Rare Earth Elements as an Indicator to Origins of Skarn Deposits: Examples of the Kamioka Zn‐Pb and Yoshiwara‐Sannotake Cu(–Fe) Deposits in Japan

Abstract

: Systematic data of rare earth elements (REEs) are presented in order to put some constraints on the origin of hydrothermal fluids responsible for two contrastive skarn deposits in Japan; the Kamioka Zn‐Pb and Yoshiwara‐Sannotake Cu(‐Fe) deposits. Carbon and oxygen isotopic studies have demonstrated that the hydrothermal fluids responsible for the Kamioka Zn‐Pb deposits are of meteoric water origin whereas those for the Yoshiwara‐Sannotake Cu(‐Fe) deposits are of magmatic water origin. The REE abundances of epidote skarn derived from aluminous rocks, garnet and clinopyroxene in calcic exoskarn derived from limestone, and interstitial calcite associated with sulfide minerals were determined for these contrastive skarn deposits by inductively‐coupled plasma mass spectrometry (ICP‐MS). A significant difference in the REE concentrations is not found between epidote skarn and aluminous original rock (plagioclase‐clinopyroxene rock, called Inishi rock) from the Kamioka Zn‐Pb deposits, indicating that the REEs are generally immobile during the formation of epidote skarn, and that the REE concentrations of the hydrothermal fluid are considerably low relative to the aluminous original rock. In contrast, the epidote skarn exhibits enrichment of Eu with increasing total REE concentrations relative to the aluminous original rock (quartz diorite) in the Yoshiwara‐Sannotake Cu(‐Fe) deposits, implying a contribution of magmatic fluid derived from granitoids during the skarn formation. Limestone generally has much lower REE concentrations related to surrounding aluminous rocks, and thus the REE concentrations of garnet and clinopyroxene in calcic exoskarn, originated from limestone, are variable due to the interaction with the hydrothermal fluids. The chondrite‐normalized REE patterns of garnet, clinopyroxene, and interstitial calcite exactly provide useful information on origins of hydrothermal fluids. The REE patterns of these minerals from the Kamioka Zn‐Pb deposits show lower (Pr/Yb)cn ratios, and negative Ce and Eu anomalies inherited from limestone with the decrease of This suggests that the hydrothermal fluids responsible for the Kamioka Zn‐Pb deposits were depleted in REEs, and were not magmatic water in origin, but presumably meteoric one. In striking contrast, the REE patterns of exoskarn minerals and calcite from the Yoshiwara‐Sannotake Cu(‐Fe) deposits exhibit a positive Eu anomaly, and high (Pr/Yb)cn ratios with the considerable increase of σREE and the disappearance of negative Ce anomaly, implying that the fluids were dominantly of magmatic origin. The REE indices are very likely to be an excellent indicator to origins of the skarn deposits.

Mineralogical and geochemical characteristics of scheelite-bearing skarns, and genetic relations between skarn mineralization and petrogenesis of the associated granitoid pluton at Sargipali, Sundergarh District, Eastern India

“…In contrast, the skarns exhibit slight enrichment of Eu with increasing total REE concentrations relative to the dolomitic marble, implying a contribution of magmatic fluid derived from granitoids during the skarn formation (cf. Kato, 2008).…”

Skarns and Genesis of the Huanggang Fe‐Sn Deposit, Inner Mongolia, China

“…Irrespective of the nature of associated igneous activity, it is also plausible that the tin content of garnet from the deposits is low, because they are formed by hydrothermal solutions of meteoric water origin (Shimazaki and Kusakabe, 1990). Some examples, however, such as the Kamaishi and Sannotake deposits, are confirmed to have formed by solutions of magmatic water origin (Morishita and Matsuhisa, 1983;Kato, 1999), and the tin content of garnets from these deposits is clearly low as shown in Table 2.…”

Genesis of the Kamioka Skarn Deposits: An Important Role of Clinopyroxene Skarn and Graphite‐bearing Limestone in Precipitating Sulfide Ore

“…The oxygen isotopic compositions of the fluids responsible for the Kamioka deposits were estimated to be as low as -4 to +3‰ (SMOW), demonstrating that the deposits were derived from the hydrothermal fluids of meteoric water origin (Shimazaki et al, 1986;Shimazaki and Kusakabe, 1990). Moreover, the REE concentrations of clinopyroxene, garnet, and calcite formed as hydrothermal products are considerably low relative to those of original crystalline limestone, indicating no significant contribution of magmatic fluids during the formation of skarn and ore (Kato, 1991a(Kato, , 1999. Three major deposits, Mozumi, Maruyama, and Tochibora, are composed of 10 to nearly 50 discrete massive orebodies.…”

“…As to the origin of the ore-forming fluids responsible for the Kamioka deposits, Shimazaki and his colleagues have demonstrated that the fluids were of meteoric water origin based on oxygen isotopes of calcite, clinopyroxene, and quartz (e.g., Shimazaki et al, 1986;Shimazaki and Kusakabe, 1990). Moreover, rare earth element (REE) data of skarn and ore calcite also have suggested that the origin of metals in the hydrothermal fluids was not magmatic (Kato, 1991a(Kato, , 1999. The transportation of the fluids has been discussed in some papers (e.g., Kawasaki et al, 1985;Sakurai et al, 1993;Hirokawa et al, 1995).…”