Indonesian Journal on Geoscience Vol.
12 No.
3 December 2025: 319-341
INDONESIAN JOURNAL ON GEOSCIENCE
Geological Agency Ministry of Energy and Mineral Resources Journal homepage: h ps://ijog.
ISSN 2355-9314, e-ISSN 2355-9306 Makassar Strait Thrust - Mamuju Segment (MSTM) Perspective on Radioactive Mineral Exploration: A Case Study in Rantedoda.
Mamuju Roni Cahya Ciputra1.
Fadiah Pratiwi1.
Aldo Febriansyah Putra2.
Heri Syaeful1.
Frederikus Dian Indrastomo1.
Tyto Baskara Adimedha1.
Yoshi Rachael1, and I Gde Sukadana1 Research Center for Nuclear Material and Radioactive Waste Technology.
National Research and Innovation Agency (BRIN).
Tangerang Selatan 15314.
Indonesia Department of Geosciences.
Faculty of Mathematics and Natural Sciences.
Universitas Indonesia.
Depok 16424.
Indonesia Corresponding Author: roni010@brin.
Manuscript received: December, 23, 2024.
revised: March, 04, 2025.
approved: August, 11, 2025.
available online: September, 24, 2025 Abstract - The Makassar Strait Thrust Ae Mamuju Segment (MSTM) is a key structural feature influencing uranium (U), thorium (T.
, and rare earth element (REE) mineralization in Mamuju.
West Sulawesi.
This study explores a relationship between tectonic deformation, weathering processes, and mineralization, focusing on the Rantedoda sector.
Integrated geomorphic, geological, radiometric, petrographic, and geochemical analyses reveal that MSTM faults act as conduits for hydrothermal fluids, promoting mineral mobilization, alteration, and enrichment in fault zones.
MSTM produced curved NW SE to N S thrusts torn by NE SW right-lateral strike-slip faults in the studied area.
Radiometric data highlight anisotropic distributions of U.
Th, and dose rates aligned with NE SW and NW SE fault trends.
Geochemical indices demonstrate that weathering is critical for REE and Th enrichment, as high eTh and low K values indicate.
Moreover, fault-facilitated hydrothermal clay alteration supports U adsorption, as noted by high values of all radiometric parameters in the area near a fault.
These findings establish the critical role of fault systems in controlling mineralization processes, providing a framework for targeted exploration strategies in tectonically complex terrains of the Mamuju area.
Keywords: Mamuju.
Rantedoda, uranium, thorium.
REE.
Makassar Strait Thrust.
Faults A IJOG - 2025 How to cite this article:
Ciputra.
Pratiwi.
Putra.
Syaeful.
Indrastomo.
Adimedha.
Rachael.
, and Sukadana, , 2025.
Makassar Strait Thrust - Mamuju Segment (MSTM) Perspective on Radioactive Mineral Exploration: A Case Study in Rantedoda.
Mamuju.
IndoAnesian Journal on GeoAscience, 12 .
, p.
DOI:
17014/ijog.
Introduction Background Nuclear energy is encouraged to be one of Indonesia programmes to fulfill its commitment to Net Zero Emission (NZE) by 2060 (Permana et al.
, 2022.
Kanugrahan and Hakam, 2023.
Shah et al.
, 2.
Nuclear Power Plant (NPP) implementation in the Indonesian electricity system simulation showed that NPP could significantly satisfy the nation electrical energy needs while simultaneously reducing CO2 emissions, given the limited implementation of other low-carbon, renewable energy sources like hydro, geothermal, solar, and wind power (Rahmanta et al.
, 2.
Other simulations noted that NPP would contribute the most to the nation energy share among all renewable energy sources (Permana et al.
, 2.
Those findings on the importance of NPP deployment also imply the importance of nuclear energy Indexed by: SCOPUS
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Vol.
12 No.
3 December 2025: 319-341 system development, including the development of the raw nuclear materials that will emerge as strategic commodities.
Indonesia's raw nuclear materials are available from uranium and thorium deposits in Kalimantan.
Sulawesi.
Sumatra.
Papua.
Bangka-Belitung, and the Riau Islands (Syaeful et al.
, 2.
Particularly in Sulawesi, the Mamuju area of West Sulawesi has volcanogenic-type deposits in the Adang Volcanic Rocks (MuAoawanah et al.
, 2019.
Rosianna et , 2020, 2023.
Sukadana et al.
, 2015, 2.
The Adang Volcanic Rock magma is highly alkaline, ranging from sodic to ultrapotassic.
It has a diverse magma series, including tholeiitic, calc-alkali, high-K calc-alkali, and shoshonite magmas.
Based on geochemical data, the rocks are basaltic trachyandesite, trachyandesite, andesite, tephriphonolite, and trachyte (Syaeful et al.
, 2.
Highly naturally occurring radioactive materials (NORM) have been identified coming from The Adang Volcanic Rock, contributing to Mamuju highest average dose rate in Sulawesi and even Indonesian regions, which can reach 2,800 nSv/h, (Syaeful et al.
, 2.
The isotope characterization reveals the 238U and 232Th concentrations of laterite and rock of the area to be 22,882 and 33,549 Bq/kg on average (Rosianna et al.
, 2.
The Rosianna et al.
study also shows that equilibrium uranium is further remobilized, interpreted as influenced by groundwater and the reduction-oxidation There are two types of uranium and thorium mineralization in Mamuju: volcanic and lateritic deposits.
The volcanic deposit can be distinguished into strata-bound and structure-bound deposits (Sukadana et al.
, 2016.
Rosianna et al.
Syaeful et al.
, 2.
The primary radioactive minerals identified in Mamuju are davidite and thorianite, while the secondary minerals are gummite and autunite.
SEM-EDS Point analysis in thorianite mineral shows 1.
16 wt.
