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.

URI
http://knowledgecommons.lakeheadu.ca/handle/2453/4277

The White Pine Fork Mo porphyry has an estimated resource of 16 Mt of Mo at 0.1% Mo.  The host intrusions are K-feldspar- and quartz-porphyritic monzo- to syeno-granites characterised by LREE enrichment, fractionated HREEs and negative Nb, Ta, Sr and Ti anomalies, consistent with a subarc mantle melt source.  The granites also have an adakitic geochemical signature.  A U-Pb age for zircon from a clast in the mineralized breccia pipe at White Pine yielded an age of 26.52±0.42 Ma, which falls within the error of the White Pine intrusion age of 26.61±0.24 Ma.  Re-Os ages for duplicate samples of the Mo-mineralised quartz breccia are 30.21±0.14 and 29.84±0.15 Ma, which correlate with the age of the Little Cottonwood stock rather than the host intrusion and may represent Re-Os inheritance.  In contrast, Buckingham Mo (-Cu) porphyry has an estimated resource of 1,000 Mt of Mo at 0.1% MO and is hosted in Cretaceous K-feldspar- and quartz-porphyritic granites.  Four feldspar- and quartz-porphyritic granites in the area were dated using LA-ICP-MS U-Pb of zircon and yielded ages of 38.68±0.53, 39.28±0.58, 40.76±0.41, and 40.81±0.51 Ma and therefore unrelated to the Buckingham deposit, and instead are correlated with Tertiary magmatism associated with Au skarns in the nearby Battle Mountain district.  The Tertiary intrusions are feldspar- and quartz porphyritic granites.  Primitive mantle-normalized geochemistry of both suites of intrusive rocks have LREE enrichment, fractionated HREE, negative Nb, Ta and Ti anomalies and a slight enrichment of Zr and Hf, consistent with a subarc mantle source for both suites.

The most prominent alteration in both systems is phyllic alteration comprising an assemblage of white micas, quartz and pyrite.  Potassic alteration was also observed at the White Pine Fork Mo breccia pipe and kaolinite and chlorite observed in SWIR data suggest advanced argillic alteration around the Buckingham system.  These petrographic observations are substantiated by the whole rock geochemistry.  The potassic, phyllic, and possible advanced argillic alteration were mapped out by the absolute values of trace elements.  The trace element geochemistry of quartz and pyrite can be used to fingerprint deposit types and as vectors toward mineralisation in alteration systems around ore deposits.  At White Pine Fork, the hydrothermal quartz is characterised by higher Ti and As than the igneous quartz.  The Li content of hydrothermal quartz is greater near the centre of the White Pine Fork deposit than in its margins.  At Buckingham, quartz in the breccia cement at the centre of the deposit shows the highest concentration of Al, Li, K, Ca, As, and Sb, and metals (i.e. Cu, Fe, Zn, and Pb), whereas the igneous and sedimentary quartz shows the highest Ti values.  The high values indicate that the primary Ti contents were not subjected to recalibration during hydrothermal alteration.  The Al and Sb contents of quartz decrease away from the centre of deposit at Buckingham.  This trend was not observed at White Pine Fork.

At White Pine Fork, pyrite occurs in a domain extending more than 1.5 km from the breccia pipe and is partially weathered to Fe-oxides and Fe-hydroxides.  LA-ICP-MS analyses showed Ni and Co compositional zoning within the pyrite grains.  The Ni content in the pyrite increases away from the centre of the White Pine Fork deposit.  At Buckingham, the pyrite was almost completely altered to Fe-oxides and Fe-hydroxides in most of the surface samples studied here.  The trace element concentrations of Au, Cu, and Cd in pyrite decreases away from the centre of the deposit.  Ni, Co and Pb zonations were also seen in the cores of the pyrite grains at Buckingham.  LA-ICP-MS element maps in most of the surface samples studied here showed that the pyrite at Buckingham is depleted in trace elements relative to the weathering rinds which are enriched in Au, Ag, Cu, As, Sb and Mo.  The increased Au concentration in the weathering rind suggests either an overprinting mineralised rind similar to the proximal skarns or Carlin-style sediment hosted Au.  The rind was then weathered during supergene alteration.  Another possibility is that the cores of the sulphides acted as traps for the precipitation of precious metals from the hydrothermal event associated with the proximal Eocene granite intrusions which were subsequently concentrated in the weathering rind during supergene alteration.

The comparison the White Pine Fork and Buckingham Mo porphyries has refined the processes associated with hydrothermal alteration around Mo porphyry deposits and the applicability of trace element chemistry of alteration minerals as exploration tools.

