Excess radiogenic argon in fluid inclusions

Abstract

Most minerals, with the possible exception of micas, commonly contain fluid inclusions, Argon contained in such inclusions may be considered a possible source of error in dating very young or low potassium minerals by the K-Ar method. Wahler [1956] first demonstrated spectrographically the presence of Ar in fluid inclusions in quartz. Elinson and Polykovskii [1961, 1963] used a vacuum ball mill to extract the gases present in fluid inclusions in various pegmatite minerals. They obtained Ar from quartz in quantities up to 8.9×10−3 cc/g. Preisinger and Huber [1964] state that they determined the Ar content of the gas emitted by heating very small samples (10−6 g) of feldspar crystals from a granite in a cycloidal mass spectrometer. The total gas emitted (water-free basis) varied from 0.8 to 3.3×10−3 cc/g. Nesmelova [1959] found up to 1.7% (Ar + Kr + Xe) in the gas from gas inclusions in sylvites from the Bereznikovsk mine in the USSR. Hoy et al. [1962] found 0.4 volume % Ar in the gases of highpressure gas inclusions in ‘popping-salt’ from the Winnfield salt dome in Louisiana. Sample weight and total gas volume were not specified. Damon and Kulp [1958] extracted excess radiogenic Ar from beryl, cordierite, and tourmaline in quantities ranging from 10−5 cc/g to 10−2 cc/g, some of which was assumed to come from fluid inclusions (p. 449). Lippolt and Gentner [1963] reported the finding of excess radiogenic Ar of the order of 10−7 cc/g in several fluorite samples and indicated that much of the excess was probably contained in fluid inclusions.