% and 31.
14 wt.
% for uranium and thorium, respectively (Sukadana et al.
, 2.
Investigation in weathered volcanic rock in Mamuju area showed a strong indication of the REE-rich mineral of zircon with values ranging from 567 -6400 ppm in the weathering profile of the phonolitic leucitite rock, specifically in Kelapa Tujuh and North Botteng Villages (Ritonga et , 2.
The Geochemical analysis on veins in Hulu Mamuju area shows several Th and REEbearing minerals of britholite, aeschynite, monazite, chevkinite-Ce, thorite, and thorutite (Sukadana et , 2.
The samples are altered, and Th content is elevated to 7.
4 %, while total REE content is elevated to 4.
8 %.
Radiometric analysis also shows enrichment of Th in the altered and weathered region of Adang Volcanic Rocks in Mamuju (Syaeful et al.
, 2014.
Sukadana et al.
, 2.
Adang Volcanic Rock is among the rock formations affected by the presence of The Makassar Strait Thrust (MST) in the west (Guntoro, 1999.
Puspita et al.
, 2.
The MST segment west of Mamuju is The Makassar Strait Thrust Mamuju Segment (MSTM) (Meilano et al.
, 2023.
Serhalawan and Chen, 2.
The MST is active and contributes to the higher crustal strain rate of Mamuju and Majene relative to their surrounding areas, causing a damaging earthquake in 2021 (Meilano et al.
, 2.
remote sensing analysis indicated that the SE NW lineament system in Mamuju controlled volcano distribution and U-Th mineralization based on their similar distribution (Indrastomo et al.
, 2.
yet how the identified lineament system influences the mineralization remains unclear.
The MSTM contribution to uranium mineralization in Mamuju needs to be discussed to address any implications for the exploration programme.
This work covers that topic by integrating geology, geophysics, and geochemistry of a sector in Mamuju as a case study to fill the gap in research.
Rantedoda Sector is one of the areas with the radiometric anomaly in Mamuju (Sukadana et al.
, 2.
A further study reveals higher U content of samples from this sector up to 0.
09 wt.
% UO2, 0.
13 wt.
% ThO2, 21 wt.
% total REE content (Pratiwi et al.
This sector was chosen for the case study, because it had high levels of U.
Th, and REE in a region affected by MSTM activity that led to the formation of a thrust belt known as The Mamuju Thrust Belt (MTB), characterized by numerous structural features.
Geological Settings The tectonic setting of Sulawesi is built by the interactions among three major plates: the PUBLISHED IN IJOG Makassar Strait Thrust - Mamuju Segment (MSTM) Perspective on Radioactive Mineral Exploration:
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Mamuju (R.
Ciputra et al.
Eurasian Continental Plate, the Oceanic-Continental Indo-Australian Plate, and the Oceanic Pacific-Philippine Sea Plate.
Tectonic events from the Late Mesozoic to the Cenozoic created four tectonic provinces, namely The WesternNorthern Sulawesi Magmatic Arc .
omprising south, west, neck, and north arm.
The Central Sulawesi Metamorphic Belt.
The East Sulawesi Ophiolite .
ast ar.
, and The Banggai-Sula and 117 40'0 E
117 50'0 E
Lineaments ( Thrust fault
Legend
118 30'0 E
118 40'0 E
119o0'0 E
118o50'0 E
119 10'0 E
119o20'0 E
119o30'0 E
119 40'0 E
Thrust fault
0 50'0 S
0o50'0 S .
Anticline .
118 20'0 E 118o10'0 E 118o0'0 E Buton-Tukangbesi Microcontinental Fragments (Maulana et al.
, 2.
This study is located in West Sulawesi region, as illustrated by Figure 1a, which is currently developed as a fold-thrust belt with active seismicity (Meilano et al.
, 2.
The tectonic evolution of West Sulawesi region began in the Late Cretaceous when the East Java-West Sulawesi Block was accreted to the margin of Sundaland (Hall and Sevast- Syncline .
Holocene Alluvium Pleistocene-Holocene Coralline Limestone Pleistocene Conglomerate Plssu Pleistocene Marl Mpu Pambuang Msu Mvu Miocene-Pliocene Cmu Rocks Intrusive Miocene-Pliocene Mapi Fm.
Qa Quaternary Alluvium Miocene-Pliocene Talaya Volcanics Plssu Pleistocene Miocene Mamuju Fm.
Miocene plutonic unit Msu Miocene Adang Volcanics 1o40'0 S 1o40'0 S sedimentary unit Mpu Miocene Miocene Miocene Mandarvolcanic Fm.
Cretaceous Cretaceous Latimojong unit Fm.
Mvu
Cmu
Adang volcanics Research
Research Area
Area
Lineament
Thrust / Reverse Fault
Anticline Syncline Legend
2 30'0 S
2o30'0 S Research Area
Elevation Lineament
High : 3069
Reverse Fault
Syncline Anticline Low : 2656
116o0'0 E
118o0'0 E
120o0'0 E
122o0'0 E
114o0'0 E
116 0'0 E
118o0'0 E
120o0'0 E
122o0'0 E
124 00'0 E
3 20'0 S
4 0'0 S
3 0'0 S
3o0'0 S 4o0'0 S 3o20'0 S 1 0'0 S 1o0'0 S 0o0'0 S 0o0'0 S 114o0'0 E
117 40'0 E
117 50'0 E
118 0'0 E
118 10'0 E
124o00'0 E
118 20'0 E
118o30'0 E
118o40'0 E
118o50'0 E
119o0'0 E
119o10'0 E
119 20'0 E
119 30'0 E
119o40'0 E Figure 1.
Regional structural map of the West Sulawesi region .
orthern part: about 0o50Ao0oS to 2o30Ao0oS.
southern part:
approximately 2o30Ao0oS to 3o30Ao0oS) and .
