The Tujuh Bukit copper project is located in the East Java province of Indonesia. Credit: Dalton Dingelstad/
The Tujuh Bukit copper project will be developed as an open-pit mine. Credit: Merdeka Copper Gold.
Construction works on the project will start in early 2024. Credit: Merdeka Copper Gold.

The Tujuh Bukit copper project is an open-pit copper mine being developed in the East Java province of Indonesia. It is considered to be one of the world’s largest undeveloped copper and gold projects.

Merdeka Copper Gold, an Indonesia-based metal and mining company, is developing the project through its wholly owned subsidiary Bumi Suksesindo.

The scoping study for the project was completed in October 2022 while the pre-feasibility study (PFS) was completed in May 2023.

The PFS highlighted a mine life of 30 years and a pre-production capital investment of $757m.

Merdeka is currently conducting a feasibility study and environmental permitting for the project. Environmental permitting is targeted for completion by 2023, with development aimed to commence in early 2024.

Location of the Tujuh Bukit project

The Tujuh Bukit copper project is situated underneath the operating Tujuh Bukit gold mine in Banyuwangi, East Java, Indonesia. It is located approximately 205km south-east of Surabaya, the capital of East Java province, and 60km south-west of the regional centre of Banyuwangi within the Sumberagung village.

The project’s operational permit for mine production covers an area of 4,998ha.

Geology and mineralisation of the Tujuh Bukit site

Tujuh Bukit is a copper-gold-molybdenum porphyry deposit situated along the Sunda Banda Arc and is overlaid by an epithermal gold-silver deposit.

The mineralisation is contained within structurally controlled porphyry apophyses and breccias, which were developed and modified further by overlapping high-sulphidation epithermal copper-gold mineralisation as the system evolved. The high-sulphidation mineralisation has undergone significant oxidation near the surface.

Reserves of Tujuh Bukit

Tujuh Bukit is estimated to contain probable reserves of 289.3 million tonnes (mt) grading 0.56% Cu and 0.65g/t Au.

Mining methods

Merdeka plans to develop the Tujuh Bukit project using two mining methods, including sub-level cave (SLC) and block cave (BC).

Mining will initially commence using the SLC method in 2024. The mine life is expected to be eight years, with a capacity of four million tonnes per annum (mtpa). The top-down mining method will include seven levels spaced 25m apart vertically and production drifts spaced 21m apart horizontally.

The SLC mine will be accessed through the current exploration decline and a new conveyor decline. The existing exploration decline will be extended to provide access to the southern part of the orebody while the conveyor decline will be developed from the surface.

The learnings from the SLC mining will be utilised to optimise and de-risk the block cave mining, which will have a capacity of 24mtpa. BC is a method used for mining large low-grade underground deposits. It will start in the south of the extraction level and progress panel by panel in a counter-clockwise direction.

The mined material will be brought from drawpoints to perimeter jaw crushers and transported to the surface stockpile using transfer conveyors after crushing.

Ore processing details

The copper-gold concentrator and other surface infrastructure will be developed in phases. The first phase will include a 4mtpa concentrator comprising a grinding, rougher flotation, and cleaner flotation circuits. It will produce a copper concentrate containing 31,000t of copper and 87,000oz of gold a year.

In phase two, the copper and gold concentrator will be expanded to increase the capacity to 14mtpa by adding Albion, solvent extraction and electrowinning (SXEW) and carbon-in-leach (CIL) circuits for the on-site production of copper cathode and gold dore. Phase two will yield a copper concentrate containing 85,000t of copper and 265,000oz of gold a year.

Processing capacity will grow to 24mtpa by the addition of a pyrite flotation circuit to produce a pyrite concentrate filter cake product in phase three. Copper concentrate with 112,000tpa of contained copper and 267,000oz of contained gold will be produced annually during this phase, in addition to a pyrite concentrate averaging 2.2mt containing 74,000oz of contained gold.

Infrastructure details

The mine site can be accessed through paved roads from major cities such as Jakarta, Surabaya, and Denpasar.

PLN, national power supplier, will supply power to the project under a memorandum of understanding (MoU) signed in September 2021 with Merdeka. It will design, construct, and maintain a new transmission line from its Genteng power station to the site substation.

The project also involves the development of a port comprising a two-lane road for container trucks and a reach stacker to move containers from the laydown area to the harbour crane pickup point. A bulk concentrate handling facility will be developed in the second phase.

Contractors involved

Stantec, an architecture, construction management and environmental services company; and DRA, a consulting firm, were appointed as the lead consultants for the PFS with contributions from consulting companies Ausenco, WSP Golder, ALS, and Hatch.

The scoping study was completed by technical consultants orelogy Consulting (orelogy) with contributions from Stantec, DRA, Ausenco, and Hatch.