Ore Geology of Skarn Ore Bodies in the Kasihan Area, East Java, Indonesia

Abstract

까시한 지역 함 동-아 연 스카른광체는 약 0.5 kb의 환경에서 초기 약 450 o C (단사휘석-석류석 및 석류석 스카른, ≈450-370 o C) 에서 시작되어 후기 300 o C (석류석-녹염석 및 녹염석 스카른, ≈370-300 o C) 에 걸쳐 진행되었다. 주요어 : 함 동-아연 스카른, 단사휘석, 석류석, 까시한 지역, 인도네시아 Copper-zinc-bearing skarns of the Kasihan area developed at limestone layers in the sedimentary facies of the Late Oli-gocene Arjosari Formation. The skarns consist mainly of fine-grained, massive clinopyroxene-garnet, garnet, garnet-epi-dote, and epidote skarns. Most copper and zinc(-lead) ore mineralization occur in the clinopyroxene-garnet and garnet-epidote skarn, respectively. Clinopyroxene occurs as a continuous solid solution of diopside and hedenbergite (from nearly pure diopside up to ≈34 mole percent hedenbergite), with a maximum 28.2 mole percent johannsenite component. The early and late pyroxenes of Kasihan skarns are diopsidic and salitic, respectively. They fall in the fields typical Cu-and Zn-dominated skarns, respectively. Garnet displays a relatively wide range of solid solution between grossular and andra-dite with up to ≈2.0 weight percent MnO. Garnet in early pyroxene-garnet skarn ranges from 49.1 to 91.5 mole percent grossular (mainly ≥78 mole % grossular). Garnets in late garnet and garnet-epidote skarns range from 2.8 to 91.4 mole percent grossular (mainly ≥70 mole % for garnet skarn). Epidote compositions indicate solid solutions of clinozoisite and pistacite varying from 65.8 to 76.2 mole percent clinozoisite. Phase equilibria indicate that skarn evolution was the result of interaction of water-rich fluids (X CO 2 ≤0.1) with original lithologies at ≈0.5 kb with declining temperature (early cli-nopyroxene-garnet and garnet skarn, ≈450 to 370 o C; late garnet-epidote and epidote skarn, ≈370 to 300 o C).