Geologic map of the southern part of the West Sulawesi region.
The maps are modified after Bachri and Baharuddin .
Calvert and Hall .
Coffield et al.
Ratman and Atmawinata .
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Indonesian Journal on Geoscience.
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A west-dipping subduction zone then developed east of the West Sulawesi region .
Moss and Chambers, 1999.
Elburg et al.
Hall and Sevastjanova, 2.
The rollback of this subduction zone caused the rifting of Makassar Strait Basin, and West Sulawesi region moved away from Kalimantan starting in Early Eocene (Simandjuntak, 1986.
Guntoro.
Hall and Sevastjanova, 2.
From the Middle to Late Eocene, the West Sulawesi region underwent a syn-rift phase that included terrestrial, transitional, and marine environments.
The marine post-rift phase began in Oligocene (Coffield et al.
, 1993.
Calvert and Hall, 2.
The subduction-related magmatism in the West Sulawesi Region stretched from Paleocene to Early Miocene .
Polvy et al.
, 1997.
Elburg et al.
, 2003.
Leeuwen and Muhardjo, 2.
Extension-related magmatism developed from Middle Miocene to Late Pliocene (Elburg et al.
Hennig et al.
, 2.
During Pliocene, the extension-related magmatism developed simultaneously with metamorphism (Hennig et , 2.
The West Sulawesi region underwent a major tectonic uplift in Plio-Pleistocene by the formation of the fold-thrust belt (Coffield et al.
Leeuwen and Muhardjo, 2005.
Calvert and Hall, 2.
Present-day structural features of the West Sulawesi region, as shown in Figure 1a, are inverted half-graben and fold-thrust belts that developed due to the Plio-Pleistocene compressional deformation (Coffield et al.
, 1993.
Leeuwen and Muhardjo, 2005.
Puspita et al.
Calvert and Hall, 2007.
Raharjo et al.
In the northern part of the region, the NE-SW half-graben system and NW-SE transfer faults were subjected to inversion (Calvert and Hall, 2007.
Raharjo et al.
, 2.
Folds in the area are trending in the N-S direction, and the mountain fronts in the northern part of the region are thrust-related (Calvert and Hall.
The fold-thrust belt in the southern part of the region, as depicted by Figures 1a and 1b, changed its trend into an N S direction, and it showed imbricating geometry (Coffield et al.
The 2021 Mw 6.
2 earthquake in Mamuju showed that the southern part of the region was related to thrusting along the east-dipping fault plane (Meilano et al.
, 2.
Stratigraphy of the Mamuju area is composed of a distribution of volcanic rocks and marine sedimentary rocks (Ratman and Atmawinata.
The constituent rocks of this area from the oldest are Middle Miocene - Pliocene Talaya Volcanic Rocks.
Middle Miocene - Late Miocene Adang Volcanic Rocks.
Middle Miocene - Late Miocene Mamuju Formation limestone with its Late Miocene Tapalang Member limestone, and Holocene coral limestone and alluvial deposits.
The Adang Volcanic Rock comprises trachytephonolite rocks with ultrapotassic magmatic affinity from an Active Continental Margin (Sukadana et al.
, 2.
The Adang Volcanic Rock also can be divided into several volcanostratigraphic units based on their volcanic features (Indrastomo et al.
, 2015.
Sukadana et al.
, 2015.
Sukadana, 2.
, as shown in Figure 2.
The researched area is Rantedoda Lava.
Takandeang Lava, and Limestone units.
Methods In this research, a geomorphic analysis desk study was done using a NASA Digital Elevation Model (NASADEM) image to identify the structural features of the area, and to guide the The NASADEM was created from the Shuttle Radar Topographic Mission (SRTM) reprocessing (Crippen et al.
, 2.
In generating NASADEM, the vertical control of SRTM was improved with ICESat (Ice.
Cloud, and Land Elevation Satellit.
elevations, a precise elevation gained from laser altimetry techniques.
The voids on the predecessor were filled with The Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model (ASTER GDEM) (Crippen et al.
, 2.
The geomorphic analysis was conducted by observing the geomorphic expressions size, shape, arrangement, and textures.
This observation led to identifying landform types and lineaments and, thus, to interpreting structural features.
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Makassar Strait Thrust - Mamuju Segment (MSTM) Perspective on Radioactive Mineral Exploration:
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Mamuju (R.
Ciputra et al.
Legend Street River Lineaments Research Area Alluvium (Q.
River Deposit (Q.
Bgpt Coralline Limestone (Bgp.
Brkl Conglomerate-Breccia (Brk.
Kgl Conglomerate (Kg.
Bps Sandstone (Bp.
Brk Breccia (Br.
Bgpk Limestone (Bgp.
Brv.
Tapalang Volcanic Breccia (Brv.
) Lvd.
Tapalang Lava Dome (Lvd.
) Brv.
Sumare Volcanic Breccia (Brv.
) Lva.
Sumare Andesitic Lava (Lva.
) Lvb.
Sumare Lava Breccia (Lvb.
) Brv.
Takandeang Volcanic Breccia (Brv.
) Lv.
Takandeang Lava (Lv.
) Brv.
Mamuju Volcanic Breccia (Brv.
) Lv.
Mamuju Lava (Lv.
) Brv.
Ampalas Volcanic Breccia (Brv.
) Lvd.
Ampalas Lava Dome (Lvd.
) Brv.
Malunda Volcanic Breccia (Brv.
) Lva.
Blp Malunda Andesitic Lava (Lva.
) Claystone (Bl.
Figure 2.
Geological Map of Mamuju area .
odified from Rosianna et al.
and Sukadana .
