The influence of country-rock assimilation and silicate to sulfide ratios (R factor) on the genesis of the Dunka Road Cu – Ni – platinum-group element deposit, Duluth Complex, Minnesota

1997 ◽  
Vol 34 (4) ◽  
pp. 375-389 ◽  
Author(s):  
Robert D. Thériault ◽  
Sarah-Jane Barnes ◽  
Mark J. Severson
Keyword(s):  
Platinum Group Element ◽  
Country Rock ◽  
Metal Sulfide ◽  
Parental Magma ◽  
Group Element ◽  
Duluth Complex ◽  
Metasedimentary Rocks ◽  
R Factor ◽  
Platinum Group ◽  
R Factors

The Dunka Road deposit is one of several Cu – Ni – platinum-group element (PGE) sulfide occurrences found along the northwestern margin of the Duluth Complex, where the host troctolitic rocks are in contact with metasedimentary rocks of the Animikie Group. Magma contamination through assimilation of sulfidic argillaceous country rocks is generally recognized as having played a key role in the genesis of the mineralization. Three main types of disseminated sulfide mineralization have been identified within the Dunka Road deposit: (i) norite-hosted sulfides, (ii) troctolite-hosted sulfides, and (iii) PGE-rich sulfide horizons. The norite-hosted sulfides are found either adjacent to country-rock xenoliths or near the basal contact. The troctolite-hosted sulfides form the bulk of the deposit, and occur throughout the lower 250 m of the intrusion. The PGE-rich sulfide horizons are typically localized directly beneath ultramafic layers. The composition of the different types of sulfide occurrences is modelled using Cu/Pd ratios. It is shown that each type results from the interplay of two main parameters, namely the degree of magma contamination and the silicate magma to sulfide melt ratio (R factor). The norite-hosted sulfides formed at low R factors and high degrees of contamination, as expressed by their PGE-depleted nature, low Se/S ratios, and elevated content in pyrrhotite and arsenide minerals. The troctolite-hosted sulfides formed at moderate R factors and small degrees of contamination, as shown by their moderate PGE content and mantle-like Se/S ratios. Finally, the PGE-rich sulfide horizons are modelled using elevated R factors from an uncontaminated parental magma, which is substantiated by their elevated noble metal content and Se/S ratios, and low pyrrhotite to precious metal sulfide ratio.

On the Mechanisms for Low-Sulfide, High-Platinum Group Element and High-Sulfide, Low-Platinum Group Element Mineralization in the Eastern Gabbro, Coldwell Complex, Canada: Evidence from Textural Associations, S/Se Values, and Platinum Group Element Concentrations of Base Metal Sulfides

2020 ◽  
Vol 115 (2) ◽  
pp. 355-384
Author(s):  
M. J. Brzozowski ◽  
I. M. Samson ◽  
J. E. Gagnon ◽  
D. J. Good ◽  
R. L. Linnen
Keyword(s):  
Base Metal ◽  
Platinum Group Element ◽  
Metal Sulfide ◽  
Group Element ◽  
Pge Mineralization ◽  
Base Metal Sulfides ◽  
Wide Range ◽  
Platinum Group ◽  
Compositional Variations ◽  
R Factors

Abstract The Eastern Gabbro, Coldwell Complex, hosts several geochemically and mineralogically distinct Cu-platinum group element (PGE) deposits, including the high-grade W Horizon (>100 ppm Pd-Pt-Au over 2 m). Several magmatic and/or hydrothermal models have previously been proposed to explain the range of enrichment in PGEs observed in the Marathon deposit, but no work has integrated textural and compositional variations in sulfides to elucidate which of these models is most suitable. Additionally, comparatively little work has been done to characterize the genesis of Cu-PGE mineralization that occurs to the northwest of the Marathon deposit in the Eastern Gabbro. Through integration of base metal sulfide (BMS) mineralogy, texture, and trace element chemistry, a wide range of magmatic and postmagmatic processes have been characterized that contributed to the formation of these deposits. In all zones of mineralization in the Eastern Gabbro, chalcophile elements were remobilized from primary chalcopyrite by hydrothermal fluids and precipitated as secondary chalcopyrite, which occurs as a replacement of pyrrhotite and as intergrowths with hydrous silicates. BMSs in the mineralized zones in the Marathon deposit (Footwall zone, Main zone, and W Horizon) experienced higher R factors than those deposits located northwest of the Marathon deposit (Four Dams, Area 41, and Redstone), with BMSs in the W Horizon having experienced the highest R factors. The silicate melts from which the Footwall zone crystallized likely experienced some degree of sulfide segregation at depth, albeit to a much lesser degree than the northern deposits. Additionally, the melts from which the mineralized zones in the Marathon deposit crystallized were likely contaminated by high-S/Se Archean sedimentary rocks, whereas the northern deposits were likely contaminated by low-S/Se igneous and/or metamorphic rocks. BMSs in a chalcopyrite-rich pod located within the vicinity of the Coldwell Complex experienced both high R factors and high degrees of contamination (cf. W Horizon and Footwall zone, respectively). This study illustrates the complexity of processes that generate and modify mineralization in conduit-type Ni-Cu-PGE systems.

