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

Permanent URI for this collectionhttps://laurentian.scholaris.ca/handle/10219/2113

Browse

Now showing 1 - 20 of 31

Processes at the mineral-water interface in the acid soils of the Sudbury area
(Laurentian University of Sudbury, 2013-10-16) Lanteigne, Sonia
Over a century of mining activities and smelting in the area of Sudbury, Ontario, Canada have resulted in the contamination of the local soils with metal(loid) bearing particulates. Minor and trace elements associated with these phases are released during their weathering. This release is therefore strongly dependent on the mineralogical and chemical character of the metal(loid) bearing phases. The metal(loid)s are then subject to transport before being attenuated through their incorporation into secondary phases. Elevated concentrations of metal(loid)s in silica rich alteration layers has recently been described for altered surfaces at the solid-water and solid-atmospheric interfaces in tailings, and in the vicinity of smelters, respectively. To determine if similar coatings occur in soils, samples were taken from areas around three major smelting centers in the area. Coated grains were extracted from these samples and individually mounted to be analysed. Particulate matter (representing primary metal(loid)-bearing phases) and coatings (secondary metal(loid)-bearing phases) were analysed using scanning electron microscopy, Raman spectroscopy, Laser-Ablation Inductively-coupled plasma mass spectroscopy, Micro-X-ray fluorescence, and X-ray photoelectron spectroscopy. The particulates were divided into three main groups: smelter-derived particles, sulfides, and nickel-oxides. Smelter derived particles contained the most elevated concentrations of metal(loid)s in their sulfide inclusions and metal(loid)-rich rims. The mobility of metal(loid)s in the identified mineral phases found within particulates mirrored the transport observed in the soil column; Zn>Cu>Ni>Pb. Once mobilized, these elements are subject to transport before being attenuated by secondary phases. Micro-coatings were found to be composed of hematite, schwertmannite, ferrihydrite, silica, and jarosite group minerals. Coatings are distinguished on the basis of their atomic Si:Fe ratios: FeOx coatings have Si:Fe <1, Si–FeOx coatings have Si:Fe between 1-10, and SiOx coatings iv have Si:Fe>10. Iron-rich coatings (FeOx) and silica-rich coatings (SiOx) have lower trace-metal concentrations than Fe-SiOx coatings. Micrometer-thick coatings are predominantly composed of hematite, schwertmannite, ferrihydrite and (amorphous) silica and contain elevated metal(loid) concentrations in the form of metal(loid)-rich phosphate minerals (mainly minerals of the jarosite group). A general model is developed that describes the formation of mineral coatings in acid soils and their important role in the uptake and retention of metal(loids). Here, micrometer-thick Fe-silica coatings form through adsorption, co-precipitation and dehydration processes involving amorphous silica and iron hydroxides. Metal(loid)-bearing phases nucleate within a gel-type matrix and are subsequently preserved during dehydration and solidification. Aluminum-rich surfaces form on mineral grains once the pH has been raised sufficiently high (pH~5-6) so as to lead to the complete removal of sulfate-bearing phases. The implications of this model are widespread in terms of the attenuation of metal(loid)s in acid soils and their retention or subsequent remobilization in recovered soils with near neutral pH.
