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Petrology and geochemistry of the Pattison Alaskite Pluton, Yukon
The Pattison Pluton is a high level Tertiary subaluminous alaskite that is part of a northwest trending chain of igneous intrusions in the Yukon Crystalline Terrane, southwestern Yukon. It is roughly circular in form with a diameter of about 18 km and a funnel-like profile. Crosscutting it are a series of shallowly dipping aplite dykes which intruded into open fractures. Compositionally and mineralogically, the alaskite body and aplite dykes are very uniform but the pluton is texturally and gradationally divided into a fine-grained upper border phase, a medium-grained graphic, strongly miarolitic, weakly porphyritic phase, and a lower coarse-grained phase. Due to eutectic crystallization, no strong major element trends are found within the pluton and dykes. Trace element chemistry, however, shows an apparent liquid line of descent with the fine grained alaskite the least differentiated and the aplite dykes the most differentiated. The medium and coarse-grained alaskites plot in between these. Rayleigh fractional crystallization of alkali feldspar accounts for these trends. Textural zonation evolved by the initial chilling of the originally H2O-poor magma at its upper edges. Crystallization of anhydrous phases from the melt had the effect of increasing the volatile pressure within the enclosed chamber. The volatiles migrated to and concentrated in the upper regions where the melting temperature was depressed, causing the pluton to crystallize from the bottom up. This allowed for the lower regions to reach more advanced stages of phenocryst crystallization, hence forming the lower coarse-grained alaskite. The volatile pressure eventually exceeded the confining pressure, resulting in failure of the surrounding rocks and retorgrade boiling, as well as vertical extension and lateral injection of residual magma due to filter pressing to form the aplite dykes. This final series of events also resulted in the formation of the graphic groundmass, straining of the minerals within the pluton, brecciation of some of the surrounding rocks, as well as quartz veining and molybdenum mineralization.
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The petrology of Nisling and Ruby Range volcanic and plutonic rocks, Yukon Territory
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Petrology and geochemistry of tin and tungsten mineralized plutons, McQuesten River Region, Central Yukon
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Mid-Cretaceous plutons in the McQuesten River region intrude Upper Proterozoic to Mississippian miogeoclinal metasedimentary rocks of Selwyn Basin. They form a belt trending east from the Tintina Trench which can be roughly subdivided into two parallel belts. Plutonic rocks fall into three main groups: 1) biotite-muscovite (two-mica) granite in the southernmost belt which follows the trend of the McQuesten Anticline; 2) biotite-hornblende quartz monzonite, granite and granodiorite in the northern belt which follows the thrust faulted contact of the Hyland Group (Grit Unit) with the Road River Formation; and 3) hornblende-biotite syenite and associated quartz syenite, quartz monzonite, granite and tourmaline-orbicular granite along the north edge of the northern belt. Tin-silver breccia veins and skarns are spatially associated with the two-mica granites, while tungsten-gold skarns and sheeted veins are associated with biotite-hornblende granite, quartz monzonite and granodiorite. The concentrically zoned syenite intrusion in the northern belt (ZETA) includes all the plutonic phases (two-mica granite, biotite-hornblende granitoids, and hornblende-biotite syenitoids), and links them cogenetically through the fractional crystallization process. The ZETA tin-silver veins are associated with the tourmaline orbicular granite, which is the most evolved phase of the concentrically zoned ZETA syenite intrusion. Plutons in the McQuesten region resemble those of the Selwyn and Tombstone Plutonic Suites. They are post to syntectonic, roughly circular in shape, and intrude miogeoclinal metasedimentary rocks of ancient North America. They show a concentric zonation and are surrounded by contact aureoles. The intrusive suite is bimodal, with a southern belt consisting of evolved two-mica granites and a northern belt consisting of less evolved biotite-hornblende granites. Lavas associated with the plutons are believed to be coeval.
Yukon Plutonic Suites
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This map shows the distribution of plutonic igneous rocks and selected intrusion-related mineral occurrences in Yukon.
Tectonic significance of plutonism in the Thirtymile Range, southern Yukon
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Two distinct but undeformed suites of granitic plutons intrude deformed siliciclastic rocks in western Dorsey Terrane. A calc-alkaline hornblende-bearing gabbro to granodiorite stock has been dated at 181.5 Ma (by the Rb/Sr method). The second suite consists of highly evolved late-orogenic granites of the Thirtymile stock and Hake Batholith, which are approximately 100 Ma. The penetrative fabric of the metasedimentary rocks indicates generally eastward-vergent layer-parallel shear. The deformation of the siliciclastic rocks is thus constrained at older than 181 Ma. The absence of resetting of the Rb-Sr isotopic ratios of the Jurassic pluton indicates that the mid-Cretaceous magmatism was emplaced at a shallow crustal depth. Since the Jurassic pluton has both a 'juvenile' Sr isotopic ratio of 0.7045 and chemistry indicative of a largely mantle-derived source, a subduction-related setting for magma generation is likely. The spatial relationship of craton-derived clastic rocks and these plutons requires that subduction had an eastward polarity.
