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A thermodynamic and experimental study of rock/melt reaction in a basanite-peridotite system: trace element partitioning and formation of wehrlite veins
(University of New Brunswick, 2022-09) Ma, Shuai; Shaw, Cliff
Enrichment of mantle previously depleted by partial melting, termed mantle metasomatism, occurs by reaction of peridotite with fluids / melts derived from deeper in the mantle. Clues provided by mantle xenoliths about the nature of the metasomatic agent include 1) discordant veins of dunite, wehrlite and clinopyroxene; 2) disseminated occurrences of phlogopite, amphibole or apatite; 3) LREE-enriched but isotopically depleted mineral phases such as amphibole and clinopyroxene; 4) preserved reaction textures such as incongruent dissolution texture and sieve texture of peridotite minerals. To understand the compositional effects of the transformations that occur during mantle metasomatism, a complete set of mineral / melt trace element partition coefficients (Kd) is an essential input into thermodynamic models. Up to now, the partition coefficients have been compiled from a variety of studies that used different melt compositions, pressure, temperature, and initial starting mineral assemblages. The first part of this study describes the development and testing of an internally consistent database of mineral / melt partition coefficients for a variety of peridotite compositions interacting with an alkaline mafic magma. The Kd values, determined at 1 GPa and 1250 °C for clinopyroxene, orthopyroxene and olivine were compared with predictions from the lattice strain model which indicates two site mixing and in some cases multivalence of single elements. Partitioning is controlled by both mineral and melt compositions. Of particular importance is the structure of the melt as indicated by viscosity and the ratio of non-bridging oxygen to tetrahedrally coordinated oxygen. In the second part of the study the new set of partition coefficients were used to model magma – peridotite interaction and its relation to the origin of clinopyroxene-dominated veins that are found in the peridotite xenoliths from the West Eifel Volcanic Field, Germany. The pMELTS algorithm used for the model examines how alkaline mafic magma reacting with mantle can modify mineral assemblages, proportions, and compositions in a variety of peridotite assemblages. The models reproduce the observed mineral assemblages and compositions in the natural samples from the West Eifel and support the earlier interpretation that these veins represent migration pathways for rising asthenospheric magma and that interaction with this magma caused significant changes to the lithospheric mantle, depleting it in orthopyroxene and enriching it in clinopyroxene. The final part of the study is an examination of an unusual type of amphibole-phlogopite-rich wehrlite vein also from the West Eifel Volcanic Field (termed a type II vein to distinguish it from the compositionally distinct magmatic veins described in the second part of the study). This vein contains clinopyroxene, phlogopite and amphibole that are identical in major and trace element composition to the same phases found as disseminations in metasomatized xenoliths in the West Eifel. Previous studies have linked the disseminated metasomatic assemblage to passage of fluids through the mantle. The vein mineralogy cannot be linked to any of the primitive silicate melts thus far identified in the Eifel region. Instead, the low Ti, Zr and high LREE abundance as well as the fractionated LREE/HREE ratio suggests a carbonatitic source for both vein and disseminated minerals. Although carbonatites are known from the Eifel region, those already studied have been interpreted to be related to extreme fractionation of mafic magmas in the upper crust. The carbonate signature in the peridotite xenolith described here is the first unequivocal evidence that such melts were an active metasomatizing agent in the sub-Eifel lithospheric mantle.
Amer Lake Map
(University of New Brunswick, 2016) Calhoun, Lydia
An integration of geological and geophysical evidence of impact at Manicouagan
(University of New Brunswick, 2016) Brown, Jessie; Spray, John
The Manicouagan impact structure has been assigned a revised collapsed cavity diameter of 65 - 85 km. This updated value reflects the results of geological mapping, analysis of the gravity anomaly, and the distribution of shock features. The minimum of 65 km is dictated by the presence of collapsed rim material at a radial distance of ~33 km from the centre of the structure. The maximum is based on the greatest possible diameter of damage zone found to replicate the observed gravity anomaly. A shock barometry survey has been carried out and finds a broad trend of decreasing shock pressures with increasing radial distance. Interestingly, relic β-quartz is identified in several of the shocked samples. Based on the observations described in the first five chapters of this work, a hydrocode model of the formation of the Manicouagan impact structure has been generated.
Assembling an Archean magmatic plumbing system: Geochemical evolution, emplacement, and metallogenic implications of subvolcanic intrusions in the Yellowknife greenstone belt, N.W.T., Canada
(University of New Brunswick, 2023-02) Speight, Sarah Catherine; McFarlane, Chris; Hanley, Jacob
The Yellowknife greenstone belt (YGB), located in the Archean Slave Province in the Northwest Territories, Canada, consists of mafic and felsic metavolcanic sequences intruded by dikes and regional plutons. The locally known “#9” dikes comprise three generations of intrusions that were not geochemically differentiated or genetically linked to a parental source, including, feldspar-quartz porphyry (FQP), quartz porphyry (QZP), and aplite dikes. Despite the spatial association with mineralization and inferred relationship to overlying volcaniclastic units, the dikes remain poorly understood. Therefore, a multi-analytical approach was needed to characterize the evolution, emplacement, and metallogenic signature of YGB magmatism. The lithogeochemical signatures of the dikes, combined with U-Pb zircon geochronology, differentiated them into three groups: 1) the Ryan Lake Pluton (RLP), represented by tonalites (2662 Ma) and granodiorites (2647 Ma), and the FQP (2674 – 2662 Ma) and aplite-1(a) dikes (2663 Ma); 2) the Defeat Suite granite (2580 Ma) and aplite-1(b) dikes (2662 Ma); and 3) the Duckfish granite (2576 Ma) and the aplite-2 dikes (ca. 2611 Ma). The intrusions were also compared to the overlying felsic volcaniclastics of the Townsite Formation and Banting Group. When combined with field observations, this confirms that only the FQP dikes are subvolcanic feeders to these units. The ambiguous lithogeochemistry of the QZP dikes (2770 Ma) and the age gap with the main diking event (ca. 2662 Ma) did not allow for a plutonic connection. Rather, the QZP and one FQP dike proximal to the Duckfish granite may reflect magmatism related to the Central Slave Basement Complex. Additionally, macro- and micro-scale textural analysis of the aplite dikes provided evidence of emplacement during crystallization of the parental magmas. The three groups of aplite dikes (1(a), 1(b), and 2) commonly have quartz cores and discontinuous quartz pods at the outcrop scale that reflect crystallization from a volatile-saturated melt. Finally, analysis of zircon-hosted melt inclusions (MI) from a subset of YGB dikes and plutons showed evidence of early precious metal-enrichment. Careful data filtering to remove contaminated inclusions produced the first MI dataset from the Archean YGB which represents primary silicate melts. Zircon-hosted MI that contains accidentally trapped phases also provide valuable information, despite the semi-quantitative nature of the data. These mixed MI provide direct evidence of Ti- and H20-saturation through the presence of (Fe)-Ti-oxides and hydrous minerals (e.g., biotite, amphibole). This preliminary work establishes that critical information related to primary metal signatures in the YGB can be obtained from Archean MI.
