Geochemistry and geochronology of VHMS mineralization in the Sangkaropi district, central-West Sulawesi, Indonesia: Constraints on its tectono-magmatic setting

Journal Pre-proofs Geochemistry and Geochronology of VHMS mineralization in the Sangkaropi district, central-West Sulawesi, Indonesia: Constraints on its tectono-magmatic setting Adi Maulana, Theo van Leeuwen, Ryohei Takahashi, Sun-Lin Chung, Kenzo Sanematsu, Huan Li, Ulva Ria Irfan PII: DOI: Reference:

S0169-1368(19)30252-5 https://doi.org/10.1016/j.oregeorev.2019.103134 OREGEO 103134

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Ore Geology Reviews

Received Date: Revised Date: Accepted Date:

19 March 2019 19 August 2019 16 September 2019

Please cite this article as: A. Maulana, T.v. Leeuwen, R. Takahashi, S-L. Chung, K. Sanematsu, H. Li, U.R. Irfan, Geochemistry and Geochronology of VHMS mineralization in the Sangkaropi district, central-West Sulawesi, Indonesia: Constraints on its tectono-magmatic setting, Ore Geology Reviews (2019), doi: https://doi.org/10.1016/ j.oregeorev.2019.103134

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Geochemistry

and

Geochronology

of

VHMS

mineralization in the Sangkaropi　district, central-West Sulawesi,

Indonesia:

Constraints

on

its

tectono-magmatic setting.

Adi Maulana1*, Theo van Leeuwen2, Ryohei Takahashi 3, Sun-Lin Chung4, Kenzo Sanematsu5 , Huan Li6 and Ulva Ria Irfan1

1Geology

Department, Hasanuddin University, Jl. Perintis Kemerdekaan KM. 10,

Tamalanrea, Makassar 90245, Indonesia 2Jl. 3

Hj Naim, Jakarta, Indonesia

Department of Earth Sciences and Technology, Akita University, Akita, Japan

4Department 5Advance 6

of Earth Sciences, National Taiwan University, Taipei, Taiwan

Institutes of Science and Technology, Tsukuba, Japan

School of Geosciences and Info-Physics, Central South University, Changsha

410083, China *Corresponding author: [email protected]

Abstract The Sangkaropi district in central-West Sulawesi is one of the few known volcanic hosted massive sulfide (VHMS) districts in Indonesia. It comprises several clusters of mostly small mineral occurrences, including Sangkaropi, Billolo and Rumanga. The mineralization is hosted by felsic volcanics that occur in bimodal association with basalt. Styles of mineralization include syngenetic banded massive and fragmented sulfides and epigenetic veins, stockwork and disseminations. The deposits are classified as zinciferous bimodal-felsic (Kuroko type) VHMS. We present for the first time preliminary results for whole rock and trace element analysis and U-Pb age dating for the bimodal volcanic hosts, together with sulfur isotope data for the mineralization and associated barite alteration. Combined with previous data, this new information suggests the mineralization in the Sangkaropi district took place around 34 Ma (boundary Eocene-Oligocene) in a continental margin arc setting, when the stress regime changed from near-neutral

to

extensional

and

volcanism

changed

from

being

andesite-dominated to bi-modal. The sulfur isotope data suggest that the mineralizing fluids had both significant magmatic and seawater components. Keywords: Volcanic Hosted Massive Sulfide (VHMS); sulfur isotopes; U-Pb zircon; Sangkaropi; Sulawesi.

1.

Introduction

The geology of the Indonesian region is characterized by the widespread occurrence of Cenozoic and older volcanic arcs with a total land extent of over 15,000 kms (Carlile and Mitchell, 1994). It is therefore somewhat surprising that, to date, relatively few volcanic hosted massive sulfide (VHMS) deposits have been found. The first VHMS discovery made in Indonesia was in the Sangkaropi district, central-West Sulawesi (Fig. 1a), where this type of mineralization occurs in several clusters. The year of discovery is not known, but the Japanese undertook mining in the district during their occupation of Indonesia between 1942 and 1945. They reportedly trucked daily 10 – 15 t of selected ore averaging 3-5% Cu to the port of Palopo on the east coast (Jurkovic and Zalokar, 1990). Since 1974, intermittent exploration has taken place in the area and a domestic company resumed mining on a small scale mining in 2010. Limited previous studies of the Sangkaropi deposits focused mainly on their geological setting, ore body styles and mineralogy (Yoshida et al., 1982; Nishiyama et al., 1983; Jurcovic and Zalokar, 1990; Sunarya et al., 2011; Nur et al., 2016). The paper by Sunarya et al. (2011) is basically the same as the Yoshida et al. (1982) paper. It was recognized early on that the deposits have a close affinity with Kuroko-type mineralization in Japan. In this paper we present for the first time major and trace element data for volcanic rocks that are spatially and temporally related to the Sangkaropi mineralization, U/Pb zircon ages obtained from two volcanic rock samples, and sulfur isotope data for selected ore samples. The data, which are preliminary in

nature, provide constraints on the origin, timing and tectonic setting of the mineralization in the Sangkaropi district.

2. Geological setting and mineralization. 2.1 Regional geology The Sangkaropi district is located in the Western Sulawesi Province at the north end of the South Arm of Sulawesi (Fig. 1a). The province consists of a basement of several continental fragments derived from Gondwanaland that docked with the southeastern Sundaland margin in the Cretaceous (van Leeuwen et al., 2010). Remnants of accretionary zones associated with this event are exposed in the southern part of the province (Parkinson et al., 1998 ; Maulana et al., 2015; Maulana et al., 2016; White et al., 2017; Maulana et al., 2019; Bohnke et al., 2019). These units are overlain by a series of turbiditic sedimentary rocks of Late Cretaceous age that are thought to have formed in a a deep marine fore-arc basin above a NW-dipping subduction zone (Sukamto and Simandjuntak, 1983; Parkinson et al.,1998; van Leeuwen and Muhardjo, 2005; Maulana et al., 2013). A thick series of Lower Cenozoic sedimentary and volcanic rocks unconformably overlies the pre-Cenozoic basement. The sedimentary rocks were initially deposited as a syn-rift sequence during rifting associated with the opening of the Makassar Strait (e.g. Hamilton, 1979; Bergman et al., 1996). Rifting started in the Middle Eocene or slightly earlier, with subsidence reaching its peak at about 36 Ma. The flanking platforms in the south arm were drowned and started to accumulate shallow marine carbonates (Lunt and van Gorsel, 2013).

The rifting period was accompanied, and locally preceded, by calc-alkaline volcanic activity. It produced volcanic rocks, predominantly andesitic in composition, with distinct subduction and continental margin arc signatures (e.g. Soeria-Atmadja et al., 1998; Elburg et al., 2002 & 2003; van Leeuwen et al., 2010), supporting the widely accepted scenerio that during the Eocene a volcanic arc formed over a northwesterly dipping subduction zone along the southeastern edge of Sundaland.

Van Leeuwen et al. (2010) noted the

volcanism took place over a strike distance of more than 1,200 km, but appears to have been relatively restricted in both time and space. A possible explanation for the apparent low intensity of volcanic activity is that subduction beneath Western Sulawesi was oblique at the time (e.g. Hall, 1996). By the end of the Eocene, volcanic activity had ceased altogether in the South Arm, possibly as the result of increasingly oblique plate convergence (van Leeuwen et al., 2010), changing the active margin into a strike-slip transform margin (Polvé et al., 1997; van Leeuwen and Muhardjo, 2005). To the north of the Sangkaropi district, a volcanic unit consisting of andesitic to dacitic lavas and volcaniclastics is present, with marl intercalations containing a late Middle to early Late Oligocene planktonic foraminifera assemblage (Ratman and Atmawinata, 1993). Still further to the north, in the northern part of Western Sulawesi, paleontological evidence, supported by limited radiometric age dating, results suggests volcanic activity in this area occurred in the mid-Eocene to mid-Oligocene (van Leeuwen and Muhardjo, 2005). Two ophiolite/volcanic terranes, formed at least in part during the Oligocene, are present along the eastern margin of the South Arm of Sulawesi, viz. the Lamasi

Complex, located to the east of the Sangkaropi district, and the Bone Group that is exposed in the Bone Mountains 150 km further south. They comprise mostly MORB and IAbasaltic-andesitic volcanics with subordinate rhyolite and red mudstone intercalations

(Priadi et al., 1994; Polvé et al., 1997; van Leeuwen et

al., 2010). A major extensional tectonic event took place in the mid-Miocene. It was accompanied by widespread shoshonitic to ultrapotassic magmatism that continued into the Late Pliocene, and locally into the Quaternary. Van Leeuwen et al. (2010) suggested the Lamasi and Bone terranes represent marginal basin crust that was juxtaposed against the continental Sundaland margin along major strike-slip faults during this mid-Miocene event.

