National Geochronological Database sample #1200

Outcrop or artificial surface exposure, Andesite

Geographic location
-117.155556, 37.695833
117° 9' 20" W, 37° 41' 45" N
Nye county, NV
Goldfield 1:62,500 scale map quadrangle
Accurate to within 0.1 minute (~500 feet)
SE 1/4 SW 1/4 NE 1/4 SEC. 9, T1S, R43E; CLIFF FACE ON BLACKCAP MOUNTAIN (TOWNSHIP SHOULD BE T3S--COMPILER)
Source of sample Outcrop or artificial surface exposure
Rock name Andesite
Description UPPER FLOW OF LABRADORITE ANDESITE CAPPING BLACKCAP MOUNTAIN. ANDESITE IS DARK GRAY TO BLACK, PORPHYRITIC, AND CONSISTS OF FINE-GRAINED PHENOCRYSTS OF ZONED LABRADORITE (68% OF THE ROCK), IDDINGSITIZED OLIVINE (8%), AUGITE (16%), MAGNETITE (6%), AND PHLOG
Laboratories Yale
Compiler name Marvin, R.F.
Date compiled 1976 04
Precision of location Accurate to within 0.1 minute (~500 feet)
Location comment SE 1/4 SW 1/4 NE 1/4 SEC. 9, T1S, R43E; CLIFF FACE ON BLACKCAP MOUNTAIN (TOWNSHIP SHOULD BE T3S--COMPILER)
Bibliographic reference Armstrong, R.L., Dick, H., and Vitaliano, C.J., 1972, K-Ar Dates and Strontium Isotope Initial Ratios Of Some Cenozoic Volcanic Rocks From West-Central Nevada: Isochron/West, no. 3, p. 23-28.
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Geologic map unit -117.155556, 37.695833
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K-Ar age determinations

Age estimate 12.11 ± 0.4Ma
age of volcanism
Type of analysis conventional K-Ar
POTASSIUM VALUE IS CONVERTED AVERAGE OF 1.30%, 1.28%, AND 1.31% K; ARGON VALUE IS CONVERTED AVERAGE OF 0.000000633 AND 0.000000589 CC/G; OTHER RADIOGENIC ARGON VALUE IS 36%; INITIAL SR-87/SR-86 RATIO IS 0.7043 +/- 0.0007
Rock or mineral analyzed whole rock
Analytical details
Lab sample ID Y-B2-7
Decay constants 4.72E-04, 0.584E-04, 1.19E-04*
K2O concentration 1.56 %
Radiogenic 40Ar concentration 0.273
Radiogenic Ar 27 %