These values can be used to delineating alteration areas, which have high Th/U ratio (30 - >3000).
Th/U ratio of fresh Tapalang lava rocks has a value of 3-30, and alterated rocks have 30 - 3000 value. The alteration product indicated that this area has been affected by hydrothermal alteration in the potassic zone. Research methods were combination of radioactivity measurement and alteration observation in the field, completed by XRF and mineragraphy analysis to measure the grade of alteration. This study objective was to find the distribution of rock alterations and their correlation to the ratio of Th/U in Tapalang Region. An alteration process increases the level of uranium solubility, so that the uranium content is depleted and the concentration of thorium and rare earth elements (REE) are significantly high. Uranium potentials localization is required since uranium is not distributed evenly. Tapalang, Mamuju, is a destination for uranium exploration due to the high radiation detected in basaltic rocks of Adang Formation. Pengembangan eksplorasi torium dapat difokuskan pada daerah dengan alterasi lanjut, sedangkan eksplorasi uranium harus difokuskan pada daerah yang bersifat reduktif, yang memungkinkan terbentuknya cebakan uranium. Rasio Th/U pada batuan lava Tapalang yang masih relatif segar memiliki nilai 3-30, dan batuan yang telah teralterasi memiliki nilai 30 - >3000. Penelitian dilakukan dengan pengukuran radioaktivitas dan pengamatan alterasi di lapangan, kemudian dilengkapi dengan analisis XRF dan analisis mineragrafi untuk mengetahui tingkat alterasi. Dengan asumsi bahwa alterasi berasosiasi dengan rasio Th/U, maka dilakukan penelitian untuk mengetahui sebaran alterasi batuan berdasarkan korelasinya terhadap rasio Th/U. Proses alterasi meningkatkan tingkat kelarutan uranium, sehingga kadar uranium berkurang dan terjadi pengkonsentrasian torium serta logam tanah jarang (REE) yang signifikan. Diperlukan lokalisasi daerah-daerah dengan tingkat potensi kandungan uranium yang tinggi. The results of the project confirm the role of radiometric parameters as a useful tool for detection of rock contacts at a scale of tens of meters.Kecamatan Tapalang, Mamuju, menjadi tujuan eksplorasi uranium dengan adanya radiasi tinggi terdeteksi pada batuan basaltik Formasi Adang. The significant difference in depth trend can be observed in the area of Klatovy (possible influence of contact metamorphism). The mean radon concentration at depths of 50 and 80 cm was compared separately in 4 areas (Fig. However, in some cases, especially in the Veselí nad Lužnicí area (a contact of weathered Variscan granitoids or Moldanubian migmatites with Cretaceous sandstones and claystones), the upward release of radon was influenced by impermeable barriers. The increase in soil gas radon concentration with depth was observed in the majority of measured profiles. The highest accordance (80 %) was found in the area of Kytlice (a contact of trachytes with Cretaceous sediments), which is illustrated in Fig. The lowest accordant radon concentration and gamma dose rate increase or decrease (55 %) on the immediate rock contact was observed in the Klatovy area, which can be explained by the presence of a wide belt of hornfelses situated in the contact zone of Variscan granitoids and Neoproterozoic metasediments. The direct evidence of rock contact at a scale of particular profiles was observed on 68 % of the measured localities. This comparison resulted in mean 79 % accordance of both local and regional trends (range 67–100 %) in 4 areas with different geological environment.
The local trend in profiles was compared with regional data from radon database of the Czech Geological Survey and with a radiometric map (Manová – Matolín 1998). Each profile comprised 3 measuring sites (25–50 m apart) with radon measurements done at a depth of 30, 40, 50, 80 cm, and gamma dose rate measurement 1 m above the surface. A total of 45 localities investigated were situated in four areas: Klatovy, Kytlice, Veselí nad Lužnicí and Chrudim showing a variable geology. AbstractThe profile measurements of soil gas radon ( 222Rn) concentration and gamma dose rate (D´) were carried out along the contact of rocks characterized by contrasting radon index (Neznal et al.
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