Role of Hydrothermal Fluids in the Formation of the Kamioka Skarn-Type Pb–Zn Deposits, Japan

Abstract

The Kamioka mine, located in Gifu Prefecture in Japan, is famous for the large water Cherenkov detector system, the Super-Kamiokande. The Kamioka skarn-type Pb–Zn deposits are formed in crystalline limestone and are replaced by skarn minerals within the Hida metamorphic rocks. The Kamioka deposits mainly consist of the Tochibora, Maruyama, and Mozumi deposits. The present study focuses on the ore-forming hydrothermal fluid activity in the Kamioka deposits and the peripheral exploration area based on the carbon and oxygen isotope ratios of calcite and rare earth element (REE) analyses. The carbon and oxygen isotope ratios of crystalline limestone (as the host rock) are not homogeneous, and depending on the degree of hydrothermal activity, they decreased to various degrees because of the reaction with the ore fluids. Thus, the carbon and oxygen isotope ratios of crystalline limestone can be used as an indicator of the influence of the hydrothermal fluids for the ore mineralization. The REE contents in the ores of igneous origin are one order of magnitude higher than the limestone origin. Further, depending on the formation temperatures, calcites precipitated during ore mineralization have a stable carbon isotope ratio and a widely varying oxygen isotope ratios. The Kamioka district fracture system is likely a major control factor on ore mineralization from hydrothermal activity. In addition, the skarnization-related ore-forming fluids are mostly meteoric in origin, confirming the conclusions from previous studies.

Hydrothermal Calcite Precipitation in Veins: Inspired by Experiments for Oxygen Isotope Fractionation between CO2 and Calcite from 1 °C to 150 °C

“…Several isotopic studies (Kushikino deposit [22,29], Ohtani and Kaneuchi deposits [24], Takatori deposit [25], and Noya deposit [26]) were introduced, assuming that the mineral assemblages were close to equilibrium. We observed varying degrees of kinetic reactions and equilibrium goals in the δ 13 C-δ 18 O relationship of limestone at the Kamioka deposit [27]. These previous findings in several hydrothermal ore deposits suggest that actual isotope fractionations in nature, even at low-to-intermediate temperatures, are similar to equilibrium fractionations among minerals with coexisting fluid.…”

“…The study on the Kamioka skarn-type Pb-Zn deposits is a good example to consider the kinetics-to-equilibrium transition in isotopes for the genesis and evolution of the oreforming hydrothermal fluid [27]. The crystalline limestone in the mining area suffered from the ore-forming hydrothermal fluid.…”

“…Oppositely, the direct precipitation of calcite into veins from the hydrothermal fluid also occurred. The calcite was supposed to be equilibrated with the hydrothermal fluid, and the δ 13 C and δ 18 O values of calcite were the end-members of the mining area [27]. The δ 13 C and δ 18 O values of the isotopically reacted limestone are distributed in a wide range of isotope ratios between the original limestone and precipitated veins in a δ 13 C-δ 18 O graph [27].…”

“…The calcite was supposed to be equilibrated with the hydrothermal fluid, and the δ 13 C and δ 18 O values of calcite were the end-members of the mining area [27]. The δ 13 C and δ 18 O values of the isotopically reacted limestone are distributed in a wide range of isotope ratios between the original limestone and precipitated veins in a δ 13 C-δ 18 O graph [27]. This confirms that the isotope exchange kinetics in the limestone changed the δ 13 C and δ 18 O values to various degrees.…”

Determination of indium isotopic ratios of geostandards with different matrices by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS)

“…J-Zn-1 was collected from the Kamioka Pb-Zn mine, which is a skarn-type deposit. 18,19 The d 115/113 In SCP value of J-Zn-1 (−0.05 ± 0.04&) is different from that of granite (0.30-0.66&), suggesting substantial In isotope fractionation during uid a Indium concentrations were obtained from the analysis of puried samples; the reference indium concentrations of BCR-2 and NIST-2711a are 94 ng g −1 (Liu et al 10 ) and 11 000 ng g −1 (Krawczyk-Coda, 16 ), respectively.…”