The massive 53.6 Ma Flat Creek granitic pluton of the Nisling Plutonic Suite intrudes flat-lying volcanic rocks of the 70 Ma Carmacks Group in the Stikine Terrane of the Intermontane Belt in the Yukon. Specimens (n = 334) from 22 sites in granite from the ~100 km2 pluton plus 3 sites in cross-cutting 51.1 Ma Eocene andesitic dikes were tested using alternating field and thermal step demagnetization and magnetic susceptibility and saturation isothermal measurements. Magnetite was the sole important characteristic remanent magnetization (ChRM) carrier. Most granitic and andesitic specimens carried a lower temperature and coercivity normal-polarity AN ChRM and an antiparallel higher temperature and coercivity reversed AR component, but some specimens of both rock types carried just AR and some granitic specimens carried just AN components. Combining the AN and AR directions, the granite pluton yielded a mean direction of declination (D) = 165.2°, inclination (I) = −76.8°, (number of sites [N] = 31, radius of cone of 95% confidence [α95] = 2.2°, precision parameter [k] = 139) and the dikes a mean D = 158.0°, I = −79.5°, (N = 3, α95 = 6.0°, k = 423). Paleomagnetic contact tests proved inconclusive because of the contemporaneous and dual polarity remanence of the specimens. The pluton's paleomagnetic pole indicates a nonsignificant northward displacement of 0.8° ± 4.6° and a significant clockwise rotation of 14° ± 10° for the Stikine Terrane relative to the North American craton after ca. 54 Ma. Regression analysis of ≤;54 Ma paleomagnetic motion estimates for all Intermontane terranes against time also shows nonsignificant translation with a significant rotation rate of 0.34° ± 0.11°/m.y. This implies that the Intermontane terranes since ca. 54 Ma have behaved as a quasi-coherent upper crustal plate that rotated atop a North American cratonic lower crust about a proximal near-vertical axis. It is speculated that the rotation was marked by westward extension in southern British Columbia and by eastward compression in the northern Cordillera, together amounting to ~550 ± 160 km of displacement orthogonal to the stable cratonic margin. The compression component in the north, driven by Pacific plate subduction and collision of the Yakutat terrane, is the suggested cause of arcuate orogenic uplift in the Mackenzie Mountains.
The Tombstone, Mayo and Tungsten plutonic suites of granitic intrusions, collectively termed the Tombstone-Tungsten Belt, form three geographically, mineralogically, geochemically and metallogenically distinct plutonic suites. The granites (sensu lato) intruded the ancient North American continental margin of the northern Canadian Cordillera as part of a single magmatic episode in the mid-Cretaceous (96-90 Ma). The Tombstone Suite is alkalic, variably fractionated, slightly oxidised, contains magnetite and titanite, and has primary, but no xenocrystic, zircon. The Mayo Suite is sub-alkalic, metaluminous to weakly peraluminous, fractionated, but with early felsic and late mafic phases, moderately reduced with titanite dominant, and has xenocrystic zircon. The Tungsten Suite is peraluminous, entirely felsic, more highly fractionated, reduced with ilmenite dominant, and has abundant xenocrystic zircon. Each suite has a distinctive petrogenesis. The Tombstone Suite was derived from an enriched, previously depleted lithospheric mantle, the Tungsten Suite is from the continental crust including, but not dominated by, carbonaceous pelitic rocks, and the Mayo Suite is from a similar sedimentary crustal source, but is mixed with a distinct mafic component from an enriched mantle source.
