Preliminary geologic map of the Medfra quadrangle, Alaska

Patton, W.W.; Moll, E.J.; Dutro, J. Thomas; Silberman, Miles L.; Chapman, R.M.

doi:10.3133/ofr80811a

Cited by 14 publications

(22 citation statements)

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“…Upper Devonian carbonate and siliciclastic rocks overlie older Devonian strata in areas C through F (Reed and Nelson, 1980;Gilbert, 1981;Bundtzen and Gilbert, 1991;Bundtzen et al, 1994Bundtzen et al, , 1997 and include distinctive minerals such as barite and phosphate that typically form in highly productive oceanographic settings. Rare shallow-water carbonate rocks of Mississippian, Pennsylvanian, Permian, and Triassic ages are found chiefly on and adjacent to the Nixon Fork platform (areas A through C, western area D; Patton et al, 1980;McRoberts and Blodgett, 2002;Gilbert, 1981;Bundtzen et al, 1994).…”

Section: Stratigraphy Of the Mystic Subterranementioning

confidence: 99%

“…2,3). These units include unnamed Permian strata in area A (Patton et al, 1980), the upper part of the Devonian-Permian Sheep Creek Formation (Bundtzen et al, 1997) in area E, and the Permian (and older?) "Mystic assemblage" of Malkowski and Hampton (2014) and the Permian Mount Dall conglomerate (Reed and Nelson, 1980;Sunderlin, 2008) in area F. Late Triassic-Early Jurassic mafic igneous rocks (areas C through F) are intercalated with and overlain by a variety of Triassic and Jurassic sedimentary strata (Reed and Nelson, 1980;Gilbert, 1981;Bundtzen et al, 1994Bundtzen et al, , 1997.…”

Section: Stratigraphy Of the Mystic Subterranementioning

confidence: 99%

“…"Mystic assemblage" of Malkowski and Hampton (2014) and the Permian Mount Dall conglomerate (Reed and Nelson, 1980;Sunderlin, 2008) in area F. Late Triassic-Early Jurassic mafic igneous rocks (areas C through F) are intercalated with and overlain by a variety of Triassic and Jurassic sedimentary strata (Reed and Nelson, 1980;Gilbert, 1981;Bundtzen et al, 1994Bundtzen et al, , 1997. Lower Cretaceous fossiliferous limestone and siliciclastic rocks form the uppermost part of the Mystic in areas A, E, and F (Jones and Silberling, 1979;Patton et al, 1980;Reed and Nelson, 1980).…”

Section: Stratigraphy Of the Mystic Subterranementioning

confidence: 99%

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The Mystic subterrane (partly) demystified: New data from the Farewell terrane and adjacent rocks, interior Alaska

et al. 2018

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The youngest part of the Farewell terrane in interior Alaska (USA) is the enigmatic Devonian-Cretaceous Mystic subterrane. New U-Pb detrital zircon, fossil, geochemical, neodymium isotopic, and petrographic data illuminate the origin of the rocks of this subterrane. The Devonian-Permian Sheep Creek Formation yielded youngest detrital zircons of Devonian age, major detrital zircon age probability peaks between ca. 460 and 405 Ma, and overall age spectra like those from the underlying Dillinger subterrane. Samples are sandstones rich in sedimentary lithic clasts, and differ from approximately coeval strata to the east that have abundant volcanic lithic clasts and late Paleozoic detrital zircons. The Permian Mount Dall conglomerate has mainly carbonate and chert clasts and yielded youngest detrital zircons of latest Pennsylvanian age. Permian quartz-carbonate sandstone in the northern Farewell terrane yielded abundant middle to late Permian detrital zircons. Late Triassic-Early Jurassic mafic igneous rocks occur in the central and eastern Mystic subterrane. New whole-rock geochemical and isotopic data indicate that magmas were rift related and derived from subcontinental mantle. Triassic and Jurassic strata have detrital zircon age spectra much like those of the Sheep Creek Formation, with major age populations between ca. 430 and 410 Ma. These rocks include conglomerate with clasts of carbonate ± chert and youngest detrital zircons of Late Triassic age and quartz-carbonate sandstone with youngest detrital zircons of Early Jurassic age. Lithofacies indicating highly productive oceanographic conditions (upwelling?) bracket the main part of the Mystic succession: Upper Devonian bedded barite and phosphatic Upper Devonian and Lower Jurassic rocks. The youngest part of the Mystic subterrane consists of Lower Cretaceous (Valanginian-Aptian) limestone, calcareous sandstone, and related strata. These rocks are partly coeval with the oldest parts of the Kahiltna assemblage, an overlap succession exposed along the southern margin of the Farewell terrane. Our findings support previous models suggesting that the Farewell terrane was proximal to the Alexander-Wrangellia-Peninsular composite terrane during the late Paleozoic, and further suggest that such proximity continued into (or recurred during) the Late Triassic-Early Jurassic. But middle to late Permian detrital zircons in northern Farewell require another source; the Yukon-Tanana terrane is one possibility.

