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1. Subsurface structure of Bali Island inferred from magnetic and gravity modeling: new insights into volcanic activity and migration of volcanic centers

Author

Suryanata, Putu Billy, Bijaksana, Satria, Dahrin, Darharta, Nugraha, Andri Dian, Harlianti, Ulvienin, Putra, Putu Raditya Ambara, Fajar, Silvia Jannatul, Suandayani, Ni Komang Tri, Pratama, Aditya, Gumilang, Mukhamad Fajar, Al Basyarah, Wisandie Syah, Paramartha, I. Komang Agus Aditya, Amir, Harman, and Nobes, David C.

Published
2024
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6. Digital Governance in Human Resources Development (HRD) Portal with Soft Systems Methodology Approach, Study of BUMN Holding Survey Services

Author

Arif Bijaksana Satria Negara and Rachma Fitriati

Subjects
e-government, digital governance, human capital, hrd portal, soes., Political institutions and public administration - Asia (Asian studies only), JQ1-6651
Abstract

The rapid development of technology has significantly impacted various aspects of human life, including in the world of work and the development of human resources (HR). Digital governance is the development of the concept of E-Government, which focuses more on user participation in its application. Implementing digital governance is a human capital application transforming how companies manage their human resources. For more than three decades, SBU Marine Services used a time-based payroll system. However, since 2021, the company switched to a competency-based approach. This change has led to an income gap between long-standing contract employees and new joiners. In addition, the salary data collection system still uses spreadsheets, which have several potential governance issues, such as transparency of the payroll system, information on employee training and grading data, etc. This study uses the soft systems methodology (SSM) approach to analyze digital governance using the HRD Portal application in SBU Marine Services. The results showed no policy governing contract employee governance in SBU Marine Services, so the HRD Portal is needed. This research recommends creating an HRD Portal SOP policy to measure and monitor employee performance more effectively and efficiently. The contribution of this study, with the HRD Portal SOP policy, can change the payroll system from a time-based system to a competency-based system, overcome the social gap in contract employee income, and increase transparency and fairness in human capital management at SBU Marine Services.

Published
2023
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7. Handling imbalanced data in supervised machine learning for lithological mapping using remote sensing and airborne geophysical data

Author

Nugroho Hary, Wikantika Ketut, Bijaksana Satria, and Saepuloh Asep

Subjects
lithological map, machine learning, random forest algorithm, imbalanced data, class weight tuning, oversampling, and imbalance ratio, Geology, QE1-996.5
Abstract

With balanced training sample (TS) data, learning algorithms offer good results in lithology classification. Meanwhile, unprecedented lithological mapping in remote places is predicted to be difficult, resulting in limited and unbalanced samples. To address this issue, we can use a variety of techniques, including ensemble learning (such as random forest [RF]), over/undersampling, class weight tuning, and hybrid approaches. This work investigates and analyses many strategies for dealing with imbalanced data in lithological classification based on RF algorithms with limited drill log samples using remote sensing and airborne geophysical data. The research was carried out at Komopa, Paniai District, Papua Province, Indonesia. The class weight tuning, oversampling, and balance class weight procedures were used, with TSs ranging from 25 to 500. The oversampling approach outperformed the class weight tuning and balance class weight procedures in general, with the following metric values: 0.70–0.80 (testing accuracy), 0.43–0.56 (F1 score), and 0.32–0.59 (Kappa score). The visual comparison also revealed that the oversampling strategy gave the most reliable classifications: if the imbalance ratio is proportionate to the coverage area in each lithology class, the classifier capability is optimal.

