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Geology, Vein Textures, and Fluid Inclusions of the Cibeber Low-Intermediate Sulfidation Epithermal Au-Ag Orefield, Western Java

This paper describes the results of surficial geological and alteration mapping combined with several laboratory analyses, including petrography, ore microscopy, ore geochemistry, and fluid inclusion studies, aimed at establishing the nature of mineralization and alteration in the Cibeber area, West Java, Indonesia, and developing a genetic model. The area forms part of the Bayah Dome Complex, which hosts several gold-silver deposits. It is underlain by andesitic lava, tuff breccia, and subordinate sandstone. Its structural framework consists of joints, normal faults, NE-SW dextral strike slip faults, and NW-SE strike-slip faults. Hydrothermal alteration can be divided into four types, viz. silicification, clay-silica, argillic, and propylitic. Mineralization is mostly hosted in quartz veins showing a variety of textures, including massive, colloform-crustiform, breccia, lattice bladed, comb, and saccharoidal. Ore minerals consist of native gold and silver, pyrite, chalcopyrite, sphalerite, galena, tennantite-tetrahedrite, covellite, malachite, hematite, and goethite, while the gangue minerals quartz, illite, epidote, and calcite. Four stages of mineralization/veining are recognized: early, middle (the main ore forming stage), late, and supergene. The highest obtained metal grades are 8.17 ppm Au, 113.6 ppm Ag, 1.23% Cu, 1.28% Pb, and 1.2% Zn. Fluid inclusions from mineralized veins yielded temperatures of 222 - 280°C and salinities of 0.36 - 1.31 wt.% NaCl eq. The hydrothermal fluids are interpreted to have been largely of meteoric origin with the mineralization having formed at a depth of about 258 - 270 m below paleosurface. Both low-sulphidation and intermediate-sulphidation styles of mineralization are present.


Introduction
The Java metallogenic belt in Indonesia is one of the most prospective gold-silver belts in SE Asia (Prihatmoko and Idrus, 2020). The Bayah Dome Complex in western Java, in particular, hosts a number of important epithermal Au-Ag deposits, such as Gunung Pongkor, Cibaliung, and Cikotok ( Figure 1) (Leeuwen, 1994;Sunarya, 1997;Angeles et al., 2002;Warmada, 2003;Harijoko et al., 2007;Rosana, 2009). Cibeber, located about 9.5 km from the Cikotok deposit (Lebak Regency, Banten Province, Indonesia), is a newly discovered ore field in the belt. The exploration has been started since 1990's by PT Aneka Tambang and Atapa Minerals Ltd., focusing on the southern part of this area. Currently, the underground mining activities and smelting process are carried out by the management of PT Multi Utama Kreasindo Mining since 2008. New wide gold bearing veins were also discovered recently in 2011 in northern part of the area. Previous studies mainly described the different mineralization styles in the dome complex and grouped them into five types, namely the Pongkor, Cirotan, Cikotok-Cikidang, Cisungsang, and Cibaliung type (Marcoux and Milesi, 1994;Widi, 2007;Rosana, 2009). However, there is no mineralogical or fluid inclusion data were reported from this studied area. In this study, an integrated study on the structural geology, hydrothermal alteration, ore mineralogy, and fluid inclusions associated with the mineralization at Cibeber is presented, and its genetic model and exploration implications are discussed.