Research Article| September 01, 2002 Absolute timing of sulfide and gold mineralization: A comparison of Re-Os molybdenite and Ar-Ar mica methods from the Tintina Gold Belt, Alaska David Selby; David Selby 1Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada Search for other works by this author on: GSW Google Scholar Robert A. Creaser; Robert A. Creaser 1Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada Search for other works by this author on: GSW Google Scholar Craig J.R. Hart; Craig J.R. Hart 2Yukon Geology Program, Box 203 (F-3), Whitehorse, Yukon Y1A 2C6, Canada Search for other works by this author on: GSW Google Scholar Cameron S. Rombach; Cameron S. Rombach 3Department of Geology and Geophysics, University of Alaska Fairbanks, P.O. Box 755780, Fairbanks, Alaska 99775-5780, USA Search for other works by this author on: GSW Google Scholar John F.H. Thompson; John F.H. Thompson 4Teck Cominco Limited, Suite 600-200 Burrard Street, Vancouver, British Columbia V6C 3L9, Canada Search for other works by this author on: GSW Google Scholar Moira T. Smith; Moira T. Smith 4Teck Cominco Limited, Suite 600-200 Burrard Street, Vancouver, British Columbia V6C 3L9, Canada Search for other works by this author on: GSW Google Scholar Arne A. Bakke; Arne A. Bakke 5Fairbanks Gold Mining Inc., P.O. Box 73726, Fairbanks, Alaska 99707, USA Search for other works by this author on: GSW Google Scholar Richard J. Goldfarb Richard J. Goldfarb 6U.S. Geological Survey, Box 25046, MS 964, Denver Federal Center, Denver, Colorado 80225-0046, USA Search for other works by this author on: GSW Google Scholar Author and Article Information David Selby 1Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada Robert A. Creaser 1Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada Craig J.R. Hart 2Yukon Geology Program, Box 203 (F-3), Whitehorse, Yukon Y1A 2C6, Canada Cameron S. Rombach 3Department of Geology and Geophysics, University of Alaska Fairbanks, P.O. Box 755780, Fairbanks, Alaska 99775-5780, USA John F.H. Thompson 4Teck Cominco Limited, Suite 600-200 Burrard Street, Vancouver, British Columbia V6C 3L9, Canada Moira T. Smith 4Teck Cominco Limited, Suite 600-200 Burrard Street, Vancouver, British Columbia V6C 3L9, Canada Arne A. Bakke 5Fairbanks Gold Mining Inc., P.O. Box 73726, Fairbanks, Alaska 99707, USA Richard J. Goldfarb 6U.S. Geological Survey, Box 25046, MS 964, Denver Federal Center, Denver, Colorado 80225-0046, USA Publisher: Geological Society of America Received: 06 Feb 2002 Revision Received: 08 May 2002 Accepted: 10 May 2002 First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2002) 30 (9): 791–794. https://doi.org/10.1130/0091-7613(2002)030<0791:ATOSAG>2.0.CO;2 Article history Received: 06 Feb 2002 Revision Received: 08 May 2002 Accepted: 10 May 2002 First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation David Selby, Robert A. Creaser, Craig J.R. Hart, Cameron S. Rombach, John F.H. Thompson, Moira T. Smith, Arne A. Bakke, Richard J. Goldfarb; Absolute timing of sulfide and gold mineralization: A comparison of Re-Os molybdenite and Ar-Ar mica methods from the Tintina Gold Belt, Alaska. Geology 2002;; 30 (9): 791–794. doi: https://doi.org/10.1130/0091-7613(2002)030<0791:ATOSAG>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract New Re-Os molybdenite dates from two lode gold deposits of the Tintina Gold Belt, Alaska, provide direct timing constraints for sulfide and gold mineralization. At Fort Knox, the Re-Os molybdenite date is identical to the U-Pb zircon age for the host intrusion, supporting an intrusive-related origin for the deposit. However, 40Ar/39Ar dates from hydrothermal and igneous mica are considerably younger. At the Pogo deposit, Re-Os molybdenite dates are also much older than 40Ar/39Ar dates from hydrothermal mica, but dissimilar to the age of local granites. These age relationships indicate that the Re-Os molybdenite method records the timing of sulfide and gold mineralization, whereas much younger 40Ar/39Ar dates are affected by post-ore thermal events, slow cooling, and/or systemic analytical effects. The results of this study complement a growing body of evidence to indicate that the Re-Os chronometer in molybdenite can be an accurate and robust tool for establishing timing relations in ore systems. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
