Twelker, Evan
O'Sullivan, P.B.
2021
U-Pb zircon data and ages for bedrock samples from the Richardson mining district, Big Delta Quadrangle, Alaska
report, tables
Raw Data File
RDF 2020-14
Fairbanks, Alaska, United States
Alaska Division of Geological & Geophysical Surveys
17 p.
https://doi.org/10.14509/30555
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 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. Uranium-lead (U-Pb) zircon geochronology results presented in this report show that similarly textured quartz-feldspar porphyry intrusions in the project area were generated by both Paleocene (56.8 +/- 0.9 Ma; 18WCW149) and middle Cretaceous (92.0 +/- 0.7 Ma; 18AW002, known as the Democrat Dike) magmatic episodes. The ages of medium-grained plutonic rocks at Birch Lake (92.4 +/- 0.6 Ma; 18ET587) and Gold Run (93.7 +/- 0.7 Ma; 18ET580) lie within error of the age of the hypabyssal Democrat Dike, indicating that the present-day depth of exposure juxtaposes rocks that were buried at widely different crustal depths during the middle Cretaceous. Phaneritic granodiorite near the Democrat prospect yielded a zircon age of 110.7 +/- 1.3 Ma (18RN565), extending the magmatic history of the prospect into the Early Cretaceous. Amphibolite-facies augen orthogneiss yielded a Late Devonian zircon age of 364.5 +/- 6.0 Ma (18ET040), consistent with similar rocks in the Lake George assemblage. Detrital zircons analyzed from siliciclastic schist along the Richardson Highway (18AW021) contain prominent age populations at 1.8 and 2.6 Ga, consistent with a Laurentian cratonic source and consistent with other results from parautochthonous North America. Pelitic schist from the Hilltop prospect (18TJN372) yielded a relatively small number (n=32) of zircon grains that define small age populations between ca. 1.7 and 1.5 Ga. All components of this data release are available on the DGGS website: http://doi.org/10.14509/30555.
DGGS's work in the Richardson mining district supports improved understanding of the area's geology and controls on gold mineralization. This work facilitates industry exploration targeting.
>geochron-data: Spreadsheets with geochronology lab results and a preferred age summary table.
>geochron-summary: Identification numbers, coordinates, sample descriptions, and summary ages of each sample.
2018
ground condition
None planned
-146.700350
-146.357620
64.426240
64.290670
ISO 19115 Topic Category
geoscientificInformation
Alaska Division of Geological & Geophysical Surveys
Age Dates
Analyses
Analyses and Sampling
Analytical Lab Results
Analytical Results
Bedrock
Bedrock Geology
Chlorite
Detrital Zircon
Exploration
Feldspar
Garnet
Geochronology
Geologic
Geology
Granite
Granodiorite
Igneous
Igneous Rocks
Isotopes
Lab Methods
Metals
Metamorphic
Metamorphic Minerals
Metamorphic Rocks
Metamorphism
Metasedimentary Rocks
Methods
Mineralogy
Minerals
Muscovite
Orthogneiss
Plagioclase
Plutonic
Plutonic Rocks
Plutons
Porphyry
Quartz
Rock Units
Rocks
Sample Location
Schist
Sericite
Sericite Alteration
U-Pb
Zircon
Alaska Division of Geological & Geophysical Surveys
Canyon Creek
Delta River Mining District
Democrat Creek
Fairbanks Mining District
Junction Creek
Redmond Creek
Richardson Mining District
Shamrock Creek
Walker, J.D., Geissman, J.W., Bowring, S.A, and Babcock, L.E., comp., 2012, Geologic Time Scale v. 4.0: Geological Society of America
Cretaceous
Devonian
Tertiary
This report, map, and/or dataset is available directly from the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (see contact information below).
Any hard copies or published datasets utilizing these datasets shall clearly indicate their source. If the user has modified the data in any way, the user is obligated to describe the types of modifications the user has made. The user specifically agrees not to misrepresent these datasets, nor to imply that changes made by the user were approved by the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys. The State of Alaska makes no express or implied warranties (including warranties for merchantability and fitness) with respect to the character, functions, or capabilities of the electronic data or products or their appropriateness for any user's purposes. In no event will the State of Alaska be liable for any incidental, indirect, special, consequential, or other damages suffered by the user or any other person or entity whether from the use of the electronic services or products or any failure thereof or otherwise. In no event will the State of Alaska's liability to the Requestor or anyone else exceed the fee paid for the electronic service or product.
