Intermediate sulfidation type base metal mineralization at Aliabad-Khanchy, Tarom-Hashtjin metallogenic belt, NW Iran

Abstract

The Aliabad-Khanchy epithermal base metal deposit is located in the Tarom-Hashtjin metallogenic belt (THMB) of northwest Iran. The mineralization occurs as Cu-bearing brecciated quartz veins hosted by Eocene volcanic and volcaniclastic rocks of the Karaj Formation. Ore formation can be divided into five stages, with most ore minerals, such as pyrite and chalcopyrite being formed in the early stages. The main wall-rock alteration is silicification, and chlorite, argillic and propylitic alteration. Microthermometric measurements of fluid inclusion assemblages show that the ore-forming fluids have eutectic temperatures between −30° and −52°C, trapping temperatures of 150° to 290°C, and salinities of 6.6 to 12.4 wt.% NaCl equiv. These data demonstrate that the ore-forming fluids were medium-to high-temperature, medium-to low-salinity, and low-density H 2 O-NaCl-CaCl 2 fluids. Calculated δ 18 O values indicate that ore-forming hydrothermal fluids had δ 18 O water ranging from +3.6 to +0.8‰, confirming that the ore-fluid system evolved from dominantly magmatic to dominantly meteoric. The calculated 34 S H2S values range from-8.1 to-5.0‰, consistent with derivation of the sulfur from either magma or possibly from local volcanic wallrock. Combined, the fluid inclusion and stable isotope data indicate that the Aliabad-Khanchy deposit formed from magmatic-hydrothermal fluids. After rising to a depth of between 790 and 500 m, the fluid boiled and subsequent hydraulic fracturing may have led to inflow and/or mixing of early magmatic fluids with circulating groundwater causing deposition of base metals due to dilution and/or cooling. The Aliabad-Khanchy deposit is interpreted as an intermediate-sulfidation style of epithermal mineralization. 2 Our data suggest that the mineralization at Aliabad-Khanchy and other epithermal deposits of the THMB formed by hydrothermal activity related to shallow late Eocene magmatism. The altered Eocene volcanic and volcaniclastic rocks, especially at the intersection of subvolcanic stocks with faults were the most favorable sites for epithermal ore bodies in the THMB.

Fluid inclusion, zircon U-Pb geochronology, and O-S isotopic constraints on the origin and evolution of ore-forming fluids of the tashvir and varmazyar epithermal base metal deposits, NW Iran

“…The geological investigations revealed that almost all the epithermal deposits in the THMB clustered around the late Eocene (~40-36 Ma, Nabatian et al, 2014;Nabatian et al, 2016;Aghazadeh et al, 2015;Kouhestani, 2018;Mokhtari et al, 2022a) granitoid intrusions (Figure 1). There is now a broad consensus that these deposits resulted from shallow magmatichydrothermal processes related to the late Eocene magmatism (e.g., Ghasemi Siani et al, 2015;Mehrabi et al, 2016;Kouhestani et al, 2018a;b, 2020. Mehrabi et al (2016) reported a biotite Ar-Ar age of 41.87 ± 0.16 Ma for the crystallization of the Goljin granite intrusion, which was considered closely related to the Au mineralization of the Gulojeh deposit.…”

“…A similar scenario has been documented for several epithermal deposits within the THMB, including Aliabad-Khanchy, Zajkan, Marshoun, Abbasabad, Rashtabad, Jalilabad, Aqkand, and Lubin-Zardeh. These deposits have δ 18 O water values ranging from +9.6‰ to -3.4‰ (Kouhestani et al, 2018a;b, 2020Zamanian et al, 2019), suggesting that their oreforming fluids were most likely magmatic-derived in the early stages, but were mixed with meteoric water in the late stages. It is consistent with the geological characteristics of these deposits that are indicative of an IS epithermal origin for these deposits.…”

