Assessment of the Ni-Cu-PGE sulphide potential of magmatic intrusions surrounding the Munali Ni-sulphide deposit, Zambia

Howe, Grace A.; Holwell, David A.

doi:10.1080/03717453.2016.1166637

Cited by 2 publications

(4 citation statements)

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“…1A), although magnetic anomalies highlight a range of potentially prospective intrusions at depth that include the gabbroic rocks at Chibuku, located directly to the north-east of T1B (Fig. 1A), some of which have indications for the presence of sulfide mineralisation (Howe and Holwell, 2016). All the intrusions and magnetic anomalies within the Munali Hills are spatially associated with the Munali Fault and/or secondary E-W trending structures (Fig.…”

Section: Geological Settingmentioning

confidence: 95%

“…Sulfur isotope signatures from disseminated sulfides in the T1B and Chibuku intrusions show δ 34 S isotopic signatures of +6.1 and +6.0‰, respectively, within the same range as the sulfide from the Munali orebody. Additionally, whole rock Cu/Pd ratios of the T1B gabbro and clinopyroxenite are extremely high and support sulfide formation and removal (Howe et al, 2016). Thus, there is evidence of widespread sulfide segregation in regional intrusive bodies with a common crustal source of S. These intrusions may form a linked magmatic plumbing system along the Munali Fault, and into the overlying stratigraphy, giving support to the possibility that the Munali sulfides have been sourced from a magma along strike, or stratigraphically higher than the Munali Intrusive Complex, such as T1B or an equivalent intrusion.…”

Section: Timing and Source Of Sulfide Mineralisationmentioning

confidence: 98%

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Mobilization and Fractionation of Magmatic Sulfide: Emplacement and Deformation of the Munali Ni-(Cu-Platinum Group Element) Deposit, Zambia

et al. 2022

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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.

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Section: Geological Settingmentioning

confidence: 95%

Section: Timing and Source Of Sulfide Mineralisationmentioning

confidence: 98%

Mobilization and Fractionation of Magmatic Sulfide: Emplacement and Deformation of the Munali Ni-(Cu-Platinum Group Element) Deposit, Zambia

et al. 2022

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“…The MIC displays a very strong magnetic anomaly, with additional anomalies present along the Munali Fault and the northern fault splay ( Fig. 1A), marking the presence of a number of proven and inferred intrusions of a similar genesis (Howe and Holwell. 2016).…”

Section: The Munali Ni Sulfide Depositmentioning

confidence: 98%

“…8D,E), though in terms of the proportion of overall grains, there are fewer mineralisation indicators than the other three samples. Chibuku is a mafic-ultramafic intrusion with indications of mineralisation potential from Cu/Pd ratios (Howe and Holwell 2016), that does not crop out, but is proven to be present at ~200 m depth from a single exploration drillhole. It would not be expected that any indicator minerals would be present from an intrusion present at such depth, although given the very limited drilling, some parts of it may be closer to the surface, which may be a source for the mineralised signatures in the overburden.…”

Section: Detrital Magnetite Petrology and Geochemistrymentioning

confidence: 99%

The use of magnetite as a geochemical indicator in the exploration for magmatic Ni-Cu-PGE sulfide deposits: A case study from Munali, Zambia

Ward

Holwell

Barry

et al. 2018

Journal of Geochemical Exploration

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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 co-existing sulfides (Ni contents >300ppm). 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.

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Assessment of the Ni-Cu-PGE sulphide potential of magmatic intrusions surrounding the Munali Ni-sulphide deposit, Zambia

Cited by 2 publications

References 1 publication

Mobilization and Fractionation of Magmatic Sulfide: Emplacement and Deformation of the Munali Ni-(Cu-Platinum Group Element) Deposit, Zambia

Mobilization and Fractionation of Magmatic Sulfide: Emplacement and Deformation of the Munali Ni-(Cu-Platinum Group Element) Deposit, Zambia

The use of magnetite as a geochemical indicator in the exploration for magmatic Ni-Cu-PGE sulfide deposits: A case study from Munali, Zambia

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