Characterization of recent pyroclastic density currents and determination of magma residence times in historic and pre-historic eruptions of Galeras volcano, Colombia: a contribution to the hazard assessment
(University of New Brunswick, 2021) Gomez, Lyzeth Johana; Shaw, Cliff
Textural and chemical patterns in plagioclase phenocrysts of three pre-historic and two 21st century eruptions of the andesitic Galeras volcano, Colombia, have been used to determine the residence time of magma within the subvolcanic system. Near-equilibrium, oscillatory zoned plagioclase and variably textured zones indicating dissolution / resorption, evidence changes in pressure, temperature, composition, and magma flux during crystal growth. Modelling of Sr and Ba diffusion in plagioclase, which crystallized at an average temperature of 975 °C, indicates that all five eruptions preserve evidence of at least two phases of magma chamber development. Oscillatory zoned grains give magma residence times of 10 to 81 years. Grains with disequilibrium textures always indicate a much shorter residence time in the subvolcanic chamber, generally less than 10 years. These results suggest that the initial magma chamber received additional fluxes of phenocryst bearing magma no more than a decade before eruption.
Chemostratigraphy and hydrothermal alteration of the Flat Landing Brook Formation, Brunswick Belt, Bathurst Mining Camp
(University of New Brunswick, 2014) Wills, Alexander Oakley; Lentz, David
The Flat Landing Brook Formation, northern New Brunswick Bathurst Mining Camp, represents a Middle Ordovician supervolcano of tremendous volume. It consists of subaqueous to subaerial volcanic flows, domes, volcaniclastic deposits, and derived sedimentary rocks, mostly within a very narrow range of original calcalkalic/transitional A-type rhyodacite/rhyolite composition but variably obscured by hydrothermal alteration and multiphase deformation. The objective of the project was accomplished: to interpret the cryptic FLB rocks along the Brunswick Belt together with footwall Upper Nepisiguit Falls Formation and hanging wall Little River Formation via: (a) chemostratigraphy employing alteration-resistant and petrogenetically-sensitive ratios of low-mobility elements with contrasting compatibilities; and (b) alteration quantified from multiple precursor mass balance, alteration reaction vector, and mineral normative calculations. The sample suite from seven diamond-drill holes has whole-rock geochemical data (n = 346; XRF and INAA), core photographs (n = 89), Sm-Nd isotopes (n = 15), and O-isotopes (n = 36). Alumina-normalization of incompatible Zr versus compatible TiO2 (TiO2/Al2O3 vs. Zr/Al2O3) reveals emergent sample groupings, and profiled by downhole core sample depth serve as the basis for the chemostratigraphy. Each division is further classified by magmatic affinity (Zr/Y), alkalinity (Nb/Y), crustal/mantle melt (Th/Hf), Fe-Ti oxides stability (Ti/Ti*), REE enrichment/depletion ([La/Yb]cn, Eu/Eu*), and εNdt-derived crust/mantle melt ratios. The sixteen chemostratigraphic divisions are assigned: Nepisiguit Falls Formation felsic volcanic-derived sedimentary rock (NF SED; Zr/TiO2 = 0.059; Nb/Y = 0.28; Zr/Y = 3.72; Th/Hf = 2.17; Ti/Ti* = 0.072; [La/Yb]cn = 4.47; Eu/Eu* = 0.39) and Brunswick Horizon Member iron formation with tholeiitic andesite input (IF; Zr/TiO2 = 0.024; Nb/Y = 0.32; Zr/Y = 3.53; Th/Hf = 1.58; Ti/Ti* = 0.116; [La/Yb]cn = 6.70; Eu/Eu* = 1.17); Flat Landing Brook Formation effusive Reids Brook Member calc-alkalic rhyodacites (A1, A2, A3; Zr/TiO2 = 0.083, 0.085, 0.094; Nb/Y = 0.33, 0.39, 0.33; Zr/Y = 7.05, 8.10, 8.51; Th/Hf = 2.14, 1.48, 1.36; Ti/Ti* = 0.075, 0.093, 0.097; [La/Yb]cn = 7.54, 6.35, 5.33; Eu/Eu* = 0.47, 0.55, 0.61; εNdt = -3.42, -2.59, -2.20; crust/mantle = 64/36, 55/45, 57/43); younger, more voluminous effusive/explosive Roger Brook Member transitional/calc-alkalic rhyolite/rhyodacite (B1, B2, B3, B4; Zr/TiO2 = 0.153, 0.143, 0.116, 0.125; Nb/Y = 0.34, 0.33, 0.34, 0.34; Zr/Y = 6.04, 6.58, 7.09, 8.87; Th/Hf = 2.41, 1.86, 1.65, 1.21; Ti/Ti* = 0.034, 0.045, 0.063, 0.076; [La/Yb]cn = 7.57, 6.62, 6.05, 5.22; Eu/Eu* = 0.38, 0.48, 0.50 & 0.60); upper FLB unnamed flowbanded effusive rhyodacites (transitional C1 and tholeiitic C2; Zr/TiO2 = 0.089, 0.107; Nb/Y = 0.31, 0.32; Zr/Y = 5.73, 3.46; Th/Hf = 2.34, 3.18; Ti/Ti* = 0.059, 0.028; [La/Yb]cn = 6.95, 6.85; Eu/Eu* = 0.45, 0.37); Little River Formation unnamed tholeiitic andesite sedimentary rock (SED; Zr/TiO2 = 0.023; Nb/Y = 0.41; Zr/Y = 4.00; Th/Hf = 3.11; Ti/Ti* = 0.136; [La/Yb]cn = 8.15; Eu/Eu* = 0.63); unnamed felsic volcanic rocks marking transition into rift-stage (transitional/tholeiitic rhyolite C3 and feldspar porphyritic alkalic trachyandesite/rhyolite D1; Zr/TiO2 = 0.200, 0.153; Nb/Y = 0.38, 0.83; Zr/Y = 4.77, 6.98; Th/Hf = 