Abstract to follow.
The Pemberton Hills study site is situated in northern Vancouver Island, British Columbia, and forms part of a northwest trending belt of porphyry deposits and prospects within the Wrangellia Terrane. The study site is underlain by late Triassic to middle Jurassic Bonanza Group volcanic rocks, with porphyry-related alteration and mineralization thought to be related to the emplacement of the Jurassic Island Plutonic Suite (181 – 141 Ma).
Whole-rock geochemistry, high precision geochronology combined with trace element and Hf isotope analysis of zircons from various intrusive units has led to an improved understanding of the magmatic evolution of plutonic rocks at Pemberton Hills. The oldest unit is a granodiorite dated at 172.34 ± 0.11 Ma. Following this is a quartz diorite with an age of 172.01 ± 0.17 Ma, which overlaps with a tonalite dyke sample dated at 171.77 ± 0.13 Ma. A second quartz diorite sample yielded the youngest reported age at 171.44 ± 0.25 Ma. These results imply that felsic and intermediate plutonism were broadly synchronous at Pemberton Hills.
Zircon trace element geochemistry reveals contrasting conditions in the felsic and intermediate plutonic magmas, despite broadly similar emplacement ages. The granodiorite and tonalite dyke samples are characterized by higher, overlapping Eu/Eu* (~0.2-0.3) and lower, overlapping Dy/Yb (~0.15-0.2) ratios, whereas the quartz diorite samples show low and increasing Eu/Eu* ratios (~0.1-0.17) as well as high and decreasing Dy/Yb ratios (0.25-0.45) over time. These results suggest that conditions remained stable throughout the emplacement history of the felsic plutonic magmas, but varied during the emplacement of the intermediate magmas. Zircon Hf isotope compositions of the granodiorite (+11.4), tonalite dyke (+11.2), and one of the quartz diorite samples (+9.5) suggest these rocks were derived from a juvenile mantle source that experienced minimal crustal contamination. Together, zircon chemistry and Hf isotope compositions suggest that the granodiorite and tonalite dyke magmas were the most fertile, meaning that felsic plutonic rocks have the most potential to be associated with a larger and more mineralized porphyry system at Pemberton Hills.
Field mapping combined with detailed petrography have shown propylitic alteration assemblages to be present throughout most of the porphyry environment at Pemberton Hills. Laser ablation inductively coupled mass spectrometry (LA-ICP-MS) analyses of epidote, chlorite, and pyrite have identified that major and trace element variations in these minerals vary systematically across the study site, and can be used to discriminate multiple porphyry-related alteration events at Pemberton Hills more effectively than whole-rock geochemistry.
Distal pathfinder elements displayed the most variation in epidote. Elements such as As and Sb in epidote were highest in a cluster of samples from the center of study site to the northeast of the lithocap. A small group of samples proximal to the southwestern margin of the quartz diorite pluton also displayed high As in epidote. Chlorite displayed clear systematic spatial distribution patterns, illustrated by increasing Ca and Sr concentrations in chlorite from samples moving towards the east from the southeast margin of the quartz diorite pluton. Fertility assessment plots of Sb vs. As in epidote and Zn vs. Mn in chlorite were used to discriminate spatially distinct groups of samples interpreted to relate to discrete porphyry alteration events at Pemberton Hills.
Pyrite mineral chemistry combined with pyrite element maps illustrate a complex paragenetic history at Pemberton Hills. Pyrite in samples located around the southeastern margin of the quartz diorite pluton are enriched in elements such as Au, As, Sb, Te, and Ag, whereas pyrite from samples overprinted by phyllic alteration assemblages are enriched in Mn, V, and Zn, consistent with abundant silicate micro-inclusions in these pyrites. Pyrite in samples located along the surficial margin of the lithocap are enriched in Re, likely reflecting the overprinting of fluids derived from the lithocap.
Trace element mineral chemistry of epidote, chlorite, and pyrite have proven to be effective at vectoring towards potential porphyry targets in an area with limited geologic context, and as a useful method to discriminate samples from different porphyry alteration events. The results of this study demonstrate the application of mineral chemistry as a tool for exploration in greenfield porphyry environments.
