GEOLOGI, KARAKTERISTIK DAN MINERALISASI HIDROTERMAL BATUAN METAMORF KOMPLEKS TEHORU DAN TAUNUSA DI PULAU SERAM-INDONESIA

HERFIEN SAMALEHU, Dr.rer.nat Ir. Arifudin Idrus, ST, M.T, IPU; Ir.Nugroho Imam Setiawan,ST,MT,D.Sc,IPM

2021 | Disertasi | DOKTOR TEKNIK GEOLOGI

Target eksplorasi emas di Indonesia saat ini telah berfokus pada sabuk metamorf dimana proses akresi dan kolisi menyebabkan terjadinya proses pengayaan primer mineralisasi logam mulia di Indonesia. Eksplorasi endapan ini berhubungan dengan ketiadaan batuan plutonik atau busur magmatik/vulkanik meskipun asal sumber biji dan asal fluida dikaitkan dengan adanya magmatisme atau proses vulkanisme. Daerah Iha - Luhu dan Tamilouw- Haya berlokasi di lengan Barat dan selatan Pulau Seram, Indonesia serta menempati batuan metamof Kompleks Taunusa dan Kompleks Tehoru. Penelitian ini bertujuan untuk mengkaji kontrol geologi mineralisasi hidrotermal, karakteristik mineralisasi bijih, geokimia dan alterasi hidrotermal, karakteristik fluida hidrotermal serta model genetik endapan cinnabar dan emas di Iha - Luhu dan Tamilouw - Haya. Metode penelitian dimulai dengan kegiatan investigasi dilapangan (fieldwork) untuk pengambilan sampel, pemetaan geologi, alterasi dan mineralisasi serta analisa laboratorium yang meliputi petrografi, sayatan poles, geokimia bijih (FA/AAS dan ICP-AES, XRF), geokimia batuan (ICP-MS dan ICP-AES), kimia mineral dan elemental mapping (SEM-EDX dan MicroXRF), XRD serta inklusi fluida. Karakteristik endapan cinnabar di Iha - Luhu terbentuk dalam 2 jenis urat (fracture-related mineralization) dan diseminasi (disseminated) dalam host batuan metapelitik dan filit kuarsa-muskovit yang dikontrol oleh sesar - sesar berarah utara barat laut - selatan menenggara dan timur laut - barat daya. Mineralisasi terdiri dari cinnabar (+Metacinnabar), arsenopirit, stibnit, sfalerit, hematit, minor pirit, pirhotit dengan gangue terdiri dari kuarsa, illit, smektit dan kaolinit. Bijih cinnabar mengandung kelimpahan Zn, Sb, Fe, As, menunjukan kehadiran logam mulia Au serta kandungan merkuri (Hg) mencapai 72,4 persen. Tipe alterasi merupakan alterasi argilik yang terdiri dari alterasi illit+kaolinit, alterasi illit+klorit dan alterasi illit+smektit+kaolinit. Analisis inklusi fluida pada urat kuarsa di Iha-Luhu menunjukkan bahwa temperatur homogenisasi pembentukan cinnabar di Bukit Tembaga antara 261-336 derajat Celcius dengan salinitas berkisar 0,70-4,65 wt.persen. NaCl.eq yang ekuivalen dengan kedalaman 6-8.5 km. Inklusi fluida di Iha-luhu merupakan inklusi dua fase (liquid dan vapour) atau liquid rich (H2O) inclusions. Endapan Tamilouw - Haya dicirikan dengan 3 jenis urat kuarsa/kuarsa+karbonat pembawa bijih (Ore - bearing fluids). Urat tipe pertama yang merupakan urat kuarsa yang sejajar dengan foliasi dan perlapisan batuan metamorf berbentuk masif, sheeted, tersegmentasi dan termineralisasi lemah. Urat tipe kedua merupakan urat kuarsa memotong perlapisan batuan, masif, termineralisasi lemah dan cenderung bersifat barren serta urat generasi ketiga yang merupakan urat kuarsa+karbonat merupakan mineralized zone, berasosiasi dan membentuk zona stockwork serta urat breksi. Mineralisasinya terdiri dari pirit, kalkopirit, emas, sfalerit, galena, pirhotit, minor sulphosalt (tetrahedrit-tenantit), markasit, arsenopirit, cinnabar, kalininit dan realgar. Alterasi endapan emas Tamilouw - Haya terdiri dari 3 (tiga) tipe alterasi yaitu alterasi karbonatisasi (kalsit+kuarsa+ankerit+klorit+epidot+llit+opak), silisifikasi (kuarsa+kalsit+illit+opak) dan seritisasi (kuarsa+serisit+opak) di sepanjang urat, stockwork serta urat breksi. Inklusi fluida pada 3 jenis urat kuarsa atau kuarsa+karbonat di wilayah Tamilouw - Haya terkristalisasi pada temperatur homogenisasi (Th) 240 derajat Celcius, salinitas fluida 3.87 - 0.70 wt.persen NaCl.eq dan Temperatur peleburan (Tm) -0.4 - 2.3 derajat Celcius. Fluida pembentuk biji terdiri dari inklusi 2 fase (VCO2 + LH2O) yang kaya cairan dan ekuivalen dengan kedalaman 5.5-9 km. Hubungan antara endapan Iha - Luhu dan Tamilouw - Haya menunjukan bahwa kedua endapan ini terbentuk oleh fase orogenesa dengan continuum model menempatkan endapan Iha - Luhu terbentuk dominan pada zona epizonal hingga mesozonal sedangkan endapan Tamilouw - Haya diperkaya dengan base metal yang dominan berada pada zona mesozonal. Berdasarkan karakteristik alterasi, mineralisasi serta fluida hidrotermal maka endapan cinnabar dan emas di Iha - luhu dan Tamilouw - Haya merupakan endapan epigenetik pada zona epizonal - mesozonal selama orogenesa seram (3,4 - 16 Juta tahun yang lalu).