The fieldwork comprised .
geological observation and mapping to obtain lithology and structural geology data, .
rock and soil sampling for geochemical analysis and petrographic analysis of the rock samples, and .
radiometric mapping for videography and anisotropy analysis of the A structural geological analysis of the fieldwork was done to confirm the geomorphic analysis.
Fault slip data were collected and analyzed using the open-source WinTensor (Delvaux and Sperner, 2.
downloaded from https://damiendelvaux.
be/Tensor/WinTensor/ win-tensor.
html to determine the faultAos type and kinematics.
Rock samples were taken from a chip sampling using a geological hammer and a portable hand drill.
Meanwhile, soil samples were obtained from the soil strata above the bedrock, free of plant organic components.
The geochemical analysis was performed with Energy Disperse X-ray Fluorescence (ED XRF) Spectro XEPOS in the BRIN laboratory for twenty- five rock samples and fourteen soil samples representing different lithologies.
Geochemical analysis for major elements using the XRF method has been conducted by several researchers in geochemistry within the exploration of rare earth mineral deposits (Hartiningsih et al.
Odigo et al.
, 2023.
and Winarno et al.
Eight samples were for petrographic analysis with the same representation purpose as the geochemical analysis.
Several indices were used to infer the rock weathering degrees: Lost on Ignition (LOI).
Chemical Index of Alteration (CIA), and Index of Lateritization (IOL).
These indices are calculated based on major element concentration in the weathered products.
Chemical Index of Alteration (CIA), noted as .
, was used to evaluate the formation of clay minerals from feldspars.
where oxides are expressed in molar proportions.
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, measured the degree of lateritization in extreme weathering conditions, which CIA cannot accurately measure.
The radiometric mapping was retrieved from a GPS-linked RS-125 gamma spectrometer carried by the moving person and measured the concentration of radionuclides in 1-minute intervals.
The variography and anisotropy analysis of the radiometric data was done using ArcGIS, followed by kriging interpolation to make radionuclides distribution maps.
All the data were then synthesized to identify the relation between the MSTM-contributed structural features of RanteA doda to the U.
Th, and REE enrichment and their implication on the exploration strategies.
Result Geomorphic And Fault Slip Analyses The studied area shows mountainous and lowrelief terrains separated by thrust-related mountain fronts (Figure 3.
The elevation ranges from sea level to 888 m.
The mountainous terrains show rugged and mottled topographic features (Figure 3.
, as the former is underlain by Takandeang Volcanic Breccia and Takandeang Lava, while the latter is underlain by limestone .
ee Figure .
The smooth, low-relief terrains correspond to alluvial .
ee Figure .
The main structural features of the thrust-related mountain fronts are curved NW SE to N S thrusts torn by NE SW right-lateral strikeslip faults (Figure 3.
The NE SW right-lateral strike-slip faults (S1.
S2, and S.
accommodate changes in the trend of the NW SE to N S thrust faults (T1.
T2, and T.
Thrust occurring in this studied area displays imbricating geometry.
The T1 and T2 Thrusts are the main faults, while the others occur as backthrusts.
The T1 and T2 Thrusts form the mountain fronts, and the backthrusts are expressed as thrust valleys (Figures 3a to 3.
the other hand, the right-lateral strike-slip faults are arranged subparallel to each other.
Geomorphic expressions of the strike-slip faults are fault ridges (The S3 Faul.
and linear fault valleys (The S1.
S2.
S4, and S5 Fault.
Due to the heavily weathered outcrops, limited fault planes are preserved for structural analysis.
However, field structural data acquired in the S4 Fault .
and b stations of Figure 3.
show NE SW right-lateral strike-slip faults formed due to WNW ESE compression (Figures 4a and 4.
Hot springs are found in a river and They are found near the S1 and T3 Faults and are interpreted to be related to the faults.
The example of a hot spring located in the c station of Figure 3a is depicted in Figure 4c.
Stratigraphy Geological observations resulted in the distribution of rock units in the researched area being divided into four units: Tasipa Lava.
Rantedoda Lava.
Sandstone, and Limestone.
Rock and soil sampling was performed in Tasipa and Rantedoda Lavas, the host rock of volcanogenic-type The geological map and sample distribution are displayed in Figure 5.
Tasipa lava appearance in the field is generally fresh, while the altered outcrops are found in the north and northeast.
The example of the Tasipa lava outcrop is depicted in Figure 6a.
It is a porphyroaphanitic foiditoid rock with phenocrysts that include leucite, biotite, pyroxene, and hornblende (Figure 6.
The Rantedoda Lava has several dome features, as observed from the circular features in the DEM (Figure .
These units have flowing structures, auto breccia, and sheeting joints (Figure It also consists of foiditoid rocks with a mineral composition of leucite, biotite, and pyroxene.
It has a porphyro-afhanitic to porphyro-phaneritic texture (Figure 6.
However, it has a relatively smaller phenocryst than the Tasipa Lava.
The Sandstone Unit consists of sandstone, claystone, conglomerate, and coal are found around the valley in the northwest and southwest.
The boulders of the conglomerate measuring 5 - 30 cm with closed packs were discovered at this location (Figure 6.
Contact outcrops between the Tasipa Lava unit and the conglomerate layers are found in the studied location, northern part of the studied PUBLISHED IN IJOG Makassar Strait Thrust - Mamuju Segment (MSTM) Perspective on Radioactive Mineral Exploration:
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Ciputra et al.
Elevation Meter Strike-slip fault T1b 1 Fault kinematic T = Thrust fault S = Strike - Slip fault 2 Fault number Thrust fault Fault Name Research area Stream Elevation proAle Fault stations Hot springs Elevation .
Distance .
Elevation Meter Figure 3.
Structural map, .
Elevation profile, .
Three-dimensional view of the studied area (MF: mountain front.
TV:
thrust valley.
FR: fault ridge.
LFV: linear fault valle.
area (Figure 6.
