The Terrace Bay Batholith is a 25 km long oval shaped granitoid intrusion located in the western portion of the Schreiber-Hemlo greenstone belt, part of the larger Wawa-Abitibi terrane. The pluton was emplaced at 2689±1.1 Ma and intrudes circa 2720 Ma metavolcanic rocks of the Schreiber assemblage. The purpose of this study was to classify the Terrace Bay Batholith petrographically and geochemically in order to investigate the petrogenesis and tectonic setting in which the pluton formed, and to characterize the association with gold and base metal mineralization.

Detailed mapping of the pluton can separate the pluton into three mineralogically distinct lithologies:  granodiorite (typically consisting of medium to coarse quartz and feldspar phenocrysts with a groundmass of fine-grained amphibole, biotite,  disseminated magnetite, and sulphide minerals), a monzogranite (composed of medium-grained quartz and feldspar with increased amounts of potassium feldspar and amphibole relative to the granodiorite), and a diorite (composed of medium-grained amphibole and plagioclase with little to no quartz or potassium feldspar present). Two types of hydrothermal alteration are present in the pluton: a chlorite- epidote and a pervasive hematite alteration. These are present across the pluton, and always in proximity to cross-cutting regional scale faults or shears; however, no association was found between gold mineralization and regional structures.

Whole-rock geochemical analyses were undertaken on 147 samples from the Terrace Bay Batholith. Geochemically, the pluton is a homogenous calc-alkaline pluton, with minimal geochemical change between lithologies. The pluton exhibits trace element signatures that are characteristically arc-related signatures: fractionated heavy rare earth elements, negative high field strength element anomalies, enrichment of Th over light rare earth elements and enrichment of light rare earth elements. The fractionated heavy rare earth elements and the Th-Nb-La systematics are consistent with formation in a subduction zone at depths where garnet is stable. The Sr/Y and La/Yb signatures support formation within the garnet stability field and suggest small amount of slab-derived melt incorporated into the mantle wedge. The isotopic signature suggests that the pluton underwent minimal crustal contamination as shown by the depleted primitive mantle εNd values ranging from +2.16 to +2.49.

The emplacement of the pluton was determined to be through multiple injections in the intrusion from a single source. The pluton underwent prolonged fractional crystallization, creating subtle mineralogical lithologies with no geochemical differences. The homogeneous nature of the pluton suggests it is unlikely that there were numerous pulses because these would result in more variation across the pluton. 

Rhenium-Osmium isotope data were obtained on molybdenite to obtain an age of mineralization for the pluton, yielding a value of 2671±12 Ma. The molybdenum mineralization is spatially associated with gold mineralization in the pluton, suggesting that they were deposited from the same hydrothermal event. As is common in Archean cratons, this age of mineralization is syn- to post- both D2 and regional metamorphism, as well as postdating the emplacement of the pluton. The gold and molybdenum mineralization in the pluton is generally disseminated throughout with local occurrences hosted in quartz veins. Although these exhibit elevated gold and molybdenum values there is no distinct mineralization style characterized with gold deposits. These features can be explained by the magmatic vapor-dispersed system theory which suggests that when a pluton is emplaced at depth, the aqueous phase will remain dispersed throughout the pluton instead of concentrating in economic amounts.

