The Geordie Lake Intrusion (GLI) consists of alternating zones of layering-free troctolite and olivine gabbro outcropping in the north-central part of the Coldwell alkaline complex, northwestern Ontario.  The troctolite exhibits harrisitic texture in which dendritic olivine (Fo_44-56), plagioclase (An_48-57), and skeletal magnetite are the main constituents.  Small amounts of clinopyroxene (Di₃₆Hd₆₀Ae₄-Di₃₀Hd₆₆Ae₄) are present in the troctolite.  The ophitic olivine gabbro consists of clinopyroxene (Di₄₁Hd₅₄Ae₅-Di₂₉Hd₆₆Ae₅), plagioclase (An_46-54), altered olivine, and skeletal magnetite.  Some gabbros contain high-alumina clinopyroxenes (Ti-Px₄CATS₄₈Ae₄₈-Ti-Px₃CATS₄₂Ae₅₀).  Mineral chemistry and whole-rock geochemistry indicate that the troctolite and gabbro are note related by differentiation and their parent magma is a relatively evolved low-alumina tholeiite.  The GLI is characterized by high Sr, Rb, Ba, Th, Ta and light rare-earth element (LREE) content but low in Ni and Cr content.  Europium anomalies are absent.  Fe-Ti oxide geothermometry and geobarometry of the troctolite and olivine gabbro give an average equilibrium temperature of 603°± 35° and oxygen fugacity of 10^-17 bar. 

Disseminated chalcopyrite is the dominant style of Cu-sulphide mineralization in the GLI.  Massive chalcopyrite aggregates are rare.  Bornite exsolved from chalcopyrite.  The other sulphides present are pyrite, millerite, siegenite with exsolved pentlandite, galena, and supergene chalcocite.  The tellurides and PGM occur as small inclusions (5 – 10 mm) in, and as coarser sunhedral to anhedral grains on the margins of, the disseminated chalcopyrite.  Small amounts of tellurides and PGM are also present in the massive chalcopyrite and silicate minerals.  The tellurides are melonite, hessite, unnamed Ag₃Te₂, and altaite.  The PGM are kotulskite, merenskyite, michenerite, sopchiete, palladium bismuthotelluride, paolovite, palladium arsenide, guanglinite, and palladium antimonide.  Sperrylite is the only platinum mineral present in the GLI.  Electrum forms small discrete and replacement minerals.  Two probable new minerals are Pd_1.6As_1.5Ni and AgSb₄.  Textural evidence from the sulphides, tellurides, PGM, and host rock silicates favour a late stage magmatic origin.  Cu-sulphide mineralization was induced by precipitation of magnetite and other Fe-bearing minerals, and subsequent mineralization resulted from cycles of sulphide and magnetite deposition.  Conditions of deposition for the tellurides and PGM associated with the disseminated chalcopyrite have been estimated to be approximately from 550°C to between 450° and 400°C, and at log P(Te₂) from -2.4 ± 0.13 bar to between -6.4 and -9.7 bar, and at log P(S₂) from between -3.7 and -0.8 to between -4.2 and -2.3 bar.  The predominance of palladium over platinum minerals reflects the relatively evolved nature of the GLI.

A copy of the thesis can be downloaded here

This thesis describes the occurrence, mineralogy and assimilation of basic xenoliths hosted by Centre 3 syenites.  Field work was carried out in two locations, one in the vicinity of Neys/Ashburton and the other a large megaxenolith hosted by Centre 1 syenites in the vicinity of Wolf Camp Lake. 

Least altered xenoliths consist of plagioclase, pyroxene amphibole, biotite, apatite and opaque phases.  With increasing assimilation this changes to a combination of plagioclase, amphibole, biotite, apatite, opaque phases, alkali feldspar, calcite, fluorite, sphene, zircon, REE phases and quartz.

Plagioclase is replaced by alkali feldspar in the form of porphyroblasts and crystals in the groundmass.  Plagioclase is also decalcified to more albitic compositions along with recrystallization.  Amphibole compositions extend over the same range of amphibole compositions in the host ferro-edenite syenite.  The general effect of xenolith assimilation is the equilibrium of a xenolith's mineral assemblage to that of the host syenite.  Assimilation processes seen at Wolf Camp Lake are similar to those seen at Neys/Ashburton.

