Titre de l'écran-titre (visionné le 29 janvier 2024) / Le gisement Upper Beaver (UB) est un système hydrothermal de Cu-Au situé dans la sous-province de l'Abitibi, au nord de la faille de Larder-Lake Cadillac. Le complexe intrusif Upper Beaver (UBIC) peut être décomposé en phases intrusives qui se succèdent et qui contiennent une abondance de magnétite primaire et secondaire. Cette abondance est associée à la minéralisation qui est riche en Cu-Au. Les contrôles structuraux complexes qui influencent la minéralisation peuvent souvent modifier la réponse géophysique mesurée en entraînant une différence de la signature pétrophysique pour des roches encaissantes qui ont pourtant des compositions minéralogiques similaires. En évaluant les propriétés électromagnétiques des roches (susceptibilité magnétique, résistivité/conductivité et polarisation provoquée), nous avons constaté qu'il est possible de différencier l'altération des unités géologiques sur la base des différences dans leur réponse pétrophysique. Ces différences sont imposées par des changements des roches par des processus tels que la formation de veines, la minéralisation et la formation de failles. Ces différences peuvent être grossièrement divisées en trois événements : (1) préminéralisation (2) minéralisation principale et (3) post-minéralisation. Dans ces travaux, nous démontrons que les valeurs de susceptibilité magnétique peuvent être utilisées pour différencier entre les veines qui sont issues de la préminéralisation, de la minéralisation principale et post-minéralisations. La susceptibilité varie en fonction de l'oxydation progressive du système, les phases préminéralisation et l'événement de minéralisation principale forment de la magnétite et nous y retrouvons des valeurs de susceptibilité magnétique supérieures à 100 x 10⁻³ SI. La formation de carbonates de quartz lors de l'événement de minéralisation principale influence légèrement l'abondance de magnétite et peut détruire une certaine portion de celle-ci. Les valeurs de susceptibilité magnétique pour ces unités sont alors contrôlées par la lithologie de l'hôte ou par l'altération dominante (qui se situent généralement entre 1 et 100 x 10⁻³ SI). La variation naturelle des valeurs de susceptibilité magnétique qui découlent de la combinaison de la formation de carbonate de quartz au sein de lithologies disparates rend cette phase difficile à identifier. Enfin, l'épisode stérile post-minéralisation est destructeur de magnétite avec des valeurs de susceptibilité magnétique inférieures à 1 x 10⁻³ SI. La résistivité électrique est fortement influencée par la géométrie des textures par rapport à la géométrie de l'instrument de mesure utilisé pour acquérir les données de forage. Nous montrons que l'épidote hydrothermale, la séricite et la minéralisation riche en Au-Cu ont un effet significatif sur la résistivité électrique à l'échelle du centimètre ou du mètre et que ces effets peuvent être déduits des résultats. Pour mieux illustrer les effets d'échelle de ces caractéristiques et, enfin de compte, la macro-texture de la masse rocheuse mesurée, nous avons introduit le rapport de résistivité N64/N8. À l'UB, la résistivité de la roche minéralisée devrait augmenter au fur et à mesure que les textures gagnent en importance. Les veines associées à la minéralisation sont dominées par le quartz, les carbonates et de l'ankérite qui sont tous des matériaux résistifs. L'altération antérieure à l'événement de minéralisation principale se situe dans une fourchette de N64/N8 entre 0,5 et 1,0. L'altération associée avec l'événement de la minéralisation principale peut être divisée en veines riches en Cu-Au et seulement riche en Au. Les veines riches en Cu-Au (qui sont dominées par l'épidote et l'altération du k-feldspath) se situent entre 1,0 et 2,5 tandis que les veines riches en Au (qui sont dominées par l'épidote, l'ankérite et l'altération de la séricite) se situent entre 2,5 et 3,5. L'altération post-minérale occupe des rapports allant de 0,5 à 1,0. Les brèches et les failles sont associées à des veines riches en carbonate et en Au et ont un effet important sur le rapport N64/N8. Nous avons également constaté que la minéralisation riche en Cu-Au à proximité de la zone de stock-work (un ensemble de veines et de brèches hydrothermales à proximité des intrusions felsiques centrales du gisement) présente un rapport de résistivité plus élevé que la minéralisation distale. Les fractures et les conditions de forage ont été étudiées. Nous avons conclu que