Application of the cross-hole radio imaging method in detecting geological anomalies, MacLennan township, Sudbury Ontario
(Laurentian University of Sudbury, 2013-10-30) Sharif, Ladan Karimi
The occurrence of conductive sulphide in an otherwise highly-resistive host rock is the ideal situation for exploring using high-frequency electromagnetic methods. The FARA radio imaging (RIM) system was deployed to explore the rock properties between two boreholes MAC104 and MAC100G, which are about 182 m apart, on the Nickel Rim South property (MacLennan Township) 22 km northeast of Sudbury. Tomographic data were collected and processed at 625 kHz and 1250 kHz. One data set has the transmitter in MAC100G and the receiver in MAC104; the other “reciprocal” data set has the transmitter in MAC104 and the receiver in MAC100G. The amplitude data were reduced, edited, and processed to generate tomograms employing the SIRT algorithm. Separate tomograms were created for the reciprocal data sets in the ImageWin software. A sensitivity analysis was conducted to assess the influence that perturbations in the ImageWin processing parameters have on the resulting tomograms. The sensitivity study of the tomograms along with the information obtained from the value of fit analysis can be used to select appropriate processing parameters. Finally, the two reciprocal sets of conductivity values were averaged and imported into Geosoft to create a final tomogram for the panel. The resistivity values of the studied zone obtained from the FARA modeling package agree fairly well with the conductivity data set generated by the ImageWin modeling package when compared using the Geosoft and GOCAD visualization software. Differences between the two tomograms are attributed to the different solver methods employed by FARA and ImageWin and the statistical analysis used for averaging the attenuation value over ray paths. Furthermore, it is shown that the tomographic results are consistent with the location of conductive zones that were identified using down-hole geophysical logging. The main focus of the project is to understand how the radio imaging (RIM) data is processed with the ImageWin software to construct an attenuation tomogram. This research showed that both tomograms created by ImageWin and FARA illustrate the same pattern with two conductive zones at the same depth; however, the values of conductivity are slightly different. The FARA resistivity values obtained for the upper zone is a factor of two lower than the resistivity calculated by ImageWin. The resistivity values obtained for the lower zone using the FARA processing is a factor of eight lower than the resistivity calculated by ImageWin. Also, there is a slight discrepancy in the orientation of the upper and lower zones on the two tomographic images generated using the two processing packages. In the tomograms generated by FARA software both upper and lower zones are continuous linear zones from one hole to the other with dips from MAC104 towards MAC100G, whereas in the tomograms created by ImageWin the upper and lower zones are less linear and do not have obvious dips.
Characteristics of diagenetic fluids affecting two major carbonate units on Victoria Island, Northwest Territories
(Laurentian University of Sudbury, 2014-03-17) Mathieu, Jordan-Paul
Diagenetic histories of Proterozoic and Paleozoic carbonate strata on Victoria Island, in the Canadian arctic, are poorly understood, and their potential to be associated with base metals or petroleum is unknown. Using fluid inclusion and geochemical techniques, it was determined that the diagenetic fluid compositions of two major carbonate units, the Wynniatt Formation and the “Victoria Island formation”, were largely controlled by fluid-rock reactions in reservoirs and by mixing of multiple fluids. Diagenesis of the Wynniatt Formation resulted from the progression from a shale-dominant fluid mixture to a meteoric-dominant mixture. Fluid composition of “Victoria Island formation” was a shale-dominant mixture. A change in fluid:rock from low to high was recorded during diagenesis of both units. Metals and hydrocarbons transported to the study sites were ac-quired by the fluids during interaction with the respective source reservoirs. Mixing of diagenetic fluids follows the established ‘mixing model’ used to explain many other min-eralised locations. The diagenetic fluids that affected the strata in this study were compa-rable to those that produced the Polaris Zn-Pb deposit. This similarity suggests that there is potential for mineralisation on Victoria Island.
High tenor NI-PGE sulfide mineralization of the south manasan ultramafic intrusion, Thompson Nickel Belt, Manitoba
(Laurentian University of Sudbury, 2014-05-16) Franchuk, Anatoliy
The South Manasan ultramafic intrusion (ca. 1880 Ma) located in the Early Proterozoic Thompson Nickel Belt (TNB) contains Ni and platinum group element (PGE) mineralization hosted by disseminated sulfide. Whole-rock Ni values range from 0.3 to 1.7 wt. % and total precious metals (TPMs) range from 0 to 1.3 ppm Pt + Pd + Au and equate to tenor values (i.e., metal in 100% sulfide) of 11-39 wt. % Ni and 8-27 ppm TPMs. The South Manasan intrusion is a steeply dipping sill-like body with a boudinaged outline having a strike length of approximately 1200 m, average width of 125 m and a minimum depth extent of 1000 m. The intrusion is composed of approximately 25% fresh dunite, 50% serpentine altered dunite and 25% tectonized and carbonate altered dunite. The most intense alteration is found near the intrusion’s margin where it is in contact with metasedimentary rocks of the Pipe Formation, part of