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Presentasi Model Endapan Mineral Dosen Dr. Ir. Irzal Nur, MTCredit to Kelompok 4
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SYARIF HIDAYATULLAH P. (D62112003)
YUNUS RANDI KATARINDI (D62112
MUH. CHAIDIR W. (D6211258)
Orogenic Gold Deposits
• Definitions
• Geological Environment
• Related Deposits
• Age
• Mineralization, Veins & Alteration
• Favorable Orogenic Gold Terranes
Orogenic Gold Deposits
•Orogenic gold deposits are precipitated from the last orogeny cycle
• common in metamorphic belt
• 25% of world’s gold is sourced from orogenic gold deposits
Generaly Overview
Orogenic Gold Deposits
OROGENIC GOLD
INTRUSION-RELATED
EPITHERMALS PLACERS
Orogenic Gold Deposits
Geological Environment
Orogenic Gold Deposits
Related Deposits
Orogenic Gold Deposits
Endapan emas orogenic ini telah terbentuk selama lebih dari 3 milyar tahun dari
sejarah bumi. Waktunya, selama Arkean ke Prakambrium dan terus-menerus
sepanjang Fanerozoikum.
Observasi yang telah dilakukan pada sabuk sekishijau Archaean hingga sabuk
metamorfik Phanerozoik mengindikasikan adanya asosiasi emas pada fasies
sekishijau.
Dominantly Archean to Phanerozoic
• Late Archean (2.7 to 2.55 Ga)
• Early Proterozoic (2.1 to 1.8 Ga)
• Late Proterozoic (700 to 600 Ma)
• Late Paleozoic (455 to 340 Ma)
• Mesozoic-Cenozoic (285 to 70 Ma)
Age
Orogenic Gold Deposits
Age
R.J. Goldfarb et al. / Ore Geology Reviews 18 (2001)
Orogenic Gold Deposits
Vein Mineralogy
•Endapan orogenik dicirikan dengan, vein yang dominan
kuarsa dengan mineral sulfida ≤ 3-5% (umumnya sulfida
Fe) dan mineral karbonat ≤ 5-15%.
•Mineral albit, fushsite, klorit, scheelite dan turmalin
sangat sering menjadi pengotor pada urat yang
ditemukan pada batuan pembawa fasies sekis hijau.
Orogenic Gold Deposits
Vein Textures
• Textures represent the local deformation process and vary according to the nature of the host
structure (extensional vs. compressional).
• Extensional veins typically display quartz and carbonate fibres at a high angle to the vein walls
and with multiple stages of mineral growth
• Compressional laminated veins are composed of massive, fine-grained quartz. When present in
laminated veins, fibres are subparallel to the vein walls
• Vein as open space infill and altered wall rock as replacements
Orogenic Gold Deposits
Alteration
• Proximal to distal assemblages
• Scale and intensity of alteration function of system depth and wall rock composition
• Best developed in ultramafic and greenstone hosts
• In sediment-hosted systems, alteration is narrow and discrete enveloping the mineralization
• Proximal alteration – sulphide minerals (py-po-aspy) and alkali-rick silicates (sericite, fuschite,
albite, biotite) -white clay alteration
• Distal alteration – carbonate minerals (lower temperature varieties) with quartz
• Amphibolite, diopside, plagioclase and garnet present with lesser carbonate in +amphibolite-grade
hosts
Orogenic Gold Deposits
Regional Metamorphism
• Host rocks are typically metamorphosed to greenschist faces, with local amphibolite and granulte
facies conditions
• Mineralization preferentially developed in metamorphic gradients (with greenschist or greenschist
to amphibolite)
• Ore forming alteration products typically
overprinted on regional metamorphic mineralogy
Orogenic Gold Deposits
Favorable Regional & District Targeting Criteria
1. Complex lithostratigraphy with competency contrasts
2. Isolation of competent units within incompetent units
3. Greenschist to greenschist-amphibolite transition facies metamorphism
4. Subjacent to major, crustal-scale structure
5. Lamprophyre and porphyry dikes
6. Fe-rich host-rocks and-or early magnetite alteration
7. Anticlines and domal structures
8. Flexures (dilational jogs) in major structural trends
9. Reactivation of earlier structures especially thrusts by strike-slip movement,
either late in the orogenic cycle or as a later overprinting event
Orogenic Gold Deposits
Favorable Orogenic Gold Terranes