Textural evidence for remobilization in metamorphic environments

Gilligan, L.B.; Marshall, Brian D.

doi:10.1016/0169-1368(87)90029-1

Cited by 67 publications

(37 citation statements)

References 52 publications

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“…In pressure shadows, and other low strain domains, granoblastic polygonal textures with no clear orientation are common. Chalcopyrite, being more ductile than pyrrhotite (Gilligan and Marshall, 1987), shows a more pronounced flow than sphalerite and galena.…”

Section: Textures and Deformation Of The Orementioning

confidence: 99%

“…Pyrrhotite grains are equigranular, sub-mm in size, contiguous, with a polygonal texture and 120 °C angles, features that are indicative of metamorphic recrystallization (Fig. 9a,b), but which can form under low-grade metamorphic conditions (Gilligan and Marshall, 1987). Coexisting chalcopyrite occurs interstitial to pyrrhotite where it forms large anhedral, undeformed grains that display linear twinning.…”

Section: Textures and Deformation Of The Orementioning

confidence: 99%

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Draa Sfar, Morocco: A Visean (331 Ma) pyrrhotite-rich, polymetallic volcanogenic massive sulphide deposit in a Hercynian sediment-dominant terrane

Marcoux

Belkabir²,

Gibson

et al. 2008

Ore Geology Reviews

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Draa Sfar is a Visean, stratabound, volcanogenic massive sulphide ore deposit hosted by a Hercynian carbonaceous, black shale-rich succession of the Jebilet terrane, Morocco. The ore deposit contains 10 Mt grading 5.3 wt.% Zn, 2 wt.% Pb, and 0.3 wt.% Cu within two main massive sulphides orebodies, Tazakourt (Zn-rich) and Sidi M'Barek (Zn-Cu rich). Pyrrhotite is by far the dominant sulphide (70 to 95% of total sulphides), sphalerite is fairly abundant, chalcopyrite and galena are accessory, pyrite, arsenopyrite and bismuth minerals are rare. Pyrrhotite is monoclinic and mineralogical criteria indicate that it is of primary origin and not formed during metamorphism. Its composition is very homogeneous, close to Fe 7 S 8 , and its absolute magnetic susceptibility is 2.10 − 3 SI/g. Ar-Ar dating of hydrothermal sericites from a coherent rhyolite flow or dome within the immediate deposit footwall indicates an age of 331.7 ± 7.9 Ma for the Draa Sfar deposit and rhyolite volcanism.The Draa Sfar deposit has undergone a low-grade regional metamorphic event that caused pervasive recrystallization, followed by a ductile-brittle deformation event that has locally imparted a mylonitic texture to the sulphides and, in part, is responsible for the elongated and sheet-like morphology of the sulphide orebodies. Lead isotope data fall into two compositional end-members. The least radiogenic end-member, ( 206 Pb/ 204 Pb = 18.28), is characteristic of the Tazakourt orebody, whereas the more radiogenic end-member ( 206 Pb/ 204 Pb 18.80) is associated with the Sidi M'Barek orebody, giving a mixing trend between the two end-members. Lead isotope compositions at Draa Sfar testify to a significant continental crust source for the base metals, but are different than those of the Hajar and South Iberian Pyrite Belt VMS deposits.The abundance of pyrrhotite versus pyrite in the orebodies is attributed to low fO 2 conditions and neither a high temperature nor a low aH 2 S (below 10 − 3 ) is required. The highly anoxic conditions required to stabilize pyrrhotite over pyrite are consistent with formation of the deposit within a restricted, sediment-starved, anoxic basin characterized by the deposition of carbonaceous, pelagic sediments along the flank of a rhyolitic flow-dome complex that was buried by pelitic sediments. Deposition of sulphides likely occurred at and below the seafloor within anoxic and carbonaceous muds. Draa Sfar and other Moroccan volcanogenic massive sulphide deposits occur in an epicontinental volcanic domain within the outer zone of the Hercynian belt and formed within a sedimentary environment that has a high pelagic component. In spite of the diachronous emplacement between the IPB deposits (late Devonian to Visean) and Moroccan deposits (Dinantian), all were formed around 340 ± 10 Ma following a major phase of the Devonian compression.

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Section: Textures and Deformation Of The Orementioning

confidence: 99%

Section: Textures and Deformation Of The Orementioning

confidence: 99%

Draa Sfar, Morocco: A Visean (331 Ma) pyrrhotite-rich, polymetallic volcanogenic massive sulphide deposit in a Hercynian sediment-dominant terrane

Marcoux

Belkabir²,

Gibson

et al. 2008

Ore Geology Reviews

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“…Pour ce faire, les objectifs spécifiques suivants se doivent d'être atteints : (Gilligan et Marshall, 1987b;Craig et al, 1998;Craig, 2001 (Gresens, 1967;Grant, 1986;MacLean, 1990;MacLean et Barrett, 1993), sont décrits à la section 5.3. Cette tâche a principalement permis d'amener des éléments quantitatifs à la caractérisation de la zonalité hydrothermale du système minéralisé.…”

