Coarse muscovite veins and alteration in porphyry systems

Runyon, Simone E.; Seedorff, Eric; Barton, Mark D.; Steele‐MacInnis, Matthew; Lecumberri-Sánchez, Pilar; Mazdab, Frank K.

doi:10.1016/j.oregeorev.2019.103045

Cited by 20 publications

(11 citation statements)

References 68 publications

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“…In these latter systems, coarse muscovite veins are generally reported only in the deepest portions of the intrusive bodies, and fluid inclusions in the veins indicate that coarse muscovite was deposited by aqueous-carbonic fluids of low salinity. Runyon et al (2017) noted that deposition of muscovite within such veins implies that Al was mobilized in the hydrothermal fluid, and this probably reflects relatively high (~ lithostatic) fluid pressures at least in some cases (Runyon et al 2019). At Gidami, we interpret that the fluids responsible for deposition of the coarse muscovite veins were lowsalinity carbonic-aqueous fluids rich in CO 2 .…”

Section: Hydrothermal Muscovite and Ore Fluidsmentioning

confidence: 70%

“…Muscovite is also present as a hydrothermal alteration product in the adjacent host rocks, which is a common feature associated with gold-bearing quartz veins in similar settings. But coarse muscovite deposited within the veins themselves is less common, and is reminiscent of quartz-muscovite veins associated with peraluminous granitoids, as well as late-stage veins associated with the highly-fractionated root zones of porphyry systems (Runyon et al 2017(Runyon et al , 2019. In these latter systems, coarse muscovite veins are generally reported only in the deepest portions of the intrusive bodies, and fluid inclusions in the veins indicate that coarse muscovite was deposited by aqueous-carbonic fluids of low salinity.…”

Section: Hydrothermal Muscovite and Ore Fluidsmentioning

confidence: 99%

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Vein-type gold formation during late extensional collapse of the Eastern Desert, Egypt: the Gidami deposit

et al. 2022

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Orogenic gold deposits, though construed to focused fluid flow during orogenesis, commonly post-date the main accretionary events. Several lines of evidence indicate that orogenic gold formation in the Arabian–Nubian Shield continued through the orogen collapse stage and associated rapid exhumation and thermal re-equilibration. The Gidami gold deposit in the Eastern Desert of Egypt is associated with post-foliation, brittle-ductile shear zones that deformed a weakly foliated tonalite-trondhjemite massif dated as ~ 704 Ma (U–Pb zircon age). Gold-sulfide quartz veins exhibit textural features indicative of repeated mylonitization, recrystallization, and muscovite crystallization. New 40Ar/39Ar ages of muscovite flakes from the auriferous quartz veins and from the altered wallrock overlap within analytical uncertainty at ~ 583 Ma, which corresponds to the climax of extension-related wrenching and rapid exhumation in the region (~ 596 to 582 Ma). Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) data coupled with microtextural characteristics suggest that early formed pyrite generations experienced substantial fluid-mediated recrystallization, and that a set of metals was remobilized by later fluids. A late generation of fibrous pyrite, ubiquitous in microfractures, deposited while the veins re-opened and deformed. The occurrence of free gold particles along with a late-paragenetic assemblage of galena-sphalerite-chalcopyrite(± hessite ± cervelleite) was related to influx of low salinity, metalliferous H2O-NaCl-CO2-CH4 fluids as indicated by the fluid inclusion laser Raman spectroscopy and microthermometry results. Au-mobilization and redeposition at T ≤ 350 °C and P ~ 1 to 1.7 kbar, triggered by intermittent fluid pluses and thermal re-equilibration, were most likely stimulated by extensional structures and within-plate magmatism. Coincident province- and deposit-scale pressure–temperature-time data highlight the pivotal role of the orogenic collapse tectonics in gold endowment in the Central Eastern Desert’s crust.

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Section: Hydrothermal Muscovite and Ore Fluidsmentioning

confidence: 70%

Section: Hydrothermal Muscovite and Ore Fluidsmentioning

confidence: 99%

Vein-type gold formation during late extensional collapse of the Eastern Desert, Egypt: the Gidami deposit

et al. 2022

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“…Despite the lack of known stockwork veining, it is possible that additional resources may yet be encountered at depth. Recent work documenting root zones of porphyry copper systems [44,45] show that these deeper parts of the system are cored by potassic alteration. However, this system lacks other features observed in the root zones of other PCDs, namely coarse-grained muscovite [44].…”

