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GEOLOGI, ALTERASI DAN MINERALISASI ENDAPAN EPITERMAL SULFIDASI TINGGI TAMBANG RISKA BARAT, LANUT, SULAWESI UTARA

Undergraduate Theses from JBPTITBPP / 2018-04-16 14:21:40
Oleh : NURESA RIANA NUGRAHA (nim : 12012075), S1 - Geological Engineering-FITB
Dibuat : 2017, dengan 11 file

Keyword : Riska, alterasi, mineralisasi, epitermal sulfidasi tinggi, breksi hidrotermal, supergen, sesar normal menganan

Lokasi penelitian secara administratif berada di Distrik Lanut, Kecamatan Modayag, Kabupaten Bolaang Mongondow Timur, Provinsi Sulawesi Utara, dan secara geografis berada pada koordinat 662000-662400 mT dan 74800-75250 mU dengan luas area sebesar 400x450 meter. Riska merupakan tambang terbuka endapan emas epitermal sulfidasi tinggi yang berada di wilayah Kontrak Karya PT. J Resources. Tambang Riska telah berhenti berproduksi sejak Desember 2015. Tujuan penelitian ini adalah untuk mengetahui kondisi geologi, menentukan zona alterasi dan mineralisasi, dan mengetahui hubungan antara kadar Au-Cu-Ag dengan zona alterasimineralisasi. Untuk mencapai tujuan tersebut, dilakukan beberapa metode seperti pemetaan geologi dan alterasi, pengamatan makroskopis batuan inti pada 11 sumur pemboran, analisis petrografi terhadap 24 sampel, analisis mineragrafi terhadap 9 sampel, analisis mineral lempung menggunakan ASD (Analytical Spectral Device) terhadap 40 sampel, dan analisis geokimia assay Au, Cu, Ag. Hasil penelitian menunjukkan bahwa Tambang Riska Barat tersusun oleh 3 satuan batuan berumur Miosen, yaitu Satuan Tuf Lapili, Satuan Breksi Tuf-Breksi Piroklastik, dan Satuan Lava Andesit. Seluruh satuan batuan telah mengalami proses alterasi dan mineralisasi pada kala Pliosen. Terdapat 4 zona alterasi di daerah penelitian, yaitu Zona Alunit-Dikit-Kuarsa, Zona Kuarsa-Kaolinit, Zona Smektit-Kalsit-Ilit±Kuarsa, dan Zona Kalsit-Klorit-Felspar sekunder±Kuarsa. Mineralisasi terdiri dari pirit yang hadir di semua zona alterasi, pirit arsenan/arsenopirit-enargit-kalkopirit yang hadir di Zona Alunit-Dikit-Kuarsa, dan bornitkovelit-goetit-hematit yang hadir sebagai mineral supergen. Paragenesis mineralisasi di daerah penelitian terdiri dari dua tahap, yaitu tahap epitermal sulfidasi tinggi dan tahap supergen. Mineralisasi supergen di daerah penelitian tersebar secara lokal pada bagian rekahan batuan di Zona Alunit-Dikit-Kuarsa pada kedalaman ≥680 m dan belum berkembang dengan baik. Endapan epitermal sulfidasi tinggi Tambang Riska Barat dikontrol oleh struktur geologi berupa sesar normal menganan berarah timur timurlaut-barat baratdaya yang terbentuk akibat pasangan sesar geser mengiri regional Inobonto. Penyebaran Au-Cu-Ag yang tinggi( > cut off grade Au=0,1 ppm, Cu=1500 ppm, Ag=10 ppm) di daerah penelitian terdapat pada zona Alunit-Dikit-Kuarsa, zona breksi hidrotermal dan zona supergen.

Deskripsi Alternatif :

The research area is administratively located in Lanut District, Modayag Subdistrict, Bolaang Mongondow Timur Regency, North Sulawesi Province, and geographically located at 662000 - 662400 mE and 74800 – 75250 mN with an area sized 400x450 meters. Riska is an open-pit mine of high-sulfidation epithermal gold deposit within the Contract of Work area of PT. J Resources. Riska pit had stopped producing since Desember of 2015. The purpose of this research is to determine geological condition, design an alterationmineralization zone and determine the correlation between Au-Cu-Ag grade and alterationmineralization zone. To achieve those goals, some methods such as geological and alteration mapping, detailed bore cores logging from 11 different wells, petrographic analysis of 24 samples, mineragraphic analysis of 9 samples, clay mineral analysis using ASD of 40 samples, and assay Au, Cu, Ag geochemistry analysis were used. Lithostratigraphic units of Western Riska pit that formed on Miocene consist of 3 units, they are Lapilli Tuff Unit, Pyroclastic Breccia-Breccia Tuff Unit and Andesitic Lava Unit respectively. All of those units had undergone alteration-mineralization processes on
Pliocene. There are four alteration zones in this research location, they are Alunite-Dickite-Quartz Zone, Quartz-Kaolinite Zone, Smectite-Calcite-Illite±Quartz Zone, and Calcite-Chlorite- Felspar sekunder±Quartz Zone. In this research location, pyrite exist in all alteration zones,
arsenian pyrite/arsenopyrite-enargite-chalcopyrite exist in Alunite-Dickite-Quartz Zone, and bornite-covellite-goethite-hematite exist as supergene minerals. Mineralization paragenesis can be subdivided into two phases: high sulfidation epithermal and supergene oxidation. Supergen mineralization only observed in fractured zone in Quartz-Dickite-Alunite zone at ≥680 msl.
High-sulfidation epithermal deposit of Western Riska pit is controlled by geological structure such as ENE – WSW right lateral normal fault that was formed by Inobonto's
regional sinistral faults. High concentration of Au-Cu-Ag ( > cut off grade of Au=0,1 ppm; Cu=1500 ppm; Ag=10 ppm) is associated with Alunite-Dickite-Quartz zone, hydrothermal breccia zone, and supergene zone.


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