and chromitite overlain by lesser gabbro and anorthosite. After emplacement but before complete crystallization, a Late Websterite Intrusion (LWI) reactivated the feeder conduit and intruded the base and the core of the BTIC, including the Black Label Chromitite Zone. LWI is a discordant to semiconcordant intrusion that produced marginal zones of heterogeneous, interfingering hybrid matrix and clasts defined as the Black Label Hybrid Zone (BLHZ). The clasts range from 1 to 200 cm in size (rarely > 5m), exhibit amoeboidal to subangular shapes, with sharp to diffuse margins, and varied in compositions from dunite to lherzolite to chromitite. The nature of these clasts appear to have been controlled by the compositions of the lithologies, the thickness of layering, the nature of the contacts between layers, and the initial temperatures of the lithologies being incorporated. There are two types of hybrid groundmass: 1) hybrid harzburgite containing xenocrystic olivine within a websterite, and 2) hybrid chromite harzburgite containing xenocrystic chromite and olivine within a websterite. Both types of hybrid rocks are exceptionally well preserved in terms of mineralogy and textures. The genesis of the BLHZ is extremely complex and involved five interdependent assimilative processes: (1) mechanical disaggregation of clasts resulting in dispersal of xenocrysts; (2) grain-boundary melting (clinopyroxene + plagioclase) resulting in selective assimilation via partial melt mixing; (3) mineral-reaction relation resulting in the dissolution of high-Mg olivine xenocrysts and subsequent growth of intermediate-Mg hybrid orthopyroxene; (4) Mineral-melt re-equilibration between entrained chromite and olivine xenocrysts in LWI melt resulting in diffusive chemical exchange; and (5) complete dissolution of xenocrystic phases very locally formed clast-free rocks of intermediate composition. From map- and core-scale cross-cutting relationships a possible emplacement model can be made: 1) initial emplacement of the BTIC and primary cumulate layers; 2) LWI reactivation of the BTIC feeder, and the diking/silling, stoping and partial assimilation of BTIC wall rocks; 3) formation of heterolithic breccias, heterogeneously hybridized rocks (BLHZ), and associated sulfide mineralization; and 4) local late stage fractional crystallization of LWI magma. The intrusion of LWI magma into the BLCZ does not appear to have consumed any of the chromitite, but has locally reduced the grade of the mineralization through dilution and dispersal. Low-grade patchy disseminated to net-textured Fe-Ni-Cu-(PGE) sulfide mineralization locally occurs in clast-rich regions of the BLHZ and appears to have been generated during the hybridization process. This is the first occurrence known to us where mixing of a magma and cognate xenoliths has led to the formation magmatic sulfides. This style of mineralization is relatively restricted within the BTIC but is consistent with the limited solubility of S in mafic-ultramafic magmas and the small amounts of magma involved.
Phytoavailability, mobility, and solid-phase speciation of antimony (Sb) and lead (Pb) in brunisolic soils surrounding a Pb-Zn smelting complex, Trail, British Columbia, Canada
(2017-01-13) Caplette, Jaime Nicole
Smelting activities in the Trail, British Columbia region since the late 1890’s has emitted metal(loid) contamination in the region (Pb, Zn, Cu, As, and Cd). The objective of this study was to determine the potential availability, mobility and operationally defined speciation of Sb and Pb in contaminated soils. Total Sb and Pb are strongly enriched in surface horizons in the profile (maximum of 737 and 26 376 mg kg-1), with concentrations decreasing with depth. Sequential extractions on soils indicate an enrichment of Sb in the operationally-defined residual > reducible > oxidizable > easily extractable fractions (< below detection limits), whereas Pb shows residual > oxidizable > reducible > easily extractable fractions. Electron optical and microchemical analysis of selected magnetic grains from LFH horizons indicate the anthropogenically derived Sb- and Pb particles to be present as discrete oxide- and sulfide/sulfate particles. The mineralogical and morphological nature of Sb- and Pb- particulate matter is diverse, ranging from angular massive Sn- bearing Sb- Pb oxides, euhedral and subrounded Sboxides, and Pb-sulfides and sulfates. These results indicate that, although soils are highly enriched in Sb and Pb relative to soil quality guidelines, minimal biological uptake and mobility should exist for both elements.
