Mineralization and Fluid Inclusion Studies in the Tarz Carbonate-Hosted Pb-Zn Deposit, Central Iran

More than 300 sediment-hosted Zn–Pb deposits and occurrences have been recognized in Iran (Rajabi et al., 2013). Most of these deposits are concentrated in the Central Alborz, Tabas-Posht-e-Badam, Malayer-Esfahan and Yazd-Anarak metallogenic belts (Rajabi et al., 2012). Several Pb–Zn deposits and occurrences such as Tarz, Tappeh-Sorkh, Deh-Askar, Abheydar, Gicherkuh, Ahmadabad (BonehAnar), Gujer, Karvangah, Tajkuh, Magasou and Gavar (Javar) occur in Kuhbanan-Bahabad area in the Central Iran zone. The Tarz deposit is situated about 15 km east of the Kuhbanan city in the Tabas-Posht e Badam metallogenic belt. The aims of this study are to investigate ore and host rock petrography, geochemical investigations of ore samples, fluid inclusions in coexisting transparent gangue minerals (calcite) and Microthermometric analysis of fluid inclusions in the various paragenetic stages present in the Tarz deposit. These studies have led to a genetic model of the Tarz deposit.

Ore samples were collected from both mining tunnels and surface outcrops of mineralization. Detailed petrographic studies were conducted on hand specimens, thin and polish sections using reflected and transmitted light microscope. Representative samples were analyzed by using inductively coupled plasma emission spectrometry (ICP-ES) for major and minor elements at the Zar Azma Company in Tehran, following acid digestion. Calcite samples of different mineralization stages were collected from all major orebodies and were prepared as doubly polished sections. Microthermometric measurements were carried out on a Linkam THMSG600 Heating–Freezing stage in Fluid Inclusion, with a German Zeiss microscope.

The primary Zn–Pb sulfide mineralization in the Tarz mine occurs as vein-type and open-space filling, consisting mainly of sphalerite and galena with minor amounts of pyrite and trace chalcopyrite. Wall-rock alteration in the Tarz deposit is also simple and consists of dolomitization and minor silicification. Within the sulfide ore zones, structures consist of massive and vein types and textures consist of anhedral to euhedral granular and open space fillings. Pyrite has cubic form. Calcite occurs as patches in width. In vein ores, sphalerite is also fine-to coarse-grained with anhedral to euhedral. Galena fills vein and fracture. Calcite crystal is an important host mineral among the two hypogene stages. Microthermometric measurements from the Tarz deposit show that ore minerals were deposited at low-temperature (85-196°C), with moderate salinities (18–22.5 wt.% NaCl). The Tarz Zn–Pb deposit has many similarities with the most important characteristics of the Mississippi Valley-type (MVT) deposits (characteristics such as tectonic setting, faults and fractures, the epigenetic nature of mineralization, ore structureand texture, the host rocks, wall-rock alteration and homogenization temperature of fluid inclusions).

The Tarz Zn–Pb deposit is a stratabound, epigenetic hosted in Upper Permian-Lower Triassic (Rajabi et al., 2013) thick sequence of carbonate rocks (dolomitic limestone). Ore mineralogy of the Tarz deposit is relatively simple. The principal economic ore minerals are galena and sphalerite. Other minor minerals include pyrite with trace chalcopyrite. The gangue minerals are mainly dolomite, calcite and minor quartz. Textural evidence shows that the ore minerals have been mostly replaced by carbonate host rocks. Smithsonite and hydrozincite, malachite, hematite, goethite and covellite are secondary minerals that have developed from the primary hypogene Zn–(Fe–Pb) sulfides through weathering. Gossan coexists with Pb–Zn sulfide ores and is usually located in the upper levels of the sulfide ores. This ore body is strata-bound and occurs along the fault. Based on crosscutting, overgrowth and replacement relationships, the paragenetic sequence of the Tarz deposit is shown. Calcite and dolomite constitute the carbonate matrix of the ore. Microthermometric measurements were performed on the primary two-phase (L-V) (the ratio of gas to liquid is 2–20%) inclusions larger than 5 μm in diameter that are interpreted as representing the fluids present at the time of hydrothermal mineral growth. The type of inclusions in Calcite is two-phase, liquid-rich that homogenize into a liquid state upon heating. Fluid inclusion shapes are elliptical, rod-shaped, round, or irregular. Homogenization temperatures (Th) values range from 85 to 196°C. The final ice melting temperatures (Tmice) values range from -14.2 to -20.2°C. Salinities of aqueous inclusions were calculated using Bodnar’s (1993) for the NaCl–H2O system and yielded 18–22.5 wt.%NaCl.