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Ore petrography, geochemistry and SWIR-reflectance spectroscopy of the Chichaklou Zn-Pb deposit, Takab Province, NW Iran

Andreas Kamradt

Abstract

This study was carried out in cooperation with the Geological Survey of Iran in order to outline a detailed investigation of the dolomite-hosted Zn-Pb mineralization in the western vicinity of the Chichaklou village. The Chichaklou Zn-Pb deposit is located approximately 20 km east to Takab in the southernmost part of the Western Azerbaijan State, NW Iran.

The major aims of this study comprise a detailed description of the hypogene-supergene ore assemblage, determination of the ore paragenesis, geochemical characterization of lithotypes related to the Chichaklou deposit as well as SWIR-spectral investigation regarding to the alteration mineral assemblage that was detected in the study area. The results were synthesized in a metallogenic model that outlines the evolution of the Chichaklou Zn-Pb deposit.

The Chichaklou Zn-Pb deposit is hosted in presumably Late Precambrian dolomite rocks that are part of a metamorphic basement complex consisting mainly of Neoproterozoic quartz-sericite schist. Lower green schist metamorphism developed by Assynthic orogeny was proved for the Neoproterozoic quartz-sericite schist, while the post-dated units show no apparently indication of metamorphism. The basement rocks are thought to be thrusted during the Oligo-Miocene in southwestern direction along the regional-scaled Gheynarjeh-Chahar Tagh thrust fault and are marginal embedded by a Tertiary volcano-sedimentary succession. The transpressional tectonic regime was reactivated in a following period of extensional uplift, exhumation and erosion in Plio-Pleistocene and caused the development of an extensional strike-slip duplex in the Chichaklou area and led to steep dipping faulting and fracturing within the dolomite body of the Chichaklou target area. Tectonic extension was assumedly responsible for the emplacement of the Pliocene dacite body that provided metal-bearing mesothermal fluids, which were mainly transported along the tectonized border to impermeable quartz-sericite schist and injected in the previous fractured, permeable dolomite. Hypogene Zn-Pb vein mineralization is of postmagmatic origin and its emplacement structural controlled. Crustal uplift and exhumation led to erosion of Miocene to Pliocene sediments and uncovered the hypogene ore-bearing dolomite body to a near-surface position above the groundwater table. The subaerial position was accessible to oxygenated meteoric waters and activated the supergene processes by the partially oxidation of the hypogene ore and accompanying production of acidic, metalliferous aqueous solutions. The circulation of these fluids within the fractured dolomite wall rock result in secondary pores space, intergranular interstices and voids by dissolution and caused equally the neutralization by carbonate buffering. The neutralization process is marked by sequent precipitation of non-sulphide zinc minerals following the change from acid to moderate alkaline pH condition and led to direct replacement in solved pores within the hypogene sulphide ore and wall rock replacement in the adjacent dolomite. Thus, the non-sulphide ore in Chichaklou represents a hybrid-type of direct as well as wall rock replacement.

Hydrothermal alteration in the southern area of the dacite dome determined using SWIR-spectroscopy and microscopic observation is characterized by the occurrence of dickite, kaolinite, illite-smectite, chlorite and epidote and can be classified as intrusion-related intermediate argillic alteration indicating a temperature range of the hydrothermal fluids of at least 200 °C in distal areas up to 300 °C in proximity to the volcanic centre.

Fig.1 Foreground present the middle and southern part of the Chichaklou Zn-Pb-deposit, whereas lighter and ocre coloured areas display supergene altered ore veins and dolomite wall rock.

Fig.1 Foreground present the middle and southern part of the Chichaklou Zn-Pb-deposit, whereas lighter and ocre coloured areas display supergene altered ore veins and dolomite wall rock.

Fig.1 Foreground present the middle and southern part of the Chichaklou Zn-Pb-deposit, whereas lighter and ocre coloured areas display supergene altered ore veins and dolomite wall rock.

Hand specimen of massive ore from Chichaklou contains preferentially supergene non-sulphide ore minerals as smithsonite, cerrusite, hemimorphite, hydrozincite.

Hand specimen of massive ore from Chichaklou contains preferentially supergene non-sulphide ore minerals as smithsonite, cerrusite, hemimorphite, hydrozincite.

Hand specimen of massive ore from Chichaklou contains preferentially supergene non-sulphide ore minerals as smithsonite, cerrusite, hemimorphite, hydrozincite.

Fig.3 The outcrop of a thin hydrothermal vein shows galena (arrow) that remains onto the weathering surface by the armouring of cerussite.

Fig.3 The outcrop of a thin hydrothermal vein shows galena (arrow) that remains onto the weathering surface by the armouring of cerussite.

Fig.3 The outcrop of a thin hydrothermal vein shows galena (arrow) that remains onto the weathering surface by the armouring of cerussite.

Fig.4 Microphotograph that illustrates the paragenetic sequence of the Chichaklou Zn-Pb-mineralization partially. It is well recognizable that cerussite (cer) replaces galena (gn) at first. The quartz (qtz) coating is assumedly partially solved hydrothermal quartz that is overgrown by bladed hemimorphite (hem I). Bladed hemimorphite is again overgrown by tabular hemimorphite (hem II) coated by iron oxi-hydroxides (gt).

Fig.4 Microphotograph that illustrates the paragenetic sequence of the Chichaklou Zn-Pb-mineralization partially. It is well recognizable that cerussite (cer) replaces galena (gn) at first. The quartz (qtz) coating is assumedly partially solved hydrothermal quartz that is overgrown by bladed hemimorphite (hem I). Bladed hemimorphite is again overgrown by tabular hemimorphite (hem II) coated by iron oxi-hydroxides (gt).

Fig.4 Microphotograph that illustrates the paragenetic sequence of the Chichaklou Zn-Pb-mineralization partially. It is well recognizable that cerussite (cer) replaces galena (gn) at first. The quartz (qtz) coating is assumedly partially solved hydrothermal quartz that is overgrown by bladed hemimorphite (hem I). Bladed hemimorphite is again overgrown by tabular hemimorphite (hem II) coated by iron oxi-hydroxides (gt).

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