Root Zones of Porphyry Systems: Extending the Porphyry Model to Depth

Seedorff, Eric; Barton, Mark D.; Stavast, William J. A.; Maher, David J.

doi:10.2113/gsecongeo.103.5.939

Cited by 108 publications

(50 citation statements)

References 73 publications

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“…The presence of coarse muscovite alteration in the Yerington district suggests that coarse muscovite alteration is a common characteristic of the roots of porphyry copper systems. We concur with suggestion by Seedorff et al (2008), that coarse muscovite alteration in the deep roots should be appended to zonation of alteration for porphyry copper systems (Lowell and Guilbert 1970;Sillitoe 2010). …”

Section: Discussionsupporting

confidence: 92%

“…Root zones of porphyry systems are rarely recognized, but Seedorff et al (2008) documented the presence of coarse muscovite-dominated alteration, referred to as "greisen," as a recently recognized form of deep hydrothermal alteration in the roots of four porphyry copper systems in Arizona (Sierrita-Esperanza, Kelvin-Riverside, Ray, and Miami-Inspiration). Nonetheless, the significance of muscovite veins and alteration in these systems is not well understood, and it is unclear whether coarse muscovite alteration is a common feature in the roots of porphyry copper systems (Seedorff et al 2005(Seedorff et al , 2008. This study documents previously unreported coarse muscovite alteration in the Yerington district, Nevada, describes characteristics of associated fluids, and evaluates implications of muscovite veins and alteration in the evolution of this well-exposed Jurassic magmatic-hydrothermal system.…”

Section: Introductionmentioning

confidence: 99%

“…Coarse-grained muscovite alteration had not been described in porphyry copper systems prior to the description of the root zones of four porphyry copper systems in Arizona (Seedorff et al 2008). Coarse muscovite veins and alteration may be lacking at presently exposed levels of these other systems or may not have been recognized.…”

Section: Introductionmentioning

confidence: 99%

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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

et al. 2017

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Veins and pervasive wall-rock alteration composed of coarse muscovite±quartz±pyrite are documented for the first time in a porphyritic granite at Luhr Hill in the Yerington district, Nevada. Coarse muscovite at Luhr Hill occurs at paleodepths of ~6-7 km in the roots of a porphyry copper system and crops out on the scale of tens to hundreds of meters, surrounded by rock that is unaltered or variably altered to sodic-calcic assemblages. Coarse muscovite veins exhibit a consistent orientation, subvertical and N-S striking, which structurally restores to subhorizontal at the time of formation. Along strike, coarse muscovite veins swell from distal, mm-thick muscovite-only veinlets to proximal, cm-thick quartz-sulfide-bearing muscovite veins.Crosscutting relationships between coarse muscovite veins, pegmatite dikes, and sodic-calcic veins indicate that muscovite veins are late-stage magmatic-hydrothermal features predating final solidification of the Luhr Hill porphyritic granite. Fluid inclusions in the muscovite-quartz veins are high-density aqueous inclusions of ~3-9 wt% NaCl eq. and <1 mol% CO 2 that homogenize between ~150°C and 200°C, similar to fluid inclusions from greisen veins in Sn-W-Mo vein 2 systems. Our results indicate that muscovite-forming fluids at Luhr Hill were mildly acidic, of low to moderate salinity and sulfur content and low CO 2 content, and that muscovite in deep veins and alteration differs in texture, composition, and process of formation from sericite at shallower levels of the hydrothermal system. Although the definition of greisen is controversial, we suggest that coarse muscovite alteration is more similar to alteration in greisen-type Sn-WMo districts worldwide than to sericitic alteration at higher levels of porphyry copper systems.The fluids that form coarse muscovite veins and alteration in the roots of porphyry copper systems are distinct from fluids that formed copper ore or widespread, shallower, acidic alteration. We propose that this style of veins and alteration at Luhr Hill represents degassing of moderate volumes of overpressured hydrothermal fluid during late crystallization of deep levels of the Yerington batholith.

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Section: Discussionsupporting

confidence: 92%

Section: Introductionmentioning

confidence: 99%

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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

et al. 2017

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“…Therefore, ore-forming materials must come from additional sources. Studies show that in addition to magmas at shallow depths (at paleodepths < 5 km), porphyry systems are usually related to underlying composite plutons at paleodepths of 5-15 km (Sillitoe, 2010), which supply magmas, fluids and other ore-forming materials for the deposits (Seedorff et al, 2008). The bulk metal budget of porphyry copper deposits is primarily controlled by the composition of the incoming fluid from an underlying magma chamber (Ulrich et al, 1999), therefore, the oscillation of hematite and magnetite crystallizations is probably also common at depths, controlling the supply of metals, sulfur and potassium.…”

Section: Adakite and Porphyry Copper Depositsmentioning

confidence: 99%

The link between reduced porphyry copper deposits and oxidized magmas

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Liang

Ling

et al. 2013

Geochimica et Cosmochimica Acta

350

118

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“…The DMIC represents a suite of hypabyssal and upper parts of plutonic intrusions, which like other 524 porphyry copper-related intrusions, was emplaced within the upper crust (Cooke et al, 2014; 525 Seedorff et al, 2008;. Overall, the DMIC shows a temporal progression from 526 dominantly silicic magmas with very minor mafic components (enclaves and intermediate dikes) 527 to more mafic magmas represented by porphyritic intermediate and basaltic andesite dikes (Fig.…”

Section: Evolution Of the Don Manuel Igneous Complex 523mentioning

confidence: 98%