Jurnal Geologi Indonesia, Vol. 5 No. 4 Desember 2010: 247-261

Alteration and Textures Associated with Gold Mineralization at the Bunikasih Area, Pangalengan, West Java

A.S. SubAndrio and n.i. bASuki

Study Program of Geology – FITB – Institut Teknologi Bandung, Jln. Ganesha 10 Bandung 40132

AbstrAct

The Bunikasih vein system in the Pangalengan district of West Java is a low-sulfidation, adularia ser- icite epithermal gold deposit. It is hosted by Late Miocene andesitic volcanic and volcanoclastic rocks occurring in the south western margin of Malabar Volcano complex. Gold ore and alteration related to deposition of gold in Bunikasih deposits superimposed on Late Tertiary-Quaternary andesitic formation that were altered and mineralized by some hydrothermal events. The veins consist almost entirely of , with small amounts of adularia, bladed , , and gold. Gold ore shoots are vertically restricted and are more continuous horizontally. The veins display complex and multi episodic filling with texture characteristics of open space precipitation such us colloform, lattice bladed, crusti- form banding, vugs, breccia, and cockade and comb texture. The presence of bladed calcite and silica after bladed calcite suggests that the hydrothermal fluids boiled. In the Cibaliung section of the area, anomalous gold is related to veins trending northeast - southwest, milky quartz with dark grey to black manganese staining is found intermittently for a length of about 800m. The mineralized andesite ore bodies exhibit broad alteration patterns adjacent to mineralization, passing from fresh rock into anargillic, chlorite zone, and then sericite-silica close to mineralization. An argillic assemblage composed of with fine-grained pyrite bulb is present in the upper portions and surrounding of the quartz vein system. The veins range from centimeter to meter in size. Of 24 vein samples collected, gold averages up to 0.3 grams per tone ("g/t"), to a high of 24.6 g/t. The Bunikasih epithermal gold deposit was mined by people for more than 10 years, mainly for the gold ore. Keywords: alteration, vein texture, gold mineralization, Bunikasih

Sari

Urat-urat yang terdapat di Bunikasih, Kecamatan Pengalengan, Jawa Barat, merupakan bagian dari suatu endapan emas tipe epitermal adularia serisit, sulfidasi rendah. Endapan emas tersebut terdapat dalam batuan vulkanik andesit dan batuan klastik vulkanik berumur Miosen Akhir yang terdapat di barat daya kompleks gunung api Malabar. Emas dan alterasi penyerta dijumpai mengubah satuan batuan andesit Tersier Akhir – Kuarter yang telah mengalami alterasi hidrotermal. Urat-urat yang dijumpai tersusun oleh kuarsa dengan sedikit adularia, bilah-bilah kalsit, pirit, dan emas. Endapan emas dalam urat penyebarannya terbatas secara vertikal, dan relatif lebih menyebar secara horizontal. Urat-urat kuarsa memperlihatkan tekstur kompleks yang menunjukkan pengendapan berulang secara episodik dalam ruang terbuka seperti koloform, mineral berbentuk bilah, perlapisan crustiform, breksi, dan tekstur cockade and comb. Dijumpainya bilah-bilah kalsit dan pseudomorph silika hasil ubahan bilah kalsit menunjukkan kemungkinan terjadinya pendidihan (boiling) pada larutan hidrotermal. Di daerah Cibaliung, keterdapatan emas berasosiasi dengan urat-urat kuarsa berwarna putih susu berarah timur laut – barat daya sepanjang sekitar 800 m, dengan bercak-bercak mangan berwarna abu gelap hingga hitam. Batuan vulkanik andesit yang termineralisasi memperlihatkan pola alterasi yang berangsur dari batuan tak terubah menjadi zona argilik dan klorit, dan kemudian menjadi zona serisit-silika mendekati

Naskah diterima 21 Juni 2010, revisi kesatu: 13 Agustus 2010, revisi kedua: 02 September 2010, revisi terakhir: 26 November 2010

247 248 Jurnal Geologi Indonesia, Vol. 5 No. 4 Desember 2010: 247-261

zona mineralisasi. Urat-urat kuarsa mempunyai lebar bervariasi dari sentimeter hingga meter. Dari dua puluh empat percontoh yang dianalisis, kadar emas rata-rata adalah 0,3 g/t, dan dapat mencapai 24,6 g/t. Endapan emas Bunikasih telah ditambang oleh penduduk setempat selama lebih dari 10 tahun. Kata kunci: alterasi, teksture urat, mineralisasi emas, Bunikasih