Bulk rock data along with mineralogical compositional variation in clinopyroxenes, suggest a tholeiitic basalt parentage for xenoliths in both areas.  Cr and Ni contents indicate an evolved nature to the parent volcanics.  Data also suggest the possible existence of a second undersaturated type of volcanic xenolith present at Neys/Ashburton.  Parental basalts are postulated to be coeval volcanics related to the formation of the Coldwell Complex.

Modelling by mass balance mixing calculations of contamination of host syenites indicates that contaminated ferro-edenite syenites are the result of direct assimilation of volcanic xenoliths by ferro-edenite syenite.  Quartz syenites are found to be unsuitable parents to contaminated ferro-edenite syenites.

A copy of the thesis can be downloaded here

The  Coldwell Alkaline Complex, situated on the north shore of Lake Superior, is of Neohelikian age.  It is intruded into Archean supracrustal rocks of the Superior Province,  near Marathon,  Ontario.  The complex has a diameter of 25 km and consists of three major magmatic centres.  Each centre represents the focus of a cauldron subsidence event.  From earliest to latest they are:  Centre I - saturated alkaline rocks with peralkaline oversaturated residua; Centre II - miaskitic undersaturated alkaline rocks; and Centre III - alkaline rocks with oversaturated residua.  This thesis documents the rocks of Centre III.

Centre III magmatism of the Coldwell Alkaline Complex is represented by alkali feldspar syenites and alkali feldspar quartz syenites.  In order of intrusion from earliest to youngest these are (1) synneuritic magnesio-hornblende syenite,  (2) perthitic ferro-edenite syenite,  (3) contaminated ferro-edenite syenite and  (4) quartz syenite.  Amphiboles are the major mafic phase in all syenite types.  Their evolutionary compositional trend ranges from magnesian hastingsite in the magnesio-hornblende syenite to riebeckite in the quartz syenite.  Pyroxenes are Ti-Al rich in the earliest syenites, but evolve to Na-Fe rich members in the youngest.  The contaminated syenites result from the assimilation of xenoliths of oligoclase basalts which are interpreted to represent contemporaneous lavas.  Varying degrees of contamination lead to an apparent plethora of syenite types.

The Centre III syenites are miaskitic and metaluminous with normative quartz content increasing from the earliest to the latest varieties.  All of the syenites are enriched in U, Th, REE, and Zr, reflecting the presence of zircon, chevkinite, REE-carbonates, Nb-rutile and aeschylite.  Centre III syenites have petrological affinities with A-type granites and are interpreted to have been formed by partial melting of lower crustal material.

A copy of the thesis can be downloaded here

The Ham diatreme and dyke are post-late Silurian intrusions located in north-central Somerset Island and are the most northerly known kimberlites in theSomerset Islandkimberlite province.  The Ham diatreme, which consists of three petrographically distinct varieties of kimberlite, formed as a series of fluidized intrusions at the intersection of several regional fracture sets.  Type 1A kimberlite is petrographically similar to the Ham dyke (a single intrusion located 1.5 km to the east) and forms the flanks of the Ham diatreme. This dark, massive rock contains phenocrysts and xenocrysts of garnet,olivine, chrome-diopside, phlogopite, spinel and carbonate in aserpentine-carbonate groundmass containing carbonate and serpentine emulsion textures.  Type 1B kimberlite, which occupies the central portion of the Ham diatreme, is a highly altered, light green, seperentine-carbonate-rich rock formed by the prograde serpentinization and carbonatization of Type 1A kimberlite. This alteration occurred during the degassing of structurally lower portions of the Ham diatreme.  Type 2 kimberliteis a carbonate-rich mineralogical equivalent of Type 1A kimberlite and formed as a late stage dyke within the Ham diatreme.