2.08, 1.38; Ti/Ti* = 0.022, 0.039; [La/Yb]cn = 6.21, 7.51; Eu/Eu* = 0.42, 0.53); Brunswick Mines Member within-plate alkalic gabbro/basalt (ALK GAB; Zr/TiO2 = 0.012; Nb/Y = 0.78; Zr/Y = 6.38; Th/Hf = 0.99; Ti/Ti* = 0.521; [La/Yb]cn = 5.95; Eu/Eu* = 0.77); unnamed enriched mid-ocean ridge basalt (E-MORB) type tholeiitic gabbro (THOL GAB; Zr/TiO2 = 0.007; Nb/Y = 0.26; Zr/Y = 3.49; Th/Hf = 0.31; Ti/Ti* = 0.605; [La/Yb]cn = 1.70; Eu/Eu* = 0.96). A lithostratigraphic progression is observed from crustal toward more mantle melt petrogenetic compositions, extensional continental to rift basin tectonics, corroborated by Sm-Nd isotopes: Nepisiguit Falls Formation (εNdt=460Ma = -8.28 to -4.80; crust = 100 to 74%, mantle = 0 to 26%); Flat Landing Brook Formation (εNdt=460Ma = -4.80 to -1.40; crust = 74 to 49 %, mantle = 26 to 51 %); Little River Formation (εNdt=460Ma = -0.12 to -5.10; crust = 39 to 0 %; mantle = 61 to 100 %). Hydrothermal alteration is determined for each sample in chemostratigraphic hole profile to show the range of pervasive weak/moderate to layer selective intensities, for K-feldspathization/albitization (Na2O vs. K2O antipathy), sericitization/paragonitization (Na2O vs. K2O antipathy, SiO2 mobility), chloritization (gain of Fe2O3T and MgO, loss of alkalis and SiO2), silica leaching/flooding (SiO2 gain/loss), and calcite/ankerite/dolomite/siderite/magnesite alteration (gain of CaO +/- Fe2O3T and MgO). Within these profiled holes, there is no evidence of intense hydrothermal alteration, discordant stockwork zone, or significant massive sulfide accumulation in the Flat Landing Brook Formation. Applying similar chemostratigraphy and quantified alteration elsewhere in the Bathurst Mining Camp will help resolve complex lithostratigraphic relationships to focus mineral exploration.
Commissioning a three-dimensional electrical resistivity imaging system for seepage monitoring at an embankment dam abutment
(University of New Brunswick, 2021) Boulay, Daniel; Butler, Karl
The Mactaquac Generating Station is a large (660 MW) hydroelectric facility on the Saint John River, approximately 19 km upstream from Fredericton, New Brunswick. An alkali-aggregate reaction within the dam's concrete structures is causing their differential expansion. This has prompted the dam's operator, NB Power, to be proactive in monitoring for any signs of concentrated seepage that could arise where the dam's clay till core abuts a concrete diversion sluiceway. Seepage is a leading cause of dam failures. An emerging method to non-invasively investigate an embankment's interior is Electrical Resistivity Imaging (ERI). ERI is sensitive to changes in water saturation, temperature and ionic content, all of which can be indicators for localized seepage. In this work, a 100 electrode areal array was installed to focus on the interface between the embankment and its concrete abutment. Numerous hurdles and challenges were solved throughout this work. The installation of a durable and effective array was achieved by drilling into the slope and injecting bentonite into the drill holes before driving in long (0.91 m) electrodes to keep contact resistances low. Limitations posed directly by the relatively short survey line lengths on the back of the dam were mitigated by implementing a pole-dipole survey geometry which yields relatively large depths of exploration and maintained sensitivity near the ends of the lines. An enigmatic current regulation issue, which affected repeatability, was solved by customization of measurement array geometries and by averaging many surveys over time with a smart-averaging processing routine designed to reject outlier measurements. Many necessary changes were made to electrode array configuration over the course of the study and data quality has steadily improved. Early results are encouraging, yielding repeatable resistivity models for the embankment that are consistent with its internal structure. Time lapse surveys were successful in observing localized resistivity changes in the embankment, interpreted as seasonal temperature change. Also observed were small resistivity change anomalies within and just outside the core of the embankment, which are inferred to be consequences of changes in saturation and water temperature as well as road salt presence in the winter. Localized seasonal resistivity anomalies have been identified that are suggestive of two paths for elevated seepage: i) water passing through the concrete abutment and entering the rockfill on the downstream of the core, and ii) a possibility of elevated seepage through the core adjacent to the abutment. Further seasonal monitoring as well as incorporating data form electrodes installed across the dam crest will be needed to confidently assess whether seepage through the core is anomalous next to the abutment.
