Master's Theses

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3D geological modelling of the northern Swayze area of the Abitibi greenstone belt: assisting mineral exploration by mapping controls on gold (Au) deposits
(2021-08-20) Mogashoa, Lawraine Lerato
A 3D geological model of the northern Swayze area is constructed through the integration of lithological, structural, geological cross-sections, and seismic information in a Leapfrog Geo® modelling software to delineate structural geometry and geological distribution of rock units in the area. Using a mineral system approach, important geological features are extracted from the 3D geological model. A log-linear 3D weights of evidence method is used to quantify the spatial association between orogenic gold (Au) mineralization and various geological features that might represent ore-controlling factors. This method reveals that the dominant controls on Au mineralization are the second and third generation of deformation zones (D2 and D3), lithological contacts, and second and third-order faults. The posterior probability model is effective in capturing most of the Au occurrences (81%) within 18% of the study area, and the predictive rate curve indicates that the model performs better than random, as it is effective in predicting 71% of the validation points within 30% of the study area.
A textural and trace-element study of pre-ore pyrite types at the Kamoa-Kakula sedimentary-rock-hosted copper deposit, Democratic Republic of Congo
(2024-03-27) Frost, Christian
Pyrite is known or assumed to be an important precursor phase in a variety of sedimentary-rock- hosted ore deposits. The probable role of framboidal pyrite has been identified in the origin of the giant Kamoa-Kakula Cu deposits in Democratic Republic of Congo, which are hosted by multiple-km-thick mid-Neoproterozoic diamictite, but the nature and paragenesis of pre-ore pyrite(s) in the system is poorly known. Using samples from a least-altered, least-mineralised drill-hole, this study identified and characterised four types of pre-ore pyrite in the Kamoa- Kakula system: (a) framboidal (‘sedimentary’) pyrite; (b) aggregate pyrite, consisting of irregular patches of pyrite microcrysts; (c) microcrystalline euhedral pyrite, consisting of independent very small euhedra; and (d) cluster pyrite, characterised by inclusion-rich amorphous centres overlain by groups of large, interlocking, inclusion-free euhedra. Textural relationships indicate that framboidal pyrite formation was followed by euhedral pyrite, aggregate pyrite, and then cluster pyrite. There is no textural evidence that euhedral or aggregate pyrite formed through recrystallisation of framboids. Trace element geochemistry indicates that framboidal, aggregate, and (some) euhedral pyrite formed under related, early diagenetic conditions, whereas (most) euhedral pyrite and cluster pyrite formed later, under different (“hydrothermal”) geochemical conditions. The trace element geochemistry indicates that, in contrast to the textural evidence, the paragenetic order of the pre-ore pyrite types is framboidal, aggregate, euhedral, and cluster. An ore-phase pyrite (clast-rimming pyrite) is texturally and geochemically distinct from all four pre-ore pyrite types.
The Archean Hammond Reef deposit: the formation of an orogenic gold deposit in a contractional step-over-zone along a major strike-slip fault system
(2023-01-20) Fouillard, Gabrielle
Hammond Reef is an orogenic gold deposit with a measured and indicated resource estimate of 3.3 Moz at an average grade of 0.84 g/t gold. It is located within the south-central region of the Wabigoon Subprovince in northwest Ontario. It is hosted within a system of north- to northeasttrending anastomosing shear zones, called the Marmion Shear System (MSS), which straddles the contact between the Mesoarchean Diversion stock to the west and Marmion Batholith to the east. Multiple shear sense indicators, including the deflection of mylonitic foliations in shear zones, drag folds, and shear bands, suggests that the MSS is a major sinistral transcurrent fault system. The bulk of gold mineralization is concentrated in an ENE-trending bend along the MSS, characterized by intense sericite and carbonate alteration. Mineralization formed between 2700- 2690 Ma and is associated with syn-tectonic hydrothermal quartz breccias and shallowly dipping quartz-carbonate veins with down-dip striations, which formed during bulk NNW-directed shortening across the bend. This suggests that the Hammond Reef deposit formed along a contractional step-over-zone between two regional sinistral transcurrent faults. Compression across the bend resulted in more fracturing that localized the migration of hydrothermal fluids and the precipitation and concentration of gold.