Layers of grey sandstone with fossilized shell material as a matrix were found on claystone layers found predominantly at the studied site, as examples in Figure 6g.
Coal seams were also found at two locations southwest of the researched location on the Rantedoda branch of the At least two locations of coal outcrops were found in the river fork (Figure 6.
The limestone unit found in the southwestern part of the studied site is close to the morphology of the lowlands in PUBLISHED IN IJOG Indonesian Journal on Geoscience.
Vol.
12 No.
3 December 2025: 319-341 Fault plane: N243oE/85o Pitch: 10oE Right-lateral fault with Fault plane: N57 E/71 Pitch: 45 E Right-lateral fault with reverse component Figure 4.
Fault-slip analysis of the S4 Fault on station a.
Fault-slip analysis of the S4 Fault on station b.
Spring on the river along the S1 Fault.
Sample ID Rock Sample Legend Soil Sample Radiometric Data Outcrop ID Strike-Slip fault Thrust fault Fault Name Outcrops (Fig.
Hot spring Fault kinematic T = Thrust fault S = Strike-Slip Fault number Dome Features Sandstone Rantedoda Lava Tasipa Lava Figure 5.
Geological map overlayed with radiometric data and sample distribution.
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Ciputra et al.
Figure 6.
Tasipa lava outcrop.
Tasipa lava megascopic appearance.
Rantedoda lava megascopic appeareance.
Rantedoda lava outcrop showing sheeting joints.
Basal conglomerate of Sandstone Unit.
Contact between conglomerate and lava.
Layers of sandstone and claystone of Sandstone Unit.
Coal seam layer outcrop of Sandstone Unit.
Limestone outcrop above lava.
location of these outcrops is depicted in Figure 5 Rantedoda Village.
The unit consists of reef and clastic limestone that grow on the claystone and Tasipa Lava (Figure 6.
The limestone has been undergoing a diagenetic process at several places that producing crystalline limestone.
Petrographic Analysis Among eight volcanic rock samples, four samples were taken from Rantedoda Lava Unit (RDD 17.
RDD 18.
RDD 5, and RDD .
, and four samples were from Tasipa Lava Unit (RDD 9.
RDD 12.
RDD 15, and RDD .
Based on petrography observation, the general mineralogy of all the samples is closely identical.
The phenocryst and groundmass predominantly are feldspathoid minerals such as leucite, pyroxene, biotite, alkali feldspar, and volcanic glass.
Volcanic rocks from the researched area do not have any quartz content, which indicates that these rocks have a low level of silica saturation.
Based on mineral composition, all the volcanic rocks in Rantedoda are Foidit (Table .
Some examples of the photomicrograph showing petrographic textures of the sample can be seen in Figure 7.
The rock samples show porphyritic texture, with a skeletal texture very common in leucite mineral groundmass.
Porphyritic texture indicates at least two crystallization processes: phenocryst crystallization occurs first, producing larger minerals, and then the groundmass crystallization process produces finer minerals.
Skeletal texture indicates the crystal mineral develops under PUBLISHED IN IJOG Indonesian Journal on Geoscience.
Vol.
12 No.
3 December 2025: 319-341 Table 1.
Mineralogical Composition of Lava Rock from Rantedoda Area
Code
RDD 17
RDD 18
RDD 1
RDD 5
RDD 9
RDD 12
RDD 15
RDD 41
Phenocryst Composition (%) Groundmass Composition (%) Leu Alf Leu Px needles Glass Lithology Foidit Foidit Foidit Foidit Foidit Foidit Foidit Foidit Leu: Leucite.
Px: Pyroxene.
Alf: Alkali Feldspar.
Bt: Biotite Chl 5 mm 1 mm 5 mm Chl Alf 1 mm 1 mm 1 mm Figure 7.
Skeletal texture observed in leucite mineral from .
RDD 1 and .
RDD 12, .
Photomicrograph of foidit lava from Rantedoda Unit, .
Photomicrograph of foidit lava from Tasipa Unit.
Abbreviation: Lc: leucite, px:
pyroxene, bt: biotite, alf: alkali feldspar, chl: chlorite.
conditions of rapid growth and a high degree of The difference between Tasipa Lava Unit and Rantedoda LavaUunit can be seen from the size of the phenocryst, percentage, and the composition of the groundmass.
The Tasipa Lava Unit has bigger phenocrysts and more phenocryst content than the Rantedoda Lava Unit, and the presence of glass groundmass in the Tasipa Lava Unit also differentiates it from the Rantedoda Lava Unit.
Some of the samples show evidence of weathering/alteration, clay masses .
rown-black in thin section.
are observed in the groundmass of the samples .
in RDD 17, 18, 1, 5, 9, and .
, zeolite is observed growing in vesicles .
in RDD 15 and .
, and chlorite is observed in groundmass and fracture of minerals .
in RDD 1, 12, and .
Calcite was found growing in fracture .
in RDD .
Geochemistry About thirty-nine rock and soil samples from different units were collected.
Major and trace element measurements were done using X-ray The XRF result for rock samples from the studied location has a SiO2 content range 09 - 60.
27 wt.
%, which means the rocks belong to the basalticAeintermediate group.
The results from various diagrams are shown below to classify the Rantedoda and Tasipa Lava groups, and to explain their tectonic environment.
Based PUBLISHED IN IJOG Makassar Strait Thrust - Mamuju Segment (MSTM) Perspective on Radioactive Mineral Exploration:
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on Winchester and Floyd .
rocks samples from Rantedoda Lava and Tasipa Lava belong to basanite-trachybasanite, phonolite, and trachyandesite (Figure 8.
, with magma affinity range from calc-alkaline series to shosonitic series (Peccerillo and Taylor, 1.
(Figure 8.
Rantedoda and Tasipa Lava groups show high alkalinity, ranging from calc-alkaline to shosonitic.
