Mantle-derived mafic-ultramafic melts are the primary host for magmatic Ni-Cu-Co-PGE deposits. One common assumption about this mineral system is that Ni-fertility is a product of high-degree melting of anhydrous mantle peridotites, including a substantial contribution from olivine. However, in metasomatised mantle rocks, which partially melt at lower temperatures than anhydrous peridotites, Ni is hosted by a range of minerals, including hydrous phases such as phlogopite and amphibole in addition to olivine and orthopyroxene. The lower melting point of these hydrous phases makes Ni in phlogopite a potentially significant contributor to the Ni enrichment of mantle melts from metasomatised assemblages. We analyse a suite of phlogopite-bearing mantle rocks which display variably metasomatised assemblages using SEM mapping to quantify mineral assemblages, and laser ablation ICP-MS to determine the Ni deportment in these rocks. Phlogopite in hydrous peridotites contains 859–1126 ppm Ni equating to 12

Magmatic Ni–sulfide ore deposits are generally associated with basaltic to komatiitic igneous rocks that originate by partial melting of the mantle, which is usually modelled as a uniform four-phase peridotite. Existing models accept that the key metal contributors to mantle melts are olivine (Ni) and sulfide (Cu, platinum group elements (PGEs) and minor Ni). However, melting in the mantle commonly begins in volumetrically minor mantle assemblages such as hydrous pyroxenites that occur as veins in the peridotite mantle, which are rich in the hydrous minerals phlogopite, amphibole and apatite. The contribution of hydrous pyroxenites to the metal endowment of mantle melts may have been underestimated or overlooked in the past, partly because evidence of their input is partially erased as melting intensifies to involve peridotite. Here, we compile new results from experiments and natural rocks which demonstrate that the hydrous minerals such as phlogopite, amphiboles and apatite all have high partition coefficients for Ni (3–20) and may be important repositories for Ni in mantle sources of igneous rocks. This implies that hydrous minerals hosted in metasomatic mantle lithologies such as hydrous pyroxenites may be important contributors to some magmatic Ni–sulfide ore systems. Hydrous pyroxenites contain hydrous minerals in large modal abundances up to 30–40 vol

The composition of magmatic sulfide deposits is controlled by the metal budget of the magma, which itself is controlled by the composition of the mantle source and degree of partial melting. Traditional models assume that high degrees of partial melting (>15%) are required to sufficiently liberate Cu and PGE from sulfide and Ni from olivine, assuming peridotitic mantle rocks. However, we show that hydrous pyroxenite in the mantle hosts Ni and other critical metals in minerals such as phlogopite and amphibole, which have significantly lower melting temperatures than olivine. We propose a classification of magmatic sulfide deposits that reflects (1) the source composition; and (2) the melting regime. We show that Ni-fertile magmas may be formed in a broader range of geotectonic settings than previously thought if sourced from metasomatised mantle, opening up exploration search spaces for critical battery metals.

The Curaca Valley, Brazil, contains a number of dominantly Cu-rich sulfide deposits hosted by orthopyroxene rich mafic and ultramafic rocks emplaced into the lower crust. The deposits are dominated by chalcopyrite-bornite with elevated Au and Te, and a strong association with abundant phlogopite. Textural evidence indicates emplacement of these sulfides as a migrating Cu-rich sulfide liquid enriched with volatiles. In addition, the Curaca Valley contains some Ni-rich deposits in identical host rocks, but with interstitial and net textured pyrrhotite-pentlandite-pyrite, with very little Cu, Au and Te. We propose that the Curaca Valley deposits, and those of the potentially analogous O'okiep district in South Africa, formed from low degree partial melting of a metasomatically enriched mantle source in a collisional setting. Sulfides within the resultant hydrous, alkaline ultramafic rocks were able to fractionate, with Ni sulfides trapped in some bodies, and the Cu-Au-Te sulfide liquid able to migrate through the plumbing system on a district scale at lower crustal temperatures over considerable time. As such, these deposits represent a distinct class of orogenic, lower crustal magmatic sulfide deposits that display sulfide liquid fractionation on a district scale.