IntroductIon Based on regional geological study, the faults in the researched area are most likely parts of, or Bunikasih area is located about 60 km to the are influenced by, regional, NE-SW trend, dextral south from Bandung, southwest of Situ Cileunca, strike-slip faults, as identified by Alzwar et al. or about 15 km from Pangalengan (Figure 1). It is (1992). These regional and local faults are inter- part of West Java Southern Mountain Zone covered preted to be formed by a relatively N-S regional by Quaternary (Pleistocene) volcanic rocks, known stress, which has been active since Late Oligocene as Waringin Andesite unit (Alzwar et al., 1992). – Early Miocene (Alzwar et al., 1992). Based on a more detailed work by Chandra (2009), The Cibaliung andesite lava unit was observed the andesite unit can be subdivided into three along the Cibaliung River (Figure 2 and 3) and is subunits; they are (older to younger): Cibaliung, characterized by whitish or greenish colour, and Cikabuyutan, and Puncak Cacing andesite lava porphyritic textures, comprising phenocrysts of units. Gold mineralization was firstly discovered in and in abundant aphanitic early 1990 by exploration of PT. Aneka Tambang. groundmass. Petrographic observation revealed Due to the small or subeconomic gold reserve, PT. that the aphanitic groundmass consists of minute Aneka Tambang has not mined this prospect. How- of pyroxene, plagioclase, glassy materi- ever, relatively high gold grade (up to 20ppm Au) als and opaque minerals. This unit shows a strong in some quartz veins made a great interest to many argillic and/or prophilitic alteration and, locally, local people to dig and mine gold traditionally. The silicification. In some places, a weak magnetic na- Bunikasih epithermal gold deposit of Pangalengan, ture of this unit can be detected by magnet. Quartz is one of small scale oberating gold mines, located veins in various sizes (1 cm to 3 m) are commonly in the southern part of West Java. The others being present, crosscutting this unit. Cineam and Salopa - Tasikmalaya, Cikondang- The Cikabuyutan andesite lava unit is present Cianjur, and Gunungpeti - Sukabumi (Widi et al., along the Cikabuyutan River (Figure 2 and 3) 1997). Based on these occurrences and the overall and is characterized by black colour, porphyritic volcanic setting, the southern belt of West Java textures that show plagioclase and pyroxene phe- has a good potential for discovering new gold ore nocrysts in an aphanitic groundmass, and by its deposits. For example, Pongkor Mount in Bogor very strong magnetic nature. Phenocrysts in this associated with the southern volcanic belt, is the unit are more abundant than those of the Cibaliung largest gold deposit in Java Island of which during andesite lava unit. Very fine pyroxene, plagioclase more than 10 years has been mined by PT. Aneka crystals, and glassy materials constitute the apha- Tambang (Warmada, 2003). nitic groundmass. The Cikabuyutan andesite lava

unit is weakly altered by (argillic), and unlike the previous unit, this unit is crosscut GeoloGy of the bunIkAsIh AreA by small-sized quartz veins (< 1 m-wide). Puncak Cacing andesite lava unit is the young- Based on a topographic map analysis and field est unit in the area and is found in Puncak Cac- observation, there are five identified (strike-slip) ing Hill as well as along some branches of the faults in the area. Two faults are NE-SW and the Cikabuyutan River near Puncak Cacing (Figure others are NW-SE (Figure 1). They are interpreted 2). This unit shows gray colour and comprises to be formed in post-Pleistocene, as they extend abundant phenocrysts of pyroxene and plagioclase across Quaternary (Pleistocene) volcanic rocks. in an aphanitic groundmass, which consists of fine Alteration and Vein Textures Associated with Gold Mineralization at the Bunikasih Area, 249 Pangalengan, West Java (A.S. Subandrio and N.I. Basuki)

Note : Rancatungku B Qd Q=Quaternary Age;

Soreang T=Tertiary Age; G. Koromong Q w b = W a r i n g i n - G. Geulis Tmb B e d i l A n d e s i t e , Qd Cipeundeuy Tmb 1151 O l d M a l a b a r : Kramat Qwb alteration of lava Cangkuang Muara breccias and tuffs, Banjaran pyroxene andesitic Bandasari Baros a n d h o r n b l e n d e a n d e s i t i c composition; Bojonglao 2 Citeuteurp Pasirpariuk Qtl= Kancana, Huyung Qtl a n d Ti l u l a v a s : Andesitic lava and basaltic-andesitic G. Bubut Gegerheos Cianjur lava of Mt. Tilu; 1333 T m b = B e s e r Ganjen Pasirhuni F o r m a t i o n : Tu f f

Kebontunggul sandstone, pumice G. Tanuaktangsi Qmt t u f f , c l a y s t o n e , conglomerate and 1514 lignite; Cikalong Q m t = M a l a b a r Ti l u G. Tikukur G. Puntang Vo l c a n i s : t u f f , l a h a r i c b re c c i a s Lamajang contains minor of G. Haruman G. Malabar pumice and lavas; Gambung 2621 Qyw=Young volcanic: Qtl E f f l a t a a n d andesitic-basaltic lava flows from Mt. Wayang Windu.; G. Tilu Puncakbebar Qkl= Kencana lavas: Rancatungku Andesitic lava and Pasirurug basaltic anadesite

Qmt lavas. Riunggunung QopuUndifferentiated Pangalengan G.Gambung E f f l a t a D e p o s i t s of Old Volcanics: Qwb Cibeureum Rancamanyar F i n e t o c o a r s e dacitic crystalline Wanasari t u f f , t u f f a c e o u s breccias contains Qopu pumices and old Barussalam andesitic-basaltic laharic deposits. Situ Cileunca G. Wayang Qd=Lake deposit:Clay Cibunihayu Qwb s i l t , f i n e t o Gunungcepu G. Windu coarse sands and gravel, commonly Puncak Cacing Banjarsari 2054 PR. Singahal Kertasari tuffaceous. Cibolang Qyw Cikowok Qopu Bunikasih N Wanasuka Qwb Samosa

