Nova-Bollinger Ni-Cu Sulfide Ore Deposits, Fraser Zone, Western Australia: Petrogenesis of the Host Intrusions

Abstract The Nova-Bollinger Ni-Cu sulfide ore deposit is the first economic Ni-Cu-Co sulfide deposit to have been discovered in the Albany-Fraser orogen in Western Australia. The host rocks are mafic-ultramafic intrusive cumulates subdivided into two connected intrusions, designated Upper and Lower. The Upper Intrusion is bowl-shaped and modally layered with alternating peridotite and norite mesocumulate layers, with a Basal Series of dominantly orthocumulate mafic lithologies. The Lower Intrusion is a much thinner, semiconformable chonolith (flattened tube-shaped intrusion) consisting of mostly unlayered mafic to ultramafic orthocumulates. The Lower Intrusion hosts all the high-grade mineralization and most of the disseminated ores. A distinctive plagioclase-bearing lherzolite containing both orthopyroxene and olivine as cumulus phases is a characteristic of the Lower Intrusion and the Basal Series of the Upper. The intrusions differ slightly in olivine and spinel chemistry, the differences being largely attributable to the more orthocumulate character of the Lower Intrusion. Sector zoning in Cr content of pyroxenes is observed in the Lower Intrusion and in the lower marginal zone of the Upper and is attributed to crystallization under supercooled conditions. Symplectite pyroxene-spinel-amphibole coronas at olivine-plagioclase contacts are ubiquitous and are attributed to near-solidus peritectic reaction between olivine, plagioclase, and liquid during and after high-pressure emplacement, consistent with high Al contents in igneous pyroxenes and estimates of the peak regional metamorphism. Original cumulus olivines had compositions around Fo86 and were variably Ni depleted, interpreted as the result of preintrusion equilibration with sulfide liquid. The Upper and Lower Intrusion rocks represent cumulates from a similar parental magma, a high-Al tholeiite with MgO between 10 and 12%, low TiO2 (0.5–0.6%), and high Al2O3 (14–17%). Modeling using alphaMELTS indicates a primary water content of around 2 wt %. The cumulates of both intrusions were derived via multiple magma pulses of liquid-olivine-sulfide slurries with variable amounts of orthopyroxene, emplaced into the deep crust at pressures of around 0.7 GPa during the peak of regional metamorphism. The intrusions developed initially as a bifurcating sill, the lower arm developing into the ore-bearing Lower Intrusion chonolith and the upper arm inflating into the cyclically layered Upper Intrusion.

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Ore Formation During Jurassic Subduction of the Tethys Along the Eurasian Margin: Constraints from the Kapan District, Lesser Caucasus, Southern Armenia

Economic Geology ◽

10.5382/econgeo.4640 ◽

2019 ◽

Vol 114 (7) ◽

pp. 1251-1284 ◽

Cited By ~ 4

Author(s):

Johannes Mederer ◽

Robert Moritz ◽

Massimo Chiaradia ◽

Richard Spikings ◽

Jorge E. Spangenberg ◽

...

Keyword(s):