The Munali Intrusive Complex is hosted within supracrustal metasedimentary rocks located along a major structural lineament within the Zambezi Belt in southern Zambia. The complex comprises unmineralised gabbro surrounded by a marginal heterogeneous mafic-ultramafic breccia unit that is host to Ni-Fe sulfide. This marginal unit comprises a range of variably evolved brecciated mafic-ultramafic rocks that include gabbro, olivine-gabbro and dolerite, alongside younger, pegmatitic, apatite-magnetite-bearing clinopyroxenite, wehrlite and dunite. The magmatic evolution is most consistent with a model whereby early mafic rocks interact with hot, MgO- and volatile-rich melts along gabbro contacts, causing localised metasomatism of gabbro and pyroxenites, and progressively replacing pyroxene-rich rocks with olivine, forming pegmatitic 'replacive dunites'. Sulfide mineralisation is characterised by a carbonate-rich apatite-magnetite-bearing assemblage predominately present as lenses of semi-massive to massive sulfide ore. The complex is enveloped almost entirely within a unit of marble, yet C and O isotope signatures of carbonate at Munali have revealed a clear mantle signature for some of the carbonate associated with sulfide, alongside a more dominant, crustally derived component. The carbonate occurring alongside sulfide displays micro to macro textures signifying the presence of carbonate melts formed from anatectic melting of the country rocks. The presence of fracture sets that define coarse breccia clasts (>1 m) indicate that the host rock was significantly crystallised and brittly deformed prior to carbonate and sulfide melt infiltration. Both carbonate and sulfide melts appear to have independently utilised these pre-existing weaknesses producing a pseudobreccia, and accounting for the seemingly chaotic nature of the orebody. The indication of sulfide being a significantly later phase suggests that the sulfide did not form in situ and was mobilised from elsewhere to be subsequently emplaced late within the Munali system.

Magmatic Ni-Cu-platinum group element (PGE) deposits are commonly located in tectonically active regions that typically undergo significant deformation and metamorphism and subsequent reworking of sulfide. The Munali Ni deposit is hosted by a dynamic intrusive mafic-ultramafic system situated within the Zambezi belt in southern Zambia. The deposit comprises Fe-Ni–dominant magmatic sulfides, present as a number of lenticular massive sulfide bodies that display a variety of magmatic and metamorphic sulfide textures. The sulfide lenses are uniformly deficient in iridium subgroup PGEs (IPGEs), Au, and Cu, with unusual but characteristically high bulk Ni/Cu ratios (~10) and a consistent precious metal mineral assemblage dominated by Pd and Pt tellurides. On a centimeter to meter scale, Cu tenors and Ni/Cu ratios are extremely variable (Ni/Cu between 0.1 and 71.5), while Ni and Pd tenors are consistent, indicative of the high mobility and variable concentrations of Cu sulfide within the deposit. Sulfur isotope signatures of the ore sulfides (δ34S ~6‰; Δ33S ~0‰) indicate a local crustal S contaminant from host marbles yet display S/Se ratios suggestive of a postmagmatic overprint. The consistent geochemical similarities of the bulk sulfide throughout the complex and the absence of primary silicate-sulfide textures suggest that the Munali ores were not sourced from a parental magma directly represented by units within the complex. Instead, it is suggested that the sulfide liquid was introduced from elsewhere in the magmatic system during the later stages of the emplacement of the complex. Fractional crystallization of the sulfide liquid during emplacement resulted in the primary segregation of a Cu-rich residual liquid that migrated away from the bulk of the Fe-Ni sulfide, accounting for the high bulk Ni/Cu ratio, with the potential for the accumulation of a separate and thus far undiscovered Cu orebody. In addition, intense deformation during the Pan-African orogeny and interaction with hydrothermal fluids have locally overprinted some of the primary magmatic textures, resulting in localized sulfide mobilization and the extreme variations of Ni/Cu ratio between sulfide samples. Munali therefore represents a complex dynamic deposit showcasing a variety of mechanisms for sulfide fractionation of an Ni-Cu-PGE orebody by both syn- and postmagmatic processes.