Published
2023
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11. A 1 Ma sedimentary ancient DNA (sedaDNA) record of catchment vegetation changes and the developmental history of tropical Lake Towuti (Sulawesi, Indonesia)

Author

Ekram, Md Akhtar‐E, primary, Campbell, Matthew, additional, Kose, Sureyya H., additional, Plet, Chloe, additional, Hamilton, Rebecca, additional, Bijaksana, Satria, additional, Grice, Kliti, additional, Russell, James, additional, Stevenson, Janelle, additional, Vogel, Hendrik, additional, and Coolen, Marco J. L., additional

Published
2024
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18. Corrigendum: Magma storage conditions beneath Krakatau, Indonesia: insight from geochemistry and rock magnetism studies

Author

Pratama, Aditya, primary, Nurfiani, Dini, additional, Suryanata, Putu Billy, additional, Ismail, Taufik, additional, Bunga Naen, Gabriela Nogo Retnaningtyas, additional, Abdurrachman, Mirzam, additional, Supriyadi Banggur, Wilfridus Ferdinando, additional, Asri, Nining Sumawati, additional, Nareswari, Ratika Benita, additional, Bijaksana, Satria, additional, Hanif, Muhammad, additional, Kriswati, Estu, additional, Kurniawan, Idham Andri, additional, and Setiawan, Nugroho Imam, additional

Published
2023
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19. Magma storage conditions beneath Krakatau, Indonesia: insight from geochemistry and rock magnetism studies

Author

Pratama, Aditya, primary, Nurfiani, Dini, additional, Suryanata, Putu Billy, additional, Ismail, Taufik, additional, Bunga Naen, Gabriela Nogo Retnaningyas, additional, Abdurrachman, Mirzam, additional, Supriyadi Banggur, Wilfridus Ferdinando, additional, Asri, Nining Sumawati, additional, Nareswari, Ratika Benita, additional, Bijaksana, Satria, additional, Hanif, Muhammad, additional, Kriswati, Estu, additional, Kurniawan, Idham Andri, additional, and Setiawan, Nugroho Imam, additional

Published
2023
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23. Magnetic susceptibility and grain size distribution as prospective tools for selective exploration and provenance study of iron sand deposits: A case study from Aceh, Indonesia

Author

Bijaksana Satria, Zakia Masrurah, and Silvia Jannatul Fajar

Subjects
Iron sand, Magnetic susceptibility, Magnetic mineralogy, Grain size distribution, Provenance study, Aceh, Science (General), Q1-390, Social sciences (General), H1-99
Abstract

Almost all of the iron sand found in Indonesia, from Sumatra to Papua, is sandy deposit. Despite its variety of minerals, iron sand is commonly mined for low economic uses such as building material. As iron sands from different localities might have different characteristics (grain-size distribution, mineralogy, magnetic properties), such characteristics might in turn be used for provenance study or for selective mining. This study aims to examine iron sand deposits from two geographically close but geologically different regions, Lampanah and Anoi Itam, and to test the grain size distributions and their relationship with magnetic susceptibility as well as Fe content. In both Lampanah and Anoi Itam, the sizes of iron sands were predominantly medium sand (MS) and fine sand (FS), but they differed in mass percentage (M%). Generally, magnetic susceptibility increases as grain size decreases. Fe content is also grain size dependent, with higher Fe content in finer sizes. The results imply that the combination of grain size distribution and magnetic mineral composition might be used not only as a provenance indicator for iron sand deposits, but also as a criterion for selective mining.

Published
2021
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27. PRELIMINARY PETROMAGNETIC STUDY OF 1849, 1926, 1963, 1968 AND 1974 SURFACE LAVAS FROM BATUR VOLCANO, BALI, INDONESIA: INSIGHT ON THE MAGMATIC PROCESS OF SOURCE AND ROCK MAGNETIC NATURE

Author

Suryanata, Putu Billy, Bijaksana, Satria, Abdurrachman, Mirzam, Dahrin, Darharta, Pratama, Aditya, Ndari, Nuresi Rantri Desi Wulan, and Fajar, Silvia Jannatul

Subjects
General Energy, vulkan Batur, magmatizam, magnetizam stijena, Bali, General Earth and Planetary Sciences, Batur Volcano, magmatism, petrogenesis, rock magnetism, Geology, Geotechnical Engineering and Engineering Geology, Water Science and Technology
Abstract