the surrounding Ospwagan Group. In fresh dunite the sulfide assemblage characterized by an intercumulate texture is dominated by pentlandite with accessory pyrite; the latter having a symplectic-like texture. The pentlandite-pyrite assemblage in the serpentinized dunite, although still characterized overall by an intercumlate-texture, has well developed platy intergrowths with chlorite and serpentine. In the most intensely modified unit (the carbonate altered dunite) the sulfide assemblage consists primarily of pyrrhotite and pentlandite. Whole-rock geochemical data (n=360), modal mineralogy and mineral chemistry obtained on representative drill core throughout the South Manasan intrusion have been used to establish a type section in order to evaluate the relative roles of primary magmatic versus secondary (i.e., serpentinization, carbonate alteration and deformation) processes. These data indicate that the primary silicate-sulfide assemblage was systematically modified during : serpentinization, carbonate alteration and deformation of the South Manasan intrusion such that a sequence of primary versus secondary events can be established. Intrusion of the original komatiitic magma and formation of the South Manasan intrusion took place at a shallow level into consolidated Ospwagan Group sediments with subsequent contamination of this melt with crustal S. This triggered sulfide saturation and generation of an immiscible sulfide melt. Calculated Ni and TPM tenor values constrain the R factor to between 500 and 2500. The early crystallization of olivine inhibited the sulfide melt from settling to the bottom of the magma column and as a consequence, the sulfides now have a primary interstitial magmatic texture. The current sulfide association dominated by pentlandite>>pyrite>chalcopyrite has a mineral paragenesis that is consistent with subsolidus re-equilibration of a primary pentlanditepyrrhotite- chalcopyrite assemblage. The subsequent processes of serpentinization, deformation and carbonate alteration resulted in modifying the primary sulfide assemblages and their textures (i.e., to platy habits), but did not greatly alter the bulk composition, in particular metal contents, except for addition of volatiles (H2O, CO2). It is concluded therefore that the enrichment of the sulfide assemblage at South Manasan in Ni and PGEs is a consequence of a primary magmatic process involving high R factor and that the effects of later overprinting processes (alteration, deformation) are not responsible for the presently observed high-tenor sulfide association.
Genesis of Cu-PGE-rich footwall-type mineralization in the Morrison deposit, Sudbury
(Laurentian University of Sudbury, 2014-05-21) Nelles, Edward William
The Morrison deposit, located at the Levack mine in the City of Greater Sudbury, is a footwall-type Cu-Ni-platinum-group-element (PGE) deposit hosted within a zone of Sudbury Breccia in the Archean Levack Gneiss Complex beneath the North Range of the Sudbury Igneous Complex. It consists of sharp-walled, sulfide-rich veins that are enriched in Cu-Pt-Pd-Au relative to contact-type mineralization and can be subdivided based on vein geochemistry, mineralogy, texture, and morphology into a pyrrhotite-rich upper domain, a chalcopyrite-rich lower domain, and a pyrrhotite equal to chalcopyrite middle domain. All domains contain steeply to vertically dipping first-order sulfide veins, irregular and discontinuous second-order sulfide veins, and disseminated sulfides in country rocks. First- and second-order veins can be further subdivided into inclusion-free veins typically within Sudbury breccia matrix or along clast-matrix boundaries, and very irregular and inclusion-rich veins associated with leucosomes in mafic gneiss clasts and granophyric-textured dikes. First-order veins consist of pyrrhotite > chalcopyrite = pentlandite > magnetite in the upper domain, pyrrhotite = chalcopyrite > pentlandite > cubanite > magnetite in the middle domain, and chalcopyrite >> pentlandite > pyrrhotite = cubanite > magnetite in the lower domain. Second-order veins consist of pyrrhotite = chalcopyrite > pentlandite > magnetite and chalcopyrite = millerite = pentlandite in the middle domain, and chalcopyrite >> millerite, millerite > chalcopyrite, bornite >> chalcopyrite, and millerite > bornite > chalcopyrite in the lower domain. Second order veins are adjacent to and in contact with epidote, amphibole, chlorite, carbonate, quartz, and magnetite alteration minerals. Sulfide mineralization in the Morrison deposit is similar to other footwall mineralization associated with the SIC. The veins appear to have been emplaced preferentially into zones of Sudbury Breccia that were within ~400m of the basal contact of the SIC, because that lithology is more permeable and because those zones are within the thermal aureole of the cooling SIC permitting penetration of sulfide melts. The mineralogical, textural, and geochemical zoning in the chalcopyrite-pentlandite-pyrrhotite-rich parts of the Morrison deposit are best explained by partial fractional and/or equilibrium crystallization of MSS and ISS. Bornite ± millerite-rich mineralization are interpreted to have formed by reaction of residual sulfide melts with wall rocks, consuming Fe and S to form actinolitemagnetite- epidote-chlorite-sulfide reaction zones and driving the sulfide melt across the thermal divide in that part of the Fe-Cu-Ni-S system to crystallize borniteSS ± milleriteSS. Gold-Pt-Pd appear to have been more mobile than other metals, forming localized zones of enrichment, although it is not clear yet whether they were mobile as Au-Pt-Pd-Bi-Te-Sb-rich melts or aqueous fluids.