2.2 Local geology The following summary of the geology of the Sangkaropi district is largely based on reports by Yoshida et al. (1982) and Jones and Kristianto (1994) (Fig. 1b). Alteration and base metal occurrences with VHMS Pb isotope signatures occupy a NE-trending zone over a distance of about 22 km. To the east of this zone, slightly metamorphosed rocks of the Cretaceous Latimojong Complex are exposed. These are unconformably overlain by a series of shales with minor calcareous sandstone and limestone (Toraja Formation). The limestone contains various large benthic foraminifera species, including Asterocyclina sp. and Biplanispira sp (P.G. Quilty, written comm., 1993), indicating a Late Eocene age and deposition in shallow marine water.

The Latimojong Complex and Toraja Formation rocks are separated from the mineralized zone by a thrust fault. This zone forms an anticlinal structure with its axis trending NNE. Andesitic lava and polymict volcaniclastics with mostly andesite fragments and thin interbeds of shale are exposed in the core of the anticline. Near Sangkaropi, they overlie an altered granodiorite. No contact metamorphism was observed in adjacent rocks, suggesting it may belong to the pre-Cenozoic

basement.

Poorly

preserved

foraminifera

in

the

shale

intercalations suggest a maximum age range of Late Eocene to Early Miocene and deposition in an inner shelf environment (P. G. Quilty, written comm., 1993). Based on its stratigraphic position, the andesitic sequence was deposited in the Late Eocene, forming part of the Toraja Formation. Elsewhere in the central part of the Western Sulawesi Province this formation also contains volcanic material, mostly as intercalations of volcaniclastic rocks (van Bemmelen, 1949; Harahap, 1993). The andesite unit is unconformably overlain by a series of felsic pyroclastics, lavas and volcaniclastics, which is at least 200 m thick (Fig. 2a). The volcaniclastics include tuff breccia and breccia with fragments of dacite, andesite, pumice, and granite. The upper part of the felsic sequence, which is up to 80 m thick, comprises rhyolitic pyroclastics (Fig. 2b) and lava flows. The felsic rocks are commonly silicified. Our age dating results (see below) suggest a latest Eocene- earliest Oligocene age for this unit. Near Sangkaropi, it is overlain by claystone and olivine-bearing basalt showing pillow structures (Fig. 2c), with a maximum thickness of 30 m. Close to the ore body the claystone is silicified and brecciated.

The anticlinal structure of the Sangkaropi area is well defined by a sequence of red/brown hematitic calcareous siltstone with subordinate limestone, which is informally called Bilolo Marl (Fig. 2d). It forms a prominent marker unit above the VHMS horizon, which occurs in the top part of the underlying felsic unit. The sedimentary rocks contain a rich planktonic foraminiferal fauna, indicating a relatively deep marine environment of deposition. Species include members of the Globigerina tripartita lineage (including G. venezuelana and G. tripartita), G. sellii, G.selii-binaiensis, G kugleri/angulisutaris, and Chiloguembelina, indicating a Late Eocene to Late Oligocene age range. In the absence of typical Eocene markers an Early to Late Oligocene age is assigned to this unit (P.G. Quilty, written comm., 1993), an interpretation that is consistent with its stratigraphic position. The Bilolo Marl is overlain by reef limestone, dated Late Oligocene to Early Miocene, and andesitic volcaniclastics and shales of Early to Middle Miocene age. Younger potassic volcanics cover the western – northwestern parts of the district.

2.3 Alteration and Mineralization Within the 22 km long zone of alteration and mineral occurrences, three main centers of mineralization are present, viz. at Sangkaropi (also referred to as Batu Marupa), Rumanga and Bilolo (Fig.1b). Two main styles of mineralization are represented, viz. syngenetic stratiform massive sulfide mineralization, which occurs at/near the top of the felsic unit, and epigenetic mineralization. The epigenetic style is found below the massive sulfide horizon and comprises veins, stockwork and sulfide (mainly pyrite) disseminations in the silicified host rock.

The disseminated mineralization is referred to as “silicified ore” by Yoshida et al. (1982) and “impregnation type” by Jurkovic and Zalokar (1990). Both styles are present at Sangkaropi (Fig. 3a) and Bilolo, while at Rumanga only the epigenetic style has been preserved.

Silicification is widespread and intense in the district

(Fig. 3f). The Sangkaropi deposit consists of a cluster of mostly small ore lenses within an area of approximately 750 m x 500 m. According to Jurkovic and Zalokar (1990) “some ten ore bodies, viz. ore outcrops, were known down to 1962”. On Figure 2 of Yoshida et al.’s (1982) paper 18 small and two larger ‘ore bodies’ are shown. Jurkovic and Zalokar (1990) mention that the largest ore body is 60-70 m long and 15-18 m wide, while Nur et al. (2016) report a length of 150 m and thickness of 60 m. The upper part of the mineralized body is composed of massive sulfides and is 15 m thick (Nur et al., 2016) and the lower part of a silicified zone with disseminated pyrite and rare base metal sulfides. The massive ore in this and other bodies commonly shows banded structures and is brecciated near the top or overlain by a layer of fragmental ore with clasts up to several meters in diameter (Fig. 3b). It is associated with silicified mudstone and overlain by a thin barite layer. Stockwork/vein mineralization is locally exposed, consisting of pyrite veins, quartz veins with pyrite and base metal sulfides, and stockworks of sulfides (Yoshida et al., 1982; Nur et al., 2016). Jurkorvic and Zalokar (1982) collected a large number of samples from an old Japanese ore dump comprising some 2,500-3,000 t of hand-picked ore. Based

on macroscopic observations they recognized three ore types: yellow ore, black ore and impregnated ore. Yellow ore consists of pyrrhotite, pyrite and chalcopyrite with subordinate tetrahedrite, sphalerite, galena, chalcocite, neodigenite, and enargite. Pyrrhotite and pyrite are the earliest minerals. Pyrrhotite occurs as irregular masses. Pyrite is strongly reabsorbed and fractured, and partly replaced by chalcopyrite. Chalcopyrite contains exsolutions of sphalerite, and inclusions of galena and tetrahedrite. It is mostly coarse grained and, like pyrite, fractured. Pyrite, sphalerite and tetrahedrite are the main ore-forming minerals in the black ore. Chalcopyrite, chalcocite and galena are present in small amounts. Pyrite is the earliest mineral and present only as relicts. It occurs commonly in the form of aggregates of regular colloidal spherules or droplets, which show concentrically banded structures. Sphalerite contains numerous chalcopyrite exsolutions as lamellae and discs. Tetrahedrite replaces chalcopyrite and pyrite. It displays a zonal structure suggesting rapid cooling. There are two generations of chalcopyrite, namely occurring as exsolutions in sphalerite and replacing sphalerite and pyrite. Yoshida et al. (1982) do not distinguish between yellow and black ore. They describe the massive sulfide ore at Sangkaropi as black and porous, consisting mainly of sphalerite together with galena, chalcopyrite, pyrite and tetrahedrite. A sample analyzed by Nur et al. (2016) yielded a small amount of gold (0.23 ppm). Spots of supergene azurite and malachite are commonly seen at the surface (Fig. 3c). In polished section galena shows a dendritic texture in places (Fig. 3d).