G. Cikepung 0 1 2 3 Km Cepu Qkl 1390 Qwb 388 G. Karancang G. Malang 1880 Studied Area 1563 A

Figure 1. Simplified map western part of Geological Map of Garut and Pameungpeuk Quadrangle (Alzwar et al., 1992). Bunikasih (boxed area) is located near Lake Cileunca and Wayang Windu geothermal field. Mt. Malabar is located in northeastern part. 250 Jurnal Geologi Indonesia, Vol. 5 No. 4 Desember 2010: 247-261

G.Puncakcacing Vein Strike/Dip Average vein thickness Q1 90°/45° 1.3m Q2 131°/83° 38cm Q3 340°/83° 1.5m Q4 108°/79° 1.0m Q5 100°/70° 1m Q6 232°/71° 0.7m

Q6

Q1 500m

Q6

Q5

Q4

N Q3

Figure 2. Topography map of Bunikasih area. Mt. Puncak Cacing is the highest landmark of this area. Gold mining is distrib- uted on quartz vein group on southwestern area.

D 920000

G. Puncakcacing

C

N 9199000

0 1 km

B

9198000 Puncak Cacing Andesite Lava Unit A Cikabuyutan Andesite Lava Unit

Cibaliung Andesite Lava Unit

9197000 0776000 0777000 0778000 0779000 07 80000 Geological Cross Section 1600 1600 Scale V:H=1:1 (m) 1500 1500 1400 1400 1300 1300

1200 1200 1100 1100 A B 1700 1600 1500 1400 C D

Figure 3. Simplified geological map of Bunikasih area (Chandra, 2009). Alteration and Vein Textures Associated with Gold Mineralization at the Bunikasih Area, 251 Pangalengan, West Java (A.S. Subandrio and N.I. Basuki) plagioclase and pyroxene and glassy materials. present in argillic and prophilitic altered rocks, ac- The lava unit is relatively unaltered and is weakly companying clay minerals, chlorite, , and magnetic. calcite. In general, primary textures of the rocks

can still be identified. The intensity of alteration decreasing from the Cibaliung lava unit (medium AlterAtIon of VolcAnIc rocks to strong) to the Cikabuyutan lava unit (weak to medium) to Puncak Cacing lava unit (weak), gives Argillic and prophilitic are the common altera- an apparent systematic alteration intensity which tion types found in the area, with argillic occur- decrease from west to east. rences are much more widespread than prophilitic Quartz veins in the area are mainly found in the (Figure 4). Argillic alteration on volcanic rocks Cibaliung lava unit. The veins can have simple to is characterized by clay mineral alteration (prob- complex textures, occurring in various sizes (wide). ably kaolinite) after primary minerals and gives Micron-sized gold particles are known to be present the altered rocks a feel like soap. Plagioclase and in quartz veins. The veins have been the primary pyroxene phenocrysts, as well as groundmass target for local miners to extract gold. The general materials show various degrees of alteration by trends of some of the studied quartz veins are consis- clay minerals, with plagioclase in general show tent with the trends of faults in the researched area, more intense alteration. Prophilitic alteration is suggesting structural control on vein formation. The characterized by the presence of chlorite, epidote, faults have probably acted as conduits for hydro- and calcite after phenocrysts of pyroxene, and thermal fluids that were responsible for alteration plagioclase, and groundmass. Quartz is commonly of volcanic rocks and formation of quartz veins.

920000

G. Puncakcacing N

0 1 km

9199000

Prophilitic zone

Argillic zone

9198000

F

9197000

0776000 0777000 0778000 0779000 0780000 Geological Cross Section 1500 Scale V:H=1:1 (m) 1400 1300 1200 1100 1000

F E

Figure 4. Simplified alteration map of Bunikasih area (Chandra, 2009). 252 Jurnal Geologi Indonesia, Vol. 5 No. 4 Desember 2010: 247-261

MorpholoGy of QuArtz is composed mostly of alternating band of quartz showing various structures. Textures classes are In epithermal systems, silica may be deposited defined by features such as grain size and form of as or amorphous silica, chalcedony or quartz quartz. A summary for structure and texture types (Morrison et al., 1990). All these phases, except in quartz veins is provided in Table 1. quartz, were precipitated from solution that were supersaturated with respect to quartz, and then re- crystallized to quartz with time because they were MethodoloGy metastable at low temperatures (Fournier, 1985a). The quartz texture in veins may reflect the original The studied samples were taken from outcrops conditions of silica saturation. that represent different lithologic units and different Classification of quartz textures in epithermal alteration types, and quartz veins (see map on Figure vein systems have been presented by many research- 3). Hand specimen and thin section petrographic ers since Adams (1920) first proposed a terminology analysis were conducted to determine primary rock for quartz. Recent studies have noted that quartz tex- textures and compositions, as well as secondary tures in epithermal gold veins can provide evidence minerals and textures. Several quartz vein samples about mineralization processes (Morrison, 1990; are cut and polished for detailed texture and mineral Dong et al., 1995). paragenetic study. Geochemical analyses of selected Structural classes are defined by features such veins were done by XRF instrument and Energy as colour, grain size, and form (comb, fine Dispersive Analysis of X-rays (EDAX), performed grained, palty, colloform and cockade). Rhythmic on laboratory of Geological Department of Free symmetrical and asymmetrical crustiform banding University Berlin – Germany.