Controls on genesis, distribution, and nature of the turbidite-hosted gold deposits, Eastbelt, Southwestern Slave Structural Province, Yellowknife, Northwest Territories
(University of New Brunswick, 2020) Richardson, Mark Wesley; Lentz, David
The Ptarmigan and Tom mesothermal gold deposits are located 10 km to the northeast of the city of Yellowknife, Northwest Territories. Both gold deposits comprise a series of en echelon veins. These veins are hosted within upper greenschist to lower amphibolite facies ~2630 Ma rocks. A low-temperature reduced hydrothermal environment during ore deposition formed as either a part of the main arsenopyrite-dominated mineralization or a distinct late-stage ore-formation event. At the deposit scale, the high-grade gold ores are preferentially developed with three contextual scenarios: (1) along contacts, especially the contact between black siltstone host rock and major barren, cleavage-parallel veins; (2) the contact between quartz laminae and carbonaceous host rock slivers; (3) proximity to bismuth telluride mineralization. Thus, competent, barren quartz veins along the axial plane of fold/thrust belts locally host superimposed gold mineralization and provide favourable targets for gold exploration. Hydrothermal apatite is a common accessory mineral in both mineralized and non-mineralized quartz veins in the metasedimentary host rocks that constitute the Ptarmigan and Tom deposits. The apatite in this study likely formed coeval with early stages of sulphide precipitation. The apatite age of 2585 ± 15 Ma is consistent with the intrusions of the 2605 and 2590 Ma two-mica granites of the Prosperous Suite. The near-concordant [superscript 204]Pb-corrected data of the LCT pegmatite hosted apatite reveals two clusters of ages. An older population with an intercept age (N = 4) of 2581 ± 15 Ma, and a younger population with an intercept age (N = 3) of 2519 ± 12 Ma . Furthermore, plotting a regression through all near – concordant data for the pegmatite hosted apatite hints that metamorpic resetting occured around ~2200 Ma. The distribution and abundance of major, minor, and trace elements from in-situ recovered apatite were studied to characterize the nature of mineralizing fluids. Most apatite from mineralized and non-mineralized veins show different Mn, Sr, and Pb contents, as well as chondrite-normalized rare-earth element (REE) and Y abundance patterns. REEs display five unique chondrite-normalized patterns: (1) negative sloped pattern with slight negative Eu anomaly, (2) a flat pattern with a positive Eu anomaly, (3) a positive slope with a negative Eu anomaly, (iv) light rare earth element (LREE) depleted pattern with positive Eu anomaly, and (v) bell-shaped pattern with a negative Eu anomaly. The REE patterns likely reflect both the source of the auriferous hydrothermal fluids and, perhaps, co-precipitating mineral phases. Apatite from the Ptarmigan vein occurs with both: (1) a flat pattern with a positive Eu anomaly and (2) bell-shaped pattern with a negative Eu anomaly. The bell-shaped and flat patterns typify orogenic gold deposits. Vein-hosted apatite commonly displays compositional zoning with a characteristic yellow cathodoluminescence (CL) emission spectra with darker cores and brighter rims. The cores have lower REE, whereas the rims are notably REE higher. It is thought that the darker cores in CL images reflect a transition from an early low REE hydrothermal fluid to one enriched in REE. Lastly, this study breaks ground for conducting a more robust study to classify the trace-element composition of apatite in gold deposits worldwide.
Electrical resistivity imaging for embankment seepage monitoring
(University of New Brunswick, 2024-04) Danchenko, Dmitriy; Butler, Karl E.
Measurements of electrical resistivity variations are of special interest for non-invasive investigation of concentrated seepage through embankment dams . An experimental resistivity monitoring system is in development at the Mactaquac Hydroelectric Generating Station in New Brunswick, Canada. With 123 electrodes distributed over a 70 m x 25 m area adjacent to a concrete sluiceway structure, the system runs autonomously each night, collecting over 7000 apparent resistivity measurements. Annually the resistivity of water in the reservoir varied by nearly a factor of four, providing a strong signal for use as a tracer to highlight regions that appear to have experienced preferential water flow. Order-of-magnitude estimates for seepage flux are calculated by analyzing the time lag between resistivity changes measured in the reservoir and the dam core. The results suggest that the electrical resistivity imaging approach is feasible for seepage monitoring at water retaining structures, even in an electrically noisy environment.
Evolution and mineralization of the Moose II Lithium-Tantalum Pegmatite Deposit, Northwest Territories, Canada
(University of New Brunswick, 2013) Anderson, Melissa O.; Lentz, David; Mcfarlane, Chris R.M.
