Unearthing Winu-Ngapakarra: A New Frontier in Western Australia's Mineral Landscape

 

Winu-Ngapakarra Copper-Gold-Silver Deposit, Western Australia

The Winu-Ngapakarra Copper-Gold-Silver deposit represents a significant and exciting new chapter in Western Australia's mining story, revealing an attractive low-risk, long-life copper-gold deposit that has been the focus of intense exploration and study by Rio Tinto. Discovered in late 2017, this project in the remote Paterson Province promises substantial future opportunities in a historically underexplored region.

Location and Setting

The Winu-Ngapakarra copper-gold-silver deposit is nestled approximately 300 km south of Broome and 320 km east of Port Hedland in the northern Pilbara region of Western Australia, within the vast expanse of the Great Sandy Desert. This remote location necessitates specific infrastructure, including the construction of a gravel airstrip for emergency response and logistical support, situated on Martu People's Country. The project lies within the Yeneena Basin of the Paterson Province, an area known for its rich geological history, though Winu itself was found under significant cover. Prior to Rio Tinto's work in 2016, no exploration had been carried out in the immediate Winu area.

Winu-Ngapakarra copper-gold-silver deposit location map

Geology and Mineralisation

Winu-Ngapakarra is classified as an intrusion-related copper-gold-silver deposit. The mineralization is hosted within Neoproterozoic metasedimentary rocks (primarily quartzites, metasandstones, metasiltstones, and metapelites), which are entirely concealed by younger Permian and Cretaceous sedimentary cover ranging from 50 to 450 meters thick. The host rocks are described as fine to medium-grained subarkosic metasandstones and biotite-rich metasiltstones.

The deposit is interpreted as a structurally controlled vein-hosted copper-gold deposit, focused on the core of an anticline or inclined monocline. Copper-gold mineralization occurs in en echelon left-stepping lodes with strike lengths between 350 and 750 meters and vertical depths exceeding 750 meters, surrounded by an extensive halo of low-grade mineralization. Multiple vein generations and orientations have been identified, with the main mineralization event associated with quartz-K-feldspar-sulphide and sulphide-carbonate veins.

A unique characteristic of Winu is that it preserves evidence for an early, reduced intrusion-related gold system overprinted by a more oxidized intrusion-related copper system, genetically related to composite ilmenite- and magnetite-stable granite intrusions. Primary sulphide mineralization, predominantly chalcopyrite and chalcocite, is notably overlain by a supergene blanket containing secondary copper minerals and native copper, with upgrading affecting mineralization to average depths of 200 meters, and locally up to 340 meters.

The Ngapakarra prospect, a gold-dominant satellite deposit, was discovered approximately 2 km east of the Winu deposit in 2018. It exhibits high-grade vein-hosted fine-grained gold, similar to Winu's metasedimentary rocks but with distinct vein characteristics. The Ngapakarra deposit is still in early stages of exploration and remains open in all directions and at depth.

The mineralization event at Winu has been dated to the Paterson Orogeny, with Re-Os ages of molybdenite indicating formation around 658-655 Ma.

Winu Regional Surface Geology Map

Winu Solid Geology Map

Winu Magnetic Hue Saturation Map

Rio Tinto has progressed Winu significantly since its discovery:

• A Maiden Inferred Mineral Resource was announced in July 2020, totaling 503 Mt at 0.45% copper equivalent (CuEq) at a 0.2% CuEq cutoff, including a higher-grade component of 188 Mt at 0.68% CuEq at a 0.45% CuEq cutoff.
• An updated Mineral Resource was reported in February 2022, including the first Indicated Mineral Resource. The total resource increased to 608 Mt at 0.49% CuEq, comprising an Indicated Mineral Resource of 249 Mt at 0.55% CuEq and an Inferred Mineral Resource of 358 Mt at 0.46% CuEq. This represented a 40% increase in contained copper metal and a 35% increase in contained gold metal compared to the initial release.
• A revised Mineral Resource was reported in December 2024 with the Total Measured and Indicated Mineral Resource of 464 Mt at 0.39% Cu, 0.32 g/t Au, and 2.24 g/t Ag and the Inferred Mineral Resource of 227 Mt at 0.41% Cu, 0.36 g/t Au, 2.12 g/t Ag. As of December 2024, Rio Tinto has reported a Total Mineral Resource at Winu of 741 MT at 0.40% Cu, 0.33 g/t Au and 2.20 g/t Ag.
• The deposit remains open at depth, as well as to the north, south, and east, with ongoing drilling to explore these extensions.
• Preliminary studies suggest the copper mineralization supports the development of a relatively shallow open-pit mine using industry-standard processing technology. A pre-feasibility study for an initial development with processing capacity of up to 10 mtpa is expected to be completed in 2025.
• In December 2024, Rio Tinto signed a Term Sheet for a Joint Venture with Sumitomo Metal Mining (SMM), where SMM will acquire a 30% equity share for $399 million. Rio Tinto will remain the managing partner, and the parties intend to develop a broader strategic partnership.

