National Geochronological Database sample #3912

Outcrop or artificial surface exposure, Rhyodacite

Geographic location
-117.165278, 37.704167
117° 9' 55" W, 37° 42' 15" N
Esmeralda county, NV
Goldfield 1:62,500 scale map quadrangle
Accurate to within 1 minute (~1 mile)
Source of sample Outcrop or artificial surface exposure
Rock name Rhyodacite
Description COARSE ALUNITE FROM ALUNITE-JAROSITE BRECCIA FILLING IN SILICIFIED PORPHYRITIC RHYODACITE
Laboratories USGS Menlo Park
Compiler name Nichols, S.L.
Date compiled 1978 04
Precision of location Accurate to within 1 minute (~1 mile)
Bibliographic reference Ashley, R.P., and Silberman, M.L., 1976, Direct Dating Of Mineralization At Goldfield, Nevada, By Potassium-Argon and Fission-Track Methods: Economic Geology, v. 71, p. 904-924.
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Geologic map unit -117.165278, 37.704167
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K-Ar age determinations

Age estimate 20.49 ± 0.4Ma
Type of analysis conventional K-Ar
9.97%, 10.09%, 10.06% K2O; ARGON EXTRACTION SYSTEM NOT BAKED-OUT OVERNIGHT
Rock or mineral analyzed alunite
Analytical details
Lab sample ID 185-79B
Decay constants 4.72E-04, 0.585E-04, 1.19E-04*
K2O concentration 10.04 %
Radiogenic 40Ar concentration 2.979
Radiogenic Ar 33 %
Comments TIME OF ALTERATION OR MINERALIZATION