ORE GENESIS AND MINOR ELEMENTS OF OROGENIC GOLD DEPOSIT AT TAMILOUW– HAYA, SERAM ISLAND, INDONESIA

The orogenic gold deposit of Tamilouw – Haya is hosted by slate and metapelitic rocks within Tehoru metamorphic complex. Gold and polymetallic sulfides mineralization at study area is predominantly formed in the form of veins, stockwork and breccia although minor dissemination is slightly appeared in the rock float samples. They are trapped and controlled by NE-SW and NNE-SSW trending geologic structure occurred during orogeny process from Late Miocene to Pliocene. The common ore minerals assemblage at Tamilouw – Haya deposit are dominated by native gold, chalcopyrite, pyrite, sphalerite, galena, pyrrhotite, tetrahedrite-tennantite (sulphosalt), marcasite,realgar, kalininite and arsenopyrite as hypogene minerals and accompanied by covellite, hematite, goethite and malachite as the supergene minerals. Ore genesis and minor elements study of pyrite, galena, and sphalerite at Tamilouw – Haya was done using 3 methods approach. There were 46 samples used for ore microscopy analysis and 10 samples for SEM-EDX and Micro-XRF analyses to obtain their mutual relationship interpretation and paragenetic sequence. Ore mineral textures showed disseminated

