Noble Gases in Tellurium and Associated Minerals and Double-Beta Decay of 1300Te.

Abstract

Tellurobismuthite, quartz and arsenopyrite minerals separated from a specimen of tellurium-bearing ores collected at the Oya mine have been analyzed for noble gas isotopes. The Te minerals released abundant 4He and 40Ar. Quartz released large amounts of noble gases, which are supposed to have been occluded in fluid inclusions. It contains excess 40Ar inherited from precursor materials. Arsenopyrite released abundant He and Ar. Argon is mostly of atmospheric origin. Definite excesses at 129Xe, 130Xe, and 131Xe isotopes but no excesses at 134Xe and 136Xe are found for the Te minerals. Xe isotopic ratios for the quartz are atmospheric and give no evidence for inherited excess 130Xe. Because the quartz, arsenopyrite and Te minerals were deposited from the same hydrothermal fluids, these indicate that the Te minerals contain inherited excess 40Ar and the isotopic ratios of trapped Xe in the Te minerals is atmospheric. Hence the 130Xe excess found in the Te mineral is attributable to the in-situ double-beta decay of 130Te, and the excesses at 129Xe and 131Xe are to the neutron-captures on 128Te and 130Te, respectively. Besides, a quartz-calcite separate from a Te ore specimen collected at the Suwa mine is enriched in 4He but the isotopic ratios of Xe is atmospheric, indicating that Xe contained in hydrothermal fluids at Suwa is atmospheric.In order to decipher the chronological sequence of mineralization of Te ores and solidification of magma, we summarize the occurrences of sample minerals, the geology of sampling sites and their field relationships. Based on noble gas data measured for the Te and associated minerals as well as geological considerations, we prefer (7.9±1.0)×1020 years to 3 ×1021 years for the absolute half-life of 130Te double-beta decay. From the excess ratio of 129Xe to 131Xe, we have 710 n/cm2y for neutron flux at the Oya mine.