Variant Offset-Type Platinum Group Element Reef Mineralization in Basal Olivine Cumulates of the Kapalagulu Intrusion, Western Tanzania

2021 ◽  
Author(s):  
M. D. Prendergast
Keyword(s):  
Precious Metal ◽  
Platinum Group Element ◽  
Early Stage ◽  
Precious Metals ◽  
Parental Magma ◽  
Group Element ◽  
Metal Enrichment ◽  
Reef Development ◽  
Platinum Group ◽  
Olivine Cumulates

Abstract The Kapalagulu intrusion in eastern Tanzania hosts a major, 420-m-thick, stratiform/stratabound platinum group element (PGE)-bearing sulfide zone—the Lubalisi reef—within a prominent, chromititiferous, harzburgite unit close to its stratigraphic base. Several features of the vertical base and precious metal distributions (in a composite stratigraphic section based upon two deep exploration drill holes) display similarities to those of offset-type PGE reefs that formed under the overall control of Rayleigh fractionation: (1) composite layering (at several scales) defined by systematic vertical variations of sulfide and precious metal contents and intermetallic ratios, indicating repeated cycles of PGE enrichment and depletion in the order Pd-Pt-Au-Cu, and (2) in the lower part of the reef, stratigraphic offsets of the precious metal peaks below peak sulfide (Cu) content. The form and geochemistry of the reef are consistent with overturns of basal liquid layers within a liquid layering system (i.e., stable density-driven stratification of a magma chamber), plus at least two minor inputs of parental magma during which the resident magma was recharged with sulfur and metals, and the effective depletion of precious metals in the magma midway through reef development. The Lubalisi reef differs from classic offset-type PGE reefs, however, principally because individual Pd, Pt, and Au enrichment peaks are coincident, not offset. The reef is set apart from other offset-type PGE reefs in three additional ways: (1) its association with olivine cumulates that crystallized soon after initial magma emplacement and well below the first appearance of cumulus pyroxene or plagioclase (implying attainment of sulfide saturation and precious metal enrichment without prolonged concentration of sulfur and chalcophile metals by normal magma cooling and differentiation), (2) the probable role of chromite crystallization in not only triggering sulfide segregation during reef formation but also facilitating precious metal enrichment in the early stages of reef development, and (3) its great width. The early stage of fractionation may also help explain the coincident precious metal peaks through its effect on apparent precious metal partition coefficients.

scholarly journals Contact-style magmatic sulphide mineralisation in the Labrador Trough, northern Quebec, Canada: implications for regional prospectivity

2020 ◽  
Vol 57 (7) ◽  
pp. 867-883 ◽  
Author(s):  
W.D. Smith ◽  
W.D. Maier ◽  
I. Bliss
Keyword(s):  
Platinum Group Element ◽  
Group Element ◽  
Common Source ◽  
Upper Crust ◽  
Sulphide Ores ◽  
Sulphide Mineralisation ◽  
Platinum Group ◽  
R Factors ◽  
Pge Geochemistry

The Labrador Trough in northern Quebec is currently the focus of ongoing exploration for magmatic Ni-Cu-platinum group element (PGE) sulphide ores. This geological belt hosts voluminous basaltic sills and lavas of the Montagnais Sill Complex, which are locally emplaced among sulphidic metasedimentary country rocks. The recently discovered Idefix PGE-Cu prospect represents a stack of gabbroic sills that host stratiform patchy disseminated to net-textured sulphides (0.2–0.4 g/t PGE+Au) over a thickness of ∼20 m, for up to 7 km. In addition, globular sulphides occur at the base of the sill, adjacent to the metasedimentary floor rocks. Whole-rock and PGE geochemistry indicates that the sills share a common source and that the extracted magma underwent significant fractionation before emplacement in the upper crust. To develop the PGE-enriched ores, sulphide melt saturation was attained before final emplacement, peaking at R factors of ∼10 000. Globular sulphides entrained along the base of the sill ingested crustally derived arsenic and were ultimately preserved in the advancing chilled margin.

Sulfide saturation mechanisms in gabbroic intrusions in the Nipigon Embayment

2007 ◽  
Vol 44 (8) ◽  
pp. 1203-1214
Author(s):  
Stephen A Kissin ◽  
Geoffrey J Heggie ◽  
James M Franklin ◽  
Alireza Karimzadeh Somarin
Keyword(s):  
Platinum Group Element ◽  
Country Rock ◽  
Group Element ◽  
Isotopic Data ◽  
Sulfide Saturation ◽  
Copper Nickel ◽  
Northwestern Ontario ◽  
Reef Type ◽  
Sulfur Saturation ◽  
Platinum Group

The Seagull and Kitto intrusions in the Nipigon Embayment of northwestern Ontario were studied to gain an understanding of the processes involved in sulfur saturation of the mafic to ultramafic magmas leading to the formation of platinum group element (PGE) concentrations. Profiles of sulfur, copper, nickel, gold, palladium, and platinum concentrations as a function of depth revealed that sulfur saturation occurred at the base of the Seagull intrusion. A higher grade horizon occurs well above the base of the intrusion, suggesting that a reef-type of process was significant here and possibly in the Kitto intrusion, as well. Olivine compositions indicate that, in both cases, the parental magmas were undersaturated with respect to sulfur. Sulfur, neodymium–samarium, and rubidium–strontium isotopic data suggest that assimilation of country rock and sulfide played a role, especially in the formation of basal concentrations of PGEs.

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