2.4. Statistical analysis
The statistical significance of the data was tested by one-wayanalysis of the variance (ANOVA), followed by the Duncan test tocompare the means that presented a significant variation(P < 0.05). The relationships between minerals were evaluatedby computing the Pearson linear correlation coefficient at theP < 0.05 confidence level. Multivariate analysis was performed bycluster analysis. In each cluster, the samples that presented anoutlier in the parameters addressed (those with a value higher or lower than three times the interquartile range) were removed. The resulting groups were then subjected to principal component analysis. All statistical analyses were performed using Statgraphics
Centurion XVI statistical software (2009).