celles-ci n'ont pas d'effets significatifs lorsqu'elles sont comparées aux effets des mécanismes d'altérations. Nous concluons que les textures qui sont souvent associées aux plus hautes teneurs de la minéralisation peuvent être séparées de la roche hôte en comparant les mesures obtenues à partir de différents espacements d'électrodes. La polarisation provoquée (IP) sert de pont entre la susceptibilité magnétique et la résistivit é, car elle est influencée par les mêmes processus géologiques (changements de grain et de texture). En raison de l'impact de l'échelle sur les caractéristiques texturales, le rapport IP IP641/IP161 a été créé. La signature IP entre les événements antérieurs, principaux et postérieurs à l'événement de minéralisation est restée relativement cohérente et n'était pas discernable par IP. La zone de stock-work contient cependant un halo de minéralisation de type skarn, qui a produit une anomalie IP notable. Des valeurs IP anormales ont également été observées aux contacts bréchifiés entre les unités I2Dm (syénite mafique) et V7 (basalte). Il s'agit probablement de magnétite aciculaire générée par le métasomatisme de contact dans ces régions, qui a été identifiée visuellement dans les forages de l'UB. Cependant, aucune microscopie n'a été réalisée sur les forages de cette étude et ne peut donc être confirmée. / The Upper Beaver Deposit (UB) is a Cu-Au hydrothermal system located within the Abitibi sub-province north of the main Larder-Lake Cadillac break. The Upper Beaver Intrusive Complex (UBIC) can be broken down into successive intrusive phases which contain abundant primary and secondary magnetite associated with Cu-Au rich mineralization. The complex structural controls on mineralization often influence the measured geophysical response, resulting in a difference in petrophysical signal for two mineralogically similar host rocks. Assessing the electrical and magnetic properties of the rocks (magnetic susceptibility, resistivity/ conductivity and induced polarization) we found that it is possible to differentiate between altered and unaltered geological units based on differences in their petrophysical response. These differences in petrophysical signature are caused by changes to the host rock from processes such as veining, mineralization, and faulting. These differences can be broadly split into three events: (1) pre-ore, (2) main ore, and (3) post ore events. In this work, we show that the magnitude of the magnetic susceptibility can be used to differentiate between rocks that have been variably altered by one of the three main geological events. The pre-ore dog's breakfast (DBF) event, the main-ore event rich in Cu-Au, the quartz-carbonate Au-only portion of the main ore and the post-ore barren event. The susceptibility varies with the gradual oxidization of the system. The pre-ore and main-ore events are magnetite forming and magnetic susceptibility values are above 100 x 10⁻³ SI. The main-ore quartz carbonate phase is magnetite neutral to slightly destructive and the magnetic susceptibility values of these units is controlled by the host lithology or dominant alteration (which are generally between 1 and 100 x 10⁻³ SI). It makes the quartz carbonate phase difficult to identify from the magnetic susceptibility data. The barren post ore event is magnetite destructive and magnetic susceptibility values fall below 1 x 10⁻³ SI. Resistivity is strongly influenced by the geometry of the textures relative to the geometry of the measurement instrument used to acquire the borehole data. We show that hydrothermal epidote, sericite, and mineralization have a significant effect on the electrical resistivity. The variations can be seen over scales that range from centimetres to a meter which can be inferred from data measured with different electrode spacing. To better illustrate the scale effects of these features and ultimately the macro texture of the rock mass measured, we have introduced the resistivity ratio N64/N8. The N64/N8 ratio compares the electrical resistivity measured at an electrode separation of 64 inches to the electrical resistivity measured with an electrode separation of 8 inches. In, this study it is used as a proxy to understand the scale of the electrical resistivity features encountered in the borehole. For a homogeneous rock mass, this ratio is 1. Ratios greater than 1 can either be caused by significant resistive veining, that is it has an effect n the numerator of the ratio, or by small conductive features that