Dr. Arifudin Idrus 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 timah Porfiri tembaga Propilitik Propilitik Argilik Filik/serisitisasi Turmalinisasi Porfiri tembaga Propilitik Argilik Filik/serisitisasi Potasik 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 Tingkat hidrolisis

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

CLASSIC MODEL OF PORPHYRY DEPOSITS

Quartz-Monzonite model Three major models: Quartz-monzonite Diorite 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 medium-tonnage. 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

Structure of an Island Arc Note mantle flow directions (induced drag), isolated wedge, and upwelling to  back-arc basin spreading system Benioff-Wadati seismic zone (x x x x) Volcanic Front h is relatively constant  depth is important 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.