The mineralization at Sangkaropi is associated with barite, quartz, sericite, and chlorite (Yoshida et al., 1982). The latter three minerals were identified by XRF analysis in samples taken from within and close to the mineralized zone (Nur et al., 2016). Barite occurs interstitially in the massive ore (Fig. 3e) Mineralization at Rumanga consists of stockwork and disseminated sulfides irregularly distributed within dacitic breccia and tuff. The mineralized zone is restricted in size and has an easterly strike direction (Nur et al., 2016). Ore minerals include sphalerite, pyrite, chalcopyrite, bornite, tetrahedrite, and chalcocite with minor galena and covellite (Yoshida et al., 1982). The latter mineral replaces margins of chalcopyrite grains (Nur et al., 2016). Yoshida et al. (1982) examined ore collected from a prospecting tunnel at Rumanga. Stockwork ore consists of quartz veins with pyrite, chalcopyrite, sphalerite and tetrahedrite aggregates. Chalcocite veinlets cut chalcopyrite and bornite, and chalcopyrite occurs as inclusions and veinlets in sphalerite crystals, which are up to 5 to 6 mm in diameter. Pyrite crystals are also relatively large and have euhedral to subhedral shapes. A single sample analyzed by Nur et al. (2016) contained 3.5 ppm Au, 159 ppm Ag, >1% Cu, 0.85% Zn, and 0.44% Pb. The

mineralization

is

accompanied

by

quartz,

sericite,

interstratified

sericite-montmorillonite, chlorite, and interstratified chlorite-saponite (Yoshida et al., 1982). A barite layer overlies the mineralized zone (Yoshida et al., 1982; Nur et al., 2016). The mineralized zone at Bilolo extends over 175 m in an east-west direction and is 70 m thick (Nur et al., 2016). It consists of a massive stratiform sulfide body, which is underlain by stockwork and overlain by a thin barite layer. The massive

sulfide ore is black and in places yellow in color. It has a banded appearance with fine-grained layers of dominantly galena and sphalerite alternating with coarser layers of pyrite and chalcopyrite. Galena shows a flow-like structure and in addition to sphalerite is accompanied by covellite and tetrahedrite (Yoshida et al., 1982). Nur et al. (2016) also observed pyrrhotite replacing chalcopyrite. Barite and quartz are the dominant gangue minerals. The former commonly contains covellite, chalcocite and bornite (Yoshida et al., 1982). XRF analysis of altered host rocks identified quartz, muscovite and anorthite (Nur et al., 2016). Available resource estimates include: 1.1 Mt @ 4% Cu, !9% Zn, 15% Pb, and 68 g/t Ag, estimated from deposit size and assays (https://minerals.usgs.gov, accessed 23/8/2018), 2) 2.5 Mt averaging 16% Pb, 22% Zn, and 0.6% Cu (Djaswadi, 1997), and 300,000 t. The latter estimate is based on the results of a recent drilling program carried out by PT Makale Toraja Mining at Sangkaropi.

3. Methodology 3.1 Sampling A total of seven samples were collected for geochemical analysis, viz. five felsic volcanic samples and one basalt sample from the Sangkaropi area, and one felsic rock sample from the Bilolo area. All felsic samples were taken close to the main mineralized bodies and the mafic sample from the basalt layer that partly covers the mineralized horizon at Sangkaropi. Two of the felsic samples from the Sangkaropi area were selected for zircon U-Pb isotope analysis. For the purpose of sulfur isotope analysis four samples were collected from the Sangkaropi deposit representing different styles of mineralization: stratiform

massive sulphide (SKR-1A), epigenetic vein (SKR-1C) and disseminated ore (SKR-2A and SKR-2B). At Bilolo three samples were taken of epigenetic style mineralization: vein (BLO-2D), vein within interpreted chimney BLO-2B) and stringer/stockwork vein material (BLO-2C). From these samples a total of 19 sulfide and two barite separates were prepared. Sulfides separates consisted of galena (4), chalcopyrite (5), pyrite (4), and sphalerite (2).

3.2 Geochemistry Major and trace element compositions were determined at the Laboratory of Geochemistry, National Taiwan University. For major element analyses, a Leeman Prodigy inductively coupled plasma-optical emission spectrometry system with high dispersion Echelle optics was used. The analytical uncertainties, based on the US Geological Survey rock standards BCR-1 and AVG-2, and the Chinese national rock standard GSR-3, were generally better than 1% for many oxides with the exception of TiO2 (1.5%) and P2O5 (2.0%). Trace elements were analyzed using an Agilent-7500a inductively coupled plasma-mass spectrometry (ICP-MS). The data quality was monitored by analyses of two US Geological Survey rock reference materials BCR-1 and BHVO-1. The analytical precision for most trace elements is better than 5%.

3.3 Sulfur isotope analysis Sulfur isotope analysis was carried out at Economic Geology Laboratory, Akita University, Japan. Measurements of sulfur isotopes were performed using conventional procedures of Robinson and Kusakabe (1975) for sulfides, and

methods of Yanagisawa and Sakai (1983) for sulfates on a VG Sira Series II mass spectrometer. Determinations were made on an 18W Quantronix 117 Nd:YAG model laser in an oxidizing atmosphere (at 25 torr oxygen pressure) and a ~35 mA current for 2 s on single or multiple sites (up to 5) to yield sufficient SO2 for analysis. All results are reported as permil (‰) variations from the Canon Diablo Troilite (CDT). The analytical precision (1δ) of sulfur based on repeated analyses of an internal standard for both sulfides and sulfates is 0.2‰.

3.4 LA-ICP-MS U-Pb zircon dating U-Pb zircon age analysis was carried out on a rhyolite sample and a tuff sample by laser-ablation inductively coupled-mass spectrometry (LA-ICP-MS) at the GeoAnalytical Lab. at National Taiwan University. Zircon grains were separated using standard gravimetric and magnetic techniques at China University of Geoscience. The grains were mounted together with standards in a 1 inch-diameter epoxy puck that was ground and polished to expose the interiors of the grains. Cathodoluminescence images acquired at the National Taiwan University were used as base maps for recording laser spot locations and to reveal growth and compositional zonation, inclusions, and to look for inherited cores. An overview of the laser-ablation techniques is given by Chang et al. (2006) and summarized below. Zircon ages were determined using a New Wave UP-213 laser ablation system in conjunction with a Thermo Scientific Element2 single collector, double-focusing magnetic sector ICP-MS. Zircons were analyzed using a 30 μm diameter beam operating at 10 Hz. The ablated material was delivered to the torch by a mixed He and Ar gas. Laser-induced

time-dependent fractionation was corrected by normalizing measured ratios in standards and samples to the beginning of the analysis using the intercept method. Static fractionation, including that caused by laser ablation and due to instrumental discrimination, was corrected using external zircon standards. Weighted average ages and Tera-Wasserburg Concordia were calculated using IsoPlot 3.0 (Ludwig, 2003).

4. Results 4.1 Geochemistry Seven samples from the Sangkaropi area including rhyolite (SKR-RT, S03.SM, S06.B, R27.B), rhyolitic tuff (SKR-TU), dacite (BHL.30) and basalt (SKR-BSLT) were analysed for major and trace elements. Whole major element data are displayed in Table 1. As the felsic sequence exposed between Sangkaropi and Bilolo is invariably silicified, it was not possible to find unaltered rock. The analytical results for the six felsic samples, in particular the major elements, may therefore not reflect the original composition of the rhyolitic volcanics. The strongest silicified samples are SKR-RT, SKR-TU and S03.SA as highlighted by their high SiO2 content (~85%) and negligable Na2O content. The basalt is characterized by low SiO2 (45.95%) and relatively high Al2O3, Fe2O3 and CaO contents. In the SiO2 versus K2O diagram (Fig. 4a), the dacite and all but one of the rhyolite samples fall into the medium-K calc-alkaline series field and the basalt into the high-K to shoshonitic field. A similar picture is shown by the Th versus Co classification diagram designed by Hastie et al. (2007) for altered and weathered volcanic rocks, suggesting that the silicification of the rhyolite did not

significantly change their original potassium content (Fig. 4b). The basalt contains normative olivine and nepheline, indicating an alkali basalt composition. Primitive mantle normalized trace element variations of the samples are shown together with Lamasi Volcanic samples in Figure 5a. The basalt sample shows relatively high transition metal (Cr, Ni, V, Ti, Mn) and total REE contents, and a negative Eu anomaly. The tuff is characterized by a medium total REE content, a strong negative Eu anomaly (Eu/Eu* = 0.87), and relatively significant fractionation between light REE (LREE) and heavy REE (HREE) ((La/Yb)N = 5.47–7.37). The REE pattern of the felsic samples is different in that it shows a lower total REE content and a slight negative Eu anomaly (Fig. 5a). Chondrite-normalized REE patterns for all six samples are characterized by enrichment in LREEs, depletion in HREEs, and strong fractionation in LREEs but no fractionation in HREEs (Fig. 5b).

