Skip to Main Content

Globally, peraluminous two-mica granites have produced significant amounts of Sn, W, U, F, Th, Be, Ta, Nb, Mo, and Li, but peraluminous granitoids in southern Arizona are known to contain significant concentrations of only W and Be. Major, minor, trace, and rare earth element data from peraluminous granitoids and pegmatites in Arizona are compared with their geochemical counterparts in western and eastern Europe, the New England states, and the Maritime Provinces of Canada. Each Arizona sample has the petrographic characteristics of a two-mica granite with varying proportions of biotite, muscovite, magnetite, garnet, apatite, fluorite, ilmenite, topaz, and zircon.

Geochemical and statistical analysis of a large data base of new analyses reveals distinct geochemical differences between peraluminous two-mica granitoids in southern Arizona and their locally productive counterparts elsewhere. All of the samples exhibit similar concentrations of the major oxides SiO2, Al2O3, and TiO2, but they differ markedly in K2O, CaO, P2O5, and Fe2O3/FeO*. Distinct groups of strictly defined I- and S-type granites cannot be distinguished either within or between the Arizona outcrop areas studied; there are, however, clear separations into ilmenite and magnetite series granitoids. Comparatively, the Arizona granitoids have lower K2O/Rb, Rb/Sr, and P2O5 values, and smaller concentrations of the lithophile elements Be, Cs, Li, Rb, Sn, U, and W relative to their European counterparts.

Correspondence analysis, a type of principal components analysis, is used to discern the statistical variations and groupings of the data and to reinforce the geochemical concepts derived from scattergram chemical plots. Six factors describe 93 percent of the data. The first three factors account for 84.2 percent of the data variation and define major-element variation, lithophile-element enrichment or depletion, and the presence or absence of P2O5.

The results of this study suggest that Sn, W, and U enrichment in peraluminous granites is largely governed by the lithophile-element concentrations of the source rocks. In addition, magmatic differentiation indices, the presence of higher levels of P2O5, and the oxidation state of the intrusion vary with the final concentration levels of lithophile elements in a granitoid. Hydrothermal redistribution appears minimal in the fresh material studied. Low contents of lithophile elements in the crustal source of peraluminous granitoids in southern Arizona appear to account for the paucity of associated economic lithophile element mineralization.

You do not currently have access to this chapter.

Figures & Tables

Contents

References

Close Modal
This Feature Is Available To Subscribers Only

Sign In or Create an Account

Close Modal
Close Modal