The Mordor Alkaline Igneous Complex, Central Australia: PGE-enriched disseminated sulfide layers in cumulates from a lamprophyric magma

Barnes, Stephen J.; Anderson, J. Alton; Smith, Tim; Bagas, Leon

doi:10.1007/s00126-008-0187-1

Cited by 19 publications

(19 citation statements)

References 44 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…These late stage Cu-rich liquids are evidently strongly wetting against silicates. A similar feature was noted in the Mordor intrusion in central Australia (Barnes et al, 2008a) where residual Cu-rich sulfides form complex intergrowths with late-forming mica and oxide grains.…”

Section: Disseminated Sulfides In Layered Intrusion Cumulatessupporting

confidence: 69%

Sulfide-silicate textures in magmatic Ni-Cu-PGE sulfide ore deposits: Disseminated and net-textured ores

Barnes

Mungall

Godel

et al. 2017

American Mineralogist

Self Cite

127

View full text Add to dashboard Cite

A large proportion of ores in magmatic sulfide deposits consist of mixtures of cumulus silicate minerals, sulfide liquid and silicate melt, with characteristic textural relationships that provide essential clues to their origin. Within silicate-sulfide cumulates, there is a range of sulfide abundance in magmatic-textured silicate-sulfide ores between ores with up to about five modal percent sulfides, called "disseminated ores", and "net-textured" (or "matrix") ores containing about 30 to 70 modal percent sulfide forming continuous networks enclosing cumulus silicates. Disseminated ores in cumulates have a variety of textural types relating to the presence or absence of trapped interstitial silicate melt and (rarely) vapour bubbles. Spherical or oblate spherical globules with smooth menisci, as in the Black Swan disseminated ores, are associated with silicate-filled cavities interpreted as amygdales or segregation vesicles. More irregular globules lacking internal differentiation and having partially facetted margins are interpreted as entrainment of previously segregated, partially solidified sulfide. There is a textural continuum between various types of disseminated and net-textured ores, intermediate types commonly taking the form of "patchy net-textured ores" containing sulfide-rich and sulfide-poor domains at cm to dm scale. These textures are ascribed primarily to the process of sulfide percolation, itself triggered by the process of competitive wetting whereby the silicate melt preferentially wets silicate crystal surfaces. The process is self-reinforcing as sulfide migration causes sulfide networks to grow by coalescence, with a larger rise height and hence a greater gravitational driving force for percolation and silicate melt displacement. Many of the textural variants catalogued here, including poikilitic or leopard-textured ores, can be explained in these terms. Additional complexity is added by factors such as the presence of oikocrysts and segregation of sulfide liquid during strain-rate dependent thixotropic behaviour of partially consolidated cumulates. Integrated textural and geochemical studies are critical to full understanding of ore-forming systems.

show abstract

Section: Disseminated Sulfides In Layered Intrusion Cumulatessupporting

confidence: 69%

Sulfide-silicate textures in magmatic Ni-Cu-PGE sulfide ore deposits: Disseminated and net-textured ores

Barnes

Mungall

Godel

et al. 2017

American Mineralogist

Self Cite

127

View full text Add to dashboard Cite

show abstract

“…It is intruded into the high-grade Palaeoproterozoic Arltunga granitic gneisses of the Arunta Orogen, at mid-crustal levels (5-25 km depth) 40 . Magmatic sulfides occur in two associations: blebby sulfides in mafic syenites or "shonkinites" 41 , and "reef-like" zones in layered, alkaline ultramafic rocks 42 . Carbonate is present in several forms at Mordor, including veins, dykes, and breccia pipes derived from late-stage CO 2 -rich fluids and/or residual carbonatitic melts 41 .…”

Section: Resultsmentioning

confidence: 99%

Fluxing of mantle carbon as a physical agent for metallogenic fertilization of the crust

et al. 2020

View full text Add to dashboard Cite

Magmatic systems play a crucial role in enriching the crust with volatiles and elements that reside primarily within the Earth's mantle, including economically important metals like nickel, copper and platinum-group elements. However, transport of these metals within silicate magmas primarily occurs within dense sulfide liquids, which tend to coalesce, settle and not be efficiently transported in ascending magmas. Here we show textural observations, backed up with carbon and oxygen isotope data, which indicate an intimate association between mantle-derived carbonates and sulfides in some mafic-ultramafic magmatic systems emplaced at the base of the continental crust. We propose that carbon, as a buoyant supercritical CO 2 fluid, might be a covert agent aiding and promoting the physical transport of sulfides across the mantle-crust transition. This may be a common but cryptic mechanism that facilitates cycling of volatiles and metals from the mantle to the lower-to-mid continental crust, which leaves little footprint behind by the time magmas reach the Earth's surface.