The Moose II rare-metal granitic pegmatite is located approximately 115 km east of Yellowknife, NWT, on the north shore of Great Slave Lake. The irregularly zoned dike is -430 m long by 61 m wide, and is discordantly hosted within polydeformed metaturbidites of the Neoarchean Yellowknife Supergroup. This deposit was mined for both lithium and tantalum (1946-1954). The pegmatite formed ca. 2652 Ma (U-Pb columbite ), which corresponds to a late magmatic period following a phase of extensive plutonism in the Slave Province. The size and orientation of the pegmatite suggest that it was emplaced into a dilatant zone along a north-trending shear zone. The dike displays extreme fractionation, manifested by the irregular spatial zonation of mineral assemblages, rare-metal enrichment, and the very high degree of chemical evolution. Mineralogical zones include: a narrow border zone, a fine-grained wall zone, several megacrystic intermediate zones, massive quartz and amblygonitemontebrasite core zones, saccharoidal ( aplitic) al bite zones, and muscovite-rich replacement zones. The degree of chemical evolution of the dike suggests that the pegmatite melt was injected a considerable distance from the progenitor pluton. Detailed internal fractionation trends show progressive evolution from the margins of the pegmatite inwards, and from the south section of the pegmatite towards the north. The economically important minerals present include: amblygonite-montebrasite (Li), spodumene (Li), and columbite-group minerals (Nb-Ta). Processes of niobiumtantalum mineralization are primarily magmatic, with enrichment during magmaticmetasomatism, and minor remobilization during hydrothermal metasomatism.
Examination of mesothermal to epithermal orogenic- to intrusion-related Sb-bearing gold systems in a southern New Brunswick segment of the Northern Appalachians
(University of New Brunswick, 2022-04) Heidarian, Hassan; Lentz, David R.
Several Sb-Au mineralization styles are diversely scattered within the boundary of Gondwana and Laurasia in southern New Brunswick. Some research has been completed regarding the timing and genesis of the structurally-controlled, mesothermal to epithermal orogenic and intrusion-related Sb-Au mineralization types in the regionally correlative Annidale (New River and Annidale belts) and Clarence Stream areas (St. Croix and Mascarene belts). LA-ICP-MS U-Pb and 40Ar-39Ar geochronology of hydrothermal rutile and white mica in the Annidale area suggested that orogenic gold type mineralization is related to Ordovician Penobscot orogeny. However, several further orogenies overprinted some mineralization in the area. The apatite and titanite U-Pb and white mica 40Ar39Ar data confirmed the Early Devonian age for intrusion-related gold type in the Clarence Stream area. Zircon U-Pb data on several mafic to felsic intrusive rocks showed the age range of Silurian to Late Devonian; however, the relation of the Early Devonian intrusions (Magaguadavic and Lower Tower Hill granites) to the gold mineralization has been reaffirmed. The sulphur isotope data suggests a mantlederived source for sulphide phases. The lead isotope results show highly radiogenic Pb, which might be due to the addition of Pb during or after ore formation, that overprinted the initial Pb isotopic system. As no later major magmatic activities occurred, Ordovician orogenic gold was preserved in the Annidale area. It is probable that similar orogenic gold mineralization was formed at the same time in the southwestern part of the New River Belt (Clarence Stream area). A combination of several factors, including preexisting orogenic gold deposits, advanced hydrothermal activities related to the emplacement of multi-phase intrusions during Devonian, and the presence of local brittle-ductile shear zones, were crucial, explaining the greater concentration of gold in intrusion-related deposits in the Clarence Stream area than the orogenic gold deposits in the Annidale area.
Genesis of gold mineralization at the Cantung W-Cu skarn deposit, N.W.T.
(University of New Brunswick, 2020) Lentz, Carlin Paul Edward; McFarlane, Chris
This study was initiated to identify what phases host the gold mineralization, which skarn assemblages it is hosted within, the relationship between the tungsten and copper mineralization and the gold and bismuth mineralization, as well as the timing of these gold mineralizing events and their relationships to nearby intrusions at the Cantung W-Cu mine, Northwest Territories, Canada. Using detailed reflected light microscopy, the main gold-bearing phase was identified as electrum (Au-Ag alloy) with an assemblage that included native bismuth, several bismuth telluride and selenide minerals, as well as silver and lead sulfosalts. The textures exhibited by these Bi-Au-Te-Se -bearing phases suggest they precipitated from aqueous solutions as polymetallic melts which remained molten throughout the growth of other skarn and vein minerals and ultimately exsolved from these melts. After ascertaining the skarn and vein assemblages hosting gold, U-Pb geochronology of allanite and titanite was conducted to determine the timing of these events.
Geochemical investigation of urban soils in Fredericton, New Brunswick, Canada
(University of New Brunswick, 2016) Sénéchal, Daniel; Broster, Bruce
Fredericton, New Brunswick, overlies an aquifer that supplies potable water to ~95% of the city. This aquifer is confined by a discontinuous clay-silt aquitard which underlies floodplain/fluvial deposits. The aquitard contains erosion scours or ‘windows’, which could serve as pathways, allowing contaminants into the aquifer. A soil geochemical survey of Fredericton included 101 sampling sites with a focus on locations near the windows. The urban centre occupies a large floodplain situated between the Saint John River and higher terrain to the west. Near-surface ‘A’ samples were collected at a depth of ~10-15 centimeters and, where possible, deeper ‘B’ samples were collected at a depth of >30 centimeters. Till samples were also collected from areas of higher elevation, where the soil has been less disturbed. Subsamples <63 microns were analyzed by INAA or TD-ICP to determine elemental concentrations for 50 elements. Samples collected in the downtown area were found to surpass the Canadian Council of Ministers of the Environment (CCME) soil content guidelines for elements such as As, Cr, Pb, and Zn. It is interpreted that anthropologic factors have contributed to elevated elemental concentrations in the downtown area. Weathering and elemental mobility are also interpreted to have facilitated the dispersion of elements. The ‘B’ till samples often displayed higher elemental concentrations than the ‘A’ samples. Unlike the till population, the urban centre population demonstrated higher elemental concentrations in the ‘A’ samples in comparison to the ‘B’ samples, suggesting anthropological contributions at ground surface. In an attempt to correlate human health with soil geochemical content, health statistics from the Fredericton area were investigated; fortunately, no illnesses or diseases seem to stand out in comparison with provincial and national statistics.
