2. basic of porphyry cu au deposit (2)
TRANSCRIPT
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Dr. Arifudin Idrus Laboratorium Bahan Galian
Jurusan Teknik Geologi, Fakultas Teknik
Universitas Gadjah Mada Yogyakarta Stolberg, Germany, 2005
PORPHYRY Cu-Au DEPOSITS
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Definisi/batasan• Porfiri (tembaga) adalah endapan mineral Porfiri (tembaga) adalah endapan mineral
mengandung sebaran tembaga, yang terdapat mengandung sebaran tembaga, yang terdapat pada batuan beku plutonik (pada batuan beku plutonik (mmonzonit kuarsa, onzonit kuarsa, granodiorit dan tonalit).granodiorit dan tonalit).
• Endapan epitermal terbentuk pada kedalaman Endapan epitermal terbentuk pada kedalaman dangkal (~1 km) dan dalam kisaran suhu 50 – dangkal (~1 km) dan dalam kisaran suhu 50 – 250250°°C.C.
• ““epithermal” (lebih dangkal/dingin)epithermal” (lebih dangkal/dingin)
• ““porphyry” (endapan lebih dalam/panas)porphyry” (endapan lebih dalam/panas)
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Mengapa endapan porfiri (dan epithermal) menarik?
• Harga emasHarga emas & tembaga & tembaga relatif tinggi relatif tinggi
• Perkembangan teknik pemisahan logamPerkembangan teknik pemisahan logam
• Banyak endapan epitermal dan porfiri ditemukan pada Banyak endapan epitermal dan porfiri ditemukan pada daerah tektonik plate-margindaerah tektonik plate-margin
• Perkembangan dalam konsep-konsep geologi untuk Perkembangan dalam konsep-konsep geologi untuk memprediksi daerah target eksplorasimemprediksi daerah target eksplorasi
• Perkembangan teknik geofisika, misalnya magnetik, IP, Perkembangan teknik geofisika, misalnya magnetik, IP, dll.dll.
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Porfiri
• Porfiri tembagaPorfiri tembaga
• Porfiri molibdenPorfiri molibden
• Porfiri emasPorfiri emas
• Porfiri timahPorfiri timah
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Sistem hidrotermal
• Sumber panasSumber panas
– Tubuh intrusi (dike atau pluton)Tubuh intrusi (dike atau pluton)
• Batuan pembawa (host rock)Batuan pembawa (host rock)
– Volkanik atau sedimen/metamorfVolkanik atau sedimen/metamorf
• Jenis fluidaJenis fluida
– Larutan magmatik & air meteorikLarutan magmatik & air meteorik
• Gradien temperaturGradien temperatur
– Tergantung kedalamanTergantung kedalaman
• UkuranUkuran
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Tipe alterasi
• Porfiri tembagaPorfiri tembaga
– PropilitikPropilitik
– ArgilikArgilik
– Filik/serisitisasiFilik/serisitisasi
– PotasikPotasik
• Porfiri timahPorfiri timah
– PropilitikPropilitik
– ArgilikArgilik
– Filik/serisitisasiFilik/serisitisasi
– TurmalinisasiTurmalinisasi
OksidasiOksidasi ReduksiReduksi
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Mineralogi alterasi• ProfilitikProfilitik
– Qtz-K-feld stabil, plag-mafic min teralterasi Qtz-K-feld stabil, plag-mafic min teralterasi m'jadi ab plag, chl, ep, carb, mont, trem, actm'jadi ab plag, chl, ep, carb, mont, trem, act
• ArgilikArgilik
– Qtz, kao, chl, sedikit montQtz, kao, chl, sedikit mont
• FilikFilik
– Qtz, ser yang disertai dengan pyQtz, ser yang disertai dengan py
• PotasikPotasik
– Qtz, K-feld, bio, interm plag (ol-and) dan Qtz, K-feld, bio, interm plag (ol-and) dan anhanh
Tin
gkat
hid
rolis
is
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Mineralisasi
• Porfiri tembagaPorfiri tembaga
kalkopirit, pirit, kalkopirit, pirit, kalkosit, bornit, kalkosit, bornit, molibdenit, molibdenit, galena, magnetit, galena, magnetit, emas, tembagaemas, tembaga
• Porfiri timahPorfiri timah
arsenopirit, frankeit, arsenopirit, frankeit, pirotit, sfalerit, kal-pirotit, sfalerit, kal-kopirit, galena, kopirit, galena, stanit, fluoritstanit, fluorit
tetrahedrit-tenantit, tetrahedrit-tenantit, seelitseelit
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CLASSIC MODEL OF PORPHYRY DEPOSITS
PERIPHERALC cp -G n-Sp-Au-Ag PERIPHERAL
C cp -G n-Sp-Au-Ag
LOW PYRITESHELLPy ~2%
M ag>Py
PY R ITES H E LLPy ~10%Ccp 0.1-3%Mo rare
M ag >Py& C cp
ORE SHELLPy 1 %C cp 1-3%M o 0 .03%
LOW GRADECORElow tota lCcp-Py-M o
?
?
SAN M ANUEL FAU LT
KALAMAZOOSEGMENT
SAN M ANUELSEGMENT
Propylitic(Chl-Ep-Carb)
A dul-A b
ArgillicQ tz-K ln-C h l
PhyllicQ tz-S er-P y
PotassicQ tz-K fs-B t-+ S er+A nh
Q tz-S er-C h l-K fs
Chl-Ser-Ep-M ag
?
?
?
??
A
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Quartz-Monzonite model
Three major models:
1. Quartz-monzonite
2. Diorite
3. Breccia
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Sistem hidrotermal
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Pasific Rim Au-Cu mineralisation models
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Southeast Pasific rim Au-Cu mineralisation
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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.
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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 medium-tonnage. Both deposit styles include deposits that contain > 100 t Au.
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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.
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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.
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Continental margin
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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)
Island Arc
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Pemadatan magma hydrousGranodiorit porfir hipotetik
•D1 = dyke
•S1 menunjukkan batas
saturasi H2O
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Pemadatan magma hydrous
Granodiorit porfir hipotetis
•Tahap kedua pendinginan lelehan jenuh H
2O, yang
disebut sebagai “second boiling” (resurgent boiling)
•BP2 dan D
2 adalah pipa
breksi dan dyke
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Pemadatan magma hydrous
Granodiorit porfir hipotetis
•Second boiling.
•BP2 dan D
2 adalah pipa
breksi dan dyke.
•Aktivitas magmatik pada pembentuk-an sistem porfiri Cu-Mo.