Lead isotope compositions have been obtained from five major volcanic and intrusive rock suites and several ore deposits on Vancouver Island. Lead, uranium and thorium concentrations and strontium isotope ratios have been obtained for a subset of these samples. The rock suites examined are the Paleozoic Sicker Group, Triassic Karmutsen Formation, Jurassic Island Intrusions and Bonanza Group volcanic rocks, and the Eocene Catface intrusions. Isotope geochemistry of the Sicker Group is consistent with the interpretation that it formed as an island arc. Relatively high 207pb/204pb ratios indicate sediment involvement in the subduction process, which suggests that the Sicker Group formed close to a continent. Buttle Lake ore deposits display decreasingly radiogenic lead isotope ratios with time, suggesting that the associated magmas become increasingly primitive. This supports the hypothesis that these deposits formed during the establishment of rifting in a back-arc environment. Karmutsen Formation flood basalts display isotopic mixing between an ocean island-type mantle source and average crust. Isotopic evidence is used to support a Northern Hemisphere origin for these basalts. Mixing is apparent in the lead and strontium isotope signatures of the Island Intrusions and Bonanza Group volcanic rocks, between depleted mantle and crustal (possibly trench sediments) components. This is consistent with formation of these rocks in an island arc environment. Eocene Catface intrusions have relatively high 207pb/204pb indicating that crustal material was involved in their formation. There are two groups of plutons corresponding to an east belt and west belt classification. Galena from the Zeballos mining camp related to the Eocene Zeballos pluton indicates that the mineralization was derived from the pluton. Galena lead isotope data from Vancouver Island may be interpreted in a general way by comparison with data from deposits elsewhere of known age and origin. No single growth curve model can be applied. Lead isotope characteristics of Vancouver Island are clearly different from those of the North American craton, reflecting the oceanic affinities of this terrane. A new technique has been developed to compare 207pb/204pb ratios between samples with differing 206pb/204pb ratios. The procedure projects 207pb/204pb ratios along suitable isochrons until they intersect a reference value of 206pb/204pb. This technique can be used for interpreting lead isotope data from old terranes, in which lead and uranium may have undergone loss or gain, and if lead and uranium abundances have not been measured. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Devonian and Early Carboniferous marine clastic rocks of the Earn Group host several economically important stratiform massive sulphide and bedded barite deposits. Due to the chaotic sedimentation, considerable regional metamorphic overprint and, relative inaccessibility, little was known about the stratigraphy, the Late Devonian conodont fauna, or the age of the stratiform mineral deposits within the Earn Group. Conodont microfossils, however, are an excellent fauna for an Earn Group biostratigraphy program because of their ability to withstand both temperatures in excess of 400° C, and significant physical stress. With standard laboratory techniques conodonts were readily extracted from fine grain calcareous elastics and carbonate lenses within the Earn Group. The conodonts are described from three specific areas where the Earn Group is known to host stratiform barite and barite-lead-zinc mineral deposits: Macmillan Pass, Midway, and Gataga. As the majority of conodonts were diverse and well preserved platform elements of the genus Palmatolepis, the taxonomic studies focused on this genus; other genera including Ancyrodella, Icriodus, Klapperina, Mesotaxis, and Polygnathus were examined as part of the biostratigraphic/taxonomic studies. Previous to this study the widespread stratiform mineralization was dated as only Late Devonian. The conodont taxonomy and biostratigraphy in the Earn Group provide age constraints for duration and formation of the stratiform mineralization. The ability to tightly constrain the age of the stratiform mineralization adds to the knowledge of Earn Group deposition, the paleogeography of the Selwyn and Kechika Basins, and has implications for stratiform mineral exploration strategies in the Earn Group. On the basis of conodont faunal ages barite mineralization at MACMILLAN PASS apparently occurs as three different levels: 1) CATHY property - Eifelian to early Frasnian; 2) PETE, JEFF, GARY, and GHMS properties - middle to late Frasnian; 3) TEA property -Early Carboniferous. In addition, barite-lead-zinc mineralization at TOM and JASON properties likely occurs during middle to late Frasnian. In the GATAGA area barite and barite-lead-zinc mineralization have been recognized at several temporally distinct levels in the early to middle Famennian: 1) Lower rhomboidea Zone; 2) Lower marginifera Zone; 3) Upper marginifera Zone. Several other mineralized horizons are loosely constrained within the same interval. Within the MIDWAY area the stratiform barite mineralization at the EWEN and PERRY properties is of Early Carboniferous, Tournaisian age, and correlates broadly with the TEA barite in the Macmillan Pass area. In summary, events that produced stratiform barite-lead-zinc and barite mineralization in the Selwyn and Kechika Basins were not coeval. The Late Givetian and early Frasnian barite mineralization took place in the Macmillan Pass and southernmost Gataga areas. During the middle Frasnian barite and barite-lead zinc mineralization events occurred at Macmillan Pass. Several episodes of barite and/or barite-lead-zinc mineralization occurred in the Gataga area during the middle Famennian. The youngest barite mineralization events in the Earn Group took place in the Early Carboniferous, Tournaisian time at Macmillan Pass and Midway. