Original paper

Geochemical characteristics of the Abgarm kaolin deposit, NW Iran

Abedini, Ali; Asghar Calagari, Ali

Abstract

The Abgarm kaolin deposit is located ~20 km south of Mianeh in East-Azarbaidjan province in northwestern Iran, and is a typical clayey deposit within an andesitic host of Oligo-Miocene age. Mineralogical studies show that the rock-forming minerals in this deposit include kaolinite, quartz, smectite, illite, chlorite, hematite, alunite, pyrophyllite, rutile, alkali-feldspar, gypsum, calcite, and hornblende. Increasing (SiO2 +Fe2 O3 +MgO+Na2 O+CaO+K2 O)/(Al2 O3 +TiO2) and SiO2 /Al2 O3 ratios from the center outward toward the peripheral zone of the deposit indicate the presence of hydrothermal zoning. Mass change calculations indicate that during the progress of the kaolinization processes, elements such as Al, Sr, Ga, and REE were enriched whereas elements like Si, Fe, Ca, Na, Mg, K, Ti, Mn, U, Ba, Hf, Co, Cs, Rb, Y, and Zr were depleted. Ce and Eu anomalies in this deposit are within the range 0.62-0.82 and 0.53-0.91, respectively. Further considerations show that negative Eu anomalies are due to the destruction of feldspars and hornblende in the andesitic host rocks by hydrothermal fluids. Negative Ce anomalies are due to the destruction of zircon by acidic-oxidizing fluids. Field evidence (e. g., the presence of silicic cap in the upper part of the deposit along with local brecciation), mineral assemblages (e. g., pyrophyllite and alunite), differentiation and enrichment of LREE relative to HREE, occurrence of negative Ce and Eu anomalies, along with mass changes of elements (depletion of Fe, Ti, and Nb and vigorous enrichment of Al and Sr) suggest that the development and evolution of the Abgarm kaolin deposit is affiliated to hypogene processes. The robust and positive correlations of (La/Lu)N, P, and S with LOI further support this.

Keywords

andesitehydrothermal alterationiranabgarmgeochemistrykaolin deposit