Table 1. Classification of Quartz Structure and Texture

Texture type Comb: a group of euhedral-subeuhedral crystals resembling the teeth of a comb under the microscope (2) Feathery: a feathery and splintery appearance seen locally or throughout quartz crystals caused by slight differ- (4) ences in the maximum extinction position under the microscope Microcrystalline: aggregates of microcrystalline quartz Fibrous: aggregates of fibrous quartz grains oriented perpendicular to the growth surface Dendritic: branching patterns of quartz (1) Colloform: rhythmic bands of microcrystalline quartz on various scales '4' Flamboyant: a radiant or flamboyant extinction of individual crystals with more or less rounded crystal outline (4) Ghost-sphere: spherical distribution of impurities within microcrystalline quartz '4' Pseudoacicular: linear arrangement of fine, elongate grains which could be caused by quartz replacement of calcite Structure type (2) Comb: a group of euhedral-subeuhedral crystals resembling the teeth of a comb Fine-grained: a group of anhedral quartz showing homogeneous grain shape; this structure is similar to the massive quartz texture defined by Dong et al. (1995) (3) Platy: aggregates of radial, bladed crystals (1) Colloform: rhythmic bands of chalcedonic silica grains with reniform habit Cockade: concentric crustiform bands of quartz, surrounding isolated fragments of host rock, or earlier pre- (2) cipitated quartz, or both

The terminology of the quartz structures and textures is based on: (1) Rogers (1917) (2) Adams (1920) (3) Urashima (1956) (4) Dong et al. (1995) Alteration and Vein Textures Associated with Gold Mineralization at the Bunikasih Area, 253 Pangalengan, West Java (A.S. Subandrio and N.I. Basuki)

results: VeIn petroloGy And GeocheMIstry Table 2. Representative Composition of selected Quartz Veins of Bunikasih Area by ICP Analyses (in ppm). Analyses were A classification of quartz veins at the Bunikasih performed in Geochemical Laboratory of Free University Berlin – Germany mine was made based on textures and cross cutting relationship in the veins, adopting classification in Sample Au Ag Pb Zn Cu As Sb Fe Shimizu et al. (1998). The epithermal quartz veins Q11 4 8 25 25 8 0 0 605 are concentrated on the southwestern part of the researched area (Figure 2). The deposit occurs in a Q12 3.7 7 30 25 7 0 0 554 southwest-northeast shear zone within Late Tertiary- Q13 1 90 40 40 13 8 5 7186 Quarternary volcanic rock. The mineralization can Q14 1 79 50 50 12 7 5 6111 be divided into six major vein groups with general Q21 15 545 45 55 60 24 6 1000 north-south Q4-Q5-Q6 (Q4-6 group) and northwest- Q22 17.4 518 40 60 60 25 6 1096 southeast Q1-Q2-Q3 (Q1-3 group) strikes. Two groups of major vein show variable internal structure Q23 7.2 617 20 111 61 21 6 2074 and texture as well as various gold and silver grade. Q24 7.7 554 15 95 50 22 5 1795 Based on crosscutting relationships and mineral Q31 24.6 618 40 55 65 22 6 954 paragenesis, the veins appear to have been formed Q32 20.6 493 35 45 55 23 7 1005 during two mineralization epochs. The earlier event is located in the northern part of River Cibaliung, fur- Q33 20.1 1164 30 131 96 38 9 1516 ther divided into three stages Q4-Q5-Q6, whereas the Q34 24.6 1056 33 123 85 40 8 1516 rest in southern part can be distinguished in the later Q41 3.1 172 19 52 11 7 6 2669 event Q-Q2-Q3). The wide veins consist of multiple Q42 3.4 160 70 55 12 7 7 2655 mineralization stages. Relatively higher Au (4.0-24.6 Q43 2.5 5 14 51 13 2 1 1168 ppm) and Ag-Cu-Pb-Zn contents are associated with the Q1-3 stage. The earlier mineralization stages are Q44 2.8 5 14 53 12 2 1 1294 represented by Q4-6 vein group and characterized by Q51 1 0 85 30 25 0 0 796 0.3-3.4 ppm Au and relatively lower base metal and Q52 1 0 85 25 25 0 0 850 silver content (Table 2). Vein group of Q1-3 shows Q53 0.3 0 61 50 45 1 1 1362 an association texture of lattice bladed, crustiform- Q54 0.4 0 80 50 40 1 0 1157 colloform banding, and ghost bladed in abundant milky white chalcedonic quartz with some intensively Q61 0.8 58 19 19 14 2 2 1313 manganese and oxide stainings (Figure 5). Lat- Q62 0.7 55 19 19 12 2 2 1139 tice bladed is a network intersecting blades of calcite Q63 0.8 73 29 88 10 11 10 14325 separated by polyhedral cavities which originate as Q64 2.7 71 10 25 15 22 4 10398 pseudomorph of lattice bladed calcite (Morrison et al.,

