Geology, mineralization and geochemistry of the Aqkand Cu occurrence (north of Zanjan, Tarom-Hashtjin zone)

Document Type : Research Article

Authors

• Maryam Feyzi
• Mohammad Ebrahimi
• Hossein Kouhestani
• Mir Ali Asghar Mokhtari

Zanjan

10.22067/econg.v8i2.49150

Abstract

Introduction
The Aqkand Cu occurrence, 48 km north of Zanjan, is located in the Tarom subzone of the Western Alborz-Azerbaijan structural zone. Apart from small scale geological maps of the area, i.e., 1:250,000 geological maps of Bandar-e-Anzali (Davies, 1977) and 1:100,000 geological maps of Hashtjin (Faridi and Anvari, 2000) and a number of unpublished perlite exploration reports, prior to this research no work has been done on Cu mineralization at Aqkand. The present paper provides an overview of the geological framework, the mineralization characteristics, and the results of geochemistry study of the Aqkand Cu occurrence with an application to the ore genesis. Identification of these characteristics can be used as a model for exploration of this type of copper mineralization in the Tarom area and elsewhere.

Materials and methods
Detailed field work has been carried out at different scales in the Aqkand area. About 35 polished thin and thin sections from host rocks and mineralized and altered zones were studied by conventional petrographic and mineralogic methods at the University of Zanjan. In addition, a total of 6 samples from ore zones at the Aqkand occurrence were analyzed by ICP-MS for trace elements and REE compositions at Kimia Pazhuh Alborz Co., Isfahan, Iran.

Results and Discussion
The oldest units exposed in the Aqkand area are Eocene volcanic rocks which are overlain unconformably by Oligocene acidic rocks. The Eocene units consist of lithic and vitric tuff with intercalations of andesitic basalt lavas (equal to Karaj Formation, Hirayama et al., 1966). The andesitic basalt lavas show porphyritic texture consisting of plagioclase and altered ferromagnesian minerals set in a fine-grained groundmass. The Oligocene acidic rocks consist of rhyolite-rhyodacite, perlite, pitchstone and ignimbrite. These rocks are exposed as domes and lava flows. The rhyolite-rhyodacite lavas usually show onion-skin weathering and locally display flow bands. Rapid cooling of rhyolitic-rhyodacitic lavas has resulted in the formation of volcanic glasses (obsidian). Hydration of these volcanic glasses by hydrothermal fluids caused perlite formation which is located in the lower parts of the rhyolitic-rhyodacitic domes.
Copper mineralization at Aqkand occurs as Cu-bearing quartz-fluorite veins in Eocene andesitic basalt lavas. The main ore vein reaches up to 50 m in length and average of 2 m in width. It has NW-trend and mostly dips NE. Six stages of mineralization can be distinguished at the Aqkand Cu occurrence. Stage-1 is characterized by

Keywords

• Geology
• mineralization
• Geochemistry
• Aqkand
• Zanjan
• Tarom-Hashtjin

20.1001.1.20087306.1395.8.2.13.4

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