URI
http://knowledgecommons.lakeheadu.ca/handle/2453/4542

The Mesoarchean Red Lake carbonate platform is the oldest (~2.93 Ga) known carbonate platform on Earth.  It is comprised of a variety of chemical sedimentary rocks including: limestone, dolostone, chert, oxide iron formation, and sulfide iron formation.  This study deals with its five different types of deeper water lithofacies, including four chemical sedimentary rocks and siliciclastic black slate, to delineate Mesoarchean ocean chemistry and comprehend the localized depositional settings.  Geochemical analysis of selected elements in the chemical sediments were used to constrain depositional processes.  Of these positive Eu anomalies in REE patterns suggests that the ocean was heavily influenced by hydrothermal activity and positive Ce anomalies in oxide iron formation indicate that a redoxcline existed in the depositional environment. Zirconium and hafnium in oxide facies iron formation were mostly derived from seawater, and their sorption was dependent on the rate of precipitation of iron hydroxide. Multiple sulfur isotope analyses revealed that mass-independent fractionation of sulfur was operating along with bacterial sulfate reduction, and the source of sulfur was diverse.  Organic carbon isotopes increase from ~ -27 ‰ to ~ -20 ‰ up-section towards the shallow portion of the carbonate shelf, possibly reflecting the presence of anoxic phototrophs in the shallows. Inorganic carbon isotopic ratios averaging ~ -1.5 ‰ fall within the range of Archean carbonate and reflect seawater values.  Also, δ18O data reveals that dolomitization occurred in a freshwater influenced environment. Evidence such as increasing Mn concentration towards the carbonate platform and positive Ce anomaly in oxide iron formation, as well as redox-sensitive element enrichment in the chemical sedimentary rocks, suggests that bacterial O2 production was somewhat active in the Mesoarchean sea. The interlayering of various types of chemical sediments at differing stratigraphic scales indicates that localized ocean chemistry changed repeatedly over both short and long time intervals.  Carbonates were perhaps formed in the slightly oxic shallow water environment, while magnetite and chert were precipitated in a suboxic environment distal to any venting fluids and iron sulfides accumulated in a reducing, anoxic environment during intervals of intense venting of hydrothermal fluids.  Shale was deposited as background sediment and accumulated during cessation of chemical sedimentation.  Finally,  the deeper water sediments repeatedly interlayered with the shallow water stromatolitic carbonate successions, which suggests multiple events of carbonate platform flooding.

URI

http://knowledgecommons.lakeheadu.ca/handle/2453/4351

Mackenzie River granites (MRG), are Archean deformed granites exposed in many locations alongside Highway 11/17 east of Thunder Bay. Microcline and plagioclase are the dominant minerals with quartz that slightly varies in proportion from one location to another. The samples that were examined petrographically are classified as ten granite samples, two granodiorite, one tonalite, and one quartz monzonite. Greenish chlorite was observed in most of the fractures in the study area. Two main populations of fracture strike were recorded in the study area. A NE-SW strike of fractures and faults was the major and dominant strike direction. This direction of strike agrees perfectly with one arm of the Midcontinent Rift (MCR). The second major population of structures strikes NW-SE with fewer fractures compared to the NE-SW strike of structures. The deformation history of MRG is documented by four main deformational features: penetrative brittle-ductile deformation, brittle deformation including a cataclasite-filled fault, chlorite-filled fractures, and quartz-filled fractures. Subgrains, serrated grain-boundaries, and undulose extinction are the main dislocation-creep features in quartz besides the bent and deformed twins of plagioclase and microcline. These dislocation-creep features were observed as evidence of penetrative brittle-ductile deformation at a depth of more than 15km for MRG at the time of deformation. Brittle deformation is indicted by the fractures in MRG and cataclasite-filled fault. Cataclasite-filled fault is identified by its 0.2-0.5mm crushed angular mineral pieces that have the same mineralogy as MRG. Chlorite-filled fractures are Archean, supported by the cross-cutting relations in the field. Quartz-filled fractures are younger than Gunflint Formation (GF) as they are present in (GF).

Heron Bay, Ontario comprises a predominantly calc-alkaline felsic to intermediate subduction-related arc setting of volcanic and plutonic rocks of mostly crystal tuff, tuff and granite. The rocks have undergone amphibolite facies metamorphism and are predominantly schists and gneisses. Trace element concentrations in pyrite, chlorite and epidote are variable. Highest values of Archean Au pathfinder elements, Au, Sb, W, Bi and As in pyrite are observed in pyrite associated with tourmaline in veins and disseminations. Highest concentrations of Au, Sb, W, Bi and As in chlorite and epidote are generally  associated with chlorite and epidote that occurs in veins rather than as major to minor constituents of rocks or as replacements. Trace element abundances in pyrite, chlorite and epidote are similar to Hemlo, the La Colosa Au-porphyry deposit and Gosowong, Toguraci and Penelope epithermal deposit pyrite, chlorite and epidote. Heron Bay chlorite is similar to metamorphic chlorite from Shebandowan and West Scotland and Heron Bay epidote is similar to metamorphic epidote from West Scotland.

