Formation of epizonal gold mineralization within the Latimojong Metamorphic Complex, Sulawesi, Indonesia: Evidence from mineralogy, fluid inclusions and Raman spectroscopy

Hakim, Andy Yahya Al; Melcher, Frank; Prochaska, Walter; Bakker, Ronald J.; Rantitsch, Gerd

doi:10.1016/j.oregeorev.2018.05.001

Cited by 11 publications

(6 citation statements)

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“…Aside from these relatively young rocks in the magmatic arc, the Cretaceous accretionary complexes also have potential for gold mineralization, as indicated by recent discoveries of gold prospects and deposits in eastern Indonesia (e.g., Idrus et al, 2017). Discoveries of gold mineralization hosted in the Cretaceous metamorphic terrains such as the Awak Mas gold deposits in South Sulawesi (Ernowo et al, 2019; Hakim et al, 2018; Tuakia et al, 2018), the Bulu gold prospect in Maluku, and the Bombana gold prospect in Southeast Sulawesi (Idrus et al, 2017) have shown that the metamorphic terrains represent an alternative for gold exploration in Indonesia.…”

Section: Introductionmentioning

confidence: 99%

Primary source of placer gold in the Luk Ulo Metamorphic Complex, Central Java, Indonesia

et al. 2022

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The Luk Ulo Metamorphic Complex, Central Java is a product of the Cretaceous subduction and accretion, and includes diverse types of protoliths. Two‐types of primary mineralization have been recognized in this area, namely, (1) seafloor basalt‐hosted massive sulfide mineralization and (2) low‐grade metamorphic rocks‐hosted vein type mineralization. Later erosion of these types of primary mineralization formed placer gold deposits along rivers. However, the source has never been identified. Thus, this study aims at understanding the source of placer gold, the characteristics of the primary mineralization, and the tectonic evolution of the study area on the basis of mineralogy, mineral chemistry, whole‐rock geochemistry, and sulfur isotope analyses. Volcanogenic massive sulfide (VMS)‐type mineralization was identified in the seafloor basalt and few deep‐sea sedimentary rocks, and both the ores and host rocks preserved pre‐metamorphic textures and minerals. The characteristics of this VMS‐type mineralization include (1) crustiform quartz veins with pyrite cutting the host rocks, (2) zonation of local silicification to interlayered chlorite/smectite‐chlorite‐laumontite‐calcite‐epidote alteration from central to outer zone, (3) pyrite‐dominated ores with minor amounts of arsenian pyrite, chalcopyrite, and marcasite, (4) unmetamorphosed host rocks and ores, and (5) sulfur isotope signature with a median δ34S of +3.1‰ suggesting sulfur derived from magmatic source and/or sulfur extracted from basaltic rocks with a small contribution of biogenic sulfur. On the other hand, low‐grade metamorphic rocks‐hosted vein type mineralization was identified as orogenic‐type gold mineralization, and the mineralized veins formed after the peak of metamorphism. It is characterized by (1) pyrite‐arsenian pyrite ores with minor amounts of arsenopyrite, galena, tetrahedrite, chalcopyrite, and sphalerite, (2) quartz‐illite‐graphite alteration assemblage, (3) mineralized veins cross‐cutting the foliation of metamorphic host rocks, (4) high antimony contents of pyrite (up to 1.7 wt%) and rutile (up to 160 ppm), (5) relatively high ore‐forming temperature (423 ± 9°C, calculated from arsenopyrite and graphite geothermometers), and (6) remobilized‐sedimentary sulfur signature of the ores with a median δ34S of −9.8‰. Several lines of evidence suggest that placer gold was likely derived from the erosion of orogenic‐type gold ores in the surrounding areas. This evidence includes the presence of gold‐bearing ores hosted by low‐grade metapelites and metagranitoid with characteristics of orogenic‐type gold mineralization, whereas the VMS‐type ores are barren in gold. The occurrence of the mid‐oceanic ridge‐ and accretion zone‐related mineralization in this area reflects the subduction and amalgamation of oceanic and continental crustal blocks during the Cretaceous period. Discovery of gold mineralization hosted in the Cretaceous basement rocks of the Sunda arc indicates the importance to broaden the gold exploration targets to include not on...

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Section: Introductionmentioning

confidence: 99%

Primary source of placer gold in the Luk Ulo Metamorphic Complex, Central Java, Indonesia

et al. 2022

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“…The Awak Mas gold deposit is situated in the southern arm of the Western Sulawesi Province, where both metamorphic basement units and arc-related igneous units prevail (Figure 1b). The Latimojong Formation is underlaid by phyllites, slates, basic to intermediate volcanics, limestones, and schists, representing a platform and/or fore arc trough flysch sequence intruded by granite, diorite, monzonite, and/or syenite plugs and stocks [16][17][18][19][20][21][22]. The other lithological formation in this area is the Lamasi Complex, composed of mafic to intermediate rocks.…”

Section: Introductionmentioning

confidence: 99%

Elemental Gains and Losses during Hydrothermal Alteration in Awak Mas Gold Deposit, Sulawesi Island, Indonesia: Constraints from Balanced Mineral Reactions

