The joint venture the Sihayo Gold Limited owned a 75% interest in PT Sorikmas Mining which in turn holds the Sihayo-Pungkut 7th Generation Contract of Work (“CoW”). PT Aneka Tambang Tbk is the Company’s joint venture partner in the CoW with a 25% interest.
As of 5 August, 2024, Provident Aurum has a relevant interest in more than 90% of the ordinary shares in Sihayo Gold, and it has acquired more than 75% of the ordinary shares in Sihayo that it offered to acquire under the Offer. Provident Aurum will acquire the remaining shares in Sihayo in which it does not have a relevant interest, under the compulsory acquisition provisions of the Corporations Act 2001 (Cth) (Corporations Act).
Sihayo Gold Limited removed from the Official List 14 August 2024 under Listing Rule 17.14, following compulsory acquisition of its remaining securities by Provident Aurum Pte. Ltd.
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Summary:
Sihayo is a replacement-style sediment-hosted gold deposit.
The additional drilling tested for extension to the gold mineralisation between 200-350 m depth below the southern end of the planned pit. Drilling results have extended the highgrade gold mineralisation by 200-250 m down its open and moderate SE-plunge projection, increasing the below-pit gold resource.
The additional below-pit resource is primary sulphide-refractory gold mineralisation where gold occurs as sub-micron-size inclusions in the arsenic-rich rims of fine-grained pyrite disseminated through clay-sulphide and jasperoidal silica altered sediments filling karstcaves within Permian limestones. The limestones are interbedded with volcaniclastic rocks, unconformably overlain by Tertiary quartz sandstones and mudstones, and intruded by diorite sills and laccolith.
The mineralised cave-fill sediments are mainly breccias composed of varying proportions of polymicitc clasts (limestone, diorite, quartz sandstone-siltstone and mudstone) supported by massive to crudely stratified silt-sand matrix. They are best developed within the limestone along the unconformity-contact with the overlying Tertiary rocks, and along or near the contacts of the diorite laccolith intrusion.
Higher-grade gold mineralisation at Sihayo is associated with stronger developed sulphide mineralisation, highly elevated arsenic, antimony and thallium geochemistry, and textural evidence for multiple stages of brecciation and jasperoid development within the cave-fill sediments.
The mineral tenement is a 7th Generation Contract of Work (CoW) is located at the western end of the 7,000 km long Sunda-Banda magmatic arc. Sumatra lies on the south- western margin of the Sundaland promontory at the edge of the Eurasian plate. The promontory basement is composed of accreted and fault-transposed continental plate and magmatic arc terranes that were derived from Gondwana during the Late Palaeozoic and Mesozoic.
The CoW straddles a NW-SE trending collisional boundary separating two basement segments: namely the Late Palaeozoic West Sumatra terrane (eastern segment) and Mesozoic Woyla terrane (western segment). The West Sumatra segment is composed of intermediate-felsic volcano-sedimentary rocks and associated shallow marine carbonate rocks. The Woyla segment is an accretionary complex composed of deep to shallow marine sedimentary rocks and associated mafic volcanic rocks. The collisional contact between these two terranes, referred to as the Medial Sumatra Tectonic Line, is stitched by Mesozoic granitic intrusions. Extension on these basement rocks during the early Palaeogene produced local rift basins that were filled by fluvio-lacustrine, coalbearing siliciclastic- volcano-sedimentary rocks. These rocks have been uplifted, structurally inverted and partly eroded by the development and formation of the Trans Sumatran Fault Zone (TSFZ), commencing in the Miocene. The evolution of the TSFZ was accompanied by Palaeogene magmatism (diorite/andesite – tonalite/dacite intrusions and volcanics) and associated hydrothermal activity and mineralisation within the CoW and surrounding region. Younger volcanic tephras erupted from nearby Quaternary volcanoes (eg Sorikmarapi, Toba) mantle the landscape in parts of the CoW.
