Coarse muscovite veins and alteration deep in the Yerington batholith, Nevada: insights into fluid exsolution in the roots of porphyry copper systems

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

doi:10.1007/s00126-017-0720-1

Cited by 24 publications

(8 citation statements)

References 19 publications

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“…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%

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: 99%

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

et al. 2022

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“…On the other hand, field observations also indicate the presence and influence of steeply dipping fault zones in the deposit, which may have been reactivated sometime during ore formation (Polya, 1988). Sub-horizontally oriented vein structures have also been described in other magmatic-hydrothermal ore deposits, such as the Zinnwald Sn-W-Li deposit, and in the root zones of some porphyry Cu deposits (Runyon et al, 2017;Webster et al, 2004).…”

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Numerical Modeling of Structurally Controlled Ore Formation in Magmatic‐Hydrothermal Systems

Codeço

Weis

Andersen

2022

Geochem Geophys Geosyst

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The genesis of hydrothermal ore deposits requires favorable geodynamic settings where fluids can transport metals from a large source area through permeable rocks to a locally confined deposition site (Heinrich & Candela, 2014;Kesler & Simon, 2015). However, the bulk permeability of upper crustal rocks generally decreases with depth, and values that permit advective heat and solute transport can be spatially and temporally limited even for tectonically active crust (Ingebritsen & Manning, 1999, 2010. For many major types of hydrothermal ore deposits, active faults and fractures are therefore inferred to serve as high-permeability pathways for focused fluid flow from deeper to shallower depths, including sediment-hosted base metal, orogenic gold, unconformity-related uranium, submarine massive sulfide, polymetallic vein-type and epithermal precious metal deposits (Cox, 2005;Heinrich & Candela, 2014). Fluid overpressure can further increase permeability by hydraulic fracturing, eventually resulting in the formation of mineralized hydrothermal veins, stockworks, and breccias (Cox, 2005;Heinrich & Candela, 2014).

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“…The onset of porphyry mineralisation is constrained by cross-cutting relationships; it is spatially and temporally associated with multiple generations of variably mineralised granite-composition porphyry and aplite dykes that clearly cross-cut the upper (Fig. 3 ; S3 ) as well as lower parts of the LHG, and appear to have been focused through apophyses of the LHG 33 , 38 , 40 – 42 , 47 , 48 . The dykes generally have sharp contacts with the LHG, with some showing chilled margins and others lobate contacts (Fig.…”

Section: Introductionmentioning

confidence: 99%

“…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%

“…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.

Figure 3 Temporal relations in the Yerington magmatic system: Field photographs of; ( a ) cross-cutting relations of multiple porphyry dyke generations which cut the LHG cupola; ( b ) lobate contacts and evidence for mingling of co-eval magmas between an aplite dyke and porphyry dyke.…”

Section: Introductionmentioning

confidence: 99%

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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 deep in the Yerington batholith, Nevada: insights into fluid exsolution in the roots of porphyry copper systems

Cited by 24 publications

References 19 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

Numerical Modeling of Structurally Controlled Ore Formation in Magmatic‐Hydrothermal Systems

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

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