Application of factor analysis and concentration-volume fractal modeling to delineation of 3D geochemical patterns: a case study of the Jinwozi gold field, NW China

Delineation of vertical distribution patterns of elements in overburden over a concealed deposit is essential for determining potential upward migration mechanism of elements and for predicting undiscovered mineral deposits. The aim of this study is to identify the vertical distribution features of elements in the regolith over the Jinwozi gold field, NW China by using factor analysis (FA) and concentration-volume (C-V) fractal modeling based on the data-set generated from 70 overburden drilling boreholes. Firstly, the zones of different gold enrichment states were obtained by the C-V fractal method. Secondly, FA was utilized to define the mineralization-related element association. Finally, the C-V method was applied to the relevant association defined by FA. The results showed that: (1) the C-V fractal method distinguished four enrichment states determined by Au thresholds of 1.6, 7.9 and 39.9 ng/g and by factor scores of -1.14, 0.33 and 1.45; (2) the first factor that describes 41.5% of the common variance has positive loadings in Au, As, Sb and Mo; (3) the zones of both high Au contents and factor scores generally showed horizontally northeasterly distribution along the ductile-shearing alteration belt and vertically top-bottom symmetric distribution in the regolith over the deposit; (4) the rest of the zones determined by the C-V fractal model properly delineated the zones of low and high backgrounds and moderate Au enrichment; and (5) the moderately-enriched zones of the raw Au data are better than those of the factor scores, and the rest of the zones have the similar distributions. These results indicate that: (1) the distribution of elements in the regolith was the product of nonlinear natural processes resulting in an enrichment pattern at the surface over the deposit; and (2) the integration of FA and C-V fractal model is effective for the delineation of 3D geochemical patterns.