Mafic-ultramafic intrusion-hosted Ni-Cu-PGE deposits are found worldwide and represent some of the world’s largest nickel deposits (Hoatson et al., 2006). Globally they include world-class examples such as Jinchuan (China), Pechenga (Russia), and Voisey’s Bay (Canada). In Western Australia, notable examples include Julimar, Nova-Bollinger, Savannah and Nebo-Babel.

As summarised by Schulz et al. (2014) and Barnes et al. (2016), mafic-ultramafic intrusion-hosted Ni-Cu-PGE deposits are high-flux systems that require large volumes of high-degree partial melts to form the host intrusions, typically (but not exclusively) associated with mantle plume activity. These large volumes of magma are transported into the crust via major lithospheric structures, where they develop dynamic subvolcanic feeder systems (Schulz et al., 2014; Barnes et al., 2016). The magmas are initially sulfur undersaturated and must either assimilate additional sulfur (Schulz et al., 2014; Barnes et al., 2016) or have additional silica added to the melt (Seat et al., 2009; Godel et al., 2011) to reach sulfur saturation. Nickel, copper, and PGEs, which are enriched in mafic-ultramafic magmas, are scavenged and concentrated in sulfide droplets. If the right conditions are met, these crystallizing magmas will accumulate sulfides (Schulz et al., 2014; Barnes et al., 2016). Figure 1 from Schulz et al. (2014) illustrates the key mineralizing processes for magmatic hosted Ni-Cu-PGE mineralization. 

While the critical processes for the formation of mafic-ultramafic intrusion-hosted Ni-Cu-PGE systems are well understood, there remain gaps in understanding specific aspects of their metallogenesis. In particular, there is uncertainty regarding which characteristics are more favourable for Ni-Cu-PGE mineralization, such as (i) the size of the intrusion, (ii) the age of the intrusion, and (iii) the geometry of the intrusion (Fig. 2). Additionally, it is unclear what processes control the difference between mineralized and non-mineralized intrusions within the same geological setting. Table 1 summarizes size and age data for well-studied mafic-ultramafic intrusions in Western Australia.

Table 1: Characteristics of well studied intrusions in Western Australia. Compiled by T. Ivanic in 2019 (GSWA).

Derived layers are grouped based on their critical features:

SOURCE – of mafic-ultramafic magmas

PATHWAY – location of lithospheric faults, ancient cratonic blocks and dyke/sill complexes, responsible for transport of mafic-ultramafic magmas through the crust

CHEMICAL TRAP – sulfur saturation of previously sulfur undersaturated magma

CHEMICAL AND PHYSICAL TRAP – sequestering metals into sulfides

PHYSICAL TRAP – concentration of metal-rich sulfides

PRESERVATION – of nickel orebodies

The Mineral System Tree is the graphical display of a mineral systems analysis showing the link between critical/constituent processes and their recommended targeting features and GIS layers.

 Mafic-ultramafic intrusion-hosted Ni-Cu-PGE

Barnes, SJ, Cruden, AR, Arndt, NT and Saumur, BM 2016, The mineral system approach applied to magmatic Ni-Cu-PGE sulphide deposits: Ore Geology Reviews, v. 76, p. 296–316, doi:10.1016/j.oregeorev.2015.06.012.

Fletcher, IR, Libby, WG and Rosman, KJR 1987, Sm-Nd dating of the 2411 Ma Jimberlana dyke, Yilgarn Block, Western Australia: Australian Journal of Earth Sciences, v. 34, p. 523–525.

Godel, B, Seat, Z, Maier, WD and Barnes, S-J 2011, The Nebo-Babel Ni-Cu-PGE sulfide deposit (west Musgrave Block, Australia), Pt 2. Constraints on parental magma and processes, with implications for mineral exploration: Economic Geology, v. 106, p. 557–584.

Hickman, AH 2016, Northwest Pilbara Craton: A record of 450 million years in the growth of Archean continental crust: Geological Survey of Western Australia, Report 160, 104p.

Hoatson, DM and Sun, S-S 2002, Archean layered mafic-ultramafic intrusions in the west Pilbara Craton, Western Australia: A synthesis of some of the oldest orthomagmatic mineralizing systems in the world: Economic Geology, v. 97, no. 4, p. 847–872, <http://econgeol.geoscienceworld.org/content/97/4/847.full.pdf+html>.

Ivanic, TJ 2016, A field guide to the mafic-ultramafic layered intrusions of the northern Youanmi Terrane: Geological Survey of Western Australia, Record 2016/6, 61p.

Ivanic, TJ 2019, Mafic–ultramafic intrusions of the Youanmi Terrane, Yilgarn Craton: Geological Survey of Western Australia, Report 192, 121p.

Kinny, PD, Williams, IS, Froude, DO, Ireland, TR and Compston, W 1988, Early Archaean zircon ages from orthogneisses and anorthosites at Mount Narryer, Western Australia: Precambrian Research, v. 38, p. 325–341.

Maier, WD, Howard, HM, Smithies, RH, Yang, S, Barnes, S-J, O'Brien, H, Huhma, H and Gardoll, S 2014, Mafic-ultramafic intrusions of the Giles Event, Western Australia: Petrogenesis and prospectivity for magmatic ore deposits: Geological Survey of Western Australia, Report 134, 82p.

Schulz, KJ, Woodruff, LG, Nicholson, SW, Seal II, RR, Piatak, NM, Chandler, VW and Mars, JL 2014, Occurrence model for magmatic sulfide-rich nickel-copper-(platinum-group element) deposits related to mafic and ultramafic dike-sill complexes: USGS, U.S. Geological Survey Scientific Investigations Report 2010-5070-I, 80p.

Seat, Z, Beresford, SW, Grguric, BA, Gee, MAM and Grassineau, NV 2009, Reevaluation of the role of external sulfur addition in the genesis of Ni-Cu-PGE deposits: evidence from the Nebo-Babel Ni-Cu-PGE deposit, West Musgrave, Western Australia: Economic Geology, v. 104, no. 4, p. 521–538, 17p., doi:10.2113/gsecongeo.104.4.521.

Barnes, SJ 2023, Lithogeochemistry in exploration for intrusion-hosted magmatic Ni–Cu–Co deposits: Geochemistry: Exploration, Environment, Analysis, v. 23, no. 1, article no. geochem2022-025, doi:10.1144/geochem2022-025.

Barnes, SJ, Cruden, AR, Arndt, NT and Saumur, BM 2016, The mineral system approach applied to magmatic Ni-Cu-PGE sulphide deposits: Ore Geology Reviews, v. 76, p. 296–316, doi:10.1016/j.oregeorev.2015.06.012.

Schulz, KJ, Woodruff, LG, Nicholson, SW, Seal II, RR, Piatak, NM, Chandler, VW and Mars, JL 2014, Occurrence model for magmatic sulfide-rich nickel-copper-(platinum-group element) deposits related to mafic and ultramafic dike-sill complexes: USGS, U.S. Geological Survey Scientific Investigations Report 2010-5070-I, 80p.

Subject matter experts:

• Steve Barnes (CSIRO)
• Margaux Le Vaillant (CSIRO)