The Early Jurassic Bokan Mountain peralkaline granitic complex (southeastern Alaska): Geochemistry, petrogenesis and rare-metal mineralization

Dostál, J.; Kontak, Daniel J.; Karl, Susan M.

doi:10.1016/j.lithos.2014.06.005

Cited by 66 publications

(32 citation statements)

References 60 publications

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“…Therefore it is possible the rocks from Hadjer Bigli were likely formed by the same process as the other silicic magmas but were highly fractionated which led to the formation of F‐rich hydrothermal fluids that enabled enrichment of the HFSE and possibly Rb and Zn. A similar model is proposed to explain the metallogenesis of the rare metal deposits in the Bokan Mountain Complex in Alaska thus the magmatic system at Hadjer Bigli is a potential target for mineral exploration [ Dostal et al ., ; Dostal and Shellnutt , ].…”

Section: Discussionmentioning

confidence: 99%

Late Cretaceous intraplate silicic volcanic rocks from the Lake Chad region: An extension of the Cameroon volcanic line?

Shellnutt

Lee

Torng³

et al. 2016

Geochem Geophys Geosyst

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Silicic volcanic rocks at Hadjer el Khamis, near Lake Chad, are considered to be an extension of the Cameroon volcanic line (CVL) but their petrogenetic association is uncertain. The silicic rocks are divided into peraluminous and peralkaline groups with both rock types chemically similar to within‐plate granitoids. In situ U/Pb zircon dating yielded a mean 206Pb/238U age of 74.4 ± 1.3 Ma indicating the magmas erupted ∼10 million years before the next oldest CVL rocks (i.e., ∼66 Ma). The Sr isotopes (i.e., ISr = 0.7021–0.7037) show a relatively wide range but the Nd isotopes (i.e., 143Nd/144Ndi = 0.51268–0.51271) are uniform and indicate that the rocks were derived from a moderately depleted mantle source. Thermodynamic modeling shows that the silicic rocks likely formed by fractional crystallization of a mafic parental magma but that the peraluminous rocks were affected by low temperature alteration processes. The silicic rocks are more isotopically similar to Late Cretaceous basalts identified within the Late Cretaceous basins (i.e., 143Nd/144Ndi = 0.51245–0.51285) of Chad than the uncontaminated CVL rocks (i.e., 143Nd/144Ndi = 0.51270–0.51300). The age and isotopic compositions suggest the silicic volcanic rocks of the Lake Chad region are related to Late Cretaceous extensional volcanism in the Termit basin. It is unlikely that the silicic volcanic rocks are petrogenetically related to the CVL but it is possible that magmatism was structurally controlled by suture zones that formed during the opening of the Central Atlantic Ocean and/or the Pan‐African Orogeny.

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Section: Discussionmentioning

confidence: 99%

Late Cretaceous intraplate silicic volcanic rocks from the Lake Chad region: An extension of the Cameroon volcanic line?

Shellnutt

Lee

Torng³

et al. 2016

Geochem Geophys Geosyst

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“…However, more recent studies (e.g., [6,17,18]) imply that both magmatic and hydrothermal processes contributed to the origin of the REE deposits. The primary magmatic mineralization was overprinted by late magmatic to hydrothermal fluids rich in REE, HFSE, Th, and U that remobilized and enriched the original mineralization during multiple metasomatic events and re-deposited them as secondary phases (e.g., [6,7,19]).…”

Section: Origin Of Alkaline Rocks and Ree Mineralizationmentioning

confidence: 99%

“…This concentrically zoned body consists of a core made up of arfvedsonite granite and an outer zone composed predominantly of aegirine granite. The major REE mineralization occur in clusters of subparallel mineralized dikes and metasomatically enriched alteration halos (albite rich) associated with shear zones [18,26]. The mineralized dikes occur both within the complex as well as in the surrounding Paleozoic granites.…”