1990). This lattice texture indicates a boiling zone in the uppermost level of epithermal system (Dong et tice bladed (Figure 8). Cockade is a typical texture al., 1995). Adularia content on this Q3 vein (Figure showing concentric crustiform bands of quartz, sur- 5) is also supported for the boiling zone environment. rounding isolated fragments of host rocks or earlier Highest gold grade with relatively higher Ag-Cu-Pb- precipitated quartz or both (Shimizu et al., 1998; see Zn-As-Sb content (Table 1) is associated with vein Table 2). Rhodochrosite (Mn-carbonate) is often group of Q3 (20.1-24.6 ppm Au); this is characterized present in this Q2 group. The lowest grade of gold on by creamy white ghost bladed chalcedony with light group Q1-3 is Q1 vein, characterized by banded chal- grey manganese oxide and sulfide staining (Figure cedonic with abundant crystalline quartz and scarcely 5). This highest gold content is detected by EDAX manganese staining (Figure 9). Lowest gold contents analysis showing an electrum image with significantly of the whole vein samples are associated with group gold and silver peaks (Figure 6 and 7). Q2 vein shows Q4-6. This vein group is characterized by 0.3 to 3.4 a lower gold content (7.2-15.0 ppm), characterized ppm gold content, banded chalcedonic, cockade with by an associate texture of cockade and carbonate lat- saccharoidal core and crustiform-colloform bands 254 Jurnal Geologi Indonesia, Vol. 5 No. 4 Desember 2010: 247-261

Q3 1 P -31

vug

ka

0.3mm

sc Q32 P - 3 2

ch mn

ad

ch vug

qz li

1cm 0.3mm

Q33 P - 3 3 mn qz

mn

mn

1cm 0.3mm

Q3 1 . Lattice bladed, Q3 2. Crustiform banding of comb structure, Q3 3. Ghost bladed with segmental zone for

chemical and microprobe analyses; P3 13, P3 2 and P3 microphotographs series of petrography in cross polar- ized light of left side quartz veins. Note: ad=adularia, ca=calcite, ch=chalcedone, cqz=cryptocrystalline quartz, ka=kaolinite, li=limonite (or limonitic staining or coating), mn=manganese oxide, qz=quartz, rh=rhodochrosite

Figure 5. Series of macro- and micro photographs of vein group Q3. Selected geochemical and microprobe analyses of the lowest photograph are available in Table 1 and Figures 6 and 7. Alteration and Vein Textures Associated with Gold Mineralization at the Bunikasih Area, 255 Pangalengan, West Java (A.S. Subandrio and N.I. Basuki)

Untitled: 2 Edax image Q3 vein (B-zone) Label:

kV: 25.0 Tilt: 0.0 Take-off: 35.0 Det Type: STD Res: 144 Tc: 40 FS: 637 Lsec: 20 4-Jul-3 17:01:41 First chalcedonic groundmass

Profile & point of analyses in gold nugets

Second chalcedonic AgLa Ka groundmass

Silver peak AgLb SiKa AuLa PbLb SiKb AuLb AuLa Gold peak S K CuKb AsKb CuKa AsKa Ag= 32.35 Wt % Au= 56.28 Wt % 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 S = 5.52 Wt % B-zone As= 0.78 Wt %

EDAX ZAF Quantification (Standardless) Element Normalized

Element Wt % At % K-Ratio Z A F SiK 4.60 17.44 0.0268 1.2104 0.4797 1.0036 S K 5.52 18.32 0.0225 1.1996 0.3371 1.0066 AgL 32.35 31.91 0.1895 1.0203 0.5741 1.0000 CuK 0.49 0.83 0.0053 1.1009 0.9166 1.0649 AuL 56.26 30.40 0.5152 0.9099 1.0065 1.0000 AsK 0.78 1.11 0.0081 1.0707 0.9676 1.0000 PbL 0.00 0.00 0.0000 0.8908 1.0119 1.0000

Total 100.00 100.00

Figure 6. Energy Dispersive Analysis of X-ray (EDAX) image of electrum founded B-zone of vein Q3 (inset). The profile shows gold and silver peak significantly. Inset table displays relative percentage of the element.

Edax image Q3 vein (Zone B)

40um Argentite

First chalcedonic groundmass

Electrum gold

Second chalcedonic groundmass

Argentite

MINERAL PARAGENESIS nd 1st chalcedony+argentite 2 chalcedony+pyrite+electrum 3rd chalcedony+Mn-oxide

Figure 7. Detail microphotograph by EDAX imaging. The precious metals (Au & Ag) are associated with late chalcedonic veinlets (light gray in colour). 256 Jurnal Geologi Indonesia, Vol. 5 No. 4 Desember 2010: 247-261

1 vug Q2 P 21 qz

li

ch qz

0.3mm

Q22 P 22 li mn

qz

qz li

ka & rh

0.3mm

P 23 Q23 ka & cqz

ka

ch

ca

0.3mm

Q21. Cockade, Q22. Cockade with rhodochrosite vug infill, Q23.Carbonate lattice bladed; P21, P22 and P23 microphotographs series of petrography in cross polarized light of left side quartz veins. Note: ad=adularia, ca=calcite, ch=chalcedone, cqz=cryptocrystalline quartz, ka=kaolinite, li=limonite (orlimonitic staining or coating), mn=manganese oxide, qz=quartz, rh=rhodochrosite.