Ore genesis and minor elements study of pyrite, galena, and sphalerite at Tamilouw -Haya was done using 3 methods approach. There were 46 samples used for ore microscopy analysis and 10 samples for SEM-EDX and Micro-XRF analyses to obtain their mutual relationship interpretation and paragenetic sequence. Ore mineral textures showed disseminated textures, simultaneous crystallization (intergrowth), inclusions, replacements, and exsolutionsdecomposition textures.
Average content of Co is 0.21 wt. % and Ni is 0.10 wt. % which may reflect the Co : Ni ratio is 2.86 in pyrite. It means that Co content is higher than Ni and indicates that pyrite origin may be related to volcano-hydrothermal, metamorphosed and skarn-hydrothermal type. In comparison with pyrite, the average contents of minor elements in sphalerite shows Fe content is 9.16 wt.%, Ga is 0.99 wt.%, Ge is 0.12 wt.% and log Ga/Ge ranging from < 0.36 to 2.27 wt.%. Moreover, average precious metal contents within galena shows that Au contents INTRODUCTION Bierlein et al. (2001) revealed that Orogenic gold deposits are related to collision settings and active orogenic belts. These deposit are formed during compressional to transpressional regimes at convergent plate margins both accretionary and collisional orogens (Groves et al., 1998;Goldfarb et al., 2001Goldfarb et al., , 2015. They are epigenetic, structurally controlled and based on their depth of formation; they are divided into epizonal, mesozonal, and hypozonal (Groves et al., 1998;Goldfarb et al., 2005).
In Indonesia, many researchers had investigated the occurrence of gold mineralization within metasediments to metamorphic rocks formation. Some large and medium scale of gold deposits such as Awak mas mesothermal (Querubin and Walters, 2011), Poboya LS -Epithermal (Wajdi et al., 2011), Bombana orogenic gold deposits (Idrus and Prihatmoko, 2011), Buru orogenic Gold deposits (Idrus et al., 2014), Mendoke -Rumbia orogenic gold (Hasria, 2018) and many gold mineralizing occurrences were successively discovered in indonesia. Except for the Tamilouw -Haya gold deposits, which are located in the southern part of Tehoru Metamorphic complex, there were no major orogenic gold deposits that have been recognised in Seram Island yet. Nevertheless, several gold occurrences have recently been identified in the western part of Seram and a previous study of metamorphic rockhosted gold mineralization was proposed for prospecting only with no classification of ore genesis deposit type and their genetic model (Franklin et al., 2013). Seram Island is located along the northern part of outer Banda arc, eastern Indonesia. It is previously located in the collision zone between Australian Continent and Banda Subduction Zone, where the Northwest Australian margin moved towards Banda Subduction Zone. The Northwest shelf of Australia itself was generated due to the break-up of Gondwana during Jurassic (Powell, 1976;Veevers, 1982).
Stratigraphically, Seram can be divided into two parts; Australian series and Seram series (Map 1A). A northern belt, covering the north part of the island in the west and all of it in the east, consists of imbricates sedimentary rocks of Triassic to Miocene age (Australian series) whose fossils and facies resemble those of the Misool and New Guinea continental shelf (Hamilton, 1979). These sedimentary formations, i.e., Kanikeh Formation, Saman-Saman limestone, Manusela Formation, Lisabata Formation and Salas block clay; others sedimentary rocks formations named Fufa and Wahai formations are classified as Seram Series. The southern belt is dominated by metamorphic rocks with the basement consists of high to low grade metamorphic rocks. The high-grade metamorphosed schists and gneisses of the Kobipoto Complex are probably Precambrian to Lower Palaeozoic, although the recent study argued its formation aged Late Miocene to Pliocene (Pownall et al., 2013). Other Palaeozoic rocks are Taunusa, Tehoru and Saku complexes (Tjokrosapoetro et al., 1993).
Center and western Seram mainly comprises of lower greenschist to upper-amphibolite facies, i.e., phyllites, schists, and gneisses of the Tehoru formation. Garnet micaschists are widespread, which are often intercalated with amphibolites. Scarce kyanite-grade schists represent the highest grade part of the complex; however, large areas are of a low metamorphic grade and preserve original sedimentary structures (Audley-Charles, 1979;Tjokrosapoetro and Budhitrisna, 1982;Linthout et al., 1989). The Taunusa Complex is very similar in many ways to the Tehoru Formation although it includes rocks previously assigned to Valk (1945) as "Crystalline Schists" and therefore is considered to be generally of higher metamorphic grade (mid/upper-amphibolite facies rather than lower-amphibolite to greenschist facies) as defined by Tjokrosapoetro and Budhitrisna (1982).
Locally, the tectonic setting of Tamilouwhaya has been influenced by regional compression of Seram Island itself; despite the tectonic setting of Seram is still subject to debate, at least there have been two times tectonic compression and two continental break-ups were related to the Seram island (Setyawan et al., 2000).The first continental break-up was followed by tectonic compression occurred in the Paleozoic. Subsequent contraction of earth's crust places high-grade metamorphic rocks such as granulite near the surface and upper mantle is uplifted to the surface to form ultramafic rocks. Hence, erosion occurred to further expose of these metamorphic rocks and followed by thermal subsidence as deposition of Australian series. The second continental break-up and sea floor spreading is occurred in middle Jurassic and it might correspond to the absence of sedimentation interval in the Australian series. The last orogenic compression or deformation occurred in the Late Miocene-Pliocene and this event is very critical for the geological evolution of Seram (Audley -Charles et al., 1979;Kemp and Mogg, 1992;Tjokosapoetro et al., 1993;Setyawan et al., 2000).
The ore mineralization process at Tamilouw -Haya is controlled by NE-SW and NNE-SSW trending geologic structure as implication of this last compression event (Map 1B). It is also notable that local geological framework indicates that the gold mineralization is probably not related to volcanic rock-related hydrothermal gold deposit, e.g. epithermal, skarn or porphyry.
The main aims of this paper are to describe and identify ore minerals assemblage and minor elements contained in pyrite, galena and sphalerite and to purpose ore forming process and their paragenetic sequence at Tamilouw-Haya, Seram Island, Indonesia. Tjokrosapoetro et al., 1993), (B) Simplified Geological map of Tamilouw -Haya.

