The Tok project area is adjacent to the Delta mineral belt volcanogenic massive-sulfide (VMS) district, the Peak gold-silver-copper skarn, and structurally controlled gold and antimony mineralization in the Stibnite Creek and White Gold areas. The project area also includes the Noah prospect, an intrusion-related copper prospect. Whereas the Delta mineral belt has been extensively mapped and explored, the detailed mapping does not continue into the 2015 Tok project area. In this area, only reconnaissance mapping has been conducted. The combination of a lack of detailed mapping, the industry interest in the adjacent areas, and the geophysical data findings prompted the Alaska Division of Geological & Geophysical Surveys (DGGS) mineral resources group to work in this area. DGGS geologists carried out a geologic reconnaissance mapping project in the Tanacross A-5, A-6, and parts of adjacent quadrangles from June 18 through 28, 2015. This dataset includes two samples with elevated gold, 1.3 and 14.5 ppm, accompanied with very high arsenic values (both over 10,000 ppm) and antimony values (352 and 97.4 ppm). The sample containing 14.5 ppm Au, 305 ppm Bi and 11.1 ppm Te (15ET026) was collected from sulfide pods in schist adjacent to a granitic intrusion near the Noah prospect, and the sample containing 1.3 ppm Au (15KS007) was collected from quartz veining in a fault zone. Major element chemistry has been obtained on the metamorphic rocks to distinguish between igneous and sedimentary protoliths of the rocks using criteria proposed by Dashevsky and others (2003) and on igneous rocks to characterize and differentiate Mesozoic and Cenozoic igneous deposits in the area. The analytical data tables associated with this report are being released in digital format as comma-delimited text (CSV) files.

Geologists from the Alaska Division of Geological & Geophysical Surveys (DGGS) and University of Alaska carried out a two-part geologic mapping and geochemical sampling project in the Tok River area of the Tanacross A-5 and A-6 quadrangles (June 12-26 and July 8-26). The Tok River area is adjacent to the Delta mineral belt volcanogenic massive-sulfide (VMS) district, the Peak gold-silver-copper skarn, and the structurally controlled gold and antimony mineralization in the Stibnite Creek and White Gold areas. The Tok River project area includes the Noah (also called Hona) prospect, an intrusion-related copper prospect. The combination of insufficient detailed geologic mapping, historical and current industry interest in the adjacent mineralized areas, and the recently published geophysical data prompted the DGGS Mineral Resources section to work in this area. Highlights of this DGGS Tok River geochemical report include identification, sampling, and characterization of prospects without previously available public data, including the Eagle, Dall, Parton, and Jacqueline prospects. This dataset has 22 samples with gold in excess of 0.5 ppm in several different locations, including a sample with 9.78 ppm Au (16ET254, Shalovsky vein), a sample with 6.25 ppm Au from nearby Hona porphyry (16ET312), a sample containing 1.22 ppm Au from a vein within schist south of Dry Tok Creek (16KS255), and a sample with 1.315 ppm Au from drill hole WG-11-05 (16RN165B, Eagle trend). Major- and trace-element geochemical analyses were obtained for the metamorphic rocks to distinguish between igneous and sedimentary protoliths and for igneous rocks to characterize and differentiate Mesozoic and Cenozoic rocks in the area.

Late Triassic mafic to ultramafic intrusions in the Wrangellia terrane are host to magmatic sulfide nickel-copper-cobalt and platinum-group element (PGE) mineralization. DGGS's mineral-resources group carried out a geologic mapping project in the eastern Denali Highway region between Watana Creek and Paxson from July 29 through August 7, 2015. This project is part of a multi-year effort focusing on improving the publicly available geological and geochemical data and assessing the mineral potential of the less-explored extension of the western Wrangellia terrane; other data resulting from this project include geophysical surveys and several geochemical datasets. This program of geologic mapping and rock sampling was conducted as part of the State of Alaska's Strategic and Critical Minerals Assessment project, an initiative designed to evaluate Alaska's potential for rare-earth elements, PGEs, and other similarly supply-challenged resources. Highlights of this project include identification, sampling, and characterization of a broad section of Wrangellia stratigraphy, including Late Triassic ultramafic and mafic intrusions thought to be a part of the Ni-Cu-Co-PGE- and Cu-Ag-mineralized Wrangellia large igneous province. This dataset includes four samples with high copper values (1.6 to 4.62 percent) and elevated silver values (10.15 to 18.25 ppm) and two samples have elevated copper (1,400 and 4,610 ppm); those samples are scattered throughout the area. Two samples from the Caribou Dome area show elevated platinum (0.113 and 0.101 ppm) and palladium (0.141 and 0.193 ppm). The analytical data tables associated with this report are being released in digital format as comma-delimited text (CSV) files.