Section: Objectifs Hypothèses De Travail Originalité Et Incidences unclassified

Architecture et origine du système de minéralisation polymétallique du secteur lac Line, région de Chibougamau, Québec /

Côté-Mantha¹

2009

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(-2703 Ma), qui provoque la superposition de la schistosité régionale et de paragenèses du pic métamorphique sur les empreintes hydrothermales préexistantes ainsi que la réactivation des failles longitudinales en zones de cisaillement à mouvement inverse. En somme, cette étude démontre que la région de Chibougamau expose un énorme système minéralisé volcano-plutonique archéen atypique, avec des dépôts Cu-Au magmatiques-hydrothermaux proximaux (camp minier du lac Doré) et des dépôts épithermaux polymétalliques distaux centrés sur des systèmes plutoniques satellites s'inscrivant dans la même lignée pétrogénétique. L'étude contribue par le fait même à mettre à l'avant-plan des processus tels l'activité volcano-plutonique calco-alcaline, la formation de caldeiras et l'implication de l'eau de mer en tant qu'agent confinant (profondeur bathymétrique) et agent chimique comme responsables de minéralisations polymétalliques atypiques en contexte d'arc. Dans l'ensemble, cela supporte l'idée que le potentiel minéral des arcs volcano-plutoniques calco-alcalins anciens a pu être sous-estimé dans le passé, surtout lorsqu'on prend conscience de l'immense richesse de leurs équivalents récents.

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“…This has been described as a ball texture (Geijer 1971) or durchbewegung texture (Vokes 1969 and1973), the latter term being widely accepted (Gilligan & Marshall 1987). The dolomite fragments are either unaltered or have been altered only slightly, possessing a thin outer rim of calcite.…”

Section: Iron Oresmentioning

confidence: 99%

Mineralogy, geochemistry and metamorphism of the early Proterozoic Vähäjoki iron ores, northern Finland

Liipo¹,

Laajoki²

1991

Bull Geol Soc Finland

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LIIPO, JUSSI AND LAAJOKI, KAUKO 1991: Mineralogy, geochemistry and metamorphism of the early Proterozoic Vähäjoki iron ores, Northern Finland. Bull Geol. Soc. Finland 63, Part 2,[69][70][71][72][73][74][75][76][77][78][79][80][81][82][83][84][85] The Vähäjoki iron ores occupy the uppermost part of the Karelian (Early Proterozoic) quartzite-dolomite sequence deposited on the late Archaean basement in southern Lapland. The ores occur as magnetite veins brecciating dolomite and as magnetite disseminations in chlorite and mica schists. Their average iron content is 40%, and they contain up to 3.8% P 2 0 5 , features which together with the division of the ores into 14 small bodies make them uneconomic.The only main ore mineral is magnetite, with which there occur accessory ilmenite, haematite, pyrite, chalcopyrite, pyrrhotite, arsenopyrite and cobaltite with small gold inclusions. The main gangue minerals classified by microanalysis are dolomite or Fe-dolomite in the dolomites, ferri-tremolite, tremolite, ferri-actinolite and ferrian actinolite, cummingtonite, magnesio-hornblende and tschermakitic hornblende in amphibole-bearing hosts rocks, green Mg-rich biotite, brown Fe-rich biotite and Ba-bearing (BaO 0.18-7.9%) biotite, and chlorite in chlorite and mica schists.Major and trace elements were analyzed in 18 samples. The dolomites contain 24-53% CaO and 3-20% MgO, while the amphibole rocks, amphibole schists, chlorite schists and mica schists are chemically rather similar, containing about 13-27% Fe lot and 7-21% MgO, the amphibole-bearing varities being a little richer in these elements than the phyllosilicate-bearing ones. The ore samples from magnetite matrix of the breccia type contain 71-85% Fe 2 0 3 and 0.05-0.2% P 2 0 ; .The garnet-biotite and calcite-dolomite geothermometers and the mineral chemistry of the Ca-amphiboles suggest that the Vähäjoki iron ores were metamorphosed under greenschist -amphibolite facies conditions ( T = 465 °C and P = 2-4 Kbar). Flunctiation in metamorphic grade is reflected in the change in amphibole composition from tremolite-actinolite to tschermakitic hornblende.The Vähäjoki iron ores were remobilized and enriched during early Proterozoic regional metamorphism and deformation, forming an epigenetic iron ore.

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Textural evidence for remobilization in metamorphic environments

Cited by 67 publications

References 52 publications

Draa Sfar, Morocco: A Visean (331 Ma) pyrrhotite-rich, polymetallic volcanogenic massive sulphide deposit in a Hercynian sediment-dominant terrane

Draa Sfar, Morocco: A Visean (331 Ma) pyrrhotite-rich, polymetallic volcanogenic massive sulphide deposit in a Hercynian sediment-dominant terrane

Architecture et origine du système de minéralisation polymétallique du secteur lac Line, région de Chibougamau, Québec /

Mineralogy, geochemistry and metamorphism of the early Proterozoic Vähäjoki iron ores, northern Finland

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