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INAYAH PUTRI ALIFIAH

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Abstrak (Bhs. Indonesia)

Endapan epitermal sulfida tinggi merupakan salah satu tipe endapan hidrotermal yang berpotensi mengandung mineralisasi emas (Au). Mineral lempung hasil alterasi hidrotermal dapat digunakan sebagai indikator dalam mengenali zonasi alterasi dan hubungannya dengan mineralisasi emas. Penelitian ini bertujuan untuk mengetahui persebaran zonasi mineral lempung dan kaitannya terhadap pola dari kadar Au pada zona mineralisasi. Metode penelitian yang digunakan berupa pemetaan geologi yang didukung dengan analisis petrografi, ore microscopy, mineral spectrometry (ASD), dan analisis fire assay untuk mengetahui kadar dari Au. Data yang digunakan berupa data hasil pemetaan serta data bor berupa data alterasi dan litologi. Hasil penelitian menunjukkan bahwa daerah penelitian tersusun oleh tiga satuan dari tertua hingga termuda, yaitu Satuan Tuf, Satuan Tuf Breksia, dan Satuan Breksi Diatrem. Struktur geologi yang berkembang berupa sesar mendatar menganan berarah Timur Laut–Barat Daya dan sesar turun berarah Barat laut–Tenggara. Alterasi hidrotermal terbagi menjadi lima zona, yaitu Silicified (Vuggy), Silicified (Massive), Alunite ± Kaolinite – Quartz ± Pyrophyllite – Dickite, Illite – Kaolinite – Montmorillonite, dan Chlorite – Epidote. Hasil ore microscopy mengidentifikasi mineral bijih berupa pyrite, chalcopyrite, galena, sphalerite, goethite, malachite, chalcosite, dan covelite. Hubungan zonasi mineral lempung terhadap mineralisasi emas menunjukkan bahwa kadar Au high grade (mean = 0,75 ppm) umumnya dijumpai pada zona K-alunite yang memiliki fitur doublet absorbsi 1429–1440 nm dan <1480 nm (H₂O dan OH), single sharp absorbsi 1760 nm (H₂O), serta doublet pada absorpsi 2160–2170 nm (AlOH) yang berasosiasi dengan Zona Silicified (Vuggy) dan Silicified (Massive), sedangkan kadar Au menurun pada zona K-alunite–kaolinite–pyrophyllite–dickite dengan rata-rata 0,24 ppm hingga zona illite–kaolinite–montmorillonite dengan rata-rata 0,04 ppm. Pola tersebut menunjukkan bahwa kadar Au cenderung lebih tinggi pada zona yang berkembang di bagian pusat sistem hidrotermal dan menurun ke arah luar. Namun, persebaran kadar Au tidak hanya dipengaruhi oleh zonasi mineral lempung, tetapi juga oleh struktur geologi, permeabilitas batuan, dan litologi.

Abtrak (Bhs. Inggris)

High-sulfidation epithermal deposits are one of the hydrothermal deposit types with significant potential for gold (Au) mineralization. Clay minerals formed by hydrothermal alteration can be used as indicators to delineate alteration zonation and to evaluate their relationship with gold mineralization. This study aims to determine the distribution of clay mineral zonation and its relationship with the distribution of Au grades within the mineralized zone. The research methods consisted of geological mapping supported by petrographic analysis, ore microscopy, mineral spectrometry (ASD), and fire assay analysis to determine Au grades. The dataset comprises geological mapping results and drillhole data, including lithological and alteration information. The results indicate that the study area is composed of three lithological units, from oldest to youngest: the Tuff Unit, Tuff Breccia Unit, and Diatreme Breccia Unit. The geological structures are represented by a northeast–southwest-trending dextral strike-slip fault and a northwest–southeast-trending normal fault. Hydrothermal alteration is classified into five alteration zones: Silicified (Vuggy), Silicified (Massive), Alunite ± Kaolinite–Quartz ± Pyrophyllite–Dickite, Illite–Kaolinite–Montmorillonite, and Chlorite–Epidote. Ore microscopy identified pyrite, chalcopyrite, galena, sphalerite, goethite, malachite, chalcocite, and covelite as the ore minerals. The relationship between clay mineral zonation and gold mineralization indicates that high-grade Au (mean = 0.75 ppm) is predominantly associated with the K-alunite zone, which is characterized by H₂O and OH doublet absorption features at 1429–1440 nm and <1480 nm, a sharp H₂O absorption feature at 1760 nm, and Al–OH doublet absorptions at 2160–2170 nm. This mineral assemblage is spatially associated with the Silicified (Vuggy) and Silicified (Massive) alteration zones. In contrast, Au grades decrease toward the K-alunite–kaolinite–pyrophyllite–dickite zone, with an average Au grade of 0.24 ppm, and further decline to the illite–kaolinite–montmorillonite zone, with an average Au grade of 0.04 ppm. This pattern indicates that Au grades are generally higher in the central part of the hydrothermal system and progressively decrease toward the peripheral zones. Nevertheless, the distribution of Au grades is controlled not only by clay mineral zonation but also by geological structures, rock permeability, and lithological.

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