URI
http://knowledgecommons.lakeheadu.ca/handle/2453/4331

The Gunflint and Biwabik Formations comprise the middle units of the Paleoproterozoic Animikie Group that crop out near the northwestern shore of Lake Superior.  Stromatolitic units were investigated and sampled at 9 outcrop sites, 4 mine sites and in 12 drill-cores.  Controversy exists as to whether the stromatolitic units that are now composed of chert were deposited as a silica gel or represent carbonate replaced by chert.  There is also debate in the literature as to whether the iron oxides that coat many microfossils are primary or deposited during later diagenesis.  Younger examples of siliceous stromatolites are very rare and iron hydroxides coating bacteria are only known for limited modern environments.  Thus, understanding the primary composition of the Gunflint microbialites will provide information on ocean chemistry during this interval.

Three stromatolitic members have previously been described within these formations: the Lower Stromatolitic Member containing stromatolites that grow directly on the peneplained Archean basement or on the conglomerate which forms the base of the Animikie Group, a Middle Member 45 to 50 meters above the base, and the Stromatolitic Limestone Member at the top of the formation directly beneath the Sudbury impact layer.  Based on this work, a new Upper Stromatolitic Member 50 meters below the Limestone Member in the Gunflint Formation was recognized.  This member contains abundant iron-silica-carbonate-manganese oncolites, and is correlative to stromatolitic units described from the Biwabik.  The oncolites represent a primary-to-very early authigenic, precipitated mineral assemblage.  The accretion of lacustrine ferromanganese nodules at the sediment-water redox boundary provides a modern analogue for the development of the oncolites described in this work.

The presence of exceptionally well-preserved, hematite coated microfossils, encased in chert in the relatively unmetamorphosed Middle Stromatolitic Member together with positive cerium and europium anomalies indicates that these sediments were deposited at a redox boundary in ocean waters near saturation with respect to silica and iron.  Conversely, precipitates, containing carbonaceous filaments in the Lower Stromatolitic Member contain a distinct negative cerium anomaly, indicating deposition in an oxidized environment.

Alternating manganese- and iron-rich laminae within the Upper Stromatolitic Member indicate a fluctuating redoxcline and oxygen levels in the shallow subtidal to peritidal environments within the Animikie Basin.  The fluctuation reduces the Fe:Mn ratio, allowing for the less readily oxidized manganese to precipitate.  The presence of dehydration cracks which cross-cut original ooid and stromatolitic laminae indicate that deposition of the silica and iron most probably occurred as amorphous gels of opal-A and iron hydroxides.

This study strongly indicates the Gunflint and Biwabik stromatolites were originally siliceous and formed by a different precipitation mechanism than that of Proterozoic carbonate stromatolites or modern agglutinated forms.

URI
https://knowledgecommons.lakeheadu.ca/handle/2453/4126

The 1.878 Ga Gunflint and equivalent iron formations of the Animikie Basin were deposited during the period after the rise in atmospheric oxygen during the Great Oxidation Event, which began at approximately 2.4 Ga. The atmospheric composition, and especially oxygen content, during this period after the rise in atmospheric oxygen, is not well known. The Gunflint and correlative formations, having been deposited in a shallow-marine setting, might provide information on oxygen levels present in the atmosphere-ocean system at this time. This is further made possible as the rocks that make up these formations are excellent records of transgression and regression of the sea. This record is reflected in up-section changes in lithology of the rocks that make up these formations. Further, the strata show evidence of exposure indicative of maximum regression. This exposure would have allowed the sediments and rocks to interact chemically with the atmosphere and meteoric water at the time. 

Stromatolites developed in the near-shore deposits and the rocks upon which the stromatolites grew showevidence of exposure during the repeated relative sea level low stands. These rocks have an alteration pattern that depends on their lithology. The rocks that comprise the Archean crystalline basement below the Gunflint show an intense alteration pattern that includes the formation of large corestones as well as increases in Fe and Mn content. Their geochemistry is largely the result of alteration by basin derived fluids. The exposure surfaces in the grainstones that make up the Gunflint and equivalent formations exhibit cementation and brecciation of the grainstones directly beneath the stromatolites.

Geochemical analysis performed on these rocks targeted the concentration of redox sensitive oxides and elements; Fe₂O₃, MnO, V, Cr, Mo and U.  Also considered were the Ce and Eu anomalies present. These oxides and elements react differently in oxidizing vs. reducing fluids. Subsequently, this analysis showed a shift in the Ce anomaly throughout the stratigraphy. The change from negative Ce anomalies in the basal samples to the positive Ce anomalies in the middle and upper lowstand layers indicate a shifting redox boundary, where the lowest stromatolite layers had produced enough oxygen to balance the flux of Fe²⁺- rich seawater in a position away from them, whereas the middle and upper stromatolite areas had redox boundary at the surface of the stromatolite themselves. Enrichment in Cr and V, as well as depleted Eu anomalies in strata associated with lowstands, points to the mixing of oxic freshwater,  probably a combination of surface runoff from the craton and diffusion of groundwaters, and the anoxic seawaters filling the basin.