Middle Jurassic ◽

Late Jurassic ◽

Ore Deposits ◽

Sulfide Deposit ◽

Short Time Interval ◽

Ore Formation ◽

Magmatic Arc ◽

Argillic Alteration ◽

Lesser Caucasus ◽

Host Rocks

Abstract The Kapan mining district in the southernmost Lesser Caucasus is one of the few locations along the central Tethyan metallogenic belt where ore-forming processes were associated with magmatic arc growth during Jurassic Tethys subduction along the Eurasian margin. Three ore deposits of the Kapan district were investigated in this study: Centralni West, Centralni East, and Shahumyan. The ore deposits are hosted by Middle Jurassic andesitic to dacitic volcanic and volcaniclastic rocks of tholeiitic to transitional affinities below a late Oxfordian unconformity, which is covered by calc-alkaline to transitional Late Jurassic-Early Cretaceous volcanic rocks interlayered with sedimentary rocks. The mineralization consists of veins, subsidiary stockwork, and partial matrix replacement of breccia host rocks, with chalcopyrite, pyrite, tennantite-tetrahedrite, sphalerite, and galena as the main ore minerals. Centralni West is a dominantly Cu deposit, and its host rocks are altered to chlorite, carbonate, epidote, and sericite. At Centralni East, Au is associated with Cu, and the Shahumyan deposit is enriched in Pb and Zn as well as precious metals. Both deposits contain high-sulfidation mineral assemblages with enargite and luzonite. Dickite, sericite, and diaspore prevail in altered host rocks in the Centralni East deposit. At the Shahumyan deposit, phyllic to argillic alteration with sericite, quartz, pyrite, and dickite is dominant with polymetallic veins, and advanced argillic alteration with quartz-alunite ± kaolinite and dickite is locally developed. The lead isotope composition of sulfides and alunite (206Pb/204Pb = 18.17–18.32, 207Pb/204Pb = 15.57–15.61, 208Pb/204Pb = 38.17–38.41) indicates a common metal source for the three deposits and suggests that metals were derived from magmatic fluids that were exsolved upon crystallization of Middle Jurassic intrusive rocks or leached from Middle Jurassic country rocks. The δ18O values of hydrothermal quartz (8.3–16.4‰) and the δ34S values of sulfides (2.0–6.5‰) reveal a dominantly magmatic source at all three deposits. Combined oxygen, carbon, and strontium isotope compositions of hydrothermal calcite (δ18O = 7.7–15.4‰, δ13C = −3.4−+0.7‰, 87Sr/86Sr = 0.70537–0.70586) support mixing of magmatic-derived fluids with seawater during the last stages of ore formation at Shahumyan and Centralni West. 40Ar/39Ar dating of hydrothermal muscovite at Centralni West and of magmatic-hydrothermal alunite at Shahumyan yield, respectively, a robust plateau age of 161.78 ± 0.79 Ma and a disturbed plateau age of 156.14 ± 0.79 Ma. Re-Os dating of pyrite from the Centralni East deposit yields an isochron age of 144.7 ± 4.2 Ma and a weighted average age of the model dates of 146.2 ± 3.4 Ma, which are younger than the age of the immediate host rocks. Two different models are offered, depending on the reliability attributed to the disturbed 40Ar/39Ar alunite age and the young Re-Os age. The preferred interpretation is that the Centralni West Cu deposit is a volcanogenic massive sulfide deposit and the Shahumyan and Centralni East deposits are parts of porphyryepithermal systems, with the three deposits being broadly coeval or formed within a short time interval in a nascent magmatic arc setting, before the late Oxfordian. Alternatively, but less likely, the three deposits could represent different mineralization styles successively emplaced during evolution and growth of a magmatic arc during a longer time frame between the Middle and Late Jurassic.

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The Samapleu mafic-ultramafic intrusion and its Ni-Cu-PGE mineralization: an Eburnean (2.09 Ga) feeder dyke to the Yacouba layered complex (Man Archean craton, western Ivory Coast)

BSGF - Earth Sciences Bulletin ◽

10.2113/gssgfbull.185.6.393 ◽

2014 ◽

Vol 185 (6) ◽

pp. 393-411 ◽

Cited By ~ 10

Author(s):

Franck Gouedji ◽

Christian Picard ◽

Yacouba Coulibaly ◽

Marc-Antoine Audet ◽

Thierry Auge ◽

...

Keyword(s):