Alaska Division of Geological & Geophysical Surveys
Metadata Manager
mailing and physical
3354 College Road
Fairbanks
AK
99709-3707
USA
(907)451-5020
(907)451-5050
dggspubs@alaska.gov
8 am to 4:30 pm, Monday through Friday, except State holidays
Please view our website (https://www.dggs.alaska.gov) for the latest information on available data. Please contact us using the e-mail address provided above when possible.
We gratefully acknowledge James V. Jones III for his assistance with the age interpretations and figures. The 2018 Richardson geologic mapping project was funded by the State of Alaska.
Burns, L.E.
Graham, G.R.C.
Barefoot, J.D.
Fugro Airborne Surveys Corp.
Stevens Exploration Management Corp.
2019
East Richardson electromagnetic and magnetic airborne geophysical survey data compilation
Geophysical Report
GPR 2018-1
Fairbanks, Alaska, United States
Alaska Division of Geological & Geophysical Surveys
12 p
https://doi.org/10.14509/29754
Graham, G.E.
Jozwik, Diana
2007
Data tables related to geology and gold mineralization in the Richardson district, east-central Alaska
Raw Data File
RDF 2007-2
Fairbanks, Alaska, United States
Alaska Division of Geological & Geophysical Surveys
32 p
https://doi.org/10.14509/15819
Naibert, T.J.
Benowitz, J.A.
Wypych, Alicja
Sicard, K.R.
Twelker, Evan
2018
40Ar/39Ar data from the Tanacross D-1 and D-2, Big Delta B-4 and B-5, and Mount Hayes A-6 quadrangles, Alaska
Raw Data File
RDF 2018-3
Fairbanks, Alaska, United States
Alaska Division of Geological & Geophysical Surveys
15 p
https://doi.org/10.14509/30112
Twelker, Evan
Benowitz, J.A.
Naibert, T.J.
2020
40Ar/39Ar data from the Richardson mining district, Big Delta Quadrangle, Alaska
Raw Data File
RDF 2020-11
Fairbanks, Alaska, United States
Alaska Division of Geological & Geophysical Surveys
10 p
https://doi.org/10.14509/30530
Twelker, Evan
Werdon, M.B.
Sicard, K.R.
Wypych, Alicja
Naibert, T.J.
Athey, J.E.
Willingham, A.L.
Lockett, A.C.
2017
Geologic mapping in the Richardson-Uncle Sam area, interior Alaska (presentation): Alaska Miners Association Annual Convention, Anchorage, Alaska, November 7-12, 2017
Poster and Presentation
Twelker, Evan and others, 2017
Fairbanks, Alaska, United States
Alaska Division of Geological & Geophysical Surveys
37 p
https://doi.org/10.14509/29811
Twelker, Evan
Wypych, Alicja
Sicard, K.R.
Naibert, T.J.
Montayne, Simone
Newberry, R.J.
Wyatt, W.C.
2018
Major-oxide and trace-element geochemical data from rocks collected in the Richardson mining district, Big Delta Quadrangle, Alaska
Raw Data File
RDF 2018-6
Fairbanks, Alaska, United States
Alaska Division of Geological & Geophysical Surveys
4 p
https://doi.org/10.14509/30119
Twelker, Evan
Wypych, Alicja
Sicard, K.R.
Naibert, T.J.
Werdon, M.B.
Athey, J.E.
Willingham, A.L.
Lockett, A.C.
2017
Major-oxide and trace-element geochemical data from rocks collected in the Richardson mining district, Big Delta Quadrangle, Alaska
Raw Data File
RDF 2017-11
Fairbanks, Alaska, United States
Alaska Division of Geological & Geophysical Surveys
4 p
https://doi.org/10.14509/29779
A summary of all interpreted U-Pb ages is included with uncertainty for all ages and isotope ratios reported at the 2 sigma level. A concordance filter was used to eliminate grains that were either heterogeneous or experienced Pb loss after formation. Filtered grains were not included in the final interpretation. These data are being released in the DGGS Raw Data File series. Reports in this series present raw field data and analytical results with limited or no interpretation by DGGS staff or project collaborators. Analytical results may include interpretations by laboratories when an interpretive review of the analytical findings is necessary to develop usable output. The reports and accompanying data have been evaluated by project staff for general readability and logical consistency but have not undergone technical peer review.
not applicable
This data release is complete. Requests for additional information regarding the parameters and definitions of the analytical values should be directed to the originating lab.