Pre-fluidization phenocrysts include Mg-rich olivine (Fo_89-93), low Cr, (<3.5 wt.% Cr₂O₃), high Ti (>0.3 wt. % TiO₂) pyrope-garnet, Al-rich, Ti-poor (<2.00 wt % TiO₂) aluminous-magnesium chromite (Cr/Cr + Al = 0.18 - 0.85) and Ti-rich phlogopite(1.0 - 4.6 wt. % TiO₂). Post-fluidization microphenocrysts include Mg-rich olivine (Fo_89-93),Ti-rich phlogopite (2.5 - 4.0 wt. % TiO₂) and spinel which evolved from Ti-bearing (2.00 wt. % TiO₂), titan-magnesium-aluminous-chromiteto Fe³⁺- and Ti-rich (max. 17.0 wt. % TiO₂) magnesium-ulv_spinel - ulv_spinel-magnetite.  Atoll spinels, formed prior to the complete crystallization of the kimberlite groundmass are present in the Ham dyke but extensive resorption of magnesium-ulv_spinel-ulv_spinel-magnetite and titan-magnesium-aluminous-chromite in the Ham diatreme has precluded their persistence.

Xenocrysts formed by the disaggregation of garnet and spinel lherzolites include Cr-rich (3.5 - 10.0 wt. % Cr₂O₃), Ti-poor (<0.30 wt. % TiO₂) pyrope-garnet, Mg-rich olivine and chrome-diopside.  Pressure temperature estimates from garnet lherzolite xenoliths range from 36 to 37 kb and 1031 to 1146EC corresponding to a depth of origin of 110 to120 km.

Multiple discriminant analysis demonstrates that cluster analysis can only distinguish between garnets of grossly different chemistry and paragenesis and that major and minor element variation diagrams are required to separate statistically,chemically similar garnets within a paragenesis.

Geophysical studies may be used to delineate kimberlite subcrop patterns and structural elements which may have controlled the intrusion of the kimberlites.

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The rocks of the Rainy Lakearea have been deformed during three distinctive episodes.  Minor structures provide the geometry which characterizes each episode.  The youngest structures include regional faults, a crenulation cleavage, kink bands and minor F₃ folds.  These D₃ structures are superimposed on structures of the D₂ episode.  These include dominant F₂ folds having axes lying in a penetrative cleavage which parallels the axial surfaces of the folds.  Some F₂ folds have a downward structural facing which is evidence that the stratigraphic succession at Rainy Lake is overturned at a regional scale.  It is proposed that this inversion took place during a D₁ deformation by the formation of large F₁ fold nappes.  Minor D₁ structures are difficult to document.

The rocks of the region were metamorphosed simultaneously with much of the deformation.  The distribution of index minerals defines the boundaries of the biotite, staurolite-cordierite and sillimanite-muscovite zones.  The non-parallel distribution of metamorphic minerals may be explained by the non-parallelism of isotherms and isobars during medium grade metamorphism.

These new data support the view that the Coutchiching biotite schists at Rainy Lake are stratigraphically younger than metavolcanic rocks of the Keewatin Group although they presently underlie theKeewatinstructurally.  This observation resolves a part of the historically important "Seine-Coutchiching problem".

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The Hemlo East property is located approximately 50 kilometres east of the town of Marathon, Ontario and is situated within the Schreiber-Hemlo greenstone belt of the Wawa-Abitibi Terrane of the Archean Superior Province. Lithologies within the Hemlo East Property are broadly divided into mafic metavolcanic, felsic metavolcanic, metasedimentary, intrusive and metaintrusive rocks. Stratigraphic continuity within the study area is demonstrated by the large number of drill holes in the area. Rock staining indicates that the K-feldspar present in felsic metavolcanic rocks in the Gouda-Thor-Carroll area of the Hemlo East Property is a product of alteration likely associated with base metal and gold mineralization.

New major and trace element, Sm-Nd isotope, and geochronology data are presented for volcanic, plutonic, and metasedimentary rocks of the Hemlo East property to investigate their origins. Positive to negative ε_Nd (-1.14 to 2.15) for tholeiitic basalts indicate that they were derived from depleted to moderately contaminated sources. FI rhyolites with steep trace element patterns (La/Yb_n = 16 to 44) and fractionated HREE (Gd/Yb_n = 2.1 to 7.5) are interpreted to have been derived from a deep mantle source. Metasedimentary rocks are geochemically similar to felsic metavolcanic rocks and are interpreted to be derived wholly, or in part, from a felsic source.

