The Dolly Varden camp, Alice Arm area, northwestern British Columbia, is characterized by stratiform and volcanogenic silver-lead-zinc-barite deposits in Early to Middle Jurassic calc-alkaline volcanic rocks of the Hazelton Group. These deposits, containing exceptional silver and significant base metal values, are in andesitic tuffaceous rocks, and occur typically as layers of quartz, carbonate, barite and jasper, with lesser amounts of pyrite, sphalerite and galena, and sparse chalcopyrite. Production from three deposits, the Dolly Varden, Northstar and Torbrit mines, totaled 1,284,902 tonnes of ore that averaged 484g silver per tonne, 0.38 percent lead and 0.02 percent zinc. The Hazelton Group is a thick, widespread assemblage of basaltic to rhyolitic volcanic flow rocks, their tuffaceous equivalents, and derived sedimentary rocks. Dolly Varden camp is underlain by more than 3,000m of Hazelton Group rocks comprised of one major volcanic and one major sedimentary formation. Volcanic rocks underlie sedimentary rocks and have been subdivided into footwall and hangingwall units based on stratigraphic position relative to the mineralized stratiform horizon. Footwall volcanic rocks consist of green ± maroon basaltic-andesite tuff, green ± maroon porphyritic andesite and green andesite shard tuff. Stratiform mineralization rests conformably upon the underlying green andesite shard tuff. Hangingwall volcanic rocks above the stratiform layer consist of pale grey basaltic-andesite ash tuff, maroon basaltic-andesite ash-lapilli tuff, grey-green porphyritic andesite, and pale green andesite ash tuff. Hangingwall volcanics are unconformably capped by sedimentary rocks consisting of maroon siltstone, calcareous and fossiliferous wacke, and black siltstone and shale; black siltstone and shale form the youngest rock unit of the Hazelton Group in the Dolly Varden area. Basalt and lamprophyre dykes intrude all rocks of the Hazelton Group. The rocks of the Hazelton group exposed in the Dolly Varden camp are folded into a series of anticlines and synclines with gentle, northwestern plunges. Two major sets of nearly vertical block faults cut all rock units; earlier faults trend northwest and younger faults trend north-northeast. Geological mapping, combined with petrologic, petrographic and isotopic data, indicate that the stratiform deposits probably formed as submarine exhalative deposits associated with andesitic volcanism of the Hazelton Group during the Early to Middle Jurassic. Evidence for a volcanogenic origin is the conformity of layered mineralization with stratigraphy, lateral and vertical mineral zonation patterns, consistent hangingwall versus footwall contact relationships, fragments of stratiform ore within tuffaceous volcanic rocks of the hangingwall, consistent differences in the stable isotopic compositions between the sulfides versus barite, quartz and carbonate gangue, and the Jurassic "fingerprint" for the lead-bearing deposits of the Dolly Varden camp. The Dolly Varden deposits display criteria for classification of a new, previously unrecognized, stratiform and volcanogenic, deposit type, named here, the "Dolly Varden type", and is characterized by silver-rich, low sulfide and high oxide stratiform mineralization within andesitic volcanic rocks. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Copper-silver mineralization at Sam Goosly occurs as a conformable lens within pyroclastic dacites of probable late early Cretaceous age. Most mineralization is contemporaneous with development of aluminous alteration minerals. Distribution zones of scorzalite, andalusite, and an innermost corundum zone, are concentric and broadly outline the mineralized zone. Southwards, along strike, the andalusite zone becomes an andalusite-pyrophyllite zone in which mineralization post-dates aluminous alteration. Regional metamorphlsm has overprinted a propylitic, or greenschist, assemblage on aluminous alteration. Country rocks and mineralization are intruded by two stocks: a 59 ± 3 m.y. quartz monzonite to the west of the ore zone, and a 51 ± 3 m.y. gabbro-monzonite stock to the east. Contact metamorphlsm associated with the gabbro-monzonite has produced a narrow, discontinuous zone of biotite hornfels and recrystallized metallic minerals in the ore zone. Alteration mineral assemblages and sulphide exsolution textures imply temperatures between 350°C and 625°C in the main ore zone. The assemblage andalusite-pyrophyllite-quartz indicates alteration temperatures of about 350°C in the andalusite-pyrophyllite zone. Chemical analysis of the altered volcanic host rocks suggests significant loss of soda and lime, and residual concentration of silica and alumina. These chemical changes probably result from exchange of Na⁺ and Ca⁺⁺ for H⁺ from a hydrothermal fluid, resulting in formation of aluminous minerals and quartz. The value of log mK+/mH+ of the fluid phase is deduced to be between 1 and 2. By analogy with other occurrences, this process probably takes place in a high-temperature solfataric, or geothermal environment. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The Owl Head mining District is located in south-central Pinal County, Arizona, within the Basin and Range province. Land forms, particularity pediments, characteristic of this province are abundant in this area. Precambrian rocks of the Owl Head mining district include the Pinal schist; gneiss; intrusions of granite, quartz monzonite and quartz diorite; and small amounts of Dripping Spring quartzite and metamorphosed Mescal limestone. These have been intruded by dikes and plugs of diorite and andesite, and are unconformably overlain by volcanic rocks and continental sedimentary rocks of Tertiary and Quaternary age. No rocks of the Paleozoic and Mesozoic eras have been recognized. The structural trends of the Owl Head mining district probably reflect four major lineament directions. The dominant structural trends found in the area are north and northwest. Subordinate to these directions are northeast and easterly trends. The strike of the northerly trend varies from due north to N30°E and was probably developed during the Mazatzal Revolution. The northwest trend has probably been superposed over the northerly trend at some later date. Copper mineralization is abundant in the area and prospecting by both individuals and mining companies has been extensive. To date no ore body of any magnitude has been found, but evidence suggests that an economic copper deposit may exist within the area. The copper mineralization visible at the surface consists mainly of the secondary copper minerals chrysocolla, malachite, azurite, and chalcocite with chrysocolla being by far the most abundant. Copper minerals are found to occur in all rocks older than middle Tertiary age. Placer magnetite deposits are found in the alluvial material of this area, and one such deposit is now being mined.

