Electronic Theses and Dissertation

Tatanan tektonik Lengan Utara Sulawesi yang dikontrol oleh subduksi aktif Palung Sangihe menghasilkan busur magmatik kenozoikum yang kaya akan endapan hidrotermal ekonomis. Penelitian ini bertujuan untuk memetakan kondisi geologi permukaan, mengidentifikasi karakteristik geomorfologi, menguraikan urutan stratigrafi, menganalisis struktur pengontrol, serta mendelineasi zona alterasi hidrotermal dan tipe mineralisasi pada "Area X" (luas 3 × 3 km, ±9 km²), Kecamatan Kotabunan, Kabupaten Bolaang Mongondow Timur, Provinsi Sulawesi Utara. Metode yang digunakan meliputi pemetaan geologi lapangan berskala detail dengan keterdapatan titik pengamatan sebanyak 183 titik yang diintegrasikan dengan analisis laboratorium berupa 11 sampel petrografi sayatan tipis (polarizing microscopy) dan 2 sampel mineragrafi sayatan poles (reflected-light microscopy). Pada kondisi lapangan mengamati 6 titik pengamatan bentang alam dan di analisis berdasarkan bentuk muka bumi (BMB) menunjukkan daerah penelitian didominasi oleh satuan geomorfologi Pegunungan Gunungapi dengan rentang elevasi yang kontras berkisar antara 5 hingga 595 meter di atas permukaan laut (mdpl). Stratigrafi daerah penelitian tersusun oleh produk vulkanik Tersier berumur Miosen, yang secara berurutan dari tua ke muda terdiri atas Anggota Lava Dasit (Tmvl) yang menjemari dengan Satuan Breksi Gunungapi (Tmv) berupa perselingan breksi vulkanik, lava, dan tufa, serta dijumpai lensa satuan batugamping berumur Miosen Awal. Interaksi fluida hidrotermal dengan batuan samping (wall rock) menghasilkan beberapa tipe zona alterasi yang berkembang secara lateral dan vertikal berdasarkan klasifikasi temperatur dan pH fluida, meliputi Zona Sub Propilitik (klorit±kalsit), Zona Filik (kuarsa + serisit + pirit), (serisit + lempung + klorit) dan Zona Skarn (klinopiroksen + kuarsa + kalsit). Mineralisasi emas dan logam dasar berasosiasi erat dengan kehadiran struktur urat (vein) dan rekahan mikro (veinlet) dengan kehadiran mineral bijih (opak) berupa, pirit, kalkopirit, galena, dan sfalerit. Karakteristik alterasi dan asosiasi mineral bijih tersebut menunjukkan bahwa Area X merupakan representasi dari sistem endapan intermediate sulfidation yang tumpang tindih (telescoping) dengan sistem skarn pada batugampingnya.

Kata Kunci: Alterasi Hidrotermal, Epitermal, Petrografi, Mineragrafi, Skarn

The tectonic setting of the North Arm of Sulawesi, controlled by the active subduction of the Sangihe Trench, generated a Cenozoic magmatic arc rich in economic hydrothermal deposits. This study aims to map surface geological conditions, identify geomorphological characteristics, delineate stratigraphic sequences, analyze structural controls, and map hydrothermal alteration zones and mineralization types in "Area X" (covering an area of 3×3" km" , 9〖" km" 〗^2), Kotabunan District, East Bolaang Mongondow Regency, North Sulawesi Province. The methodology involves detailed field geological mapping across 183 observation points, integrated with laboratory analyses comprising 11 thin-section petrographic samples (polarizing microscopy) and 2 polished-section mineragraphic samples (reflected-light microscopy). Field observations included 6 landform observation points, which were analyzed based on geomorphological forms. The results reveal that the study area is dominated by Volcanic Mountain geomorphological units, featuring contrasting topography with elevations ranging from 5 to 595 meters above sea level (masl). The stratigraphy of the study area consists of Tertiary volcanic products of Miocene age. From oldest to youngest, the sequence comprises the Dacite Lava Member (Tmvl), which interfingers with the Volcanic Breccia Unit (Tmv)—consisting of interbedded volcanic breccia, lava, and tuff—along with localized Early Miocene limestone lenses. Interactions between hydrothermal fluids and host rocks generated several alteration zones developing laterally and vertically based on fluid temperature and pH classifications, including Sub-propylitic Zone (chlorite + calcite), Phyllic Zone (quartz + sericite + pyrite), Sericite-Clay-Chlorite Zone (sericite + clay + chlorite), and Skarn Zone (clinopyroxene + quartz + calcite). Gold and base metal mineralization is closely associated with vein structures and micro-veinlets, containing ore (opaque) minerals such as pyrite, chalcopyrite, galena, and sphalerite. These alteration characteristics and ore mineral assemblages indicate that Area X represents an intermediate sulfidation epithermal system telescoped over a skarn system within the limestone unit. Keywords: Hydrothermal Alteration, Epithermal, Petrography, Mineragrophy, Skarn