New U-Pb age dates include 2704.8 ±1.1 Ma and 2705.6 ±1 Ma from the Gouda and Thor metarhyolites, respectively; 2694.5 ±1 Ma from the DC Lake metadacite; 2691.6 ±1.1 Ma from the Upper Anomalous Zone volcaniclastic unit; 2693.1 ± 1 Ma from the Moose Lake Porphyry at Hemlo; 2683.4 ± 1.7 Ma from the Cedar Lake Pluton granodiorite; 2686.5 ±1.3 Ma from the White River Pluton monzogranite; and a maximum age of ~2696 Ma from the Frank Lake felsic metasedimentary unit. Results from the new and compiled U-Pb geochronological data indicate that there are two associations of felsic volcanism and two associations of plutonism, with a new association of felsic volcanism at 2705 Ma. This 2705 Ma phase represents the oldest felsic volcanic unit dated in the greenstone belt. This data points toward a northward younging of stratigraphy in the Gouda-Thor-Carroll area implying that the stratigraphy is right way up.

A long lived oceanic subduction zone produced the arc rhyolites and granitic intrusive rocks seen in the Hemlo East Property. There is no indication from this study as to what comprised the crust that the pre-tectonic plutons were intruded into. High La/Yb_n ratios for the rhyolites suggest that their source magmas were derived at depth from the melting of the subducting slab. Island arc tholeiites (metabasalts) erupted from a primitive back-arc behind the island arc. The area between the arc and back-arc would have allowed for island arc tholeiites to be deposited alongside rhyolites in conjunction with sediments coming off of the volcanic arc to produce the stratigraphic associations seen in the Gouda-Thor-Carroll area. These supracrustal units were later intruded by TTG plutons.

A copy of the thesis can be downloaded here

The Coldwell Complex, northwestern Ontario, is a multiphase alkaline intrusion that is host to rare earth element, actinide and other high field strength element mineralization. Preliminary studies have shown that these minerals are concentrated in pegmatites associated with Center One ferrorichterite-ferroaugite syenites and Center Three syenites. The Center One syenites differentiate to pegmatitic residua and are characterized by cumulus perthitic-to-cryptoperthitic alkali feldspar, hedenbergite-aegirine pyroxenes, and intercumulous quartz, calcite, and calcic-to-sodic-calcic-to-sodic amphiboles. Center Three residua are similar, except that amphiboles are limited to calcic varieties (hastingsite) and precipitate before feldspar (as opposed to after). All pegmatitic residua are of the niobium-yttrium-fluorine (NYF) type. Back-scattered electron petrography has been used to characterize the mineral paragenesis. Pegmatitic syenitic residua emplaced in, but not derived from the border gabbro (Border Gabbro pegmatite), and residua within ferroaugite syenite units (Railway pegmatites) contain a wide range of rare element minerals which include britholite, chevkinite, fergusonite, monazite, allanite, kainosite, xenotime, REE fluorocarbonates bastnaesite, synchysite and parisite. Other rare element enriched minerals include apatite, thorite, zircon, zirconolite, niobium rutile and U-Th-Si-pyrochlore. Early-formed rare element minerals such as allanite, britholite, chevkinite, kainosite, and pyrochlore are commonly replaced by complex aggregates of later-forming phases such as REE-fluorocarbonates. Other riebeckite-quartz (Upper Marathon Shore pegmatites), richterite-quartz (Black pegmatites) and hastingsite-quartz (Center Three pegmatites) bearing pegmatitic residua contain a more restricted  range of rare element minerals, which include zircon, xenotime, monazite and fluorocarbonates together with REE-bearing apatite, thorite and pyrochlore. The differences in rock forming and accessory mineralization suggest that most, if not all, residua are derived from different batches of ferroaugite syenite and syenite magma.

Intensive parameters have been estimated using the habit of perthites, the coexistence of zircon and baddeleyite, Fe-Ti-oxide compositions, amphibole mineralogy, and fluorocarbonate stability. These parameters indicate all pegmatitic units are similar, with initial silica activities of 10-0.75, alkali-feldspar precipitation at approximately 750°C, magnetite-ilmenite subsolidus equilibration temperatures of 531 to 633°C and oxygen fugacities of 10-16.5 to 10-22.9 bars, subsolidus quenching of magnetite occurs at approximately 450°C, and subsequent 200°C hydro- and carbothermal induced recrystallization of rare earth mineral and REE-bearing minerals.