Biostratigraphy of the sekwi and rockslide formations (lower to middle Cambrian; Wrigley lake and Sekwi mountain areas; NTS 95M and 105P, Northwest Territories, Canada); implications for basin development and regions correlation
(2023-05-17) Scott, R. William
The lower and middle Cambrian, carbonate-dominated Sekwi and Rockslide formations were deposited in the Selwyn basin, a Neoproterzoic-Paleozoic depositional entity that occupied most of the ancestral western margin of Laurentia and spans parts of modern-day Yukon and Northwest Territories. Biostratigraphic data and limited chemostratigraphic data (δ13Cvpdb) from two Sekwi Formation sections in the Sekwi Mountain map-area (NTS 105P) are used to refine the current understanding of the spatial and temporal distribution of trilobite faunas in the area and to correlate the Sekwi Formation with other units throughout the Canadian Cordillera. Two species-based trilobite biozones (in ascending order: the Nevadia addyensis and Nevadella eucharis zones) previously best known from Arizona, California, and Nevada are documented in the lower Sekwi Formation, and a new genus-based assemblage zone, the Elliptocephala Zone, is proposed for the lower Dyeran of the Selwyn basin and surrounding areas. Trilobite data from three sections in the Wrigley Lake area (NTS 95M) are used to determine the chronology of basin events adjacent to the Redstone arch during the early and middle Cambrian, and lithostratigraphic data from other locations in the same map area is discussed to illuminate the nature of the basin events. There is evidence for two tectonic events during the late (traditional) early Cambrian and earliest middle Cambrian: (1) Event I, a regional uplift that eroded strata proximal to the Redstone Arch, and (2) Event II, a regional deepening event that heralded the onset of Rockslide Formation deposition. Trilobite biostratigraphy remains a mainstay of correlation in the Cambrian and is a powerful tool. However, further refinement is needed for the current biostratigraphic synthesis of the Cambrian of Laurentia, and biostratigraphy is enhanced when combined with chemostratigraphic curves.
Can magnetic susceptibilities measured on outcrops be used for modelling (and constraining inversions of) aeromagnetic data?
(2019-09-07) McNeice, William John
Magnetic susceptibilities measured on outcrop and drill-core samples using hand-held instruments have been shown in the literature to be useful for identifying mineralogical changes. It is not yet clear how useful these measurements are for constraining magnetic modelling and inversion. We have generated estimates of the apparent magnetic susceptibility of the ground by mathematical transformation of an aeromagnetic data and assumed that these values can be used to model the magnetic data. In the same area we have a large number of measurements on outcrop and have compared these two independent estimates. When the measured values are below 1x10-3 S.I., there is a no correlation between the measured and apparent values, interpreted to be likely due to the influence or interference from nearby or underlying magnetic sources. Hence, in this case the measured values cannot be used to constrain modelling and inversion. When the measurements are above this value there is a limited correlation, with values only agreeing to within a factor of about 10, so these values can be used as very rough constraints. The poor correlation is interpreted as due to the presence of remanent magnetization or heterogeneity of the magnetic susceptibility within the rock. A large database of outcrop measurements gives an indication of the range of the variation in magnetic susceptibility values that could be used in modelling.
Characterization of alteration and mineralization at the Archean Grey Fox and Hislop magmatic-hydrothermal gold deposits, Matheson, Ontario
(2021-06-30) Kelly, Christopher Hugh
The Abitibi Greenstone belt (AGB) is host to some of the world’s largest gold deposits and their study has led to various gold deposit models and classifications. The latter includes a syenite- associated deposit type, which was first recognized in the early 2000s. This type of mineralization is present at the Grey Fox and Hislop deposits, which are located 80 km east of Timmins, Ontario. A study of their geologic setting, alteration, mineralogy, mineral chemistry, veining styles, and metal associations, suggest that these deposits, as well as others in the area, developed in different zones of a larger magmatic-hydrothermal system associated with alkalic intrusions of probable Timiskaming age (i.e., <2680 Ma). As such, they formed relatively early in the deformation history of the belt and predate the formation of the more common orogenic or greenstone-hosted quartz- carbonate vein deposits, such as the nearby Black Fox, which make up much of the gold budget in the AGB. A strong host-rock control is present at both deposits and their complex alteration histories provide insights on the formation of multiple mineralization styles within a single system. These different mineralization styles are described here to provide guidelines for mineral exploration for this deposit type in the Abitibi greenstone belt, as well as in other greenstone belts globally.