Section: Uplift and Exhumation Of The Dmic And Porphyry Copper Systemmentioning

confidence: 99%

“…Recent work documenting root zones of porphyry copper systems [44,45] show that these deeper parts of the system are cored by potassic alteration. However, this system lacks other features observed in the root zones of other PCDs, namely coarse-grained muscovite [44]. Although bornite was observed in the drill core, it is rare; a true central bornite-chalcopyrite zone, often present in porphyry copper deposits and present in all known economic Miocene-Pliocene systems, was not encountered in the core at Don Manuel, leaving open the possibility that this zone may not have been reached by drilling.…”

Section: Uplift and Exhumation Of The Dmic And Porphyry Copper Systemmentioning

confidence: 99%

Duration of Hydrothermal Alteration and Mineralization of the Don Manuel Porphyry Copper System, Central Chile

et al. 2021

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The Don Manuel porphyry copper system, located in the Miocene–Pliocene metallogenic belt of central Chile, contains spatially zoned alteration styles common to other porphyry copper deposits including extensive potassic alteration, propylitic alteration, localized sericite-chlorite alteration and argillic alteration but lacks pervasive hydrolytic alteration typical of some deposits. It is one of the youngest porphyry copper deposits in the Andes. Timing of mineralization and the hydrothermal system at Don Manuel are consistent with emplacement of the associated intrusions (ca. 4 and 3.6 Ma). Two molybdenite samples yielded consistent ages of 3.412 ± 0.037 and 3.425 ± 0.037 Ma. 40Ar/39Ar ages on hydrothermal biotites (3.57 ± 0.02, 3.51 ± 0.02, 3.41 ± 0.01, and 3.37 ± 0.01 Ma) are associated with potassic alteration. These ages are younger than the youngest intrusion by ~300 k.y. recording the cooling of the system below 350 °C. Such a time gap can be explained by fluxing of hot magmatic fluids from deeper magmatic sources.

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“…3 b–d), which indicates multiple intrusion events, with some generations emplaced penecontemporaneously with porphyry dykes and others later. In the palaeo-vertically deepest (> 6 km) exposures of the LHG (or the ‘root zone’ for the porphyry deposits 30 ), the majority of aplite dykes pre-date the spatially associated late-stage coarse muscovite veins and alteration 48 , 49 , as well as Na-Ca alteration. However, in deep exposures of the LHG, certain aplite dykes, which appear to post-date the muscovite and Na-Ca alteration, are thought to have been emplaced from a larger, longer-lived, deeper source 48 ; as these post-date the hydrothermal alteration they are not considered further in this paper.…”

Section: Introductionmentioning

confidence: 99%

A rapid change in magma plumbing taps porphyry copper deposit-forming magmas

Carter

Tapster

Williamson

et al. 2022

Sci Rep

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Porphyry-type deposits are a vital source of green technology metals such as copper and molybdenum. They typically form in subduction-related settings from large, long-lived magmatic systems. The most widely accepted model for their formation requires that mantle-derived magmas undergo an increase in volatiles and ore-forming constituents in mid- to lower crustal reservoirs over millions of years, however, this is mostly based on observations from shallow, sporadically exposed parts of porphyry systems. To examine this paradigm, we have evaluated the timeframe and geochemical signatures of magmatism in a ~ 8 km palaeodepth cross-section through plutonic and volcanic rocks of the classic Yerington magmatic system, Nevada. We show that the magmas in the upper parts of the system (< 8 km) underwent a major and rapid change in chemistry over a period of < 200 kyrs that is coincident with the initiation of ore formation. We attribute this change to a shift from extraction of quartz monzodiorite and quartz monzonite magmas evolving in mid-crustal reservoirs, and that had relatively poor ore-forming potential, to extraction of volatile-rich granitic magmas from greater (~ 30 km) depths. As the granites crystallised, late stage melts were intruded through the carapace as aplite dykes which contain traceable expressions of the porphyry deposit-forming fluids. The rapid nature of the shift in ore-forming potential narrows the temporal-geochemical footprint of magmas associated with porphyry mineralisation and provides new constraints for exploration models.

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Coarse muscovite veins and alteration in porphyry systems

Cited by 20 publications

References 68 publications

Vein-type gold formation during late extensional collapse of the Eastern Desert, Egypt: the Gidami deposit

Vein-type gold formation during late extensional collapse of the Eastern Desert, Egypt: the Gidami deposit

Duration of Hydrothermal Alteration and Mineralization of the Don Manuel Porphyry Copper System, Central Chile

A rapid change in magma plumbing taps porphyry copper deposit-forming magmas

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