Geological, alteration, mineralogy and geochemical studies of the Copper deposit in the Kalatehno prospect area, northwest of Gonabad (Khorasan Razavi province)

Document Type : Research Article

Authors

• Sedigheh Zirjanizadeh ¹
• Roohollah Miri Bydokhti ²

¹ Assistant Professor, Department of Geology, Faculty of Sciences, University of Gonabad, Gonabad, Iran

² Department of Geology, Faculty of Sciences, Gonabad University, Gonabad, Iran

10.22067/econg.2024.1118

Abstract

The Kalatehno prospecting area is located at 23 Km northwest of Gonabad, Khorasan Razavi province, and north of the Lut Block. The geology of the area includes subvolcanic units with monzonite, monzodiorite and diorite porphyry, volcanic units, pyroclastic and Quaternary units. Mineralization occurred epigenetically and as vein, in volcanic and pyroclastic units. The ore vein extends to 100-300 m along, and 1-3 m wide. The hypogene mineralization is characterized by chalcopyrite as the main ore mineral and minor amount of bornite, pyrite, galena with quartz as gangue minerals. Malachite, chrysocolla, chalcocite and secondary iron oxides (hematite, goethite) constitute the mineralization of oxidation and supergene zone. The main alteration in the area are silicification propylitic and argillic. According to geochemical study, the amount of copper is between 750 to 19500 ppm, Pb from 62.8 to 30400 ppm and Zn from 258 to 1800 ppm. Based on the structural control of mineralization, alteration types, mineralization and geology features, the Kalatehno deposit is similar to vein type copper deposits.
 
Introduction
The Kalatehno area is situated 23 km northwest of Gonabad city, Khorasan Razavi province, and in geographic latitude 34°28´30̋ to 34°29´30̋ N and longitude 58°31´30̋ to 58°32´30̋ E. This area is located in the north of the Lut Block zone. Due to different tectonic situations and the huge amount of magmatism with different geochemical characteristics, the Lut Block has very good potential for various mineralization. Mineralization events in Lut Block have occurred over the Tertiary. Previous studies in the prospecting area of the Kalatehno copper deposit include studies by Zirjanizadeh et al., (2016) and Zirjanizadeh (2015), which focus on petrology, geochemistry, mineralization, and alteration of igneous rocks northwest Gonabad and Kalatehno area. Bemani et al. (2023) discuss the processing of satellite images for extracting alterations with field evidence in the Kalatehno deposit. The purpose of this research is to identify rock units, alteration, mineralization and geochemistry and characterize the ore-forming processes to recognize mineralization type in the Kalatehno prospecting area.
 
Materials and methods
The methods include fieldwork, laboratory work, and interpretation. The fieldwork includes direct observation and sampling. After conducting field surveys and collecting 100 rock samples from different geological units and 60 samples from mineral veins, suitable samples were selected and prepared for laboratory studies. 30 thin sections were prepared and studied for a geological and alteration map with a scale of 1:5000. The texture and mineralogy were studied by preparing 10 polished block sections. For geochemical analysis, Laboratory analysis is conducted using Fire Assay (FA) for gold grade and Atomic Absorption Spectrophotometry (AAS) for Cu, Ag, Pb, As, Zn and other elements that were analyzed at Zarazma laboratory.
 
Result and Discussion
The lithological units found in the study area include volcanic and tuff units, subvolcanic rocks, dacite porphyritic dykes, and Quaternary units. The volcanic rocks are mostly composed of pyroclastic rocks, rhyolite, andesite and trachyandesite with porphyritic textures. Rhyolites are observed in the northwest of the study area.
The phenocrysts at rhyolite include quartz, potassium feldspar, plagioclase, and opaque minerals. The groundmass comprises microcrystalline quartz and alkali feldspars, and the alkali feldspars are altered to clay minerals. Subvolcanic outcrops as stocks in different parts of the area. These units include biotite granodiorite porphyry, monzodiorite porphyry, biotite monzonite porphyry and biotite quartz monzodiorite porphyry. Propylitic and silicic alterations are common alterations of the Kalatehno prospect. The silicic alteration zone is divided into four main sub-zones: strong siliceous, strong siliceous + strong propylitic + weak argillic, and strong siliceous + epidote. The important minerals of these zones are quartz 50-60 %, sericite (less than 1-2 %), calcite (less than 2 %-5 %), epidote (veins and scattered up to 2%), chlorite (less than 2 %) resulting from alteration of hornblende and biotite, pyrite in about 1 % and clay minerals resulting from the alteration of feldspars. Quartz exists as disseminated, veins, veinlets and crystalline (milky quartz and amethyst) in rock units and is accompanied by mineralization in the Kalatehno area.
The propylitic alteration has different intensities and has affected the entire area. Chlorite reaches from 1% to 5% in strong propylitic. Epidote is seen as a vein and coarse crystal in groundmass and also a replacement in plagioclase and hornblende, and in some cases, because of high abundance, can be mentioned as a separate alteration. In the Kalatehno prospecting area, mineralization is observed in different forms: vein, disseminated, stockwork, replacement, colloform, and hydrothermal breccia. The mineralization in the Kalatehno area has occurred as veins in the host rock (pyroclastic rocks) and is observed with variable lengths and thicknesses. The mineralization is controlled by structures and faults. The vein mineralogy includes primary sulfide minerals, pyrite, chalcopyrite, bornite, and galena. Quartz grains with chalcopyrite and bornite were found. Both minerals are surrounded by chalcocite. Due to supergene processes, secondary minerals comprise malachite, azurite, chrysocolla, chalcocite, and Mn and Fe oxides with quartz as gangue mineral. The amount of copper is between 750 to 9100 ppm, Pb from 62.8 to 30400 ppm, and Zn from 258 to 1800 ppm. The source rock related to mineralization in the area is monzodiorite porphyry. Silicic and propylitic alteration zones are the most important alteration.
 
Conclusion
In Kalatehno prospect area, vein-type epigenetic mineralization occurring along fault zones with main trending NW–SE. Mineralization is mainly hosted in pyroclastic rocks (tuffs) with silicification and propylitic alterations.  Ore minerals at study area comprise pyrite, chalcopyrite, bornite, galena, and Secondary minerals include malachite, azurite, chrysocolla, chalcocite, Fe oxides (hematite, goethite) and Mn oxides. quartz is main gangue mineral. Vein copper deposits include various vein-type deposits in which copper is the dominant metal. The ore minerals are deposited as open-space filling. Mineralogy of ore and texture, structurally controlled mineralization and type of alterations are similar to vein copper deposits.
 
Acknowledgments
We thank from anonymous reviewers and the editor for their thoughtful reviews.

Keywords

• Subvolcanic units
• Mineralization
• vein type copper
• Kalatehno
• Gonabad

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