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The Beaverdell silver, gold, lead, zinc, vein camp is located approximately 88 km south of Kelowna, in south-central British Columbia at 49.43° north latitude and 119.06° west longtitude. The camp has been a silver producer since the turn of the century and some gold was produced in the early part of the century. This thesis examines the deposits in the regional area and examines, in detail, zoning in the Lass vein system on Wallace Mountain, and represents the first comprehensive study of zoning and genesis of the veins. Galena-lead isotopes are examined within the regional setting of the deposits. Fluid inclusion, sulphur isotope, mineralographic and major and minor element zonation studies yield definitive information about the genesis of the deposits. Granodiorite of the Westkettle batholith, probably Jurassic, underlies much of the area and has been Intruded by stocks of Tertiary quartz monzonite, such as the Beaverdell stock. Remnants of pendants and/or screens of Wallace Formation metamorphosed volcanic and sedimentary rocks, believed to be Permian, are contained in the granodiorite. Silver mineralization occurs in the Beaverdell mines on Wallace Mountain mainly within the West-kettle batholith. Numerous showing and old workings of silver and/or gold mineralization are found throughout the surrounding region. The gold-bearing veins at Carmi contain a different mineral assemblage than the silver-bearing veins on Wallace Mountain. Galena-lead analyses of samples collected throughout the region fall into two distinct clusters on the ²º⁶Pb/ ²º⁴Pb versus ²⁰⁷Pb/ ²⁰⁴Pb and ²⁰⁶Pb/²⁰⁴Pb versus ²⁰⁸Pb/²⁰⁴Pb diagrams. The first group is represented by the Carmi gold veins and the second by the Beaverdell silver veins. Models for the generation of lead in these deposits used Permian (0.27 Ga), Jurassic (0.15 Ga) or Tertiary (0.05 Ga) ages of mineralization on the basis of geological and K-Ar data. The model that is believed to be the best approximation of the system that formed these deposits assumes that the two groups of deposits formed at different times, under markedly different geological conditions. The parameters of this model indicate that: 1. the Carmi-type, gold-bearing vein mineralization is probably Jurassic and formed as a result of the intrusion of the Westkettle batholith, with the metamorphosed Wallace Formation as the probable lead source; 2. the Beaverdell-type, Silver-bearing vein mineralization is probably Tertiary and can be linked genetically to intrusions of that age, such as the Beaverdell stock; 3. ore fluid flow direction for the solutions that formed the Beaverdell-type mineralization was outward through the Westkettle batholith, away from the Beaverdell stock. Within the Lass vein system on Wallace Mountain, a distinctive, depth related, east-west zonation pattern in Au, Ag, Pb and Zn can be defined. Many of the other 11 elements analysed (Cu, Fe, Mn, Cd, Ca, Mg, Co, Ni, Hg, As, Sb) also show this pattern. Two zones are defined. The deeper portions of the orebody (at the east end of the vein system) contain high gold values, low silver values, and moderate to high zinc and lead values. High silver values, accompanied by moderate lead and zinc values, are found at a higher elevation in the system, in the western part of the vein system. Veins in the lower section have a greater average thickness than those in the western, upper section, and generally contain less gangue material. Fluid inclusions in sphalerite and quartz samples from the Lass vein system can be divided into three groups based on their homogenization temperatures. These are: Group 1: primary inclusion (with and without CO²), formed between 260°C and 310°C, from solutions with an average of 13 equivalent weight percent NaCl; Group 2: pseudosecondary inclusions formed between 230°C and 260°C, with salinities from 0.6 to 14 equivalent weight percent NaCl; Group 3: pseudosecondary and secondary inclusions formed between 180°C and 220°C, from solutions containing 0.4 to 14 equivalent weight percent NaCl. Arithmetic means of salinities for pseudosecondary, and secondary inclusions are, respectively, 8 and 6 equivalent weight percent NaCl. Sulphur isotope thermometers calculated for sphalerite-galena pairs (268°C to 320°C) are in close agreement with temperatures of homogenization of primary fluid inclusions. Seven stages of mineral paragensis can be recognized in the Lass vein system. Therfirst three stages (pyrite, arsenopyrite and dark sphalerite) are associated with the higher temperature, higher salinity, CO₂-bearing, primary inclusions. Pseudosecondary and secondary inclusions appear to be related to stages 4 to 6, which consist of galena, paler sphalerite, silver minerals and late quartz. Estimated depths of formation, based on a system under hydrostatic pressure, fall into two groupings. The minimum estimated depths of formation for primary, group 1 inclusions average 720 m, while depths calculated for groups 2 and 3 overlap in range, with-averages of 370 m and 175 m. The model-developed to explain the formation of this orebody accounts for the major and minor element zonation in the vein, the decreasing temperature, salinity and pressure (depth), and the loss of CO2 from the ore-forming fluid. The model explains two spatially distinct areas of mineralization represented by: 1. a zone of high temperature, high salinity, .arid" moderate pressure below a throttling point; and 2. a lower temperature, low salinity area caused by ground water mixing on the lower pressure side of the throttling point. CO₂ is present in the system below the throttling point, but is not found in any inclusions in Groups 2 and 3, on the lower temperature side of the throttling point. The association of CO₂ with gold deposition, suggests that gold would be expected in those areas where CO₂ is present in some of the inclusions. The definition of these two zones is critical for exploration. High silver values would not be expected to reappear further at depth to the east of the present workings, because this type of mineralization would only occur above the throttle point. Gold mineralization can be expected to continue for some time at depth if this model holds true. The abrupt change from the gold to the silver zone represents the throttle point in this model, and is highly visible in the major and minor element distribution patterns for the Lass vein system. Several different analytical procedures have been shown to differentiate between the two types of vein mineralization in the Beaverdell area. The use of these methods for exploration and development would allow the determination of key parameters concerning mineralization prior to extensive development of a showing or property. The level within the hydrothermal system, and therefore the type of ore expected can be determined by fluid inclusion studies for the younger, Tertiary veins. The age of vein mineralization, and therefore, the type of mineralization, also can be predicted by the use of galena-lead isotope ratios. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

No description available.

