The Kago low-sulfidation gold and silver deposit: A peripheral mineralisation to the Nansatsu high-sulfidation system, southern Kyushu, Japan

Thomas Tindell, Koichiro Watanabe, Akira Imai, Ryohei Takahashi, Adrian J. Boyce, Kotaro Yonezu, Anders Schersten, Laurence Page, Takeyuki Ogata

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Abstract

The Kago deposit is a small deposit located at the southern tip of the Satsuma Peninsula of Southern Kyushu, Japan. It lies proximal to the well-known Nansatsu-type mineralisation province dominated by high-sulfidation type epithermal deposits. The deposit was heavily mined in the 18 th Century, largely for its relatively higher gold compared to that of surrounding and regional deposits. The Kago deposit is a typical low-sulfidation deposit, characterised by adularia-quartz veins, composed of electrum, Ag-tetrahedrite, polybasite, chalcopyrite and pyrite. Based on mine records, the grade ranged from 4.1 to 13.3 g/t Au and 2.6–6.6 g/t Ag. Alteration grades from low to high temperature argillic into a propylitic zone at the extremes of the vein exposures. Carbonate is absent. Fluid inclusion microthermometry reveals a typical temperature range of 220–240 °C with salinity of 0.7–2.6 NaCl eq. wt%. Electrum from high-grade ore ranges from 66 to 69 wt% Au. 40Ar/39Ar age dating of adularia bearing colloform/crustiform and brecciated veins, suggests a mineralisation event from 4.23 to 4.0 Ma. δ18O of veined and silicified quartz ranges from +4.0 to +18.4‰. δ18OH2O of fluids in equilibrium with quartz, in the dominant range of measured fluid inclusion temperatures, ranges from −6.5‰ to −0.2‰. δ34S of pyrite has a narrow range from −1.8 to 2.7‰. The deposit lies at the northern extent of the classic Nansatsu high-sulfidation epithermal area, in which a number of silicified bodies punctuate the region in a roughly semi-circular shape. The Kago deposit lies within the principle mineralisation age range of the high-sulfidation deposits, which range from 5.5 to 3.7 Ma. The structural displacement of the Kago deposit from the Nansatsu mineralisation and the differing host rocks has greatly influenced alteration, ore and rock-water interaction of the ore depositing fluids. Here we seek to establish the relationship that this extended mineral province has between the differing styles of mineralisation.

Original languageEnglish
Pages (from-to)951-966
Number of pages16
JournalOre Geology Reviews
Volume102
DOIs
Publication statusPublished - Nov 2018

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All Science Journal Classification (ASJC) codes

  • Geology
  • Geochemistry and Petrology
  • Economic Geology

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