Materials and Research Methods
Detailed geological and alteration mapping were conducted at and around the Cibeber deposits (across a 12 km 2 area) aimed at observing relevant geological features and delineating lithological and alteration boundaries. Altered rock and epithermal vein samples were collected from outcrops and mining tunnels. Fifteen wallrock and three vein samples were prepared for petrographic thin sections, and twenty-three vein samples for polished thick sections. Ore macro-/ micro-petrographic observations were carried out in the Laboratory of Optical Geology at the Department of Geological Engineering, Gadjah Mada University, with a Euromex trinocular polarizing microscope. Petrographic identification was based on standard mineral properties of rock forming minerals described by Barker (2014) and ore mineral optical properties by Marshall et al. (2004). Six altered rocks were X-Ray Diffractometry (XRD) analyzed at the Central Laboratory of the Department of Geological Engineering (Gadjah Mada University), using a Rigaku Multiflex 2KW Diffractometer. Three different treatments were performed namely bulk rock, air-dried, and ethylene glycollated. Peak identification was carried out manually based on the table of key line standards of Chen (1977). Thirty-three ore vein and twenty-two host-rock samples were analyzed by Fire Assay-Atomic Absorption Spectroscopy (AAS) at the laboratory of PT Multi Utama Kreasindo Mining. Gold-silver contents were analyzed with the wet method using aqua regia digestion (HCl:HNO 3 = 3:1). Base metals were analyzed and dissolved in a mixture of perchlorate acid, nitric acid, and hydrochloric acid. The detection limits of Au, Ag, Cu, Pb, and Zn are 0.02, 0.50, 2.00, 4.00, and 2.00 ppm, respectively. Representative polished thin sections were analyzed with Scanning Electron Microscope -Energy Dispersive X-Ray Spectroscopy (SEM-EDS) for the mineral contents, using a JEOL JSM.6360 Figure 1. Location map of the Java metallogenic belt, showing the distribution of major ore fields associated with pre-Quaternary volcanism. Note that the western Java is mostly dominated by epithermal-type deposits, whilst the eastern Java is dominated by porphyry-type deposits (modified after Harahap et al. 2013 Potter (1977).

Geological Setting
The Cibeber deposits/ore field, and other deposits in the Bayah Dome Complex are part of a calc-alkaline magmatic arc, which started to develop probably in the Paleogene in an active continental margin setting (Bemmelen, 1949;Whitford, 1975). The Bayah Dome Complex is a volcanic centre, which comprises the Cikotok Formation, Jampang Volcanics, and the Cihara Granodiorite ( Figure 2  Figure 2. Regional stratigraphic column of the Bayah Dome Complex and its various intrusive phases where Cikotok Formation is the main ore host in the area (modified after Sujatmiko and Santosa, 1992). hosted in volcanic breccia/tuff and andesitic lava of the Upper Eocene-Upper Oligocene Cikotok Fm. (Sujatmiko and Santosa, 1992). At Cibeber, these rock types are mostly altered and intruded by mineralized and barren quartz veins. Geochemical analyses show that the Cikotok Formation formed in an island-arc setting (Hutabarat, 2016). The Upper Eocene Cicarucup Formation is composed of conglomerate, quartz arenite, claystone, tuff, and limestone. Pulungguno and Martodjojo (1994) reported three structural patterns on Java Island, i.e., Late Cretaceous NE-trending structures (termed the Meratus Pattern), Early Eocene-Late Oligocene N-S-trending structures (termed the Sunda Pattern), and Mio-Pliocene E−W-trending structures (termed the Java Pattern). At Cibeber, only the Java Pattern (represented by E−W trend-ing thrust faults and folds) and the Sunda Pattern (represented by N−S trending strike-slip faults) were observed.