Map (1): (A) Geological map of Seram (modified after
MATERIALS AND METHODS The present study is based on desk study, fieldwork and sampling for laboratory analysis i.e ore mineralogy, SEM-EDS and Micro-XRF. There is no previous detailed study in the Tamilouw -Haya area that was focused specifically on the gold mineralization. A detailed ore microscopy is conducted at Department of Geological Engineering, Universitas Gadjah Mada, a single mineral chemistry (SEM-EDS) analysis is carried out at LPPT, Universitas Gadjah Mada and Micro-XRF for mineral mapping and identification is analysed at BATAN-Jakarta.
In total 46 double polished sections were prepared for ore microscopy to identify ore minerals and their textures. There were twelve data of shoot points for pyrite, sphalerite and galena identification are based on ore microscopy observation for further elemental mapping and identification using SEM-EDX and Micro-XRF. Mineral chemistry from SEM-EDX was performed using a JSM-6510LA type with resolution 1 -10 nm and magnification 10 -300,000x.
MicroXRF M4Tornado plus tool at BATAN, Jakarta is used for elemental mapping and minerals identification. It was performed by tube parameter high voltage 50 Kv, anode current 600µA pixel time 25 ms/pixel, pixel size 30 µm and total number of pixel is 360,000 pixel.

RESULTS AND DISCUSSION
Tamilouw -Haya is located within Tehoru metamorphic complex, Seram Island-Indonesia. The extent of researched area is 101.46 km 2 and is predominantly occupied by metapelitic rocks (intercalated of metasandstone and metasiltstone), slate, phyllite and locally is covered by coralline limestone and recent alluvial deposit. Primary gold mineralization is hosted by slate and metapelitic rocks and controlled by NE-SW and NNE-SSW trending geologic structure. Concordant and discordant veins are associated with gold mineralization although minor disseminated type appeared in several rock float samples.

(A) General features of ore minerals assemblage at Tamilouw -Haya
Characteristics of primary ore mineralization at Tamilouw-Haya are generally occurred within quartz veins associated with silicification, carbonatization and serisitic alterations. There are 3 vein types as the ore-bearing fluids (V1-V3) and only V3 (quartz± carbonate veins) with precious metals and anomalous high basemetal contents. 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 2vein (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 composed of quartz± carbonate, segmented, deformed, cross to the foliation of metamorphic/metapelitic rocks and characterized by stockworkbreccia vein textures. In some other locations, concordant veins are cross-cut by discordant veins as an indication of late stage of ore deposition. Based on ore microscopy analysis and elemental mapping, there are common ore minerals assemblage at Tamilouw -Haya deposit i.e native gold, chalcopyrite, pyrite, sphalerite, galena, pyrrhotite, tetrahedrite-tennantite (sulphosalt), marcasite, realgar, kalininite and arsenopyrite as hypogene minerals and accompanied by covellite, hematite, goethite and malachite as the supergene minerals.
Native gold: Very small size < 0.25 mm, subhedralanhedral and it is found as free gold grain within quartz gangue. At Way Yala river-Tamilouw, gold is enriched by supergene process and very abundant as secondary deposit (Pl. 1A).
Pyrite: Generally euhedralsubhedral, yellow colour and very abundant as vein and disseminated texture filled in quartz gangue at Tamilouw-Haya (Pl. 1A-D). In the altered and mineralized host rock, pyrite is slightly appear as dissemination ore and accompanied by chalcopyrite. Some of pyrite replaces pyrrhotite and has an intergrowth relation with galena. In quartz gangue, chalcopyrite, sphalerite, galena and pyrrhotite show their disseminated texture.
Chalcopyrite: Bright yellow colour, size is 0.25 -0.50 mm, subhedralanhedral, showing ex-solution texture or blebs of chalcopyrite within sphalerite (Pl. 1D). Chalcopyrite is associated with pyrite and very abundant as disseminated texture. In some polished section, chalcopyrite is replaced by tetrahedrite and covellite (Pl. 1B).
Galena: White grey colour, specified by triangular pits, size is often > 0.25 mm (Pl. 1C). Its presence is very abundant within quartz gangue, associated with sphalerite and pyrite in intergrowth texture and occasionally appears in the disseminated texture.
Sphalerite: Grey colour, occasionally showing ex-solution texture or blebs of chalcopyrite within sphalerite or "chalcopyrite disease" (Barton and Betkhe, 1987) (Pl. 1D). Sphalerite is associated with galena and reflecting intergrowth/interlocking texture. It means that sphalerite and galena are precipitated at the same time of ore deposition. Sphalerite is in line with chalcopyrite, pyrite, pyrrhotite and galena to form disseminated texture within quartz gangue. Generally, its appearance indicates as "late stage" than others sulphide minerals.
Pyrrhotite: It is also called magnetic pyrite and recognized by brown yellow colour. The size is 0.35 -0.5 mm of single anhedral grain. Pyrrhotite and marcasite are rare and their presence is only in quartz segregation/gangue to form disseminated texture.
Marcasite: Occasionally in shape of subhedralanhedral, single grains, size is 0.16 -<0.32 mm and it is also called "white iron pyrite". Although marcasite is not abundant within quartz gangue, its appearance is related to disseminate texture and replaced by Fe-iron oxide (hematite).
Arsenopyrite: Grey to silver white colour, 0.5-15 mm, appears as vein/veinlets and is filling fracture/shear joints of metapelitic rocks.
Tennantite: Represent sulfosalt mineral, gray to gray black colour, 0.25 -0.5 mm, its mutual relationship with galena is intergrowth, in some observation tennantite replaced pyrite and is substituted by hematite (Pl. 1C).
Kalininite: It is an isometrichexoctahedral black mineral, gray to black colour, 0.05 -0.25 mm, its appearance is associated with pyrite and hematite (Pl. 1E).
Covellite: Blue colour, 0.01-0.05 mm, single grain, its presence is rare within quartz gangue and only observed to replace chalcopyrite.
Malachite: It is a copper carbonate hydroxide mineral. Its appearance is identified at Wae-Satu, Tamilouw and adjacent to silica-carbonate alteration.