No strong trace element trends towards the Heron Bay Au mine are apparent. The lack of strong vectoring trends may be attributed to metamorphic overprint, the small size of the Heron Bay Au system and variability in trace element concentrations among the differing occurrences of pyrite, chlorite and epidote.

Alto Ventures’ Miner Lake property is located 55 kilometers northeast of Beardmore, Ontario.  Historically, this property has been prospected for gold, which is Alto’s current target.  For this study two trenches, Trench 35 and the Musketeer trench, were investigated.  The outcrops were divided into five lithozones based upon the intensity of alteration, noticeable fabric, grain-size, strain observable within mineral grains, and strain observable within porphyroclasts. The rock within both trenches is ultramylonitic quartzofeldspathic schist originating from deformation and metamorphism of a plutonic tonalitic protolith.  Ductile deformation is largely homogenous throughout every lithozone, and brittle deformation is only observed within lithozones three, four, and five.  Brittle deformation becomes more pronounced with each increasing lithozone and provides an important route for hydrous fluids to enter the system.  Increasing amounts of fluid are correlated to increasing amounts of alteration minerals, such as chlorite and white micas, and are also correlated to increasing amounts of ductilely deformed quartz veins.  Areas of the trenches that display a higher abundance of deformed quartz veins have typically returned higher gold assay values, providing a possible control on the gold mineralization within the study area.

Therefore, it is suggested that rocks with greater abundances of alteration minerals and deformed quartz veins are better targets for gold mineralization.

The Mines Gaspé property hosts multiple Cu-Mo skarn and porphyry orebodies and is located adjacent to the town of Murdochville in the northeastern part of the Gaspé Peninsula, Québec. Both types of orebodies occur within the zoned Copper Brook and overlapping Porphyry Mountain alteration aureoles in calcareous Lower Devonian sedimentary rocks. The strata are intruded by numerous multiphase porphyry sills, dykes, and plugs of Devonian age. Underground and open pit mining at Mines Gaspé ceased in1999 after 141 Mt of 0.9% Cu-equivalent had been extracted from two open pits and eight underground mining areas within the Copper Mountain and Needle deposits. The Porphyry Mountain deposit is the most promising undeveloped resource on the property, containing 437 Mt of ore at 0.89% Cu-equivalent. The Porphyry Mountain intrusion and a sill in the Copper Mountain pit have been dated at 378.80 ± 0.57 Ma and 377.60 ± 0.62 Ma, which better constrains the timing of intrusions at Mines Gaspé than previous studies. Epidote UPb ages at Mines Gaspé overlap within error from 367–352 Ma. Epidote at Mines Gaspé is ~10 million years younger than the Porphyry Mountain intrusion. The time period between the Porphyry Mountain intrusion and epidote formation, as well as the range in epidote ages suggests that the Mines Gaspé system was active for a protracted period of time and more than one generation of epidote is likely, similar to the multiphase occurrence of intrusive units.

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses of epidote and chlorite from within and between the Copper Mountain and Porphyry Mountain deposits have identified major and trace element spatial variations in mineral chemistry. Epidote analyses show the highest values of Mg, U, Zr, Ti/Co, U/Co, Mg/Sb, and Mg/Zn proximal and As, Mn, Sr, Sr/U, As/U distal to the Porphyry Mountain deposit. Chlorite analyses show the highest values of Li, Ti, V, Ti/Co, Ti/Sb, V/Co, and Zn/Mg proximal and Mn, Zn, Zn/Li, and Zn/V distal to the Porphyry Mountain deposit.

Trace element concentrations in epidote and chlorite show a geochemical footprint surrounding the Porphyry Mountain deposit that allows for the use of mineral chemistry as a tool for vectoring towards porphyry-style mineralisation at Mines Gaspé.

The modern ocean is a complex system that is continually mixed by circulatory ocean currents that keep ocean water relatively homogeneous. This process means that both deep water and shallow water carbonates in today’s ocean have similar isotopic ratios of carbon, as they are direct chemical precipitates of sea water. This however is not true for Archean carbonates.