Geology of The Cibeber Deposits
The following geological description of the Cibeber deposits is mainly from Dana et al. (2018a and2018b) with some additional data. The Cibeber deposits are hosted in three rock units from three different major rock formations, which are from old to young: (1) Cicarucup Fm. sandstonemudstone, (2) Cikotok Fm. tuffaceous breccia, and (3) Cikotok Fm. andesitic lava (Figure 3). Andesitic lava is also locally found intercalated in the tuffaceous breccia. Formations (2) and (3) have typical subaerial volcanic features and can be classified as proximal volcanic facies. The ore veins are  (Dana et al., 2018a and2018b).
hosted by the intensely-altered tuffaceous breccia and andesitic lava, in which most of the primary minerals were replaced by secondary quartz, illite, chlorite, and epidote. Remnants or pseudomorphs of clinopyroxene and plagioclase phenocrysts are locally recognizable in the andesitic lava. Major structures at Cibeber are dominated by NNE-SSW strike-slip faults as well as some extensional and shear joints. The extensional and shear joints are NE-trending. The faults can be divided into pre-ore, syn-ore, and post-ore. The pre-ore NEtrending normal faults are possibly related to caldera formation in the Bayah Dome Complex. The syn-ore NNE-trending dextral strike-slip faults have formed other dilational structures in the area, which is quite common structural features found in epithermal system (e.g. Corbett and Leach, 1996;Garwin et al., 2013;Corbett, 2013), whilst the post-ore NW-trending dextral strike-slip faults cut the syn-ore structures. Cooling/decompression structures such as sheeting and columnar joints were also observed in the andesitic lava unit.
Propylitic alteration occurs dominantly in the periphery of the deposits, mainly associated with the andesitic lava unit ( Figure 3). Pyrite is common occurring as disseminations or in fine stockworks, whilst magnetite is patchy. Epidote and chlorite mostly replace clinopyroxene and plagioclase, but epidote can also be found as veinlets in some outcrops. The original igneous intergranular and trachytic texture is still partially preserved (Figure 4). Argillic alteration is well-developed in Figure 4. Photomicrographs of the different alteration styles at Cibeber. (a-b) Epidote veinlet in selectively-altered andesitic lava with primary quartz and plagioclase; (c-d). Quartz-clay replacement in tuffaceous breccia with comb-textured quartz veinlet; (e-f). Clasts are mostly replaced by clay and groundmass by microcrystalline quartz. Disseminated pyrite are common; Epidote-chlorite alteration, with quartz veinlet in andesitic lava and relict texture; (g-h). Sericite replaced both feldspar phenocrysts and groundmass; Quartz-epidote vein with disseminated sulfide (dominantly galena and sphalerite) mineralization; (i-j). Epidote almost entirely replaced clinopyroxene phenocrysts in the andesitic lava; (k-l). Some plagioclase laths also remain in the selectively chlorite-sericite-altered groundmass; Intense oxidation indicated by hematite-rich tuffaceous breccia, whose clasts are mostly replaced by quartz. tuffaceous breccia, and locally in a highly-fractured andesitic lava. This alteration style is characterized by pervasive clay and quartz replacement, except in the Cicarucup sandstone and claystone, due to their higher quartz content and lower permeability. XRD analysis indicates that some primary minerals (e.g. plagioclase and K-feldspar) still remain in the altered rocks (Dana et al., 2018a; Figure 5).
Silicic alteration is characterized by pervasive silica replacement, which comprises mostly quartz and minor cristobalite and chalcedony, as indicated by XRD analysis. This alteration zone occurs mostly as halos along the quartz veins, except at Cirahong and Curug Engang where the alteration is pervasive. Many silicic-altered rocks were also later oxidized, as indicated by the reddish hematite stain.

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Hydrothermal Vein System and Ore and Gangue Mineralogy Hydrothermal veins were found across the studied area. Mineralized veins are commonly thicker than ore-barren veins, occurring in the form of massive veins, stockworks, and hydrothermal breccias (Dana et al., 2018a; Figure 6). The following is a description of the features of hydrothermal veining in the three major prospects at Cibeber (i.e. Lebak Dadap, Cilulumpang, and Pasir Ela).

Lebak Dadap Prospect
This area is characterized by hydrothermal breccia stockwork, comprising three main vein systems (i.e. Lebak Dadap, Lamping, and Pasir Suung). The veins are mostly mineralized composed of pyrite-oxide-rich with minor base metal sulfides; some ore-bearing and barren veins have comb textures. The Lebak Dadap veins are N-Strending and ~1.5 m thick, the Lamping veins are NE-trending and ~1 m thick, whilst the Pasir Suung veins are NW-trending and also ~1 m thick. The Pasir Suung veins have lattice bladed textures, with quartz, calcite, and chlorite as the dominant gangue minerals.