Magmatic arcs are terrestrial environments where lithospheric cycling and recycling of metals and volatiles is enhanced. However, the first-order mechanism permitting the episodic fluxing of these elements from the mantle through to the outer Earth’s spheres has been elusive. To address this knowledge gap, we focus on the textural and minero-chemical characteristics of metal-rich magmatic sulfides hosted in amphibole-olivine-pyroxene cumulates in the lowermost crust. We show that in cumulates that were subject to increasing temperature due to prolonged mafic magmatism, which only occurs episodically during the complex evolution of any magmatic arc, Cu-Au-rich sulfide can exist as liquid while Ni-Fe rich sulfide occurs as a solid phase. This scenario occurs within a ‘Goldilocks’ temperature zone at ~1100–1200 °C, typical of the base of the crust in arcs, which permits episodic fractionation and mobilisation of Cu-Au-rich sulfide liquid into permeable melt networks that may ascend through the lithosphere providing metals for porphyry and epithermal ore deposits.

Iron oxide copper-gold (IOCG) deposits host Cu and Au, as well as numerous other potential by-products such as U, Ag, Co, and rare earth elements. The Kitumba IOCG deposit in Zambia has undergone multiple stages of alteration and sulfide formation and subsequent supergene enrichment, with Cu reaching up to 30% in supergene zones down to depths of several hundred metres. Quantitative mineralogy characterised five styles of mineral-isation. Stage 1 hypogene chalcopyrite and pyrite, is progressively replaced by Stage 2, a continuum of supergene stages: 2a chalcocite and minor covellite; 2b cuprite and native Cu, 2c malachite and 2d brochantite. In addition, a distinct zone of Au enrichment (up to 2 ppm) is found in Fe-oxide breccia near the upper parts of the deposit which appears to be hosted by a pocket of folded and heavily Fe-altered Katangan metasedimentary rocks. Replacement of hypogene sulfides by chalcocite occurred under acidic conditions (pH 5.5-6); with the precip-itation of cuprite, native Cu under near neutral, more oxidising conditions (pH > 6) and precipitation of mal-achite under further oxidising conditions (pH 6.5-8), with localised zones of acidity (pH 5.9-7) that encouraged the precipitation of brochantite. Cobalt is notably depleted in the supergene zone relative to hypogene, whilst Ag is enriched. We present a genetic model for supergene mineralisation at the Kitumba IOCG deposit, and as such has implications for other supergene altered IOCG deposits with a similar supergene mineralogy. Importantly, the Cu mineralisation styles established each have distinctive geometallurgical characteristics, and as such, has implication for processing of ore.

The Ivrea Zone of NW Italy records the polyphased evolution of a magmatic sulfide mineral system, which occurred at multiple stages over a >80 Ma time interval. Between 290 and 250 Ma, a series of hydrated and carbonated ultramafic alkaline pipes containing Ni-Cu-PGE-(Te-Au) mineralisation was emplaced in the lower continental crust. At 200 Ma, a subsequent mineralising event occurred in association with the emplacement of the La Balma-Monte Capio (LBMC) intrusion. Modelling of the LBMC parental magma shows derivation from up to 60% partial melting of an anhydrous depleted juvenile mantle outside of garnet stability. The inferred composition of the parental melt is consistent with magmatism associated with the Central Atlantic Magmatic Province (CAMP). However, its tellurium-enriched composition together with the S-C-O isotope signature of the associated magmatic sulfide mineralisation (634S = +0.53 to +1.00%0; 613C = & minus;10.41 to & minus;4.07%0; 618O = +6.57 to +13.74%0) cannot be reconciled with the CAMP source. It is argued that the geochemical and isotopic signature of the LBMC intrusion reflects interaction and mixing of a primitive magma sourced from a juvenile source with localised domains enriched in carbonate and metal-rich sulfides located in the lower crust, consistent with the composition of the Permo-Triassic pipes. We propose that this interaction resulted in sulfidesupersaturation and enrichment in volatiles and metals of the LBMC magma. Upwards magma transport may have been facilitated by devolatisation of magmatic carbonate from the pipes and the generation of a CO2 supercritical fluid that acted as buoyancy aid for the dense sulfide liquid. Evidence of this magmatic interaction informs on the first-order processes that control enhanced metallogenic fertility along the margins of lithospheric blocks. The scenario depicted here is consistent with reactivation and enrichment of a Gondwana margin Ni-Cu-PGE(Te-Au) mineral system during the breakup of Pangea. (C) 2021 Elsevier B.V. All rights reserved.

