Post-entrapment modification of He and Ar isotopes

He and Ar isotopes that are trapped within minerals can be modified in one of four ways and must be either ruled out as significant sources or a correction applied before interpretation can be made  

The effects of these modification mechanisms will obviously increase with sample age and with lithophile element content. Previous studies have shown that the postentrapment production of He and He within sulfides (pyrite, sphalerite and galena) is insignificant when compared to the measured values. Thrower (1999) studied sulfides from deposits of the Colorado mineral belt (60-15 Ma) and determined post-entrapment isotope production to be 0.6% in all cases which was well below the error for each measurement, making corrections unnecessary. However, in studies of older deposits or 

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