Cilulumpang Prospect
The area comprises the Cilulumpang Vein Complex and the Gunung Keris vein system. These veins are generally 1 m thick and variably textured. The Cilulumpang Vein Complex has a massive and saccharoidal texture and a NNW-strike. Lattice bladed texture can also be seen. Microcrystalline quartz and illite-sericite are the most common gangue minerals. The Gunung Keris veins are characterized by their lattice bladed texture, relatively low ore mineral contents, and with quartz and chalcedony as the dominant gangue minerals. The veins are commonly 1.5 m wide and NE-trending.

Pasir Ela Prospect
The area has three main vein systems, i.e. Cidikit, Curug Engang, and Pasir Ela. The Cidikit veins contain mainly massive quartz and base metal sulfides (mostly galena and sphalerite), and epidote. The veins are commonly 1 m wide and ENE-trending. The Curug Engang veins are thinner (0.25 m wide), NE-trending, and have a colloform texture. These veins have pyrite and base metal sulfides with quartz-calcite gangue. The Pasir Ela vein system includes both miner- alized and barren veins. The formers are mostly colloform-crustiform, containing mainly galena, sphalerite, and chalcopyrite. Supergene enrichment also occurs, as indicated by the presence of by covellite and malachite. The veins are 0.6 to 1.2 m thick and are NE-or NW-trending. Breccia veins are also locally found. Ore-bearing and barren veins (0.2 to 0.7m thick) comprise mostly quartz-chalcedony ± amethyst, and are dominantly comb (minor crustiform)-textured.
The barren veins have various directions and represent a late-stage post-ore phase.

Ore Mineralogy and Geochemistry
Ore minerals in the studied area include hypogene and supergene ones. Representative sulfides (pyrite, sphalerite, chalcopyrite, and galena) were analyzed for their chemical compositions. Alteration/mineralization paragenesis was mostly determined based on the mineral assemblages and vein crosscutting relationships. Mineralization mostly occurs in hydrothermal veins and to a minor extent in altered wall-rocks. Three major groups of ore minerals include Au-Ag-bearing sulfides, base metal sulfides, and supergene metallic minerals. Ore microscopic images of the various minerals are shown in Figure 7.

Base Metal Sulfides
Pyrite is the most abundant sulfide mineral at Cibeber. It is euhedral cubic (1−5 mm), and has an average content of 43.95 wt.% sulfur (S) and 55.17 wt.% Fe, together with 0.17 wt.% Cd, 0.13 wt.% Ag, and minor Co, Ni and Cu (0.1 wt.% each). Manganese was detected in only one sample (0.28 wt.%). Chalcopyrite is mostly found in the Pasir Ela, Curug Engang, Cidikit, and Citajin vein systems, and is associated with other base metal sulfides. It can be distinguished from pyrite by its lower reflectance. The chalcopyrite on average 26.86 wt.% S, 34.62 wt.% Fe, and 38.52 wt.% Cu. Galena (size: 1 -5 mm) Figure 7. Ore microscopic images: (a, c). Covellite and digenite are found replacing the Cu-bearing minerals such as chalcopyrite; (b). Pyrite is the most common sulfide found either disseminated or aggregates; (d, f). Another minor ore mineral such as tennantite-tetrahedrite and greenockite also can be found; (e). Sphalerite is typically characterized by the presence of chalcopyrite disease (cf. Craig and Vaughan 1994); (g). Galena can be easily distinguished by the presence of triangular pits (cf. Marshall et al. 2004); (h). Covellite also can be found replacing the sphalerite as the consequence of chalcopyrite disease occurrences; (i, j). Gold and Ag-sulfide can be identified as free grain; (k). Gold also can be found as inclusion within pyrite; and (l). pyrite is oxidized to be hematite and goethite. Abbreviations: Py: pyrite; Cv: covellite; Dg: digenite; Ccp: chalcopyrite; Gn: galena; Sp: sphalerite; Grn: greenockite; Tnt: tennantite; Gth: goethite; Hem: hematite; Au: gold. Sulfidation Epithermal Au-Ag Orefield, Western Java (C.D.P. Dana et al.) is mostly disseminated in quartz veins, which is easily distinguished under the microscope by its triangular pits.

