Discrimination geochemical interaction effects on mineralization at the polymetallic Glojeh deposit, NW Iran by interative backward quadratic modeling

Abstract

The physico-chemical exchanges between hydrothermal fluids and the host rock are usually controlled by elemental interaction effects. A criterion-based backward elimination approach applies the iterative regression analysis and analysis of variance to investigate the geochemical features of the polymetallic Glojeh (Au–Ag–Cu–Pb–Zn) deposit in NW Iran. A statistical definition of the elemental interaction effects (Xi−j2, Xi × Xj) could elucidate the relationship between variables and the performance of a full quadratic polynomial model (QPM). The model optimization procedure was carried out by the removal of insignificant predictors (P value 95% CL) based on R2(pred.) criterion. In order to straighten the convergent trend with R2 and R2(adj.), R2(pred.) gradually increased from 0% to 77.8% by 15-steps optimization. The miniature-scale geochemical changes indicate double ordinal Au (Ag, Pb) and Au (Ag, Zn) interactions within the vein and host rock, in QPM. Results show that the Au (Pb–Zn) commonly presents ordinal effect at the vein and disordinal interaction at the host rock. This ordinal–disordinal interaction revealed that elements Pb and Zn have similar geochemical features during mineralization. In addition, Akima’s polynomial contour map confirms the results from Pb–Zn interaction effects by dependency tracing between Au–Pb–Zn at different populations. However, it is noteworthy that Pb and Zn occur together in the second phase of Pb–Zn–Cu ± (Ag ± Cd) sulfide mineralization at Glojeh, which implies intergrowth and interaction of Pb–Zn on Au concentration. Pb and Zn demonstrate relatively high mobility and are generally concentrated in the near surface zones. Nb is an immobile element during alteration and high content Hg zone is mainly restricted to narrow stripes above ore vein and veinlets.