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

M.S.

The Big Horn Mountains are a geologically complex range that extends over 500 square km in west-central Arizona. Three major lithologic terranes outcrop: (1) Proterozoic amphibolite, phyllite, schists, gneiss, and granite; (2) Mesozoic monzonite to diorite intrusives; and (3) Cenozoic mafic to silicic volcanic rocks and clastic rocks. The entire area is in the upper plate of a detachment fault and, consequently, contains many low- to high-angle normal faults. Each lithologic terrane has its associated mineral occurrences. The Big Horn district is exclusively hosted in the pre- Tertiary terrane. Most of its mineral occurrences are spatially related to the Late Cretaceous intrusive rocks. One occurrence, the Pump Mine, may be a metamorphic secretion deposit, and therefore, would be middle Proterozoic. The vast majority of the mineral occurrences in the Big Horn Mountains are middle Tertiary in age and occur in three districts: the Tiger Wash barite - fluorite district; the Aguila manganese district; and the Osborne base and precious metal district. Fluid inclusions from Tiger Wash fluorite (T(h) 120 to 210° C, NaCl wt. equivalent 17 to 18 percent not corrected for CO₂) and nearby detachment - fault- hosted Harquahala district fluorite (T(h) 150 to 230° C., NaC1 wt. equivalent 15.5 to 20 percent not corrected for CO₂) suggest cooling and dilution of fluids as they are presumed to evolve from the detachment fault into the upper plate. Mass-balance calculations suggest that the proposed evolution of fluids is sufficient to account for the observed tonnage of barite and fluorite. The Tiger Wash occurrences grade directly into calcite- gangue-dominated manganese oxides of the Aguila district. A wide range of homogenization temperatures (T(h) 200 to 370° C.), an absence of CO₂ and low salinities (NaC1 wt. equivalent 1 to 2 percent) in the Aguila district calcite-hosted fluid inclusions argue for distillation of fluids during boiling or boiling of non saline-meteoric waters. Mass - balance calculations modeling the evolution of Ca and Mn during potassium metasomatism of plagioclase in basalt suggest that little if any influx of these cations is necessary to form the calcite –dominated manganese oxide tonnage observed. The Aguila district grades directly to the east into the base-metal and precious-metal occurrences of the Osborne district. Preliminary data describing geological settings, fluid inclusions, and geochemistry suggest that the Osborne district has a continuum between gold-rich to silver-rich epithermal occurrences. The gold-rich systems have dominantly quartz gangue, with or without fluorite, and are hosted in a variety of rocks, but are proximal to Precambrian phyllite or mid-Tertiary rhyolite. Fluid inclusions from two occurrences representative of the gold -rich systems spread across a minor range (T(h) 190 to 230° C., NaC1 wt. equivalent 17 to 23 percent not corrected for CO₂). Dilution of highly saline fluids is the inferred mechanism for precipitation of gold in the gold-quartz systems. The silver-rich systems have dominantly calcite gangue with or without quartz, and are hosted in mid-Tertiary basalt. Calcite fluid inclusions from a representative high-silver occurrence display a wide range of homogenization temperatures and salinities (T(h) 120 to 370° C., NaC1 wt. equivalent 7 to 23 percent). Boiling and consequent neutralization of acidic solutions is the inferred mechanism for the silver-rich, calcite gangue systems. A model inferring a regional fluid-flow regime and local sources of metals is proposed. Four possible regional and local causes of fluid flow in upper-plate detachment regimes are proposed: (1) regional elevation of geothermal gradients as a result of middle-crustal, lower-plate rocks rising to upper crustal levels; (2) meteoric water recharge along the southeast flank of the Harquahala antiform and consequent displacement of connate waters in the upper-plate of the Big Horn Mountains; (3) local emplacement of feeder stocks to rhyolitic flows; (4) and tilting of major upper-plate structural blocks.