Hybrid Zone ◽

Ivory Coast ◽

Country Rock ◽

Parental Magma ◽

Massive Sulfide ◽

Contact Metamorphism ◽

Sulfide Deposit ◽

Sulfide Liquid ◽

Melt Composition ◽

Layered Complex

Abstract The Yacouba layered complex intrudes the Archean (3.5–2.7 Ga) Kenema-Man craton in the Samapleu-Yorodougou area, western Ivory Coast. In Samapleu area, the complex was recognized in drill holes at three locations: Samapleu Main (SM); Samapleu Extension 1 (E1) and Yorodougou (Yo). It comprises websterites, peridotites and gabbro-norites arranged symmetrically with mafic layers at the center and ultramafic layers at both margins. The complex is inclined at 70–80° to the SE. The thickness of individual layers varies from 2 to 60 m and the total thickness is 120 to 200 m. At the E1 site, the complex extends to depths > 500 m. Contacts with the country rock gneiss are characterized by a hybrid zone that is a few meters thick and composed of plagioclase-orthopyroxene bearing metabasites, and locally (E1 site) a metamorphic assemblage of sapphirine-cordierite-sillimanite-spinel ± rutile. This assemblage is attributed to contact metamorphism during intrusion of the complex in the lower crust at a depth of about 25 km. Zircons in country rock gneisses and granulites, as well as in the hybrid facies, yield Archean ages of ~ 2.78 Ga, similar to ages reported in the Man craton. Rutiles in the hybrid zone give a U-Pb age of 2.09 Ga, which is interpreted as the age of contact metamorphism and emplacement of the intrusion. The Samapleu Main and Samapleu Extension 1 sites contain Ni and Cu sulfide deposit with reserves estimated as more than 40 million tons grading 0.25% Ni and 0.22% Cu (Sama Nickel-CI, August 2013). The Ni-Cu mineralization is composed of pentlandite, chalcopyrite, pyrrhotite and rare pyrite, which is disseminated mainly in pyroxenite or occurs as subvertical and semi-massive to massive sulfide veins. The sulfide textures range from matrix ore, net-textured, droplets or breccia textures. Zones enriched in PGM, particularly Pd, are associated with the sulfides and several chromite bands are also present. These observations suggest that an immiscible sulfide liquid formed from a parental silicate liquid and percolated through the crystal pile. The parental melt composition, determined using the Chai and Naldrett [1992] method, has a SiO2-rich mafic composition with 53% SiO2 and 10% MgO. This result, the presence of the hybrid zone, and the trace-element signature determined using the Bedard [1994] method, suggest a mantle-derived basaltic parental magma that had assimilated abundant continental crust. These observations indicate that Samapleu intrusion corresponds to a magmatic conduit of the Yacouba complex as at Jinchuan (China), Voisey’s bay (Canada), Kabanga (Tanzania) or Nkomati (South Africa).

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Geochemistry and origin of the Regan Intrusive Suite and other granitoids in the northeastern Slave Province, northwest Canadian Shield

Canadian Journal of Earth Sciences ◽

10.1139/e85-108 ◽

1985 ◽

Vol 22 (7) ◽

pp. 1048-1065 ◽

Cited By ~ 7

Author(s):

R. A. Frith ◽

B. J. Fryer

Keyword(s):

Rare Earth ◽

Regional Metamorphism ◽

Volcanic Rocks ◽

Parental Magma ◽

Quartz Diorite ◽

Heavy Rare Earth Elements ◽

Flow Differentiation ◽

Felsic Volcanic ◽

Intrusive Suite ◽

Host Rocks

The Regan Intrusive Suite of about 100 plutons of tonalite, granodiorite, and quartz diorite intruded the Yellowknife Supergroup and migmatite terrain in the northwest Slave Structural Province 2.59 Ga ago. Rare-earth-element (REE), trace-element, and major-element analyses from 39 representative whole rocks from the suite suggest it was derived by batch melting of the crust, producing a parental magma of tonalitic or granodioritic composition. By analysing REE from different parts of a zoned pluton, it was concluded that REE distribution was controlled by early separation of quartz diorite from the parent magma by flow differentiation and that the bulk of the REE were contained in early, cumulate, accessory apatite and monazite. The residual magma was further fractionated in pipelike magma chambers during ascent into more leucocratic rocks. Chondrite-normalized REE patterns of single-lithology plutons are similar to lithologies in zoned plutons, and it is proposed they initially segregated during ascent. It was found that granites, which were formerly grouped with the suite, formed in three ways, only one of which is related to the Regan Intrusive Suite.Study of 2.67 Ga old synvolcanic tonalite pluton revealed a strong covariance of light REE with those of the bimodal, calc-alkaline Hackett River Group of volcanic rocks. The data imply a common crustal source, but mass balance requires larger volumes of felsic volcanic rocks than are presently preserved, suggesting that much of the erupted felsic pyroclastic rocks were eroded. Partial melts from synvolcanic tonalite during subsequent regional metamorphism differentially depleted host rocks in REE and concentrated Eu and heavy rare-earth elements (HREE) in trondhjemite pegmatites.