Winu resource tonnage over time

Winu resource grade over time

Environment and Social Aspects

Rio Tinto has demonstrated a commitment to engaging with the Nyangumarta and Martu Traditional Owners, on whose Native Title Determination Areas the project is located. Extensive cultural heritage surveys have been conducted since 2018, contributing to ongoing consultation and co-design efforts. Agreements securing permission for planning were signed in 2023, with formal Land Use Agreements and Project Agreement negotiations progressing.

Formal environmental approvals with the Environmental Protection Authority (EPA) commenced in November 2023, with the Winu project requiring the highest level of assessment – a Public Environmental Review. The proposal is subject to assessment under both the Commonwealth EPBC Act and the Western Australian EP Act. Extensive environmental studies have been undertaken, covering crucial factors such as:

• Land and soils (including subsurface materials)
• Biodiversity (flora, vegetation, terrestrial fauna)
• Water resources (surface water and groundwater)
• Rehabilitation and mine closure planning

The proposed mine infrastructure includes a below-watertable open pit, waste rock landforms, ore processing facilities, and associated support infrastructure within a Development Envelope of approximately 37,344 ha.

Comparison to Other Structurally Controlled Vein-Hosted Copper-Gold Deposits

The Winu-Ngapakarra deposit holds a unique position within the Paterson Province and globally, distinguishing itself from other significant deposits in the region:

• Telfer: While also located in the Yeneena Basin and an intrusion-related gold-copper mine, Telfer's dominant mineralization styles are bedding-parallel reefs, contrasting with Winu's discordant vein arrays and lesser breccias and stockworks.
• Nifty: This is primarily a sediment-hosted copper mine, representing a different style of mineralization entirely.
• Havieron: A recently discovered Au-Cu deposit with a similar mineralization age to Winu (~653 Ma), Havieron is characterized by nested, vertically extensive hydrothermal breccia columns and a different host rock sequence. However, like Winu, gold at Havieron is closely associated with bismuth, and copper sulfides generally postdate much of the gold mineralization.
• Malanjkhand (India): Winu exhibits similarities in style, dimensions, and mineralogy to this large Archean/Paleoproterozoic granitoid-hosted porphyry copper deposit.

Winu's distinctiveness lies in its preservation of evidence for an early, reduced intrusion-related gold system overprinted by a more oxidized intrusion-related copper system. This genetic relationship to composite ilmenite- and magnetite-stable granite intrusions, and the switch in stress regimes from extension to compression, sets it apart as a unique deposit style.

Exploration Implications

The discovery and ongoing evaluation of Winu-Ngapakarra highlight the immense, yet largely underexplored, potential of the Paterson Province in Western Australia. Despite its remote nature, the success at Winu reinforces the viability of finding large-scale, concealed deposits in this region.

Key implications for future exploration include:

• Expansion Potential: The Winu deposit remains open at depth and in multiple directions, with Ngapakarra also in early stages of exploration. This indicates potential for multiple ore bodies within one system and future expansion.
• New Deposit Model: The unique overprinted gold and copper systems observed at Winu offer a new deposit style for explorationists, which may help to improve future success in identifying similar concealed deposits in the province.
• Rio Tinto's Strategic Position: Rio Tinto holds a large land package in the Paterson region, having explored only about 2% of its tenements as of July 2020. The ongoing exploration on wholly owned and joint venture licenses (e.g., Citadel with Antipa Minerals, Waukarlycarly with Alloy Resources, West Paterson with Carawine Resources) underscores the company's commitment to unlocking further potential in the region.
• Strategic Partnerships: The joint venture with Sumitomo Metal Mining not only de-risks the Winu project but also sets the stage for a broader strategic partnership to explore opportunities in copper, other base metals, and lithium, signaling a collaborative approach to regional exploration.

The Winu-Ngapakarra Copper-Gold-Silver deposit is not just a new mine in the making; it's a testament to the ongoing discovery potential of Australia's mineral-rich landscapes, particularly in areas where traditional exploration methods have been limited by cover. Its continued development will undoubtedly provide valuable insights for future discoveries in the Paterson Province.