The Guichon Creek Batholith (GCB) is a Late Triassic calc-alkaline intrusive complex approximately 60km x 35km in size and located approximately 54km southwest of Kamloops, British Columbia, Canada. The Guichon Creek Batholith forms part of the Quesnel Terrane, comprised of stacked volcanic-arc assemblages and associated sedimentary units, which in addition to the Stikine and Cache Creek terranes, comprise the Intermontane Belt of central British Columbia. The Guichon Creek Batholith intrudes the western volcanic belt of the Upper Triassic Nicola Group and is partially overlain by volcanic and sedimentary rocks belonging to the Kamloops Group and are of Jurassic age and younger.
The Guichon Creek Batholith is host to the Highland Valley Cu-Mo porphyry system comprised of at least five known significant porphyry centers (Valley, Lornex, Highmont, Bethlehem and J.A.). It is one of two mineralized calc-alkaline batholiths that form a Late Triassic belt parallel to younger mineralized, alkaline and calc-alkaline belts to the east. Most of this belt is buried under a thin veneer of Jurassic and younger cover. Understanding the petrogenesis and composition of the Guichon Creek Batholith is important in developing exploration strategies to locate similar buried porphyry deposits along this belt.
The Guichon Creek Batholith consists of six concentrically zoned intrusive facies ranging from diorite in the core to granodiorite in the margin. Field relationships indicate that the facies young towards the centre of the batholith although observable contacts are rare in outcrop. The six intrusive facies are from the margin inward: 1) Border facies; Highland Valley facies [subdivided into the 2) Guichon sub-facies; and 3) Chataway sub-facies]; 4) Bethlehem facies; 5) Skeena facies; and 6) Bethsaida facies.
The marginal Border facies is the most heterogeneous facies and contains numerous autoliths near the contact between Guichon Creek Batholith and the host Nicola Group basalts which are brecciated and intruded by the Border facies. Rocks belonging to the Border facies are olivine-bearing leuco-gabbros to diorites with equigranular, phaneritic textures.
The Highland Valley facies is comprised of the Guichon and Chataway sub-facies. The composition of both sub-facies is similar, varying from quartz monzodiorite to granodiorite compositions and the Guichon sub-facies is most prominent to the northeast of the batholith whereas the Chataway sub-facies is most prominent to the southeast. The key difference between both sub-facies is the presence of conspicuous pink K-feldspar in the Guichon sub-facies and white K-feldspar in the Chataway sub-facies. Optically continuous, interstitial, sub-ophitic amphibole, K-feldspar and quartz are characteristic of all rocks belonging to the Highland Valley facies.
The three youngest facies are all similar in composition (granodiorite) and show a progressive increase in quartz and K-feldspar, decrease in total mafic minerals (with an increase in biotite relative to hornblende) and nearly constant plagioclase contents progressing from the Bethlehem facies to the Bethsaida facies. The Bethlehem facies is characterized by ophitic amphibole phenocrysts that poikilitically enclose smaller plagioclase chadacrysts, whereas the Bethsaida facies is characterized by biotite and amoeboid quartz phenocrysts. The Skeena facies is texturally and compositionally intermediate to the Bethlehem and Bethsaida facies, lacking both amphibole and biotite phenocrysts but containing finer-grained amoeboid quartz phenocrysts than those present in the Bethsaida facies.
Weak chlorite-epidote-sericite alteration is ubiquitous across the batholith, and even least altered samples typically contain biotite and amphibole crystals that have been affected by <5 to 60% alteration to chlorite and epidote and plagioclase that has been weakly to moderately sericitized. Alteration is most prominent in samples of the Bethsaida facies, particularly those closest to the mineralized porphyry centers.
The Guichon Creek Batholith is a magnesian, calcic to calc-alkalic (MALI = -5 to 7.3) and metaluminous to weakly peraluminous (ASI = 0.77 to 1.28; AI = 0.02 to 0.13) batholith. Major and trace element geochemistry are consistent with fractional crystallization of the predominant minerals observed petrographically and plots of Zr vs. molar Al/Ti and Al2O3 vs. TiO2 are effective at discriminating between the Border, Highland Valley and Bethlehem-Skeena-Bethsaida facies.
The petrographic and geochemical characteristics of the Guichon Creek Batholith in addition to cross-cutting relationships between facies and recent U-Pb ages suggest that the batholith was emplaced as at least two, but possibly three different magma pulses.