Geochemical and petrographic characterizations were carried out on five episodic effusive eruptions from Batur Volcano on the Island of Bali, Indonesia, and revealed that these lavas are basaltic to andesitic in composition. Various micro-textures were identified, reflecting pre-eruptive magmatic processes, magma mixing, and adiabatic decompression. Apart from XRF analyses, the five lava flows (L849, L926, L963, L968 and L974) were subjected to magnetic analyses in the form of magnetic susceptibility and magnetic hysteresis measurements. The presence of cyclicity in the magmatic process is suggested by the variation of micro-texture types, CaO content, and magnetic susceptibility values. Two possible models of this cyclicity are presented. In the first model, cyclicity is driven by the variation of influx from the lower magma chamber that affects the interaction of magma with the surrounding rocks. In the second model, cyclicity is affected by the appearance of a new magmatic vent, which causes intense interaction with surrounding rocks. This study infers that combined micro-texture, composition, and magnetic susceptibility analyses might provide insight into the cyclicity of lava episodes observed in active volcanos such as Batur., Geokemijska i petrografska istraživanja provedena na pet epizodnih efuzivnih erupcija iz vulkana Batur na otoku Baliju, Indonezija, otkrila su kako su te lave bazaltnoga do andezitskoga sastava. Prepoznate su različite mikroteksture odražavajući magmatske procese koji su prethodili erupcijama, kao i miješanje magme te adijabatska dekompresija. Načinjene su XRF analize, uz koje su pet tokova lave (L849, L926, L963, L968 i L974) također ispitani magnetskim analizama mjerenja magnetske susceptibilnosti i histereze. Na cikličnost magmatskoga procesa upućuju varijacije vrsta mikrotekstura, sadržaja CaO i vrijednosti magnetske susceptibilnosti. Prikazana su dva moguća modela navedene cikličnosti. U prvome modelu cikličnost je prouzročena varijacijom dotoka iz donje komore magme, što je utjecalo na njezino međudjelovanje s okolnim stijenama. U drugome modelu na cikličnost utječe pojava novoga magmatskog toka koji ima snažno međudjelovanje s okolnim stijenama. Studija upućuje na to da zajedničko korištenje analize mikrotekstura, sastava i magnetske susceptibilnosti može dati uvid u cikličnost epizoda istjecanja lave opaženih u aktivnim vulkanima kao što je Batur.

Published
2023

29. Magnetic Susceptibility and Hydrogen Cyanide Levels as Proxy Indicator for Gold Mining Pollution in River Sediment.

Author

Zulaikah, Siti, Juliansyah, Arif, Hasan, Muhammad Fathur Rouf, Iswanto, Bambang Heru, Mariyanto, Mariyanto, Ardyanto Tanjung, Bijaksana, Satria, and Hirt, Ann Marie

Subjects
MAGNETIC susceptibility, RIVER sediments, HYDROCYANIC acid, RIVER pollution, PEARSON correlation (Statistics), HEAVY metals, GOLD mining, MERCURY, HEAVY metal content of water
Abstract

Sumbawa's Kuris River is one of the rivers contaminated by the island's traditional gold mine. In order to detect contaminant levels, we examine the magnetic susceptibility, HCN levels, and the heavy metal contents on the river's surface sediment. Environmental pollution has been widely assessed using a combination of magnetic properties and geochemical analysis. The goals of this research are to discover how magnetic susceptibility (X) can be used as a first-order proxy for pollution. The relation between susceptibility and HCN is of particular interest, as this is a major contaminant associated with gold mining. The surface sediment samples were collected at ten different locations along the rivers. The magnetic susceptibility was determined using the Bartington MS2B, and the hydrogen cyanide (HCN) concentration was determined using Argentometric titration. The element content was determined by an Atomic Absorption Spectrometer (AAS). The low-frequency magnetic susceptibility (X1f) ranges from 71 to 115×10-8 m³/kg, with an average of 97×10-8 m³/kg, and the Xfd(%) analysis ranges from 2% to 4%. The presence of spherical iron oxides, which are indicative of combustion byproducts, was also confirmed by SEM. The samples have low magnetic susceptibility but high levels of Hg and HCN. AAS results showed high Fe, Zn, and Cu concentrations in river sediments, with more variable concentrations of Hg, Mn, As, Cr, and Au. Because Fe, Cu, As, Hg, and HCN have a significant Pearson's correlation with Xfd(%), this parameter can be a useful indicator for contamination caused by gold mining waste. [ABSTRACT FROM AUTHOR]