To explore this idea, deep water chemical sediments were collected from across the Archean Superior province from Red Lake, Schreiber, Beardmore, and Wawa. These samples were compared with shallow water chemical sediment. A total of 28 carbonate samples were gathered from the Uchi, Wabigoon, and Wawa sub-provinces and analyzed for their geochemical properties. The carbonate samples were processed via partial dissolution so as to only dissolve the chemical precipitate, thus assessing the water from which they formed. The samples went through ICP-MS and ICP-AES analysis and through carbon and oxygen isotope analysis in order to better understand their chemistry.

When comparing the REE geochemistry of deep vs shallow water chemical precipitate it was found that Schreiber, Beardmore, and Wawa localities were chemically distinct. These locations all showed a more positive Eu anomaly in deep water. Deep water Schreiber and Wawa had lower Y/Ho ratios than their shallow water counterparts. Heightened Eu values are indicative of greater hydrothermal leaching of basaltic oceanic crust. Lower Y/Ho ratios are due to more hydrothermally sourced Y/Ho ratios with more chondritic values of ~26. Additionally, Schreiber and Beardmore locations showed a greater degree of LREE depletion and heightened HREE enrichment. Red Lake samples however show that both deep and shallow samples had very similar positive Eu anomalies, and super chondritic Y/Ho ratios with some fluctuation.

δ 18O‰ analysis and comparison of deep water samples to shallow water samples found that in Schreiber, Red Lake, and Wawa there was no variation with depth. This proved that δ 18O‰ was unaffected by depth in the water column. δ 13C‰ analysis showed that in Schreiber and Wawa deep water carbonate there is more δ 13C‰ depletion than in shallow water carbonate. The δ 13C‰ of the Red Lake samples did not vary with depth.

Throughout this study the Red Lake samples have been an outlier, with no evidence of stratification, whereas the three other locations did have evidence of Archean ocean stratification. The hydrodynamic system at the Red Lake site may have been governed more by upwelling of deeper water onto the shallow shelf than at the other sites. Due to this unique scenario, it is fair to conclude that the Red Lake locality does not accurately represent typical shallow water in the Archean ocean. This leaves the conclusion that, for the cases of Schreiber, Beardmore, and Wawa, the formative water that precipitated carbonate minerals in these locations varied from depths below storm wave base to the shallow shelf. This is compatible with a greater hydrothermal influence in deep water than in shallow, and more negative δ 13C‰ values in deeper water, suggesting Archean ocean stratification with respect to REE and δ 13C‰.

The Revell Batholith is located in the Western Wabigoon subprovince, near Ignace, Ontario. The batholith was emplaced at 2737 Ma and intrudes the Bending Lake greenstone belt. The purpose of this study was to mineralogically and geochemically classify the Revell North granitoid rocks and provide insight into the petrogenesis of the Revell Batholith.

The Revell North granitoid rocks were identified as three mineralogically distinct lithologies: 1) quartz-rich granitoid (that typically consists of a higher quartz content than the rest of the samples with a groundmass of fine-grained plagioclase feldspar, potassium feldspar and quartz); 2) granodiorite (composed of medium-grained quartz and feldspar phenocrysts with a groundmass of medium-fine grained quartz and plagioclase with minor sericite alteration); 3) monzogranite (consisting of medium-fine grained quartz making up the matrix with medium-fine grained plagioclase with a higher modal abundance of potassium feldspar). Three types of alteration are present in the Revell North: chlorite, epidote and sericite. Both chlorite and epidote alteration are minor, however, sericite alteration is present throughout the Revell North.

The Revell North granitoid rocks display a homogeneous calc-alkaline signature, showing minimal geochemical changes between lithologies. The Revell North is a calc-alkaline granite that is classified as an I-type granitoid with slight S-type characteristics. The Revell North granitoid rocks are considered to be pre-tectonic as the ages that are associated with the Revell are contemporaneous with volcanism in the Western Wabigoon Subprovince, and elsewhere for granitoid rocks of the Superior province. The emplacement of the Revell Batholith is suggested to be via multiple injections from a single magmatic source. The Revell North granitoids underwent fractional crystallization, creating some subtle mineralogical lithologies with little to no geochemical differences.