Chemostratigraphy and structural framework for gold mineralization at the Goliath Deposit, Western Wabigoon Subprovince, Ontario
(2022-05-15) McRae, Mattea
The Goliath deposit (32 Mt at 1.09 g/t Au and 3.42 g/t Ag) is one of the larger gold deposits within the western Wabigoon subprovince, 20 km east of Dryden, Ontario. The economic potential of the Goliath deposit makes it important to understand its geological setting to improve exploration models for such significant targets. Felsic volcanic sedimentary rocks (maximum age of ~ 2703 Ma) host the mineralization, were sericitized, and metamorphosed into the muscovite- sericite schist and biotite-muscovite schist. This package is enclosed within a similarly aged turbidite sequence (maximum age of ~2701 Ma). The mineralization consists of base metal sulphides with gold and silver hosted in As-rich pyrite and remobilized along pyrite fractures. The mineralization is likely pre-deformation as the regional compressional D1 deformation and transpressional D2 deformation reoriented the grade shells to be subparallel to the S1 foliation (075°/78°), and higher-grade shells subparallel to the intersection lineation of S1 and S2 fabric (52°/218°), and subparallel to the F1 fold axial plane (28°/81°). The Goliath gold deposit is thus interpreted to have formed in a synvolcanic, pre-orogenic environment.
Compositional and textural analysis of host-rock diamictite matrix at the Kakula copper deposit, Democratic Republic of Congo
(2019-10-11) Dabros, Quinn
The Kakula deposit is a high-grade sedimentary-rock-hosted Cu deposit (628 Mt, 2.72% Cu indicated resource, 1% cut-off) ~10 km south of the Kamoa deposit (759 Mt, 2.57% Cu indicated resource, 1% cut-off) in the central African copperbelt, Democratic Republic of Congo. Copper-sulphide ore (chalcocite, bornite, chalcopyrite) at Kakula is predominantly disseminated in the fine-grained matrix of clast-poor (≤20% clasts ≥2 mm) subaqueous debrite (diamictite), at the base of the nearly flat-lying midNeoproterozoic “grand conglomérat” (Mwale formation). Scanning electron microscopy was used to document matrix texture and composition to develop a matrix paragenesis, recorded in five phases of the matrix evolution: sedimentation, pre-ore diagenesis, mainore mineralisation, post-ore alteration, and weak tectonism. The ore-zone matrix is porous, up to 12.5%, and consists of clay- to silt-sized muscovite, quartz, chlorite, Kfeldspar, dolomite, and biotite, whereas least-altered matrix, several hundred metres above copper-sulphide mineralisation, consists of clay- to silt-sized quartz, albite, chlorite, K-feldspar, calcite, and dolomite. Copper-sulphide precipitation is contemporaneous with chlorite and biotite (+/- hematite, quartz, and K-feldspar) and fit in a paragenetic sequence between diagenetic pyrite (± Fe-dolomite) and later muscovite. Hematite is ore-stage and most abundant in areas containing chalcocite. Areas of mm- to cm-scale “aligned” matrix (nearly vertical microfabric of aligned, elongated grains) consists of a higher abundance of muscovite, locally elongated copper-sulphides, and a lower concentration of copper than non-aligned matrix, suggesting that copper-sulphide development pre-dated fabric development and that copper-sulphide grains were later dissolved and possibly remobilised. Although determining the original mineralogy and texture of the diamictite matrix is challenging, the depositional matrix characteristics (clast-rich versus clast-poor diamictite) and the availability of reactive agents (e.g., diagenetic pyrite) may have been important controls on copper grade and distribution. More work is required to constrain the absolute timing of mineralisation, which is a major debate at Kakula and Kamoa.