Gold-/Silver-bearing Sulfides
Precious metal minerals from Cibeber are in general very fine-grained (identifiable only under the microscope), although some visible free gold grains (size: 0.5−1 mm) were observed at Lebak Dadap. Gold can be found both as free grains and inclusions in pyrite. Silver sulfides, possibly acanthite (size: 10−40 µm), occur as disseminations in quartz veins, have only been identified in the Pasir Ela vein. No chemical analysis has been conducted of these minerals.

Supergene Minerals
The most common supergene minerals are hematite and goethite, probably formed from hypogene pyrite and magnetite. Intense oxidation is found mostly at Pasir Suung, where hypogene pyrite is abundant. Malachite and covellite are the most common Cu-bearing supergene minerals at Cibeber. Malachite is generally found in the supergene zone, along with other carbonate and sulfate minerals such as chrysocolla and chalcanthite. Chalcocite and covellite are the major secondary Cu sulfides in the supergene zone. Malachite can be readily identified both in outcrop and in float samples, especially in the Pasir Ela prospect. Meanwhile, covellite is identified by its characteristic blue colour and brownish-red anisotropy. Optical microscopic analysis indicates that covellite replaces chalcopyrite and sphalerite, and locally replaces pyrite.

Bulk-ore Metal Grades
Ore assay data were obtained from thirty-three vein and twenty-two altered wall-rock samples. Gold grades of the vein samples range from <0.02 to 8.17 ppm (average 0.8 ppm), with the highest grade found in the Curung Engang vein. The highest gold grade (0.45 ppm) in wall-rocks is found in the propylitic-altered andesitic lava. Silver grades range from 0.6 to 113.6 ppm (average 26 ppm) in the vein samples, and from 0.5 to 5.1 ppm in the wall-rock samples. The highest Ag grades occur in a colloform vein from the Pasir Ela prospect, and in a silicified andesitic lava sample in the Curug Engang. However, some samples, both vein and wall rock, have silver grades below the detection limit. Copper grades in the vein samples range from 9 ppm to 1.23%, and in the the wall rock samples from 8 to 110 ppm. Lead grades in the vein and wall rock samples range from 34 to 1,280 ppm, and from 21 to 1,460 ppm, respectively. The vein samples contain 8 to 1,200 ppm Zn, while that of and the wall rock samples 13 to 1,570 ppm. Base metal grade analyses were only carried out on samples with > 0.15 ppm gold grade. The highest base metal grades were found in colloform veins in the Pasir Ela prospect and in propylitic-altered andesitic lava around the Cidikit vein.

Fluid Inclusion Study
Fluid inclusions (FIs) from five quartz vein samples with different textures (massive, colloform, breccia, lattice bladed, and comb) were analyzed to characterize the ore-forming fluids. Most of the vein samples are mineralized, except for the lattice bladed-and comb-textured ones. Massive and colloform veins have much higher base metal sulfide contents than the breccia veins. Primary, secondary and pseudo-secondary FIs are all three found in all samples. Types of primary FIs include L-type (single-phase), LV-type (twophase), and VL-type (two-phase) (Goldstein, 2003;Pirajno, 2010;Pohl, 2011