Published
2023
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32. PEDOGENESIS OF LATERITIC SOILS AND THE ENRICHMENT OF CRITICAL METALS: A STUDY FROM SOUTHEAST SULAWESI, INDONESIA

Author

Ibrahim, Khalil, Bijaksana, Satria, Harlianti, Ulvienin, Suryanata, Putu Billy, Ngkoimani, La Ode, Asfar, Suryawan, and Fajar, Silvia Jannatul

Subjects
critical metals, lateritic soil, pedogenesis, magnetic susceptibility, Southeast Sulawesi, Kritični metali, lateritno tlo, pedogeneza, magnetna susceptibilnost, jugoistočni Sulawesi
Abstract

Lateritic soil is a prospective source of metals termed critical or strategic metals due to their use in high-technology industries. Critical metals include rare earth elements (REEs). In this study, two profiles of lateritic outcrops from the Ni-producing area of Southeast Sulawesi in Indonesia were sampled for magnetic susceptibility as well µ-XRF analyses to identify how the concentration of critical metals changed during pedogenesis. The results show that there are three different patterns from the bottom layer up. The first pattern is enrichment experienced by Sc, La, Cr, and Ti. The second pattern is depletion experienced by Ni, Nd, and Ho. The third pattern is the localization of high concentration at a certain depth, as experienced by Co, Ce, and V. The concentration of certain critical metals correlates either positively or negatively with magnetic susceptibility, inferring that magnetic susceptibility might be used as a proxy indicator for critical metal concentration in lateritic soil., Lateritno tlo je potencijalni izvor metala koji se nazivaju kritični ili strateški metali zbog njihove upotrebe u industrijama visoke tehnologije. Kritični metali uključuju elemente rijetkih zemalja (REE). U ovom istraživanju uzorkovana su dva profila lateritnih izdanaka iz područja proizvodnje nikla u jugoistočnom Sulawesi u Indoneziji, s ciljem definiranja promjene koncentracija kritičnih metala tijekom pedogeneze korištenjem magnetne susceptibilnosti i μ-XRF analiza. Rezultati su ukazali na postojanje tri različita obrasca od donjeg sloja prema gore. Prvi obrazac predstavlja obogaćivanje Sc, La, Cr i Ti. Drugi obrazac predstavljen je sniženjem koncentracija Ni, Nd i Ho. Treći obrazac predstavlja lokalizaciju visokih koncentracija određenih metala na određenoj dubini, kao što su Co, Ce i V. Koncentracija nekih kritičnih metala korelira bilo pozitivno ili negativno s magnetnom susceptibilnosti, što upućuje na to da bi se magnetna susceptibilnost mogla koristiti kao indikator kritičnih koncentracija metala u lateritnom tlu.