An integrated structural and geochemical study of auriferous sheeted quartz veins within the 2740 Ma Côté Gold deposit, Swayze Greenstone Belt, Ontario
(2016-08-04) Smith, Joycelyn
The Archean Côté Gold deposit (8.3 M oz) is a low-grade, high-tonnage Au(-Cu) deposit located within the 2741 Ma Chester Intrusive Complex (CIC) on the southeast limb of the Swayze Greenstone Belt (SGB) in the Abitibi Subprovince of northern Ontario. Steeply-dipping, auriferous sheeted veins that form part of the mineralized setting can be interpreted as either orogenic in origin and associated with the formation of the proximal Ridout deformation zone or as older and intrusion-related. Structures that overprint CIC are similar to those of the RDZ and are interpreted to post-date the intrusion and mineralized veins. A geochemical study of an alteration profile related to a mineralized vein reveals elemental enrichment in K, Rb, Li, Cs, Ba, Na, F, S and LREEs with a Au-Cu-Te-Pb-Bi-S association. In situ SIMS analysis of δ34S and δ18O are consistent with a magmatic signature for the fluid with a minor component of seawater, and supports the previously proposed high-level, subaqueous setting for the deposit. The combination of temporal, spatial, and geochemical characteristics of the sheeted veins suggests an intrusion-related origin.
The cortaderas zone, Pirquitas Mine, NW Argentina: an example of miocene epithermal Ag-Zn-Pb-Sn mineralization in the Andean Tin Belt
(2016-09-07) Slater, Evan Thomas
The Pirquitas mine, located in the highly elevated Puna plateau region of NW Argentina hosts Ag-rich polymetallic mineralization that defines the southern limit of the prolific Andean Tin Belt. Approximately 500 m north of its currently active open pit is the Cortaderas Zone which hosts the large Ag-Zn-rich Cortaderas Breccia whose nature and origin were previously unknown. This thesis serves as the first academic study of the Cortaderas Zone that incorporates data pertaining to its geological setting, metal distributions, breccia bodies, mineralogy, ore textures, alteration and fluid inclusions to interpret the origin of its mineralization. The results of this study suggest that the Cortaderas Zone represents the high-level and distal expression of the richly endowed hydrothermal system once present at the Pirquitas mine. Its mineralization formed in a dynamic intermediate-sulfidation epithermal system where ore formation was facilitated by transient fluctuations in confining pressure that were caused by cyclical opening and closing of the system. These insights into the formation of the Cortaderas Zone have implications for understanding the formation and subsequent modification of ores in epithermal settings globally.
Gold mineralization in the Missanabie-Renabie district of the Wawa subprovince (Missanabie, Ontario, Canada)
(2016-07-15) McDivitt, Jordan Alexander
The geological processes responsible for the formation of hydrothermal gold deposits are often equivocal. For example, gold-bearing, shear zone-hosted laminated quartz veins in the Missanabie-Renabie gold district (Archean Wawa subprovince, Ontario, Canada) have been interpreted as both intrusion-related and metamorphic-hydrothermal in origin. The veins were mined at the past-producing Renabie mine, which yielded ~1.1 Moz of gold during production from 1941-1991. Whereas the intrusion-related interpretation links the veins to magmatic-hydrothermal fluids released during the crystallization and solidification of their hosting tonalitic pluton, the metamorphic interpretation suggests the veins were deposited from hydrothermal fluids produced during greenschist-facies metamorphism. This study integrates detailed structural field mapping with a number of geochemical techniques to unravel the evolution of the historically controversial ore zones. Results suggest that: (1) the laminated veins and their alteration envelopes pre-date regional deformation, and spatially localized later shear zones, which subsequently focused hydrothermal activity resulting in the formation multistage, composite ore zones; (2) the laminated veins formed during an early, intrusion-related gold event, and the later, co-spatial hydrothermal events are orogenic in nature, and thus more likely to be the products of metamorphic fluids; and (3) discriminating intrusion-related from orogenic events requires constraints provided by geological field mapping. Whereas pressure-temperature information from fluid inclusions and U-Pb geochronology facilitate discrimination, the geochemical signatures of the different hydrothermal events are largely overlapping and do not aid in classification.

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