Mineralogical and Geochemical Characteristics of Kojanagh Kaolinite and Alunite Deposits, Northwest of Meshkinshahr, Ardebil Province.


Geology Department, Faculty of Natural Sciences, University of Tabriz, Tabriz, Iran


      Kaolinite and alunite deposits at Kojanagh are located in ~18 km northwest of Meshkinshahr, Ardebil province. Field and microscopic studies show that these deposits are the alteration products of Eocene volcanic rocks with andesitic to trachy-andesitic compositions. These deposits lie on the Ahar-Jolfa (Arasbaran) alteration axis. The alteration zones at Kojanagh are principally argillic (kaolinite), advanced argillic (alunite+ kaolinite), and silicified (quartz + cristobalite) that have a lenticular planar expression. According to the mineralogical data, the main rock-forming minerals in these deposits are kaolinite, alunite, quartz, and cristobalite accompanied by minor amounts of hematite, montmorillonite, anatase, and rutile. Based upon geochemical indicators like (Ti+Fe), (Cr+Nb), (Ba+Sr), and (Ce+Y+La) along with mobility degree of REEs in altered rocks relative to primary trachy-andesitic rocks, it seems that the hypogene rather than supergene hydrothermal solutions played more effective role in evolution of these deposits. The obtained geochemical data indicate that the mobility degree and distribution of major, minor, trace, and rare earth elements during kaolinization and alunitization processes were functioned by factors such as temperature and pH variations of altering solutions, adsorption, scavenging and concentration by metallic oxides, and existing in resistant mineral phases. Except Si and Al, the major elements show depletion related to fresh parent rocks toward siliceous alteration zone. The presence of K and Na in alunite structure caused their increase in alunite alteration zone. Large ion lithophile elements (LILE) are depleted during alteration. LREEs relative to HREEs in kaolinite and alunite samples display enrichment. Field and mineralogical evidences such as presence of alunite and native sulfur in the studied samples reveal that epithermal acid sulfate solutions were the main agent for progression of kaolinitization and alunitization processes during the evolution of Kojanagh deposits. Camparison of Kojanagh kaolinite deposit with some of other similar types from Iran showed that Kojanagh kaolin in view of geological characteristics best matches Zonooz and Ghalandar deposits in East-Azarbaidjan. Since such epithermal enviroments are accompanied with mineralization of precious metals like Au, therefore further investigations are well justified in this area.


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