Terrane accretion forms lithospheric-scale fault systems that commonly experience long and complex slip histories. Unraveling the evolution of these suture zone fault systems yields valuable information regarding the relative importance of various upper crustal structures and their linkage through the lithosphere. We present new bedrock geologic mapping and geochronology data documenting the geologic evolution of reactivated shortening structures and adjacent metamorphic rocks in the Alaska Range suture zone at the inboard margin of the Wrangellia composite terrane in the eastern Alaska Range, Alaska, USA. Detrital zircon uranium-lead (U-Pb) age spectra from metamorphic rocks in our study area reveal two distinct metasedimentary belts. The Maclaren schist occupies the inboard (northern) belt, which was derived from terranes along the western margin of North America during the mid- to Late Cretaceous. In contrast, the Clearwater metasediments occupy the outboard (southern) belt, which was derived from arcs built on the Wrangellia composite terrane during the Late Jurassic to Early Cretaceous. A newly discovered locality of Alaska-type zoned ultramafic bodies within the Clearwater metasediments provides an additional link to the Wrangellia composite terrane. The Maclaren and Clearwater metasedimentary belts are presently juxtaposed by the newly identified Valdez Creek fault, which is an upper crustal reactivation of the Valdez Creek shear zone, the Late Cretaceous plate boundary that initially brought them together. 40Ar/39Ar mica ages reveal independent post-collisional thermal histories of hanging wall and footwall rocks until reactivation localized on the Valdez Creek fault after ca. 32 Ma. Slip on the Valdez Creek fault expanded into a thrust system that progressed southward to the Broxson Gulch fault at the southern margin of the suture zone and eventually into the Wrangellia terrane. Detrital zircon U-Pb age spectra and clast assemblages from fault-bounded Cenozoic gravel deposits indicate that the thrust system was active during the Oligocene and into the Pliocene, likely as a far-field result of ongoing flat-slab subduction and accretion of the Yakutat microplate. The Valdez Creek fault was the primary reactivated structure in the suture zone, likely due to its linkage with the reactivated boundary zone between the Wrangellia composite terrane and North America in the lithospheric mantle.

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Authority to print this and other publications is based on Alaska Statute 41.08.020, which charges DGGS to "…determine the potential of Alaskan land for production of metals, minerals, fuels, and geothermal resources; the location and supplies of groundwater and construction materials; the potential geologic hazards to buildings, roads, bridges, and other installations and structures; and… conduct such other surveys and investigations as will advance knowledge of the geology of Alaska. " Statute 41.08.030 adds, "The state geologist shall print and publish an annual report and such other special and topical reports and maps as may be desirable for the benefit of the state…" In addition, Alaska Statute 27.05.050-060 states, "The department shall conduct a continuing survey of the mineral resources and mining operations of the state and shall disseminate information regarding them to assist prospectors and miners, safeguard the lives and health of miners, protect investors in the mining industry, and foster and promote the best interests of the mining, mineral, and related industries of the state…The department shall make an annual report to the governor on all essential matters with regard to mining in the state…" ALASKA'S MINERAL INDUSTRY 2015Jennifer E. Athey, Melanie B. Werdon, Evan Twelker, and Mitch W. Henning Special Report 71Cover photo. Gold pan with clean-up from placer operation in the Nelchina mining district northeast of Anchorage. EXECUTIVE SUMMARYThis summary of the status of Alaska's mineral industry for 2015 is the 35th annual report produced by the Department of Natural Resources, Division of Geological & Geophysical Surveys with assistance from the Division of Mining, Land & Water. Published for more than one-third of a century, the annual report endeavors to provide a consistent, factual snapshot of mineral industry activity in Alaska, and also serves as the authoritative, historical record of mining in the state. Alaska's Mineral Industry 2015 The total reported value of Alaska's mineral industry decreased in 2015 to $3.13 billion, almost 15 percent lower than its $3.66 billion value in 2014. The total value is a composite of the year's expenditures on exploration and development plus the estimated first market value of the commodities produced. Gross income reported by mining operators indicated the continued strength of the industry by increasing nearly 3 percent in 2015, to $2.50 billion, from $2.43 billion in 2014. The estimated first market value of production dropped almost 16 percent in 2015, from $3.28 billion in 2014 to $2.76 billion in 2015. The decreased mineral production value in 2015 resulted from decreased metal production as well as lower metal prices. The average 2015 price for silver had the largest drop-nearly 21 percent. Zinc was the top metal produced in 2015, according to its production value of almost 45 percent of total Alaska metal production. Gold followed at 37.5 percent, along with lead at 9.1 percent, and silver at 8.8 percent. Development expenditures in Alask...

We report U-Pb zircon geochronology results for one metavolcanic and one metaplutonic rock sample from the Mount Hayes A-6 Quadrangle of central Alaska. These samples are representative of rock units assigned to the Clearwater terrane of Jones and others (1987), a sequence of greenschist-grade metavolcanic and metasedimentary rocks of poorly constrained age and tectonic origin. Our results indicate a crystallization age of 277.33 ± 11.84 Ma for a felsic metavolcanic rock, and a 268.05 ± 11.64 Ma crystallization age for a granitic metaplutonic unit intruding the former.