Currently, gold exploration target has focused on the metamorphic belt where accretion and collision were led to the primary enrichment of precious metal mineralization in Indonesia. Exploration of this deposit is related to absence of plutonic rocks or magmatic/volcanic arcs although the origin of ore sources and fluid origins were associated with presence of magmatism or volcanism processes. Iha-Luhu and Tamilouw-Haya areas are located in the western and southern arms of Seram Island, Indonesia and occupy Taunusa and Tehoru metamorphic complexes. This research is aimed to study geological control of ore mineral charactristics, geochemistry and hydrothermal alteration, fluid characteristics and genetic models of cinnabar and gold deposits at Iha - Luhu and Tamilouw - Haya. Research methods are conducted using fieldwork activities for sampling, geological mapping, alteration and mineralization and completely supported by advanced laboratory analysis inlcuding petrography, polished sections, ore geochemistry (FA/AAS ICP-AES and XRF), rocks geochemistry (ICP-MS and ICP-AES), mineral chemistry and elemental mapping (SEM-EDX and Micro-XRF), XRD and fluid inclusions as well. Characteristics of cinnabar deposits at Iha - Luhu are 2 types of fracture-related mineralization and disseminated within metapelites and quartz-muscovite phyllite host rock and controlled by NNW-SSE and NE-SW - trending faults. Ore mineralization are consists of cinnabar (+metacinnabar), arsenopyrite, stibnite, sphalerite, hematite, minor pyrite, pyrrhotite and accompanied by quartz, illite, smectite and kaolinite as gangue minerals. Cinnabar ore contains an abundance of Zn, Sb, Fe, As, indicating presence of precious metal (Au) and grade of mercury (Hg) reached 72.4 percen. Argillic alteration are enveloped by broadly alteration salvages which consists of illite+kaolinite, illite+chlorite (adjacent to ore body) and illite+smectite+kaolinite zones. Fluid inclusions study from quartz veins reveal homogenization temperature (Th) of cinnabar formation at Bukit Tembaga ranging from 261 to 336 degree Celcius, fluid salinity ranging from 0.70-4.65 wt.percen NaCl.eq which is equivalent to a depth of 6-8.5 km. Mostly, the fluid inclusions were two-phase (L+V) or liquid-rich (H2O) inclusions. Tamilouw - Haya deposit is characterized by 3 types of quartz veins/quartz+carbonate (Ore - bearing fluids). Concordant vein, namely quartz type 1- vein (V1) is characterized by massive shape, sheeted, segmented, tends to parallel to the foliation of metamorphic rocks and weak mineralized to barren. Discordant veins are separated into two vein types ; Quartz type 2 vein (V2) which is cross to the foliation, massive, weak mineralized to barren and associated with silicification and serisitic alterations. The last, the so-called mineralized veins (V3) are compose of quartz+carbonate, segmented, deformed, cross to the foliation of metamorphic/metapelites rocks and characterized by stockwork - breccia vein textures. The common ore minerals assemblage at Tamilouw - Haya deposit are dominated by native gold, chalcopyrite, pyrite, sphalerite, galena, pyrrhotite, minor tetrahedrite-tennantite (sulphosalt), marcasite, realgar, kalininite and arsenopyrite as hypogene minerals and accompanied by covellite, hematite, goethite and malachite as the supergene minerals. There were 3 types of hydrotermal alteration namely carbonatization (cal+qz+Ank+chl+ep+ill+opq), silicification (qz+cal+ill+opq) and seritization (qz+ser+opq) along veins, stockwork and breccia veins. Fluid inclusions in 3 types of quartz/quartz+carbonate veins crystallized at homogenization temperature (Th) 240 to 340 degree Celcius , fluid salinity ranging from 3.87 - 0.70 wt.percen NaCl.eq and melting temperature (Tm) -0.4 - 2.3 degree Celcius. The ore -forming fluids consist of two phase inclusions (VCO2 + LH2O) which are liquid rich inclusion and equivalent to a depth of 5.5-9 km. The relationship between Iha - Luhu and Tamilouw - Haya deposits show that these two deposits were formed by orogenic phase where the continuum model placing Iha - Luhu deposit is predominantly occupy epizonal to mesozonal zones while the Tamilouw - Haya deposit is enriched with a dominant base metal in mesozonal zone. Based on characteristics of alteration, mineralization and hydrothermal fluids thus the results of this study show that Iha - Luhu and Tamilouw - Haya are an epigenetic, developed by orogenic style at the transition between epizonal and mesozonal zone during seram orogeny (ca. 3.4 - 16 Ma).

Kata Kunci : Endapan orogenik, epigenetik, fluida hidrotermal, urat kuarsa+karbonat