A copy of the thesis can be downloaded here

The Lower Steel River - Little Steel Lake area is located about 25 km east of Terrace Bay , Ontario .  Seventeen iron-formations were investigated within this metamorphosed Archean volcanic and sedimentary terrain, which represents a portion of the Abitibi - Wawa Subprovince of the Superior Structural Province .

Sulphide-facies iron-formations are the dominant chemical sedimentary rocks in the Schreiber - Terrace Bay area, and represent deposition during quiescent periods of clastic accumulation and in volcanic activity.  The iron-formations commonly mark contacts between the volcanic and sedimentary rocks.  They are interbedded with carbonaceous slates at the base of sedimentary successions and overlain by DE turbidites.  This suggests chemical sedimentation on a subaqueous basinal plain slightly distal to an outer fan.

Sulphide-facies iron-formations consist of a mixture of chemical and clastic components, and while highly variable, the iron-formation in the study area contain three commonly recognizable units:  1) pyretic-carbonaceous slate;  2) disseminated, massive, laminated and nodular pyrite; and  3) chert of siliceous sedimentary rock.  Sedimentary textures and structures combined with trace element abundances and geochemical components, and a hydrothermal source for the iron.  Exhalative discharge probably occurred episodically as moderate- to low-temperature solutions percolated through near-surface pillowed volcanics and, once vented, deposited a blanket of chemical sediment.  Vent-proximal deposits include massive and layered pyrite; the domal and colloform varieties support the existence of organic mats.  The presence of carbon is interpreted as a relic of the organic activity.  Pyritic-carbonaceous slates consisting of alternating chemical and clastic components represent vent-distal deposits.  Radial structures within pyrite nodules provide evidence of diagenetic transformation and tectonic deformation.

Structural evidence suggests that the study area was affected by a complex folding event related to one deformational episode, probably preceded by syn-sedimentary slumping in some areas.  The competency differences between sedimentary and volcanic rocks, combined with the fine-grained nature of the sedimentary rocks (DE turbidites and iron-formation) at major volcanic-sedimentary contacts, focused deformation and dike emplacement in the contact areas.

A copy of the thesis can be downloaded here

The Kitto intrusion is a Mesoproterozoic 1117.7 ±1.8 Ma peridotitic to gabbroic intrusion, that formed as a result of plume magmatism and was emplaced along Mesoproterozoic and Archean faults in the East Nipigon Embayment of northern Ontario.  The plume signature for the Kitto intrusion is suggested by five samples with OIB (ocean island basalt)-like primitive mantle normalized multielement patterns in the lherzolite-olivine websterites.

In the southern part of the intrusion, the sequence of lithologies from top to bottom is lherzolite, olivine websterite, vari-textured pyroxenite, pyroxenite and melanogabbro.  The basement is banded iron formation and mafic metavolcanic rocks.  Lithologies on surface are dominantly lherzolite, with olivine websterite present in the area of the Phoenix mineralized occurrence.  The Kitto intrusion is dominated by lherzolite that exhibits cumulate to pyroxene-poikilitic textures dominated by olivine with lesser clinopyroxene and poikilitic orthopyroxene.  The lithologies crop out as a 15 to 30 cm thick layer cake bed dipping from 0 to 30° to the SE and SW.  The olivine websterite displays similar cumulate to pyroxene-poikilitic textures, but contains more abundant clinopyroxene.  The pyroxenite exhibits orthocumulate textures consisting of cumulate clinopyroxene and intergranular plagioclase.  The melanogabbro comprises poikilitic plagioclase and minor cumulate clinopyroxene.  In the central part of the intrusion, lithologies from east to west are lherzolite, olivine websterite, pyroxene-porphyritic melanogabbro and granophyric gabbro.  Lherzolite and olivine websterites in the central part of the intrusion are more fractionated than at the southern part of the intrusion, and are characterized by the presence of secondary pyroxene and minor plagioclase.  The pyroxene-porphyritic melanogabbro also contains secondary pyroxene and, along with cumulate clinopyroxene, there is enrichment in intercumulus plagioclase component.

