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Alkali-Alumina and MgO-Alumina Molar Ratios of Altered and Unaltered Rhyolites

2006; Volume: 15; Issue: 1-2 Linguagem: Inglês

10.2113/gsemg.15.1-2.75

1878-6715

James F. Davies, R. E. Whitehead,

Geochemistry and Geologic Mapping

Research Article| January 01, 2006 Alkali-Alumina and MgO-Alumina Molar Ratios of Altered and Unaltered Rhyolites J.F. DAVIES; J.F. DAVIES 1Department of Earth Sciences, Laurentian University, Sudbury, Ontario P3E 2C6. Search for other works by this author on: GSW Google Scholar R.E. WHITEHEAD R.E. WHITEHEAD 1Department of Earth Sciences, Laurentian University, Sudbury, Ontario P3E 2C6. Search for other works by this author on: GSW Google Scholar Author and Article Information J.F. DAVIES 1Department of Earth Sciences, Laurentian University, Sudbury, Ontario P3E 2C6. R.E. WHITEHEAD 1Department of Earth Sciences, Laurentian University, Sudbury, Ontario P3E 2C6. Publisher: Canadian Institute of Mining, Metallurgy and Petroleum Received: 01 Oct 2003 Accepted: 15 Nov 2005 First Online: 09 Mar 2017 © 2006 Canadian Institute of Mining, Metallurgy and Petroleum Exploration and Mining Geology (2006) 15 (1-2): 75–88. https://doi.org/10.2113/gsemg.15.1-2.75 Article history Received: 01 Oct 2003 Accepted: 15 Nov 2005 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation J.F. DAVIES, R.E. WHITEHEAD; Alkali-Alumina and MgO-Alumina Molar Ratios of Altered and Unaltered Rhyolites. Exploration and Mining Geology 2006;; 15 (1-2): 75–88. doi: https://doi.org/10.2113/gsemg.15.1-2.75 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyExploration and Mining Geology Search Advanced Search Abstract Alkali-alumina and MgO-alumina plots are an effective instrument for displaying chemical and mineralogical compositions of altered and unaltered rhyolites and rhyodacites. They reveal that most supposedly unaltered rhyolites, apart from those of Cenozoic age, have undergone losses in Na2O and gains in K2O. The extreme loss of Na2O from highly altered rhyolites immediately adjacent to VMS deposits is strikingly illustrated by alkali-alumina plots. MgO/Al2O3 vs. K2O/Al2O3 diagrams display a strong negative correlation between MgO and K2O that results from the conversion of sericite to chlorite. A similar negative correlation between MgO and whole-rock δ18O is apparent on plots of these two parameters.Alkali-alumina plots underscore problems in selecting appropriate precursor compositions required for mass-balance calculations. Molar ratio plots are a viable alternative to such calculations. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.