Rocks of the Quesnel Lake area are divided into three units: unit 1, a continental margin sequence; unit 2, The Crooked Amphibolite (an ocean-floor sequence); and unit 3, the Quesnel sedimentary and volcanic sequence. Two conglomerate localities within unit 3 contain clasts identified as being derived from deformed rocks of units 1 and 2. Deformation of the combined package of units 1 and 2 must have accompanied the emplacement of unit 2 onto unit 1 sometime between the deposition of unit 2 (Mississippian - Permian) and the deposition of unit 3 (Triassic - Jurassic). Rocks of unit 1 have been divided by earlier workers into the Barkerville and Cariboo terranes, separated by the Pleasant Valley Thrust. An extensive review shows that the two terranes are stratigraphically similar and share most of their structural history. The Pleasant Valley Thrust, if it exists, is an extremely early structure. These data do not satisfy the criteria for naming these units 'terranes'. The rocks of unit 1 and 2 experienced an extra phase of deformation not seen in rocks of unit 3. A total of five phases of folding are present. Phases 1 through 4 are approximately coaxial with northwest axes and variably oriented axial planes. Phase 5 has northeast trending axes and vertical axial planes. F₁ is seen in units 1 and 2 only and is visible in outcrop as rootless isoclinal folds and a transposed foliation. In thin section, S₁ is only preserved within the earliest garnet porphyroblasts. F₂ folding is the major deformational event. Peak metamorphism accompanied and outlasted it. Major F₂ folds are present in the field and are accompanied by an axial planar foliation. In thin section, S₂ wraps around earlier porphyroblasts but is overgrown by later ones (staurolite, kyanite). F₃ folding is responsible for the major map-scale structures. It postdated the peak of metamorphism and isograds axe folded by it. In thin section S₃ is commonly a crenulation cleavage or transposed foliation. Some late mineral growth accompanied the early stages of F₃. F₄ and F₅ are buckle folds and kinks and may be conjugate fold sets from a single deformational event. They are not generally visible in thin section. The assemblage silica - garnet - aluminosilicate - mica (SGAM) is common in amphibolite grade meta-pelitic rocks, and can be used as a thermobarometer if the activities of muscovite and biotite can be calculated accurately. A new method of calculating the ideal activity of mica components is proposed. Standard models do not adequately account for the degree of coupled substitution that takes place. The proposed method stores the site occupancies in a 4-dimensional array and manipulates the entries to satisfy three criteria. 1: That non-permitted ionic configurations (species) have an activity of zero. 2: That the sum of all activities is unity. 3: That the sum of all activities of species containing a particular ion in a particular site is the site occupancy of that ion. The method is computationally simple and yields activity values that satisfy the distribution of species equations of an ideal complex solution model. Standard state properties for annite and Margules solution parameters for biotite are determined using mathematical programming techniques on published experimental and natural assemblage data. Published volume data indicate that Fe-Mg mixing in biotite is ideal. The data permit the calculation of four Margules parameters (MgTi, FeTi, MgAl, FeAl). The differences MgTi - FeTi and MgAl - FeAl are similar to those found by previous workers but the treatment of the data suggests moderately large individual values for the Margules parameters (up to 75 kJ/mol). Using these activity models the SGAM thermobarometer is applied to several sets of published analyses which show that this calibration offers distinct improvements over previous calibrations. Pressures determined using the new calibration are consistent with other barometers and the aluminosilicate polymorph present. In addition, several data sets show field gradients, particularly in P, not previously recognized and which agree with field observations. The SGAM barometer applied to the analytical data from the Quesnel Lake area yields pressures and temperatures that are consistent with the mapped isograds. The pressure and temperature gradients indicate that the final setting of the thermobarome-ter was diachronous across the area and during the early stages of F₃ folding. Hot rocks in cores of anticlines 'set' at later times and at shallower depths than cooler rocks in adjacent synclines. Tight spacing of isograds is more consistent with post-metamorphic folding than with high thermal gradients. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate