KuliahS1 sttnas-2

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Definisi/batasan

• Porfiri (tembaga) adalah endapan mineralmengandung 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 padadaerah tektonik plate-margin

• Perkembangan dalam konsep-konsep geologi untukmemprediksi daerah target eksplorasi

• Perkembangan teknik geofisika, misalnya magnetik, IP,dll.



Porfiri

• Porfiri tembaga

• Porfiri molibden

• Porfiri emas

• Porfiri timah



The gold endowment of Indonesia and the Philippines, as defined by combinedpast production and existing resources, exceeds 8300 metric tonnes (t).



The majority of gold in Indonesia and the Philippines occurs in porphyry,

epithermal and skarn deposits. The gold reserves at Grasberg constitute~23% of the 8300 t Au total.



Sistem hidrotermal

• Sumber panas

– Tubuh intrusi (dike atau pluton)

• Batuan pembawa (host rock)

– Volkanik atau sedimen/metamorf• Jenis fluida

– Air meteorik dan air magmatik

• Gradien temperatur – Tergantung kedalaman

• Ukuran



Tipe alterasi

• Porfiri tembaga

– Propilitik

– Argilik

– Filik/serisitisasi

– Potasik

• Porfiri timah

– Propilitik

– Argilik

– Filik/serisitisasi

– TurmalinisasiOksidasi Reduksi



Mineralogi alterasi• Profilitik

– Qtz-K-feld stabil, plag-mafic min teralterasim'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) dananh

T i n g

k a

t h i d r o

l i s i s



Mineralisasi

• Porfiri tembaga

kalkopirit, pirit,kalkosit, bornit,molibdenit,

galena, magnetit,emas, tembaga

• Porfiri timah

arsenopirit, frankeit,

pirotit, sfalerit, kal-kopirit, galena,

stanit, fluorit

tetrahedrit-tenantit, seelit

Zoning p ada m ineral i sas i h ip og en sang at m enar ikun tuk d ipakai pada permo delan ku ant i tat i f end apanmineral .



CLASSIC MODEL OF PORPHYRY DEPOSITS

PERIPHERALCcp-Gn-Sp-Au-Ag PERIPHERAL

Ccp-Gn-Sp-Au-Ag

LOW PYRITESHELLPy ~2%

Mag>Py

P Y R I T E S H E L LP y ~ 10%Cc p 0 .1-3%Mo r a r e

Mag>Py& Ccp

ORE SHELLPy 1%Ccp 1-3%Mo 0.03%

LOW GRADECORElow totalCcp-Py-Mo

?

?

SAN MANUEL FAULT

KALAMAZOOSEGMENT

SAN MANUEL

SEGMENTPropylitic(Chl-Ep-Carb)

Adul-Ab

ArgillicQtz-Kln-Chl

PhyllicQtz-Ser-Py

PotassicQtz-Kfs-Bt-+Ser+Anh

Qtz-Ser -Chl-Kfs

Chl-Ser-Ep-Mag

?

?

?

??

A



Quartz-Monzonitemodel

Three major models:

1. Quartz-monzonite

2. Diorite

3. Breccia



Sistem hidrotermal



Pasific Rim Au-Cu mineralisation models



Southeast Pasific rim Au-Cu mineralisation



Three major episodes of gold deposit formation are recognized in SoutheastAsia, including Early Miocene, Middle to Late Miocene and Plio-Pliestocene.These epochs may reflect plate tectonic collisions and reorganization, with theyoungest 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 therelative abundance of young deposits.



The grade-tonnage plot for Southeast Asian gold deposits shows two major clusters ofdata: 1) porphyry deposits, which are low-grade and high-tonnage and 2) low-andintermediate-sulfidation deposits, which are medium- to high-grade and low- to medium-tonnage. Both deposit styles include deposits that contain > 100 t Au.



The copper deposits indicate a similar relationship between coppercontent and time of deposit formation to that shown by gold deposits,which reflects the close spatial and temporal relationships between copperand gold in Southeast Asia. Note the nearly logarithmic increase in coppercontent with time.

O l d A ( A)



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



Structure of an Island Arc

Schematic cross section through a typical island arc after Gill (1981), Orogenic Andesites and PlateTectonics. Springer-Verlag. HFU= heat flow unit (4.2 x 10 -6 joules/cm 2/sec)

Island Arc



Pemadatan magma hydrousGranodiorit porfirhipotetik

•D1 = dyke

•S1 menunjukkan batas

saturasi H 2O



Pemadatan magma hydrous

Granodiorit porfir hipotetis

•Tahap kedua pendinginanlelehan jenuh H 2O, yang

disebut sebagai “second boiling” (resurgent boiling)

•BP 2 dan D 2 adalah pipa breksi dan dyke



Pemadatan magma hydrous

Granodiorit porfirhipotetis

•Second boiling.•BP 2 dan D 2 adalah pipa

breksi dan dyke.

•Aktivitas magmatik pada pembentuk-an sistem porfiri Cu-Mo.



Porphyry deposits in Indonesia

INDONESIA

Eurasian



GEOLOGY OFTHE BATU HIJAU

DEPOSIT



ALTERATION OFTHE BATU HIJAU DEPOSIT

Early : Bt zone (potassic)

Act zone (inner propylitic)Chl-Ep zone (outer propylitic)

Transitional : Chl-Ser zone (interm. argillic)Late :

Prl-And zone (advanced argillic)

Ser-Pg zone (argillic)Very late :

Ill-Ser zone with Qtz+basemetal veins/veinlets

DISTALCHLOR ITE-EPIDOTECHLOR ITE-SER ICITE

TEXTUR E DESTR OYED( Undif f )CHLOR ITE-SER ICITE CHLOR ITE- EPIDOTE

CE NTR ALBIOTITE

345 ElvPR OXIMALACTI NOLITE

ILLITICPR OXIMALACTI NOLITE

DISTALCHLOR ITE-EPIDOTECHLOR ITE-SER ICITE

TEXTUR E DESTR OYED( Undif f )CHLOR ITE-SER ICITE CHLOR ITE- EPIDOTE

CE NTR ALBIOTITE

345 ElvPR OXIMALACTI NOLITE

ILLITICPR OXIMALACTI NOLITE

Chl-Ep

Act

Chl-Ser

Bt

Prl-And

Und iff. arg illic

Ser-Pg

Un d if f. a r g illic

4 8 5 0 0 0 E

4 8 5 6 0 0 E

4 8 6 2 0 0 E

9010200N

9009600N

9009000N

900840 0N

4 8 5

0 0 0 E

4 8 5 6 0 0 E

4 8 6 2 0 0 E

9010200N

9009600N

9009000N

9008400N

Chl-Ep

Act

Chl-Ser

0 100 200 m

N

Prl-And

S e r - P g

Ill-Ser



Porphyry vein-veinlet system

a) Collahuasi/Chileb) Grasberg/Irian Jaya

a

b



Porphyry vein-veinlet system

A

2 cm



Cu-Au-hosting potassic alteration zone



3. Tembaga (Cu)

• Ditemukan dalam wujud: – Native copper – Sulfida tembaga ( Cu-bearing sulphides )

Native copper :• Native copper primer berasosiasi dengan lava basaltik, dari proses reaksi larutan hidrotermal denganmineral oksida besi.

• Native copper sekunder berasosiasi dengan zonateroksida pada endapan tembaga, umumnya

berasosiasi dengan kuprit (Cu 2O), malakhit(Cu 2(OH) 2CO 3) dan azurit (Cu 3(OH) 2(CO 3)2).



Endapan magmatik-hidrotermal tembaga sebagai penghasilbijih tembaga utama di dunia:

1. Endapan tembaga porfir (70.6 %), e.g. Chuciacamata, El-Tiniente(Chiele), Bingham (USA), Batu Hijau & Grasberg (Indonesia). 2. Sediment-hosted stratiform copper deposits (14.7 %), e.g. White

River (USA), Kupfershiefer (Eropa Timur).3. Endapan VMS ( Volcanigenic Massive Sulphide ) (6.4 %), e.g. Flin

Flon (Kanada), Mt. Isa (Australia), Kuroko (Jepang).4. Endapan tembaga skarn (0.5 %), e.g. Tintaya (Peru), Erstberg(Indonesia)

