Abstract
We present the first finding of skarn rocks in Cemorosewu area of East Jiwo Hill, Bayat, Central Java, Indonesia. The geological conditions of this area which related to the appearance of the skarn is also reported. The methods used in this research are DEM acquisition using drone to generate basemap for geological mapping and thin section petrographic analyses. The geological map shows that Cemorosewu area consists of metamorphic rocks (mica phyllite, graphite phyllite, with quartzite and marble lenses), sedimentary rocks (carbonate breccia and siltstone), and igneous rock (microdiorite). Based on the field observation and geological map, the regional metamorphic rocks are the oldest units in this area followed by sedimentary rocks and igneous rock which intruded both rocks. Skarn rocks were cropped out as a boulder along the Kluwihan creek with the maximum size of 8 m in length. The skarn consists of garnet, clinopyroxene, zoisite, actinolite, and minor quartz. Metasiltstone and skarn rock are suggested formed by contact metamorphism of microdiorite intrusion. The marble, which lenses within the phyllites, is suggested to be the protolith of the skarn formation in this area.
Highlights
Jiwo Hills in Bayat is well known for the occurrences of regional metamorphic rocks in Central Java, Indonesia, together with Luk-Ulo Complex and Ciletuh Complex in West Java [1]
We present the first finding of skarn rocks in Cemorosewu area of East Jiwo Hill, Bayat, Central Java, Indonesia
The regional metamorphic rocks are considered to be the oldest rocks in this area, which are unconformably overlain by Paleogene and Neogene sedimentary rocks, which were intruded by Oligo-Miocene igneous rocks [2]
Summary
Jiwo Hills in Bayat is well known for the occurrences of regional metamorphic rocks in Central Java, Indonesia, together with Luk-Ulo Complex and Ciletuh Complex in West Java [1]. Metasomatic skarn was reported in the Pagerjurang area of West Jiwo as a product of contact metamorphism between microgabbro and marble [1; 3] even though similar geological condition with the West Jiwo, the skarn in East Jiwo have never been reported. Skarn rocks crop out as a boulder along the Kluwihan creek of Cemorosewu area with the maximum size of 8 m in length (Figures 1 and 2). The purpose of this study is to investigate the geological conditions of the Cemorosewu area, East Jiwo related to the first finding of the skarn rock, by geological mapping and petrographic analyses.
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