(B) Paragenetic sequence
Microscope observation and elemental mapping using Micro-XRF are used to interpret mutual relationship among minerals and their assemblage. The paragenetic sequence is obviously inferred from these interpretation and observation. Ore textures at Tamilouw-Haya show disseminated texture, simultaneous crystallization (intergrowth), inclusions, replacements and exolutions-decomposition textures. Ore minerals and gangue paragenetic sequence from epizonalmesozonal orogenic gold deposit at Tamilouw -Haya are shown in Table (1). Disseminated texture is found in almost all vein sample types, consisting of ore minerals from various type minerals such as pyrite, chalcopyrite and sphalerite, but mostly often found in pyrite. Gold dissemination is also found as "free gold grain". The gold paragenetic sequence against other ore minerals is unable to be determined yet, but it is assumed that the process of its formation coincides with ore minerals formation in the disseminated texture.
Simultaneous or intergrowth crystallization textures are occurred in both galena and sphalerite as well as chalcopyrite and galena. These showed paragenetic relationship between galena, sphalerite and chalcopyrite, are simultaneously formed or at the same time of deposition. Replacement textures are formed in chalcopyrite and sphalerite minerals as well as tennantite and galena which are replaced by hematite and covellite minerals. Additionally, chalcopyrite is also replaced by tetrahedrite. Replacement minerals paragenesis indicates its formation at the end of ore deposition.
The ex-decomposition texture found was "chalcopyrite disease" (Barton and Betkhe, 1987); it was formed by blebs or chalcopyrite mineral emulsion/inclusions in the sphalerite which showed chalcopyrite formed at earlier time. Kalogeropoulos (1982) stated chalcopyrite disease is a cancerous replacement produced by reacting FeS in sphalerite with Cu in aqueous solution. In general, sphalerite is formed as late stage than other sulfide minerals such as chalcopyrite and galena. Covellite, hematite, goethite and malachite are supergene minerals; formed in the end of mineralization.