Petrography and Fluid Inclusion Types
The comb vein sample (CV-01CJ) was taken from the Citajin area. Primary FIs (size: 3-15 µm) have various forms, including ellipsoid, rectangular, bipyramidal, and irregular. Necking is commonly observed in this vein. All three primary Fl types are present. Secondary FIs are dominated by ellipsoidal LV-type, while pseudo-secondary FIs are dominantly bipyramidal and small.
The lattice bladed vein sample (CV-19GK) was taken from Gunung Keris area, characterized by very low metal content (0.1 ppm Au, <0.5 ppm Ag, 20 ppm Cu, 243 ppm Pb, 580 ppm Zn). Both primary and secondary FIs were observed in this sample. Most FIs are very small (2-10 µm) and irregularly-shaped. The FIs are dominantly LVtype. Meanwhile, L-type FIs were also observed in minor amounts and smaller than LV-type.
The breccia vein sample (CV-12LD) was taken from the Lebak Dadap area. This vein is pyrite rich and has relatively high metal contents (0.85 ppm Au, 5.6 ppm Ag, 450 ppm Cu, 84 ppm Pb, 335 ppm Zn). Pseudo-secondary FIs are difficult to distinguish from secondary FIs due to indistinct crystal growth lines in the quartz crystals. Primary FIs are smaller than secondary ones, and are dominated by ellipsoidal and irregular shapes. Both L-type and LV-type FIs were observed either as primary or secondary FIs.
The colloform vein sample (CV-02PE) was taken from the Pasir Ela area, that is characterized by high Ag and base metal contents (0.64 ppm Au, 113.6 ppm Ag, 12,300 ppm Cu, 410 ppm Pb, 10,200 ppm Zn). Petrographic analysis on five quartz bands reveals various forms of FIs (size: 3-30 µm), including ellipsoid, irregular, rectangular, and (bi)pyramidal. LV-type FIs are the most common FI type in the sample, and minor L-type FIs are also found.
The massive vein sample (CV-14PE), which was taken from the Pasir Ela area, is characterized by high metal contents (1.23 ppm Au, 46.9 ppm Ag, 12,100 ppm Cu, 700 ppm Pb, 3,700 ppm Zn). Fluid inclusions in the sample are typically small (3-5 µm), and are dominantly ellipsoidal and rectangular. Necking can be well observed in this sample and both L-and LV-type FIs were found.

Fluid Inclusion Microthermometry
This analysis was conducted to determine the temperatures of melting (Tm), homogenization (Th) and salinity. The Tm and Th for the comb-vein FIs are -0.3 to -0.1°C and 245-205°C, respectively. Salinity ranges from 0.18 to 0.53 wt.% NaCl eq. The Tm, Th and salinity for the lattice bladed-vein FIs are -0.2°C, 230-237°C and 0.36 wt.% NaCl eq., respectively. The Tm, Th,` and salinity for the breccia-vein FIs are -0.6 to -0.3°C, 238-263°C, and 0.53-1.07 wt.% NaCl eq. (higher than the previous two samples), respectively. The colloform-vein FIs also have higher Th (231-293°C), whilst its Tm and salinity are -1.2 to -0.1°C and 0.18-2.13 wt.% NaCl eq., respectively. The highest FI salinity (1.07-1.60 wt.% NaCl eq.) is found in the massive vein sample, with its Th and Tm being 274-286°C and -0.9 to -0.6°C, respectively. Microthermometric data and some important petrographic images of fluid inclusions hosted by Cibeber quartz veins are shown in Figure 8.

Alteration/mineralization Paragenetic Sequences
Based on hydrothermal mineral assemblages and field/microscopic crosscutting relationships, the paragenetic sequences of alteration/mineralization can be divided into four major stages (modified from Dana et al., 2018a) namely (I) early-ore, (II) medium-ore, (III) late-ore, and (IV) supergene (Figure 9). Stage I is characterized by the formation of massive veins with abundant base metal sulfides (e.g. galena, sphalerite, and chalcopyrite), together with minor gold and silver sulfides. Gold inclusions in pyrite indicate that gold is formed before pyrite, whilst some samples show that silver sulfides replaced pyrite.
Stage II is characterized by the formation of colloform-crustiform and breccia veins; this is the main Au-Ag mineralization stage. Base metal sulfides are also common but less abundant than in Stage II. Ore textures indicate that Stage II pyrite I J O G Geology, Vein Textures, and Fluid Inclusions of the Cibeber Low-Intermediate Sulfidation Epithermal Au-Ag Orefield, Western Java (C.D.P. Dana et al.) 167 mostly replaces Stage I base metal sulfides. Stage II chalcopyrite and galena are formed before sphalerite, as indicated by replacement texture. The presence of chalcopyrite disease texture indicates that some chalcopyrite coprecipitated with the sphalerite (e.g. Schwartz, 1951;Craig and Vaughan, 1994;Inesom, 1989). Stage III is characterized by the formation of comb-/bladed-/saccharoidal-textured barren veins, which are typically found in the uppermost part of epithermal mineral systems (e.g. Wilson and Tunningley, 2013). Mineralization is insignificant, except for some pyrite, rare gold, and silver sulfides.
Stage IV is characterized by the replacement of hypogene minerals by supergene minerals, such as covellite, malachite, hematite, and goethite.
In terms of alteration zoning, the silicic zone was formed before the argillic and propylitic zones. Hydrothermal quartz was deposited throughout the various alteration stages, whilst cristobalite was formed only in Stage I to II. Clay minerals (mostly illite) were formed in Stage II and propylitic minerals such as chlorite, epidote, and calcite in Stage III.