4.2 Sulfur isotopes The samples of sulfide minerals from the Sangkaropi deposit (n = 10) and the Bilolo deposit (n = 7) exihibit restricted values of δ34S, ranging between –0.5 to +4.4 ‰ (Tables 2 and 3). The δ34S values of sulfide from Sangakaropi vary from +2.0 to +4.4 ‰, with the exception of one sample having a value of +0.5 ‰. Excluding this outlier, the average is +3.5 ‰. The δ34S values of sulfide minerals from Bilolo show a similar narrow range, but with slightly lower values (-0.5 to +2.6 ‰), averaging +1.8 ‰. Sulfate sulfur in barite, one sample each from Sangkaropi and Bilolo, yields δ34S values of +23.6 and +20.9 ‰, respectively.

4.3 U-Pb zircon geochronology U-Pb analytical results and calculated ages are listed in Table 4 and shown as isotope plots in Figure 8. Only 207Pb/ 206Pb

206Pb/238U

ages are shown since

207Pb/235U

and

ages are not applicable due to young, lower concordia intercepts.

The zircons separated from the rhyolite sample SKR-RT are transparent and brown in color (Fig. 6a). They are subhedral to euhedral with length to width ratios of 1 to 2. Some grains are crystal fragments. The grain size ranges from about 200 to 400 μm. Five fractions analyzed are concordant or nearly concordant (Fig. 7). By weighted averaging of 206Pb/238U ages (t206), a weighted average t206 age of 34.24 ± 0.52 Ma with MSWD value of 1.7 was obtained (Fig. 7). This apparent age is interpreted as the crystallization age of the rhyolite. The zircons separated from the tuff sample SKR-TU are transparent, yellow, brown to light pink in color, sub-hedral to euhedral with the length to width ratios of about 1.5 to 2.5. The crystal lengths range from about 120 to 350 μm and a few grains are crystal fragments (Fig. 6b). Six fractions were analyzed. Five fractions are concordant and the sixth plotted close to the concordia (Fig. 7). The calculated

206Pb/238U

age is 34.4± 1.2 Ma (MSWD = 3.4) (Fig. 7), which is also

considered to be the crystallization age.

5. DISCUSSION In this section we discuss first the significance of the sulfur isotope and REE data. This is followed by a discussion on the timing and tectono-magmatic setting of the Sangkaropi mineralization. We then compare the VHMS deposits

in the Sangkaropi district with VHMS deposits elsewhere (mainly Kuroko-type deposits in Japan) and, finally, present a model for the mineralization.

5.1 Sulfur isotopes Sulfur isotope values from the Sangkaropi and Bilolo deposits show near 0 to + 4.5‰ for sulfide and +20.9 to +23.6 ‰ for barite (Tables 2 and 3). It is reported that δ 34SCDT value of modern seawater sulfate is +21.0 ± 0.2‰ (Seal et al., 2006). Sulfur isotopic values near 0 can be regarded to be of magmatic origin as those of pristine mid-ocean ridge basalts have δ34SCDT = +0.3 ± 0.5‰ (Sakai et al. 1984; Seal, 2006). In the study of the Sangkaropi and Bilolo deposits, we consider that sulfur was provided from both the magma and seawater. The former was a heat source and also provided the heavy metals, while the latter was the main component of the hydrothermal fluid that circulated beneath the seafloor. Though the mixing rate of magmatic and igneous sulfur is uncertain and would have been fluctuating, there were dissolved sulfur species of both bisulfide and sulfate sulfur such as HS- and SO42, respectively, because both the sulfide and sulfate minerals occur in the deposits. Under the equilibrium condition, isotopically heavier sulfur incorporates into barite >> pyrite > sphalerite > chalcopyrite > galena, in order, based on the isotopic fractionation (e.g. Ohmoto and Rye, 1979), and most of the samples in this study show a similar trend except for SKR-1C and BLO-2B (Tables 2 and 3). Although it is uncertain whether or not the sulfide and sulfate minerals precipitated under equilibrium conditions, the elevated value +23.5‰ of barite (SKR-2 A in Table

2), which is higher than that of average seawater is likely to be due to isotopic fractionation between the sulfide and sulfate minerals.

5.2 Interpretation of REE results Before discussing the tectono-magmatic origin of the volcanic rocks, parental magmatic evolutionary processes such as fractional crystallization, wall-rock contamination/assimilation, and fluid alteration should be taken into account (Du et al., 2016; Li et al., 2019). In this study, the flat REE patterns and negligible Eu anomalies of these rocks indicate that fractional crystallization is weak for the magma. The slightly enriched U, Th, and LREEs relative to HREEs, and slightly depleted Nb relative to Th and La indicate that upper crustal contamination played a limited role in the evolution of the parent magmas of these rocks (Li et al., 2012; Richan et al., 2015; Wu et al., 2017). The anomaly of HREE, especially depletion of Ho in sample S.03M and enrichment of Yb-Lu in sample R.27B and S.06S reflects the mobility of this element during the regional metamorphism and hydrothermal alteration (Aliyari et al., 2014). In addition, there is no firm evidence of fluid alteration of the parental source of the rocks, though some mobile elements exhibit variable concentrations. Thus, bulk geochemistry of the rocks largely reflects the composition of the original magma. The major- and trace-element analyses of the Sangkaropi district show that these rocks are enriched in Si, Al, and large-ion-lithophile elements (LILE, e.g., Rb, Th, U) but depleted in Ca, Mg, and high-field-strength elements (HFSE, e.g., P, Ti, Nb, Ta), typical of subduction-related continental arc volcanic rocks (Li et al., 2013; Sun et al., 2019).

5.3 Timing of mineralization Several authors have suggested that the VHMS deposits in the Sangkaropi district formed in the Miocene, without presenting any supporting evidence (Yoshida et al., 1982; Nishiyama et al., 1983; Sunarya et al., 2011). Van Leeuwen and Pieters (2011) assigned an Oligocene age to the mineralization based on the age of the Bilolo Marl. A coeval relationship between mineralization and felsic volcanics is suggested by their spatial association, lack of alteration and mineralization in the overlying rock units, and the colloform and banded textures of part of the mineralization. The latter feature is indicative of growth in open spaces, suggesting the stratiform sulfides were initially deposited in or near the surface of the sea floor. We propose the mineralization event occurred around 34 Ma, which is the age obtained from the two rhyolite samples, taken from sites close to the stratiform mineralization horizon. As the stratiform ore bodies occur in the uppermost part of the felsic volcanic sequence, the ore bodies most likely formed during the waning stage of the felsic volcanic activity. Lack of veining in the massive sulfide bodies and overlying strata suggests the epigenetic mineralization is not younger than the syngenetic mineralization. It is also unlikely to be older as the two styles are juxtaposed without an obvious structural or lithological break. From this we conclude that the silicified vein/stockwork zones represent cogenetic chimneys.

5.4 Tectonomagmatic setting of the Sangkaropi district.

Concurrently with the formation of the VHMS mineralization around 34 Ma two important tectonic/magmatic events took place in the Sangkaropi district: 1) volcanism changed from dominantly andesitic to bimodal felsic-mafic, and 2) the environment of deposition changed from shallow marine to deep marine. The andesitic volcanism occurred in a continental margin arc setting during the Eocene (see 2.1). The geochemical characteristics of the rhyolite and basalt rocks at Sangkaropi suggest that this setting remained unchanged during the bimodal volcanic activity. In addition to the REE characteristics, discussed above, this includes the following evidence. On the Th/Yb vs Ta/Yb and Th/Yb vs Nb/Yb diagrams all samples plot in/close to the continental margin arc field (Fig. 8). The basalt sample plots in or close to the continental arc field in various tectonic discrimination diagrams, including Ba/Nb vs La/Nb, Zr/Y vs Zr, K20/P2O5/TiO2, and MnO*10/P2O5*10/TiO2 (Fig. 8), and the Nb*2-Zr/4-Y diagram for basaltic rocks. A relatively high normalised Nb/Zr ratio, and a positive Sr anomaly in the normalized trace element diagram displayed by the basalt are further evidence for a continental arc setting (M. Elburg, written comm., 2018) While it appears that the overall tectono-magmatic setting remained unchanged, i.e. a continental margin arc setting, the shift from a shallow to deep environment of deposition in the Sangkaropi district suggests a change in stress regime from near-neutral to extensional. This interpretation is supported by Franklin et al’s (2005) observation that rifting in a continental arc environment can be identified by the presence of high silica rhyolite and alkaline basalt. The nature and cause of the rifting event is unknown, but it may have been part of a larger regional

event. In the South Arm, phases of rapid fault-controlled subsidence took place during the latest Eocene-earliest Oligocene (Wilson et al., 2000), and in oil wells drilled in the Makassar Strait a marked reduction in sedimentation rates was observed around 34 Ma (Lunt and van Gorsel, 2013). During this time the main extensional direction was east-west (Wilson et al., 2000), suggesting that extension/rifting took place parallel to the axis of the volcanic arc.