The long-lived geodynamic evolution of the Permo-Triassic boundary between Laurasia and Gondwana may have created the ideal conditions for the genesis of a trans-continental Ni-Cu-PGE-(Au-Te) mineralised belt in Europe. This working hypothesis stems from the recent understanding that orogenic processes play a fundamental role in the onset of chemical and physical triggers for the transport of metals from the metasomatised mantle through to various crustal levels. An insight into our renewed framework for the polyphased genetic evolution of magmatic sulfide mineral systems is provided by a series of mineralised occurrences in the Ivrea Zone of NW Italy, which formed at multiple stages over a > 80 Ma time interval. Between 290-250 Ma, a series of hydrated and carbonated ultramafic alkaline pipes containing Ni-Cu-PGE-(Te-Au) mineralisation was emplaced in the lower continental crust. At ~200 Ma, a subsequent mineralising event occurred in association with the emplacement of the La Balma-Monte Capio (LBMC) intrusion. Modelling of the LBMC parental magma shows derivation from ~30% partial melting of an anhydrous juvenile mantle at moderate pressure (< 7 GPa). The inferred composition of the parental melt is consistent with magmatism associated with the Central Atlantic Magmatic Province (CAMP). However, its tellurium-enriched composition together with the S-C-O isotope signature of the associated magmatic sulfide mineralisation cannot be reconciled with the CAMP source. It is argued that the geochemical and isotopic signature of the LBMC intrusion reflects interaction and mixing of a primitive magma sourced from a juvenile source with localised domains enriched in carbonate and metal-rich sulfides located in the lower crust, consistent with the composition of the Permo-Triassic pipes. Evidence of this magmatic interaction informs on the first-order processes that control enhanced metallogenic fertility along the margins of lithospheric blocks. The scenario depicted here is consistent with reactivation and enrichment of a Gondwana margin Ni-Cu-PGE-(Te-Au) mineral system during the breakup of Pangea. The lessons learnt in the Ivrea Zone natural laboratory may inform on the genesis of other Permo-Triassic magmatic mineral systems in continental Europe, such as the deposits in north-west Czech Republic and southern Spain, which display significant analogies with their counterparts in the Ivrea Zone. We suggest that these systems may have a common DNA related to a metallogenic belt forming at different stages during the complex evolution and multi-phase activation of the margin between Laurasia and Gondwana. The nature and localisation of the magmatic sulfide mineral systems along this belt indicate that enhanced potential for ore formation at lithospheric margins may be due not only to favourable architecture, but also to localised enhanced metal and volatile fertility. Importantly, this hypothesis may explain why ore deposits along the margins of lithospheric blocks are not distributed homogeneously along their entire extension but generally form clusters. As mineral exploration is essentially a search space reduction exercise, this new understanding may prove to be important in predictive exploration targeting for new mineralised camps in Europe and elsewhere globally, as it provides a way to prioritise segments with enhanced fertility along extensive lithospheric block margins.

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.

Pentlandite is the dominant Ni-hosting ore mineral in most magmatic sulfide deposits and has conventionally been interpreted as being entirely generated by solid-state exsolution from the high-temperature monosulfide solid solution (MSS) (Fe,Ni)1–xS. This process gives rise to the development of loops of pentlandite surrounding pyrrhotite grains. Recently it has been recognized that not all pentlandite forms by exsolution. Some may form as the result of peritectic reaction between early formed MSS and residual Ni-Cu–rich sulfide liquid during differentiation of the sulfide melt, such that at least some loop textures may be genuinely magmatic in origin. Testing this hypothesis involved microbeam X-ray fluorescence mapping to image pentlandite-pyrrhotite-chalcopyrite intergrowths from a range of different deposits. These deposits exemplify slowly cooled magmatic environments (Nova, Western Australia; Sudbury, Canada), globular ores from shallow-level intrusions (Norilsk, Siberia), extrusive komatiite-hosted ores from low and high metamorphic-grade terranes, and a number of other deposits. Our approach was complemented by laser ablation-inductively coupled plasma-mass spectrometry analysis of palladium in varying textural types of pentlandite within these deposits. Pentlandite forming coarse granular aggregates, together with loop-textured pentlandite where chalcopyrite also forms part of the loop framework, consistently has the highest Pd content compared with pentlandite clearly exsolved as lamellae from MSS or pyrrhotite. This is consistent with much of granular and loop pentlandite being formed by peritectic reaction between Pd-rich residual sulfide liquid and early crystallized MSS, rather than forming entirely by subsolidus grain boundary exsolution from MSS, as has hitherto been assumed. The wide range of Pd contents in pentlandite in individual samples reflects a continuum of processes between peritectic reaction and grain boundary exsolution. Textures in metamorphically recrystallized ores are distinctly different from loop-textured ores, implying that loop textures cannot be regenerated (except in special circumstances) by metamorphic recrystallization of original magmatic-textured ores. The presence of loop textures can therefore be taken as evidence of a lack of penetrative deformation and remobilization at submagmatic temperatures, a conclusion of particular significance to the interpretation of the Nova deposit as having formed synchronously with the peak of regional deformation at temperatures within the sulfide melting range.

