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Whole rock and mineral concentrates were split and analyzed separately for potassium and argon. Potassium was analyzed by a lithium metaborate flame photometry technique. Argon was analyzed standard techniques of isotope dilution and mass spectrometry.
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Lead was extracted from the samples by ion-exchange columns and electrodeposition. Contamination by airborne particulate matter was minimized by the use of laminar-flow hoods using an absolute prefiltered air supply. Isotope abundance measurements of lead were made with the silica gel technique. National Bureau of Standards common lead isotopic standard was used to measure fractionation. The lead isotopes were depleted in the heavy isotopes by less than 0.05 percent per mass unit. No correction factor was applied. Uranium and thorium solutions which passed through the first lead resin column were collected and isolated on nitrate resin.
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K/Ca ratios for each sample were calculated from measured 39Ar/37Ar isotopes and knowledge of the flux monitor K/Ca (~24). Ar was extracted from each sample in a double-vacuum, resistance-heated furnace with temperature accuracy of better than +/- 5C. Gas clean-up was accomplished by SAES getter pumps. Ar isotope analyses were performed using an automate Nuclide 4.5-60-RSS mass spectrometer equipped with an on-line date reduction program.
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All analyses were done in the Argon Laboratory, U.S. Geological Survey, Denver, Colorado using a Mass Analyzer Products 215 Rare Gas mass spectrometer with a Faraday cup.
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The 40Ar/39Ar was measured by a Nuclide mass spectrometer.
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The 40Ar/39Ar was measured by a Nuclide mass spectrometer.
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Determined using stadard isotope dilution techniques for extraction and measurement of argon and flame photometry for potassium.
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Duplicate potassium analyses were done with a Baird KY-2 flame photometer, using a lithium internal standard. Argon was analyzed by isotope dilution with a bulb argon-38 tracer and a Reynolds-type mass spectrometer.
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Potassium was determined by flame photometry using a lithium metaborate fusion technique (Engels and Ingamells, 1970). Argon extraction and measurement was accomplished using standard techniques of isotope dilution mass spectrometry, as described by Dalrymple and Lanphere (1969).
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Rb and Sr contents and Sr isotope rations were analyzed on a 9
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Rb and Sr contents and Sr isotope rations were analyzed on a 9
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