Download or read book Mid Cretaceous Plutonic related Gold Deposits of Interior Alaska written by Daniel Thomas McCoy and published by . This book was released on 2000 with total page 354 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Mid-cretaceous gold deposits in interior Alaska are hosted in or near apices of low magnetite plutons that are formed in a broad continental arc. Ore is hosted in 1) anastomosing quartz veins with potassic or albitic envelopes, 2) planar veins and shear zones with sericitic alteration, and 3) pyroxene-rich skarn deposits. This study was undertaken to constrain the fluid and metal source and composition, formation conditions, gold associative mineralogy, age relationships, and areal extent of this mineralizing event. Techniques included reflected light petrographic, 40Ar/39Ar step-heating, stable isotope, fire assay, Mossbauer spectroscopy, electron microprobe, and scanning ion mass spectroscopy analysis. Results suggest ages between 85 Ma and 107 Ma with a 0 to 2 million-year differential between magmatic biotite and hydrothermal veins in the same deposits. Deposits are 10 t0 20 million years younger than local metamorphism. Fluid calculated stable isotopic ratios (ð13C = -9 to -10 per mil; ð18O = 5-10 per mil; ðD = -47 to -100; ð34S = -5 to +5 per mil) suggest gold precipitated from magmatic fluids. Fluid inclusions in ore-bearing quartz contain high CO2 with trapping temperatures and pressures of 270 ̊to 570C̊ and 0.5 to 2 kb respectively. The Fort Knox and Pogo deposits have a strong Au-Bi association and high relative amounts of potassic and albitic alteration with mineralogical evidence for the original existence of maldonite (Au2Bi) or Au-Bi melt subsequently overprinted by native gold + bismuthinite. The True North deposit has a strong Au-As association and no Au-Bi association. It lacks potassic or albitic alteration and contains only sub-micron gold; approximately half chemically bound to arsenopyrite or arsenian pyrite. The Dolphin and Ryan Lode deposits are intermediate in Au-Bi association, gold-associative mineralogy and alteration features. Arsenopyrite geothermometry yield temperatures between 300 ̊and 630C̊ for albitic and potassic alteration and between 250 ̊and 420C̊ for sericitic alteration. 40Ar/39Ar dating and metal ratios suggest that gold mineralization is 1) solely mid-Cretaceous in the Fairbanks mining district, 2) mid-Cretaceous and late Cretaceous in the Kantishna mining district, and 3) mid-Cretaceous and early Tertiary in the Livengood mining district"--Leaves iii-iv.

Download or read book Mineral Deposits of Alaska written by R. J. Goldfarb and published by . This book was released on 1997 with total page 496 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Data for Plutonic Rocks and Associated Gold Deposits in Interior Alaska written by Rainer J. Newberry and published by . This book was released on 1995 with total page 122 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Geologic Studies in Alaska by the U S Geological Survey 1996 written by John E. Gray and published by . This book was released on 1998 with total page 212 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Geologic Studies in Alaska by the U S Geological Survey 1996 written by and published by . This book was released on 1998 with total page 216 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Tintina Gold Belt written by and published by . This book was released on 2000 with total page 244 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book U S Geological Survey Professional Paper written by and published by . This book was released on 1984 with total page 368 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Gold and Base Metal Mineralization of the Dolphin Intrusion related Gold Deposit Fairbanks Mining District Alaska written by Luke M. Raymond and published by . This book was released on 2018 with total page 166 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Dolphin deposit is an intrusion-related gold deposit (IRGD) located approximately 30 km north of Fairbanks, Alaska. The deposit is in--and adjacent to--a composite mid-Cretaceous pluton intruding amphibolite facies metamorphic rocks. An NI43-101 compliant gold resource estimation for the deposit (utilizing a 0.3 g/t cut-off grade) is 61.5 Million tonnes (Mt) at 0.69 g/t indicated (1.36 million oz = Moz) and 71.5 Mt at 0.69 g/t inferred (1.58 Moz). Due to extensive hydrothermal alteration of the intrusion, identifying rock types in hand sample and thin section, as well as by standard compositional techniques (e.g., SiO2 vs. Na2O + K2O), has proven problematic. By plotting wt % TiO2 vs. P2O5 obtained from XRF analyses and four-acid digest ICP-MS data, two distinct population clusters appear. By comparison with least-altered intrusive rock analyses from the Fairbanks district, the igneous units were originally granite and tonalite. Because there is no gradational transition through an intermediate granodiorite unit, they were most likely derived from two separate magmatic bodies rather than in-situ fractionation from a single parent. Tonalite is concentrated along the northern and eastern margins of the stock with granite composing the rest of the body. Tonalite xenoliths in granite and granite dikes intruding tonalite prove that tonalite is the older unit. Investigations of hydrothermal alteration (based on chemical analyses, X-ray diffraction, and thin section examination) show albitic and advanced argillic (kaolinite-quartz) alteration are the dominant styles with sericite common throughout. Advanced argillic is a low temperature (

