An empirical calibration for 4He quantification in minerals and rocks by laser fusion and noble gas mass spectrometry using Cerro de Mercado (Durango, Mexico) fluorapatite as a standard

An empirical calibration with a natural mineral standard (fluorapatite from Cerro de Mercado, Mexico) is proposed as a method to determine the 4He concentration of mineral and rock samples. The procedure is based on the fusion of several aliquots of the fluorapatite standard with a well-spaced weight distribution in order to obtain a good correlation in coordinates of 4He peak height versus fluorapatite weight. The weight is then converted to moles using the accepted mineral age (31.4 Ma) and appropriate formula. Experimental peak height of 4He for the unknown samples are converted to moles with the regression determined for fluorapatite. The procedure is fast and inexpensive, and both precision and accuracy are always below 10% and usually about 3-5%.