Deformation history and gold mineralization of the Cadillac Group north of the Larder Lake-Cadillac deformation zone, southern Abitibi greenstone belt, Quebec
(2019-08-16) Samson, Brendon
The Cadillac Group is located immediately north of the Larder Lake–Cadillac deformation zone (LLCDZ) along the southern margin of the Abitibi greenstone belt in the Archean Superior Province, Quebec. The LLCDZ is a major 250 km long structure known for hosting several gold deposits. It is generally east-trending over a distance of 170 km, and then it swings to the southeast over a distance of 35 km along the so-called Malartic segment, before resuming its easterly trend for another 45 km. With its thick sequence of <2687 Ma turbiditic sandstone interlayered with mudstone and polymictic conglomerate, the Cadillac Group provides favourable rocks for studying the structural history of the Malartic segment which, due to its unique trend, is important for understanding the overall tectonic evolution of the LLCDZ. Deformation of the Cadillac Group began with large-scale isoclinal folding and the formation of a regional cleavage parallel to the trend of the Malartic segment (D1 event). These structures overprint a 2675.5 ± 2 Ma quartzfeldspar-phyric (QFP) intrusion providing a maximum age for the D1 event and a minimum age for the deposition of the Cadillac sequence. The deformation of the Cadillac Group resumed with bedding-parallel sinistral shearing and the emplacement of gold-bearing extensional quartz veins (D2 event), and continued with bedding-parallel dextral shearing, Z-shaped folding, the formation of a cleavage oriented oblique (anticlockwise) to the trend of the Malartic segment, and by the rotation and segmentation of the gold-bearing veins (D3 event). Contrary to previous interpretations of the Malartic segment as an early pre-D1 accretionary structure, it is interpreted as the short limb of a broad Z-shaped flexure that formed during D3 folding of the LLCDZ and that postdates the emplacement of gold-bearing veins in the Cadillac Group. Mineralized veins at the nearby worldclass Canadian Malartic deposit were emplaced during the same D2 event but they differ in alteration mineralogy and geochemistry to the Cadillac veins suggesting different sources for the mineralizing fluids. Mineralization at the Lapa deposit is similar in sulphide mineralogy and metal association to the Cadillac veins but was emplaced earlier during the deformation history of the LLCDZ.
Depositional history of the Ament Bay Assemblage in the Sturgeon Lake Greenstone Belt, Northwestern Ontario: implications for gold metallogeny
(2023-02-01) Tamosauskas, Michael
The Sturgeon Lake greenstone belt makes up the easternmost portion of the western Wabigoon terrane of the Superior craton, and is comprised of mostly Neoarchean volcanic assemblages, minor siliciclastic successions, and subalkalic- to alkalic intrusions. The Ament Bay assemblage is the youngest supracrustal assemblage of the Sturgeon Lake greenstone belt with a newly determined maximum depositional age of 2695.2 ± 7.8 Ma. Ament Bay consists dominantly of polymictic conglomerates, subarkosic- to arkosic arenites and wacke-mudstone sequences, interpreted as a sub-aerial fan delta that is transitional into subaqueous turbidites. These lithofacies are intruded by syenites of the Sturgeon Narrows Alkalic Complex (ca: 2693.2 ± 0.9 Ma), which are also incorporated as clasts in conglomerates of the Ament Bay assemblage, indicating a coeval relationship between alkalic magmatism, uplift erosion and sedimentation. Both the Ament Bay assemblage and Sturgeon Narrows Alkalic Complex are cross-cut by the Sturgeon Lake fault zone. Coeval alkalic magmatism and sedimentation in a fault-controlled basin are features of the 2680-2670 Ma Timiskaming assemblage which controls much of the orogenic-style gold endowment in the Abitibi greenstone belt. The Ament Bay assemblage has similar features but gold mineralization is not recognized in the belt. The lack of gold endowment in the Ament Bay assemblage could be a result of crustal influence on the alkalic melts and shallow-penetrating faults, in contrast to the juvenile nature of alkalic magmatism and deep-penetrating faults associated with the Timiskaming assemblage.
