Karakteristik Geologi Batuan Induk dan Distribusi Spasial Kadar Al2O3 pada Endapan Bauksit di Simpang Dua, Kabupaten Ketapang, Provinsi Kalimantan Barat

Tamara Fauzi Handoko, Prof. Dr.rer nat. Ir. Arifudin Idrus, S.T., M.T., IPU.

2026 | Skripsi | TEKNIK GEOLOGI

Penelitian dilakukan di Kavling T, IUP ‘Tara’ PT Cita Mineral Investindo Tbk, Dusun Sungai Dua, Kecamatan Simpang Dua, Kabupaten Ketapang, Provinsi Kalimantan Barat yang bertujuan untuk mengetahui karakteristik mineralogi batuan induk di daerah penelitian, mengetahui distribusi spasial kadar Al2O3 pada endapan bauksit laterit, serta mengetahui hubungan aspek geologi berupa morfologi, litologi, dan struktur terhadap distribusi kadar tersebut. Pemetaan geologi permukaan mencakup kondisi geomorfologi dan litologi, dengan pengambilan lima sampel batuan induk untuk dianalisis secara petrografi. Data sekunder berupa hasil analisis geokimia XRF sebanyak 152 data dari 92 titik test pit yang menembus lapisan bauksit milik perusahaan sebagai dasar estimasi sumber daya. Data kadar dikompositkan lalu dievaluasi secara statistik dan geostatistik melalui pemodelan variogram, kemudian diestimasi dengan metode interpolasi Ordinary Kriging pada blok model. Klasifikasi sumber daya ditentukan berdasarkan kerapatan test pit, nilai kriging efficiency, regression slope, dan radius pencarian. Hasil penelitian menunjukkan batuan induk daerah penelitian berupa batuan beku monzogranit dengan mineral felsik dominan berupa kuarsa, ortoklas, dan plagioklas, serta mineral mafik minor berupa biotit dan mineral opak. Rata-rata kadar Al2O3 48,63?ngan sebaran tidak homogen mengikuti morfologi, kadar tertinggi (50,01–54,35%) terkonsentrasi pada perbukitan denudasional yang dengan puncak relatif datar di bagian utara dan barat laut kavling, sedangkan kadar rendah (39,67–45,00%) berkumpul di dataran aluvial yang berdekatan dengan Satuan Pasir Kerakalan. Topografi dan litologi monzogranit sebagai batuan sumber merupakan faktor dominan yang mengontrol distribusi kadar Al2O3, sedangkan struktur geologi belum ditemukan dilapangan. 

This research was conducted in Block T, the “Tara” Mining Business Permit Area (IUP) of PT Cita Mineral Investindo Tbk, Sungai Dua Hamlet, Simpang Dua District, Ketapang Regency, West Kalimantan Province. It aimed to determine the mineralogical characteristics of the parent rock in the study area, to determine the spatial distribution of Al2O3 grades of lateritic bauxite, and to examine the relationship between geological aspects, namely morphology, lithology, and structure, and the distribution of these grades. Surface geological mapping covered geomorphological and lithological conditions, and five parent rock samples were collected for petrographic analysis. Secondary data consisted of 152 XRF geochemical analysis results from 92 test pits that penetrated the company’s bauxite layer, used as the basis for resource estimation. The grade data were composited and then evaluated using statistical and geostatistical methods, including variogram modeling, and subsequently estimated on a block model using the Ordinary Kriging interpolation method. Resource classification was determined based on test pit density, kriging efficiency, regression slope, and search radius. The results show that the parent rock in the study area is monzogranite, an igneous rock, with quartz, orthoclase, and plagioclase as the dominant felsic minerals, and biotite and opaque minerals as minor mafic minerals. The average Al2O3 grade is 48.63%, with a heterogeneous distribution that follows the morphology. The highest grades (50.01-54.35%) are concentrated in denudational hills with relatively flat summits in the northern and northwestern parts of the block, whereas the lowest grades (39.67-45.00%) are clustered in the alluvial plain adjacent to the Gravelly Sand Unit. Topography and the monzogranite lithology as the source rock are the dominant factors controlling the distribution of Al2O3 grades, while no geological structures were found in the field.

Kata Kunci : bauksit laterit, batuan induk, monzogranit, kadar Al2O3, Ordinary Kriging, sumber daya mineral