A section of the Quetico Gneiss Belt north of Thunder Bay, referred to as The Keelor Lake Area, was investigated to ascertain whether there was a relationship between metamorphism and the magnetic expression by the rocks of the area.

Three rock units were distinguished:  1) pelitic schists,  2) basic amphibole bearing schists and  3) quartzofeldspathic rocks.  Petrographic studies revealed the presence of upper amphibolite to granulite facies rocks in the central portion of the Quetico belt bounded both to the North and South by amphibolite facies rocks.  Chemical analysis of the pelitic rocks revealed that their chemical composition was very homogeneous thus providing evidence that the appearance of certain minerals was not due to a change in chemical composition.  Cordierite, garnet and sillimanite assemblages predominate near the centre of the Quetico Gneiss Belt.  Since the chemical composition consistently is the same, the appearance of higher grade mineral assemblages is suggested to be a result of their deeper crustal origin.  The highest grade rocks of the central portion of the Keelor Lake Area are in close proximity to the area which exhibits highest magnetic values.

The Winston Lake mine is located 145 km northeast of Thunder Bay, Ontario, in the Archean Superior Province.  Although the orebody is classified as a typical volcanogenic massive sulfide deposit, it differs in the fact that it was intruded by a large gabbro sill prior to regional metamorphism.  Presumably, the orebody experienced high T, low P contact metamorphism.  Based on the alteration assemblage of anthophyllite-cordierite-sillimanite-staurolite, the regional metamorphism that followed reached the sillimanite zone of the amphibolite facies.  The silicate assemblages suggest a temperature range for metamorphism of approximately 610-640°C and pressures of 2.2 to 5 kbars, assuming that P(H₂O) = P(Total) and that cordierite contains magnesium.

Sphalerite in 38 samples from seven drill-holes through the Winston Lake orebody and the adjacent Pick Lake zone was analyzed on a scanning electron microscope.  The samples are separated into three occurrences:  sphalerite-pyrrhotite-pyrite equilibrium assemblages, sphalerite-pyrrhotite contacts, and sphalerite encapsulated in pyrite.  The compositions of sphalerite from the triple junctions and sphalerite-pyrrhotite contacts are similar, yielding 11.04 ± 0.67 (P = 8.82) and 11.54 ± 0.87 mole % FeS.  Sphalerite enclosed in pyrite fell into three compositional ranges:  5 - 6 mole % FeS indicating sphalerite-pyrite equilibrium, approximately 11 mole % FeS indicating sphalerite-pyrrhotite-pyrite equilibrium, and a single sample yielding 15.2 mole % FeS (P = 4.36 kb).

Sphalerite compositions indicate that any effects of contact metamorphism has been obscured by regional metamorphism.  The relative lack of monoclinic pyrrhotite formation indicates that retrograde alteration is not responsible for the high calculated pressures obtained from the majority of the sphalerite compositions.  It is suggested that equilibrium of sulfides at peak pressure of metamorphism may have been attained before peak temperatures as represented by the silicate assemblages and thus account for the discrepancy in pressure between the sphalerite geobarometer and the silicates.

Bol©o is a 525 Mt sediment-hosted, stratiform Cu-Co-Zn district located along the eastern side of the Baja California Peninsula.  Mineralization consists of low-grade (0.71% Cu, 0.06% Co, and 0.71% Zn) sulfides and oxides disseminated through a series of laterally extensive conformable horizons of laminated and brecciated claystone.  Formation of such extensive mineralization implies a source(s) that is either highly enriched in metals or is volumetrically significant, or both.  Possible metal sources for the Bol©o district and mechanisms for their extraction include: i) low to high temperature leaching of arc volcanic and basement plutonic rocks; and, ii) leaching of red-bed conglomerate by low temperature fluids.

Mass balance calculations were carried out in order to evaluate leaching of arc to early rift volcanic rocks, plutonic basement rocks and intraformational conglomerate.  The calculated maximum metal yield from the conglomerate relative to the total metal budget of the entire Bol©o district is 14.3% for Cu, 81.3% for Co and 32.6% for Zn.  Mass balance determinations indicate that up to 8.6% of the Cu, 4.1% of the Co and 16.6% of the Zn in the total metal budget could be produced from leaching arc andesite.  Lead isotope compositions indicate leaching of the basement plutonic complex, but this source would have yielded only 23.2% of the Cu, 9.3% of the Co and 20.8% of the Zn in the Bol©o district metal budget.  Additional metal enrichment of the hydrothermal fluid is postulated to occur by the admixture of magmatic volatiles.  A magmatic component is inferred from: i) the inability of leaching to account for the total metal budget; ii) the spatial and temporal proximity of rift-related high-K andesite magmatism that is approximately coeval with the timing of sedimentation of ore mineralization; and, have the appropriately high 'O2 conditions of the high-K andesite melts required to transport large quantities of metals.
 
