A preliminary study of geology and skarn of Cemorosewu Area, Bayat, Central Java, Indonesia

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.