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Section: Stratigraphy Of the Mystic Subterranementioning

confidence: 99%

Section: Stratigraphy Of the Mystic Subterranementioning

confidence: 99%

Section: Stratigraphy Of the Mystic Subterranementioning

confidence: 99%

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The Mystic subterrane (partly) demystified: New data from the Farewell terrane and adjacent rocks, interior Alaska

et al. 2018

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“…Neither a spatial nor genetic relationship with the Late Cretaceous-Tertiary magmatism has been observed at Reef Ridge (Patton et al, 1980;Andrews and Rishel, 1982). However, considering the proximity of the deposit to the porphyry systems of the Mystery Mountain area (Copenhagen Hill, Frozen Creek, and Tarn Von Frank deposits), and to the Nixon Fork Au deposit, one must consider the possibility that Reef Ridge is part of a distal polymetallic sys-tem, related not only to the Iditarod-Denali fault displacement (Late Cretaceous-Early Tertiary), but also to the contemporaneous magmatic processes in the area.…”

Section: Exploration History and Mineralizationmentioning

confidence: 99%

A cold supergene zinc deposit in Alaska: The Reef Ridge case

Santoro

Boni

Mondillo

et al. 2015

Geological Society of America Bulletin

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The Reef Ridge deposit is a typical supergene "nonsulfi de" zinc mineralization, located in the Yukon-Koyukuk region of west-central Alaska (USA). It is hosted in sedimentary rocks of the Farewell terrane, a continental fragment sandwiched between the Siberian and Laurentian cratons during the early Paleozoic. The mineralization occurs in Lower-Middle Devonian shallowwater dolomite of a Paleozoic carbonate platform succession belonging to the Nixon Fork tectonic unit. The mineralization consists of oxidized minerals associated with minor remaining sulfi des (pyrite/marcasite and sphalerite). In the oxidation zone, smithsonite is the predominant mineral, mixed with Fe-(hydr)oxides (goethite and hematite).A complete petrographic and mineralogical study was performed. Samples were analyzed by X-ray diffraction, inductively coupled plasma-mass spectrometry and emission spectrometry, energy dispersive scanning electron microscopy, and QEMSCAN ® (quantitative evaluation of minerals by scanning electron microscopy). The most abundant mineral in the nonsulfi de ore is smithsonite. Similar to other nonsulfi de Zn deposits worldwide, the fi rst generation of smithsonite has replaced both primary sphalerite and the host carbonates. A second smithsonite generation precipitated as cement in vugs, cavities, and fractures. Minor zinc amounts also occur in the Fe-(hydr) oxides , and zinc traces have been identifi ed in clay minerals.The carbon and oxygen isotope values of smithsonite at Reef Ridge vary from -0.7 to 2.1‰ relative to Vienna Peedee belemnite (VPDB) and 19.1‰ to 21.9‰ relative to Vienna standard mean ocean water (VSMOW ). The δ 13 C values are similar to those of the host rock, suggesting that the predominant carbon source for smithsonite was the host carbonates, with only a limited contribution from organic carbon. The oxygen isotope ratios of Reef Ridge smithsonite are more depleted in 18 O compared to supergene nonsulfi des from other parts of the world formed under warm-humid, temperate, or semiarid climates. The oxygen isotope fractionation between water and smithsonite, which relates the δ 18 O value of the mineralizing solution, the formation temperature of smithsonite, and its δ 18 O composition, indicates that the δ 18 O composition of Reef Ridge smithsonite is related to very low formation temperatures (~10 °C), and strong depletion in 18 O of the precipitating waters.The δ 18 O smithsonite composition, the strong 18 O depletion, and the relationship of the formation of the Reef Ridge nonsulfi de deposit with the development of the Sleetmute upland surface (which started in the Late Tertiary and continues to the present) indicate that the formation of the Reef Ridge nonsulfi de deposit is probably related to cold/humid weathering episodes during a period comprised between Late Tertiary and Holocene.The "traditional" interpretation on the genesis of Zn nonsulfi de deposits in warmhumid, temperate, or semiarid conditions should be questioned where other climate zones are indicated.