(C) Mineral Chemistry Minor Elements in Pyrite from Tamilouw -Haya deposit:
The most abundant sulphide mineral at Haya -Tamilouw epizonal -mesozonal orogenic gold is pyrite. This Fe-sulphide fills altered metapelitic to slate wallrocks as vein/veinlets and reflecting euhedral to subhedral shape within quartz gangue in ore microscopy. In this research, SEM -EDS and Micro-XRF are used to describe elemental mapping and elements composition contained in pyrite. The SEM -EDS and Micro-XRF results reveal that nearly all pyrite samples contain a significant amounts and a wide range of other minor elements such as Co, Ni, Cd, Au, Ag and As (Tab. 2).
Elements including Se and Te are under detection limit or absent and might indicate that deposit is not associated with low sulfidation epithermal and igneous rocks or intrusionrelated deposit. High concentrate of Se and Te is related to igneous rock, low sulfidation epithermal and Carlintype deposit (Keith et al., 2018;Shao et al., 2018).

Minor Elements in Galena from Tamilouw -Haya deposit:
Twelve spot representatives for galena analysis from Tamilouw -Haya deposit were analyzed for Fe, Hg, Sb, Ag, Au, Bi and Se using SEM-EDS and Micro-XRF (Tab.5). This table showed that the Hg contents are very low (0.01-0.28wt.%) to below detection limit (< 0.01wt.%).

Note:* SEM-EDX analyses ** Micro-XRF analyses < 0.01 is below detection limit
The Se, Au and Fe contents are extremely low and in the ranges less than 0.01 wt.%, 3.2 wt.% and 3.31 wt.%, respectively. Sb, Ag, and Bi are generally used to demonstrate oreforming temperature of galena. Foord and Shawe (1989) discussed the crystallochemical relationships of Ag, Sb and Bi with galena and this can be explained by the coupled substitution between them as follow: Fleischer (1955) stated that the content of Ag, Bi and Sb declined with decreasing temperature of formation. The presence of bismuth (Bi) itself in galena is indication of high temperature magma-near deposits (Schroll, 1955). In addition, the examined Bi-bearing galena are relatively high-temperature which agrees with the experimental data for arising of such solid solutions (Bonev, 2007). At Tamilouw -Haya deposit, galena shows the Ag, Sb and Bi contents are very low to below detection limit with slightly variation. Ag is within the ranges < 0.01-0.31 wt.% (average 0.20 wt.%), Sb and Bi are below detection limit (<0.01 wt.%). Although Galena is an Ag-carrier, it seems like galena in Tamilouw -Haya is nonargentiferous galena. The best sample for non-argentiferous galena is able to found in Alanish Locality, Northern Iraq (Awadh and Nejbert, 2016). Therefore, it can be inferred that galena from Tamilouw -Haya deposit may be formed in low temperature.

