Dating native gold by noble gas analysesOur recent work on He, Ne, and Ar in Alpine gold samples has demonstrated that gold is extremely retentive for He and could thus, in principle, be used for U/Th-He-4 dating. For vein-type gold from Brusson, Northern Italy, we derived a U/Th-He-4 age of 36 Ma, in agreement with the K-Ar formation age of associated muscovites and biotites. However, in placer gold from the Napf area, Central Switzerland, we observed large excesses of both He-4 and radiogenic Ar-40 (Ar-40 sub rad, defined as Ar-40-295.5-Ar-.36). The gas release systematics indicate two distinct noble gas components, one of which is released below about 800 C and the other one at the melting point of gold (1064 C). We now present results of He and Xe measurements in a 1 g placer gold sample from the river Kruempelgraben, as well as He and Ar data for Brusson vein-type gold and for gold from the Lily Gold Mine, South Africa. We calculate reasonable U/Th-He-4 as well as U-Xe ages based on those gases which are released at approximately 800 C. Probably the low-temperature components represent in-situ-produced radiogenic He and fission Xe, whereas the gases evolving when gold melts have been trapped during gold formation. Therefore, only the low-temperature components are relevant for dating purposes.
Niedermann, S. (Bern Univ. Bern, Switzerland)
Eugster, O. (Bern Univ. Bern, Switzerland)
Hofmann, B. (Bern Univ. Bern, Switzerland)
Thalmann, CH. (Bern Univ. Bern, Switzerland)
Reimold, W. U. (Witwatersrand Univ. Johannesburg, South Africa)
September 6, 2013
January 1, 1993
Publication: Lunar and Planetary Inst., Twenty-Fourth Lunar and Planetary Science Conference. Part 3: N-Z
INORGANIC AND PHYSICAL CHEMISTRY
Work of the US Gov. Public Use Permitted.
IDRelationTitle19940015909Analytic PrimaryWorkshop on the Martian Northern Plains: Sedimentological, Periglacial, and Paleoclimatic Evolution19940016163Analytic PrimaryTwenty-Fourth Lunar and Planetary Science Conference. Part 3: N-Zvisibility_off