Abstract:
This geodatabase contains a point data set of over 50,000 records of
geochemical indices of igneous rocks in Alaska. Major and trace element
data were compiled from Alaska Geochemical Database version 2 (AGDB2),
Alaska Division of Geological and Geophysical Surveys (ADGGS), peer-reviewed
literature, and unpublished USGS data. Data was screened to included
only high-resolution analyses. This data set contains calculations
of various ratios and displacements from established boundaries on
x-y plots to help classify igneous rocks. The point data set is also
provided as a shapefile.
Purpose:
Feature class all_igneous_ratios is used to identify permissive rock
types for REE deposits and Sn-W-Mo deposits. The ratios for the
aluminum saturation index, ASI, (Al/[Ca-1.67xP)+Na+K], and ANK,
Al/[Na+K], allow for the differentiation between peraluminous,
metaluminous, and peralkaline rocks. Trace element concentration
ratios Nb/Y and Ga/Al can distinguish alkaline and subalkaline
igneous rocks. Also, the modified alkali-lime index, MALI,
(Na2O+K2O-CaO), and Fe_no, FeO/[FeO+MgO], can used to distinguish
alkaline vs calcic, and ferroan vs magnesian rocks.
Supplemental_Information:
The method for screening high-resolution analyses is as follows. All the
elements used to calculate the geochemical index need to be of similarly
high precision. In general, major-element data were used only for samples
where all major rock forming element oxides were measured by x-ray
fluorescence (XRF) methods. For trace elements such as Y and Nb, only
XRF and inductively coupled plasma mass spectrometry (ICP-MS) analyses
were used.
Theme:
Theme_Keyword_Thesaurus: None
Theme_Keyword: igneous rock
Theme_Keyword: peraluminous
Theme_Keyword: metaluminous
Theme_Keyword: peralkaline
Theme_Keyword: alkaline
Theme_Keyword: subalkaline
Theme_Keyword: calcic
Theme_Keyword: ferroan
Theme_Keyword: magnesian
Theme:
Theme_Keyword_Thesaurus: ISO 19115 Topic Category
Theme_Keyword: geoscientificInformation, 008
None. Users are advised to read the publication text and metadata to
understand the appropriate use and data limitations.