“…As a part of the AHOB, the THMB was formed associated with Cenozoic closures of the Neo-Tethyan oceanic branches, i.e., Khoy-Zanjan ocean, and related microcontinental collisions (e.g., Azizi and Jahangiri, 2008;Asiabanha and Foden, 2012;Castro et al, 2013). The THMB is one of the most significant metallogenic belts in northwestern Iran and hosts many epithermal precious and base metal deposits and occurrences, such as Nikoueieh, Marshoun, Zajkan, Zehabad, Khalyfehlou, Chargar, Abbasabad, Chodarchay, Tashvir, Aliabad-Khanchy, Lubin-Zardeh, Aqkand, Jalilabad, Gulojeh, Varmazyar, Chomalou, and Shah Ali Beiglou (Figure 1B; Esmaeli et al, 2015;Mehrabi et al, 2016;Kouhestani et al, 2017;2018a;b, 2020Yasami et al, 2017Yasami et al, , 2018Mikaeili et al, 2018;Yasami and Ghaderi, 2019;, 2021Shahbazi et al, 2019;Zamanian et al, 2019;Ghasemi Siani et al, 2022). These deposits are mostly hosted by Eocene volcanic-volcaniclastic rocks of the Karaj Formation and generally cluster around the late Eocene granitoid intrusions which are thought to be genetically related (Ghasemi Siani et al, 2015;Mehrabi et al, 2016;Kouhestani et al, 2018a).…”

“…The THMB is one of the most significant metallogenic belts in northwestern Iran and hosts many epithermal precious and base metal deposits and occurrences, such as Nikoueieh, Marshoun, Zajkan, Zehabad, Khalyfehlou, Chargar, Abbasabad, Chodarchay, Tashvir, Aliabad-Khanchy, Lubin-Zardeh, Aqkand, Jalilabad, Gulojeh, Varmazyar, Chomalou, and Shah Ali Beiglou (Figure 1B; Esmaeli et al, 2015;Mehrabi et al, 2016;Kouhestani et al, 2017;2018a;b, 2020Yasami et al, 2017Yasami et al, , 2018Mikaeili et al, 2018;Yasami and Ghaderi, 2019;, 2021Shahbazi et al, 2019;Zamanian et al, 2019;Ghasemi Siani et al, 2022). These deposits are mostly hosted by Eocene volcanic-volcaniclastic rocks of the Karaj Formation and generally cluster around the late Eocene granitoid intrusions which are thought to be genetically related (Ghasemi Siani et al, 2015;Mehrabi et al, 2016;Kouhestani et al, 2018a). On the basis of the sulfidation states, epithermal precious and base metal deposits in the THMB belong to three subtypes: 1) HS (i.e., Chodarchay and north Gulojeh deposits), 2) IS (i.e., Abbasabad, Zehabad, Zajkan, Marshoun, Lubin-Zardeh, Aliabad-Khanchy, south Gulojeh, Jalilabad, Aqkand, Chomalou, and Shah Ali Beiglou deposits), and 3) LS (i.e., Nikoueieh, Khalyfehlou, and Chargar deposits).…”

Geochemical constraints on the origin and tectonic setting of Chargar intrusions in the Alborz orogenic belt, NW Iran

“…The Tarom intrusions range in composition from quartz monzo-gabbro to diorite, quartz monzodiorite, monzonite, quartz monzonite, monzogranite, granodiorite, alkali granite, granite and syeno-granite (e.g., Nabatian et al 2014Nabatian et al , 2016Esmaeli et al 2015;Mehrabi et al 2016;Kouhestani et al 2017Kouhestani et al , 2018Yasami et al 2018). These I-type intrusions have high-K calc-alkaline to shoshonitic affinity and metaluminous characteristics (Irannezhadi et al 2007;Azizi et al 2009;Nabatian et al 2014Nabatian et al , 2016Yasami et al 2018) and show enrichment in Large Ion Lithophile Elements (LILE) and Light Rare Earth Elements (LREE) and negative anomalies in High Field Strength Elements (HFSE) and depletion in Heavy Rare Earth Elements (HREE) (Nabatian et al 2014(Nabatian et al , 2016Yasami et al 2018).…”