Geochronologic, petrographic, geochemical, and isotopic constraints on the origin of the uraniferous Lac Turgeon Intrusive Complex, Quebec
(University of New Brunswick, 2014) Beal, Kristy-Lee; Lentz, David; McFarlane, Chris R.M.
The Lac Turgeon Intrusive Complex (LTIC), along the north shore of the St. Lawrence Seaway in the Grenville Province of Quebec, is host to pegmatite-related uranium mineralization. The main zone has an inferred resource of 81.5 million tons U₃O₈, averaging 0.013% U₃O₈; isolated occurrences, including the Grandroy Zone, have revealed 20 m of 0.174% U₃O₈ in channel sampling and up to 0.213 % U₃O₈ over 5.4 m and 0.089 % U₃O₈ over 10.5 m in drill holes completed in 2009. The intrusion’s main lithologies include granite, pink pegmatite, and white pegmatite that contain biotite, muscovite, zircon, ilmenite, hematite, and magnetite with minor apatite, uranothorite, uraninite, monazite, and xenotime as accessory minerals. Previous mineralogical studies have also noted the presence of pyrochlore, churchite (YPO₄*2H₂O), zoned samarskite, allanite, titanite, bastnaesite, and titanobetafite. The texturally diverse complex has irregular and sharp contacts, highly radioactive late-stage felsic intrusives, local magmatic layering, and breccias. Mineral geochemistry and textures provide evidence of crystallization depths > 4-5 km in a fluid-rich environment and mineral saturation temperatures (monazite, zircon, and apatite) average between 686-894°C. The samples at the LTIC came from the same source with the granite less fractionated than the pegmatite phases (white pegmatite commonly more fractionated than the pink pegmatite) based on the fractionation factors of the large ion lithophile and high field strength elements. The granite and white pegmatite phases towards the outer rim of the complex reveal ages (U-Pb Monazite) of 969 Ma (±7Ma and ±6 Ma, respectively); a Double S Zone granite phase towards the center of the intrusion revealed a concordant age of 941 ± 2.7 Ma (U-Pb Monazite, Xenotime) confirming there are several fractionated intrusive phases present at the LTIC. The dates indicate the LTIC is a post-orogenic complex that crystallized at the current level of emplacement towards the end of the Rigolet orogenic phase but outside the area of penetrative Rigolet metamorphism. Geochemical evidence identify that the LTIC is a peraluminous granite-pegmatite intrusion with a complex mixture of previously melted, lower crustal and more juvenile crustal sources giving a crustal A-type (higher Ga, Nb and lower Ba) to S-type (high Rb, Al) affinity. Similar to other uranium deposits including the Limousin pluton in the French Massif Central, the complex increases in peraluminosity with a slight decrease in fractionation indicative of an L-type granite. L-type granites are the result of low degrees of partial melting of a Proterozoic, metasediment source (high ¹⁸O signature) that contains elevated uranium content. Batch-type melting would have commenced by adiabatic melting during uplift related to the orogenic collapse and reworking of normal-sense shear zones following the completion of the Ottawan orogenic phase of the Grenville Orogen. The U and Th values are highly variable (<2-4485 ppm and 0.7-620 ppm, respectively) with U/Th ratios ranging between 0.28 and 25. The average U/Th for the LTIC is 2.3 (+4.0/-1.5; based on log transform data). In most samples, uraninite is accompanied by increased accessory mineral content explaining the close relationship of uranium with La, Ce, Zr, and Y. The main zones associated with highly uraniferous phases, including the Double S, MA, and MB-zones, have a close association with hybridization that would have occurred during magma ascent or in the magma reservoir prior to ascent, as measured by higher CaO + MgO + FeOt. Hybridization is believed to be the main control for concentrated uranium mineralization for other post-orogenic Grenvillian pegmatites. Fractional crystallization is still a factor related to mineralization elsewhere in the intrusive complex including the J- and Lac Turgeon zones. The Grandroy Zone reveals evidence that albitization or sodium metasomatism (higher Na₂O and lower SiO₂ and K₂O and textural evidence) could play a role in uranium mineralization at that location.
Geology and geochemistry of sedimentary ferromanganese ore deposits, Woodstock, New Brunswick, Canada
(University of New Brunswick, 2012) Way, Bryan Curtis; Lentz, David; Keighley, David
The Early-Silurian Woodstock Fe-Mn Deposits are a series of six, northeast-trending, low grade manganiferous-iron deposits in western New Brunswick that collectively represent the largest Mn resource in North America (194,000,000 tonnes; 13% Fe and 9% Mn). Recent expansion of Route 95 has allowed a more detailed local stratigraphy, mineralogy, and geochemistry of the Fe-Mn deposits within the context of the regional stratigraphy to ascertain the genesis of these deposits. Geological mapping during the field seasons of 2008 and 2009 has revealed six Lithofacies Associations (O, I, II, III, IV, V) within the area, that, generally, are lying conformably on top of each other. However complications due to folding and interbedding have resulting in juxtaposition of the lithofacies associations so they are not always in stratigraphic order. These lithofacies associations are composed of a turbidite-rich section of blue grey calcareous sandstone (O) overlain by black pyritic mudstone (I), associated mineralized and nonmineralized green (II) and red siltstone (III), and laminated to massive grey green calcareous sandstone (IV and V). Na/Mg ratios, chondrite-normalized REE patterns, and mineralogical evidence of rapid changes in ocean redox conditions suggest the Fe-Mn mineralized lithofacies were formed in the offshore zone of a continental shelf on a stable cratonic margin. Al-Fe-Mn ternary and SiO[subscript 2]/Al[subscript 2]O[subscript 3] binary plots developed from archived drill core data indicate the Fe-Mn mineralization was initially derived from hydrogenous-detrital sources without any indication of a hydrothermal input as a source of Fe and Mn.