Sample location coordinates (in WGS84 datum) were obtained using GPS-enabled field tablets, with a typical reported accuracy of +/- 10 meters.
Sample selection - Fresh, unweathered samples from surface bedrock outcrops were collected by DGGS field geologists; samples of representative rock types and important intrusive bodies were prioritized for analysis. Rocks were collected in summer 2018. Petrographic thin sections of each rock were examined to determine suitability for U-Pb geochronologic analysis. In some cases, samples from several closely adjacent outcrops were combined to create a composite sample of sufficient volume for analysis.
2018
Sample preparation and data analysis - Zircon grains from rock samples were analyzed to obtain U-Pb isotopic geochronologic ages using the methods described in the accompanying report.
2018
point
0.0001
0.0001
decimal degrees
World Geodetic System of 1984
WGS 84
6378137
298.257223563000025
rdf2020-14-geochron-data.zip, rdf2020-14-geochron-data-dictionary.csv
Spreadsheets with geochronology lab results and a preferred age summary table.
U-Pb geochronology analyses were performed by Paul O'Sullivan of GeoSep Services
geochron-data
rdf2020-14-geochron-summary.csv, rdf2020-14-geochron-summary-dictionary.csv
Identification numbers, coordinates, sample descriptions, and summary ages of each sample.
Alaska Division of Geological & Geophysical Surveys
geochron-summary
Alaska Division of Geological & Geophysical Surveys
Metadata Manager
mailing and physical
3354 College Road
Fairbanks
AK
99709-3707
USA
(907)451-5020
(907)451-5050
dggspubs@alaska.gov
8 am to 4:30 pm, Monday through Friday, except State holidays
Please view our website (https://www.dggs.alaska.gov) for the latest information on available data. Please contact us using the e-mail address provided above when possible.
RDF 2020-14
The State of Alaska makes no expressed or implied warranties (including warranties for merchantability and fitness) with respect to the character, functions, or capabilities of the electronic data or products or their appropriateness for any user's purposes. In no event will the State of Alaska be liable for any incidental, indirect, special, consequential, or other damages suffered by the user or any other person or entity whether from the use of the electronic services or products or any failure thereof or otherwise. In no event will the State of Alaska's liability to the Requestor or anyone else exceed the fee paid for the electronic service or product.
DGGS publications are available as free online downloads or you may purchase paper hard-copies or digital files on CD/DVD or other digital storage media by mail, phone, fax, or email from the DGGS Fairbanks office. To purchase this or other printed reports and maps, contact DGGS by phone (907-451-5020), e-mail (dggspubs@alaska.gov), or fax (907-451-5050). Payment accepted: Cash, check, money order, VISA, or MasterCard. Turnaround time is 1-2 weeks unless special arrangements are made and an express fee is paid. Shipping charge will be the actual cost of postage and will be added to the total amount due. Contact us for the exact shipping amount.
Contact DGGS for current pricing
report, tables
20210108
Spreadsheets with sample locations, geochronology lab results, preferred age summary, and data dictionary.
https://doi.org/10.14509/30555
Free download
20210108
Alaska Division of Geological & Geophysical Surveys
Simone Montayne
Metadata Manager
mailing and physical
3354 College Road
Fairbanks
AK
99709-3707
USA
(907)451-5020
(907)451-5050
dggspubs@alaska.gov
8 am to 4:30 pm, Monday through Friday, except State holidays
FGDC Content Standard for Digital Geospatial Metadata
FGDC-STD-001-1998
If the user has modified the data in any way they are obligated to describe the types of modifications they have performed in the supporting metadata file. User specifically agrees not to imply that changes they made were approved by the Alaska Department of Natural Resources or Division of Geological & Geophysical Surveys.
https://dggs.alaska.gov/metadata/dggs.ext
dggs metadata extensions