Figure 8. Series of macro- and micro photographs of vein group Q2. Selected geochemical analyses of vein are available in Table 1. Alteration and Vein Textures Associated with Gold Mineralization at the Bunikasih Area, 257 Pangalengan, West Java (A.S. Subandrio and N.I. Basuki)

Q1 P6 qz mn ad

qz

mn li

0.3mm

Q4 P4 li

vug

cqz

0.3mm

Q5 P5 cqz

vug

qz

li 0.3mm

Q1. Banded chalcedonic with manganese film Q4. Cockade with saccharoidal core , Q5. Crustiform- colloform bands; P1, P4 and P5 microphotographs series of petrography in cross polarized light of left side quartz veins. Note: ad=adularia, ca=calcite, ch=chalcedone, cqz=cryptocrystalline quartz, ka=kaolinite, li=limonite (or limonitic staining or coating), mn=manganese oxide, qz=quartz, rh=rhodochrosite

Figure 9. Series of macro- and micro photographs of quartz vein group Q1, Q4 and Q5. Selected geochemical analyses and microprobe profile and image of vein Q4 are available in Tabel 1 and Figure 6. 258 Jurnal Geologi Indonesia, Vol. 5 No. 4 Desember 2010: 247-261

(Figure 9 and 10). The relative higher gold grade textural superzone and the base metal interval over- in this Q4-6 group is Q4 (3.4 ppm Au) detected laps the crystalline chalcedonic zone, quartz, adular- by EDAX as a smaller electrum included in pyrite ia and sulfide ore (Figure 12). Geochemical analyses crystal (Figure 11). Significant different between of certain texture samples have demonstrated that group of Q1-3 and Q4-6 is the presence of lattice within individual deposits there is a consistent grade bladed texture and the colour as well as clarity of range for each texture assemblage. For example, chalcedonic veins. The colour of Q1-3 group that creamy white – light grey chalcedony with lattice has lattice bladed texture, shows milky white colour and ghost bladed texture on vein Q1-3 has highest with light grey fleck or staining, whereas veins of range of gold grade (> 1.0 to 24.6 ppm Au) and also group Q4-6 are dominated by crustiform texture shows by elevated of Ag-Pb-Zn-Cu-As-Sb. Light with abundant glassy transparence appearance grey colour on the chalcedony is presumably due of crystalline quartz (Figure 10). A summary for to relative higher content of base metal and manga- characteristics of quartz vein in the Bunikasih area nese oxide. In contrast, the vein assemblage of Q4-6 is provided in Table 3. displays more clear and transparent chalcedony

or crystalline quartz with combination between banded chalcedonic, crustiform and saccharoidal dIscussIon textures showing relatively lower range of gold grade (0.3 – 3.1 ppm). High grades Au of Q1-3 In the Buchanan model of gold distribution (Bu- is also characterized by the presence of adularia, chanan, 1981) there are specific intervals that host sulfide bands, and manganese oxide in association base and precious metal mineralization (Figure 12). with crustiform banding texture (Figure 3 on Q3 2 In the textural model, the precious metal interval and P-32 ). Relative higher Cu-Pb-Zn-Mn is a good essentially corresponds to the crustiform-colloform indicator for the presence of base metal in Q1-3.

Q6 P - 6 cqz

Vug & druse ch py

qz

0.3mm

Q6. Crustiform bands with vug and druse texture (lower right), P6 microphotographs series of petrography in cross polarized light of left side quartz veins.

Note: ad=adularia, ca=calcite, ch=chalcedone, cqz=cryptocrystalline quartz, ka=kaolinite, li=limonite (or limonitic staining or coating), mn=manganese oxide, qz=quartz, rh=rhodochrosite

Figure 10. Q6 is a representative of barren quartz vein and its petrography image. The colour of quartz is more clear and transparent than gold bearing milky quartz. Alteration and Vein Textures Associated with Gold Mineralization at the Bunikasih Area, 259 Pangalengan, West Java (A.S. Subandrio and N.I. Basuki)

Table 3. Characteristic Features of Quartz Veins in the Bunikasih Area

Earlier mineralization epoch (Q4-6) Characterized by development of barren comb texture quartz and few variations of quartz textures (comb-texture and microcrystalline quartz) Microcrystalline quartz partly associated with electrum in stage Q4 (Figure 7) Characterized by less developed crustiform bandings of comb- and fine-grained structure quartz compared to the later epoch Barren comb structure developed in stages Q5 (Figure 7) and Q6 (Figure 8) Fine-grained structure associated with manganocalcite (rhodochrosite) and johannsenite Cockade structure developed throughout stages Later mineralization epoch (Q1-3) Characterized by crustiform banding of comb-structure, fine-grained, platy, colloform, and cockade quartz Comb structure recognized throughout stages

Colloform structure commonly observed in quartz of crustiform banding in stage Q32 (Figure 5) and in quartz showing botryoidal surfaces at stage Q2 3 Cockade structure commonly developed in stages Q21 and Q22 (Figure 6) Characterized by various textures: comb, feathery, microcrystalline, fibrous, dendritic, colloform, ghost-sphere, flamboyant, and pseudoacicular (Figure 5)

Comb-texture quartz developed without ore minerals except stage Q32 and Q33 ; alternate precipitation of barren comb-texture

quartz and microcrystalline quartz; growth bands developed in comb-texture quartz of stage Q3 3and not in quartz from other stages

Microcrystalline quartz intimately associated with ore minerals and interstratified chlorite-smectite in stage Q32 (Figure 5) Feathery texture apparently found as patches or zones in comb-texture quartz throughout vein formation Fibrous texture with colloform structure quartz developed in stage Q5 and Q6 (Figure 7 and 8)