5.5 Classification of the Sangkaropi deposits and comparison with other VHMS deposits VHMS deposits have been variably classified based on various criteria including metal content (e.g. Cu, Cu-Zn, Zn-Pb-Cu) and type locality (e.g. Kuroko, Besshi, Cyprus). Currently, the most common classification uses lithostratigraphic and litho-tectonic environment of formation as the main criteria. This scheme includes five types: 1) bimodal-mafic, 2) mafic, 3) pelitic-mafic, 4) bimodal-felsic, and 5) felsic siliciclastic (e.g. Barrie and Hanington, 1999; Franklin et al., 2005). The Sangkaropi deposits show a close affinity with the bimodal-felsic type, which is roughly equivalent with the Kuroko-type. Main features of this category are bimodal sequences with felsic>mafic rocks, submarine felsic volcanic host rocks, a Zn-Pb-Cu-(Au-Ag) metal association, and a rifted continental arc/back-arc setting

(e.g. Barrie and Hannington, 1999; Franklin et al., 2005; Piercy et al.,

2010). The Sangkaropi occurrences can be further classified as a zinciferous VMS deposit. This type of deposit is characterized by a high Zn content (>6.2%) and contained Zn being <1.27 Mt (Piercy et al., 2015).

The total sulfide ore reported for the Sangkaropi deposits by Djaswadi (1997) is similar to the geometric mean of bimodal-felsic deposits, i.e. 2.5 Mt vs 3.3 Mt, but its total metal content is significantly higher than the mean, i.e. 965,000 t metal vs 198,461 t metal (Franklin et al., 2005), reflecting an average Zn+Pb grade of 38% that is much higher than the global average grade (7.5%, Piercy et al., 2015). The Cu content (0.6%) on the other hand is lower than the global average Cu grade of bimodal-felsic deposits (1.36%). As shown in Figure 9, the sulfur isotope values for sulfides in the Sangkoropi district fall within the overall range of sulfur isotope values for sulfides in VHMS deposits elsewhere in the world. Ranges for individual deposits vary considerably. The narrow ranges displayed by the Sangkaropi and Bilolo deposits with the lower values being close to 0 ‰ have also been observed in a number of other ancient VHMS

deposits. Some examples, in addition to the

ones shown in Figure 10, include Kuroko-type deposits in the Eastern Black Sea Province, Turkey (0-7‰, Upper Cretaceous; Çagatay and Eastoe, 1995), the Tasik Chini district in Peninsular Malaysia (-2.9 to +8.7‰, Permian; Basori et al., 2017), and SW Hokkaido and Kuri Islands, Japan (2-8 ‰. Late Cenozoic; Ishihari and Sasaki, 1994). Several authors have pointed out similarities that exist between the Sangkaropi deposits and Kuroko deposits in Japan including host rock types, mineralization styles and ore assemblages (Yoshida et al., 1982; Nishima et al., 1983; Sunarya et al., 2011; Nur et al., 2016). Significant features of the deposits in the Sangkaropi district in common with Kuroko deposits include: 1) a thin barite layer occurring above the ore zone, 2)

Kuroko (black ore), comprising in decreasing order of abundance sphalerite, galena, barite, chalcopyrite, pyrite, and tetrahedrite, 3) Keiko (siliceous ore), which is a zone of silica replacement of the underlying footwall volcanics with sulfides (mainly pyrite and chalcopyrite) occurring as disseminations, veins and stockwork, and 4) association with bimodal volcanism (e.g Lambert and Sato, 1974). There are differences too. Banded conformable masses of anhydrite-gypsum with pyrite, referred to as Sekkoko, which are a typical feature of Japanese Kuroko deposits, have not been observed in the Sangkaropi district. Furthermore, according to Yoshida et al. (1982) and Nishiyama et al. (1983) Oko (yellow ore), which commonly occurs in the lower part of Kuroko deposits and comprises massive cupriferous pyrite poor in barite and quartz, is absent in the Sangkaropi district. Note though that this contradicts Jurkovic and Zalokar‘s (1990) classification of a part of samples collected from an old ore dump at Sangkaropi as yellow ore (see 2.3). A third difference is the reported presence of pyrrhotite in the Sangkaropi and Bilolo ores (Jurkovic and Zalokar, 1990). This mineral is absent in Kuroko deposits in Japan, except as a contact metamorphic product near the contacts of post-mineralization dykes (Misra, 1999; Shikazono, 2003). Fluid inclusions data obtained from druse quartz in stratiform ore at Sangkaropi suggest ore temperature formations of 280⁰ to 200⁰ C at the seafloor interface, a temperature range that is similar to that of Kuroko deposits in Japan. However, fluid temperatures calculated for sphalerite in stockwork mineralization at Rumangga, viz. 184⁰ - 160⁰C are significantly lower than ore forming

temperatures for Japanese deposits (Yoshida et al., 1982). The lack of boiling features indicates the depth of seawater at the time of ore deposition was greater than 640 m, assuming the maximum temperature was 230° (Yoshida et al., 1982). Maximum seawater depths of 400 m to >1,000 m have been proposed for various Kuroko deposits (Plimer, 1981). Deposits in the Sangkaropi district formed towards the end of a volcanic cycle, a feature they share with many bimodal-felsic deposits in Japan (and elsewhere in the world) (e.g. Allen et al., 2002; Yamada and Yoshida, 2011). However, in these cases the volcanic activity took place mostly in a back-arc setting.

5.6 Geological model

The geological record of the Sangkaropi district starts in the Late Eocene when andesitic volcanics were deposited in a shallow marine basin (Fig.10.a). They formed part of a 1,200 km long magmatic arc along the southeastern margin of Sundaland, that developed over a westerly dipping subduction zone. The volcanic activity took place in an extensional tectonic environment that began to develop in the mid-Eocene and caused the opening of the Makassar Strait further to the West. Towards the end of the Eocene, around 34 Ma, a peak extensional event took place, which resulted in a significant deepening of the basin in the Sangkaropi region (Fig.10.b). It was accompanied by a change in the nature of the volcanic activity from andesitic to bimodal felsic-mafic. Volatile-rich felsic magma

ascended to the surface along extensional faults without significant upper crustal contamination, forming lava (? domes) and associated pyroclastics. Towards the end of the volcanic cycle, ore fluids separated from the residual liquid in the underlying magma chamber and reached the seafloor along the same conduits as the felsic magma. Massive sulfides were deposited at or near the sea floor, while the underlying feeder zones and adjacent rocks underwent intense silicification, accompanied by quartz-sulfide veins and stockworks. A thin barite layer was deposited at the top of the massive sulfide horizon. Ore fluid temperatures may have been unusually high as suggested by the reported presence of pyrrhotite as the earliest sulfide phase. A rapid fall in temperature and pressure is reflected in the abundant presence of inclusions, intimate intergrowth and exsolution textures shown by the sulfides. This was partly due to mixing of the ore fluids with seawater in the footwall rocks and at the sea bottom. Soon after the formation of the VHMS deposits the felsic volcanism ceased, as did subduction. It was locally succeeded by the deposition of alkaline basalts. The mineralized strata were then buried under a sequence of deep marine sediments. In the mid-Miocene an extensional block faulting event took place. The Sangkaropi block was uplifted relative to adjacent blocks and the volcanic-sedimentary strata within the block folded into an anticline with shallowly dipping flanks (Fig.10.c). The extensional tectonic regime prevailed throughout Western Sulawesi and heralded the start of a period of intensive potassic magmatism.

6. Conclusions 1. VHMS mineralization in the Sangkaropi district can be classified as bimodal-felsic. It shows similarities with Kuroko-type deposits in Japan, but also some salient differences. 2. It is associated with a series of felsic and subordinate alkaline basalt volcanics displaying a distinct continental arc geochemical signature, similar to that of underlying Eocene volcanics. 3. The bimodal volcanic activity and mineralization took place around 34 Ma (boundary Eocene-Oligocene) during a period of extension that changed the environment of deposition from shallow to deep marine. 4. Sulfur isotope values from the Sangkaropi and Bilolo deposits show near 0 to + 4.5‰ for sulfide and +20.9 to +23.6 ‰ for barite. Each sulfide-sulfate mineral assemblage show the sulfur isotopic values of barite >> pyrite > sphalerite > chalcopyrite > galena in order, due to the isotopic fractionation.