Published
2023

33. GEOCHEMICAL AND MAGNETIC CHARACTERISTICS OF PLACER GOLD DEPOSITS FROM CENTRAL KALIMANTAN, INDONESIA

Author

Nahan, Gusfrimanuel, Bijaksana, Satria, Suryanata, Putu Billy, and Ibrahim, Khalil

Subjects
ASGM, REE, magnetna susceptibilnost, nanosna ležišta, središnji Kalimantan, magnetic susceptibility, placer deposits, Central Kalimantan
Abstract

Massive tailings have resulted from the extensive use of placer deposits in Central Kalimantan, Indonesia, by artisanal and small-scale gold mining (ASGM) activities. Recently, the placer deposits and their tailings have been exploited for heavy minerals. In this study, geochemical and magnetic analyses were carried out on these deposits to identify the prospect of REE (rare earth element) exploration in the materials already collected by ASGM activities. Samples were collected from ten different locations. For each location, two different fractions were prepared for analyses, i.e. the heavy mineral (HM) fraction and the panned (M60) fraction. All HM and M60 samples were subjected to magnetic susceptibility measurements, but only representative samples were subjected to x-ray fluorescence (XRF) measurements (for Si, Ti, Fe, Zr, and Al) and to inductively coupled plasma-emission spectroscopy (ICP-OES) measurements (for Eu, Tb, Dy, and Sc). The results showed that the concentrations of major elements (Ti, Fe, Zr, and Al) vary significantly from deposits along one river to another, while the concentration of Si is rather similar. Compared to M60 samples, the HM samples have higher concentrations of Ti, Fe, Zr, Al, and Sc, implying that the sluice-box separation enhances the concentration of valuable minerals. Magnetic susceptibility is found to be correlated with Fe and Sc concentrations, confirming the potential use of magnetic measurements as a complementary tool for Fe and Sc exploitation in placer deposits. It is believed that both the source rocks and the sedimentary settings of these deposits determine whether certain elements (Sc, Fe, and Zr) are present or absent in Central Kalimantan placer deposits. The prospect of exploring and exploiting Sc in these placer deposits might augment the ASGM activities in Central Kalimantan., Ogromne količine jalovine rezultat su prekomjerne eksploatacije nanosnih ležišta u središnjem Kalimantanu, Indonezija,zanatskim rudarenjem zlata malih razmjera (ASGM). U novije vrijeme iz tih ležišta i njihove jalovine eksploatirani su i teški minerali. U ovom istraživanju, provedene su geokemijske i magnetne analize uzoraka nanosnih ležišta kako bi se utvrdile mogućnosti istraživanja REE (elemenata rijetkih zemalja) u materijalima koji su već prikupljeni ASGM aktivnostima. Uzorci su prikupljeni s deset različitih lokacija. Sa svake lokacije za analizu su pripremljene dvije različite frakcije, tj. frakcija teških minerala (HM) i šlih (M60). Svi uzorci i njihove frakcije (HM i M60) su podvrgnuti mjerenju magnetne susceptibilnosti, dok su samo reprezentativni uzorci analizirani rendgenskom fluorescencijom-XRF (Si, Ti, Fe, Zr i Al) i induktivno spregnutom plazmom-emisijskom spektroskopijom-ICP-OES (Eu, Tb, Dy i Sc). Rezultati su pokazali da koncentracije glavnih elemenata (Ti, Fe, Zr i Al) značajno variraju u ležištimarazličitih rijeka, dok je koncentracija Si vrlo slična. U usporedbi s uzorcima M60, uzorci HM imaju više koncentracije Ti, Fe, Zr, Al i Sc, što upućuje na to da separacija na uređaju za ispiranje zlata povećava koncentraciju vrijednih minerala. Utvrđeno je da je magnetna susceptibilnost u korelaciji s koncentracijama Fe i Sc, što potvrđuje potencijalnu upotrebu magnetnih mjerenja kao komplementarnog alata za eksploataciju Fe i Sc u nanosnim ležištima. Vjeruje se da izvorišne stijene kao i sedimentni dijelovi ovih ležišta određuju jesu li određeni elementi (Sc, Fe i Zr) prisutni ili odsutni u nanosnim ležištima središnjeg Kalimantana. Perspektivnost istraživanja i eksploatacije Sc u nanosnim ležištima mogli bi povećati ASGM aktivnosti u središnjem Kalimantanu.