Goldilocks and the three craters: Finding conditions that are just right for shock vein formation
(University of New Brunswick, 2023-08) Hopkins, Randy; Spray, John G.; Shaw, Cliff S.J.
Hypervelocity impacts on rocky planetary bodies generate many shock effects within the target rock on both microscopic and macroscopic scales. These features allow impact geologists to estimate the spatial shock pressures realized within the target rock during an impact event. Shock veins are unique among these features as both the pressure and temperature of their formation can be deciphered leading to a critical variable in understanding shock wave passage: time. Shock veins are typically thin (<2 mm wide) anastomosing veins that display textures ranging from glassy to a fine-grained crystalline matrix; indicative of melting followed by rapid cooling. Shock veins commonly contain locally derived clasts that are suspended within the once molten matrix. High-pressure/temperature polymorphs may be developed within shock vein systems crystallizing from the matrix or developing via solid-state transition within the suspended clasts or adjacent wall rock. Polymorphs within shock vein systems are key indicators of the pressure/temperature conditions realized by shock veins during their formation. This thesis focusses on obtaining a relationship between shock vein pressure-temperature-time (P-T-t) conditions and crater morphology for all three in situ terrestrial shock vein-bearing impact structures: Vredefort (South Africa), Steen River (Canada), and Manicouagan (Canada). The relationship is then explored further by calculating the P-T-t path of the shock vein-bearing paired lunar meteorites NWA 3163 et al. to estimate the crater size from which the meteorite originated on the lunar surface. A finite difference model has been developed (via MathWorks MATLAB) to calculate the P-T-t cooling paths of shock veins. The developed code simulates the passage of a shock wave through the target, while simultaneously forming and cooling the shock veins via 2-D steady-state conduction. The model was applied to all three in situ terrestrial shock vein systems. Calculated P-T-t results agree with petrologic observations of high-pressure/temperature polymorphs present within the studied shock vein systems. A relationship between the impact crater diameters and shock waves that formed them was then established. This relationship was applied to paired lunar meteorites NWA 3163 et al., and the origin crater diameter was determined to be approximately 216 km.
In situ multiphase LA-ICP-MS U-Pb Geochronology of terrestrial impact structures
(University of New Brunswick, 2020-08) McGregor, Maree; Spray, John G.; McFarlane, Christopher R. M.
In an attempt to improve the chronologic record of impact events on Earth, U-Pb geochronology has been conducted on shocked and thermally metamorphosed accessory phases (zircon, titanite and apatite) from several terrestrial impact structures using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). All dated phases occur as inherited grains derived from the underlying target lithologies and now occur within impact melt-bearing breccias and clast-laden melt rocks. This study provides the first application of the apatite U-Pb geochronometer from a terrestrial impact structure, and emphasizes the complexity of dating inherited grains within impact melt-bearing lithologies. Unlike newly-grown (igneous) grains within impact melt sheets, the results presented here highlight the challenges of obtaining precise and accurate impact ages from variably reset grains within complex lithologies. This approach requires an understanding of the relationship between isotopic resetting, extreme pressure-temperature (P-T) conditions and variable temperature-time (T-t) histories realized during impact events, impact-induced deformation microstructures, solid-state recrystallization, and pre-impact radiation damage within inherited grains. The results from this study have contributed to the chronological record of terrestrial impact events and the current understanding of U-Pb isotope systematics within U-bearing accessory phases during hypervelocity impact events. The use of a multiphase, in situ LA-ICP-MS U-Pb geochronological approach has permitted an inter-phase assessment on the comparative reliability of zircon, apatite and titanite as impact chronometers, while also providing insights into the U-Pb isotope systematics of these phases under extreme P-T-t conditions. The results reveal that isotopic resetting in apatite is thermally induced, inferred to be the result of apatite’s lower closure temperature and rapid Pb diffusivities. Consequently, apatite is determined to be more susceptible to isotopic resetting during short-lived temperature excursions compared to zircon and titanite. As such, this study demonstrates that, in the absence of coherent impact melt sheets and where structures remain tectonically undeformed, apatite is the most reliable U-Pb geochronometer for accurately dating terrestrial impact structures. Under the same P-T-t conditions, zircon and titanite are found to be less useful impact chronometers and may yield geologically unmeaningful ages. Similar to apatite, isotopic resetting in titanite is primarily thermally induced. However, due to numerous factors including its higher closure temperatures and slower Pb diffusivities, titanite is prone to incomplete isotopic resetting, and is considered a particularly complex U-Pb impact chronometer. Unlike apatite and titanite, isotopic resetting in zircon is deformation enhanced. In addition to recrystallization-driven Pb loss, the results presented here demonstrate that, for the first time, radiation damage within pre-impact zircons facilitates isotopic resetting. However, metamict zircons are found to be susceptible to recent Pb loss and common Pb contamination, with lower intercept ages typically yielding anomalously young impact ages that are consistantly unreliable. The application of multiphase in situ LA-ICP-MS U-Pb geochronology has provided the first higher precision age constraints for four terrestrial impact structures in Canada: Nicholson Lake (387 ± 5 Ma), Lac La Moinerie (453 ± 5 Ma), Steen River (141 ± 4 Ma) and Brent (452.8 ± 2.7 Ma). Excluding Nicholson Lake, all structures yield ages that overlap with biological extinction events, with Steen River forming at, or close to, the Jurassic-Cretaceous boundary, and both Lac La Moinerie and Brent forming at, or close to, the Sandian-Katian boundary in the Upper Ordovician.
