The Halab deposit, SW Zanjan: Volcanogenic massive sulfide Zn–Pb (Ag) mineralization, Takab–Takht-e-Soleyman–Angouran metallogenic district

The Halab Zn–Pb (Ag) deposit, 125-km southwest of Zanjan, is located in the Takab–Takht-e-Soleyman–Angouran metallogenic district (TTAMD), Sanandaj-Sirjan zone. Several types of deposits are present in the TTAMD, including nonsulfide Zn–Pb deposits, sediment-hosted epithermal gold deposits, epithermal precious and base metal deposits, skarn and volcano-sedimentary iron deposits, and massive sulfide Pb-Zn (Ag) deposits. The most important deposits discovered to date within the TTAMD are the Angouran nonsulfide Zn–Pb deposit (Gilg et al., 2006; Boni et al., 2007; Daliran et al., 2013), Zarshuran sediment-hosted epithermal gold deposit (Mehrabi et al., 1999; Asadi et al., 2000; Daliran et al., 2002), and Agdar’reh epithermal gold deposit (Daliran, 2008). Other important deposits or occurrences include Touzlar, Ay Qalasi, Arabshah, Qozlou, Shahrak, Goorgoor, Mianaj, and Halab (Heidari et al., 2015; Mohammadi Niaei et al., 2015; Najafzadeh et al., 2017; Nafisi et al., 2019).To date, no detailed study has been reported to understand the characteristics of Zn–Pb (Ag) mineralization at the Halab deposit. This paper presents the geologic framework, mineralization characteristics, and lithogeochemical signatures of the Halab deposit with emphasis on ore genesis. Identification of these characteristics can serve as a model for exploration of Zn–Pb (Ag) mineralization in the Halab area and other parts of the TTAMD.

Detailed field work was carried out in the Halab deposit. Sixteen polished-thin and thin sections from host rocks and ore horizon were studied by conventional petrographic and mineralogic methods at the University of Zanjan. In addition, a total of 10 samples from barren host rocks and ore horizon at the Halab deposit were analyzed by ICP–MS for trace elements and REE compositions at Zarazma Co., Tehran, Iran.

The host rocks in the Halab area consist of Precambrian deformed metamorphic rocks (equal to the Kahar Formation) that are unconformably overlain by dolomitic marble of the Jangoutaran unit. The metamorphic sequence is composed of pelitic (garnet mica schist, biotite muscovite schist, calcite biotite schist), mafic (biotite amphibole schist and actinolite schist), and felsic (quartz schist) schists intercalated with marble, and quartzite. These rocks are metamorphosed in green schist to amphibolite facies.Mineralization in the Halab deposit occurs as NE-trending foliation-parallel Zn‒Pb (Ag) stratiform horizon hosted by quartz schist units. The ore horizon reaches up to 300 m in length and 3 to 5 m in width, and it is generally 75° SE dipping. Chloritization and silicification of the host rocks are close to the ore horizon, while the sericitic alteration is envelope of the chloritization and silicification. Sphalerite, galena, pyrite and chalcopyrite are the main sulfide minerals in the Halab deposit based on mineralography. Smithsonite, cerussite, chalcocite, covellite and goethite have formed as supergene minerals. Quartz, calcite, chlorite and epidote also present as gangue minerals. The ore minerals show laminated, disseminated, massive, brecciated, replacement and vein-veinlet textures. Chondrite-nonmineralized REE pattern of barren quartz schist host rocks and mineralized samples indicate that mineralized samples are enriched in REE.The main characteristics of the Halab deposit reveal that Zn‒Pb (Ag) mineralization at Halab is comparable with laminated and disseminated parts of Bathurst types of massive sulfide deposits.