Minor Elements in Sphalerite from Tamilouw -Haya deposit :
Sphalerite composed of Zn and S atoms arranged in a tetrahedral coordination within a face-centred cubic lattice (Lockington et al., 2014). Sphalerite is the main ore for zinc and the dominant mineral in most types of zinc sulphide deposits. In this study, SEM-EDX and Micro-XRF are used to analyze 12 spot representatives of sphalerite samples from Tamilouw-Haya orogenic deposit. Some detected of minor elements contained in sphalerite are Ga, Ge, Cd, Fe, Ag and Au. The results are listed in Table (6). This table shows that Tamilouw -Haya sphalerites hardly contain Fe which is in the range of 4.92-14.92 wt.%.. The Cd contents range from 0.06 wt. % to 0.22 wt.% of which a half of them are below detection limit (<0.01wt.%). The Ga, Ge, and Ag contents are within the ranges 0.4-1.87wt.%, <0.01 -0.41 wt.%, and <0.01 -0.24 wt.%, respectively. Nearly all researchers agreed that sphalerite from low temperature deposits such as those of the Mississippi Valley type tend to be higher in germanium content than those from mesothermal or high temperature deposits (Warren and Thompson, 1945), but many exceptions were noted. The data of Moller (1985) showed practically that Ga/Ge ratio will imply to temperature of ore formation. If the Ga concentration is higher than Ge, it may indicate of high temperature deposits. In this case, the maximum content of gallium (Ga) in sphalerite at Tamilouw -Haya deposit achieved 1.87 wt. % and it means that the deposit occurred under high-temperature formation. Jonasson and Sangster (1978) concluded that the Cd contents and Zn/Cd ratios in sphalerites vary with the genetic types of deposit and the metallogenetic epochs. The classification of ore-deposit type is distinguished by observing some sulphide ores in Canada. This classification is described as follows: Since a half of Cd contents of sphalerite are below of detection but the Zn contents are the highest presence in the investigated area, therefore Zn:Cd ratios are incomparable with this classification. They show a significance of very high Zn/Cd ratios (262.86 -6488, average= 4137.95) due to very low of Cd contents. Moller (1985) used geothermometry (Ga/Ge) sphalerite to determine temperatures in the source region of ore solutions to estimate mixing degree of the ore fluid. The combination of (Ga/Ge) sphalerite and homogenization temperature will assist in evaluating ore forming process. In this study, Geothermometry (Ga/Ge) sphalerite analysis at Tamilouw -Haya using SEM-EDS and Micro-XRF presented in Table (6). Based on Table 6, the average of germanium (Ge) content is 0.12 wt.% in sphalerite. In addition, the value of gallium (Ga) in the sample shows a range of 0.4 to 1.87 wt.% with an average of this element is 0.99 wt.%. This shows that sphalerite in the study area tends to be formed in relatively high temperature conditions. Moreover, the iron (Fe) content in sphalerite reaches 14.92 wt.% which may support and indicates that the temperature of ore formation is relatively a high temperature. The iron content generally increases with increasing formation temperature and can reach up to 40% in sphalerite (Nesse, 2013).

(D) Geothermometry (Ga/Ge) Sphalerite
From the results of the log Ga/Ge calculation at Tamilouw-Haya deposit, the maximum value is 2.27, while the minimum value shows a value of 0.22. Based on geothermometry (Ga/Ge) analysis of sphalerite which is then plotted on the equilibrium feldspar-mica-quartz graph and comparing with pressure and depth, the value of homogenization temperature (Th) shows temperature ranging from 210-305 o C (Diag. 1).
The paragenesis deciphered that quartz, calcite, ankerite, siderite, illite, chlorite and epidote were gangue minerals and ore mineralization are embedded within 3 types of quartz/quartz carbonate veins. Pyrite field in Tamilouw -Haya has cobalt content but Ni does not show a significant signature (Co > Ni) which means that the Tamilouw -Haya gold deposit was formed in relatively a high-temperature deposit. The Co/Ni ratios for Tamilouw -Haya pyrites are higher than those for sedimentary pyrites, lower than those for volcanogenic and skarn-hydrothermal pyrites, and more similar to those for the volcano-hydrothermal, metamorphosed and skarn hydrothermal type. Furthermore, the enrichment of cobalt, nickel and arsenic in pyrite indicates that these elements are available during certain metamorphic phases. Galena is characterized by below detection limit of Sb and Bi elements, while the Ag contents are relatively low, so it can be concluded that galena from the Tamilouw -Haya deposit was formed at decreasing temperature.
The minor elements of sphalerite in Tamilouw-Haya shows the element of Ga > Ge and increasing of Fe content which indicates the formation of sphalerite at a relatively high temperature. Moreover, the Ga/Ge sphalerite microtermometry has an elevated homogenization temperature (Th) ranging from 210 o -305 o C.