In conjunction with hosting field trips for the Association of American State Geologists 2016 annual meeting in Girdwood, Alaska, Alaska Division of Geological & Geophysical Surveys (DGGS) staff collected rock samples and obtained geochemical analysis from several readily accessible, but relatively unstudied outcrops. Samples were collected from Turnagain Arm (mile 104 Seward Highway), Whittier, Crow Pass, and Panorama Mountain (roughly mile 217 Parks Highway). Mineralized samples from veins and veinlets in granitic rocks from the Crow Pass and Whittier sites contain anomalous levels of gold ranging from 0.129 to 0.650 parts per million (ppm). Although none of the samples are from areas open to mineral entry, geochemical analyses of rocks from these localities may support interpretation of regional mineral-distribution trends. The analytical data tables associated with this report are available in digital format as comma-separated value (CSV) files. Additional details about the organization of information are noted in the accompanying metadata file. All files can be downloaded from the DGGS website (http://doi.org/10.14509/29725).

In 2016, geologists from the Alaska Division of Geological & Geophysical Surveys (DGGS) and University of Alaska Fairbanks carried out a two-part geologic mapping and geochemical sampling project in the Tok River area of the Tanacross A-5 and A-6 quadrangles (June 12-26 and July 8-26). This report provides results of stream-sediment sampling for trace-element geochemistry. An initial suite of sediment samples was collected from streams draining known gold occurrences, including the Stibnite Creek and Noah prospects, and numerous prospects in the White Gold area. These samples were split in half and the two splits were sieved to -200 mesh and -80 mesh, respectively. The splits were then both analyzed to determine which size fraction was best for identifying gold anomalies in this part of the Alaska Range. In most samples, the -200 mesh fraction showed higher gold levels, and hence, all additional samples we collected were analyzed at -200 mesh. In some -80 mesh samples, gold and tungsten appear to show "nugget" effects not seen in the -200 mesh samples. The other trace elements are largely equivalent between the two mesh sizes. The second suite of samples was collected throughout the map area from streams draining color anomalies, from areas where DGGS mapping identified igneous rocks upstream, and from areas with suspected potential for base-metal or gold mineralization. Highlights of the analytical results include two samples draining the Noah prospect with greater than 1 part per million gold. The analytical data tables associated with this report are available in digital format as comma-separated value (CSV) files.

During the 2017 field season, geologists from the Alaska Division of Geological & Geophysical Surveys (DGGS) conducted geologic mapping and sampling of part of the Richardson Mining District southeast of Fairbanks, including parts of the Big Delta B-4, B-5, and C-5 quadrangles. The project area is about 30 miles west of the Pogo gold mine and covers the currently active Montecristo and Uncle Sam gold-exploration properties. The goal of DGGS's work in this area is to conduct a mineral-resource assessment and to build an improved understanding of the area's geology and controls on gold mineralization to facilitate industry exploration targeting. This report is based on 17 days of fieldwork completed June 23-July 3, July 18-20, and August 11-13, 2017 by two to seven DGGS geologists. The study area is bound by the Pogo Road to the southeast and the Trans-Alaska Pipeline access road to the southwest (fig. 1); the crew accessed the interior of the study area by helicopter, all-terrain vehicles, and foot. The Richardson area is characterized by moderate-relief hills and boreal spruce and deciduous forest typical of interior Alaska. Loess deposits of variable thickness blanket the area, and deposits of forest-covered eolian sand, including well-formed dune fields, cover the southeastern quadrant of the area along Shaw Creek. Rock outcrop accounts for much less than one percent of the study area, consequently, the majority of rock samples were collected from pits, up to 1-meter-deep, dug with shovels into rocky colluvial deposits below the surficial loess or sand. Highlights of geochemical results include 2.67 parts per million (ppm) gold and 68.4 ppm silver from a float sample collected at the Naosi prospect. An in-place, surface rock sample collected from the Mon prospect area assayed 2.42 ppm gold and 23 ppm silver. Both prospects are part of the Montecristo property. Whole-rock analyses indicate the granitic dikes that are abundant on the Montecristo and Uncle Sam properties are peraluminous granites of arc character. They most closely resemble the Early Cretaceous peraluminous felsic dikes documented in the southeastern Richardson district by Graham (2002); they are less similar (less peraluminous) to the ca. 90 Ma Gold Run intrusion (Graham, 2002) and Birch Lake pluton (Burns and others, 1993). Amphibolite samples are basaltic in composition and have island-arc tholeiite or mid-ocean ridge basalt character, similar to unit MzPza amphibolites in the Salcha River-Pogo area (Werdon and others, 2004). The analytical data tables associated with this report are available in digital format as comma-separated value (CSV) files. Additional details about the organization of information are noted in the accompanying metadata file. All files can be downloaded from the DGGS website (http://doi.org/10.14509/29779).