Sulfidation State and Deposit Type
Epithermal deposits have been divided into low-/intermediate-/high-sulfidation (LS, IS, HS) types (e.g. Hedenquist et al., 2000;Einaudi et al., 2003;Sillitoe and Hedenquist, 2003;Simmons et  al., 2005; Hedenquist and Arribas, 2017). Binary plots between homogenization temperature and salinity within Wilkinson (2001) deposit type classification indicate that the mineralization in the researched area can be categorized as an epithermal, because of its low temperature and salinity. Our FI homogenization temperature and salinity data indicate that the epithermal mineralization is of high-to low-S type (cf. Bodnar et al., 2014). Binary plot of Au vs. Ag grade indicates that the samples from Cibeber can be divided into two groups. High Ag:Au samples come mostly from the southern Cibeber (at/around Pasir Ela), whereas the northern Cibeber (at/around Lebak Dadap) is characterized by low Ag:Au samples ( Figure 10). IS epithermal deposits commonly have higher Ag:Au ratios than their LS counterparts (Einaudi et al., 2003;Gemmell, 2004).
Thus, the mineralization is proposed to change from IS in southern Cibeber to LS in northern Cibeber. An IS state of mineralization in southern Cibeber (Figure 11) is further supported by the absence of arsenopyrite and abundance of base-metal sulfides (Giggenbach, 1997;Einaudi et al., 2003).
Sphalerite from Cibeber can be divided into low-Fe (<10 mol% FeS) and high-Fe (>10 mol% FeS) type. IS deposits typically have low-Fe sphalerite while LS deposits have high-Fe one (Einaudi et al., 2003). The low-Fe and high-Fe sphalerite from Cibeber have 3.07-3.89 and 11.03-11.82 mol% FeS, respectively, and thus both low-and intermediate-S epithermal systems are present in the studied area. The low-S epithermal system is typically found in northern Cibeber as indicated by lack occurrence of base  Figure 11. Estimated sulfidation state of the Cibeber epithermal deposits based on formation temperature and Fe content in sphalerite (diagram after Einaudi et al., 2003).
metal-bearing minerals, whereas the intermediate-S epithermal system is in southern Cibeber as indicated by the abundance of base metal-bearing minerals. The Fe content of sphalerite from northern Cibeber is also typically lower than those which come from southern Cibeber.

Fluid Source And Evolution
Hydrothermal fluid changes can be estimated by the fluid inclusion homogenization temperature vs. salinity plot (Figure 12; Shepherd et al., 1985), which indicate two major hydrothermal evolution processes in the studied area: (1) simple cooling  (2) isothermal mixing with fluid which has highly contrast salinity (3) boiling with slower cooling process (4) simple cooling (5) inclusion leaking during heating process (6) necking down. (b) Correlation plot of homogenization temperature and paleo-depth of vein formation (after Haas 1971). It shows that the massive-and colloform veins were formed at deeper level than the breccia-, lattice bladed and comb veins.  caused by the interaction between hydrothermal fluid with the cooler wall rock, and (2) mixing with a cooler and less saline fluid, e.g. meteoric water.
Fluid inclusions from the massive-/colloform-/ breccia veins indicate higher fluid temperatures and salinity than those from the comb-/lattice bladed veins. This suggests that the latter may have formed via fluid mixing. In Figure 12, it is also shown that there may have been two fluid sources. The first source may have been meteoric water (as indicated by its low salinity), which was heated by a deep-seated intrusion. The fluid may have only undergone simple cooling during its evolution. However, an indication of a boiling process can also be identified in colloform and breccia veins (e.g. Guoyi et al., 1995). This fluid was likely the ore-forming fluid. The second fluid was likely resulted from mixing of the first fluid with the circulating meteoric water and may have formed the Stage III barren veins.

