Composition changes in an ash-flow cooling unit during K metasomatism, west-central Arizona

Kurt Hollocher, Jon Spencer, Joaquin Ruiz

Research output: Contribution to journalArticle

17 Citations (Scopus)

Abstract

A variably altered rhyolitic ash-flow cooling unit in west-central Arizona was sampled and analyzed to gain a better understanding of compositional changes that took place during Tertiary K metasomatism. Mn, Cu, Zn, and other metals of economic importance were removed from the K-metasomatized rocks during alteration, making them a likely source for these metals in vein and stratiform Mn deposits and base metal ores related to detachment faults in western Arizona. Using a single cooling unit to understand the compositional changes during K metasomatism reduces the primary chemical variability inherent in the sampling of multiple units, a problem with most previous studies. The least altered samples (group 1) experienced a moderate degree of K metasomatism, having K 2O/Na 2O ratios of 3.1 to 5.5, compared to likely igneous values of <2. The most altered samples (group 2) were severely K metasomatized with K 2O/Na 2O ratios of 17.9 to 29.5. K 2O, P 2O 5, and Ba increased in concentration substantially during K metasomatism, and MnO, Na 2O, Cu, Zn, Sr, Mo, and Cs decreased. All immobile elements decreased in concentration by approx.9 percent, which is attributed to a dilution effect caused by net mass gain in the group 2 rocks, principally as K 2O and SiO 2. Mineralogical zoning in small late veins seen in thin section is quartz ± K feldspar ± calcite from vein wall to center. The strong covariance in CaO and loss on ignition (L.O.I.) with observed calcite in thin section and the lack of correlation of CaO and L.O.I. with other components indicates that their variability is unrelated to K metasomatism. Calculations indicate that the loss of Mn, Cu, Zn, and other metals from K-metasomatized volcanics is easily large enough to account for middle Tertiary Mn and detachment-related Cu and Zn ore deposits in west-central Arizona.

Original languageEnglish (US)
Pages (from-to)877-888
Number of pages12
JournalEconomic Geology
Volume89
Issue number4
DOIs
StatePublished - Jun 1994
Externally publishedYes

Fingerprint

Ashes
ash flow
ashes
metasomatism
Metals
veins
Cooling
cooling
Calcium Carbonate
calcite
Chemical analysis
detachment
metals
ignition
Ignition
thin section
deposits
Rocks
minerals
rocks

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics

Cite this

Composition changes in an ash-flow cooling unit during K metasomatism, west-central Arizona. / Hollocher, Kurt; Spencer, Jon; Ruiz, Joaquin.

In: Economic Geology, Vol. 89, No. 4, 06.1994, p. 877-888.

Research output: Contribution to journalArticle

@article{99a6f14d3e864257bb3844a734d777a9,
title = "Composition changes in an ash-flow cooling unit during K metasomatism, west-central Arizona",
abstract = "A variably altered rhyolitic ash-flow cooling unit in west-central Arizona was sampled and analyzed to gain a better understanding of compositional changes that took place during Tertiary K metasomatism. Mn, Cu, Zn, and other metals of economic importance were removed from the K-metasomatized rocks during alteration, making them a likely source for these metals in vein and stratiform Mn deposits and base metal ores related to detachment faults in western Arizona. Using a single cooling unit to understand the compositional changes during K metasomatism reduces the primary chemical variability inherent in the sampling of multiple units, a problem with most previous studies. The least altered samples (group 1) experienced a moderate degree of K metasomatism, having K 2O/Na 2O ratios of 3.1 to 5.5, compared to likely igneous values of <2. The most altered samples (group 2) were severely K metasomatized with K 2O/Na 2O ratios of 17.9 to 29.5. K 2O, P 2O 5, and Ba increased in concentration substantially during K metasomatism, and MnO, Na 2O, Cu, Zn, Sr, Mo, and Cs decreased. All immobile elements decreased in concentration by approx.9 percent, which is attributed to a dilution effect caused by net mass gain in the group 2 rocks, principally as K 2O and SiO 2. Mineralogical zoning in small late veins seen in thin section is quartz ± K feldspar ± calcite from vein wall to center. The strong covariance in CaO and loss on ignition (L.O.I.) with observed calcite in thin section and the lack of correlation of CaO and L.O.I. with other components indicates that their variability is unrelated to K metasomatism. Calculations indicate that the loss of Mn, Cu, Zn, and other metals from K-metasomatized volcanics is easily large enough to account for middle Tertiary Mn and detachment-related Cu and Zn ore deposits in west-central Arizona.",
author = "Kurt Hollocher and Jon Spencer and Joaquin Ruiz",
year = "1994",
month = "6",
doi = "10.2113/gsecongeo.89.4.877",
language = "English (US)",
volume = "89",
pages = "877--888",
journal = "Economic Geology",
issn = "0361-0128",
publisher = "Society of Economic Geologists, Inc",
number = "4",