Acknowledgments This research has been financially supported by Penelitian Dasar from KEMENRISTEKDIKTI (2018-2019). MIT-Research Alliance (MIRA) 2019 Project of Hasanuddin University is also appreciated for some technical support to the first author. Dr. Hinako Sato is thanked for providing sulfur isotope analyses in Akita University. We would like to acknowledge Dr. Hao Yang-Lee from National Taiwan University for zircon preparation. We also thank two anonymous journal

reviewers for their constructive comments and Franco Pirajno for handling the manuscript. Sara Beavis from ANU is highly appreciated for editing the final draft.

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List of Figures Fig. 1 (a) Regional geology of West and East Sulawesi province. (b) Local geology of the Sangkaropi Deposit showing sample sites analysed in this study.

Fig. 2 (a) Outcrop of highly altered dacitic breccia at Sangakropi. (b) Outcrop of rhyolitic tuff showing intensive weathering and alteration　(c) Field occurrence of basalt covering the ore body at Sangkaropi. (d) Bilolo marl outcrop in the Sangkaropi area.

Fig. 3 (a) Field occurrence of mineralization in the Sangkaropi district. Two main mineralization styles are exposed at surface consisting of syngenetic stratiform massive sulfide mineralization in the upper part and epigenetic vein and stockwork mineralization in the lower part. (b) Fragmental ore (pyrite, chalcopyrite and sphalerite) occurs as clast on top of massive ore body at Sangkaropi. (c) Azurite and malachite found in stratiform massive ore layer as products of supergene processes. (d) Dendritic texture of galena. (e) Barite occurs as typical gangue mineral covering ore layer (f) Typical of intensive silisification alteration in Sangkaropi deposit

Fig.4 (a). SiO2 vs K2O diagram of volcanic rocks from Sangkaropi district. Data for volcanic rocks from the Lamasi Complex to the east of the Sangkaropi district (Priadi et al.,1994) are shown for comparison. (b) Th-Co diagram of the Sangkaropi samples. Note the calc-alkaline affinities for most of the samples.

Fig. 5. (a) Primitive mantle- and (b) chondrite-normalized REE patterns (Sun & McDonough, 1989) of samples from the Sangkaropi District. Data for volcanic rocks from the Lamasi Complex (Priadi et al., 1994) are shown for comparison.

Fig. 6. (a) Representative cathodoluminescence (CL) images of zircons from rhyolite sample SKR-RT showing U–Pb analytical spots. (b) Representative cathodoluminescence (CL) images of zircons from tuff sample SKR-TU showing U–Pb analytical spots.

Fig. 7. Laser-ablation inductively coupled mass spectrometry (LA-ICP-MS) data for zircons from rhyolite (SKR-RT) and tuff (SKR-TU), Sangkaropi Deposit. 206Pb/238U

ages plotted along with the weighted mean age (left) and Tera

Wasserburg diagrams with concordia shown. Sigma uncertainties (one), error bars, and error ellipses are shown.

Fig. 8. Various geochemical discrimination diagrams for volcanic rocks from the Sangkaropi area demonstrating these rocks were formed in a continental margin arc setting. Symbols are the same as in Figure 4.

Fig.9. Comparison of sulfur isotope values from the Sangkaropi deposit with other massive sulfide deposits in the world. (Data are from Çagatay and Eastoe, 1995; Ishihari and Sasaki, 1994; Basori et al., 2017).

Fig. 10. Schematic sections showing the geological development of the Sangkaropi District in its regional tectonic setting. Not to scale; certain features exaggerated. a)

Eocene: Western Sulawesi starts to rift away from

Sundaland time resulting in the formation of the Makassar Strait; an andesitic volcanic arc forms over a west dipping subduction zone. b) Eocene-Oligocene boundary: extensional tectonic event accompanied by an abrupt deepening of the marine basin in the Sangkaropi District region, ceasing of subduction and a change to bimodal volcanism; formation of VHMS mineralization during the waning stage of the volcanism. c) Mid-Miocene: mineralization covered by a sequence of deep marine sediments during the Oligocene; basin shallows during the Early Miocene; major tectonic event in the mid Miocene characterized by block faulting and the onset of a major phase of potassic magmatism; block movements cause gently folding of the strata in the Sangkaropi district.

List of Tables Table 1 Major (wt%) and trace elements (ppm) data for the volcanic rocks in the Sangkaropi area. Table 2 Sulfur Isotope ratio of Sangkaropi area Table 3 Sulfur Isotope ratio of Bilolo area Table 4. LA-ICP-MS data and calculated U-Pb zircon ages of rocks from rhyolite and tuff in Sangkaropi Deposit

Sample

SKR-BSLT

SKR-RT

SKR-TU

S. 03. SM

S.06. B

R. 27.B

BHL. 30

Major Element (wt%) SiO2

45.95

85.64

84.75

86.41

80.30

79.51

69.19

TiO2

0.97

0.12

0.11

0.09

0.14

0.12

0.47

Al2O3

15.02

5.81

7.30

3.86

9.80

10.49

12.90

Fe2O3

10.84

3.98

0.95

2.29

1.16

1.65

4.50

MnO

0.17

0.00

0.01

0.01

0.01

0.01

0.10

MgO

6.36

0.22

0.54

0.10

0.73

0.08

3.84

CaO

11.78

0.08

0.11

0.05

0.06

0.19

0.32

Na2O

1.85

0.07

0.01

0.06

0.12

3.81

3.28

K2O

2.70

1.42

1.92

0.85

2.65

2.14

1.07

P2O5

0.55

0.07

0.03

0.01

0.02

0.01

0.10

LOI

3.14

1.95

3.05

2.94

4.08

2.27

4.01

Total

99.29

99.20

98.76

96.66

99.07

100.30

99.77

Sc

45.16

23.77

20.40

1.60

2.50

2.20

10.60

Ti

5998

691

633

140

766

684

1432

V

324.50

15.58

6.14

96.42

9.92

4.56

71.49

Cr

67.74

6.23

5.72

17.66

1.06

1.06

26.12

Mn

1355.00

34.35

91.69

45.11

38.33

48.79

734.00

Co

38.63

0.08

0.67

3.11

2.54

3.11

8.09

Ni

41.12

2.33

2.42

6.67

3.45

4.44

7.39

Cu

114.40

150.20

115.90

2330.06

46.77

15.73

14.09

Zn

75.39

2.96

64.73

12328.11

176.15

16.15

93.28

Ga

17.26

9.12

7.89

9.88

9.00

8.15

8.89

Rb

71.06

33.77

54.57

19.01

60.00

17.99

18.76

Sr

521.50

2.53

5.15

28.11

41.40

113.64

49.29

Y

17.91

12.30

13.79

4.56

23.11

17.09

21.55

Zr

81.33

81.82

83.80

50.06

137.82

84.19

140.27

Nb

4.96

5.46

6.03

6.70

5.23

5.01

5.79

Cs

1.13

0.15

0.17

2.03

0.50

0.46

1.40

Trace element (ppm)

Ba

1060.00

202.30

107.50

2860.20

1320.40

510.46

99.48

Hf

2.39

1.98

2.34

1.40

3.50

2.90

4.60

Ta

0.26

0.37

0.47

0.25

0.41

0.51

0.38

Pb

15.84

26.21

2.51

4870.67

69.09

10.00

4.17

Th

12.42

3.57

4.57

2.80

7.40

6.50

6.40

U

1.98

1.17

1.23

0.57

2.40

2.30

1.77

La

23.82

1.70

10.70

11.70

18.80

12.30

20.00

Ce

47.87

3.82

22.71

23.66

39.80

24.55

43.00

Pr

5.95

0.48

2.68

3.55

2.05

2.11

2.71

Nd

24.34

2.06

9.98

8.00

14.00

7.26

12.54

Sm

4.82

0.64

2.00

0.90

3.10

2.30

4.10

Eu

1.36

0.21

0.46

0.70

1.10

0.86

1.29

Gd

4.09

1.03

1.85

3.12

1.46

2.91

2.88

Tb

0.59

0.21

0.31

0.40

0.23

0.31

0.33

Dy

3.32

1.50

1.99

2.22

1.81

2.99

1.82

Ho

0.66

0.35

0.46

0.16

0.56

0.56

0.35

Er

1.78

1.16

1.42

1.45

1.39

1.48

1.81

Tm

0.25

0.21

0.25

0.23

0.21

0.22

0.23

Yb

1.59

1.44

1.74

0.90

3.20

3.20

3.40

Lu

0.23

0.23

0.27

0.14

0.53

0.53

0.57

120.663

15.01

56.798

57.123

88.233

61.576

95.018

Total REE

No.sample

δ34S (‰)

