Relation between Zonal Arrangements of Skarns and Temperatures of Formation at the Kamaishi Mine, Northeastern Japan

Abstract

This paper describes the skarns of the Nippo, Shinyama (8D and 4D-7D) and Tengumori deposits at the Kamaishi iron-copper mine, and compares each other. These deposits are situated on the west flank of the Ganidake igneous complex, and are arranged from north to south. Zonal arrangements of the skarns are as follows:
Nippo
diorite Pl Ga Cpx limestone hornfels Cpx Cpx
Shinyama 8D
diorite Pl Ep Ga Cpx limestone Cpx Cpx Cpx
Shinyama 4D-7D
dioriteporphyry Pl Ep Ep Ga Ga Cpx limstone Amp Amp Cpx Cpx
Tengumori
sandstone Ep Ep Ga Cpx Ga limestone Amp Cpx Cpx (I) Cpx (II)
(Pl: plagioclase, Ep: epidote, Ga: garnet, Amp: amphibole, Cpx: clinopyroxene)
Based on the phase equilibria in the system CaO-MgO-AL₂O₃-SiO₂-H₂O-CO₂ and CaO-Fe-AL₂O₃-SiO₂-H₂O-CO₂-O ₂, it is concluded that this variation in zonal arrangement is attributable to the difference in the forma-tion temperature (Nippo: 540-490°C, Shinyama 8D: 490-440°C, Shinyama 4D-7D: 440-400°C and Tengumori: 400-360°C at 1 kbar and XCO₂=0.02). The formation temperature increases northward. Based on this conclusion, the inversion temperature of isotropic-anisotropic garnet is estimated to be between 400 and 440°C. The temperature gradient is considered to be provoked by diorite to diorite porphyry which belongs to the Ganidake igneous complex.