Magmatic Sulphide Deposits

These deposits play a foundational role in the global mineral supply chain, especially as the world accelerates toward clean energy, electric vehicles, and a low - carbon economy.

What makes these deposits especially significant is not just their metal content, but their unique geological formation process. These deposits form deep within the Earth’s crust when metal-rich sulphide liquids separate out from molten mafic or ultramafic silicate magmas. The metals - particularly Ni, Cu, and PGEs - prefer to bond with sulphur rather than remain in the silicate melt, and as a result, they become concentrated in dense sulphide liquids. These liquids, heavier than the surrounding magma, tend to sink and pool in traps such as the bottoms of magma conduits or at the base of large intrusive bodies.

Where and How These Deposits Form

These deposits are typically associated with mafic and ultramafic igneous rocks - gabbros, peridotites, norites, and komatiites - formed from magmas originating in the mantle. They can occur in a variety of tectonic settings, including:

• Archean greenstone belts with high - Mg komatiite flows
• Rift zones and continental margins hosting large layered intrusions
• Back-arc and subduction-related settings containing Alaskan-type intrusions
• Cratonic interiors where ancient stable crust preserves layered complexes

Over time, geologists have classified these deposits into several subtypes, each with its own formation environment and mineralisation style. These include:

• Komatiite-associated Ni - Cu deposits, formed in ancient high-temperature lava channels (e.g., Kambalda, Australia)
• Conduit-type deposits, where massive sulphide accumulations form in magma feeders and dunitic channels (e.g., Voisey’s Bay, Canada)
• Layered intrusion-hosted deposits, associated with large mafic bodies like the Noril’sk - Talnakh complex in Russia or the Duluth Complex in the USA
• Alaskan-type or zoned ultramafic intrusions, common in arc settings
• PGE-rich layered intrusions, such as the Bushveld Complex in South Africa, where platinum and palladium dominate the economic value

Critical Metals for Strategic Technologies

The importance of these deposits lies in the metals they provide, all of which are essential to modern technologies:

• Nickel is a key ingredient in high-performance batteries, particularly in EVs and grid storage systems.
• Copper is the backbone of electrical infrastructure, used in everything from solar panels to transmission lines.
• Cobalt plays a crucial role in battery stability and energy density.
• Platinum Group Elements (PGEs) are vital for catalytic converters, hydrogen fuel cells, and emerging green technologies.

As demand for these metals continues to grow, securing new sources from these mineral systems is becoming an economic and strategic imperative.

Exploration Techniques

Successful exploration of mafic - ultramafic sulphide systems requires an integrated approach that combines modern technology with solid geological understanding. The most effective prospecting methods include:

Strategic Importance and Global Potential

Mafic – ultramafic magmatic sulphide deposits have long been recognised for their economic importance. But in today’s rapidly evolving geopolitical and technological landscape, they are more vital than ever. Countries seeking to secure clean energy supply chains are investing heavily in exploring and developing new Ni-Cu-Co-PGE sources.

Mafic–ultramafic magmatic sulphide and PGE deposits in New Zealand

In New Zealand, there are only two types of mafic–ultramafic magmatic sulphide deposits - dunitic Ni - Cu and gabbroid-associated Ni-Cu. The dunitic Ni-Cu deposits fit the conduit-type model (e.g., Voisey’s Bay, Canada) and the gabbroid-associated Ni-Cu deposits fit the layered mafic intrusion-hosted Ni-Cu deposit model (e.g., Duluth Complex, USA). For an overview of PGE occurrences in New Zealand, see Christie et al., 2006.

Occurrences of Dunitic Ni-Cu ± PGE   Deposits

In New Zealand, this deposit type is associated with disseminated sulphide mineralisation in ultramafic and mafic intrusive rocks and has the potential to be hosted in the Permian serpentinite, dunite and peridotite of the Dun Mountain Ultramafic Group rocks, as well as the Mesozoic lensoid schistose serpentinite of the Pounamu Ultramafics and in areas associated with other ultramafic igneous complexes. The occurrence of disseminated nickel mineralisation in the form of awaruite ± magnetite ± heazlewoodite ± pentlandite ± native copper in serpentinised peridotites in the Dun Mountain ultramafics in east Nelson (Brathwaite et al. 2016, 2017) is similar to disseminated awaruite in serpentinised ophiolitic peridotites of the Cache Creek complex in British Columbia (Britten 2017) that have economic potential for nickel. Chromite lenses in cumulate dunite at Baldy Ridge, Matakitaki occurrences have elevated Pt (up to 1070 ppb) and Pd (up to 530 ppb) contents (Brathwaite et al. 2017).