Download or read book Quartz Normative Plutonic Rocks of Interior Alaska and Their Favorability for Association with Gold written by L. E. Burns and published by . This book was released on 1991 with total page 84 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Placer Gold Deposits of the Eagle Trough Upper Yukon River Region Alaska written by James C. Barker and published by . This book was released on 1986 with total page 32 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Evaluation of Selected Lode Gold Deposits in the Chugach National Forest Alaska written by Robert B. Hoekzema and published by . This book was released on 1987 with total page 72 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Gold in Placer Deposits written by Warren E. Yeend and published by . This book was released on 1990 with total page 28 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Geology of Bulk minable Plutonic hosted and Plutonic related Gold Deposits of the North Pacific written by Rainer Newberry and published by . This book was released on 1997 with total page 277 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Fifth Hutton Symposium written by Shuns? Ishihara and published by Geological Society of America. This book was released on 2005-01-01 with total page 391 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Professional Report written by and published by . This book was released on 1982 with total page 128 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Short Notes on Alaskan Geology written by and published by . This book was released on 1995 with total page 556 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Geochemical Spatial and Temporal Relationships of the Intrusives and Meta intrusives of the Pogo Deposit Eastern Interior AK written by William Daniel Thompson and published by . This book was released on 2020 with total page 276 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Pogo deposit is an intrusion-related gold deposit (IRGD) located approximately 90 km southeast of Fairbanks, Alaska. It consists mainly of shallowly NW dipping quartz veins hosted in amphibolite facies paragneiss and predominately granite orthogneiss bodies. To date the deposit has produced over 4 million ounces of gold. U-Pb zircon dating of the orthogneisses shows they have Devonian-Mississippian protolith ages. Dates from the metamorphic zircons, established by microprobe Th data and cathodoluminescence studies, constrain a mid-Cretaceous metamorphic event to ~116 Ma. Recrystallization of kyanite to sillimanite and zircon recrystallization indicates this was a large fluid flux event that predated mineralization by 10 million years. Due to the fine-grained nature of the intrusive rocks at Pogo, identifying rocks in hand sample proved problematic. By combining XRF analysis of the rocks' major and trace elements and age data from this and previous studies, I identified and differentiated several suites of igneous rocks. The oldest is peraluminous granite, emplaced at ~2.5 ± 0.5 kb at ~109-107 Ma, predating mineralization at 104 Ma at a pressure of 2.0 kb. Non-peraluminous granite is less common and of uncertain relationship to the peraluminous granite. Next, temporally, is a body named the Football pluton (and associated dike) of granodioritic to tonalitic composition, emplaced at 2.0 ± 0.5 kb at 103 ± 2 Ma. Not only indistinguishable from age and depth of mineralization, a dike of this body is present downdip underneath the Liese veins (main zone of mineralization), making it the most likely candidate for being the causative pluton for mineralization. The final mid-Cretaceous body is the Liese pluton (and associated dikes), of quartz diorite to tonalite. This forms a large body with E-W dikes cutting the Pogo mineralization and post-dating it at 95.4 ± 0.2 Ma, emplaced at a pressure of 1.0 kb. Thermobarometry and radiometric dating indicate a consistent uplift rate of about 0.6 mm/year during the mid-Cretaceous, 116 to 95 Ma. Initially an extensional event, subduction-related magmatism began at about 105 Ma. At the same time, the thrust faults were re-activated as low angle normal faults that apparently acted as pathways for the Liese mineralization.