From June 12-21, 2017, the Alaska Division of Geological & Geophysical Surveys (DGGS) geologists carried out geologic mapping and geochemical sampling in the northeastern Tanacross D-1, and parts of the C-1, and D-2 quadrangles. The project area lies within the Yukon-Tanana Uplands, and encompasses the boundary between Fortymile and Lake George assemblages. It includes porphyry copper-molybdenum-gold deposits and prospects including: Taurus, Fishhook (also known as SW Pika), and Pika Canyon, and is adjacent to the Fortymile Mining District to the north. Highlights of this geochemical report include sampling and characterization of the Pika Canyon, Fishhook, and Taurus prospects. This dataset contains four samples with gold in excess of 0.1 parts per million (ppm) in several different locations, including two samples from Fishhook with 2.15 ppm and 0.697 ppm gold, respectively (17MBW119, 17MBW130), and a sample with 4,420 ppm silver and greater than 30 percent lead (17MLW002) collected nearby Pika Canyon. The DGGS Tanacross project area includes a section of Paleozoic and Mississippian- to Devonian-age, metasedimentary and metavolcanic rocks, as well as Jurassic(?) to Tertiary intrusive and volcanic rocks. Major- and trace-element geochemical analyses were obtained for metamorphic rocks to distinguish between igneous and sedimentary protoliths, and for igneous rocks to characterize and differentiate Mesozoic and Cenozoic rocks in the area. The analytical data tables associated with this report are available in digital format as comma-separated value (CSV) files. Additional details about the organization of information are noted in the accompanying metadata file. All files can be downloaded from the DGGS website (http://doi.org/10.14509/29778).

The Iniskin-Tuxedni Bay area contains excellent exposures of nearly all of the lower Cook Inlet Mesozoic succession, including most of the stratigraphic sections that define the interval and the petroleum source rocks that comprise the basin. An underdeveloped understanding of the Mesozoic petroleum system has led the Alaska Department of Natural Resources' Division of Geological & Geophysical Surveys and Division of Oil and Gas, and the U.S. Geological Survey to collaborate on a multi-year project that includes two major mapping campaigns. Geologic mapping between Chinitna Bay and the Johnson River during the 2015 field season encompassed volcanic arc rocks northwest of the Bruin Bay fault system, and Mesozoic forearc basin stratigraphy extending to the Cook Inlet coast. To understand and represent the complexity of the volcanic arc systems in the region, we analyzed ten samples of volcanic rocks, two samples of gabbro sill, and one mafic dike sample for major and minor oxides and trace elements. Although mineralization was not noted in the samples collected for major oxide analysis, findings of interest include: one sample with weak Cr and Ni enrichment, three samples with lightly elevated As, and slight S anomalies (0.37 wt percent and 0.25 wt percent) in samples described as Talkeetna Formation. The Talkeetna Formation sample with 0.37 wt percent S also had elevated Cu (321 ppm) and As (58 ppm). The analytical data tables associated with this report are available in digital format as comma-separated values (CSV) file.

During the 2018 field season, geologists from the Alaska Division of Geological & Geophysical Surveys (DGGS) conducted geologic mapping and sampling of part of the Richardson mining district southeast of Fairbanks, including parts of the Big Delta B-5 and B-6 quadrangles. The project area has produced approximately 122,000 ounces of gold (Singh and others, 2017), mostly from placer mines, and it includes the Richardson, Tower, and Hilltop lode gold exploration properties. Rock outcrop accounts for much less than one percent of the study area, consequently, many of the rock samples were collected from up to 1-meter-deep pits dug with shovels into rocky colluvial deposits below the surficial loess. Highlights of the geochemical results include 43.3 and 9.77 parts per million (ppm) gold sampled from arsenopyrite-bearing quartz veins at the Hilltop prospect. At the Democrat prospect, formerly the site of small-scale mining, a sample of sulfide-rich material returned 3,790 ppm silver and 4.72 ppm gold. Other samples from the Democrat prospect assayed 6.81 and 5.01 ppm gold. The analytical data tables associated with this report are available in digital format as comma-separated value (CSV) files. All files can be downloaded from the DGGS website (http://doi.org/10.14509/30119).