For more details about this thesis contact Dr. Andrew Conly

The Mattabi Mine, a volcanogenic massive sulfide deposit located 60 km north of Ignace, Ontario, in the Archean Superior Province, produced 13.5 mt of ore with an average grade 7.5% Zn, 0.88% Cu, 0.77% Pb and 3.10 oz/t Ag in the period 1970-1983.  Preliminary studies indicated the presence of an especially varied mineral assemblage, which was studied in detail.  As well as chalcopyrite and sphalerite, the deposit contains abundant galena accounting for its unusual lead production.  Argentian Tetrahedrite, or frelbergite, is also abundant, and in the absence of native silver and acanthite, is clearly a major carrier of silver.  Other sulfide minerals include pyrite, pyrrhotite, arsenopyrite, bornite, mackinawite, pyragyrite, boulangerite, freleslebenite, stephanite and veenite.  Oxide minerals include magnetite, hematite, llmenite, rutile, jacobsite, cassiterite and gahnite.

The mineral zoning in the orebody is pronounced.  Sphalerite, tetrahedrite, galena and the sulfosalts all occur in the upper portion of the orebody, whereas pyrrhotite and chalcopyrite are concentrated in the lower portion.  The oxide minerals, except for jacobsite, occur in the ore zone as well as in the footwall alteration zone.

A Brillouin zone model for tetrahedrite in which 204 to 208 electrons are accommodated in the 51^st Brillouin zone is verified in analytical data from 60 grains.  However, when three or more Ag atoms per unit formula are present, the number of valenic electrons increases from 204 to 208 as Ag atoms increase from three to six.  The presence of (Fe+Zn) in excess of two atoms per unit formula appears to stabilize the 52^nd Brillouin Zone with >208 valence electrons per unit cell.

Analyses of sphalerite yielded a mean mole % FeS = 12.11 " 0.70, indicating a pressure of metamorphism of 7.53 kbar, using the sphalerite geobarometer.  This pressure is approximately 2 to 3.77 kbar too high in comparison with pressures suggested by silicate systems.  A possible explanation is that sphalerite-pyrite-pyrrhotite equilibrated at peak pressure, whereas silicate assemblages indicate conditions of peak temperature in the P-T-t history of metamorphism of the deposit.  Retrograde alteration variably affected sphalerite composition, producing some scatter in data, as well, as evidenced by variable occurrence of late-stage monoclinic pyrrhotite.

The low gold content, high lead content, diversity of sulfosalt species and abundance of silver in tetrahedrite are features more similar to those of kuroko-type deposits of the Phanerozoic than to Noranda or primitive-type massive sulfide deposits characteristic of the Archean.

When dealing with acid mine drainage (AMD), the common accepted practice is to develop a predictive model using methodologies such as acid-base accounting (ABA).  These models are used to evaluate the neutralization potential (NP) and evaluate acid potential (AP) of geological materials that comprise mine waste and tailings; however, creating accurate predictive models for rocks of low neutralizing and low acid producing potentials is difficult.  Through modeling a series of synthesized alkalic igneous rock compositions, static acid-base accounting (ABA) testing methods were conducted.  These rock compositions were designed over a range in feldspar compositions: quartz syenite (Or > Ab); quartz monzonite (Or = Ab); albite-bearing quartz monzodiorite (Or < Ab); and labradorite-bearing quartz monzodiorite (Or < Lab).  By means of ABA testing, the experiments demonstrated that with minimal change in sulphide content (increasing from 0.1% to 0.5%) the neutralization potential of the rock can be overcome. 

In addition to ABA testing, static water-rock reaction experiments were conducted; in which the synthesized rocks were reacted at a 1:50 ratio with sulphuric acid solutions with varying pH values (2.0, 4.0, and 6.0) for a 4 week and 8 week period.  The intent of each solution was to simulate a different AMD scenario: pH 2.0 to be an analogue of highly acid waters; pH 4.0 to be weakly acid and natural waters mixture; and pH 6.0 to be more representative of natural waters.    The low to near neutral waters (pH 4.0 and pH 6.0) showed that feldspar composition has little to no effect in changing the buffering capacity, as the pH condition for initial pH 4.0 and 6.0 waters were neutralized to a pH in the range of 8.58 to 9.44.  For pH 2.0 waters, the pH of the sulphuric acid solution were moderately buffered by the rock compositions to varying degrees; however, did not fully neutralize the waters (final pH ranged from 2.69 to 4.04).  Feldspar composition in this situation is important in controlling the extent of buffering achieved. The largest buffering capacity was from the albite-bearing quartz monzodiorite, followed by labradorite-bearing quartz monzodiorite, and with the least amount by buffered by the quartz syenite.