Mineral

SKR-1 A

+2.0

Galena

SKR-1 A

+3.3

Chalcopyrite

SKR-1 A

+4.0

Pyrite

SKR-2 A

+3.1

Chalcopyrite

SKR-2 A

+3.6

Pyrite

SKR-2 A

+23.5

Barite

SKR-2 B

+0.5

Sphalerite

SKR-2 B

+2.1

Chalcopyrite

SKR-1 C

+4.4

Pyrite

SKR-1 C

+4.2

Sphalerite

SKR-1 C

+4.3

Chalcopyrite

Table 2 Sulfur Isotope ratio of Sangkaropi area

Table 3 Sulfur Isotope ratio of Bilolo area No. Sample

δ34S (‰)

Mineral

BLO-2D

+2.4

Galena

BLO-2D

+2.6

Chalcopyrite

BLO-2C1

+2.2

Galena

BLO-2C1

+2.7

Pyrite

BLO-2C

+0.93

Galena

BLO-2B

-0.50

Chalcopyrite

BLO-2B

+1.9

Galena

BLO-2B

+20.9

Barite

S K R T U

U-Th-Pb ratios

Ages (Ma)

Disco

I

rdan

n

ce

f e

U S

(

p p o p t

m )

T h ( p p m

20

T

7

h

P

/

b

U / 20

)

20

20

7

6

P

P σ /

23

23

5

8

U

U

6

P b

20

8

7

P

P

b

1 b 1 b 1 σ /

20

/

σ

23

r

1 σ

b / 20

2

6

T

P

h

b

20

20

7

6

P

P

1 b 1 b 1 σ /

σ /

23

23

5

8

U

U

r

20

σ

8

<

>

P

1

1

0

0

0

0

0

0

b / 23

1 σ

2

M M

T

a

a

h

1

K R T U -

.

0

2 3 8

.

0 7 5

3

2 3 1

2

5

0

2 S

0

K

.

T U -

. 0 0 5

0 . 0 0 6

0 . 0 0 0

0 . 2 6 6

0 0 .

.

0 9 0 0 9 0

1 1 5

6 5 6 7 2 1

0 . 0 4 7

0 . 0 1 1

0 . 0 0 6

0 . 0 0 0

0 . 0 3 7

0 0 .

.

0 9 0 0 9 0

d A

1 σ

g e ( M )

0 . 0 0 3

0

3

.

5

0

7

0

0

0

.

0 . 0 0 2

1

2 1

6

.

.

0

1

0 5 .

1

2 9 .

0

9

0

R

0

e

a

r S

r

4 6 . 0

5 2

3

7 .

( 5 2

. 0

1 7 1

0

0

0

3

.

6 2

0

2 1

0

.

0

0 0

.

5 . 7

0 . 2

2 5 3 8 2

.

. 0 0

1

3 0

0

5

0

)

3 2

2

7 .

3

. 0 0

9

7

8

3

2

5 8

1

2

3 S

0

K R T U -

.

0

1 1 5

.

8 0 7

0

1 4 5

4

3

8

1 S

1

K T U -

.

0

1 1 3

.

2 5 2

0

0 9 2

4

5

7

2 S

1

K T U -

.

0

1 1 1

.

1 3 0

0

9 2 6

4

9

9

2 S

0

K R T

8 7

U

2 8

1 6 S

0 9

0 0 6

. 0 0 0

0 . 0 3 6

0 0 .

.

0 9 0 0 8 0

0 . 0 0 2

0

2

.

8 7

0

1 9

0

.

0

0 0

.

5 . 6

0 . 2

2 5 3 0 0

.

. 0 0

3 2

0 . 0 1 2

0 . 0 0 6

0 . 0 0 0

0 . 0 3 6

0 0 .

.

0 9 1 0 0 0

0 . 0 0 2

0

3

.

5 5

0

2 0

0

.

0

0 0

.

5 . 7

0 . 2

2 6 2 4 9

.

. 0 0

0 . 0 2 0

0 . 0 0 5

0 . 0 0 0

0 . 0 3 6

0 0 .

.

0 9 1 0 7 0

0 . 0 0 2

0 . 0 0 0

1 5 2 . 0

5 9 4 . 0

5 . 4

0 . 3

2 2 9 . 0

.

0

9

.

4

0

2

4

9

7

0 . 0 2 7

0 . 0 0 6

0 . 0 0 0

0 . 0 3 5

0 0 .

.

0 9 2 0 3 0

0 . 0 0 2

0

8

.

2 3

0

4 6

0

.

0

0 0

.

5 . 6

0 . 4

2 2 5 . 0

0 0 0 0 0 0 0

0 0

3 2

3

. 0

0

0 9

6

8

5

3 2

2

4 .

2

. 0

9

0 9

7

8

7

5 0

6 4

1 0

3 3

6

6 .

.

. 0

0

0

2 1 2 0 9 6 9

3

8

4

1 4

3 4

3

2 .

.

. 0

0

0

4 1 1 0

2

9 .

3

4

-

0

.

0

6

3

R

.

0

5

9

R

0

5 0 2 5

2 1 2 4 5 3 9

8

8

9

3 2 9

8 2 5

K

6 1

.

R

1 7 7

T

.

.

.

.

.

.

.

.

.

6 9

. .

2 3

0 0 0 0 0 0 9

0 0

. 4

6 2 4

2

4 1 0 0 3 0 0

0 0

0

U

2

7 0 5 0 5 8 0

-

2

2

5

.

.

. 0

2 0

0

0

0

1

.

2 6

0

6 9

0

.

0

0 0

1 .

8

4 2 3

. 0

4

0

1 S

1

K R T U -

.

0

2 3 1

.

9 3 3

0

5 4 1

4

5

7

1

0 . 0 0 4

0 . 0 0 5

0 . 0 0 0

0 . 0 3 5

0 0 .

.

0 9 0 0 4 0

0 . 0 0 2

.

5 . 5

0 . 1

2 2 2 5 3

.

. 0 0

3 1

2

. 0

3

0

3

7

2

1 .

9

8

8

8

2 5

S K

0

R

.

T U -

1 0 3

5 5 4 3

1

0 4

0 . 0 4 7

0 . 0 1 7

0 . 0 0 5

0 . 0 0 0

0 . 0 3 5

0 0 .

.

0 9 1 0 4 0

0 . 0 0 2

0

5

.

4 1

0

4 1

0

.

0

0 0

.

5 . 5

0 . 3

2 8 2 8 3

.

. 0 0

3 4

0

K R T U -

.

0

2 1 8

.

2 8 0

0

6 2 8

4

2

7

1

K R T

. 0 0 9

0 . 0 0 5

0 . 0 0 0

0 . 0 3 5

0 0 .

.

0 9 0 0 8 0

0 . 0 0 2

0

2

.

5 8

0

9 0

0

.

0

0 0

.

5 . 4

0 . 2

2 4 2 9 0

.

. 0 0

1 2 8 9 6 1

1

0 0 0 0 0 0 0

0 0

( 3

.

.

.

.

2 0

5

0 0 0 0 0 0 9

0 0

2 1

6

4 1 0 0 3 1 0

0 0

4

.

.

.

.

.

.

.

6 . 2

3

0 9

8

8

0

3 2

2

1 .

2

. 0

0

0

3

5 S

0

2

. 0

8 S

2

9 .

9

7

8

3

0 2 6

3 2

.

5 .

2

. 0 9

0

0

2

2 4

3 0

.

. 0

7

2 2 0

8 8

4 9

6 4

U

6

1 1 6 0 5 0 0

2 0

. 0

-

7

0

2

3

)

0

2 S K R T U 1 4 S K R T U 0 9

0 .

0

1 1 7

.

9 4 1

0

6 0 7

4

1

6

0 . 0 0 7

0 . 0 0 5

0 . 0 0 0

0 . 0 3 5

0 0 .

.

