Nature and origin of dolomitization associated with sulphide mineralization: new insights from the Tappehsorkh Zn‐Pb (‐Ag‐Ba) deposit, Irankuh Mining District, Iran

Abstract

Several types of dolomitization are observed in the Lower Cretaceous carbonate sequence of the Tappehsorkh deposit, Irankuh Mining District, Iran: 1) regional and extensive early diagenetic dolomitization (D1), and 2) localized hydrothermal dolomitization (D2 and D3). D1 regional dolomite, which partly to completely replace limestone, is characterized by fine‐grained euhedral to subhedral dolomite rhombs. There is no evidence for Zn‐Pb sulphide mineralization associated with this type of dolomite. Medium to coarse‐grained D2 and D3 hydrothermal dolomites occur along the syn‐sedimentary Gushfil‐Baghabrisham normal fault, about 40 m above the Lower Cretaceous sequence within black siltstone, dolostone, and crystal lithic tuff and lava rocks. Hydrothermal dolomite cross‐cuts and brecciates the host rocks. This dolomite was replaced by quartz and sulphide minerals of the main ore stage. D1 regional dolomite has average values of ‐7.37‰ and 2.20‰ for δ18O and δ13C, respectively. The δ13C values of this dolomite fall well within the range of the Lower Cretaceous carbonates. D2 hydrothermal dolomite has average δ18O and δ13C values of ‐7.92‰ and 2.93‰, respectively. The respective δ18O and δ13C values of D3 hydrothermal dolomite are ‐12.27‰ and 2.39‰. The δ18O values of D2 and D3 dolomites are more negative than those of D1 regional dolomite; this can be due to their hydrothermal origin. Fluid inclusion studies on D3 dolomite and quartz show temperatures of 170‐260 °C. The concentrations of Fe and Mn in D1 regional dolomite are very similar to those of limestone, suggesting that they likely precipitated from the same fluid (seawater), whereas those of D2 and D3 dolomites are relatively high, in agreement with the hydrothermal origin for these dolomites. Precipitation of gypsum, which is ubiquitous in the study area, could have lowered the Ca/Mg ratio of seawater. While the extensive regional dolomitization formed from low‐temperature (evolved) seawater during the early diagenesis, D2 and D3 dolomites associated with the main stage of sulphide mineralization were formed by high‐temperature hydrothermal fluids moving along the Gushfil‐Baghabrisham Fault. Copyright © 2016 John Wiley & Sons, Ltd.

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

“…However, dolomitization is common in these deposits, but silicification is the major hydrothermal alteration at the Emarat (Ehya et al, 2010), Lakan, Robat, Kuhkolangeh (Peernajmodin et al, 2018;Niroomand et al, 2019), Khanabad and Eastern Haft-Savaran deposits (Mahmoodi, 2018;Rajabi et al, 2019a). Fe-rich dolomite is also a frequently observed alteration in these deposits (Boveiri et al, 2018;Mahmoodi et al, 2019).…”

“…Detailed tectonic studies and measurement of kinematic indicators in Tiran and Irankuh mining districts and also in Kouhkolangeh, Shamsabad, and Ab-Bagh II deposits suggest that the formation of these deposits are related to syn-sedimentary normal faults of the early Cretaceous (Yarmohammadi et al, 2016;Boveiri et al, 2017;Peernajmodin, 2018;Movahednia et al, 2020), some of which were subsequently reactivated as reverse faults after the late Cretaceous tectonic event (Nakini, 2013;Boveiri, 2016). Yarmohammadi (2015) reported some igneous components, sedimentary breccias, and debris flows adjacent to the normal fault at the Vejin-Paein deposit (Fig.…”

“…The origin of the Cretaceous Zn-Pb (±Ag±Ba) deposits in Iran has been the subject of lively and prolonged discussion since their discovery, and despite a number of studies (e.g., Momenzadeh, 1976;Rastad, 1981;Ghazban et al, 1994;Ehya et al, 2010;Rajabi et al, 2012a;Yarmohammadi et al, 2016;Boveiri et al, 2017Boveiri et al, , 2018Karimpour & Sadeghi, 2018;Karimpour et al, 2017;Rajabi et al, 2019a;Rajabi, 2022), there is still considerable uncertainty regarding their genesis. Based on geologic studies, Momenzadeh (1976) suggested a syngenetic and sedimentary exhalative (SedEx) model for the origin of these deposits.…”

Combination of Machine Learning Algorithms with Concentration-Area Fractal Method for Soil Geochemical Anomaly Detection in Sediment-Hosted Irankuh Pb-Zn Deposit, Central Iran

“…One of the essential features in the IMD is the WNW-ESE trending Gushfil-Baghabrisham fault, which was common in the Lower Cretaceous (contemporaneous with the formation of a back-arc basin and sulfide deposition) but changed to reverse fault due to inversion tectonic of Late Cretaceous compression tectonism [61]. Based on [62][63][64], this fault is the main conduit controlling the movement of ore-bearing fluids that deposited economic stratiform and stratabound sulfide minerals in the proximal host rocks.…”

“…Based on the geology, tectonic setting, mineralogy, ore texture, geochemical, and isotopic analytical results, the IMD and included ore deposits have been classified as sub-seafloor diagenetic replacement SEDEX-type deposits [62][63][64]. Karimpour and Sadeghi [65,66], based on the deposition of sulfide minerals within or close to dolostone and shale-siltstone units and replacement and open space filling textures of ore minerals, suggested this deposit occurred as an MVT-type deposit.…”