URI
http://knowledgecommons.lakeheadu.ca/handle/2453/758

The Sudbury Impact Layer (S.I.L.) is dated at 1850 Ma and is located between the underlying Gunflint Formation, with an age of 1878±1 Ma that was obtained from zircons in a tuffaceous zone approximately 105 meters below the S.I.L., and the overlying Rove Formation that has an U-Pb zircon age of 1832 Ma which was obtained from tuffs 5-6 meters above the S.I.L.  There is an 18 Ma hiatus between the Sudbury Impact Layer and from where the zircon was extracted from the overlying Rove Formation, and a 46 Ma hiatus between the Sudbury Impact Layer and the underlying Gunflint Formation.  These large age anomalies associated with the hiatuses, along with little sedimentation between the tuffs that supplied the ages, suggest that periods of non-deposition and sub-aerial exposure eroded the land, resulting in a lack of sedimentation in the allotted age gaps.

The time interval was investigated in a number of outcrops and cored drill-holes in the northern portion of the basin.  Sedimentological aspects of the rocks were noted and samples collected for geochemical studies.  The upper portion of the Gunflint Formation contains grainstones that were deposited in shallow water along with chemical sediments precipitated from Paleoproterozoic seawater.  Positive Ce anomalies indicated oxygen production by stromatolites in the inter-tidal to very shallow sub-tidal lead to some oxygenation of the shallow nearshore.  The chemical sediments in the limestone that overlies the Gunflint ankerite and chert had their calcite cement formed in meteoric phreatic conditions, with extremely elevated contents of vanadium and large negative cerium anomalies indicating these waters were significantly oxic.  The overlying Sudbury Impact Layer shares these characteristic, though in the southeast it was probably deposited in a very wet, likely marine, setting.   Ankeritic grainstones overlying the Sudbury Impact Layer refute the idea that the impact caused an end to iron formation deposition and show a transition from flooding and sub-tidal deposition to extensive sabkha development.  The common occurrence of gypsum is indicated by the presence of its pseudomorphs forming bladed crystals, desert roses and vein systems.  The Rove sea flooded over this surface after lithification.

URI
http://knowledgecommons.lakeheadu.ca/handle/2453/4252

Over the last few decades it has become increasingly difficult to discover new ore deposits and as existing deposits are exhausted, techniques for improving exploration success are becoming vital. In this study I investigated the application of trace element mineral geochemistry, in the context of well-defined petrology and field mapping, to the identification and characterization of hydrothermal alteration of a small porphyry Mo deposit located in southeastern B.C., Canada.  Detailed geochemical analysis of the MAX Mo-porphyry deposit was undertaken and the use of trace element geochemistry signatures of hydrothermal alteration minerals were established. Ninety-six samples were collected from surface, underground and drill core and graphic core logging was carried out on five holes. Whole rock geochemistry was obtained for all samples in order to observe any general alteration trends. The trace element concentrations of quartz, chlorite and epidote were analysed using laser ablation inductively coupled plasma mass spectrometry. Cathodoluminescence was used to show textural differences and growth zoning in quartz and to observe different generations of quartz. The results indicated that in hydrothermal quartz Ti, Al and Li showed systematic increases in concentration towards the porphyry center and could be used to infer the temperature of formation. The concentrations of Ti, Al, Li, Ge, Mg and Fe could be used to distinguish between different types of quartz. Hydrothermal quartz showed the most variance when it came to concentrations of individual trace elements, whereas regional metamorphic quartz that was unaffected by hydrothermal alteration had the lowest concentration of trace elements and a uniform trace element chemistry regardless of proximity to the deposit center. Igneous quartz was depleted in Ge relative to hydrothermal and metamorphic quartz.

For chlorite it was found that Ti, V and Sr concentrations varied depending on distance from the porphyry center. Both Ti and V decreased in concentration away from the deposit center, whereas Sr peaked around 350 - 400 meters and then decreased away from the deposit center. The trace element alteration vectors identified in this study combined with subtle, but identifiable, field criteria may assist exploration companies in the search for hidden deposits.