Investigation of seepage near the interface between an embankment dam and concrete structure: monitoring and modelling of seasonal temperature trends
(University of New Brunswick, 2018) Yun, Tana; Butler, Karl; MacQuarrie, Kerry T.B.
The temperature monitoring method, which makes use of the fact that increased seepage flow may locally alter the natural temperature distributions within embankment dams and their foundations, is regarded as a useful approach for seepage monitoring and evaluation. In this study, spatial and temporal variations of temperature have been monitored and modelled at the interface between the compacted clay till core of an embankment dam and an adjoining concrete diversion sluiceway structure at the Mactaquac Generating Station, located on the Saint John River near Fredericton, NB. The measurements were acquired using a fibre optic distributed temperature sensing (DTS) system installed in a 50 m long borehole drilled into the concrete structure within 0.5 m of the interface. Two significant temperature anomalies were observed. A three-dimensional finite element model was developed to simulate the temperature distributions within the dam resulting from the seasonal variations of air and headpond water temperatures. Anomalous seepage zones near the interface were simulated in the concrete and along the dam/concrete interface (in the embankment) independently, and in both locations simultaneously. The results demonstrate that passive DTS monitoring is a feasible approach to identify potential seepage zones near an embankment dam/concrete structure interface. Anomalous temperature zones, and associated gradients, can be clearly identified and numerical modelling can indicate, in some cases, whether such anomalies are related to seepage in the concrete or in the embankment; however, other details such as the water flow path geometries and seepage rates are not as well constrained.
Investigation of the effects of in situ chemical oxidation on the electrical and diffusive transport properties of porous fractured rock.
(University of New Brunswick, 2012) Turner, Kathryn; Al, Tom
Two sets of diffusion-reaction experiments were conducted to: 1) to investigate the reaction mechanisms of the oxidation of naturally occurring reductants by permanganate during In-Situ Chemical Oxidation (ISCO) in porous fractured rock and 2) to study the effects ISCO has on the electrical and transport properties of the rock. The first set of experiments was carried out on black shale samples that were soaked in permanganate solution for up to 24 months. Results of SEM and (S)TEM image analysis suggest that permanganate can react with pyrite present in the rock in a two-step reaction process that is first transport limited, with permanganate diffusion and reaction with organic carbon and reduced mineral particles in pores to form MnOx(s), then electronically driven as permanganate oxidizes the mineral grains via solid state electron transfer through the MnOx(s) network in the pores. The second set of diffusion-reaction experiments was carried out on sandstone samples that were treated alternately with dextrose and permanganate with the goal of producing MnOx(s) inside pores of the matrix. The bulk resistivity values of the samples were monitored over the course of the treatment, and the porosity and pore diffusion coefficients of the treated sandstone samples measured. There was an overall decrease in resistivity and an increase in pore diffusion coefficients for treated sandstone samples compared to untreated samples. These observations are consistent with a decrease in tortuosity of the treated samples. Tortuosity factors Ꞇfd and Ꞇfe changed by factors of 2.1 to 2.6 times for samples treated with permanganate compared to untreated samples. The decrease in tortuosity could be the result of oxidation of small reduced particles such as organic carbon in the pore throats of the treated rock.
Isotopic constraints on timing of deformation and metamorphism in the Thor–Odin dome, Monashee Complex, southeastern British Columbia.
(University of New Brunswick, 2003) Kuiper, Yvette Dominique; Williams, Paul; Carr, Sharon
New and existing U–Pb and [superscript 40]Ar/[superscript 39]Ar geochronological data, and oxygen and hydrogen stable isotope data, are combined with structural and metamorphic data from Thor–Odin, the southern culmination of the Monashee Complex. This leads to a new interpretation of the timing of deformation and metamorphism. Amphibolites in Thor–Odin with hornblende [superscript 40]Ar/[superscript 39]Ar dates between ~75–70 and ~51 Ma experienced more [superscript 18]O- and D-depletion than amphibolites with older dates. The younger dates that were previously interpreted as cooling ages, may have resulted from complete or partial Ar loss in the presence of meteoric fluids that were introduced into the rock during extension. Monazite crystals in pelitic schist, quartzite and orthogneiss, which have U–Pb ages younger than [superscript 40]Ar/[superscript 39]Ar hornblende ages in amphibolite in northwest Thor–Odin, may have grown during extension in the presence of fluids. Titanite, xenotime and zircon dates may be interpreted in the same way. Thus, the U–Pb dates that were previously interpreted as representing peak of metamorphism and the hornblende [superscript 40]Ar/[superscript 39]Ar dates that were previously interpreted as representing cooling ages, may be interpreted as reflecting meteoric fluid penetration of the crust during regional extension. This implies that the age of the thermal peak of metamorphism is older than ~75–70 Ma. Migmatisation in a basement orthogneiss in Thor–Odin occurred at ~1.8 Ga. Dissolution rims are preserved in zircon between ~1.8 Ga domains and 52 Ma overgrowths. Because growth of new zircon (and possibly other U–Pb accessory phases) did not take place, any geological event that occurred during the ~1.8 Ga to 52 Ma time interval is not recorded. Cordilleran deformation and metamorphism may have taken place within that time interval, e.g. in the Middle Jurassic and/or mid- to Late Cretaceous, the time of Cordilleran deformation and metamorphism in the rocks overlying the Monashee Complex. The Joss Mountain orthogneiss, west of the Monashee Complex in the Selkirk Allochthon, is dated at 362 ± 13 Ma. F[subscript 3] folding in pelitic schist at Joss Mountain is constrained between ~73 and ~70 Ma. Existing structural, metamorphic and geochronological data in, and close to, the Shuswap Metamorphic Complex in the southern Canadian Cordillera are shown to be consistent with a channel flow model.

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