Rocks with high alkalinity are usually found in tectonic settings Comendite.
Pantellerite K2O weight % Trachyte Andesite Phonolite Sub-alkaline Tasipa Lava ic series Calc-al Rantedoda Tasipa Lava e se -alk Hig Basanite.
Rantedoda Rhyodacite.
Rhyolite SiO2 wt.
related to continental crust, further away from the trench, and rarely in early subduction processes (Pearce and Cann, 1973.
Winter, 2.
Tectonic setting determination using ThZr/117-Nb/16 diagram, depicted in Figure 9a (Wood, 1.
, suggest that both Rantedoda and Tasipa Lava groups was formed in the Arc Basalt Environment.
On Zr/Y vs Zr diagram, displayed in Figure 9b (Pearce, 1.
, both of the groups Tholeiit Zr/TiO2 .
SiO2 weight % Figure 8.
Zr/TiO2 vs SiO2 diagram and .
SiO2 vs K2O diagram.
Zr/117 Rantedoda Lava Rantedoda Lava Tasipa Lava Tasipa Lava Continental arcs Alk e basal Oceanic arch Nb/16 La/Yb La/Yb Alkaline arcs MORB Oceanic island Major ocean Alkaline arcs Rantedoda Lava Tasipa Lava Oceanic island Th/Nb Continental Oceanic arch Zr .
Oceanic arch Continental Nb/La Zr/Y N-MORB Rantedoda Lava Tasipa Lava Figure 9.
Tectonic setting discriminant diagram: .
Th-Zr/117-Nb/16 diagram (Wood, 1.
Zr/Y vs Zr diagram (Pearce, .
La/Yb vs Nb/La and .
La/Yb vs Th/Nb diagrams (Kurt Hollocher et al.
, 2.
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La/Yb vs Nb/La and La/Yb vs Th/Nb diagrams on Figure 9c and 9d (Kurt Hollocher et al.
, 2.
show that rocks from the studied area are dominantly plotted as an alkaline arc with some samples plotted as a continental arc.
Based on geochemical characteristic above, rocks in the thestudied area indicate that they were formed in a continental margin transitioning from subduction to late-subduction The rock samples used in this study have been weathered to different degrees.
Thus, all of the data have high Loss on Ignition (LOI) values.
LOI values of the rock samples range from 2 Ae 10 wt.
%, and the LOI values of the soil samples range from 13 Ae 21 wt.
The geochemical analysis was carried out on the main and trace elements, considering trace elements had more immobile properties even though the rock had experienced weathering.
The CIA values in Tasipa Lava Unit range 12 to 99.
In the weathering rocks CIA values under 60 suggest lower weathering, 60Ae80 is moderate weathering, and more than 80 is extreme weathering samples from this unit.
Thus plotted using A-CN-K ternary diagram (Figure 10.
, the soil fell under extremely weathered and the plot gathered at Al2O3 peak, which could be linked to the presence of clay mineral in the soil
A12O3
SiO2 Index of Lateritization (IOL) Chemical Index of Alteration (CIA) (Nesbitt and Young, 1982.
Fedo et al.
, 1.
The IOL value ranges from 24.
55 to 58.
The progression from foidit rock to soil can be seen in Figure 10b, which depicts loss of Si and enrichment of Fe and Al during the lateritizion.
Some of the soil was placed in kaolinitization stage, and some in weakly lateritization stage (Schellman.
Babechuk et al.
, 2.
The SiO2 content in the rock and soil in Tasipa Lava Unit is considerate low ranging between 59 to 57.
29 wt.
CaO ranges from 0.
004 to 22 wt.
Na2O ranges from 0.
00 to 9.
42 wt.
K2O ranges from 0.
03 to10.
11 wt.
These four show decrease from the rock to soil.
Al2O3 ranges between 7.
11 to 22.
10 wt.
%, and Fe2O3 ranges between 8.
09 to 25.
34 wt.
They both increase from rock to soil.
The decrease of silica, natrium, potassium, and calcium.
The increase of aluminum contents from rock to soil display the formation of clay mineral from the weathering of feldspathoid, the high Fe2O3 content in the soil indicates that the clay formed could be Fe-rich clay or the soil is high in iron oxide minerals.
The total REE content in rock and soil in Tasipa Lava Unit ranges from 1077.
80 to 7833.
60 ppm.
Th ranging between 204.
30 to 883.
60 ppm, and U ranging from 46.
30 to 189.
10 ppm.
Th is enriched in weathering product, meanwhile U shows irregular trend (Figure 11a and 11.
Among REE
CaO Na2O
K2O
A12O3
Fe2O3 Figure 10.
A-CN-K ternary plots illustrating different degrees of alteration experienced in rocks and soil of Tasipa Lava Unit, the chemical index of alteration (CIA) is integrated into A-CN-K ternary plots.
SAF ternary plots illustrating the different degrees of alteration in rocks and soil of Tasipa Lava Unit, the index of lateritization (IOL) is integrated into SAF ternary diagram.
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Rock
Rock
Rock
Soil
Soil
LOI
Soil
CIA
IOL
LOI
Rock
Rock
Soil
Rock
Soil
Soil
LOI
CIA
IOL
Rock
Soil
TREE
Rock
Soil
LOI
Soil
Rock
CIA
IOL
Rock
Soil
Rock
Soil
Rock
Soil
LOI
CIA
IOL
Figure 11.
Selected element vs weathering indices: .
U, .
Th, .
Total REE (TREE), and .
Ce.
detected in these samples (Figure 11.
, only Ce shows enrichment during weathering (Figure 11.
, while the other shows irregular trends.
Radiometric Data Analysis The variography analysis shows anisotropy in eU, eTh, and dose rate data in the NE SW direction.