Emplacement history of mafic-ultramafic volcanic rocks in the northern Pontiac subprovince, Quebec, Canada
(2020-05-15) Rehm, Adrian Gerhard Nutting
Detailed geological mapping of volcanic, sedimentary and intrusive rocks in the northern Pontiac subprovince of the Superior Province has identified multiple volcanic-sedimentary contacts at the margins of a 30 km long volcanic package of high-Fe tholeiites and Munro- to Barbertontype komatiitic flows and sills. Breccias displaying blocky, globular and tendril-like juvenile clasts in a massive sedimentary matrix were observed along the contacts of mafic-ultramafic intrusions with their host sedimentary rocks. These textures are consistent with peperite, a rock formed by the mixing and mingling of magma with wet, unconsolidated sediments. Geochemical data for one of the peperites indicates that the igneous component has a similar trace element composition to spinifex-bearing komatiite flows and the sedimentary component has a similar composition to the Pontiac Group wackes. Additionally, conformable unstrained contacts were observed between effusive volcanic rocks and turbiditic wackes. These relationships indicate a previously unrecognized ca. 2682 Ma mafic and ultramafic volcanic event synchronous with the deposition of the Pontiac subprovince sedimentary rocks. This suggests that the mafic-ultramafic volcanic package is synsedimentary and autochthonous, which is not consistent with previous interpretations of these rocks as structural thrust panels. We propose that the mafic-ultramafic volcanic package was emplaced during a previously unrecognized plume-related extensional event that facilitated the upward flow of mantle-derived magmas along major, mantle-penetrating structures during Pontiac sedimentation. Shortly after, tectonic compression folded and imbricated the Pontiac rocks and accreted them to the southern margin of the Abitibi subprovince.
Emplacement of sharp-walled sulphide veins during reactivation of impact-related structures at the Broken Hammer Mine, Sudbury, Ontario
(2019-08-26) Hall, Marshall Francis
Broken Hammer is a hybrid, Cu-Ni-Platinum Group Element (PGE) footwall deposit in the North Range of the ca. 1.85 Ga Sudbury impact structure. The sulphide vein system and associated low sulphide PGE mineralization were mined as an open pit operation over a 15-month period, providing a unique opportunity to study a complete 90-meter vertical section across a footwall deposit. The deposit is hosted within Archean basement rocks and impact-induced Sudbury breccia, 1.5 km north of the Sudbury Igneous Complex (SIC) – basement contact. The low sulphide mineralization consists of disseminated to blebby chalcopyrite (<5%), minor pyrite, chalcocite, galena, sphalerite and platinum group minerals, associated with Ni-bearing chlorite overprinting alteration patches of epidote, actinolite and quartz. The veins comprise massive chalcopyrite and minor magnetite, chalcocite, millerite, and rare sperrylite, surrounded by thin epidote, actinolite and quartz selvedges. They are grouped into five, steeply-dipping, NE-, SW-, SE-, S- and EWstriking sets, which intersect in a common line controlling the plunge (60°) and trend (220°) of ore shoots. The veins were emplaced along syn-impact fractures that were reactivated multiple times during stabilization of the impact crater floor. Early reactivation of the fractures created pathways for the migration of hydrothermal fluids from which quartz and chlorite precipitated sealing the fractures. Renewed slip and reactivation shattered the quartz-chlorite veins into fragments that were incorporated in massive sulphide veins that crystallized from strongly fractionated sulphide melts or high temperature (400°C-500°C) hydrothermal fluids which migrated outward into the basement rocks from a cooling and crystallizing impact melt sheet represented by the SIC. Hydrothermal fluids syn-genetic with the epidote-actinolite-quartz alteration distributed the PGE into the footwall rocks, or late hydrothermal fluids associated with the Ni-bearing chlorite leached Ni and PGM’s from the sulphide veins and re-distributed them within the footwall rocks, forming the low-sulphide high-PGE mineralization. During post-impact tectonic events, reactivation and slip at temperatures below the brittle-ductile transition for chalcopyrite (<200°C-250°C) produced striations along the vein margins. The Broken Hammer deposit exemplifies how Cu-Ni-PGE footwall deposits formed by the reactivation of syn-impact fractures that provided conduits for the migration of melts and hydrothermal fluids.