Genetic Model
Integrating field deposit geology, mineralogy, geochemistry, and hydrothermal fluid features, the following genetic model was proposed for the Cibeber deposits ( Figure 13). The Cibeber epithermal deposits are hosted in a Paleogene volcanic centre. A previous study mentioned that the abundance of mineral deposit in this area is mostly controlled by advanced magma evolution that increases the alkali content of the magmatichydrothermal system (Setijadji et al., 2006). The mineralization is interpreted to have occurred during the Mio-Pliocene period based on K-Ar dating from surrounding areas (McInnes et al., 2004;Yuningsih et al., 2014). Syn-ore structures are likely the result of subduction activity in southern Java as indicated by the lineament pattern, while the pre-ore structures are associated with caldera formation in the Bayah Dome Volcanic Complex as suggested by the presence of a regional circular (caldera-like) structure.
Limited input from magmatic fluids suggests a distal heat source, possibly outside the studied area. The pressure vs. mineralization depth plot (Haas, 1971) (Figure 12) indicates that the mineralization depth was around 258 -700 m below the paleosurface when the pressure was about 28 -55.1 bar. The positive silver vs. base metal grade correlation indicates that these metals are cogenetic. Positive gold vs. silver grade correlation indicates that the two metals occur possibly as electrum rather than as native metals. Higher gold grades are typically found in colloform and   Figure 14. Evolution of vein texture and mineral assemblages, ore grade and fluid temperature and salinity from the early-to late-stage epithermal mineralization at Cibeber. Relation between vein texture and ore grade is also shown. breccia veins, whilst breccia veins are commonly silver-rich ( Figure 14). Higher base metal contents are typically found within massive veins. Other vein textures (e.g., lattice bladed, comb, and saccharoidal) typically have lower ore grades. These features suggest that the gold-rich veins were formed at a deeper level than the silver-rich ones, whereas the low-grade and ore-barren veins were formed at the shallowest level. Since fluid inclusion data can reveal fluid trapping conditions (Bodnar, 2003), Au-Ag mineralization likely occurred at 245-275°C (coeval with colloform-/ breccia-veining). Based on published hydrothermal mineral stabilization temperatures (Henley et al., 1984;Reyes and Giggenbach, 1992;White and Hedenquist, 1995;Zhu et al., 2011), Stage III ore mineralization temperatures are estimated to be 225-265°C, while supergene mineralization occurred at 140-200°C.

Conclusions
The Cibeber epithermal deposits are hosted by the Cikotok Formation in the Bayah Dome complex, structurally controlled by NE-trending faults. Low-and intermediate-sulfidation mineralization styles are found in the northern-and southern Cibeber, respectively. Hypogene hydrothermal processes can be divided into early Au-Ag-dominated mineralization, middle base metal-dominated mineralization, and late orebarren hydrothermal veining stages. Fluid inclusion evidence suggests that the ore-forming fluids have had relatively low temperature and salinity sourced mainly from meteoric water, with their circulation being driven by a concealed heat source, possibly a deep-seated pluton outside Cibeber. The vein texture-ore grade-hydrothermal fluid correlation established in the current study will be a useful guide for further exploration in this area and surroundings. However, detailed mineral chemistry and whole rock geochemistry of the host rock need to be carried out to determine the geochemical signature of the deposits.