For K data, however, it has not detected anisotropy as the range in all directions is the Hence, an omnidirectional experimental variogram was used for K data, while the other used a directional experimental variogram.
The variogram was then modeled with a spherical and nested spherical variogram model.
The variogram models are depicted in Table 2 with their corresponding variogram maps.
The results are displayed in Figure 12, with an overlaying a geological map.
The radiometric maps of Rantedoda reveal how the structural features affected the distribu331 PUBLISHED IN IJOG Indonesian Journal on Geoscience.
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12 No.
3 December 2025: 319-341 Table 2.
Variogram Modes of Each Parameters And Their Corresponding Variogram Maps Nugget Parameters Model Type Effect (C.
Sill (C) Range .
Variogram maps Minor
Major
Minor
Major
Nested Spherical Nested Spherical Spherical Dose rate
Nested Spherical Rantedoda
Rantedoda
Rantedoda
Rantedoda
(K)
U) .
(Dose Rat.
Figure 12.
Kriging Result of each parameter with overlaying geological maps and structural features.
tion of K, eU, eTh, and dose rate values.
It is also backed up by the anisotropic detected on the variogram maps of eU and eTh that follow the strike-slip faults trend of NE SW.
Meanwhile, the lithology does not comply with the radiometric map, except for the limestone unit, where all radiometric parameters show lower values.
The high value of all radiometric parameters occurs in the southern part of the studied area near the T2c thrust fault.
For K, the high radiometric value is limited near the T2c thrust fault, while for eU, eTh, and dose rate, the high radiometric value extends to the east.
Moreover, the eU case follows the S5 strike-slip fault.
The radiometric value trend that elongated along a fault was also observed in several locations.
The K value is high along the PUBLISHED IN IJOG Makassar Strait Thrust - Mamuju Segment (MSTM) Perspective on Radioactive Mineral Exploration:
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S4 strike slip-fault, while the opposite is observed in the eTh distribution.
This phenomenon is also observed in the uphill of Tasipa region, between S1 and S4 fault.
The eU, eTh, and dose rate values also seem bound to the T3 thrust fault, while there is only a slight increase in value for the K case.
High values along the S1 strike-slip fault are seen on K and eU, whereas noncontinuous increasing values are detected in eTh and dose rate along the The higher values of eU were also spotted near hot springs along the S1 strike-slip fault, and T3 thrust fault.
This case has somehow faded on dose rate distribution, but the values are still high.
Discussion The results of Rantedoda and Tasipa Lava Groups are similar to other volcanic rocks found in the Mamuju area.
Volcanic rocks from Tapalang.
Ampalas.
Malunda, and Adang Complexes show the same magma series ranging from calc-alkaline to shoshonitic series, formed in subduction-related settings, with magma formation strongly influenced by the continental crust (Sukadana et al.
, 2015.
Draniswari et al.
, 2.
The geomorphic analysis, supported by ground checking of structural features, indicates that MSTM strongly contributed to the deformation of the studied area.
The anisotropic distribution of radiometric parameters in NE-SW and NW -SE directions align with the fault trends, confirming structural control.
Faults add a weak plane to the earth's surface, facilitating water movement.
The interaction between water and rock below the surface may alter the composition, leading to the alteration and exogenic processes such as weathering and erosion.
This is what happened to the volcanic rocks of Rantedoda.
The deformation affected the radiometric distribution, but it is not the only factor controlling the U.
Th, and REE enrichment, as weathering also plays a role.
The geochemical behaviours of K.
U, and Th in soils are governed by complex interactions involving mineralogy and environmental conditions.
The U is relatively more mobile than Th and Under oxidizing conditions.
U is more soluble and mobile, contributing to its redistribution in soil profiles, and conversely, it will precipitate and become immobile in reducing conditions (OmelAoyanenko et al.
, 2007.
Veerasamy et al.
On Rantedoda a high content of eU was noticed near the hot spring controlled by faults, such as the S1 strike-slip and T3 thrust faults.
This suggests an outflow of subsurface water containing leached U from the volcanic rocks where faults become pathways, that further facilitate uranium transport into hot springs.
Elevated U content from the leaching of surrounding rock where fault zones and weathering are heavily present is a common phenomenon, such as in U-rich black shales and granite in Okchun Belt.
South Korea (Lee et al.
, sandstone in Eastern Cape.
South Africa (Madi et al.
, 2.
, metamorphites U deposit in Caldas Novas.
Brazil (Lunardi and Bonotto, 2.
, and uranium-rich volcanic rocks in Ardabil Province.
Iran (Hadad and Doulatdar, 2.
These hot spring acidic and high-temperature conditions make them prime environments for uranium mobilization (Honda et al.
, 1.
Another phenomenon regarding radiometric response in Rantedoda is the inverse of K and eTh values in the northern part of the studied This may be caused by the behaviour of K and Th in the soil.
Thorium exists almost exclusively as ThAA, making it highly immobile under most environmental conditions.
Its low solubility restricts its leaching and transport in soils, leading to accumulation in weathered horizons and residual soils (Buriynek et al.
Potassium is significantly more mobile than thorium, especially in soils with low cationexchange capacity or sandy textures (Guagliardi et al.
, 2020.
Tzortzis and Tsertos, 2.
High Th values indicated enrichment due to weathering, where Th is left and other mobile elements, such as K and U, are leached.
This is confirmed by geochemical analysis, which shows that Th and REE levels are higher in the soil than in the rock when plotted to the weathering indices (Figure .
On the contrary, the high K with low Th values reflect relatively fresh rocks.
This finding agrees with the slope angle map is depicted in Figure 13.
Although almost all areas PUBLISHED IN IJOG Indonesian Journal on Geoscience.
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Comparison of K and eTh radiometric map with slope angle map from DEM (Slope angle classification adapted from Zuidam .