5. Endapan tembaga di karbonatit (1.4 %), e.g. Palabora (AfrikaSelatan)

6. Endapan tipe Olympic Dam ( iron-oxides-copper deposits ) (0.9 %),e.g. Olympic Dam (Australia), Moghrain (Mauritania).

7. Endapan tembaga magmatik, e.g. Sudbury (Kanada), Kambalda(Australia), Norisk (Rusia).



GEOCHEMICAL DISCRIMINATION



GEOCHEMICAL DISCRIMINATION:Alteration zonesMajor elements (R1-R2 diagram)

0

500

1000

1500

2000

0 1000 2000 3000 4000 5000 6000 7000

R (4Si-11[Na+K]-2[Fe+Ti])1

Hbl

Qtz

Chl

Ser Bt

Pl (core)

Prl

Pg

Least alteredBt zone

Act-(Chl-Ep) zoneChl-Ser zonePrl-And zoneSer-Pg zoneMinerals

Least-altered

Proximal Act andDistal Chl-Ep zones

Central Bt and

transitionalChl-Ser zones

Late Prl-And andSer-Pg zones

(after De La Roche et al., 1980)



Fluida bijih (ore fluid)• Inklusi fluida

– Kisaran: 250-750 °C dengan salinitas 15-70wt.% pada sistem orthomagmatik, dan <15wt.% pada sistem konvektif

– Kedalaman: <4 km (Cerro Verde, 1-2 km)

– Jenis air: air magmatik dan meteorik

• Sumber metal

– Produk sampingan dari kristalisasi magmatik(incompatible elements).

– Metal dan sulfur berasal dari batuan samping



Phase separation

partitioning

Bulk salinity rangeof magmatic fluid

phaseseparation

510°

8 0 0 °

6 0 0 °

5 5

0 °

5 0 0 °

5 1 0 °

4 0 0 °c r i t i c a l c u r v e

NaCl +

vapour

N a C l + v a p

o u r +

l i q u i d

LIQUIDVAPOUR

0.1 1.0 10.0 500

0.5

1

3

2

1

0

Salinity (NaCl wt.% eq.)

L i t h o s

t a t i c d e p

t h ( k m

)

e x s o l v e d f l u i d f r o m

m a g m a

CAUSATIVE TONALITE INTRUSIONS



CAUSATIVE TONALITE INTRUSIONS:Thermobarometry

200 400 600 800 10000

2

4

0.5

6

8

1.0

1.5

Temperature (°C)

1

2

3

4

5

6

NaCl +VAPOUR

0 .1

0. 5

2 . 0

5 . 0

7 0

8 0

6 0

5 0 4 0

3 0

2 0

1 0

LIQUID

LIQUID+

VAPOUR

B r i

t t l e

P l a s t i c

Cri t ica l

c u r v e

5 . 0

Exsolvedmagmatic

fluid

Phase separation600 bars; 2.2 km

Early centralBt zone

Early distalChl-Ep zone

LateSer-Pgzone

(after Hedenquist, 1998)

ORE FLUID EVOLUTION: Microthermometry

T = 760°C; P = 1.5 kbarsPaleodepth = 5.5 km (lower part)

500400 600 700 800 900

-25

-20

-15

-10

T (°C)

o g

f

2

F M Q

N N O

H E M M A

G

S O 2

H S 2

PY PO+S

P Y

M AG + S

f O 2 pattern

T = 760-540°Clog f O2 = -12 to -20

Bt : 510°C, 400 barsChl-Ep: 250°C, 125 barsSer-Pg: 225°C, 100 bars

THE BATU HIJAU GENETIC MODEL



THE BATU HIJAU GENETIC MODEL

2 1 1 2 km

Equigranular quartz diorite

P p re - m i

n e t o p o g r a h y

Andesiticvolcaniclasitic

rocks

MAGMA

P a l e o s u r fa c e

1

0

2

3

4

5

6

5.5 km

Young tonalite(Cu-Au depleted)

Intermediate tonalite(high Cu-Au)

Chl-EpAct

Chl-Ser

ActChl-Ep

Bt (potassic)

Highest grade(~0.5% Cu)

Mediumgrade

Lowgrade

Compositional changeCompositional change Physicochemical changePhysicochemical change

Argillic



Layout of Batu Hijau project area



The Batu Hijau open pit



Terima kasih...

Stolberg Germany 2005

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