Mining Intelligence and News

Sihayo Project

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Mine TypeOpen Pit
  • Gold
Mining Method
  • Truck & Shovel / Loader
Mine Life... Lock


PT Aneka Tambang (Antam) 25 % Indirect
Sihayo Gold Ltd. 75 % Indirect
PT Sorikmas Mining (PTSM) (operator) 100 % Direct
The Sihayo Gold Project (the Project) is within the Sihayo-Pungkut 7th Generation Contract of Work (COW) held by PT Sorikmas Mining (PTSM). PTSM is an Indonesian foreign investment company operated under a joint venture agreement between the Company (75%) and PT Aneka Tambang Tbk (Antam) (25%).

Deposit type

  • Sedimentary - Volcanogenic
  • Sediment-hosted
  • Epithermal
  • Porphyry


The Sihayo gold belt, which hosts the Sihayo and Sambung gold resources, is a 15 km long NW-SW trending corridor of Permian calcareous volcano-sedimentary rocks and associated intrusions. These rocks are highly prospective for sediment-hosted gold, epithermal gold-silver veins, and porphyry-related gold and copper mineralisation. The Sihayo gold belt is located on fault strands from the western margin of the dextral transtensional jog in the TSFZ. The bulk of the gold resources at Sihayo and Sambung is hosted by a NW-SW striking, moderately NE-dipping package of Permian shallow marine fossiliferous limestones. The gold is generally submicron size and, unless weathered (oxidised), it is locked in disseminated fine-grained arsenian pyrite mineralisation in multiple stratabound replacement-style jasperoid lenses and discordant bodies within the karstified, hydrobrecciated and tectonised host rocks. The resources are classified as sediment-hosted gold (SHG) deposits.

The mineralised Permian limestones and volcaniclastic rocks are disconformably overlain by Tertiary siliciclastic sandstones and carbonaceous mudstones. Uplift and erosion have removed most of the caprock at Sambung, but about 70% of Sihayo is covered by Tertiary caprock, which is up to 150 m thick or more on the eastern side of the resource. Diorite intrudes the Permian rock package in dykes, sills and laccolith, and some of these intrusions extend across the disconformity into the Tertiary caprocks.

Karstification features are well-developed within the Permian limestones. The karst cavities commonly contain cave-fill sediments showing a large range of facies and sedimentary structures including finely laminated oxidised and carbonaceous muddy-silty sediments with dropstones, graded bedded sandy-gritty sediments, poorly-sorted matrix-supported polymictic breccias and fragment-supported monomictic shingle breccias. The cave-fill sediments are unconsolidated or show varying degrees of lithification caused by hydrothermal alteration and mineralisation. Breccia clasts and dropstones, including mixed carbonate and siliciclastic rock types, also show varying degrees of alteration and intra-clast veining.

An unconsolidated bouldery clay regolith (eluvial-colluvial overburden) overlies parts of the Sihayo and Sambung gold resources. This is locally mineralised with variably oxidised jasperoid boulders and detrital gold in the gritty clay matrix. The latter has been extensively worked by artisanal miners to about 5 m average depth over the Sambung resource area. The thickness of the regolith varies dramatically where influenced by the occurrence of sinkholes and other irregularities on the underlying karstified bedrock.



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CommodityUnitsAvg. AnnualLOM
Gold koz 80635
All production numbers are expressed as metal in doré.

Operational metrics

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* According to 2020 study.

Production Costs

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All-in sustaining costs (AISC) Gold USD  ....  Subscribe
Assumed price Gold USD  ....  Subscribe
* According to 2020 study / presentation.

Operating Costs

OP mining costs ($/t mined) USD 2.12 *  
OP mining costs ($/t milled) USD  ....  Subscribe
Total operating costs ($/t milled) USD  ....  Subscribe
* According to 2020 study.

Project Costs

MetricsUnitsLOM Total
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After-tax NPV @ 8% $M USD  ......  Subscribe
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Mine Management

Job TitleNameProfileRef. Date
....................... Subscription required ....................... Subscription required Subscription required Dec 24, 2023
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