Dear Kurt and all,
the problem you mentioned with isocon diagrams is largely overcome
if the intention of the diagram is directed towards establishing a line of
best fit to potentially immobile elements, none-the-less there are obvious
and inherent visual/statistical problems of the sort you mention. One thing
you mention is also routine but rarely published is to plot ratios of
altered to unaltered against position on periodic table etc, but equally
easy is to put those ratios at the bottom of your data spreadsheet as a way
of quickly identifiying immobile element likelihood. For most (but not all)
alteration systems this can be tweaked quickly by looking for likely
immobiles (Ti, Zr, Y, Ga, Al etc). There are far fancier and more robust
ways to do this in Baumgartner, L.P. and Olsen, S.N., 1995, A least-squares
approach to mass transport calculations using the isocon method, Economic
Geology: v. 90, p. 1261-1270.
Hope this helps
Nick Oliver
Professor of Economic Geology
Director, Economic Geology Research Unit
School of Earth Sciences
James Cook University
Townsville, Qld, 4811 Australia
email [log in to unmask]
Fax (INT-61-7) 07 47251501
Ph 07 47815049 (Nick)
07 47814726 (EGRU)
07 47814546 (front office)
http://www.es.jcu.edu.au/dept/earth/e/egru2.shtml
(EGRU home page)
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