The Late Cretaceous Carmacks Group, a thick subaerial volcanic succession that once covered much of southwest Yukon, was deposited on an uplifted terrane and is divisible into a lower fragmental unit and an upper flood basalt unit. Coeval hydrothermal activity resulted in widespread alteration and gold mineralization. The lavas are shoshonites, enriched in large ion lithophile and light rare earth elements, but depleted in high field strength elements. Ankaramitic absarokite flows in the upper Carmacks Group range up to 15 wt% MgO, requiring a high liquidus temperature (1400 °C at 1 bar, dry). High K 2 O contents (>3%) of these magnesian lavas indicate that the potassic character of the volcanic suite was established in the mantle. Although previously interpreted as subduction related, the Carmacks Group was erupted during a Cordilleran-wide magmatic lull and lacks coeval calc-alkalic batholiths. The lavas are petrologically similar to plume-related Eocene to Pliocene potassic lavas of the western United States. New paleomagnetic collections, combined with previous work, place the Carmacks Group 17.2° ± 6.5° (1900 ± 700 km) south of its present position relative to the craton during deposition, near the paleolocation of the Yellowstone hotspot. The spatial coincidence, similarity of tectonic setting, and lithologic similarity of the Carmacks Group and Yellowstone volcanic successions suggest that the Carmacks Group is the 70 Ma effusion of the Yellowstone hotspot. Subsequent northward displacement of the Carmacks Group is attributed to coupling with the Kula plate. Correlation of the Carmacks Group and the Yellowstone hotspot fixes the paleolatitude and the paleolongitude of the terranes of the northern Intermontane belt at 70 Ma.
Aquamarine of distinctly dark blue color was discovered during the summer of 2003 in the Pelly Mountains, southern Yukon Territory, Canada. The beryl is found within quartz veins that fill sigmoidal tension gashes, which cut a syenite of Mississippian age. The True Blue showing is differentiated from other beryl occurrences in the northern Cordillera by the color of the beryl, the host rock, mineral associations, timing, and mineralizing fluid. The syenite was emplaced within an extensional setting into undeformed Paleozoic sediments of the Cassiar Platform and felsic volcanic rocks of the Pelly Mountain Volcanic Belt. Post-late-Triassic tectonics resulted in a number of northeasterly directed thrust panels that were subsequently cut by Cretaceous granitic magmatism. Accessory minerals in the veins include siderite, ankerite, allanite-(Ce), fluorite, and minor albite, sulfides, and Fe–Ti–Nb oxides. Electron-microprobe analyses of beryl ( n = 192) revealed that FeO values range up to 5.92 wt.%, Na 2 O up to 2.66 wt.%, MgO up to 3.42 wt.%, CaO up to 0.11 wt.%, and H 2 O (calculated) up to 3.10 wt.%, whereas little to no Cr or V was detected. The darkest blue examples of beryl also have the highest concentrations of FeO. The allanite-(Ce) contains up to 26 wt.% REE 2 O 3 , and exhibits Fe 2+ > Fe 3+ . The fluorite that coprecipitated with beryl from several veins has been dated using Sm–Nd geochronology at 171.4 ± 4.8 Ma. In situ and whole-mineral δ 18 O values of the beryl and whole-mineral δ 18 O values of the quartz are variable; temperature estimates derived from these data suggest fluid temperatures between ~275 and ~400°C. Fluid-inclusion data from quartz, beryl, and fluorite suggest variable but high salinity (~6 to 24 wt.% NaCl equivalent) and CH 4 -absent mineralizing fluids. Conventional models to explain the formation of gem beryl, and consequently exploration parameters, applied in Yukon involve late-stage magmatic fluids. Evidence gathered in this study points to a metamorphic origin for the mineralizing fluid and a local derivation of vein constituents, which distinguish the fluids at True Blue from other intrusion- related beryl-forming fluids in the northern Cordillera.
