Noble Gases in Tellurium and Associated Minerals and Double-Beta Decay of ¹³⁰Te

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.