Estimating overburden thickness in resistive areas from on-time airborne em data
(2019-09-27) Bagley, Thomas
We propose a method to invert two-component time-domain EM data to a thick-sheet over half-space model, as a solution representing an overburden on top of bedrock. We first estimated the conductivity of the lower half-space using a combination of inversion for half-space (if appropriate) or a thin sheet over half-space (also when appropriate). This yielded a number of estimates, which could be combined to give a reasonable estimate of the lower half-space conductivity for the survey area. With this estimation an equation solver was used to solve the thick-sheet over half-space model for sheet thickness and sheet conductivity. The output of the algorithm was generally stable when applied to GEOTEM data in an area of moderately resistive overburden over a generally more resistive half-space. Although it did not reliably reproduce the overburden thicknesses as measured in the reference drill holes, it did give an estimate that was reasonable in the conductive areas.
A fluid inclusion study of the Little Nahanni LCT-Type Pegmatite Group, NWT Canada: implications for the nature and origin of fluids in LCT-Type Pegmatites and Pegmatite evolution
(2016-12-19) Burns, Michael George Garrett
The Cretaceous (82 Ma) Little Nahanni Pegmatite Group , Canada, is a 15 km long swarm of LCT-type pegmatite dikes that intrude Precambrian to Lower Cambrian siliciclastic metapelites and carbonate rocks. The dykes are dominated by a primary assemblage of quartz, spodumene, K-feldspar ± muscovite lacking both graphic textures and core zones, but characterized by combtextured spodumene and K-feldspar intergrowths. Varying degrees of albitization and lesser phyllic alteration accompany ore-grade oxide enrichment (Ta-Nb and Sn, respectively).A comprehensive fluid inclusion study using a wide variety of methods (petrography , CL, microthermometry, SEM/EDS evaporate mound analysis, LA ICP-MS, laser Raman spectroscopy, δ13C) on minerals (quartz, K-feldspar, albite, spodumene, muscovite, garnet, and tourmaline) from barren and mineralized samples indicate the fluid inclusions are secondary and appear to post-date pegmatite crystallization. The presence of secondary fluid inclusions may instead represent entrapment during the late-stage (sub-solidus to post crystallization) metasomatic evolution stage of the pegmatites. Three fluid types occur, and listed in paragenetic order are: (A) an aqueous-carbonic fluid (≤1 wt. % eq. NaCl) with varying XCO2 (0.1 to 0.78), purity (TmCO2= -57o to -61oC), and density; (B) a low-salinity (≤2 wt. % eq. NaCl) aqueous fluid; and (C) an aqueous-methane-nitrogen fluid. SEM-EDS analysis indicates that the fluids are Na (-K) - dominant, but with significant S and enrichment in transition and chalcophile elements. Fluid inclusion extracts have δ13C values (-9.7 to -27.7‰; n=7) which indicates exchange of the fluids with the immediate, carbon-bearing wall rocks occurred. Collectively the data indicate: (1) fluids were trapped during the later, metasomatic stage of pegmatite evolution; (2) fluids were trapped at <2.5 kbars and <350°C with pressure fluctuating between lithostatic and hydrostatic; (3) variable degrees of fluid:rock interaction occurred with the exocontact zone, resulting in varying XCO2and CO2:CH4 values; and (4) metasomatism and rare metal mineralization occurred in the presence of meteoric water. These findings indicate that the LNPG pegmatites are not a closed system, some of the carbonic component of H2O-CO2 fluids is exotic, and that low-salinity fluids of meteoric origin infiltrated during the subsolidus stage of pegmatite evolution.
