• Economic and Environmental Geology
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• v.28 no.2
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• pp.109-121
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• 1995

The hydrothermal vein type deposits which comprise the Kasihan, Jompong and Gempol mineralized areas are primarily copper and zinc deposits, but they are also associated with lead and/or gold mineralization. The deposits occur within the Tertiary sedimentary and volcanic rocks in the Southern Mountain zone of the eastern Java island, Indonesia. Mineralization can be separated into two or three distinct stages (pre-and/or post- ore mineralization stages and main ore mineralization stage) which took place mainly along pre-existing fault breccia zones. The main phase of mineralization (the main ore stage) can be usually classified into three substages (early, middle and late) according to ore mineral assemblages, paragenesis, textures and their chemical compositions. Ore mineralogy and paragenesis of the three areas in the district are different from each other. Pyrite, pyrrhotite (/arsenopyrite), iron-rich (up to 20.5 mole % FeS) sphalerite and (Cu-)Pb-Bi sulfosalts are characteristic of the deposits in the Kasihan (/Jompong) area. On the other hand, pyrite + hematite + magnetite + iron-poor (2.7 to 3.6 mole % FeS) sphalerite assemblage is restricted to the Gempol area. Fluid inclusion data suggest that fluids of the main ore stage evolved from initial high temperatures (near $350^{\circ}C$) to later lower temperatures (near $200^{\circ}C$) with salinities ranging from 0.8 to 10.1 equiv. wt. percent NaCl. Each area represents a separate hydrothermal system: the mineralization at Kasihan and Jompong were largely due to early fluid boiling coupled with later cooling and dilution, whereas the mineralization at Gempol was mainly resulted from cooling and dilution by an influx of cooler meteoric waters. Fluid inclusion evidence of boiling indicates that pressures of ${\geq}95$ to 255 bars (${\geq}95$ bars for the Gempol area: $\approx$ 120 to 170 bars for the Jompong area: $\approx$ 140 to 255 bars for the Kasihan area) during portions of main ore stage mineralization. Equilibrium thermodynamic interpretation indicates that the evolution trends of the temperature versus fS2 variation of ore stage fluids in the Pacitan district follow two fashions: ore fluids at Kasihan and Jompong changed from the pyrite-pyrrhotite sulfidation stage towards pyritehematite- magnetite state, whereas those at Gempol evolved nearly along pyrite-hematite-magnetite reaction curve with decreasing temperature. The sulfur isotope compositions of sulfide minerals are consistent with an igneous source of sulfur with a ${\delta}^{34}S_{{\Sigma}s}$ value of about 3.3 per mil. The oxygen and hydrogen isotopic compositions of the fluids in each area indicate a progressive shift from the dominance of highly exchanged meteoric water at early hydrothermal systems towards an un- or less-exchanged meteoric water at later hydrothermal systems.

• Economic and Environmental Geology
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• v.44 no.1
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• pp.1-10
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• 2011

The geology of the Pacitan district which occupies Southern mountain zone in the southwestern margin of East Java, Indonesia, consists of a pile of clastics and pyroclastics grading upwards into a series of sediments of Middle Miocene age which are intruded by a number of quartz porphyries and subvolcanic dacitic to andesitic bodies in after that time. The geochemical exploration in the Pacitan district to find out anomalous areas related with metallic mineral dispersion from the concealed ore deposits had been carried out using traditional exploration techniques of geological mapping, stream sediment, panned concentrate and outcrop sampling. The anomalous zones of each element were detected in the following areas: Gempol for Cu; Jompong for Au; Kasihan for Cu-Pb-Zn. The strongest Cu-Pb-Zn anomalous values are overlapped at the Kasihan area. The geochemical survey of soil was conducted with the geological survey at the Kasihan area. The statistical values were calculated by the statistical analysis method. The patterns for Cu, Pb and Zn are similar to the normal distribution. The anomalous values of copper-lead-zinc and/or copper and zinc are overlapped at five zones surrounding quartz porphyry at the central part of the Kasihan area. The area was interpreted and chosen as an anomalous zone related with stockwork and skam mineralization, extending to approximately NNW-SSE direction.

• Economic and Environmental Geology
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• v.45 no.1
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• pp.1-8
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• 2012

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 ${\approx}34$ 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 ${\approx}2.0$ weight percent MnO. Garnet in early pyroxene-garnet skarn ranges from 49.1 to 91.5 mole percent grossular (mainly ${\geq}78$ mole % grossular). Garnets in late garnet and garnet-epidote skarns range from 2.8 to 91.4 mole percent grossular (mainly ${\geq}70$ 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 ($X_{CO_2}{\leq}0.1$) with original lithologies at ${\approx}0.5$ kb with declining temperature (early clinopyroxene-garnet and garnet skarn, ${\approx}450$ to $370^{\circ}C$; late garnet-epidote and epidote skarn, ${\approx}370$ to $300^{\circ}C$).