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Petrogenetic significance of chromian spinels from the Sudbury Ignecus Complex, Ontario, Canada

Canadian Journal of Earth Sciences ◽

10.1139/e17-113 ◽

1997 ◽

Vol 34 (10) ◽

pp. 1405-1419 ◽

Cited By ~ 15

Author(s):

Mei-Fu Zhou ◽

Reid R. Keays ◽

Peter C. Lightfoot ◽

Gordon G. Morrison ◽

Michelle L. Moore

Keyword(s):

Magma Mixing ◽

Ore Deposits ◽

Chromian Spinel ◽

Triangular Diagram ◽

Element Abundances ◽

Sudbury Igneous Complex ◽

Magmatic Sulfides ◽

Sulfide Ore ◽

Host Rocks ◽

Chamber Floor

Chromian spinels occur in mafic–ultramafic inclusions in the Sublayer of the Sudbury Igneous Complex (SIC) as well as in mafic–ultramafic rocks in the immediate footwall of the Sublayer. The host rocks are pyroxenite and melanorite with minor dunite, harzburgite, and melatroctolite. As common accessory phases in these rocks, the chromian spinels display euhedral or subhedral forms and are included in olivine and orthopyroxene. Chromian spinel grains generally have ilmenite lamellae and contain abundant inclusions (zircon, olivine, diopside, plagioclase, biotite, and sulfide). All the chromian spinels have similar trace element abundances and are rich in TiO2 (0.5–15 wt.%). They have constant Cr# (100Cr/(Cr + Al)) (55–70) and exhibit a continuum in composition that traverses the normal fields of spinels in a Al–(Fe3+ + 2Ti)–Cr triangular diagram. This continuum extends to that of the composition of chromian magnetite in the host norite matrix to the mafic–ultramafic inclusions. This continuum in composition of the spinels suggests that the noritic matrix to the Sublayer formed from the same magma as the inclusions. A positive correlation between the Cr and Al contents of the spinels was probably produced by dilution of these elements by Fe3+ contributed, perhaps, by a plagioclase-saturated melt. Zircon inclusions in a chromian spinel grain reflect incorporation of crustal, felsic materials into the magma before crystallization of chromian spinel. The chemical characteristics and mineral inclusions of the spinels suggest that the Sublayer formed in response to magma mixing. It is suggested that subsequent to the formation of the crustal melt, mantle-derived high-Mg magmas mixed vigourously with this and generated the magmatic sulfides that eventually formed the Ni – Cu – platinum-group elements sulfide ore deposits. Some of the early crystallization products of the high-Mg magma settled to the chamber floor, where they partially mixed with the crustal melt and formed the mafic–ultramafic inclusions and footwall complexes.

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The Scott Lake deposit: a contact-metamorphosed volcanogenic massive sulfide deposit, Chibougamau area, Quebec

Canadian Journal of Earth Sciences ◽

10.1139/e90-018 ◽

1990 ◽

Vol 27 (2) ◽

pp. 180-186 ◽

Cited By ~ 1

Author(s):

James A. Saunders ◽

Gilles O. Allard

Keyword(s):

Regional Metamorphism ◽

Massive Sulfide ◽

Contact Metamorphism ◽

Sulfide Deposit ◽

Massive Sulfide Deposit ◽

Volcanogenic Massive Sulfide ◽

Silicate Minerals ◽

Granitoid Intrusion ◽

Volcanogenic Massive Sulfide Deposit ◽

Sulfide Ore

The Scott Lake volcanogenic massive sulfide deposit lies near the margin of a large, early kinematic granitoid intrusion in the vicinity of Chibougamau, Quebec. The deposit was contact metamorphosed by the intrusion, and subsequently it was metamorphosed to the greenschist facies during the Kenoran Orogeny. Pyrite, magnetite, and sphalerite are the most abundant metallic minerals, and minor amounts of chalcopyrite, pyrrhotite, and loellingite are also present. Both pyrite and magnetite locally occur as porphyroblasts up to several centimetres in diameter. Metamorphic textures developed in the massive sulfide ore appear to have formed during contact metamorphism, and they remained intact through the subsequent regional event. However, silicate minerals (biotite and possibly amphibole) that grew during contact metamorphism were largely retrograded during regional metamorphism. The presence of biotite indicates that contact metamorphism took place at 400°–500 °C. Application of the sphalerite geobarometer gives a pressure of approximately 4.5 kbar (450 MPa), which probably reflects the later regional event.

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