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.

The lower crustal domains of the Ivrea Zone of NW Italy record the polyphase evolution of a Ni-Cu-PGE-(Te-Au) magmatic sulfide mineral system, which formed during multiple stages over an 80 Myr interval along the NW margin of Gondwana. Between 290-250 Ma, a series of hydrated and carbonated ultramafic alkaline pipes containing Ni-Cu-PGE-(Te-Au) mineralisation was emplaced in the lower continental crust of the Ivrea Zone. Subsequently, at 200 Ma Ni-Cu-PGE mineralisation was associated with emplacement of the La Balma-Monte Capio (LBMC) ultramafic intrusion. The composition and metal endowment of the LBMC reflects interaction and mixing between a deeply sourced juvenile and relatively dry primitive magma, most likely associated with the Central Atlantic Magmatic Province, with localised pods enriched in volatiles, metals, sulfur and tellurium, consistent with the composition of the Permo-Triassic pipes. The scenario depicted here may explain why ore deposits along the margins of lithospheric blocks are not distributed homogeneously along their entire extension but generally form clusters. As mineral exploration is essentially a search space reduction exercise, this new understanding may prove to be important in predictive exploration targeting for new mineralised camps, as it provides a way to prioritise segments with enhanced fertility along extensive lithospheric block margins.

The 'fertility' of arc magmas to form porphyry Cu-Au deposits in the upper crust is dependant on a number of processes occurring within the source-pathway-sink framework of the evolution of any particular magmatic system. One of the first barriers to fertility is the so-called 'sulfide trap' whereby sulfides in lower crustal cumulates will sequester metals such as Cu and Au, thus rendering any subsequent upper crustal melts infertile. Textural evidence from the Ivrea zone in Italy, alongside numerical modelling for lower crustal cumulate complexes, shows that although sulfides may be present in these rocks, they are not necessarily a 'trap' as such. Instead, the typical temperatures of these systems allows for incongruent melting and potentially mobilization of Cu-Au sulfide associated with melt networks within these cumulate intrusions. This allows for a mechanism whereby partially molten Cu-Au-rich sulfide can be fractionated from solid Ni-Fe-rich sulfide, which could potentially be mobilized into the upper crust and ultimately supply metals to form porphyry-fertile intrusions.

Tellurium and selenium are essential elements in third generation photovoltaic cells for solar power. Production is currently almost entirely as by-products from copper refining. Therefore, these elements are defined as 'critical' in terms of their projected increasing demand for future energy technologies, and their supply being determined by the economics of a separate commodity. Iron Oxide Copper Gold (IOCG) deposits are complex hydrothermal systems and whilst all deposits, by definition, contain economic Cu and Au, many deposits also have significant by-products, including U, REE, Co, Ag and As and a host of other potential by-products, including Te and Se. Thus, IOCGs represent vast potential resources for a number of critical elements. We show that resources of these elements can be effectively estimated using reliable ratios to the major, reported commodities. For example, Cu/Se and Au/Te ratios are consistent enough to be able to determine potential resources in the ores, but also an indication of recoverability by considering the respective ratios in the concentrates and tailings.

