NURADHI, CHRISMA WIDHI (2013) GEOLOGI DAN ALTERASI PADA “LOW GRADE PORPHYRY”, DAERAH NAGAMAS DAN SEKITARNYA, KECAMATAN SEKONGKANG, KABUPATEN SUMBAWA BARAT, PROPINSI NUSA TENGGARA BARAT. Other thesis, UPN "Veteran" Yogyakarta.
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Abstract
SARI
Secara administratif, daerah penelitian termasuk dalam wilayah Nagamas,
Kabupaten Sekongkang, Kecamatan Sumbawa Barat, Provinsi Nusa Tenggara Barat.
Secara geografis, daerah telitian terletak pada posisi UTM 0480600 – 0484400 dan
9008400 – 9011200 Zona 50 M. Pemetaan geologi dilakukan dengan luasan ± 11
km
2
dengan skala peta 1:10.000. Nagamas terletak 2 km di sebelah barat open pit
Batu Hijau. Metode penelitian yang dilakukan adalah pengambilan data lapangan
dengan analisis petrografi, XRD, ASD, petrologi, dan struktur geologi untuk
menghasilkan peta lintasan, peta geomorfologi, peta geologi, peta alterasi, dan peta
struktur.
Satuan geomorfologi daerah penelitian dibagi menjadi 4 (empat) bentuk
lahan, yaitu: Perbukitan Intrusi Terkikis (D1), Lereng Vulkanik Terkikis (D2),
Lembah Terkikis Struktur Sesar (S1) dan Tubuh Sungai (F1). Pola pengaliran yang
berkembang berupa pola pengaliran subdendritik.
Stratigrafi daerah penelitian dibagi menjadi 5 (lima) satuan tidak resmi
dengan urutan dari tua ke muda sebagai berikut: Satuan Tuf Litik (Miosen AwalMiosen Tengah), Satuan Intrusi Andesit Porfiritik (Miosen Tengah), Satuan Intrusi
Diorit Kuarsa (Miosen Akhir), Satuan Intrusi Breksi Diatrem (Pliosen Akhir), dan
Satuan Endapan Aluvial (Holosen). Struktur geologi yang berkembang pada daerah
penelitian berupa kekar yang menunjukkan arah umum tegasan yang bekerja berarah
utara-selatan (N-S) hingga baratlaut-tenggara (NW-SE) dan sesar mendatar kiri
dengan arah baratlaut-tenggara (NW-SE).
Zona alterasi daerah penelitian dibagi menjadi 4 (empat), yaitu: zona biotitaktinolit-magnetit-kuarsa (zona potasik), zona kuarsa-serisit-klorit (zona filik), zona
kaolinit-smektit-illit (zona argilik), dan zona klorit-epidot (zona propilitik).
Mineralisasi yang paling dominan pada daerah penelitian berupa mineral sulfida
jenis pirit (FeS2) dengan sedikit kehadiran kalkopirit (CuFeS
2
). Daerah penelitian
merupakan tipe endapan porfiri low grade yang dicirikan oleh tipe urat kuarsa A+B,
vein density 1-≥5%, alterasi biotit sekunder+klorit+epidot+mineral lempung, dan
mineralisasi berupa pirit±kalkopirit.
Kata kunci: Geomorfologi, Stratigrafi, Struktur Geologi, Alterasi, Mineralisasi, Low
Grade
ABSTRACT
Administratively, the location of study area is in Nagamas, Sekongkang District,
District of West Sumbawa, West Nusa Tenggara Province. Geographically, the area
lies in the UTM position from 0480600 to 0484400 and 9008400 to 9011200 Zone
50 M. Geological mapping done by ± 11 km
2
area with a map scale of 1:10,000.
Nagamas is located 2 km to the west of the open pit mining Batu Hijau. Research
methodology is a collection of field data with petrographic analysis, XRD, ASD,
petrology, and structural geology to make tracking maps, geomorphological maps,
geological maps, alteration maps, and structure maps. Geomorphological units of the
study area was divided into 4 (four) of land forms, namely: Intrusion Eroded Hills
(D1), Eroded Volcanic Slope (D2), Eroded Valley Fault Structure (S1), and Body
River (F1). Drainage pattern that develops in the study area is subdendritik.
Stratigraphy of the study area is divided into 5 (five) units which are not authorized
to order from the young to the old as follows: Unit Lithic Tuff (Early Miocene -Middle Miocene), Porphyritic Andesite Intrusion Unit (Middle Miocene), Quartz
Diorite Intrusion Unit (Late Miocene), Diatrem Breccia Intrusion Unit (Late
Pliocene), and Unit Alluvial deposits (Holocene). Geological structures that develop
in the study area was showing the fractures with north - south (NS) trending to the
northwest - southeast (NW - SE) and the left slip fault with the northwest - southeast
(NW - SE). Alteration zone of the study area was divided into 4 (four), namely: zone
of biotite - actinolite - quartz - magnetite (potassic zone), , zone of quartz - chlorite -sericite (phyllic zone), kaolinite zone - illite - smectite (argillic zone), and zone of
chlorite - epidote (propylitic zone). The most dominant mineralization in the area of
research is a type of sulfide minerals pyrite (FeS2) with little presence of
chalcopyrite (CuFeS2). The study area is the low grade porphyry are characterized
by the type A + B quartz veins, vein density 1 - ≥ 5 %, alteration biotite + epidote +
chlorite + clay minerals, and pyrite ± chalcopyrite mineralization.
Keywords: Geomorphology, Stratigraphy, Structural Geology, Alteration,
Mineralization, Low Grade.
| Item Type: | Thesis (Other) |
|---|---|
| Subjek: | Q Science > QE Geology |
| Divisions: | x. Faculty of Engineering, Science and Mathematics > School of Engineering Sciences |
| Depositing User: | Ratna Sufiatin |
| Date Deposited: | 11 Oct 2016 06:32 |
| Last Modified: | 11 Oct 2016 06:32 |
| URI: | http://eprints.upnyk.ac.id/id/eprint/7534 |
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