Published
2023

36. Subsurface structures of Sianok Segment in the GSF (Great Sumatran Fault) inferred from magnetic and gravity modeling

Author

Dahrin, Darharta, primary, Amir, Harman, additional, Suryanata, Putu Billy, additional, Bijaksana, Satria, additional, Fajar, Silvia Jannatul, additional, Ibrahim, Khalil, additional, Harlianti, Ulvienin, additional, Arisbaya, Ilham, additional, Pebrian, Mutiara Qalbi, additional, Rahman, Adinda Aisyah, additional, and Kasendri, Adibbian, additional

Published
2022
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37. Reply to Lu et al.: Robust Intertropical Convergence Zone variability reconstructed from Maritime Continent speleothem δ18O records.

Author

Shufang Yuan, Hong-Wei Chiang, Guangxin Liu, Bijaksana, Satria, Shaoneng He, Xiuyang Jiang, Imran, Andi M., Wicaksono, Satrio A., and Xianfeng Wang

Subjects
INTERTROPICAL convergence zone, CONTINENTS, ATMOSPHERIC sciences, LAST Glacial Maximum, CLIMATIC zones
Abstract

This document is a reply to a previous article by Lu et al. regarding the reconstruction of the Intertropical Convergence Zone (ITCZ) variability using speleothem δ18O records from the Maritime Continent. The authors of this reply argue that the two components of ITCZ variability, migration and contraction-expansion, are not necessarily independent and are strongly affected by interhemispheric thermal contrast. They also contend that the compilation of records used by Lu et al. may be less representative and produce biased results. The authors suggest that a combined theoretical and model-proxy approach is needed to better understand ITCZ variability and tropical climate change. [Extracted from the article]

Published
2024
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40. Integration of remote sensing and geophysical data to enhance lithological mapping utilizing the Random Forest classifier: a case study from Komopa, Papua Province, Indonesia.

Author

Hary Nugroho, Wikantika, Ketut, Bijaksana, Satria, and Saepuloh, Asep

Subjects
REMOTE sensing, GEOPHYSICS, RANDOM forest algorithms, PETROLOGY, MACHINE learning
Abstract

Lithological information is important in mineral resource exploration, geological observations, mine planning or degradation vulnerability assessment. Currently, lithology mapping can be performed in a fast, inexpensive, and easy way using remote sensing data and machine learning. Remote sensing techniques have become a valuable and promising tool for mapping lithological units and searching for minerals. Typically, the integration of remote sensing data with geophysical data provides a better diagnosis to lithological units than single-source mapping methodologies. Accordingly, this study used a combination of remote sensing and airborne geophysical data utilizing the Random Forest algorithm with small training samples to enhance lithology mapping in Komopa, Papua Province, Indonesia. Geophysical data consisting of magnetic, electromagnetic, and radiometric were added one by one gradually to the remote sensing data, which includes Sentinel 2A, ALOS PALSAR, and DEM (digital elevation model) to compare the accuracy of the classification results from each dataset. The results showed that the model that combined remote sensing data and the three types of geophysical data produced the best classification, with an overall accuracy of 0.81, precision of 0.66, recall of 0.47, and F1 score of 0.52. This fused data can increase the accuracy of the classification results by 8% overall accuracy, 6% precision, 11% recall, and 13% F1 score when compared to the model that only used remote sensing data. [ABSTRACT FROM AUTHOR]

Published
2023
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45. A one-million-year isotope record from siderites formed in modern ferruginous sediments

Author

Vuillemin, Aurèle, primary, Mayr, Christoph, additional, Schuessler, Jan A., additional, Friese, André, additional, Bauer, Kohen W., additional, Lücke, Andreas, additional, Heuer, Verena B., additional, Glombitza, Clemens, additional, Henny, Cynthia, additional, von Blanckenburg, Friedhelm, additional, Russell, James M., additional, Bijaksana, Satria, additional, Vogel, Hendrik, additional, Crowe, Sean A., additional, and Kallmeyer, Jens, additional

Published
2022
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