Wetar Island is composed of Neogene volcanic rocks and minor oceanic sediments and forms part of the Inner Banda Arc. The island preserves ~4.7 million-year-old precious metal-rich volcanogenic massive sulphide and barite deposits.

The polymetallic massive sulphides are dominated by pyrite, with minor primary chalcopyrite and lesser bornite cut by late fractures infilled with sulphosalts, tennantite-tetrahedrite and enargite. The sulphosalts have replaced primary chalcopyrite and bornite to varying extents across Kali Kuning, Lerokis and Partolang, and these have in turn been replaced by supergene chalcocite and covellite to varying extents.

Barite-rich orebodies are developed on the flanks of the sulphide units and locally overly the massive sulphides.

Sulphide mounds showing talus textures are localised onto faults, which provided the main pathways for high-temperature hydrothermal fluids and the development of associated stockworks.

Known orebodies are closely associated with quartz-porphyry dacites which occur within the basalts/andesites and are surrounded by widespread propylitic and argillic alteration haloes. Hydrothermal alteration around the various orebodies is zoned and dominated by illitekaolinite- smectite with local alunite and pyrophyllite.

The sulphide mounds and related barite bodies were covered and preserved by post-mineralisation chert, gypsum, calcareous siltstone, limestone, lahars, subaqueous debris flows, volcaniclastic rocks and locally fresh dacitic lava flows at Partolang.

Gold-silver mineralisation occurs predominantly within barite-rich units, including sands, tuffs and breccias (after original dacitic rocks), which are strongly ferruginised locally. In some of the dacitic rocks, barite and hydrated iron minerals have completely replaced the host units, with original breccia textures no longer visible.

The economic copper mineralisation occurs predominantly within coherent massive sulphide units and locally in dacitic breccia units which, have been almost completely replaced by sulphides, with some minor lower-grade material occurring in fractures and as stockworks within intensely altered andesitic and dacitic tuffs and volcanics in the footwall and lateral extent of the massive sulphides. Not all massive sulphides are mineralised.

The contact between the massive sulphides, barite, footwall and hangingwall units is generally quite sharp.

Wetar Copper is a copper mine located on Wetar Island, Maluku Barat Daya Regency, Maluku Province.

Commercial production of Wetar Copper started in 2010, consists of open pit mine, associated heap leach operation and solvent extraction-electrowinning (SX-EW) plant which produces copper metal.

Wetar comprises three open pits: Lerokis, Kali Kuning and Partolang. Mining activities at Lerokis and Kali Kuning pits were completed. Since October 2020, mining operations commenced at the Partolang Pit.

With the development of the AIM project, the focus going forward will be on extracting maximum value from the Wetar ore including production of copper at Wetar and the sale of ore to the AIM project to be used to produce acid, iron, steam, copper, gold and silver.

Partolang ore is processed via heap leaching SX-EW and incorporated into the existing 28 kt/a operation located in the Kali Kuning valley 2 km distant.

Nine columns in total are being prepared and eight of the column tests are underway for Partolang. Three of the columns have been active for 100 days, three other columns have been active for 83 days and 2 others for 46 days. The columns are designed to test each of the main ore units (i.e. MPY, PBX2 and SBX), run of mill composites, column height, high ferric/ferrous ratio in lixiviant, low acid, and low iron content in lixiviant.

Results from the initial columns suggest reasonable recoveries, with 75.2% recovered from SBX, 47.3% recovered from MPY, and 66.4% recovered from PBX2 etc after 100 days under irrigation. The columns that have been active for 83 days, testing ROM composites, high ferric and lower column height have recovered 58-65%, whilst those for 46 days testing lower acid and TDS have recovered 50-56%.

The AIM Project will purchase high-grade pyrite ore from Wetar. The AIM plant, under construction at IMIP, is designed to treat the pyrite ore from Wetar at a nominal rate of 1,060,000 tonnes per year. The plant will produce sulphuric acid, saturated steam, iron ore pellets, copper cathode, leadzinc hydroxides, gold and silver doré.

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