Miles Canyon basalt is an informal term used to describe numerous exposures of young alkaline olivine basalt flows in southern Yukon. The volcanic rocks are part of the Northern Cordilleran volcanic province. K-Ar and Ar-Ar whole-rock dates indicate that the Miles Canyon succession of flows at the Whitehorse Rapids are clearly Late Miocene in age (ca. 8.4 Ma). The largest exposure of the Miles Canyon basalt occurs at the Alligator Lake volcanic complex where two nearly concordant Pliocene Ar-Ar dates indicate eruption at ca. 3.2 Ma. K-Ar analyses from other sites yield dates of 2.4 and 7.1 Ma and indicate an episodic Neogene volcanic history for the region. There is no evidence of Quaternary or postglacial volcanism. The dates are older than assumed by previous workers, and in some cases the K-Ar dates are strongly discordant from Ar-Ar determinations. More accurate Ar-Ar determinations may result from the method's ability to select smaller amounts of better material for analysis. Excess 40 Ar was not encountered. As a result, the accuracy of any single or several discordant K-Ar determinations for Neogene subaerial volcanic rocks, particularly low-K rocks such as basalts, should be questioned and resulting interpretations made with caution. Models accounting for the eruption of the Northern Cordilleran volcanic province lavas have typically relied upon extension along north-trending faults that were generated by stresses along the continental margin. However, we consider a slab window model which better accounts for the initiation and distribution of northern Cordilleran Neogene volcanic activity.
Mihir Deb and Richard J. Goldfarb, Editors. Pp. 309. 2010. Alpha Science International Ltd. Oxford. ISBN 978-1-84265-646-4. Price £150.00.
India has an extraordinarily strong historical, religious, and cultural association with gold since mining of the precious metal has been documented to have occurred there as long as 4,000 years ago. Currently, India has the highest consumption of consumer gold of any country on the planet, at approximately 1,000 t/year. However, gold production remains dismally small, with perhaps only 3 to 4 t/year recovered during modern times, and only as much as ~20 t/year during its contemporary apogee about 100 years ago. This massive gap will widen further as economic prosperity brings greater disposable income to India’s burgeoning middle class, and production shows no signs of increasing. The lack of any likely near-future increase in production for India has its roots in an historically inadequate minerals policy, poor geoscience datasets, and bureaucratic administrative shenanigans. India consistently ranked amongst the lower percentiles on all questions dealing with policy or data availability in the Fraser Institute’s 2009–2010 Survey of Mining Companies, In which it kept company with other mining-unfriendly regimes such as those in Zimbabwe, Venezuela, and Washington state (although India was just dropped from the list in 2010).
It was with this background that Prof. Mihir Deb hosted a field workshop in December 2008 to bring researchers, explorers, and government officials together to …
'/%3e%3c/defs%3e%3cpath fill='%23012169' d='M0 0h10080v5040H0z'/%3e%3cpath stroke='%23fff' stroke-width='.6' d='m0 0 6 3m0-3L0 3' clip-path='url(%23b)' transform='scale(840)'/%3e%3cpath stroke='%23e4002b' stroke-width='.4' d='m0 0 6 3m0-3L0 3' clip-path='url(%23c)' transform='scale(840)'/%3e%3cpath stroke='%23fff' stroke-width='840' d='M2520 0v2520M0 1260h5040'/%3e%3cpath stroke='%23e4002b' stroke-width='504' d='M2520 0v2520M0 1260h5040'/%3e%3cg fill='%23fff'%3e%3cuse xlink:href='%23d' x='2520' y='3780'/%3e%3cuse xlink:href='%23a' x='7560' y='4200'/%3e%3cuse xlink:href='%23a' x='6300' y='2205'/%3e%3cuse xlink:href='%23a' x='7560' y='840'/%3e%3cuse xlink:href='%23a' x='8680' y='1869'/%3e%3cuse xlink:href='%23e' x='8064' y='2730'/%3e%3c/g%3e%3c/svg%3e)
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)