Using trace element data

A trace element may be defined as an element which is present in a rock in concentrations of less than O.i wt %, that is less than 1000 parts per million (ppm). Sometimes trace elements will form mineral species in their own right but most commonly they substitute for major elements in the rock-forming minerals. 

Trace element studies have become a vital part of modem petrology and are more capable of discriminating between petrological processes than are the major elements. Particularly important is the fact that there are mathematical models to describe trace element distributions which allow the quantitative testing of petrolo cal hypotheses. These are most applicable to processes controlled by crystal-melt or crystal-fluid equilibria. 

In this chapter we first develop some of the theory behind the distribution of trace elements and explain the physical laws used in trace element modelling. Then various methods of displaying trace element data are examined as a prelude to showing how trace elements might be used in identifying geological processes and in testing hypotheses. 

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Certain ore deposits may partially overlap in their lead isotope composition. In such a case, it might not be possible to decide on the basis of the lead isotope data alone which of the ore deposits in question provided the ore for metal artifacts that have lead isotope compositions that fall into the overlapping space. Sometimes, one of these ore deposits can be ruled out by using trace element data, particularly from gold and silver analyses (6). Lead isotope analyses by themselves can make a negative statement with absolute certainty in a way which chemical analysis can never hope to do. If the lead isotope composition of an artifact falls well outside the lead isotope field characteristic of a particular ore deposit then it is certain that the metal... 

A number of inorganic materials have provided useful trace element data including obsidian (2,3,4,5,6), ceramics (7,8), coins (9), and... 

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