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“…3, column 7). Rocks considered basement to Farewell terrane Paleozoic strata (Patton et al, 1980 are exposed in the northeastern Medfra Quadrangle and consist of amphibolite to greenschist facies metasedimentary and metavolcanic rocks. Rhyolitic metatuff and granitic orthogneiss yielded U-Pb zircon ages of 979 +8/-3 Ma and 850 ± 1 Ma, respectively (McClelland et al, 1999).…”

Section: Lithofaciesmentioning

confidence: 99%

Lithostratigraphic, conodont, and other faunal links between lower Paleozoic strata in northern and central Alaska and northeastern Russia

Dumoulin¹,

Harris²,

Gagiev³

et al. 2002

Tectonic Evolution of the Bering Shelf-Chukchi Sea-Artic Margin and Adjacent Landmasses

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Lower Paleozoic platform carbonate strata in northern Alaska (parts of the Arctic Alaska, York, and Seward terranes; herein called the North Alaska carbonate platform) and central Alaska (Farewell terrane) share distinctive lithologic and faunal features, and may have formed on a single continental fragment situated between Siberia and Laurentia. Sedimentary successions in northern and central Alaska overlie Late Proterozoic metamorphosed basement; contain Late Proterozoic ooid-rich dolostones, Middle Cambrian outer shelf deposits, and Ordovician, Silurian, and Devonian shallow-water platform facies, and include fossils of both Siberian and Laurentian biotic provinces. The presence in the Alaskan terranes of Siberian forms not seen in wellstudied cratonal margin sequences of western Laurentia implies that the Alaskan rocks were not attached to Laurentia during the early Paleozoic.The Siberian cratonal succession includes Archean basement, Ordovician shallow-water siliciclastic rocks, and Upper Silurian-Devonian evaporites, none of which have counterparts in the Alaskan successions, and contains only a few of the Laurentian conodonts that occur in Alaska. Thus we conclude that the lower Paleozoic platform successions of northern and central Alaska were not part of the Siberian craton during their deposition, but may have formed on a crustal fragment rifted away from Siberia during the Late Proterozoic. The Alaskan strata have more similarities to coeval rocks in some peri-Siberian terranes of northeastern Russia (Kotelny, Chukotka, and Omulevka). Lithologic ties between northern Alaska, the Farewell terrane, and the peri-Siberian terranes diminish after the Middle Devonian, but Siberian afµnities in northern and central Alaskan biotas persist into the late Paleozoic. *

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Preliminary geologic map of the Medfra quadrangle, Alaska

Cited by 14 publications

References 0 publications

The Mystic subterrane (partly) demystified: New data from the Farewell terrane and adjacent rocks, interior Alaska

The Mystic subterrane (partly) demystified: New data from the Farewell terrane and adjacent rocks, interior Alaska

A cold supergene zinc deposit in Alaska: The Reef Ridge case

Lithostratigraphic, conodont, and other faunal links between lower Paleozoic strata in northern and central Alaska and northeastern Russia

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