Colloform and flamboyant textures with fine-grained structure developed in stage Q32 (Figure 5) Dendritic quartz partly observed in comb-texture quartz (stage Q6) and microcrystalline quartz Q2 ) 3 Lattice bladed and ghost-sphere texture is partly observed in microcrystalline quartz in stages Q3 1 and Q3 .3

Untitled: 2 Label: Edax image Q4 (Zone H) kV: 25.0 Tilt: 0.0 Take-off: 35.0 Det Type: STD Res: 144 Tc: 40 FS: 547 Lsec: 20 24-Jul-3 11:34:34 AgLa First chalcedonic groundmass

Profile & point of analyses AgLb S Ka

Silver & peak

S Kb SiKb SiKa PbLa MnKb AsKa PbLb MnKa AuLa AuLb

2.00 4.00 6.00 8.00 10.00 12.00 14.00

EDAX ZAF Quantification (Standardless) Element Normalized Element Wt % At % K-Ratio Z A F SiK 2.47 7.27 0.0132 1.1711 0.4490 1.0115 Zone H S K 12.09 31.10 0.0888 1.1612 0.6184 1.0237 Ag= 69.04 Wt % AgL 69.04 52.81 0.5463 0.9710 0.8149 1.0001 CuK 0.57 0.86 0.0048 1.0464 0.7950 1.0031 Au= 3.71 Wt % AuL 3.71 1.55 0.0321 0.8583 1.0080 1.0000 S = 11.68 Wt % AsK 2.25 2.48 0.0221 1.0114 0.9689 1.0000 PbL 9.87 3.93 0.0837 0.8374 1.0133 1.0000 As= 2.25 Wt %

Total 100.00 100.00

EDAX ZAF Quantification (Standardless) Element Normalized Element Wt % At % K-Ratio Z A F SiK 3.01 8.66 0.0162 1.1676 0.4546 1.0124 S K 12.24 30.83 0.0951 1.1577 0.6539 1.0258 Ag= 71.49 Wt % AgL 71.49 53.52 0.5784 0.9672 0.8365 1.0001 Mnk 0.29 0.43 0.0024 1.0428 0.7946 1.0024 Au= 0.00 Wt % Fek 0.53 0.77 0.0048 1.0665 1.8355 1.0035 S = 12.24 Wt % Cuk 0.52 0.66 0.0050 1.0451 0.9168 1.0095 Aul 0.00 0.00 0.0000 0.8545 1.0071 1.0000 As= 0.71 Wt % Ask 0.71 0.77 0.0070 1.0070 0.9682 1.0000 Pbl 11.20 4.37 0.0946 0.8336 1.0126 1.0000

Total 100.00 100.00

Figure 11. EDAX image of electrum founded H-zone of vein Q4 (inset). The profile shows gold and silver peak significantly. Inset table displays relative percentage of the element. 260 Jurnal Geologi Indonesia, Vol. 5 No. 4 Desember 2010: 247-261

molds) )

crustiform) bladed ) adularia (+ agate (+ agate + crustiform) (+ lattice (+ lattice (+ needle (+ needle (+ + SULFIDE (+ + SULFIDE ., 1990). Based on the Based 1990). .,

et al et CARBONATE CARBONATE (+ agate (+ agate parallel + bladed + (+ lattice (+ lattice bladed moss + + CRYSTALLINE CRYSTALLINE CARBONATE CARBONATE ADULARIA CHALCEDONIC > adularia) adularia) -Colloform, and X=Crystalline, and X=Crystalline, -Colloform, disseminated sulfides) > MOSS > MOSS + QUARTZ + QUARTZ + QUARTZ

CHALCEDONIC CHALCEDONIC 84% NaCl. Alteration zones PR=propylitic;Alteration NaCl. 84% (op cit. Morrison cit. (op MASSIVE MASSIVE MOSS + CRYSTALLINE CARBONATE CARBONATE CRYSTALLINE BLADED + BLADED LATTICE + sulfide bands + moss TEXTURES CRYSTALLINE CRYSTALLINE + sulfide bands + CRYSTALLINE CRYSTALLINE CRYSTALLINE

CC CH

X

Fl) Calcite

(Clays)

F1) (Agate) Quartz Fluorite Pyrite

Pyrhotite Pyrite Arsenopyrite Quartz Calcite Pyrite (Bar, Calcite Zeolites Agate Stibnite Realgar (Cal, Chl, Chl, (Cal, Quartz Adularia Sericite Pyrite Empty Empty Zeolotes, Zeolotes,

Clay

in pyrite gold

Argentite Electrum

Galena Sphalerite Chalcopyrite Argentite Pyrargyrite Pyrargyrite Proustite Argentite Electrum Gold in Gold Ag-sulfosalts ORE GANGUE

Rare usually usually

pyrite METAL METAL

=Alunite, kaolinite, pyrite. CH=Chalcedonic, CC=Crustiform CH=Chalcedonic, pyrite. kaolinite, =Alunite, PRECIOUS INTERVAL

BASEMETAL BASEMETAL INTERVAL l for boiling under hydrostatic condition of a fluid containing 2. containing a fluid of condition hydrostatic under boiling for l and gangue mineralogy in a typical boiling zone epithermal vein epithermal zone boiling in a typical gangue mineralogy and

