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