High Sr/Y, low La/Yb, fractionated LREE and HREE relative to MREE and concave primitive-mantle-normalized multi-element diagrams indicate fractional crystallization of hornblende and clinopyroxene in a deep crustal magma reservoir. These geochemical signatures also preclude a significant role for garnet in magma genesis, either as a restite phase left behind by adakite melts of eclogite-facies subducted slabs or by assimilation and contamination by garnetiferous metamorphic rocks in the deep crust. This is consistent with Sm-Nd systematics (∈Nd(T) = +6.7 to +7.5) which are consistent with <2% contamination of primitive mantle melts by partial melts of subducted sediment, although 87Sr/86Sri values of 0.703367 to 0.703493 suggest minor contamination of the Border and Guichon facies by radiogenic Sr derived from Nicola Group limestones or contaminated Nicola Group basalts.
Plots of Sr/Y, Al2O3 and V/Sc vs. SiO2 suggest that the parent magmas for the Guichon Creek Batholith were hydrous and oxidized, two criteria key for the production of porphyry deposits. Amphibole chemistry indicates temperature, pressure and ƒO2 conditions of crystallization were 712 ± 23.5 to 846 ± 23.5°C, 2.5 ± 0.3 to 0.9 ± 0.1 kbar (equivalent to 7.4 to 2.6km depth) and ΔNNO = 0.03 to 1.81, respectively. Pressure estimates are consistent with gentle tilting to the northeast, and imply that the Valley deposit may have formed at pressures where a single-phase supercritical fluid would have been stable, possibly leading to mineralization styles and an alteration footprint that are atypical of porphyry environments.
The Rainy River gold mine is located in northwestern Ontario and has been operating since 2015. The deposit has three major high-strain zones striking NW to SE across the main ore zones. Thin sections taken from sampling transects across each zone provide evidence that these high strain zones are ductile shear zones. Microstructural evidence including strong preferred mineral orientation, folded quartz veins and grainsize reduction indicate dislocation creep as the ductile deformation mechanism in these zones. These shear zones also seem to influence the shape of each mapped ore zone, seeming to bound each ore zone and separating them from each other. It is likely that these major structures are responsible for the multiple ore zones and the shape of each ore body being mined today.
New roadside outcrops along the Trans-Canada Highway 11/17 near Pass Lake, ON, expose the basal unconformity between Archean basement rock and the Proterozoic Gunflint Formation. Shear fractures, joints, and the Blende Lake fault damage zone seen in these two outcrops record the brittle deformation history of the area before and after the Gunflint Formation was deposited. The unconformity represents a temporal gap in the stratigraphic sequence of at least 800 million years. The Archean rock belongs to the Wawa subprovince of the Superior province, in close proximity to the Wawa-Quetico subprovince boundary. Structural measurements, stereographic projections, and qualitative observations have allowed deeper insight and analysis of how structural controls have changed over an approximately 2.7 billion year-old geological history. The Archean basement unit underneath the unconformity is a coarse-grained amphibolite that contains accessory epidote and biotite, and is homogeneous throughout the length of both high-standing outcrops. This is interpreted to be a mafic pluton that has undergone amphibolite-facies metamorphism. The amphibolite records a scatter in orientation of joints and shear fractures, but some trends align well with data from Mackenzie River granite plutons, including an overall east-northeast and west-southwest strike. Later Proterozoic features, including the Blende Lake fault, have a common strike of east-northeast, which aligns with the orientation of the 1.1 Ga Mid-Continent Rift in Thunder Bay. This similarity is further reflected by the Blende Lake fault being oriented subparallel to silver veins related to the Mid-Continent Rift. Similarities between orientations of brittle structures in the amphibolite and Gunflint Formation suggest that the Mid-Continent Rift in Thunder Bay may have reactivated some Archean-aged orogenic-related faults and shear fractures. Minor folding in the Gunflint Formation truncated by the Blende Lake fault, as well as reverse reactivation along the plane, may be evidence of compression during the later stage of the Mid-Continent Rift.