Structural and stratigraphic setting of the Rey de Plata volcanogenic massive sulfide deposit in the Guerrero Composite Terrane, Mexico
(Laurentian University of Sudbury, 2014-07-24) Monter, Ahiram Ramirez
The Rey de Plata volcanogenic massive sulfide (VMS) deposit is located in southern Mexico and within the Teloloapan subterrane of the Guerrero Composite Terrane. It is hosted by the Middle to Late Cretaceous Villa Ayala Formation, which is itself subdivided into three informal members. The lower Ahuehuetla member consists of basaltic flows, sills, and volcaniclastic rocks. The middle Rey de Plata member, which hosts the Rey de Plata deposit, consists of rhyolitic to rhyodacitic flows, sills, and volcaniclastic rocks. The timing of felsic volcanism and the formation of the Rey de Plata deposit is constrained between 139.1 ± 0.4 Ma to 129.4 ± 0.7 Ma by U/Pb dating of zircons from an aphyric flow. The upper Villa Ayala member consists of basaltic amygdaloidal sills and volcaniclastic rocks. The slightly LREE enrichment, negative Nb and positive Zr anomalies of the mafic rocks suggest that they formed either in a primitive to slightly evolved arc to backarc setting with minor contamination by older arc (or continental) crust. The slight LREE enrichment, flat HREE pattern, and pronounced negative Nb anomaly of the felsic volcanic rocks are consistent with FII rhyolites, which indicate their formation and emplacement during rifting within an arc or nascent back-arc environment; an interpretation consistent with the geochemical signature of the associated basaltic rocks. The Rey de Plata and Villa Ayala members are unconformably overlain by argillite of the Acapetlahuaya and turbiditic sandstone of the Miahuatepec Formations, which are capped by Eocene conglomerates of the Balsas Group. Detrital zircons from the Acapetlahuaya Formation have U/Pb ages ranging from 115 ± 4 Ma to 152 ± 4 Ma, similar to the age of volcanic rocks of the Villa Ayala Formation. This suggests that the Acapetlahuaya sedimentary rocks were deposited in an intra-arc basin or in a back-arc basin, which separated the Villa Ayala arc from continental Mexico. This basin was closed during deposition of the younger Miahuatepec Formation sedimentary rocks as these strata yielded older, 800 Ma to 1200 Ma, zircon populations derived from the erosion of older terranes previously accreted to continental Mexico. D1 at Rey de Plata corresponds to the Upper Cretaceous to Lower Tertiary Siever- Laramide Orogeny. A shallowly SW-dipping S1 cleavage, L1 stretching lineation, and NE-verging F1 folds formed in altered volcanic rocks, argillite and turbiditic sandstone during NE-directed D1 thrusting. D2 extensional collapse of the orogen occurred either during or shortly after D1. It produced asymmetrical W-verging folds folding S1, and an S2 shear band cleavage (C’), indicating normal, west-directed slip down the dip of the S1 foliation. During D2, gold- and silver-rich epithermal veins were emplaced. These veins may have contributed to the high grade gold and silver zones of Rey de Plata deposit. Deformation of the Teloloapan subterrane resumed in the Eocene with the formation of D3 normal brittle faults ii linked by strike-slip brittle faults. W-verging F3 drag folds are associated with the normal faults. Extensional basins formed during D3 and were filled by fluvial conglomerate and ignimbrites of the Balsas Group. Late, NW-SE-directed, D4 compression produced upright to inclined, NE- and SW-verging F4 folds that overprint S1 and S2. Rey de Plata is a bimodal-felsic type VMS deposit. It formed during rifting of an arc or backarc and consists of stratigraphically stacked Zn-Cu-Pb massive sulfide ore lenses with high Ag-Au grades. The lenses range in thickness from 3m to 60m, in length from 300m to 1500m, and in width from 100m to 500m. They consist of massive, semi-massive, and disseminated pyrite ± sphalerite ± galena ± chalcopyrite ± silver sulphosalts ± gold, together with gangue minerals of quartz ± barite. Extensive quartz-sericite-pyrite alteration surrounds the ore lenses. Graphitic argillite units up to 40m in thickness typically occur at the top and bottom contacts of the ore lenses. The ore lenses underwent the same deformation history as their host rocks. During D1, they developed a strong S1 foliation, they were stretched parallel to L1, and their base metal zonation reflects clockwise rotation of the lenses (looking NW). Thereafter, during D2 and D3, the ore lenses were displaced southwestward by 200 meters along normal faults and shears and then openly folded by F4 during D4.