A fluid-flow modeling approach for predictive mapping of orogenic gold mineralization in the Malartic camp, Canada
(2021-09-21) Xu, Limin
Orogenic gold deposits are structurally controlled and commonly formed in the transition zone between brittle and ductile crustal domains. Formation of disseminated or localized gold mineralization involves structural features (e.g., fault zones, fold hinges), contrasts in physical properties (e.g., rock competency and permeability, lithostatic and hydrostatic pressure, temperature) or chemical variability (e.g., rock chemistry, fluid composition). Orogenic gold deposits form in convergent tectonic settings, at crustal depths of between 3 and 18 km, from the Paleoarchean to the present. However, the goal of this study is just to investigate the hydrothermal properties of a model and predict the influence of deformation zones, rock types and the associated physical parameters on fluid-flow associated with orogenic gold systems, and subsequently develop new feature-engineered layers for mineral exploration purpose. Open-source numerical modeling software OpenGeoSys, has been used to reconstruct the major fault network in the Malartic mining district, in an area 19.7 km long and 7.3 km wide. This model can compare thermal convection fluid flow with deformation induced fluid flow. Results of numerical simulations conducted in OpenGeoSys and relative calculations from different physical parameters along faults or intrusive contacts explain the existence of a spatial association with the distribution of orogenic gold prospects and mines in the Malartic camp. Results of Weight of Evidence demonstrate that the incorporation of faults in 3D finite element models for coupled fluid and heat transport simulations has the potential of indicating favorable areas for gold mineralization in a 3D space, which can ultimately lead to new mineral discoveries.
Geochemistry of gold from Ontario gold deposits
(2023-10-12) Melo-Gómez, Julian David
Gold is one of the most crucial metals in human history, and still, few investigations have directly studied gold composition to understand gold systems. Ontario (Canada) provides a natural example of gold systems because of the abundance and distribution of world class gold deposits. The present study constrains the geochemical signature of free gold using SEM-EDS, EPMA and LA-ICP-MS to characterize 242 samples from 71 gold deposits and occurrences. Generally, Ag, Cu, and Hg occur over 100 ppm, with Sb, Pd, Cd, and Bi typically as trace elements between 0.001 and 100 ppm. The geochemical signature of gold varies at the craton scale but is consistent at the camp scale. These spatially distinct trace element signatures are independent of local host rock and deposit types, which have implications regarding the controls on ore-forming mechanisms and reflect district-scale variations in the primary and secondary composition of gold. This elemental signature has important practical applications for industry; for example, in using elemental vectors that reflect local gold composition and/or in metallurgical processing.
Geology and structural evolution of the Tashota Deformation Zone and implications for orogenic gold mineralization
(2023-10-18) Mark, Benjamin
The Tashota Deformation Zone (TDZ) is a north-striking, ductile structure within the Onaman- Tashota Belt in the eastern Wabigoon subprovince of the Archean Superior Province in northwestern Ontario. The < 2700 Ma TDZ has never been studied in detail, despite its location along the boundary between a large batholith and Mesoarchean and Neoarchean volcanic rocks, its north trend in a belt where most ductile structures trend east-west, and the presence of orogenic gold mineralization. The TDZ is a high strain zone that formed along the batholith- volcanic rock boundary during the development of a dome-and-keel architecture in the central Onaman-Tashota Belt. During this deformation event, gold was emplaced along the TDZ contemporaneously with significant gold deposit formation to the south in the Beardmore- Geraldton Belt during syn-accretionary imbrication of volcanic and sedimentary rocks along the southern margin of the Wabigoon subprovince.
The geology of the Windfall gold deposit, Québec, Canada
(2021-04-21) Choquette, Brandon G.
