Table 1.

The statistic values of Fe and Zn contents in calibration and validation sets.

Element	Data set	Samples	Range (ppm)	Mean (ppm)	Standard deviation (ppm)
Fe	Calibration	70	39.951–134.254	79.245	21.945
	Validation	20	40.011–133.992	80.649	24.003
	All samples	90	39.951–134.254	80.935	23.669
Zn	Calibration	70	9.085–49.927	23.710	9.221
	Validation	20	9.103–49.849	23.134	9.518
	All samples	90	9.085–49.927	23.408	9.928