Differences between deeper water and shallow water iron-formation (IF) deposited during the Archean are poorly understood. Sedimentology, bulk rock geochemistry combined with laser ablation geochemistry, X-ray fluorescence false-colour mapping and 34S isotopes were utilized to compare a variety of IFs deposited at different water depths. These are the deeper water Morley sulfides, Deloro, Temagami, and Soudan IFs; the intermediate depth IF at Red Lake; and the shallow water Lake St. Joseph and Beardmore IFs. The Morley sulfides are massive to laminated sulfides associated with hydrothermal venting deposited at depth. The Deloro IF contains both oxide-facies IF (OIF) and sulfide-facies IF (SIF) and was deposited within a deeper water volcanic assemblage. The Temagami IF is entirely OIF sitting atop volcanics and banded chert with overlying siliciclastic rock. The Soudan IF is located within the Ely greenstone containing both volcanics and siliciclastics. The intermediate depth IF at Red Lake was deposited on the basinward slope of the oldest known carbonate platform on Earth. The shallow water IFs at Lake St. Joseph and Beardmore were deposited within deltaic successions, associated with the distributary channel mouth bars and proximal prodeltas.
The Morley massive and laminated sulfides have the same REE(PAAS) patterns as overlying mudstones, indicating that REE signatures within these sulfides are derived from what was scavenged on clay minerals. Small negative Y anomalies are present in the sulfides and mudstones, with the resulting Y/Ho ratios almost exclusively subchondritic (<28). 34S isotopes of the Morley and nearby sulfide deposits show heavier 34S values in laminated and mudstone associated sulfides compared with the lighter, hydrothermal-magmatic range of 34S within the massive sulfides, indicative of inorganic sulfate reduction deep in the Archean ocean.
The deeper water IF of the Deloro, Temagami, and Soudan are similar geochemically but vary greatly in jasper content and magnetite layer thickness. REE(PAAS) patterns are HREE enriched, containing large Eu and Y anomalies in each IF, with Y/Ho ratios from 28 to 55. Enrichments in V and low Th/U ratios are present in each deeper water IF, indicating scavenging of V and U from at least somewhat oxidizing sub-aerial weathering conditions and adsorption of these elements onto the iron-hydroxides in the deep ocean. P/Fe ratios range from 0.001 to 0.006, overlapping with shallow water IF but greater than the Morley sulfides by up to a factor of 30. Magnetite within these deeper water IFs appears to contain trace amounts of Ti (<0.1% TiO2) within its structure, which was most likely supplied by detrital material. δ34S values within the Deloro SIF are very light, suggesting biologic reduction of sulfate rather than a reduced hydrothermal source of the sulfur. However, SIF at Temagami shows 34S values similar to the Morley massive and laminated sulfides, indicating a dominantly hydrothermal source of S.
The IF present at Red Lake was deposited at intermediate depths of a few hundred meters yet resembles deeper water IF with HREE enriched REE(PAAS) patterns and similar ranges for Y anomalies. However, Eu anomalies are smaller by up to a factor of 2 and there are some samples with larger Y/Ho ratios (up to 75) than the highest deeper water values. V and Cr appear enriched within the Red Lake IF and Th/U ratios are lower than in both deep and shallow IFs. P/Fe ratios are generally much lower than the deep and shallow water IF, owing to P sequestration from the water into organisms on the carbonate platform.
The Beardmore and Lake St. Joseph IFs show flat REE(PAAS) patterns with very small Eu and few Y anomalies, due to significant amounts of siliciclastic contamination. Y/Ho ratios are near chondritic due to this as well. Laser ablation REE(PAAS) show Beardmore to have a HREE enriched signatures with small Eu anomalies. P/Fe ratios are comparable to deeper water.
The major difference between deep and shallow IF is chert content, which is much greater in deeper water IF. REE(PAAS) patterns are similarly HREE enriched at all depths but this is masked by siliciclastic contamination in the shallow water IF. Eu anomalies decrease from deep to shallow water, while Y/Ho ratios appear highest in intermediate depths. Redox elements such as V, Cr, and U appear enriched in deep and intermediate IFs, rather than in shallow IFs.