show abstract

“…Sron Garbh and Ivrea pipes are both tens to a few hundreds of metres in thickness), yet they can occur over significant areas, such as the Coldwell Complex, Canada, which has an area of~350 km 2 , although the mineralised mafic-ultramafic rim makes up only a small percentage of the complex. One of the largest examples of exposed alkaline mafic-ultramafic rocks is in the mid-crustal Mordor Alkaline Igneous Complex (MAIC), in Northern Territory, Australia (Langworthy and Black 1978;Barraclough 1981;Hoatson et al 2005; Barnes et al 2008). The MAIC is a zoned intrusion comprising an ultramafic-mafic portion and a slightly offset syenitic rim, covering a total area of 35 km 2 .…”

Section: Electronic Supplementary Materialsmentioning

confidence: 99%

“…The MAIC is a zoned intrusion comprising an ultramafic-mafic portion and a slightly offset syenitic rim, covering a total area of 35 km 2 . The ultramaficmafic portion is host to two styles of magmatic sulfide mineralisation: disseminated stratiform PGE 'reef' style mineralisation in the layered alkaline-ultramafic rocks in the centre of the complex, which have been described by Barnes et al (2008); and more voluminous blebby Cu-(Au-PGE-Ni) sulfides in mafic syenites, or 'shonkinites', which have never been studied in detail. Here we describe the nature of the shonkinite-hosted mineralisation for the first time, compare it with alkaline-hosted deposits elsewhere and assess the significance of this deposit in terms of the mid-crustal expression of magmatic sulfides in alkaline magmatic systems.…”

Section: Electronic Supplementary Materialsmentioning

confidence: 99%

Emplacement of magmatic Cu-Au-Te(-Ni-PGE) sulfide blebs in alkaline mafic rocks of the Mordor Complex, Northern Territory, Australia

Holwell

Blanks

2020

Miner Deposita

View full text Add to dashboard Cite

Magmatic Ni-Cu-PGE sulfide mineralisation is mostly confined to tholeiitic to komatiitic mafic-ultramafic intrusions, yet there have been an increasing number of occurrences recorded in alkaline-ultramafic, post-collisional magmatic systems, particularly in the lower and middle crust that generally display a characteristic Cu-Au-Te enrichment over more conventional Ni-Cu(-PGE) mineralisation. The Mordor Alkaline Igneous Complex, Australia, is a mid-crustal, zoned alkaline complex comprised of a syenite body with an alkaline mafic-ultramafic subcomplex containing dunites, wehrlites and shonkinites. Sulfide mineralisation is present either in thin, PGE-enriched stratiform ‘reefs’ within layered ultramafics in the centre of the subcomplex, or in thicker zones of Cu(-Au-PGE-Te) sulfide hosted by phlogopite-rich shonkinites towards the intrusion margins. This latter style comprises blebs of pyrite, chalcopyrite and minor millerite and PGE tellurides formed from the cooling of a Cu-dominant sulfide liquid. Primary igneous calcite is present in intimate association with the sulfide. We note that the circular nature of the complex, with a dunite core and shonkinite rim with chalcophile element mineralisation, is comparable to the pipe-like, intracratonic, alkaline-ultramafic Aldan Shield intrusions in Russia. As such, Mordor may have an intracratonic rather than post-collisional affinity. Nevertheless, sulfide mineralisation is typical of other alkaline-hosted occurrences, with a Cu-Au-Te-rich signature, low Ni contents and textural association with calcite, supporting models of chalcophile metal and S fluxing alongside carbonate in alkaline systems derived from low degrees of partial melting of hydrous and carbonated mantle sources. Mordor illustrates that alkaline igneous rocks are prospective for magmatic Cu-Au-PGE-Ni sulfide mineralisation, and the classic ‘marginal base metal– and sulfide-rich’ and ‘stratiform PGE-rich and sulfide-poor’ mineralisation styles may both be found in such intrusions.

show abstract

The Mordor Alkaline Igneous Complex, Central Australia: PGE-enriched disseminated sulfide layers in cumulates from a lamprophyric magma

Cited by 19 publications

References 44 publications

Sulfide-silicate textures in magmatic Ni-Cu-PGE sulfide ore deposits: Disseminated and net-textured ores

Sulfide-silicate textures in magmatic Ni-Cu-PGE sulfide ore deposits: Disseminated and net-textured ores

Fluxing of mantle carbon as a physical agent for metallogenic fertilization of the crust

Emplacement of magmatic Cu-Au-Te(-Ni-PGE) sulfide blebs in alkaline mafic rocks of the Mordor Complex, Northern Territory, Australia

Contact Info

Product

Resources

About