Sihayo Gold Belt
The Sihayo Gold Belt straddles the Angkola fault segment and associated fault strands (western margin) of the Barumun -Angkola dextral transtensional jog in the NW -SE trending TSFZ and is immediately adjacent to a major dilatational pull -apart basin (Panyabungan Graben: approximately 100 km long, 12 km wide and 1 km deep) that is controlled by the TSFZ. The TSFZ and associated deep seated dilatational structures that control the pull -apart basin are interpreted to be major structural controls on the alignment and evolution of Tertiary magmatism and mineralisation within the CoW.
The Sihayo Gold Belt is one of three parallel/near -parallel prospect -aligned mineral belts recognised across the CoW area. It is a +15 km long NW -SW trending corridor of Permian calcareous volcano -sedimentary rocks, Tertiary siliciclastic -volcaniclastic rocks and associated intrusions. These rocks are highly prospective for replacement -style carbonate -hosted gold, epithermal gold -silver veins, polymetallic skarn and porphyry -related gold and copper mineralisation. It is host to the Sihayo -Sambung gold resources and near -mine prospects of Sihayo -2, -3, -4, -5, Bandar Lasiak, Sihayo -Sambung Link Zone, Hutabargot Julu and Dolok.
Sihayo – Sambung gold deposits
Sihayo and Sambung resources are located about 800m apart but are interpreted to occur at about the same stratigraphic position and on the same controlling regional fault structures.
Primary gold mineralisation is hosted in stacked stratabound lenses of hydrothermally altered (‘jasperoid’ or sulphidic microcrystalline silicification and argillic/clay -sulphide alteration), microbrecciated silty -sandy (“dirty”) limestone and calcareous carbonaceous mudstone -siltstone, and in pods of similarly altered cavity -fill sediments within karstified fossiliferous limestone/marble. These rocks occur at the top of a Permian mixed carbonate -clastic volcano -sedimentary rock unit that has been openly folded and strongly faulted. The Permian rock unit is unconformably overlain by a package of Tertiary fluvio -lacustrine carbonaceous siliciclastic sedimentary “cap” rocks (sandstone, siltstone, mudstone, lignite, conglomerate, and agglomerate) that are sometimes mineralised at the basal unconformity with the underlying Permian rock unit. Diorite intrusions as dykes, sills and laccolith are locally spatially associated with mineralised jasperoid lenses.
A steeply dipping discordant jasperoid body (feeder structure) is apparent within the Sambung deposit. Similar large mineralised discordant jasperoid bodies (feeder structures) are predicted to occur below Sihayo.
Sihayo and Sambung are stratabound carbonate -hosted gold deposits or more broadly categorised as Sedimentary Rock Hosted Disseminated Gold Deposit type (SRHGD). Northwest to northerly striking vertical faults controlled by TSFZ dextral movement and associated northeast to easterly striking cross -faults were probably conduits for mineralising hydrothermal fluids from depth. Where vertical structures have met favourable sub horizontal to moderately northeast -dipping lithological contacts, and likely the meteoric fluid interface, hydrothermal fluids have migrated laterally depositing gold mineralisation.
Favourable lithological contacts for the development of gold -bearing jasperoid at Sihayo and Sambung are rheologically different stratigraphic units, most notably: i) on the unconformity/contact between Permian calcareous rocks and Tertiary carbonaceous argillaceous rocks, ii) between silty -sandy (“dirty”) limestone and fossiliferous limestone/marble or volcaniclastic rocks within the Permian stratigraphy; iii) within Permian calcareous rocks near diorite intrusion contacts.
The subordinate regolith -hosted (eluvium/colluvium) mineralisation occurs on the present land surface and is associated with Quaternary residual weathering and erosion of the primary mineralisation.
Dimensions
The updated Sihayo resource (to include the deep drilling) extends laterally NNW-SSE~2530m and extends from surface (highest point at or near ~1260mRL to a maximum depth at or near ~890mRL for a total of ~370m below surface.