Transcript Dr. Arifudin Idrus PORPHYRY Cu-Au DEPOSITS Laboratorium Bahan Galian

PORPHYRY Cu-Au DEPOSITS
Dr. Arifudin Idrus
Laboratorium Bahan Galian
Jurusan Teknik Geologi, Fakultas Teknik
Universitas Gadjah Mada
Yogyakarta
Stolberg, Germany, 2005
Definisi/batasan
• Porfiri (tembaga) adalah endapan mineral
mengandung sebaran tembaga, yang terdapat
pada batuan beku plutonik (monzonit kuarsa,
granodiorit dan tonalit).
• Endapan epitermal terbentuk pada kedalaman
dangkal (~1 km) dan dalam kisaran suhu 50 –
250°C.
• “epithermal” (lebih dangkal/dingin)
• “porphyry” (endapan lebih dalam/panas)
Mengapa endapan porfiri (dan
epithermal) menarik?
• Harga emas & tembaga relatif tinggi
• Perkembangan teknik pemisahan logam
• Banyak endapan epitermal dan porfiri ditemukan pada
daerah tektonik plate-margin
• Perkembangan dalam konsep-konsep geologi untuk
memprediksi daerah target eksplorasi
• Perkembangan teknik geofisika, misalnya magnetik, IP,
dll.
Porfiri
• Porfiri tembaga
• Porfiri molibden
• Porfiri emas
• Porfiri timah
Sistem hidrotermal
• Sumber panas
– Tubuh intrusi (dike atau pluton)
• Batuan pembawa (host rock)
– Volkanik atau sedimen/metamorf
• Jenis fluida
– Larutan magmatik & air meteorik
• Gradien temperatur
– Tergantung kedalaman
• Ukuran
Tipe alterasi
• Porfiri tembaga
• Porfiri timah
– Propilitik
– Propilitik
– Argilik
– Argilik
– Filik/serisitisasi
– Filik/serisitisasi
– Potasik
– Turmalinisasi
Oksidasi
Reduksi
Mineralogi alterasi
Tingkat hidrolisis
• Profilitik
– Qtz-K-feld stabil, plag-mafic min teralterasi
m'jadi ab plag, chl, ep, carb, mont, trem, act
• Argilik
– Qtz, kao, chl, sedikit mont
• Filik
– Qtz, ser yang disertai dengan py
• Potasik
– Qtz, K-feld, bio, interm plag (ol-and) dan
anh
Mineralisasi
• Porfiri tembaga
kalkopirit, pirit,
kalkosit, bornit,
molibdenit,
galena, magnetit,
emas, tembaga
• Porfiri timah
arsenopirit, frankeit,
pirotit, sfalerit, kalkopirit, galena,
stanit, fluorit
tetrahedrit-tenantit,
seelit
CLASSIC MODEL OF PORPHYRY DEPOSITS
SAN MANUEL FAULT
SAN MANUEL
SEGMENT
?
?
Propylitic
(Chl-Ep-Carb)
Adul-Ab
KALAMAZOO
SEGMENT
?
?
Phyllic
Qtz-Ser-Py
Potassic
Qtz-Kfs-Bt+Ser+Anh
Argillic
Qtz-KlnChl
?
PERIPHERAL
Ccp-Gn-Sp-Au-Ag
LOW PYRITE
SHELL
Py ~2%
Py ~10%
Ccp 0.1-3%
Mo rare
?
Qtz-SerChl-Kfs
A
ORE SHELL
Py 1%
Ccp 1-3%
Mo 0.03%
PYRITE
SHELL
?
Chl-SerEp-Mag
PERIPHERAL
Ccp-Gn-Sp-Au-Ag
Mag>Py
LOW GRADE
CORE
low total
Ccp-Py-Mo
Mag>Py
& Ccp
Three major models:
1. Quartz-monzonite
2. Diorite
3. Breccia
Quartz-Monzonite
model
Sistem hidrotermal
Pasific Rim Au-Cu mineralisation models
Southeast Pasific rim Au-Cu mineralisation
Three major episodes of gold deposit formation are recognized in Southeast
Asia, including Early Miocene, Middle to Late Miocene and Plio-Pliestocene.
These epochs may reflect plate tectonic collisions and reorganization, with the
youngest episode related to collisions in Taiwan (5 Ma) and the Banda arc (4 to
3 Ma). Uplift and erosion of pre-Pliocene deposits may also contribute to the
relative abundance of young deposits.
The grade-tonnage plot for Southeast Asian gold deposits shows two major clusters of
data: 1) porphyry deposits, which are low-grade and high-tonnage and 2) low-and
intermediate-sulfidation deposits, which are medium- to high-grade and low- to mediumtonnage. Both deposit styles include deposits that contain > 100 t Au.
The copper deposits indicate a similar relationship between copper
content and time of deposit formation to that shown by gold deposits,
which reflects the close spatial and temporal relationships between copper
and gold in Southeast Asia. Note the nearly logarithmic increase in copper
content with time.
Ocean-ocean  Island Arc (IA)
Ocean-continent  Continental Arc or Active Continental Margin
(ACM)
Principal subduction zones associated with orogenic volcanism and plutonism. Triangles are on the overriding plate. PBS =
Papuan-Bismarck-Solomon-New Hebrides arc. After Wilson (1989) Igneous Petrogenesis, Allen Unwin/Kluwer.
Continental margin
Island Arc
Structure of an Island Arc
Schematic cross section through a typical island arc after Gill (1981), Orogenic Andesites and Plate
Tectonics. Springer-Verlag. HFU= heat flow unit (4.2 x 10-6 joules/cm2/sec)
Pemadatan magma hydrous
Granodiorit porfir
hipotetik
•D1 = dyke
•S1 menunjukkan batas
saturasi H2O
Pemadatan magma hydrous
Granodiorit porfir hipotetis
•Tahap kedua pendinginan
lelehan jenuh H2O, yang
disebut sebagai “second
boiling” (resurgent boiling)
•BP2 dan D2 adalah pipa
breksi dan dyke
Pemadatan magma hydrous
Granodiorit porfir
hipotetis
•Second boiling.
•BP2 dan D2 adalah pipa
breksi dan dyke.
•Aktivitas magmatik pada
pembentuk-an sistem
porfiri Cu-Mo.