PR

AL RESIDUE

SI

SER ILL-CEL

AD

SI LEVEL PR

BOILING

TABLE

°C) 250

200 100 T( 150

WATER

0

400 500 300 200 100 (M) DEPTH SI=Silica; AD=Adularia; ILL=Illite; SER=Sericite; CEL=Celadonite, AL CEL=Celadonite, SER=Sericite; ILL=Illite; AD=Adularia; SI=Silica; model of Buchanan (1981) with temperature reflecting the leve reflecting temperature (1981) with of Buchanan model Figure 12. Scale model for zoning of textures, alteration, ore alteration, of Figure 12. model Scale textures, for zoning

Alteration and Vein Textures Associated with Gold Mineralization at the Bunikasih Area, 261 Pangalengan, West Java (A.S. Subandrio and N.I. Basuki)

conclusIons Acknowledgements---The authors thank Prof. Dr. Peter Halbach of Free University Berlin for the technical support and permission to work in the laboratory for EDAX and ICP Quartz morphology combined with petrog- analyses during our visiting study in Marine Geology in Ger- raphy and analyses of gold content by Energy many at 2003. The authors especially thank Julius Chandra, Dispersive Analyses of X-ray (EDAX) studies for the field work, report writing, and finishing thesis about suggest that boiling of the fluid occurred repeat- gold mineralization in Bunikasih area. The authors also edly, leading to silica-supersaturated conditions thank unit Geomin of PT. Aneka Tambang Tbk. for giving permission to visit the mining concession area in Bunikasih. with respect to quartz and resulting in the for- mation of the certain silica textures. Recrystal- lization of silica to quartz occurred throughout vein formation. The geochemistry data combined references with parageneses, quartz textures, and petrog- Adams, S.F., 1920. A microscopic study of vein quartz; raphy studies suggest the following model for Economic Geology, 15, p. 623-664 the Bunikasih gold-silver deposits. The veins Alzwar, M., Akbar, N., and Bachri, S., 1992. Geologi Lem- show two distinct mineralization epochs, an bar Garut dan Pameungpeuk, Jawa Barat (1208-6), earlier and a later one, which were responsible Skala 1 : 250.000. Pusat Penelitian dan Pengembangan for type 1 (vein group Q4-6) and 2 (vein group Geologi, Bandung. Buchanan, L.J., 1981. Precious metal deposits associated Q1-3) hydrothermal fluids, respectively. Both with volcanic environments in the Southwest Arizona types are dominantly meteoric in origin. Geological Society Digest, 14, p.237-262. The most prospected gold in Bunikasih district Chandra J., 2009. Geologi dan Prospeksi Emas Hidrotermal is associated with vein group Q1-3. It occurs in Daerah Bunikasih, Pangalengan Jawa Barat, Tugas Akhir the southwestern part characterized by the tex- Sarjana Strata-1 Prodi Teknik Geologi – FITB – ITB, ture assemblage such as milky white chalcedony unpublished. Dong, G., Morrison, G.W., and Jaireth, S., 1995. Quartz with often grey staining of manganese oxide and Textures in epithermal veins, Queensland – classifica- sulfide bands, lattice and ghost bladed, presence tion, origin, and implication. Economic Geology, v.90, of adularia, and a relatively higher range of gold p. 1841-1856 content between 1.0 to 24.6 ppm Au. Based on Fournier, R.O., 1985a. The behavior of silica in hydrothermal the systematic evaluation of the vertical and solution, Reviews in Economic Geology, 2, p. 45-61 horizontal distribution of textures associated with Morisson, G., Guoyi, D., and Jareith, S., 1990. Textural Zoning in Epithermal Quartz Vein, Amira Project P247, an epithermal system (Buchanan, 1981), the vein Gold Research Group, James Cook University of North group Q4-6 is associated with Crystalline Super- Queensland, p. 33 zone or X-zone (Figure 12) and is characterized Shimizu, T., Matsueda, H., Ishiyama, D., and Matsubaya, by common crustiform bands, dominantly clear O., 1998. Genesis of Epithermal Au-Ag Mineralization crystalline and saccharoidal quartz, and also a of the Koryu Mine, Hokkaido, Japan. Economic Geol- general decrease in the proportion of sulfides and ogy, 93, p. 303-325. Urashima, Y., 1956. “Bosa” quartz veins, especially the gold-silver content (see Table 1). The vein group fine-grained quartz aggregates, of the Konomai mine Q1-3 is presumably mineralized in a higher level in Hokkaido, Japan: Hokkaido University. Journal of than Q4-6, deposited between the Crustiform- Faculty of Science, 9, p. 371–387. Colloform Superzone (CC) and Chalcedonic Su- Warmada, I.W., 2003. Ore mineralogy and geochemistry of perzone (CH). These CC and CH zones dominated the Pongkor epithermal gold-silver deposit, Indonesia, by milky white chalcedonic quartz and associated Clausthal-Zellerfeld. Papierflieger. Widi, B.N., Sunarya, Y., Judawinata, K., and Setiawan, B., with carbonate or bladed pseudomorph after car- 1997. The Epithermal Gold-Silver-Tellurides Deposits bonate, e.g. lattice bladed of sample Q3 (Figure of Citambal-Cineam, Tasikmalaya, West Java, Indone- 5) indicate the uppermost level and boiling zone sia. Proceedings of Mineral Exploration Technology in the epithermal system (Morrison et al., 1990; in Indonesia, BPP-Technology, Jakarta, paper no. 10, Dong et al., 1995). p. 1-18.