The Windfall deposit is an advanced-stage exploration gold project owned and operated by Osisko Mining Inc. and is located in the northeastern portion of the Abitibi greenstone belt, Québec, Canada. This is the first deposit-scale study and as such aims to provide an understanding of its geological setting and the evolution with a focus on the origin of gold mineralization. The study integrates several aspects, including: 1) geological mapping; 2) characterization of the various host rock lithologies and their alteration; 3) results of new age dating; and 4) characterization of the different vein types, their mineralogy and chemical and textural nature of the gold mineralization. The overall conclusion of the study suggests that the gold deposit formed ca. 2.7 Ga due to a magmatic-hydrothermal fluid exsolved from an underlying magma now represented by a swarm of felsic dike rocks spatially associated with the ore body.
Geostatistical analysis and integration of soil chemistry data with remote sensing information in the Sudbury area, Ontario.
(2022-03-28) Nethavhani, Phathutshedzo Molly
The presence of anomalous concentrations of metals within the soil profile can strongly affect its biological availability to plants, causing potential toxicity when exceeding threshold concentrations, and favoring numerous chemical exchanges. These interactions further facilitate metal dispersion in the hydrogeological and ecological systems, in response to weathering and erosion. Studies of the geospatial distribution of trace metal contaminants in Sudbury soils is thus important to unravel the dominant processes controlling dispersion patterns, contributing to sustainability of mining practice. A kriging geostatistical approach was applied to geochemical data obtained from the Sudbury Soil Survey to map multiscale geographic, enrichment trends in metal concentrations. Ordinary kriging prediction maps were developed to re-evaluate the multiscale spatial distribution of the chemicals of concern. Results show an anomalous distribution of metals centered on historical smelters, forming dominant northeast and southwest enrichment trends. The existence of these trends was validated by implementing a geostatistical Gaussian conditional simulation method, which reproduced the same spatial variability observed in the ordinary kriging maps and efficiently replicated the observed trends. The correlation analysis of the trends with remote sensing data, suggests that prevailing wind directions are likely one of the dominant driving forces controlling the trends. Integrating these results with satellite data showed improved vegetation regrowth patterns consistent with the geochemical northeast-southwest trend providing further, independent validation of the kriging results. Re-evaluation of the regional, geospatial distribution of the measured trace element concentrations will assist the monitoring and improved understanding of soil contamination trends and their impact on vegetation and other aspects of the biosphere in the Greater Sudbury area.
Gold mineralisation in a chemically reactive host: the Archean Gold Mineralised Vickers Dioritic Intrusive Complex, Nunavut Canada.
(2023-03-31) Tokaryk, Scott Arnold Jack
The Vickers albitised dioritic intrusion (VDI, 2668 ± 6 Ma), located in the central Hearne sub- domain of Nunavut, hosts a significant gold discovery (2012; e.g., hole PB-12-09 164.41 m @ 5.39 ppm Au). The intrusion (equilibrated to lower-greenschist-facies) is located in the northern part of the 2.72 to 2.65 Ga Tavani greenstone belt, an area that has been interpreted to contain the Pistol Bay Corridor, a west-northwest-trending brittle/ductile deformation zone. The VDI is an elliptical (900 x 600 m) heterogeneous igneous intrusion emplaced into the siliclastic Evitaruktuk Formation, part of the sedimentary Kaminak Group, and contains highly anomalous Au mineralisation focused along its northeastern contact. Pyrite and arsenopyrite, spatially associated with gold mineralisation, occur proximal to quartz- carbonate± chlorite veins that increase relative to the severity of hydrothermal alteration. Several gradational alteration assemblages are present in the mineralised zone, including chlorite- (CF1+CF2) and silica-facies (SF1I + SF2I) that are restricted to the VDI, and sericite-facies (SF1FW+SF2FW) in the footwall. By integrating petrographic observations, LA-ICP-MS analysis (sulphide mapping, Pb isotopes), in situ SIMS δ18Oquartz and δ34Spyrite, arsenopyrite, and other geochemical data (whole rock, SEM, etc.), a working model is proposed. The preferred model suggests that a metamorphic fluid carrying Au as a bi-sulphide complex was focused along a rheologically favourable contact and subsequently reacted with the Fe-oxide - rich VDI and precipitated Au via sulphidation reactions.

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