Coarse muscovite veins and alteration in porphyry systems

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

Research output: Contribution to journalArticle

Abstract

Coarse muscovite veins and alteration occur in porphyry copper and porphyry molybdenum-copper systems within the Laramide arc in Arizona, as well as at the Yerington district in Nevada. This work describes coarse muscovite in veins and altered wall rock in porphyry systems in this region and documents mineral assemblages, mineral compositions, spatial and temporal relationships, and hydrogen isotopic compositions. Coarse hydrothermal muscovite is documented in the roots of porphyry Cu ± Mo systems, as well as in and above the ore bodies in porphyry Mo-Cu systems, and it is compared to coarse hydrothermal muscovite (greisen) in lode Sn-W-Mo systems. Basin and Range extension has exposed coarse hydrothermal muscovite in several Laramide and Jurassic porphyry Cu (±Mo) systems, at paleodepths of ~3 to 12 km: Miami-Inspiration, Sierrita-Esperanza, Copper Basin (Crown King), Granite Mountain (roots of the Ray porphyry system), Gunnison (Texas Canyon stock), Grayback (Kelvin-Riverside district), Sycamore Canyon, the New Cornelia mine (Ajo district), and two systems in the Yerington district. Muscovite is the dominant mica in these coarse muscovite veins and associated alteration, with common K-feldspar and albite (An00-06), common accessory hematite, rutile, pyrite, and apatite, and rare accessory chalcopyrite, fluorite, molybdenite, wolframite, and scheelite. Coarse hydrothermal muscovite yields δD compositions that suggest formation from fluids that are dominantly magmatic-hydrothermal in origin. Whole-rock compositions of coarse hydrothermal muscovite show common gains in K and loss of Ca ± Na. Coarse muscovite veins and alteration in porphyry copper systems postdate mineralized potassic veins and form too deeply to overlap with shallower acidic forms of alteration (sericitic, advanced argillic). Variation in mineral assemblage, mineral compositions, and mineralization of coarse hydrothermal muscovite correlate with the composition of Laramide stocks. Porphyry Mo-Cu systems contain coarse muscovite alteration assemblages with the highest mineral diversity and trace-element enrichment. Coarse muscovite veins and alteration in porphyry Mo-Cu systems related to stocks ranging from quartz monzonite to granite in composition form at shallower paleodepths and occur within and above the associated orebodies. In contrast, coarse muscovite veins and alteration associated with subalkaline porphyry copper systems occur at deeper levels, in some cases overlapping with the bottom of potassic alteration and the ore body but extending well into the roots of the system in the underlying granitoid cupola. In these latter systems, zones of coarse muscovite alteration typically are poorly mineralized and mineral assemblages are less varied. These characteristics suggest that coarse muscovite-forming fluids are predominately of magmatic-hydrothermal origin and exsolved from late-stage, fractionated magmas of the larger pluton that sourced porphyry stocks and dikes responsible for porphyry copper mineralization. In some instances, however, the exposed coarse muscovite alteration is associated with a petrologically unrelated, commonly more felsic, later intrusion, rather than being related to late exsolution of fluid from the same crystallizing stock or batholith.

Original languageEnglish (US)
Article number103045
JournalOre Geology Reviews
Volume113
DOIs
StatePublished - Oct 2019

Fingerprint

porphyry
muscovite
Copper
Minerals
copper
Chemical analysis
mineral
Accessories
ore body
Ores
canyon
Fluids
fluid
granite
Wall rock
mineralization
wolframite
greisen
Apatites
Levees

Keywords

  • Coarse muscovite alteration
  • Greisen
  • Hydrothermal alteration
  • Porphyry copper
  • Porphyry molybdenum

ASJC Scopus subject areas

  • Geology
  • Geochemistry and Petrology
  • Economic Geology

Cite this

Runyon, S. E., Seedorff, E., Barton, M. D., Steele-MacInnis, M., Lecumberri-Sanchez, P., & Mazdab, F. K. (2019). Coarse muscovite veins and alteration in porphyry systems. Ore Geology Reviews, 113, [103045]. https://doi.org/10.1016/j.oregeorev.2019.103045

Coarse muscovite veins and alteration in porphyry systems. / Runyon, Simone E.; Seedorff, Eric; Barton, Mark D.; Steele-MacInnis, Matthew; Lecumberri-Sanchez, Pilar; Mazdab, Frank K.

In: Ore Geology Reviews, Vol. 113, 103045, 10.2019.

Research output: Contribution to journalArticle

Runyon, Simone E. ; Seedorff, Eric ; Barton, Mark D. ; Steele-MacInnis, Matthew ; Lecumberri-Sanchez, Pilar ; Mazdab, Frank K. / Coarse muscovite veins and alteration in porphyry systems. In: Ore Geology Reviews. 2019 ; Vol. 113.
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AU - Runyon, Simone E.

AU - Seedorff, Eric

AU - Barton, Mark D.

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AU - Lecumberri-Sanchez, Pilar

AU - Mazdab, Frank K.

