STUDI ALTERASI HIDROTERMAL DAN MINERALISASI ENDAPAN PORFIRI Cu-Au BERDASARKAN ANALISIS DATA CORE PADA SECTION 040 DAERAH TAMBANG TERBUKA BATU HIJAU, KABUPATEN SUMBAWA BARAT, NUSA TENGGARA BARAT
Abstract
Daerah penelitian berada di Batu Hijau, yang merupakan salah satu lokasi tambang terbuka yang di kelola oleh PT. Amman Mineral Nusa Tenggara. Secara administratif Batu Hijau berada di Kecamatan Sekongkang, Kabupaten Sumbawa Barat, NTB. Tujuan dari penelitian ini yaitu untuk mengetahui kondisi geologi, penyebaran zona alterasi, zona mineralisasi dan korelasi hubungannya dengan persebaran kadar Cu-Au pada Section 040 (timurlaut-baratdaya) tambang terbuka Batu Hijau. Penelitian dilakukan menggunakan data pemboran inti batuan dari 10 sumur bor yaitu, SBD293, SBD654, SBD257, SBD229, SBD183, SBD566, SBD002, SBD270, SBD009, dan SBD467. Metode penelitian yang dilakukan berupa detail core logging, analisa petrografi, analisa mineragrafi, dan melakukan analisis statistik untuk mengetahui hubungannya dengan sebaran grade Cu-Au. Stratigrafi pada daerah penelitian terdiri atas 4 satuan berurutan dari tua ke muda, antara
lain, Satua breksi vulkanik; intrusi diorit kuarsa; intrusi tonalit porfir 1; dan intrusi tonalit porfir 2. Alterasi pada daerah penelitian di bagi menjadi 4 zona alterasi yaitu, zona biotit + magnetit + k-feldspar (tipe potasik); zona biotit + k-feldspar + klorit (tipe potasik); zona klorit + epidot + kuarsa (tipe propilitik); dan zona serisit + klorit + kuarsa (tipe filik). Sedangkan zona mineralisasi dibagi berdasarkan banyaknya kandungan mineral sulfida dominan antara lain, zona bornit (bornit ± kalkopirit ± pirit); zona kalkopirit (kalkopirit ± bornit ± pirit); zona pirit (pirit ± kalkopirit ± bornit). Berdasarkan analisis statistik diagram Boxplot sebaran kadar Cu–Au dibagi menjadi 3 zonasi yaitu, zona low grade;, zona medium grade; dan zona high grade. Hasil analisis menunjukan zona alterasi dan mineralisasi di daerah penelitian dikontrol oleh kemunculan intrusi tonalit porfir 1. Zona low grade Cu (0,01-0,5%) berasosiasi dengan semua zona alterasi, mineralisasi zona kalkopirit dan pirit. Medium grade Cu (0,5-1%) berasosiasi dengan zona alterasi biotit+magnetit dan zona serisit+klorit, mineralisasi zona
bornit dan zona kalkopirit. High grade Cu (>1%) berasosiasi dengan zona alterasi biotit+magnetit, mineralisasi zona bornit dan zona kalkopirit. Low grade Au (0,00-0,5g/t) berasosiasi dengan semua zona alterasi, mineralisasi zona kalkopirit dan zona pirit. Medium grade Au (0,5-1g/t); zona alterasi biotit+magnetit, zona
alterasi serisit+klorit, mineralisasi zona bornit dan zona kalkopirit. High grade Au (>1g/t); zona biotit+magnetit, mineralisasi zona bornit dan zona kalkopirit.
Kata-kata kunci: Alterasi, Mineralisasi, Zonasi Grade Cu-Au, Section 040
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DOI: https://doi.org/10.31315/jigp.v5i2.9668
DOI (PDF (Bahasa Indonesia)): https://doi.org/10.31315/jigp.v5i2.9668.g5390
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