Acid mine drainage (AMD) is one of the greatest challenges facing the mining industry globally. Methods for addressing this issue have been widely studied; however, few studies have addressed sites with a less common water quality problem resulting from AMD: neutral pH, metal-poor, and sulphate-rich water. The Steep Rock Iron Mine site in Atikokan, Ontario is utilized as a case study where AMD-affected waters have acidity neutralized by carbonate rocks, and metals precipitate out of solution as the pH rises. This process alleviates major environmental hazards associated with acidic waters and toxic metal concentrations; however, sulphate is not removed and presents toxic conditions for aquatic fauna. These sites are also a risk to human health, and can potentially contaminate drinking water supplies. Funding for the remediation of abandoned mine sites is limited, and innovative solutions utilizing passive treatment mechanisms are needed in order to deliver efficient and effective remediation. The goals of this project were: 1) to assess the capability of a permeable reactive barrier (PRB) system to remediate sulphate-rich, pH neutral, metal-poor water, 2) to assess nutrient balance within the system to ensure the availability of nutrients is not a rate-limiting factor for sulphate reduction, and 3) to improve reactive substrate selection procedures by determining which assessment tools are most useful in selecting substrates effective at stimulating sulphate reducing bacteria (SRB).
Candidate reactive substrates including cow, horse, poultry, rabbit, and sheep manures, as well as leaf compost and hay, were assessed according to their concentrations of vital nutrients for SRB, including carbon, nitrogen, and phosphorous. Additionally, their relative degradability was tested via a procedure known as easily available substances (EAS). This testing determined how readily a given substrate could be broken down by bacteria, as well as the change in concentration of desired nutrients in the substrate before and after EAS testing, which gives an indication as to the availability of those specific nutrients. Plant and manure substrates were tested, with one of each type used in each reactive mixture. Based on this testing, poultry and sheep manures were selected as the most likely manure substrates to provide effective nutrition for SRB. In contrast, there was no significant difference found between hay and leaf compost. Poultry consistently performed the best in each test, with a C:N ratio of 11, a C:N:P ratio of 1772:160:1, and an EAS mass loss of 71%.
Eight flow-through reactors were constructed and operated for a period of 23 weeks. Six of these reactors contained organic materials to stimulate SRB, while two were controls. Of the six reactors using organic materials, three mixtures were used, each containing a different combination of the four substrates. One control reactor assessed the impact of zero-valent iron which was also added to all of the organic reactors, while an additional control simulated the natural environment and contained only creek sediment and silica sand. Reactors 3 and 7 were the most effective at sustaining high rates of sulphate removal, with >80% sulphate removal maintained for the first 14 weeks. These reactors utilized a mixture of poultry manure and hay, validating the measures which indicated poultry manure as the most effective manure-based substrate. However, poultry manure was also used in reactors 1 and 5 in combination with leaf compost, and were not as effective for sulphate removal. These results indicate that hay was a more effective substrate than leaf compost. Comparing this finding against the original substrate testing presents two differences between hay and leaf compost; the C:N:P ratio and the availability of phosphorus in EAS testing both had stronger results for hay. This result indicates that phosphorus is a critical nutrient for SRB, and that tests considering phosphorus should be an integral part of reactive substrate selection procedures in systems attempting to stimulate SRB. The control reactors found that the addition of only zero valent iron did not have a significant impact on sulphate removal, as performance in this reactor was similar to the natural aquifer conditions control reactor. Eh/pH conditions supported the activity of SRB; but did not support the stability of sulphide produced by SRB, and it is unclear of SRB were in fact active within the flow-through reactors.
Significantly reduced sulphate concentrations in reactor effluent initially appeared to indicate the sulphate reduction was occurred as intended. However, in post-experiment analysis there was no evidence of iron sulphide formation that would confirm sulphide production by SRB, and Eh/pH conditions were not supportive of sulphide stability. Furthermore, saturation index calculations using PHREEQC determined that iron sulphides were highly under saturated in effluent waters. In contrast, sulphate minerals including barite, gypsum, and jarosite were slightly oversaturated, and present a viable sink for the sulphate removed from solution. Following experiment completion it was found that the reactors with the greatest sulphate removal also had the most significant declines in nutrient concentration, with 52-64% C, 45-58% N, and 24-62% P losses in reactors 3 and 7. This is strong evidence of a bacterially driven process for sulphate mineral precipitation. The reduced availability of these nutrients may have played a role in the decline of sulphate removal over time.