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N2 - Coarse muscovite veins and alteration occur in porphyry copper and porphyry molybdenum-copper systems within the Laramide arc in Arizona, as well as at the Yerington district in Nevada. This work describes coarse muscovite in veins and altered wall rock in porphyry systems in this region and documents mineral assemblages, mineral compositions, spatial and temporal relationships, and hydrogen isotopic compositions. Coarse hydrothermal muscovite is documented in the roots of porphyry Cu ± Mo systems, as well as in and above the ore bodies in porphyry Mo-Cu systems, and it is compared to coarse hydrothermal muscovite (greisen) in lode Sn-W-Mo systems. Basin and Range extension has exposed coarse hydrothermal muscovite in several Laramide and Jurassic porphyry Cu (±Mo) systems, at paleodepths of ~3 to 12 km: Miami-Inspiration, Sierrita-Esperanza, Copper Basin (Crown King), Granite Mountain (roots of the Ray porphyry system), Gunnison (Texas Canyon stock), Grayback (Kelvin-Riverside district), Sycamore Canyon, the New Cornelia mine (Ajo district), and two systems in the Yerington district. Muscovite is the dominant mica in these coarse muscovite veins and associated alteration, with common K-feldspar and albite (An00-06), common accessory hematite, rutile, pyrite, and apatite, and rare accessory chalcopyrite, fluorite, molybdenite, wolframite, and scheelite. Coarse hydrothermal muscovite yields δD compositions that suggest formation from fluids that are dominantly magmatic-hydrothermal in origin. Whole-rock compositions of coarse hydrothermal muscovite show common gains in K and loss of Ca ± Na. Coarse muscovite veins and alteration in porphyry copper systems postdate mineralized potassic veins and form too deeply to overlap with shallower acidic forms of alteration (sericitic, advanced argillic). Variation in mineral assemblage, mineral compositions, and mineralization of coarse hydrothermal muscovite correlate with the composition of Laramide stocks. Porphyry Mo-Cu systems contain coarse muscovite alteration assemblages with the highest mineral diversity and trace-element enrichment. Coarse muscovite veins and alteration in porphyry Mo-Cu systems related to stocks ranging from quartz monzonite to granite in composition form at shallower paleodepths and occur within and above the associated orebodies. In contrast, coarse muscovite veins and alteration associated with subalkaline porphyry copper systems occur at deeper levels, in some cases overlapping with the bottom of potassic alteration and the ore body but extending well into the roots of the system in the underlying granitoid cupola. In these latter systems, zones of coarse muscovite alteration typically are poorly mineralized and mineral assemblages are less varied. These characteristics suggest that coarse muscovite-forming fluids are predominately of magmatic-hydrothermal origin and exsolved from late-stage, fractionated magmas of the larger pluton that sourced porphyry stocks and dikes responsible for porphyry copper mineralization. In some instances, however, the exposed coarse muscovite alteration is associated with a petrologically unrelated, commonly more felsic, later intrusion, rather than being related to late exsolution of fluid from the same crystallizing stock or batholith.

AB - Coarse muscovite veins and alteration occur in porphyry copper and porphyry molybdenum-copper systems within the Laramide arc in Arizona, as well as at the Yerington district in Nevada. This work describes coarse muscovite in veins and altered wall rock in porphyry systems in this region and documents mineral assemblages, mineral compositions, spatial and temporal relationships, and hydrogen isotopic compositions. Coarse hydrothermal muscovite is documented in the roots of porphyry Cu ± Mo systems, as well as in and above the ore bodies in porphyry Mo-Cu systems, and it is compared to coarse hydrothermal muscovite (greisen) in lode Sn-W-Mo systems. Basin and Range extension has exposed coarse hydrothermal muscovite in several Laramide and Jurassic porphyry Cu (±Mo) systems, at paleodepths of ~3 to 12 km: Miami-Inspiration, Sierrita-Esperanza, Copper Basin (Crown King), Granite Mountain (roots of the Ray porphyry system), Gunnison (Texas Canyon stock), Grayback (Kelvin-Riverside district), Sycamore Canyon, the New Cornelia mine (Ajo district), and two systems in the Yerington district. Muscovite is the dominant mica in these coarse muscovite veins and associated alteration, with common K-feldspar and albite (An00-06), common accessory hematite, rutile, pyrite, and apatite, and rare accessory chalcopyrite, fluorite, molybdenite, wolframite, and scheelite. Coarse hydrothermal muscovite yields δD compositions that suggest formation from fluids that are dominantly magmatic-hydrothermal in origin. Whole-rock compositions of coarse hydrothermal muscovite show common gains in K and loss of Ca ± Na. Coarse muscovite veins and alteration in porphyry copper systems postdate mineralized potassic veins and form too deeply to overlap with shallower acidic forms of alteration (sericitic, advanced argillic). Variation in mineral assemblage, mineral compositions, and mineralization of coarse hydrothermal muscovite correlate with the composition of Laramide stocks. Porphyry Mo-Cu systems contain coarse muscovite alteration assemblages with the highest mineral diversity and trace-element enrichment. Coarse muscovite veins and alteration in porphyry Mo-Cu systems related to stocks ranging from quartz monzonite to granite in composition form at shallower paleodepths and occur within and above the associated orebodies. In contrast, coarse muscovite veins and alteration associated with subalkaline porphyry copper systems occur at deeper levels, in some cases overlapping with the bottom of potassic alteration and the ore body but extending well into the roots of the system in the underlying granitoid cupola. In these latter systems, zones of coarse muscovite alteration typically are poorly mineralized and mineral assemblages are less varied. These characteristics suggest that coarse muscovite-forming fluids are predominately of magmatic-hydrothermal origin and exsolved from late-stage, fractionated magmas of the larger pluton that sourced porphyry stocks and dikes responsible for porphyry copper mineralization. In some instances, however, the exposed coarse muscovite alteration is associated with a petrologically unrelated, commonly more felsic, later intrusion, rather than being related to late exsolution of fluid from the same crystallizing stock or batholith.

KW - Coarse muscovite alteration

KW - Greisen

KW - Hydrothermal alteration

KW - Porphyry copper

KW - Porphyry molybdenum

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