0 9 0 0 6 0

0 . 0 0 2

0 . 0 0 0

( 3 . 0 )

2 2 0 . 0

5 . 5

0 . 2

2 3 1 7 9

.

. 0 0

3 2

.

0

1 1 0

.

4 4 0

0

7 9 8

4

2

6

0 . 0 1 4

0 . 0 3 8

0 . 0 1 3

0 . 0 0 6

0 0 .

.

0 9 0 0 0 0

0 . 0 0 2

0 . 0 0 0

( 1 . 0 )

4 6

3

8

8

.

.

0

0

1 3 . 0

0

R

.

T

5 3 6

U

5 6 5

-

2

1

8

9

0

7

1

3 2

9

.

1 .

3

. 0

. 0

9

0

0

0 . 0 4 8

0 . 0 2 6

0 . 0 4 0

0 . 0 2 4

0 . 0 0 6

0 0 .

.

0 9 0 0 0 0

0 . 0 0 1

0

K

.

0

R

1 1 8

.

T

3 1 5

0

U

5 6 5

4

-

7

6

0

8

0 . 0 1 2

0 . 0 3 7

0 . 0 1 1

0 . 0 0 6

0 0 .

.

0 9 0 0 0 0

0 . 0 0 2

7

2

0 3

1

0 .

9

0

4

0

.

0

0

0 0 1 . 0

4 0 . 0

2 3 . 0

3 2

2 5

9

.

8 .

( 3

. 0

. 0

1 9

0

0

0 S

3

1 3

S 0

1

9

3 2

9

K

1

. 0

6 1

2

4 .

0

( 4

.

1 2

3

0

5 7

7

0

.

.

.

0

0 0

0

)

1 1 . 0

(

4

3

1

)

)

3 1

3 2

8

.

7 .

3

. 0

. 0

8

0

0

1 3 3

9

2

1

7 S K

0

R

.

T

9 6 7

U

7 9 0

-

7

0

2

0 . 0 4 6

0 . 0 1 5

0 . 0 3 5

0 . 0 1 3

0 . 0 0 6

0 0 .

.

0 9 0 0 0 0

0 . 0 0 2

0

5

.

1 3

3

0

4 3

5

0

.

.

.

0

0 0

0

1 3 . 0

3 1

3 3

5

.

8 .

3

. 0

. 0

5

0

0 6

4

0

S

0

K R T U -

.

0

1 1 9

.

3 2 5

0

5 8 1

4

7

7

0 S

U -

.

0

2 1 7

.

0 4 1

0

4 7 7

4

1

6

1 S

U -

4

3 5

0 1 2

. 0 0 5

0 0 .

.

0 9 0 0 0 0

0 . 0 0 1

0

4

.

5 8

3

0

8 7

5

0

.

.

.

0

0 0

0

1 2 . 0

0 . 0 0 7

0 . 0 3 5

0 . 0 0 6

0 . 0 0 5

0 0 .

.

0 9 0 0 0 0

0 . 0 0 2

.

0

2 1 8

.

0 7 4

0

1 0 8

4

6

6

1

0 . 0 0 7

0 . 0 3 4

0 . 0 0 6

0 . 0 0 5

0 0 .

.

0 9 0 0 0 0

0 . 0 0 1

2 2

5

.

9 .

3

. 0

. 0

( 5

0

0

6 )

0

2

.

1 7

3 6 3 1

3 2

0

6 6

4 .

5

.

3 .

3

0

.

. 0

. 0

. 0

5

0

0 0

0

0

0

.

4

0

( 2

.

1 5

3 6 3 1

3 1

0

5 5

4 .

5

.

0 .

3

0

.

. 0

. 0

. 0

5

0

0 0

0

0

0

.

)

4 3

1 2 1

0 0 0 0 0 0 0

0 0

9 4

3 1 3 2

3 2 (

( 3

K

6 4

.

.

6 8

5 2 4

3 .

1 4

.

.

.

.

.

.

1

1 3

.

1

5

S

.

2

6

4

2

0

3 2

3

0

K T

1

0

.

0

6

1

R

0

.

0

0

0

K T

.

0

5

5

R

0

1

.

3

2

R

6 1 4

0 0 0 0 0 0 9

0 0

. 3

. .

T

5

4 1 3 1 0 0 0

0 0

0

0 0 0

U

4

8 4 5 2 5 0 0

2 0

0

-

8

0

2

0

5

.

6 0

3

0

4 8

4

0

.

.

.

0

0 0

0

.

. 0

. 0 )

8

0

2 )

3 S K

0

R

.

0

T

1 1 6

.

U

6 1 9

0

-

6 6 7

4

0

5

7

5

2

0 . 0 1 5

0 . 0 3 4

0 . 0 1 2

0 . 0 0 5

0 0 .

.

0 9 0 0 0 0

0 . 0 0 2

1 2 . 0

3 2

3 3

4

.

2 .

3

. 0

. 0

4

0

0

0

S

1

K T U -

.

0

3 5 4

.

9 9 9

0

4 1 7

4

6

7

0 S

1

K T U -

7 3 1

1 0 0 5

0

K R T

. 0 0 3

0 . 0 3 4

0 . 0 0 3

0 . 0 0 5

0 0 .

.

0 9 0 0 0 0

0 . 0 0 2

.

0

3

.

7

0

6

4

1

8

0 . 0 0 2

0 . 0 3 4

0 . 0 0 2

0 . 0 0 5

0 0 .

.

0 9 0 0 0 0

0 . 0 0 2

3 3 9 6 3 7

)

0

1

.

4 5

3 3 3 0

3 1

3

0

7 6

4 .

3

.

0 .

3

0

.

. 0

. 8

. 0

0

0 0

0

6

0

.

0 .

9

0

9

0

.

0

0

8 4 . 0

(

.

(

4 6

1

0

)

)

3 2 3 0

3 1

3

4 .

3

.

3 .

( 3

. 0

. 8

. 0

1

0

5

0

8

2 S

0

1

6

R

8 8

R

R

(

2

.

(

9 5

1

6

)

)

0

0 0 0 0 0 0 0

0 0

( 2

3 6 3 1

3 2

.

.

.

.

1 5

2 .

3

.

5 .

1 3

9

0 0 0 0 0 0 9

0 0

4 0

. 0

. 0

. 0

4 3

3

4 0 3 0 0 0 0

0 0

.

0

0

0

.

.

.

.

.

.

.

3

2

0 . 8

0 . 8

1

U

4

-

2

0

9

6 7 3 6 5 0 0

2 0

0 0 )

8 S

0

K R T U -

.

0

2 1 7

.

0 5 4

0

9 5 3

7

3

3

0

0 . 0 1 3

0 . 0 4 8

0 . 0 1 1

0 . 0 0 5

0 0 .

.

0 9 0 0 0 0

0 . 0 0 2

0

1 4

.

0 0

4

0

1 6

7

0

6

.

.

0

. 0

0

0 . 0

3 1

4 3

(

1

1 .

3 3

. 0

. 0 (

1 1

0

0

5

7

2

7

)

)

.

0

4

1

1

1

S K R R T U-Th-Pb ratios

Ages (Ma)

Disco

I

rdan

n

ce

f e

U S

(

p p o p t

m )

T h ( p p m )

20

T

7

h

P

/

b

U / 20 6

P b

20

20

7

6

P

P σ /

23

23

5

8

U

U

20

8

7

P

P

b

1 b 1 b 1 σ /

20

/

σ

23

r r

1 σ

b / 20

2

6

T

P

h

b

20

20

7

6

P

P

1 b 1 b 1 σ /

σ /

23

23

5

8

U

U

r

20

σ

8

<

>

P

1

1

0

0

0

0

0

0

b / 23

1 σ

2

M M

T

a

h

a

r e d A g e ( M a )

1 σ

S

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Geological model of Sangkaropi Deposit, South Sulawesi

Geochemistry and Geochronology of VHMS mineralization in the Sangkaropi　district, central-West Sulawesi, Indonesia: Constraints on its tectono-magmatic setting.

Highlight

- Syngenetic and epigenetic VHMS mineralization is hosted by felsic volcanics that occur in bimodal association with alkaline basalt.

- The volcanic suite shows geochemical signatures typical of continental margin arc volcanics.

- The bimodal volcanism and associated mineralization took place around 34 Ma in a rift environment following a period of andesitic volcanic activity.

-Sulphur isotopes indicate contribution to the mineralization from both magma and seawater.