Section: Bokan Mountain Alaska Usamentioning

confidence: 99%

Rare Earth Element Deposits of Alkaline Igneous Rocks

Dostál

2017

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Alkaline igneous complexes host deposits of rare earth elements (REE), which represent one of the most economically important resources of heavy REE and Yttrium (Y). The hosts are differentiated rocks ranging from nepheline syenites and trachytes to peralkaline granites. These complexes usually occur in continental within-plate tectonic settings associated with rifts, faults, or hotspot magmatism. The REE mineralization is found in layered alkaline complexes, granitic stocks, and late-stages dikes and rarely trachytic volcanic and volcaniclastic deposits. The bulk of REE is present in accessory minerals, which can reach percentage levels in mineralized zones. The mineralization contains various REE-bearing minerals that can display complex replacement textures. Main REE minerals present in these deposits are bastnäsite, eudialyte, loparite, gittinsite, xenotime, monazite, zircon, and fergusonite. The parent magmas of alkaline igneous complexes are derived from partial melts of mantle sources. Protracted fractional crystallization of the magma led to an enrichment in REE, particularly in the late stages of magma evolution. The primary magmatic mineralization is commonly overprinted (remobilized and enriched) by late magmatic to hydrothermal fluids. Elevated abundances of U and Th in the deposits make a gamma-ray (radiometric) survey an important exploration tool, but also represent a significant environmental challenge for exploitation.

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“…The replacement of arfvedsonite by aegerine has also been ascribed to hydrothermal alteration at many peralkaline intrusions (Marks et al, 2003;Salvi and Williams-Jones, 2006), although Dostal et al (2011Dostal et al ( , 2014 attribute the compositional differences of the granites at Bokan Mountain to late phase crystallization of the parent magma.…”

Section: Discussionmentioning

confidence: 99%

“…A significant amount of research has been conducted on the uranium and REE mineralization at Bokan Mountain since the late 1950s (MacKevett, 1959(MacKevett, , 1963Staatz, 1978;Thompson et al, 1982;Thompson, 1988;Warner and Barker, 1989;Philpotts et al, 1996;UCore Rare Metals Inc., 2011;Dostal et al, 2011Dostal et al, , 2013Dostal et al, , 2014Barker and Van Gosen, 2012). Uranium mineralization was recognized in the mid-1950s at the Ross-Adams deposit, which brought more interest and scrutiny to the geology at Bokan Mountain, eventually leading to the recognition of rare earth mineralization.…”

Section: Mineralizationmentioning

confidence: 99%

Geophysical interpretation of U, Th, and rare earth element mineralization of the Bokan Mountain peralkaline granite complex, Prince of Wales Island, southeast Alaska

2014

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A prospectivity map for rare earth element (REE) mineralization at the Bokan Mountain peralkaline granite complex, Prince of Wales Island, southeastern Alaska, was calculated from high-resolution airborne gamma-ray data. The map displays areas with similar radioelement concentrations as those over the Dotson REE-vein-dike system, which is characterized by moderately high %K, eU, and eTh (%K, percent potassium; eU, equivalent parts per million uranium; and eTh, equivalent parts per million thorium). Gamma-ray concentrations of rocks that share a similar range as those over the Dotson zone are inferred to locate high concentrations of REE-bearing minerals. An approximately 1300-m-long prospective tract corresponds to shallowly exposed locations of the Dotson zone. Prospective areas of REE mineralization also occur in continuous swaths along the outer edge of the pluton, over known but undeveloped REE occurrences, and within discrete regions in the older Paleozoic country rocks. Detailed mineralogical examinations of samples from the Dotson zone provide a means to understand the possible causes of the airborne Th and U anomalies and their relation to REE minerals. Thorium is sited primarily in thorite. Uranium also occurs in thorite and in a complex suite of AETi AE Nb AE Y oxide minerals, which include fergusonite, polycrase, and aeschynite. These oxides, along with Y-silicates, are the chief heavy REE (HREE)-bearing minerals. Hence, the eU anomalies, in particular, may indicate other occurrences of similar HREE-enrichment. Uranium and Th chemistry along the Dotson zone showed elevated U and total REEs east of the Camp Creek fault, which suggested the potential for increased HREEs based on their association with U-oxide minerals. A uranium prospectivity map, based on signatures present over the Ross-Adams mine area, was characterized by extremely high radioelement values. Known uranium deposits were identified in the U-prospectivity map, but the largest tract occurs over a radioelement-rich granite phase within the pluton that is likely not related to mineralization. Neither mineralization type displays a well-defined airborne magnetic signature.

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The Early Jurassic Bokan Mountain peralkaline granitic complex (southeastern Alaska): Geochemistry, petrogenesis and rare-metal mineralization

Cited by 66 publications

References 60 publications

Late Cretaceous intraplate silicic volcanic rocks from the Lake Chad region: An extension of the Cameroon volcanic line?

Late Cretaceous intraplate silicic volcanic rocks from the Lake Chad region: An extension of the Cameroon volcanic line?

Rare Earth Element Deposits of Alkaline Igneous Rocks

Geophysical interpretation of U, Th, and rare earth element mineralization of the Bokan Mountain peralkaline granite complex, Prince of Wales Island, southeast Alaska

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