Major-oxide and trace-element geochemical data from rocks collected in the Richardson mining district, Big Delta Quadrangle, Alaska

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).

Tags: analyses, analyses and sampling, analytical lab results, analytical results, base metals, big delta quadrangle, chemistry, critical minerals, economic geology, economic study, exploration, geochemical data, geochemical surveys, geochemistry, geologic, geology, lab methods, major oxides, mccoy creek, metals, methods, mineral assessment, mineral deposit, mineral localities, mineral prospect, mineral resources, minerals, mining, minor oxides, minton creek, monte cristo creek, non-metals, ore deposit, ores, precious metals, prospecting sites, resource assessment, resource information, resources, richardson mining district, sample location, stream sediments, trace elements, trace geochemical, trace metals, uncle sam prospect
Organization: State of Alaska