A-type granite plutons and tin skarns in southeast Yukon: Mindy prospect and surrounding granite of 105C/9
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In the southeast Yukon, immediately southwest of the mid-Cretaceous Cassiar suite plutons,is a northwest-trending suite of anorogenic one-mica granites called the Seagull suite. This suite is comprised of the Seagull and Hake batholiths, Ork and Thirtymile stocks and an un-named intrusion to the northwest. These B and F enriched granites are associated with various forms of tin mineralization, including skarns. The Mindy prospect in the Thirtymile Range contains a variety of metasomatic silicate and borate and fluoride minerals. Tin (Sn) mineralization is found as cassiterite and borate mineral phases. Mapping has shown that faulting active during metamorphism-metsomatism controlled the distribution of the skarn mineralization. Both mineral chemistry and structural control of mineralization have a significant effect on the economic potential of the Mindy prospect.
Petrology, chemistry, age, and isotope study of the high potassium Emerald Lake Pluton, eastern Yukon Territory
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A copy of this thesis is available at the EMR library – QE446.Y8 S65 1984.
Petrology and mineralogy of the Yukon antimony stibnite deposit, Yukon Territory
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A copy of this thesis is available at the EMR library – QE446.Y8 H94.
Micropetrology and mineral geochemistry of the Tombstone and Deadman plutons, Tombstone Plutonic Suite, central Yukon.
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Micropetrographic observations and mineral geochemistry data, along with previously reported whole-rock geochemistry, defined an A-type granite-affinity for the Tombstone and Deadman plutons of the 120-km-long, mid-Cretaceous Tombstone-Tungsten plutonic belt. This plutonic belt was intruded into the western Selwyn basin, the western-most edge of the ancestral North American craton, and is situated well inboard of any potential subduction-zone plutonism, which is found in the accreted terranes that were juxtaposed with the North American craton during the Jura-Cretaceous. More than a dozen mineral specimens were petrographically observed and five were chemically analysed. Similarities found among the two plutons are their alkalic nature, minimal quartz content, presence of igneous andradite garnets and the presence of rare-earth-bearing minerals. Differences between the two plutons include the fact that the Tombstone pluton contains Th, Ce and La with magnetite and titanite, while the Deadman pluton contains Nd with Ce and La, as well as Ba-rich alkali feldspars. These observations are not commonly found in tectonic-related I- or S-type granitoids, and distinguish the Tombstone plutonic suite as being most similar to A-type granites.
Atlas of Late Triassic to Jurassic plutons in the Intermontane terranes of Yukon
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This Atlas presents an extensive geoscience data set for the Late Triassic to Jurassic plutons that intrude the Intermontane terranes in Yukon. Plutons of this age are associated with significant porphyry Cu ± Au ± Mo deposits in British Columbia. In Yukon, Cu–Au–Ag deposits at Minto and Carmacks Copper are hosted by an Early Jurassic batholith but are not typical porphyry deposits. This project aims to provide the regional framework for Late Triassic to Jurassic plutons and associated mineral occurrences in southern Yukon. We systematically describe over 34 plutons and present new data for most of these, including 47 U-Pb zircon dates, 44 Ar-Ar dates, 187 whole-rock geochemical analyses, 30 whole-rock Sr and Nd isotope analyses, 27 feldspar Pb isotope analyses, zircon Hf isotope analyses for 22 samples and 26 pressure estimates from aluminum-in-hornblende analyses. Complementing these analytical data are extensive photomicrographs, photographs and maps.
Petrology & geology of high level rhyolite intrusives of the Skukum area, 105 D SW, Yukon Territory
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The Skukum area is located 58 km south-southwest of Whitehorse. It is an elliptical area of volcanic rocks, Tertiary in age, and surrounded by hypabyssal rhyolite intrusives. Field and petrographic evidence, fluorite and tourmaline stockwork, breccia pipes, roof pendants, miarolitic cavities and spherulites in the nine Skukum rhyolites suggest that they were emplaced at a high level. The intrusives vary in composition from rhyolite to dacite. The variation in texture within and between the intrusives can be explained by different rates of crystallization, temperature differences and compositional variability. Chemical data are in accord with the expected trends in a cogenetic suite of igneous rocks. Relatively low CaO and MgO, high SiO2 and anomalously low Sr concentrations indicate that the rhyolites were formed from a highly differentiated magma. Sr and Ba versus Al2O3 plots show that both k-feldspar and plagioclase were important fractionating phases. Rare earth element data further support this conclusion and also suggest that some accessory phase(s), such as monazite, allanite or fluorite help control the rare earth element behaviour. Partial melting of an already depleted source rock with residual plagioclase can also explain the patterns. The Bennett Lake ring and associated dykes are petrographically and chemically similar to the Skukum intrusives. However, Zr and TiO2 are present in higher concentrations in the Bennett Lake complex, indicating that they were derived by a slightly different fractionation process.
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