40Ar/39Ar data from the Richardson mining district, Big Delta Quadrangle, Alaska

Description

During the 2017 and 2018 field seasons, geologists from the Alaska Division of Geological & Geophysical Surveys (DGGS) conducted geologic mapping and sampling in the Richardson mining district southeast of Fairbanks, including parts of the Big Delta B-4, B-5, B-6, and C-6 quadrangles. The project area has produced approximately 122,000 ounces of gold, mostly from placer mines, and it includes the Uncle Sam, Montecristo, Richardson, Tower, and Hilltop lode 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. The four 40Ar/39Ar ages reported here are all from samples at or near mid-Cretaceous intrusion-related gold prospects. Skarn hornblende from the Banner Creek area (18RN069) yielded an age of 104.0 +/- 1.6 Ma, which places its formation relatively early in the magmatic history of the district. Fine-grained, holocrystalline granodiorite in the immediate vicinity of the Democrat prospect yielded a biotite cooling age of 96.9 +/- 2.0 Ma (18RN568), slightly older than the white mica age reported for the nearby mineralized rhyolite dike (89.4 +/- 0.7 M). White mica from a sericite-pyrite altered, quartz-feldspar porphyry dike in the Rosa Pass area yielded an age of 87.0 +/- 1.5 Ma (17MBW526). Sericite-altered intrusive rock from drill core at the Lone Tree prospect yielded an age of 93.2 +/- 1.2 Ma (18ET057), somewhat younger than the 40Ar/39Ar age determined for presumably magmatic white mica from a dike at the nearby Naosi prospect on the Montecristo property (100.0 +/- 0.7 Ma). The complete report and digital data are available through the DGGS website: http://doi.org/10.14509/30530.

Resources

Name Format Description Link
0 CSDGM IMPORT ERROR: No digtinfo/formcont https://doi.org/10.14509/30530
0 https://doi.org/10.14509/30112
0 https://doi.org/10.14509/15819
0 https://doi.org/10.14509/29779
0 https://doi.org/10.14509/30530
0 https://doi.org/10.14509/29811
0 https://doi.org/10.14509/30119

Tags

  • mica
  • plutonic
  • pyrite
  • methods
  • fluorite
  • 40ar/39ar
  • rocks
  • exhumation
  • resources
  • sample location
  • geochronology
  • twentyfive mile creek
  • porphyry
  • granite
  • cretaceous
  • isotopes
  • mining
  • minerals
  • geologic
  • richardson mining district
  • analyses
  • bedrock
  • democrat prospect
  • banner creek
  • geology
  • bedrock geology
  • skarn
  • ar-ar
  • chlorite
  • disseminated
  • buckeye creek
  • analyses and sampling
  • hornblende
  • plagioclase
  • potassium
  • fairbanks mining district
  • epidote
  • sericite
  • lab methods
  • age dates
  • crystals
  • k-feldspar
  • exploration
  • rhyolite
  • mineralogy
  • granodiorite
  • muscovite
  • petrography
  • analytical results
  • feldspar
  • analytical lab results
  • quartz

Topics

  • Local Government

Categories