lowers the denominator. This approach allows to rapidly identify homogeneous portions of the rock mass and to highlight heterogeneous sections. At the UB, the resistivity of the mineralized rock is expected to increase as the scale of the textures increase. In this case, this occurs because the veins associated with mineralization are dominated by resistive quartz, carbonate and ankerite. Pre-ore alteration occupies a N64/N8 range between 0.5 - 1.0. Main ore-event alteration can be split between Cu-Au and Au rich veining. The Cu-Au rich veining (which is dominated by epidote and k-feldspar alteration) plots between 1.0 and 2.5 while the Au rich veining (which is dominated by epidote, ankerite and sericite alteration) plots between 2.5 and 3.5. The post-ore alteration occupies ratios that range from 0.5 to 1.0. Breccias and faults are associated with carbonate Au rich veins and are shown to have a compounding effect on the N64/N8 ratio. We also found that Cu-Au rich mineralization close to the stock-work zone (a collection of veins and hydrothermal breccias close to the central felsic intrusions within the deposit) sees an increased resistivity ratio when compared to distal mineralization. Fractures and hole conditions were investigated but did not have significant effects on the resistivity measurements in comparison to alteration. We conclude that textures which are often associated with the highest grades of mineralization can be separated from host rock by comparing electrical resistivity measurements acquired with different electrode spacing. Induced polarization (IP) is a physical property which is affected by both minor grain inclusions and textural alignment of grains. IP may therefore help to confirm some of the textrual effects noted on these two other methods. Due to the scale impact on textural features the IP ratio IP641/IP161 was created. Like the N64/N8 ratio, the IP ratio consists of the IP channels at the 16 inches and 64 spacing, with the following 1 denoting the first time window of recording. The IP signature measured on areas of the pre, main and post ore events remained relatively consistent and was not useful in discerning between them. The stock-work zone, however, contains a halo of skarn-like mineralization, which produced a noticeable IP anomaly, anomalous IP values were also observed on the brecciated contacts between I2Dm (mafic syenite) and V7 (Basalt) units. This is likely acicular magnetite generated from contact metasomatism in these regions, which has been visually identified in boreholes at the UB. However, no microscopy has been conducted on samples taken from the boreholes within this study and this supposition cannot be confirmed.

The thesis map area is located in northeastern Ontario in and west of the Adams Mine site. The Adams Mine produces iron ore and is situated 15 km southeast of the town of Kirkland Lake. Kirkland Lake is the largest population centre in the Kirkland Lake-Larder Lake gold camp. The Adams Mine lies south of this camp. The thesis map area is underlain by volcanics (most of which are komatiitic), clastic, chemical and pelitic sediments and various intrusives (peridotite sills, layered peridotite-gabbro and gabbro sills, discordant gabbro bodies, alkali-rich dykes and diabase dykes. The syenitic Lebel Stock forms the northern boundary of the map area. The map area lies entirely within the Larder Lake Group which forms the lower part of the second major volcanic cycle (cycle II) in the Archean aged Abitibi greenstone belt. The Kinojevis and Blake River Groups overlie the Larder Lake Group north of Kirkland Lake and are also part of cycle II. The Skead Group constitutes the upper most part of cycle I. The top of this group marks the southern boundary of the map area. The fold axis of the Lebel Syncline passes through the northern half of the map area. This fold is isoclinal and has no plunge. The fold axis and the stratigraphy are broadly conformable to the shape of the Lebel Stock. Tight folds with north-south trending axial surface traces and a drag fold occur on the south limb of the Lebel Syncline. The Lebel Syncline and these second-order folds are believed to pre-date Intrusion of the Lebel Stock. The stock may have modified the trend of the Lebel Syncline fold axis so that it and the strata parallel the stock's shape. Five faults with unknown but apparently little displacement were recognized. Faulting is not prominent in the map area. The northern half of the map area has been metamorphosed