An introduction to Irish-type Zn-Pb deposits in early Cretaceous carbonate rocks of Iran

Abstract

Early Cretaceous carbonates are the most common host rocks for Irish-type deposits in Iran. They are largely concentrated in the Malayer-Esfahan metallogenic belt (MEMB) in southwestern Iran, and Yazd-Anarak metallogenic belt in Central Iran. They include some world‐class ore deposits such as Mehdiabad, Irankuh, and Ahangaran. These stratabound deposits are hosted mostly in carbonates with minor siltstones and volcanic components, that formed in extensional and passive margin environments that are related to the Nain-Baft back-arc basin. The deposits are stratabound and comprise wedge-shaped to tabular sulphide-barite orebodies and occur in several different stratigraphic horizons. Dolomitization and silicification are the main wall-rock alteration styles. Replacement textures are common, and orebodies represent complex textures of sulphides and barite, such as brecciated, colloform, zebra, minor laminated, and banded replacement. Barite is an important gangue mineral in the MEMB and YAMB deposits, partly replaced by coarse-grained galena, sphalerite, and chalcopyrite. Sulphides from these Irish-type deposits have a wide spread of light δ34S values (with the majority falling between -25 to +5‰) with mostly bacterial sulphate reduction (BSR) origin. Fluid inclusion studies show that homogenization temperatures of ore minerals are typically 120 to about 280°C (majority 225-275°C), and salinities range from 2 to 24 wt.% NaCl eq, with the majority falling between 8 and 22 wt% NaCl eq. Using the criteria outlined in this study, early Cretaceous extensional sedimentary basins (e.g., Nain-Baft) are highlighted as target areas for exploration of world-class Irish-type ore deposits and correspond well with the periods of expulsions of Cretaceous CaCl2-rich brines.

The Ballynoe Stratiform Barite Deposit, Silvermines, County Tipperary, Ireland

“…Elsewhere in Europe bedded barite is associated with sediment-hosted Pb-Zn deposits in Germany (Meggen and Rammelsberg), Belgium (Chaudfontaine). The Cretaceous agreed Zn-Pb (±Ag±Ba) deposits in the Malayer-Esfahan Metallogenic belt of Iran have been described as Irish-type and have many features in common with Ballynoe (Silvermines) [61][62][63].…”

Carbonate-hosted Zn-Pb-Cu-Ba (-Ag) mineralization in the Mehdiabad deposit, Iran: new insights, new discoveries

“…More than 350 sediment-hosted Zn-Pb±Ag±Ba deposits have been reported in Iran (Rajabi et al, 2012a(Rajabi et al, , 2019aRajabi, 2022) occuring in a wide variety of siliciclastic and carbonate rocks from early Cambrian to Tertiary age (Fig. 1A).…”

“…Rajabi et al (2012a) suggested an Irish-type model for forming the Mehdiabad deposit. Based on geochemistry and geological evidence, Maghfouri et al (2019) suggested the sedimentary exhalative (Aghanabati, 1998) and distribution map of carbonate-hosted (MVT and Irish-type) Zn-Pb and F-rich deposits according to the age of host rocks in the Central Alborz, Tabas-Posht e Badam, Malayer-Esfahan, and Yazd-Anarak metallogenic belts (Rajabi et al, 2012a;2019a;2022). B) Simplified terrane map of the western Tethysides, and crustal domains of Iran (Rajabi et al, 2019a).…”