The Tujuh Bukit Copper Project is an underground copper-gold porphyry deposit. It is being developed in the East Java Province, Indonesia.
The project is 100% owned by PT Merdeka Copper Gold, a public company established in 2012 by shareholders including PT Saratoga Investama Sedaya Tbk, PT Provident Capital Indonesia (through PT Mitra Daya Mustika and PT Suwarna Arta Mandiri), and Garibaldi Thohir.
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Being one of the largest pre-production copper projects in the world, Tujuh Bukit Copper consists of a Sub-Level Cave (SLC) mine and the larger Block Cave (BC) mine.
The SLC mine has an estimated life of eight years and a production rate of four million tonnes per annum (4Mtpa).
The BC mine has a mine life of 22 years. The lift one of BC will produce 368.8Mt of material containing copper and gold at gradings of 0.53% and 0.60g/t respectively.
Merdeka completed a scoping study on the project in October 2022. The owner has invested $200m since 2018 on detailed feasibility work for the project including a 1,890m exploration decline and May 2023 Pre-Feasibility Study (PFS).
The PFS supported the start of construction of the SLC mine in 2024 with staged construction of the processing plant modules.
The production from the staged expansion of the SLC mine from four Mtpa to 24Mtpa will peak at 112 kilo tonnes per annum (ktpa) to 366 kilo ounces per annum (kozpa) of contained copper and gold in concentrate.
The project will produce first concentrate in 2026. As per the PFS, the project will have an initial mine life of 30 years. For both mines, the maximum funding required in $1.1bn.
Merdeka is expanding the layouts of the SLC and BC mines to include indicated resources to the resource estimate. The ongoing study work is expected to be completed in the second half of 2024.
The company is also drilling and assessing near surface porphyry copper targets which could add increased production over the initial SLC operations. The exploration targets are Candrian, Katak, and Gua Macan porphyrites.
The other prospects with copper potential are Pit C copper (Supergene), Lompongan, and Salakan North respectively.
The maiden resource estimates for the Katak and Candrian porphyrites will be delivered in early 2025 after the planned drilling.
Tujuh Bukit Copper Project Location
Tujuh Bukit Copper is located beneath the Tujuh Bukit Gold Mine surface.
The project is approximately 205km southeast of Surabaya, the capital of the East Java Province, and 60km southwest of Banyuwangi regional centre in Sumberagung Village, Pesanggaran District, Banyuwangi Regency.
Through its wholly owned subsidiary PT Bumi Suksesindo (PT BSI), Merdeka owns the Mining Business Licence (IUP) for the operation and production of the Tujuh Bukit Project. The permit covers 4,998 hectares (ha) of area.
The permit is valid for 20 years initially and extendable by two different 10-year options.
PT Damai Suksesindo, a wholly owned subsidiary of PTI BSI, owns the adjoining IUP Exploration covering 6,623.45 ha of area.
The project would be accessible by reaching Banyuwangi via flights. From here, the project can be reached via sealed public roads (approximately 60km).
Geology and Mineralisation
The Tujuh Bukit porphyry deposit is a deep-seated deposit formed within a 2,500m extensional northwest to southeast divergent strike slip fault regime.
The deposit was formed during the southern Java volcanism of the Old Andesite Formation in lower Miocene to lower Pliocene.
The deposit consists of two mineralisation styles: the gold-copper high sulphidation epithermal mineralisation and the copper-gold-molybdenum porphyry mineralisation.
The gold-copper high sulphidation epithermal mineralisation is spread along structural features and accumulated in the lithological contact.
The doughnut-like copper-gold-molybdenum porphyry mineralisation is found at the deeper level and surrounds young tonalite, old tonalite, diorite, and volcano-sedimentary host rocks (pre-porphyry and porphyry).
Mineral Resource and Reserve Estimates
At a 0.2% copper cut off, the indicated mineral resource estimate of the project is 755.1Mt containing 4.50Mt of copper at a grading of 0.60% and 16.1 million ounces (Moz) of gold at a grading of 0.66g/t.
The inferred mineral resources of the project are 982.4Mt containing 3.68Mt of copper at a grading of 0.37% and 11.8Moz of gold at a grading of 0.37g/t.
The total (Indicated + inferred) mineral resources of Tujuh Bukit Copper are 1,737.5Mt containing 8.17Mt of copper at a grading of 0.47% and 27.9Moz of gold at a grading of 0.50g/t.
The probable mineral reserves of the Tujuh Bukit Copper Project are 289.3Mt containing 1.61Mt of copper at a grading of 0.56% and 6.66Moz of gold at a grading of 0.65g/t.
Mining Methods
The SLC mine will use a top-down mining method for extracting ores. The mine will be constrained from 4,750 to 4,900m RL in the orebody.
As recommended by WSP Golder, seven SLC levels were designed at 25m intervals along with 21m horizontal production drift spacings.
For the BC mine, a staged concentrator strategy has been engineered. As the production from BC expands, additional two 10Mtpa modules will be installed in the concentrator.
The extraction level of 4,508m RL has been selected after geomechanical considerations and Footprint Finder. Both mines will be developed separately.
Processing of Ore
The ores will be processed in the copper-gold concentrator. Detailed evaluation and metallurgical testing are progressing on the Albion, SXEW, and CIL circuits to produce copper cathode and gold doré onsite.
Phase 1 will include a 4Mtpa copper-gold concentrator consisting of a griding, a rougher, and a cleaner flotation circuit. Phase 1 processing period will be from 2026 to 2031.
In phase 2, the concentrator will be expanded with the construction of a 10Mtpa processing stream, totalling to 14Mtpa (phase 1 + 10Mtpa) capacity.
The concentrator will be expanded further in phase 3 by the installation of an additional 10Mtpa processing stream (24Mtpa total) and a pyrite flotation circuit to produce a pyrite concentrate filter cake product.
The third phase will operate from 2034 to the Life of Mine (LOM).
The material will undergo processing in a SAB mill followed by copper rougher flotation, concentrate regrinding, and two-stage cleaning.
The cleaned material will be thickened and filtered to produce a copper concentrate.
Phase 1 will produce copper concentrate at 31kt average contained copper and 87koz average contained gold.
Phase 2 will process ores from 2031 to 2034 and produce copper concentrate averaging 85kt of contained copper with 265koz of contained gold.
Copper concentrate peaking at 112kt of contained copper, 267koz of contained gold, and pyrite concentrate averaging 2.2Mt containing 74koz of contained gold will be produced from the third phase.
Tujuh Bukit Copper Project Infrastructure
The project leverages the existing infrastructure of the Tujuh Bukit Gold Mine.
The key infrastructural facilities include a processing plant, material handling facilities, power supply, surface and underground mining infrastructure, a tailings management facility, and port infrastructure.
The port facilities comprise a dual lane access road, loading and discharged containers, and terminals.
Tujuh Bukit Copper will receive power from PLN, the national power supplier of Indonesia. The transmission line will be constructed and will connect the Genteng Power Station and the project site substation.
Merdeka and PLN signed a Memorandum of Understanding (MoU) in September 2021 to supply 260MVA of power to the project.
The negotiations are advancing for the final commercial terms between both companies.
Tujuh Bukit Copper Project Contractors
The PFS for the project was prepared with the support of engineering consultants including Stantec, DRA, Ausenco, WSP Golder, ALS and Hatch.
The scoping study was prepared by ORELOGY, an Australian technical consultant, with contributions from Stantec, DRA, Ausenco and Hatch.
The technology of Mergin Maps, a geospatial data provider, has been used for the geological surveys of the project area.
