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Mamuju is one focus area of radioactive mineral exploration in Indonesia. For almost a decade, geology, geochemistry, and geophysical exploration activities were conducted in the area. To estimate the uranium and thorium undiscovered resources in the area, a quantitative 3-part assessment is applied. The 3-part form of assessment assumes that mineral resources, contained in undiscovered deposits of a particular geological type, can be quantified using statistical distributions that characterize grades, tonnages, and the spatial distribution of known deposits of the same type. The 3-part assessments include three stages: (1) determination models of grades and tonnages of deposits, (2) delineation of permissive tracts, (3) estimation of the likely number of undiscovered deposits, and finally the estimation of the total undiscovered metal endowment. This paper focused on the delineation of permissive tracts from a regional to local geology point of view. Permissive tracts represent extended frontiers of terrains for which geologic environments permit a deposit type to form. Based on the geological analysis, volcanogenic uranium represents the deposit model for uranium in the area, while alkaline represents the deposit model for thorium. From the analysis of geology, geochemistry, and geophysical data, the permissive tract is delineated for further undiscovered resource assessment. Compared to the previous permissive tract delineation, the method integrating statistically processed radiometric and geochemical data, as well as geological map and deposit model was better and more effective for delineating permissive tract for undiscovered resources assessment. [ABSTRACT FROM AUTHOR]

Rare Earth Elements (REE) and Uranium (U) are found in several locations in West Kalimantan. The presence of this strategic mineral becomes a fascinating object to study. Tanah Merah is a potential sector in West Kalimantan which contains uranium and rare earth metals. Geological mapping, mineralization observations, and sampling of uranium and rare earth elements bearing ore have been carried out by geological and geochemical mapping to determine the potential of the research area. Geologically, the source rock in the study area is meta-silt, quartzite, mica schist, and igneous rock composed of rhyolite, rhyodacite, and several weathered granite intrusions. Monazite and uraninite mineralization occurs as lenses, veins, and disseminated in weathered granite bodies. In the Tanah Merah area, uranium and REE carrier minerals are found in the form of uraninite and monazite. The characteristics of monazite as a uranium and REE-bearing minerals have the characteristics of monazite formed in granitic rocks (La+Ce+Pr>75 and Ce/(Y+Nd) >2. This monazite has a low thorium content compared to uranium. The presence of monazite is associated with biotite, epidote, tourmaline, apatite, rutile, ilmenite, tetrahedrite, pyrite, chalcopyrite, and arsenopyrite. Weathered granite in the study area shows that monazite was formed in orthomagmatic and pneumatolytic zones. [ABSTRACT FROM AUTHOR]

The Semelangan area of West Kalimantan has the potential for radioactive minerals, namely monazite and thorite, which are concluded from the results of petrographic analysis and mineral grain analysis of granite rocks based on research that has been carried out since 1989. The petrographic data shows that the type of granite is granite and alkali-feldspar granite. Radioactive mineralization that occurs in granite (remaining magma) in addition to monazite and zircon is also found in thorite, which fills between minerals indicated by the track of alpha particles in thorite based on autoradiography results. In addition to petrographic analysis and autoradiography analysis, the presence of monazite and thorite in the study area, mineral grain analysis has been carried out which produces mineral content presentation data from 16 samples, and one of the samples containing 63% monazite mineral. [ABSTRACT FROM AUTHOR]

To support U, Th and REE exploration, in 2020 and 2021 radon and thoron gas measurements have been carried out in the Pompong valley, Toboali, South Bangka to see the pattern of radon and thoron gas in paleo-channel deposits which are believed to contain monazite. On Bangka Island, monazite, which is a by-product of tin mining, cassiterite, both primary tin mining in granite rocks and secondary tin mining in alluvial deposits. Geologically, monazite is formed in acidic to medium igneous rocks, moderate to high grade metamorphic rocks and sedimentary rocks, especially sandstones and alluvial deposits resulting from detrital of the three rock groups. In general, monazite contains uranium, thorium, phosphate and rare earth metals so that at this time it is considered to have significant economic value, especially its rare earth element content. Radon and thoron are the natural decay products of naturally occurring radioactive materials, uranium and thorium. Radon comes from the decay of 238U and thoron from 232Th. Measurement of the intensity of radon and thoron on the surface can be used as a pathfinder for the location of monazite trapped in the paleo-channel below the surface which is paleo-river deposits in a braided environment. Identification of the presence of monazite by mapping of radon and thoron gases provides an overview of the distribution pattern of monazite in this location and at the same time the presence of cassiterite as a tin-bearing mineral can be mapped well. As for achieving these objectives, the methodology used includes reviewing the results of previous studies including geological data and the presence of monazite (U, Th) both surface and subsurface, mapping of radon gas, data processing and analysis and evaluation. From the resulting of radon gas iso map, it showed that in general the pattern of radon and thoron gases in Pompong Valley area has a relative pattern of SSW –NNE and WNW-ESE to EW with the highest reading of radon gas reaching 28,000 Bq/m3 while for thoron it is 110,000 Bq/m3. This pattern was not much different from the paleochannel distribution in the Pompong Valley, especially in the south region. It remarked that the using of radon and thoron measurement can be a pathfinder for tin and monazite-bearing paleochannel, although further direct exploration still should be conducted. [ABSTRACT FROM AUTHOR]

Tebidah Formation is a 20,000 km wide and 1,000 m thick sedimentary rock in Melawi Basin. The formation in the Ella Hilir area shows the possibility of becoming a uranium deposit host rock based on the environment and physical properties. Geological mapping and radiometric surveys were carried out in the area to identify the uranium contents on the surface. Radon-thoron gas measurement in soil was carried out to find the reflection of uranium content in the subsurface. The geology of the research area is composed of sandstone, claystone, sandy-conglomerate, and alluvium units. Radiometric surveys show the presence of uranium and thorium anomalous zones to the north and slightly south of the area. Measurement of soil radon gas ranges from 11.52 – 47650.63 Bq/m3. Radon anomalies area is determined by concentration 7875.45 – 47650.63 Bq/m3 or 50.13 – 303 CPM and a radon-thoron ratio of 1.24 to 358.27. Radon strong anomaly distribution showed several anomalous zones trending northwest-southeast, which correlated with normal fault structures and sag pond morphology. The reflection of uranium deposit potential zones is in areas with high radon content and strong anomaly classification. A further study of the potential zones should be proposed to characterize subsurface lithologies. [ABSTRACT FROM AUTHOR]