The Coldwell Complex of the Superior Province is known to host multiple lamprophyric dykes varying from ultramafic to alkaline affinities. The Ney’s Lookout dyke is located within the Center II portion of the Coldwell Complex, crosscutting assimilated syenites. This area of Center II is highly brecciated and assimilated, which is interpreted to be representative as evidence of the cauldron collapse. The lamprophyre is devoid of diamonds, and has not been thoroughly analyzed other than brief field assessments. The objective of this research was to classify the lamprophyre according to the IUGS classifications of lamprophyre-clan rocks.

The main minerals that comprise the lamprophyre are euhedral zoned pyroxene phenocrysts and flow-aligned anorthoclase laths in a fine-grained groundmass composed of biotite, pyroxene, amphibole and feldspars. The pyroxene phenocrysts are poikilitic with inclusions of biotite, amphibole and relic olivine similar to the groundmass. Relic chloritized olivine phenocrysts are present in the groundmass and as inclusions in pyroxenes. The pyroxenes present in the sample are classified as diopside with minor augite. Mineralogical compositions of the Ney’s Lookout amphibole classify as Ferroan Paragasitic Hornblende. When compared to other lamprophyres within the Coldwell Complex, there were mineralogical and textural similarities between Ney’s Lookout Lamprophyre and local sannaites, such as porphyritic texture and mantling of amphiboles on pyroxene. Aside from minor variances in modal mineralogy, the lamprophyre best resembles a sannaite under the alkaline lamprophyre classification.

The chill margin along the dyke is a fine-grained rim with no contact metamorphism present, interpreted as representing a moderate emplacement temperature. Laths of anorthoclase are directionally aligned in the lamprophyre and are interpreted as flow textures. Zonation in the pyroxene is distinct in the phenocrysts, representing increasing Cr and Ti outward toward the rim with increased Fe in the core and decreasing amounts in the rim. Uralitization is the altertion of pyroxene phenocrysts to amphibole around the outer rim. The zonation and uralitization often occur from magma mixing events.

The Archean atmosphere is known only as bits and fragments – that often are at odds with each other, and certainly do not ultimately contribute to a “big-picture” composition of this atmosphere on the whole.  That said, there is still far more literature available for the Archean atmosphere than there is for Archean-aged offshore sedimentary deposits; there is virtually nothing out there that attempts to connect the two aspects together.

Because there is such controversy over the most probable composition of the Archean atmosphere, at a glance this makes it very difficult to try to narrow down the individual components to their most likely concentrations.  Comparing the Archean atmosphere to the present Martian one proved to be quite useful for this investigation – the only differences were for methane and water vapour, and being due to the presence of methanogens in the Archean Earth and to the simple size-difference between Earth and Mars (Earth’s larger size meant larger atmosphere which means more vapour), respectively.

Using data from the literature that has been produced concerning Archean-aged storm-related deposits, in particular of ripple formation, beaches (or lack thereof), and of hummocky cross-stratification, helped in constraining the average Archean surface temperature.  From there, it was only a matter of plugging the now-constrained (relatively-speaking) atmospheric values into known and novel methods for determining the specifics of the dynamics of sediments of certain grain-sizes – in particular, using the Shields method.

After all was said and done, the final task was to try to make physical sense of the sedimentary dynamics results.  The results themselves were consistent with each other, and helped to explain in particular, with some logic, why known hummocky bedding in Archean units appears so thin compared to present-day examples.  The results predict that any eolian ripples and dunes found in the Archean should be noticeably smaller in size than more modern examples, and also predict that in general winds and storms should have been noticeably weaker during the Archean when compared to today.

Diamond-bearing macrocrystic, and xenolithic rocks have been identified as occurring within the Rabbit Foot dyke within claim blocks held by Rio Tinto Diamonds Exploration Inc., 15km west of the town of White River, Northwestern Ontario.  Initial assessment of these rocks has led to their being classified “melnoite”, a term used to describe potentially diamondiferous ultramafic lamprophyres.