Early neoproterozoic marine redox conditions recorded in black shale from the little Dal Group, Northwest Territories, Canada
(Laurentian University of Sudbury, 2014-08-11) O’Hare, Sean Patrick
Black shale in the Little Dal Group (ca. <817 Ma), Mackenzie Mountains Supergroup (<1005 Ma; >779 Ma), was deposited during the early Neoproterozoic, and is one of the few known black shale deposits from this crucial time in Earth’s evolutionary history. Relative iron enrichment (FeT/Al) and conventional iron speciation (DOP), along with enrichment in molybdenum, total sulphur, and total organic carbon, were studied. Iron systematics (FeT/Al >0.5 and DOP <0.80) indicate ferruginous, anoxic, and possibly oxic bottom-water conditions over the time of deposition of the entire black shale unit. The enrichment factors of several of the authigenic redox-sensitive trace elements (U, Mo, V) are strongly correlated, and appear to be related to both the FeT and the organic carbon content of the black shale. Molybdenum enrichment (<10 ppm) is limited, which is in very good agreement with data from Mesoproterozoic black shales, but is much lower than Mo enrichments in Paleozoic black shales (typically >100 ppm). Several black muddy siltstones yielded similar results, but authigenic iron was greatly overwhelmed by siliciclastic sedimentation. These new data support the theory that ocean bottom-waters returned from sulphidic to ferruginous prior to development of oxygenated conditions in the Ediacaran open ocean. This study documents a predominantly open-marine basin that was characterised by ferruginous conditions, similar to Archean and early Paleoproterozoic conditions, with brief intervals when oxic conditions developed.
Modelling radio imaging method data using electric dipoles in a homogenous whole space
(Laurentian University of Sudbury, 2014-12-17) Naprstek, Tomas
Information as to how the signal of the Radio Imaging Method (RIM) changes when the system parameters change or the rock properties change is not well documented. Having a better understanding of the impact of these changes would assist in the design of surveys and the interpretations of RIM data. To quantify the impacts, a modelling program was created by representing the transmitter as an electric dipole. It outputs the amplitude and phase of the electric field in a homogeneous whole space. The system parameters were varied to investigate their effects on the measured signal. It was found that increasing the conductivity or the magnetic permeability resulted in amplitude attenuation and sharper anomalies, while increasing the dielectric permittivity resulted in increased amplitude and broader anomalies. A case study was performed using data from Drury Township, near Sudbury, Ontario, Canada. The mostly homogeneous section of field data was fit with synthetic data whose conductivity values ranged in the 10-3 S/m magnitude. A better fit was found using a conductivity of 3*10-4 S/m, by increasing the relative dielectric permittivity from 1 to between 18 and 20. It was concluded that the program was effective at fitting homogeneous sections of field data, and was developed into RIM forward model software for easy use.
A comparative study of hand-held magnetic susceptibility instruments.