to the hornblende hornfels facies. This occurred during contact metamorphism following intrusion of the Lebel Stock. Greenschist facies mineralogy is present in the southern half of the map area and developed during an earlier regional metamorphic event. There are eight volcanic sequences on the south limb of the Lebel Syncline. Seven of these are komatiitic. There are three komatiitic sequences on the north limb. Komatiitic sequences are characterized by volcanic flows which show decreases in MgO contents stratigraphically upwards. Komatiites occur at the base of each sequence and are overlain by one or more of high MgO komatiitic basalt, high MgO komatiitic andesite, low MgO komatiitic basalt, low MgO komatiitic andesite, low komatiitic dacite, high A12O3 komatiitic basalt, andesite and dacite and high Fe2O3, Α12Ο3 komatiitic basalt. . Most low MgO komatiitic basalts and andesites on the south limb of the Lebel Syncline have anomously high Cr (>1000 ppm) and Ni (>200 ppm) contents when compared to similar lithologies in other Archean terranes. The high Cr abundances are linked to high chromite contents. Sequences with Cr and Ni-rich volcanics do not contain high A12O3 komatiitic volcanics; the latter have low Cr (approximately 400 ppm) and Ni (approximately 80 ppm) contents. High Fe2O3, Α12Ο3 komatiitic basalt occurs in sequences with high A12O3 komatiitic basalts. High Α120β and high Fe203, Al203 komatiitic basalts are not found in other Archean terranes. Cr and Ni-rich komatiitic volcanics are found in Destor Township in Quebec (within the Abitibi greenstone belt). They are not otherwise found. Sequence 1 basalts are regarded as tholeiitic or calc-alkalic. There are no ultramafic or high MgO flows in this sequence and lithological variation with stratigraphic height is not observed. The high Cr and Ni contents in the komatiitic basalts and andesites are explained by rapid cooling in a magma chamber. This process stops or reduces olivine and chromite crystallization in the magma as it reaches a MgO content of 12 % to 15 %. The residual magma is thus enriched in Cr and Ni. The production of high komatiitic volcanics can also be explained by rapid cooling in a magma chamber. This process lowers the temperature of plagioclase crystallization resulting in A12O3 enrichment in the magma. Many of the sedimentary rocks in the map area are deposits from submarine debris flows and turbidity currents. The flow mechanism is not known for massive sandstones. The presence of conglomerates (debris flow deposits) suggests a proximal depositional environment, using a submarine fan model. The source area is comprised of sedimentary, volcanic and plutonic lithologies. Peridotite sills are believed to syn-volcanic with komatiitic volcanism. Peridotite-gabbro and gabbro sills are likely syn-volcanic with tholeiitic volcanism now preserved in the Kinojevis Group north of Kirkland Lake. The discordant gabbro Intrusions are believed to be syn- volcanic with calc-alkalic volcanism now preserved in the Blake River Group north of Kirkland Lake. Lateral equivalents to both groups may have once overlain the Larder Lake Group but have since been eroded. This is consistent with the fact that higher metamorphic grades prevail south of the Larder Lake Break. The sills and discordant gabbros were emplaced prior to regional metamorphism. The Lebel Stock, syenite, biotite lamphrophyre, feldspar porphyry and diabase dykes were emplaced following deformation and greenschist metamorphism. The alkali-rich intrusions are likely contemporaneous with Archean trachytic volcanism now preserved in the Timiskaming Group. / Thesis / Master of Science (MSc)

<p> The Lake Shore Mine has accounted for over a quarter of the gold produced in the Kirkland Lake camp. Petrography suggests that gold is a later phase in the paragenesis of ore minerals. Sulphides precipitated first followed by tellurides and gold. Wallrock alteration adjacent to the quartz veins was studied by thin section and geochemical analysis. Petrography enabled an alteration facies scheme based on predominant alteration minerals to be established. The alteration assemblages suggest the fluid had a high K and CO2 content, low Na, and reduced S content. Geochemical analysis of these samples confirm petrographic observations and suggests major additions of K2O, SiO2, Rb, Sb and Au to the wallrock, and losses of Na2O, Ba and Zr from the wallrock.</p> / Thesis / Bachelor of Science (BSc)

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