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of Rantedoda have steep slope angles, there is a difference in the area where high Th values lie in steep slope angles, and K is mostly high on very steep angles.
Meteoric water tends to run off on the steeper slope, which coincides with the high K area, thus not accommodating further weathering.
Meteoric water infiltrates the surface on a gentler slope, leading to rock weathering, thus enriching Th.
Conversely, on this condition.
K and other mobile elements stay on the rock as leaching is low.
This suggests that direct faulting is not primary to control Th enrichment in the studied area, and weathering is more influential.
Micro-XRF study on Rantedoda demonstrated that the apatite and clay minerals, specifically montmorillonite and chlorite, which are present on the altered groundmass, are the sites of concentration for U and Th (Pratiwi et al.
This is the case for elevated K, eU, and surrounding the T2c Fault.
Petrographic analysis confirms the presence of chlorite in RDD 1 and clay masses in RDD 1 and 5, which are the samples located near the area.
K adsorption in clay minerals is a common and significant process in natural soils (Goli-Kalanpa et al.
Simonsson et al.
, 2009.
Li et al.
, 2.
Many studies have explained U adsorption in alteration-product clay minerals, including kaolinite, montmorillonite, and smectite (Simonsson et al.
, 2009.
Campos et al.
, 2013.
Schindler et , 2015.
Yang, 2.
The clay mineralogy influences U adsorption by providing specific pH conditions and ionic strength.
On the granitic system.
Th is immobile or has limited mobility during hydrothermal alteration like albitization and K-feldspathization (Leroy and Turpin.
Abd El-Naby, 2.
Th is also found to be minimally mobilized in felsic volcanic rocks.
Even under acidic conditions, its transport was negligible (Morales-Arredondo et al.
, 2.
This finding suggests hydrothermal alteration of the Rantedoda volcanic rocks, which produced clay minerals, adsorb K and U while Th persists, leading to their enrichment, and may be facilitated by the T2c fault.
Based on these results, the exploration programme on U.
Th, and REE on Rantedoda should address MSTM faults in the area.
Faulting allows weathering that leads to Th and REE enrichment, controls leached U redistribution, and facilitates hydrothermal clay alteration that absorbs U.
The radiometric method helped distinguish enriched alteration zones .
igh on all radiometric parameter.
from the weathering zones .
igh on eTh, low on K) and resistant rock .
igh on K, low on eT.
Exploration programmes should intensively studied areas with clay alteration for potential secondary U.
Th, and REE enrichment.
While surface anomalies are valuable indicators, drilling programmes must confirm the vertical extent of mineralization in fault systems.
Geophysical methods should be implemented to assist subsurface zones of hydrothermal activity identification.
Weathered profiles near fault zones should be systematically sampled and analyzed for U.
Th , and REE content.
The findings in this study might not provide a comprehensive understanding across different geological settings other than the alkaline rocks of Adang Volcanics that are affected by MSTM as their geological setting provides sources and processes for U.
Th, and REE Nevertheless, the targeting strategy can be implemented for future U.
Th, and REE prospection in other Mamuju areas.
Conclusions The findings show that the MSTM fault system controls the mobilization and enrichment of U.
Th, and REEs in the Rantedoda area.
Faults are noted to create favourable conditions for They make pathways for subsurface fluids, facilitate hydrothermal alteration, and influence weathering processes.
Exploration programmes in Rantedoda should integrate structural analysis into geochemical, geological, and geophysical data to areas with clay alteration for potential secondary U.
Th, and REE enrichment and weathered areas for lateritic Th and REE
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Vol.
12 No.
3 December 2025: 319-341 Acknowledgments The authors extend sincere appreciation to the local communities of Tasipa and Rantedoda for their invaluable support and assistance during the Their contributions were instrumental in facilitating this research.
The Authors also acknowledge Muhammad Wira Maulana.
Faneza Nur Mardania.
Sylviana Mulia.
Adriel Sebastian, and Hera Agung Silaltopa for their efforts in sample preparation for petrographic and geochemical analyses.
Furthermore, we express our gratitude to Sylviana Mulia.
Alhayyu Druvadi Adnoor, and Mochamad Ikral Pamungkas for their assistance in processing the initial data.
We also thank Rizky Firmansyah for the supplementary field documentation.
Part of the scientific results in this work were obtained using Win-Tensor, a software developed by Dr.
Damien Delvaux.
Royal Museum for Central Africa.
Tervuren.
Belgium.
The authors gratefully acknowledge the anonymous reviewer insightful comments and critical evaluations.
Their thorough reviews and constructive feedback greatly contributed to this manuscript refinement and overall quality.
This research was supported by the RP HITN 2024 Grant RO2-REA-C-006, awarded by the Research Organization of Nuclear Energy.
National Research and Innovation Agency (BRIN).
Author Contribution Conceptualization.
Heri Syaeful.
Roni Cahya Ciputra.
Heri Syaeful.
Roni Cahya Ciputra.
I Gde Sukadana.
formal analysis.
Roni Cahya Ciputra.
Fadiah Pratiwi.
Aldo Febriansyah Putra.
Tyto Baskara Adimedha.
data acquisition.
Heri Syaeful.
Frederikus Dian Indrastomo.
I Gde Sukadana.
data curation.
Yoshi Rachael.
Frederikus Dian Indrastomo.
writing-original draft preparation.
Roni Cahya Ciputra.
Fadiah Pratiwi.
Aldo Febriansyah Putra.
Yoshi Rachael.
writing-review and editing.
Heri Syaeful.
I Gde Sukadana.
Tyto Baskara Adimedha.
Roni Cahya Ciputra.
Fadiah Pratiwi.
Aldo Febriansyah Putra.
I Gde Sukadana.
Frederikus Dian Indrastomo.
All authors have read and agreed to the published version of the References