(Laurentian University of Sudbury, 2015-01-27) Deng, Deng Ngang
A study to compare six magnetic susceptibility (MS) instruments (the KT-10 supplied by Terraplus Inc., RT-1 produced by Fugro, SM30 produced by ZH Instruments, MS2K & MS2C produced by Bartington Instruments and MPP-EMS2+ probe produced by GDD Instruments (denoted as GDD)) was conducted to characterize the equipment on the basis of their accuracies, resolution, reproducibility, ease of use and response to drift. MS data were collected on BQ core from 3 holes, NQ core samples, 2 rock samples and 2 calibration samples at the Vale office in Thompson, Manitoba. The results show that the GDD and MS2K are most affected by temporal drift whereas the KT-10 and MS2C gave more repeatable results. The MS2C, MS2K and GDD generally gave higher susceptibility readings than the rest of the meters. It was also noted that measurements on the flat face of half-core samples were always higher compared to measurements on their respective whole core samples. There is a correlation between instruments, frequencies and sensitivities, but no relationship between frequencies of operation and temporal drift. Keywords
Determining the feasibility of a real-time geophysical magnetic and electric measurement system for monitoring strain underground
(Laurentian University of Sudbury, 2015-02-24) Schaub, Christoph
In deep mining environments, rockbursts can occur in areas of high stress. The unpredictable nature, and sometimes fatal consequences of the rockbursts, makes identifying increases in stress that occur prior to failure events, important for mine safety. The piezoelectric, electrokinetic, and seismo-electric/magnetic effects result in rocks that are stressed emitting electric and magnetic fields that can potentially be measured in (or close to) a rock mass. Electric, magnetic and seismic data were collected during a four-day period at Coleman Mine, Sudbury, Ontario, and later analysed. No signals due to strain were evident in the magnetic or electric data, so a more careful three-part experiment was proposed to see if strain related signals could be identified in magnetic data. In the first part of the experiment thirty-two rocks were stressed until failure. Measurable magnetic signals associated with audible cracking sounds were found for most rock samples, as well as consistent signals across all samples prior to failure. The implementation of real-time monitoring of these signals has the potential to significantly improve deep mine safety by mapping the evolution of strain underground and potentially indicating areas susceptible to failure.
A study of the crystal chemistry, cathodoluminescence, geochemistry and oxygen isotopes in Scheelite: application towards discriminating among differing ore-deposit systems
(2016-05-20) Poulin, Rémy S.
Scheelite (CaWO4) from a total of 37 of world-wide, differing ore-deposit settings (orogenic, sediment- and greenstone-hosted, skarn, porphyry, greisen, volcanogenic massive sulfide, breccia and polymetallic deposits) were examined using cathodoluminescence, SEMEDS, LA-ICP-MS and whole-grain stable isotopic analyses. The goal of this study was to assess whether the crystal-chemistry of scheelite (i.e., major, minor and trace elements, stable isotopes, CL response) could be used to distinguish between differing environments of formation. Results show: (1) weak to strong CL responses, these varying from grains with complex, oscillatory zonation patterns, to discordant patterns to those where no zonation is evident; (2) the predominant elemental substitutions involve As5+ or Mo6+ ↔ W6+, and Sr2+ or REE3+ ↔ Ca2+; (3) the trends in REE vary in terms of ΣREEs (104 range in CN values). The degree and type of REE fractionation patterns (flat, convex, concave) are variable and both positive and negative Eu anomalies (<0.1 to >20-30) may be present; and (4) the δ18O values are highly variable, ranging from -4.6 to +12.7‰. The broad ranges do not independently fix a single parent fluid during scheelite formation. The intensity of CL zonation was found to correlate with Mo content: increases in Mo ↔ W substitution correlates with a reduction in CL signal. Further, the nature of the type zonation revealed by CL was found to directly correlate with geological environment: where zonation is absent (i.e., a homogeneous CL response), the scheelite is associated with metamorphic-related systems and where the zonation is pronounced, the scheelite is associated with magmatic-related systems. The variability in REE patterns suggest that other factors are likely controlling the incorporation of REEs into scheelite (e.g., changes in fluid chemistry and mineral precipitation). The presence of substitutions involving Mo and As are particularly relevant, as both are redox sensitive. In particular, enrichments in Mo (>100 ppm) suggest formation in highly oxidizing environments wherein, Mo may be mobile. The crystal-chemistry of scheelite has been demonstrated to be both a strong indicator of ore-forming conditions and the general geological environment.
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.
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.
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.
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.
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.
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.
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.

Browse

Browsing Earth Sciences / Sciences de la Terre - Master's Theses by Issue Date