}

TY - JOUR

T1 - Composition changes in an ash-flow cooling unit during K metasomatism, west-central Arizona

AU - Hollocher, Kurt

AU - Spencer, Jon

AU - Ruiz, Joaquin

PY - 1994/6

Y1 - 1994/6

N2 - A variably altered rhyolitic ash-flow cooling unit in west-central Arizona was sampled and analyzed to gain a better understanding of compositional changes that took place during Tertiary K metasomatism. Mn, Cu, Zn, and other metals of economic importance were removed from the K-metasomatized rocks during alteration, making them a likely source for these metals in vein and stratiform Mn deposits and base metal ores related to detachment faults in western Arizona. Using a single cooling unit to understand the compositional changes during K metasomatism reduces the primary chemical variability inherent in the sampling of multiple units, a problem with most previous studies. The least altered samples (group 1) experienced a moderate degree of K metasomatism, having K 2O/Na 2O ratios of 3.1 to 5.5, compared to likely igneous values of <2. The most altered samples (group 2) were severely K metasomatized with K 2O/Na 2O ratios of 17.9 to 29.5. K 2O, P 2O 5, and Ba increased in concentration substantially during K metasomatism, and MnO, Na 2O, Cu, Zn, Sr, Mo, and Cs decreased. All immobile elements decreased in concentration by approx.9 percent, which is attributed to a dilution effect caused by net mass gain in the group 2 rocks, principally as K 2O and SiO 2. Mineralogical zoning in small late veins seen in thin section is quartz ± K feldspar ± calcite from vein wall to center. The strong covariance in CaO and loss on ignition (L.O.I.) with observed calcite in thin section and the lack of correlation of CaO and L.O.I. with other components indicates that their variability is unrelated to K metasomatism. Calculations indicate that the loss of Mn, Cu, Zn, and other metals from K-metasomatized volcanics is easily large enough to account for middle Tertiary Mn and detachment-related Cu and Zn ore deposits in west-central Arizona.

AB - A variably altered rhyolitic ash-flow cooling unit in west-central Arizona was sampled and analyzed to gain a better understanding of compositional changes that took place during Tertiary K metasomatism. Mn, Cu, Zn, and other metals of economic importance were removed from the K-metasomatized rocks during alteration, making them a likely source for these metals in vein and stratiform Mn deposits and base metal ores related to detachment faults in western Arizona. Using a single cooling unit to understand the compositional changes during K metasomatism reduces the primary chemical variability inherent in the sampling of multiple units, a problem with most previous studies. The least altered samples (group 1) experienced a moderate degree of K metasomatism, having K 2O/Na 2O ratios of 3.1 to 5.5, compared to likely igneous values of <2. The most altered samples (group 2) were severely K metasomatized with K 2O/Na 2O ratios of 17.9 to 29.5. K 2O, P 2O 5, and Ba increased in concentration substantially during K metasomatism, and MnO, Na 2O, Cu, Zn, Sr, Mo, and Cs decreased. All immobile elements decreased in concentration by approx.9 percent, which is attributed to a dilution effect caused by net mass gain in the group 2 rocks, principally as K 2O and SiO 2. Mineralogical zoning in small late veins seen in thin section is quartz ± K feldspar ± calcite from vein wall to center. The strong covariance in CaO and loss on ignition (L.O.I.) with observed calcite in thin section and the lack of correlation of CaO and L.O.I. with other components indicates that their variability is unrelated to K metasomatism. Calculations indicate that the loss of Mn, Cu, Zn, and other metals from K-metasomatized volcanics is easily large enough to account for middle Tertiary Mn and detachment-related Cu and Zn ore deposits in west-central Arizona.

UR - http://www.scopus.com/inward/record.url?scp=0028444361&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0028444361&partnerID=8YFLogxK

U2 - 10.2113/gsecongeo.89.4.877

DO - 10.2113/gsecongeo.89.4.877

M3 - Article

AN - SCOPUS:0028444361

VL - 89

SP - 877

EP - 888

JO - Economic Geology

JF - Economic Geology

SN - 0361-0128

IS - 4

ER -