Ernowo¹,

Idrus

Meyer

2022

Minerals

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Hydrothermal gold mineralization is commonly associated with metasomatic processes resulting from interaction of hostrock with infiltrating hot aqueous fluids. Understanding of the alteration mechanism requires quantification of element changes in altered rock, relative to the unaltered or least-altered rock, representing the protolith. Balanced mineral reactions are used to gain quantitative insight into the alteration process associated with gold mineralization at the Awak Mas deposit. Three representative samples were carefully selected from the least-altered pyllite and the two alteration zones bordering the mineralization. Mineral mode, textural features, and mineral compositions were studied by microscopy and electron microprobe analyzer (EMPA). Quantitative modal analysis was performed with a Quanta 650 F QEMSCAN® system. The hydrothermal alteration sequence around the mineralization starts with the proximal albite–ankerite–pyrite alteration zone via the distal albite–chlorite alteration zone to the least-altered phyllite wall-rock. Balanced mineral reaction calculations were performed to evaluate elemental gains and losses. Most noticeable is the addition of Si, Na and Ca to each alteration zone. This alteration is represented by the almost complete replacement of muscovite by albite. The addition of Fe and S was highest in the albite–ankerite–pyrite alteration zone. Alteration of the least altered phyllite to the albite–chlorite zone involved a mass increase of 14.5% and a neglectable volume increase of 0.6%. The mass and a volume increase from the least altered phyllite to the albite–ankerite–pyrite zone was 40.5% and 0.47%, respectively. The very low volume change during alteration is also corroborated by the textural preservation indicating isovolumetric metasomatic reactions. The replacement of muscovite by albite may have had an important effect on the change of the rock failure mode from ductile to brittle, with consequences for the focusing of fluid flow.

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“…Previous studies suggest that these deposits vary by the type of mineralization. The Au mineralization in Palopo was suggested to be related to granitic intrusion (Van Leeuwen & Pieters, ), Poboya is a low‐sulfidation epithermal gold deposit (Wajdi et al, ), and Awak Mas was previously classified as mesothermal or orogenic‐type ( i.e ., Querubin & Walters, ; Idrus et al, ; Harjanto et al, ; Hakim et al, ).…”

Section: Introductionmentioning

confidence: 99%

“…). Available literature in the area focused on the Awak Mas prospect (Querubin & Walters, ; Idrus et al, ; Harjanto et al, ; Hakim et al, ), with few studies covering the Salu Bulo prospect (Hakim et al, ). The latter has an estimated resource of 5.6 million tons at 2.2 g/t Au, with an additional 0.5 million tons of inferred resource at 1.1 g/t Au.…”

Section: Introductionmentioning

confidence: 99%

“…The four domains in the Salu Bulo prospect (Biwa, Lelating, Bandoli and Freddie) have been explored by Placer Dome Inc. in 1999 and One Asia Resource Ltd. in 2011–2013 through 132 drilled holes with average length of 100 m. Recent study by Hakim et al . () concluded that the ore‐forming fluid of the Awak Mas project was metamorphic in origin, and it migrated during retrograde metamorphism of the host rocks. This study aims to further contribute to the understanding of the Salu Bulo prospect in terms of the source and precipitation of the ore‐forming fluids.…”

Section: Introductionmentioning

confidence: 99%

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Geological and Geochemical Characteristics of Gold Mineralization in the Salu Bulo Prospect, Sulawesi, Indonesia

2018

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The Salu Bulo prospect is one of the gold prospects in the Awak Mas project in the central part of the western province, Sulawesi, Indonesia. The gold mineralization is hosted by the meta-sedimentary rocks intercalated with the meta-volcanic and volcaniclastic rocks of the Latimojong Metamorphic Complex. The ores are approximately three meters thick, consisting of veins, stockwork, and breccias. The veins can be classified into three stages, namely, early, main, and late stages, and gold mineralization is related to the main stage. The mineral assemblage of the matrix of breccia and the veins are both composed of quartz, carbonate (mainly ankerite), and albite. High-grade gold ores in the Salu Bulo prospect are accompanied by intense alteration, such as carbonatization, albitization, silicification, and sulfidation along the main stage veins and breccia. Alteration mineral assemblage includes ankerite AE calcite, quartz, albite, and pyrite along with minor sericite. Pyrite is the most abundant sulfide mineral that is spatially related to native gold and electrum (<2-42 μm in size). It is more abundant as dissemination in the altered host rocks than those in veins. This suggests that water-rock interaction played a role to precipitate pyrite and Au in the Salu Bulo prospect. The Au contents of intensely altered host rocks and ores have positive correlations with Ag, Ni, Mo, and Na. Fluid inclusions in the veins of the main stage and the matrix of breccia are mainly two-phase liquid-rich inclusions with minor two-phase, vapor-rich, and single-phase liquid or vapor inclusions. CO 2 and N 2 gases are detected in the fluid inclusions by Laser Raman microspectrometry. Fluid boiling probably occurred when the fluid was trapped at approximately 120-190 m below the paleo water table. δ 18 O SMOW values of fluid, +5.8 and +7.6‰, calculated from δ 18 O SMOW of quartz from the main stage vein indicate oxygen isotopic exchange with wall rocks during deep circulation. δ 34 S CDT of pyrite narrowly ranges from −2.0 to +3.4‰, suggesting a single source of sulfur. Gold mineralization in the Salu Bulo prospect occurred in an epithermal condition, after the metamorphism of the host rocks. It formed at a relatively shallow depth from fluids with low to moderate salinity (3.0-8.5 wt% NaCl equiv.). The temperature and pressure of ore formation range from 190 to 210 C and 1.2 to 1.9 MPa, respectively.

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Formation of epizonal gold mineralization within the Latimojong Metamorphic Complex, Sulawesi, Indonesia: Evidence from mineralogy, fluid inclusions and Raman spectroscopy

Cited by 11 publications

References 64 publications

Primary source of placer gold in the Luk Ulo Metamorphic Complex, Central Java, Indonesia

Primary source of placer gold in the Luk Ulo Metamorphic Complex, Central Java, Indonesia

Elemental Gains and Losses during Hydrothermal Alteration in Awak Mas Gold Deposit, Sulawesi Island, Indonesia: Constraints from Balanced Mineral Reactions

Geological and Geochemical Characteristics of Gold Mineralization in the Salu Bulo Prospect, Sulawesi, Indonesia

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