"Unravelling the dynamic emplacement of the carbonate-rich Munali Ni–Cu–PGE breccia deposit, Zambia." Applied Earth Science, 128(2), pp. 39–40

The Munali magmatic sulfide complex is an enigmatic mafic-ultramafic breccia deposit, comprised of atypical Cr-poor magmatic host rocks and an unusual Ni rich/Cu-poor carbonate-apatite-magnetite sulfide assemblage. Mineralisation is present as a sulfide matrix breccia, in which the clasts are present as an array of lithologies and sizes ranging from < 0.5 cm to > 5 m and is mined principally for its Ni resource, with Cu, PGE and Co as supplementary by-products. Several mineralisation styles have been identified which contain a similar sulfide mineralogy (pyrrhotite >> pentlandite > chalcopyrite pyrite), but display differences in sulfide abundance, gangue mineralogy and geochemical characteristics. Additionally, variations of Pd and Co within pentlandite and pyrite between the styles, suggest complexities in emplacement timing and/or sulfide melt interactions. The bulk sulfide at Munali displays high Ni/Cu ratios and an extreme negative Au anomaly, which is atypical for a mafic-ultramafic complex. Therefore, Munali may represent a sulfide system where the primary sulfide melt that crystallised was unusually low in Cu and Au or may instead suggest that syn-to-post magmatic processes may have altered or displaced the Cu(-Au)-rich component of the orebody and that these may now reside elsewhere in the system.

Magmatic sulfide deposits hosted by mafic-ultramafic intrusions are the most important source of Ni and PGE on Earth. Exploration strategies rely on geophysics to identify the host intrusions, and surface geochemistry to identify anomalous concentrations of Cu, Ni, Co, Cr, As and other associated elements. The use of geochemical indicator minerals in overburden is used widely in diamond exploration and mineral chemistry in fresh rock is increasingly used to identify proxies for mineralisation in magmatic-hydrothermal systems. However, no indicator mineral techniques are routinely applied to magmatic sulfides. Magnetite represents an ideal indicator mineral for this mineralisation style due to its ubiquity in such deposits, its resistance to weathering, its recoverability from soil samples, and its chemical variability under differing conditions of formation. We use the Munali Ni sulfide deposit to test the use of magnetite as an indicator mineral. Magnetite from mafic, ultramafic, and magmatic sulfide lithologies in fresh rock at Munali show discernible differences in the most compatible elements (V, Ni, Cr). We propose a new Cr/V versus Ni discrimination diagram for magnetite that can be used to indicate fractionation of the parent magma (Cr/V increases from ultramafic to mafic), and the presence of coexisting sulfides (Ni contents > 300 ppm). The signatures of these three elements at Munali are comparable to sulfide-related magnetites from other deposits, supporting the broad applicability of the discrimination diagram. Samples taken from overburden directly on top of the Munali deposit replicate signatures in the fresh bedrock, strongly advocating the use of magnetite as an exploration indicator mineral. Samples from areas without any geophysical or geochemical anomalies show weak mineralisation signatures, whereas magnetite samples taken from prospects with such anomalies display mineralisation signatures. Magnetite is a thus a viable geochemical indicator mineral for magmatic sulfide mineralisation in early stage exploration.