Olivine occurs in at least two distinct phases within the rocks of the Rabbit Foot dyke; macrocrystal olivine and groundmass olivine.  Macrocrystal olivine ranges in Mg/(Mg+Fe) from Fo₉₁ to Fo₉₃, while phenocrystal and groundmass olivine ranges from Fo₈₅ to Fo₈₇.  Phlogopite compositions range from Ba-phlogopite to tetraferriphlogopite. Spinel-group minerals commonly have chromite cores with titanomagnetite rims.  Spinel compositions follow the “Magmatic trend 2”, the titanomagnetite trend. Spinel-group minerals can be observed displaying atoll textures.  Spinel and perovskite are commonly spatially related, and can be observed surrounding larger macrocrysts such as olivine in a necklace texture.  Perovskite compositions are relatively pure CaTiO₃, lacking any REE concentrations.  In at least one outcrop of xenolithic rock, spherical magma clasts up to 10cm in diameter, which contain cores of olivine macrocrysts, can be observed.

The rocks of the Rabbit Foot dyke are in many ways analogous to kimberlite in texture and mineralogy, however, significant petrogenetic overlap with melnoites, or ultramafic lamprophyres, is evident.  The diamondiferous macrocrystic and xenolithic rocks of the Rabbit Foot Dyke can therefore be considered as kimberlite with melnoitic (ultramafic lamprophyre) affinity.

Kaminak’s Coffee Gold Project located south of Dawson City, Yukon is a structurally controlled gold deposit.  The Coffee Gold Project is hosted within the Yukon –Tanana Terrane, bounded between the Tintina and Denali Faults and along the strike of the Teslin Fault.  Microstructural analysis was completed on three zones within the project, the Kona, Latte and Supremo, to assess controls on mineralization, as well as to classify the protoliths at each zone.  Microstructures indicate significant deformation in the Latte and Supremo zones, and the least deformation in the Kona zone.  The Kona zone is a weakly deformed granite, composed of approximately 2mm euhedral grains of feldspar, quartz, and biotite. Microstructures in the quartz include subgrains, serrated grain boundaries, and undulose extinction, indicating deformation by dislocation creep.  The Supremo and Latte zones show more deformation; in these zones, feldspar has deformation twins and forms rigid porphyroclasts.  A well-developed foliation is defined by the parallel alignment of muscovite.  Each of the three zones contains porphyroclasts of feldspar that give evidence for the protolith being coarse-grained and felsic, likely a felsic plutonic rock.  The Latte zone is mapped as a biotite schist; however, biotite is present in only small amounts. Additionally, the mineralogy in the Latte zone consists dominantly of quartz and feldspar, consistent with an igneous origin.  A relationship between deformation and mineralization is observed; as deformation increases, the gold mineralization increases.  Gold mineralization, based on published assay values from Kaminak, were lowest in the Kona zone and higher in the Latte and Supremo zones. The protolith of all three zones is likely a deformed felsic plutonic rock with varying degrees of metamorphism and deformation.

The two breccia pipes that comprise the Albany graphite deposit, located near Hearst, Ontario are examples of fluid-derived, igneous-hosted graphite. Both the East and West pipes have been have been subjected to post-emplacement alteration at levels near the unconformity with the overlying Paleozoic carbonate rocks of the Gravel River Basin, and as a result have undergone various types of alteration. Carbonate and hematite alteration affect the supergene zone, while sericite alteration affects the known vertical extent of the deposit. Post-emplacement intrusions at depth within both pipes result in additional carbonate and hematite alteration zones within the graphite breccia.

The transitional trend in limestones/dolostones from continuous veins to isolated anhedral masses which underlain Paleozoic carbonate rock is attributed marine transgression of the Ordovician oceans. Sericitization is present in both pipes for the entire sampling depth and is controlled by the potassium feldspars. The degree of sericite alteration decrease with depth from the supergene zone into the breccia. Hematite alteration of the feldspars within the supergene zone correlates nicely with sericite alteration.

A combination of core logging, optical microscopy, x-ray diffraction, and whole-rock geochemistry have been used to document and determine the origin of this shallow level alteration of the Albany graphite deposit.  The alteration styles are similar for both pipes but there are key in differences for each. The spatial relationship among the three style is complex. At least two of the three alteration types noted above, are present at depth of within the deposit, often with all three overlapping.

The presence of each alteration type will have an impact on metallurgical beneficiation of the ore based on extent and degree of alteration. By delineating the zones and distinguishing between supergene alteration and alteration occurring at depth within the breccias, processing techniques can be varied as each complicating zone is encountered.