STUDY OF CHARACTERISTIC OF LATERITE NICKEL DEPOSITS AND CHROMIUM (CR) ELEMENT ABUNDANCE IN LATERITE NICKEL DEPOSITS IN BULI REGION, EASTERN HALMAHERA, NORTH MOLUCCA

• Main Author: Fadhilan Rahman Agustiansyah, M
• Format: Final Project
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/78276
• Institution: Institut Teknologi Bandung

Halmahera Island, especially its eastern part, contains abundant reserve of laterite nickel deposits formed due to the weathering of ultramafic rocks. In the industrial world, nickel is used to make stainless steel and batteries for electric cars. Besides having high nickel content, the weathering of ultramafic rocks also enriches chromium (Cr) in the limonite zone through residual enrichment. The study area is in Buli region, Eastern Halmahera, North Molucca which is included in the IUP PT Aneka Tambang Tbk. This research aims to understand the characteristics of these lateritic nickel deposits, their relationship with the abundance of Cr, and the distribution of Cr in nickel laterite deposits. The data used consist of geochemical data and descriptions from 82 borehole locations, XRD data, observations of laterite profiles, rock samples, Digital Elevation Models (DEM), and other literature data for this study. The geochemical data were subsequently statistically analyzed using boxplots, linear graphs, Spearman correlation, and ternary diagrams. The profile of laterite nickel deposits in the research area is divided into four zones: topsoil, limonite, saprolite, and bedrock. The bedrock found in the research area consists of peridotite, specifically dunite and harzburgite types. The laterite in the study area has undergone strong lateritization, characterized by the enrichment of Fe2O3 and the formation of a limonite zone as the final product of lateritization. There are two types of laterite nickel deposits in the research area: oxide-type and hydrous Mgsilicate-type nickel deposits. Based on the geochemical analysis, Cr element shows abundance in the limonite zone. Spearman correlation analysis indicates a strong positive correlation between Cr element and Fe2O3, a moderate positive correlation with Mn, Co, and Ni, and a strong negative correlation with SiO2. Topography influences the limonite thickness. Areas with slight slopes tend to have relatively thicker limonite, while areas with intermediate slopes tend to have relatively thinner limonite. The abundance of Cr element is correlated with the thickness of limonite, the content of goethite minerals, and the v presence of silica in limonite zone. Thicker limonite layers tend to have relatively higher concentrations of Cr element. Higher goethite mineral content in the limonite zone tends to have higher concentrations of Cr element. The higher presence of silica in the limonite zone tends to have lower concentrations of Cr element. The estimation of Cr element distribution was conducted using the Inverse Distance Weighting (IDW) method in the limonite zone. The estimation results indicate that the high concentration of Cr element is located in the northwest and south of the study area, which is dominated by slight slope topography, thick limonite layers, and relatively low silica content. In addition to chromite as a carrier mineral of Cr element in the limonite zone, the presence of high goethite mineral content can also enrich Cr element in the limonite zone. The low concentration of Cr element is found in the west and east of the study area, particularly in areas with intermediate slope and slight slope topography, thin limonite layers, and relatively high presence of silica.