URI
http://knowledgecommons.lakeheadu.ca/handle/2453/4283

The Coldwell Complex is situated within the Archean Schreiber-White River metavolcanic and metasediment of the Superior Province. Spanning over 25km in diameter, it is the largest alkaline intrusion in North America. The 1108 ± 1 Ma age of the Coldwell Complex and its close spatial proximity supports a strong relationship to the magmatism of the Keweenawan Midcontinent Rift. Early studies define three magmatic centers of the Coldwell Complex, which in order of intrusion are Center I, Center II, and Center III. Center I consists of an oldest phase gabbro, which borders a ferroaugite syenite to the east and north. Center II includes a nepheline-bearing biotite-gabbro and several intrusions of nepheline syenite, and Center III is composed of four syenites which in order of intrusion are: magnesiohornblende syenite, contaminated ferroedenite syenite, ferroedenite syenite, and quartz syenite. This study evaluated the formation of the layered series nepheline syenite in Center II of the Coldwell Complex. Field mapping and sampling were completed along the shoreline of Neys Provincial Park, where extensive exposures of massive, hybrid, and layered syenite; together with xenolith-rich zones, biotite-gabbro, lamprophyre dykes and pegmatitic syenite of diverse composition are preserved. In the layered series, perthitic K-feldspar with secondary plagioclase forms the cumulus phase. Feldspar observed through cathodoluminescence (CL) imaging demonstrated multiple feldspar species within single crystals. K-feldspar ranged in orthoclase component from 87-100%, whereas plagioclase exsolution and alterations were characterized as albite, with anorthite components ranging from 0-3%. Amphibole (classified as ferro-pargasite) and minor apatite represent post-cumulus phases, forming interstitially to feldspar laths or in amphibole-rich laminae at the base of individual layers. Biotite, also a post-cumulus phase, was classified as the iron-rich end member annite. Fluorapatite is the most abundant accessory mineral, hosting light rare earth elements (LREE), along with less abundant britholite, wöhlerite, pyrochlore, titanite and other minor accessory minerals hosting incompatible elements. Layers commonly display modal grading from amphibole-dominant laminae, to a mixture of amphibole and feldspar, followed by a section of ‘normal syenite’ (dominantly feldspar with disseminated amphibole). Hydrodynamic processes are favoured for the origin of the layered series, specifically surge-type density currents and separation and reattachment vortex cells, are proposed to have formed the modally graded cumulate layers. In conjunction with graded layers, other magmatic “sedimentary” features including slumping, scour channels, flame structures, load casts, and various stages of hybridization and deformation of mafic xenoliths produced during hydrodynamic processes, indicate a strong convecting current operating during the formation of these rocks. The formation of the layered series was a product of fractional crystallization, varying deposition mechanisms, and reworking through erosion or deformational processes.

URI
http://knowledgecommons.lakeheadu.ca/handle/2453/4212

Texturally and geochemically, the MMD can be broadly divided into an Upper and Main Zones, with a subdivision of the Main Zone into an upper and lower sequence and a pegmatitic segregation subzone. The Upper Zone consists of ferrodiorite and likely represents the end product of extensive fractionation. The Main Zone is characterized by troctolite, augite troctolite, olivine gabbro, and gabbro with MgO, CaO, Al2O3, and Ni concentrations decreasing upwards and SiO2, TiO2, K2O, Na2O, P2O5, and incompatible trace element concentrations increasing, consistent with bottom-up fractional crystallization. Strong differentiation of the MMD magma is indicated by the habit change of clinopyroxene from ophitic (intercumulus) to granular (cumulus), which is the basis for the subdivision of the lower and upper sequences. The lower sequence of the Main Zone also hosts a 24 m thick interval containing 1 to 2 m wide gabbroic pegmatite layers. These pegmatites are interpreted to be the result of localized enrichment of magmatic volatiles.

The presence of an evolved core in the MMD surface expression, coupled with the mineral composition of olivine, plagioclase, and clinopyroxene, remaining at relatively constant Fo, An, and Mg# values, respectively, below the pegmatitic layers suggests that there was some degree of lateral crystal fractionation as well as bottom up fractionation. The well-defined fractionation sequence as well as an absence of abrupt geochemical changes suggests that the MMD fractionally crystallized from a single pulse.

Liberation of external sulphur from the surrounding Rove Formation, is suggested by the greater than mantle S/Se values as well as δ34S values between +4.0 and +21.0‰ of the sulphides within the CLG.  The addition of external sulphur evidently resulted in sulphur saturation during initial emplacement of the CLG magmas.  Primitive mantle normalized multi-element diagrams and trace element ratios provide supporting evidence for a localized shallow level of crustal contamination, as well as a deeper more widespread contamination component of both the CLG and MMD magmas.

The estimated parental magma compositions and average primitive mantle normalized trace element concentrations of the CLG and MMD suggest that they shared similar, if not the same, magma source. The CLG parental magma was slightly more evolved than the MMD suggesting that the magmas were sourced from a fractionating staging chamber. The estimated parental magma compositions of the CLG and MMD closely resemble those of the Layered Series intrusions of the Duluth Complex, supporting previous speculation that the CLG may be a satellite intrusion of the Duluth Complex. Despite current geochronology data to the contrary, the results of this study strongly suggest that the CLG and the MMD are petrogenetically linked, if not parts of the same intrusive system.

URI
http://knowledgecommons.lakeheadu.ca/handle/2453/4177