The lithologies of the Kitto intrusion have geochemical signatures consistent with crustal contamination of a primitive magma.  The lherzolite-olivine websterites are characterized by primitive mantle normalized multielement patterns with negative Nb and Ti anomalies, consistent with assimilation of Archean continental crust.  All the lithologies have εNd contents of -5.54 to -6.53 consistent with contamination by an older crustal source.  Trace element modeling of assimilation-fractional crystallization suggests the lithologies probably assimilated metasedimentary rock of the QST (Quetico Sedimentary Terrane) and mafic metavolcanic rock of the BGB (Beardmore-Geraldton Greenstone Belt) at depth. Emplacement at shallower depths was accompanied by assimilation of mafic metavolcanic rock and banded iron formation.  In the central part of the intrusion, pyroxene-porphyritic melanogabbros have more pronounced negative Nb anomalies indicative of greater assimilation of continental crust.

Emplacement of the Kitto intrusion occurred with an initial pulse of pyroxenite-melanogabbro followed by a pulse of lherzolite-olivine websterite magma in the southern part of the intrusion.  The initial pyroxenite-melanogabbro pulse is suggested by a trend of increasing forsterite and enstatite contents, and decreasing ferrosilite in olivine and pyroxene minerals from the melanogabbro to the higher pyroxenite.  A second pulse is suggested by a trend of replenishment to higher forsterite, enstatite, and ferrosilite contents, but lower wollastonite content in olivine and pyroxene minerals in the lherzolite-olivine websterite.  Towards the top of the intrusion trends of decreasing forsterite, enstatite and ferrosilite contents, but increasing wollastonite content, in olivine and pyroxene are consistent with fractionation of the magma. 

The Kitto intrusion was probably emplaced along north-south Proterozoic and east-west Archean faults in the East Nipigon Embayment.  Possible north-south orientated faults include the Nipigon River and Pijitawabik Faults.  As the magmas came in contact with the east-west orientated Blackwater, Empire, Princess Lake, Standingstone and Sandy Creek Faults of the BGB, they were displaced east or west along the faults, creating the ring-shaped form of the intrusion.

Mineralization of the Kitto intrusion is represented by interstitial Ni-Cu-PGE sulphides in one zone at the bottom of the lherzolite-olivine websterite, two zones in the underlying pyroxenite, and one zone at the contact of the melanogabbro and the basement iron formation.  On the surface outcrops, high Ni contents in the lherzolites and trends of increasing Ni with MgO in all the lithologies, show that Ni partitioned into olivine as the magma evolved.  On the surface outcrops in the central part of the intrusion, lower Ni contents are associated with higher Cu contents in the pyroxene-porphyritic melanogabbros, suggesting the lithologies did not contain sufficient olivine that would partition the Ni.  Generally, anomalous PGE contents occur with anomalous Ni and Cu contents in the lithologies.  Se and S data suggest that externally derived sulphur resulted in sulphur saturation and the precipitation of Ni-Cu-PGE sulphides.  High Se contents are detected in the main mineralized zone at the bottom of the lherzolite-olivine websterite, and in the zones of the underlying pyroxenite.  High Se contents have also been detected in basement iron formation and SVU (Southern Volcanic Unit) mafic metavolcanic rocks consistent with these lithologies being sulphur sources for contamination and mineralization.

A copy of the thesis can be downloaded here

Jordan is currently working on his PhD at the University of Western Ontario

Historic drill core form the Shuniah Mine and more recent drill core from the Keystone and Porcupine Mines have provided the basis for a study of these past silver-producing veins as a function of depth.  Precipitation was initiated from a boiling fluid at temperatures in excess of 370EC.  Cooling of the fluid and precipitation of calcite and sulfides followed generally at 100EC.  Several episodes of deposition separated by fracturing events are evidenced.  From fluid boiling temperatures the depth of emplacement for the veins is 1 km with the pressure regime alternating between hydrostatic and lithostatic.  The ore-depositing solutions appear, therefore, to have arisen from depth and deposited their ores in proximity to diabase sills, which cap the various vein systems, in response to hydrologic factors.