Thermochronology for the granitic pluton related to lead-zinc mineralization in Tsushima, Japan

Hiroaki Ikemi, Nobutaka Shimada, Hitoshi Chiba

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

K-Ar datings and oxygen isotope analyses revealed a cooling history of the Uchiyama granitic pluton, which is genetically related to the Pb-Zn deposits (Taishu mine) in the Tsushima Islands, Japan. The pluton intrudes into the Paleogene Taishu Group to form the biotite-hornfels zone, while the Taishu vein-type Pb-Zn deposits occur in fissures developed in the non-hornfels zone about 1 to 3 km westward from the contact. Amphibole and biotite K-Ar ages of the pluton have a wide range from 19 to 13 Ma. Oxygen isotopes of the biotite and coexisting quartz grains indicate that isotopic exchange reactions have occurred under subsolidus conditions, and that the K-Ar ages are affected by various cooling rates in the pluton. The mineralization age of the Taishu ore deposits is obtained for the first time to be 15.4±0.8 Ma by a K-Ar age of 2M1-muscovite in a calcite-quartz-muscovite-chlorite veinlet of the Shintomi orebody. Whole rock K-Ar ages of biotite-hornfels near the pluton represent similar ages to the ore deposits. Using blocking temperature calculated from reported diffusivity for argon, the pluton was cooled from 560 to 350°C in the period of 17 to 14 Ma. The vein formation took place after the time when temperature in wall rocks of the pluton had dropped below the brittle-plastic transition (about 400°C). These results imply that the cooling of the pluton has caused injection of magmatic fluids into meteoric hydrothermal systems, and the Pb-Zn mineralization has occurred due to this mixing at the age of about 15 Ma.

Original languageEnglish
Pages (from-to)229-238
Number of pages10
JournalResource Geology
Volume51
Issue number3
DOIs
Publication statusPublished - Sep 1 2001

Keywords

  • K-Ar dating
  • Oxygen isotope
  • Taishu ore deposits
  • Thermochronology
  • Uchiyama granitic pluton

ASJC Scopus subject areas

  • Geology
  • Geochemistry and Petrology

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