Ore Geology of Skarn Ore Bodies in the Kasihan Area, East Java, Indonesia
인도네시아 까시한지역 스카른광체의 광상학적 특성

Jin-Kyun Han, Sang-Hoon Choi
2012 Economic and Environmental Geology  
Copper-zinc-bearing skarns of the Kasihan area developed at limestone layers in the sedimentary facies of the Late Oligocene Arjosari Formation. The skarns consist mainly of fine-grained, massive clinopyroxene-garnet, garnet, garnet-epidote, and epidote skarns. Most copper and zinc(-lead) ore mineralization occur in the clinopyroxene-garnet and garnetepidote skarn, respectively. Clinopyroxene occurs as a continuous solid solution of diopside and hedenbergite (from nearly pure diopside up to ≈34
more » ... 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 andradite 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 clinopyroxene-garnet and garnet skarn, ≈450 to 370 o C; late garnet-epidote and epidote skarn, ≈370 to 300 o C).
doi:10.9719/eeg.2012.45.1.001 fatcat:olr4syiqdjhfnevltueevieq6m