Abstracts from the 2017–2018 Mineral Deposits Studies Group meetings from the 2017–2018 Mineral Deposits Studies Group meeting Cobalt recovery from Katanga ores (DRC): the importance of mineralogical evaluation L. Santoro, St. Tshipeng Yav, E. Pirard and A. Kaniki Natural History Museum (l.santoro@nhm.ac.uk); University of Lubumbashi (Tshipeng@sgs.com); University of Liege (eric.pirard@ulg.ac. be) ABSTRACT Cobalt in the Congolese Copperbelt mines is commonly recovered from Co-oxi-hydroxides (i.e. heterogenite, asbolane) by acid-leaching under reducing conditions. However, most operations face a limit in the leaching yields of cobalt, which usually do not exceed 80%. The main aim of this work was to investigate the causes of the poor recovery, in order to reconcile the Co recovery with processing techniques. Several concentrate samples from different mine plants of Katanga Copperbelt (Kalukuluku, Mutanda, Mabaya, Kamwali and Fungurume) were selected and subjected to a full mineralogical characterisation by Optical Microscopy (OM), X-Ray Diffraction (XRD), automated mineralogy and Scanning Electron Microscopy by Energy Dispersive Spectroscopy (SEM-EDS) prior and after leaching tests. OM and XRD results were used as background information to build a mineral list for mineral identification during automated mineralogy analyses by Mineralogic Mining System (Zeiss ltd.). Automated mineralogy allowed obtaining mineral maps, modal mineralogy, chemical assays and Co deportment for each specimen prior and after leaching. Mineral maps of the leached samples were useful to observe the occurrences of poorly leached Co-bearing particles which were further investigated by SEM-EDS and X-mapping. The results showed that heterogenite (rarely associated with asbolane) is the main cobalt mineral in Katanga. Mineralogic Mining System was able to discriminate between pure heterogenite, and Si-Al-K-bearing heterogenite, asbolane/heterogenite, Heterogenite+Fe-oxi-hydroxide and Co-bearing mixed phases, which resulted more refractory to leaching. The comparison between modal mineralogy of preand post-leached samples indicates a decrease, but not a full leaching of these Co phases: chemical assays and Codeportment, in fact, still reveal the presence of low Co% within Co phases listed above (Table 1). SEM-EDS and Xmapping on single particles of some specimens corroborated the results obtained by Mineralogic.Cobalt in the Congolese Copperbelt mines is commonly recovered from Co-oxi-hydroxides (i.e. heterogenite, asbolane) by acid-leaching under reducing conditions. However, most operations face a limit in the leaching yields of cobalt, which usually do not exceed 80%. The main aim of this work was to investigate the causes of the poor recovery, in order to reconcile the Co recovery with processing techniques. Several concentrate samples from different mine plants of Katanga Copperbelt (Kalukuluku, Mutanda, Mabaya, Kamwali and Fungurume) were selected and subjected to a full mineralogical characterisation by Optical Microscopy (OM), X-Ray Diffraction (XRD), automated mineralogy and Scanning Electron Microscopy by Energy Dispersive Spectroscopy (SEM-EDS) prior and after leaching tests. OM and XRD results were used as background information to build a mineral list for mineral identification during automated mineralogy analyses by Mineralogic Mining System (Zeiss ltd.). Automated mineralogy allowed obtaining mineral maps, modal mineralogy, chemical assays and Co deportment for each specimen prior and after leaching. Mineral maps of the leached samples were useful to observe the occurrences of poorly leached Co-bearing particles which were further investigated by SEM-EDS and X-mapping. The results showed that heterogenite (rarely associated with asbolane) is the main cobalt mineral in Katanga. Mineralogic Mining System was able to discriminate between pure heterogenite, and Si-Al-K-bearing heterogenite, asbolane/heterogenite, Heterogenite+Fe-oxi-hydroxide and Co-bearing mixed phases, which resulted more refractory to leaching. The comparison between modal mineralogy of preand post-leached samples indicates a decrease, but not a full leaching of these Co phases: chemical assays and Codeportment, in fact, still reveal the presence of low Co% within Co phases listed above (Table 1). SEM-EDS and Xmapping on single particles of some specimens corroborated the results obtained by Mineralogic. The poor recovery of cobalt was ascribed to the mineralogical complexity making the routine processing strategy poorly effective. More attention must hence be placed during the processing stages of Co-ores, in order to avoid inappropriate leaching conditions, inappropriate pulp density and liberation issues caused by the occurrence of Co-bearing phases refractory to leaching treatments. The Cristal mineralisation (Amazonas region, Northern Peru): An example of supergene zinc enrichments in tropical areas G. Arfè, N. Mondillo, M. Boni, M. Joachimski, G. Balassone and A. Mormone Dipartimento di Scienze della Terra, dell’Ambiente e delle Risorse, Università degli Studi di Napoli Federico II, Complesso Universitario di Monte S. Angelo, Napoli 80126, Italy; GeoZentrum Nordbayern, University of Erlangen-Nuremberg, Schlossgarten 5, Erlangen 91054, Germany; INGV Osservatorio Vesuviano, Via Diocleziano 328, Napoli 80124, Italy Email address: boni@unina.it Table 1. KALUKULUKU MUTANDA MABAYA KAMWALI FUNGURUME Co content 0.02% 0.22% 5.18% 2.11% 0.05% Co-bearing mixed phases 87.49 16.7 33.12 22.46 85.47 Heterogenite 57.83 32.15 27.18 1.14 Si, Al, K-bearing heterogenite 12.5 18.59 32.68 42.61 12.63 Heterogenite+Fe-oxi-hydroxides 6.88 1.21 4.15 0.76 Asbolane 0.83 3.6 © 2018 Institute of Materials, Minerals and Mining and The AusIMM APPLIED EARTH SCIENCE (TRANS. INST. MIN. METALL. B) 2018, VOL. 127, NO. 2, 46–79 https://doi.org/10.1080/25726838.2018.1487425