Radioactive Mineral Occurrences on Submarine Alkaline Volcanic Rocks in West Tapalang, Mamuju, West Sulawesi, Indonesia

Mamuju Region recently has become one of radioactive minerals prospecting area in Indonesia. High radiometric
concentration of uranium and thorium in Mamuju are distributed in basaltic to intermediate rocks (foidite to
andesite) of Adang Volcanic. Radioactive minerals(uranium and thorium) occurrences were detected by using gamma spectrometer (model RS-125). The field measurements of RS-125 resulted dose rate, uranium and thorium equivalent (eU and eTh) contents of rock and soil. West Tapalang Area, part of Mamuju Region dominantly composed by lava and autobrecciaphonolite rocks. There are three volcanic domes identified in the area. They are Ahu, Labuhan Rano, and Sumare domes. Ahu dome is the biggest domes and characterized by the occurrences of leucite rich lava rocks. Some of the lava around the volcanic neck were formed in pillow lava structure shape. The other domes were composed by autobreccia rocks. Meanwhile, sedimentary rocks (limestones) were distributed in the southern part of the area and some of them were silicified. Based on measurements result, lava and autobreccia phonolite rocks as product of sub marine volcanic are the most radioactive rocks in these area.