Occurrences of Gabbroid-Associated Ni-Cu ± PGE  Deposits

The most significant occurrence is Ni-Cu sulphide mineralisation associated with the Riwaka mafic-ultramafic complex of Late Devonian age in the Graham Valley, Northwest Nelson (Turnbull et al. 2017). The complex is a series of layered intrusions emplaced along a fault zone in marble, phyllite and biotite schist. The Graham Valley Ni-Cu mineralisation occurs mainly within the cumulus gabbro between the Graham and Pearce valleys (e.g. Prospect, Field and Price’s creeks), where sulphide content ranges from 1 to 50%, characteristically with Ni>Cu. Nickel sulphide mineralisation is also associated with mafic-ultramafic rocks in the Cobb Valley (upper Takaka, e.g. Meter Creek) and at Blue Mountain in Marlborough. Minor occurrences are found in mafic-ultramafic rocks of the Red Hills range of Westland and Otago, the Darran Mountains of Fiordland (e.g. Camera Lake and Falls Creek), various locations in Southland, including West Dome, Otama Igneous Complex, Longwood Igneous Complex (Ashley et al., 2012), Greenhills Complex (Spandler et al. 2000) and Takitimu Mountains, and in the Anglem Complex of Rakiura / Stewart Island.

PGEs are associated with Ni-Cu nickel-copper sulphides in Gabbroid-Associated deposits. Complexes that have been identified as prospective by the presence of in situ PGE, or nearby placer PGE, include the Riwaka, Rotoroa, Longwood (Hekeia gabbro) and Greenhills (Bluff) complexes.

Additional reading

Ashley P, Craw D, MacKenzie D, Rombouts M, Reay A. 2012. Mafic and ultramafic rocks, and platinum mineralisation potential, in the Longwood Range, Southland, New Zealand, New Zealand Journal of Geology and Geophysics, 55(1):3-19, DOI:10.1080/00288306.2011.623302 

Barnes SJ, Cruden AR, Arndt NT, Saumur BM. 2016. The mineral system approach applied to magmatic Ni–Cu–PGE sulphide deposits. Ore Geology Reviews, 76, 296–316.

Brathwaite RL Christie AB, Jongens R. 2016. Exploration for chromite, platinum group element and nickel mineralisation in the Dun Mountain Ophiolite Belt, East Nelson. In: Christie AB, editor. Mineral deposits of New Zealand: exploration and research. Carlton (AU): Australasian Institute of Mining and Metallurgy. p. 463–470. (Australasian Institute of Mining and Metallurgy monograph series; 31).

Brathwaite RL, Christie AB, Jongens R. 2017. Chromite, platinum group elements and nickel mineralisation in relation to the tectonic evolution of the Dun Mountain Ophiolite Belt, East Nelson. New Zealand Journal of Geology and Geophysics. 60(3):255–269. https://doi.org/10.1080/00288306.2017.1313279(external link) 

Christie AB, Mortimer N, Waterman P, Barker RG. 2006. New Zealand platinum prospects in arc-type layered igneous complexes. Australasian Institute of Mining and Metallurgy Monograph 25:37-42.

Britten R. 2017. Regional metallogeny and genesis of a new deposit type – disseminated awaruite (Ni3Fe) mineralisation hosted in the Cache Creek terrane. Economic Geology, 112, 517-550.

Durance PMJ, Hill MP, Turnbull RE, Morgenstern R, Rattenbury MS. 2018. Nickel and Cobalt Mineral Potential in New Zealand. Lower Hutt (NZ): GNS Science. 223 p. (GNS Science consultancy report; 2018/64).

Lawley C J M, Tschirhart V, Smith JW, Pehrsson SJ, Schetselaar  EM, Andrew J. Schaeffer AJ, Houlé MG, Eglington BM. 2021. Prospectivity modelling of Canadian magmatic Ni (±Cu±Co±PGE) sulphide mineral systems. Ore Geology Reviews, 132, 103985. https://doi.org/10.1016/j.oregeorev.2021.103985(external link) 

Johnston, Mike. High Hopes: the history of the Nelson Mineral Belt and New Zealand's first railway(external link) / Mike Johnston. 

Naldrett, A. (1999). World-class Ni-Cu-PGE deposits: key factors in their genesis. Mineral. Deposita 34, 227–240.

Spandler CJ, Eggins SM, Arculus RJ, Mavrogenes JA. 2000. Using melt inclusions to determine parent-magma compositions of layered intrusions: application to the Greenhills Complex (New Zealand), a platinum-group-minerals-bearing, island-arc intrusion. Geology 28, 991–994.

Turnbull RE, Size WB, Tulloch AJ, Christie AB. 2017. The ultramafic–intermediate Riwaka Complex, New Zealand: summary of the petrology, geochemistry and related Ni–Cu–PGE mineralisation. New Zealand Journal of Geology and Geophysics. 60(3):270–295. https://doi.org/10.1080/00288306.2017.1316747(external link)