DGGS Raw Data File 2022-6, Electron probe microanalytical data of minerals and glass from rock samples from Okmok volcano, Alaska, provides electron probe microanalytical data (EPMA) from minerals and glasses from samples collected at Okmok volcano by Alaska Volcano Observatory (AVO) geologist Jessica Larsen. AVO geologists conducted fieldwork at Okmok volcano between 1998 and 2016. The samples included in this report are from the 2050 +/-50 yBP Okmok II eruption of Okmok caldera. All files are available from the DGGS website: http://doi.org/10.14509/30853.

A detailed methodology has been devised and tested for establishing metal zoning patterns in and about oreshoots within the plane of Ag-Pb-Zn veins of the Keno Hill - Galena Hill mining camp, Yukon, using whole rock vein geochemistry of run-of-mine samples. These ideal metal distribution patterns are easily interpretable in more classical zoning terms as mineral distribution patterns. To establish a zoning model samples that span a wide range of grades are rearranged in order of decreasing silver contents. The resulting "rearranged" profiles for other elements are then evaluated relative to silver. Computer-based curve fitting methods are useful means of generalizing these "rearranged" metal profiles. The foregoing procedure has been used to develop a general model for the Keno Hill - Galena Hill camp based on analytical results from 3 main deposits (Keno, Husky, No Cash) including 6 veins. Essential character of the model is embodied in analyses of Ag, Pb, Zn, and Ca and the Zn/Ag ratio. Additional but in cases ambiguous detail is added to the model by Hg, and Co and/or Ni analyses. These elements allow vein mineralogy to be monitored in a quantitative manner and provide a practical zoning model that can be used as an exploration, tool in evaluating underground workings for proximity to oreshoots in the more than 60 deposits known in the camp. A companion study involving whole rock K-Ar age determinations of small stockwork zones adjacent to Ag-Pb-Zn veins indicated an age of mineralization of about 87±2 Ma. for the Ag-Pb-Zn veins.

not_specified

From 2017-2019, framework metallogenic studies were completed in the eastern Yukon-Tanana upland in eastern Alaska. Numerous previously undated plutons known or suspected to contain components of porphyry, epithermal, and intrusion-related gold systems and associated deposit types were sampled for age and zircon trace element determinations between the Black Mountain area and the Yukon border, north of the Tanana River and south of the Yukon River. A collection of 54 samples were collected by Douglas Kreiner (USGS, Alaska Science Center). Zircon grains were separated from each sample. The samples were examined by U-Pb analysis by laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) in a USGS laboratory in Denver, CO. The samples contain evidence of several discrete periods of magmatic activity, with concordant zircon dates that range from ca. 53.3-2727 Ma. The bulk of analyzed samples are between ca. 68-72 Ma. Other specific periods of magmatism based on zircon dates range from ca. 55 Ma, ca. 100-112 Ma, ca. 130 Ma, and ca. 180-211 Ma. The ca. 340-365 Ma dates are likely inherited from host rocks that were previously unidentified in the field area but are known in the regional framework geology. Archean and Proterozoic zircon dates are not common, but likely represent inheritance from sedimentary and metasedimentary protoliths from the region.

From 2017-2019, framework metallogenic studies were completed in the eastern Yukon-Tanana upland in eastern Alaska. Numerous previously undated plutons known or suspected to contain components of porphyry, epithermal, and intrusion-related gold systems and associated deposit types were sampled for age and zircon trace element determinations between the Black Mountain area and the Yukon border, north of the Tanana River and south of the Yukon River. A collection of 54 samples were collected by Douglas Kreiner (USGS, Alaska Science Center). Zircon grains were separated from each sample. The samples were examined by U-Pb analysis by laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) in a USGS laboratory in Denver, CO. The samples contain evidence of several discrete periods of magmatic activity, with concordant zircon dates that range from ca. 53.3-2727 Ma. The bulk of analyzed samples are between ca. 68-72 Ma. Other specific periods of magmatism based on zircon dates range from ca. 55 Ma, ca. 100-112 Ma, ca. 130 Ma, and ca. 180-211 Ma. The ca. 340-365 Ma dates are likely inherited from host rocks that were previously unidentified in the field area but are known in the regional framework geology. Archean and Proterozoic zircon dates are not common, but likely represent inheritance from sedimentary and metasedimentary protoliths from the region.

A copy of this thesis is available at the EMR library – QE195.L96 1989. This thesis is available online at https://doi.org/10.7939/R38K75524

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.

Epithermal vein and porphyry-related gold-silver deposits in the Mount Nansen area are mainly hosted in Paleozoic Yukon-Tanana Terrane metasedimentary rocks and Early Jurassic Big Creek Batholith intrusive rocks. Mineralization is spatially, and probably temporally, related to a northwest-trending belt of mid-Cretaceous hypabyssal felsic intrusions and dykes along the Mount Nansen Trend. The proximal relationship between the veins and mid-Cretaceous intrusive rocks suggests that mineralization may be genetically related to felsic magmatism. The Dickson stock yields a U-Pb zircon age of 108.3 ± 0.7 Ma, and proximal dykes in the Flex, Dickson, Brown-McDade and Weber zones give ages of 107.9 ± 0.9 Ma to 109.0 ± 0.7 Ma, similar to the age of the Mount Nansen Group volcanic rocks. Granodiorite that hosts the Dickson deposit gives a U-Pb titanite age of 191.5 ± 2.9 Ma, and is likely part of the Big Creek Batholith. Previous studies indicated two periods of mineralization in the Dawson Range: mid-Cretaceous and Late Cretaceous. Dating indicates that Mount Nansen mineralization is associated with the mid-Cretaceous emplacement of the high-level felsic intrusions.

This dataset contains 99 electron microprobe analyses of cassiterite, chalcopyrite, galena, pyrite, sphalerite, and tetrahedrite from seven Sheep Creek drill core samples and one outcrop; and a table that describes the textures, mineralogy, and rock type of 15 thin sections of Sheep Creek drill core and observations from our study and from drill core logging by industry. These data were used to compare this prospect with others in the Bonnifield district. The dataset also contains tables of sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon dates, zircon characteristics (crystal shape, external morphology, internal features, color, aspect ratio, and cathodoluminescence zoning), and 139 U-Th-Pb analyses of the zircons from 11 metaigneous rocks collected during 1997-2005 fieldwork in the Bonnifield mining district, Alaska Range. Our zircon geochronology indicates that volcanogenic massive sulfide deposits in the Bonnifield district are hosted in felsic metavolcanic rocks that yield ages based on weighted averages of 206 Pb/238U ages (± 2-sigma errors) of 362 ± 2 Ma. These rocks overlie the stratigraphic sequence at the Sheep Creek prospect, where metaigneous rocks give ages of 372 ± 4 Ma to 366 ± 4 Ma.