The early Cambrian Chahmir shale-hosted Zn-Pb deposit, Central Iran: an example of vent-proximal SEDEX mineralization

• Published in: Mineralium Deposita
• Main Authors: Rajabi, Abdorrahman, Rastad, Ebrahim, Canet Miquel, Carles, Alfonso Abella, María Pura
• Other Authors: Universitat Politècnica de Catalunya. Departament d'Enginyeria Minera, Industrial i TIC, Universitat Politècnica de Catalunya. GREMS - Grup de Recerca en Mineria Sostenible
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2015
• Subjects: Àrees temàtiques de la UPC::Enginyeria civil::Geologia::Mineralogia; Mineralogy > Iran; Hydrothermal vents; Sulfur > Isotopes; Sulfate reduction; Posht-e-Badam Block; Sulfur isotopes; Fluid inclusions; Pyrite framboids; Sedex; Western brooks range; Fluid inclusion; Mcarthur basin; Stable-isotope; Marine sulfate; Ag deposits; Australia; Pyrite; Mineralogia > Iran; McArthur; Selwyn; Brooks Range
• Online Access: http://hdl.handle.net/2117/181148; https://doi.org/10.1007/s00126-014-0556-x

This is a post-peer-review, pre-copyedit version of an article published in Mineralium deposita. The final authenticated version is available online at: http://dx.doi.org/10.1007/s00126-014-0556-x. The Chahmir zinc-lead deposit (1.5 Mt @ 6 % Zn + 2 % Pb) in Central Iran is one among several sedimentary-exhalative Zn-Pb deposits in the Early Cambrian Zarigan-Chahmir basin (e.g., Koushk, Darreh-Dehu, and Zarigan). The deposit is hosted by carbonaceous, fine-grained black siltstones, and shales interlayered with volcaniclastic sandstone beds. It corresponds to the upper part of the Early Cambrian volcano-sedimentary sequence (ECVSS), which was deposited on the Posht-e-Badam Block during back-arc rifting of the continental margin of Central Iran. Based on crosscutting relationships, mineralogy, and texture of sulfide mineralization, four different facies can be distinguished: stockwork (feeder zone), massive ore, bedded ore, and distal facies (exhalites with barite). Silicification, carbonatization, sericitization, and chloritization are the main wall-rock alteration styles; alteration intensity increases toward the proximal feeder zone. Fluid inclusion microthermometry was carried out on quartz associated with sulfides of the massive ore. Homogenization temperatures are in the range of 170-226 A degrees C, and salinity is around 9 wt% NaCl eq. The size distribution of pyrite framboids of the bedded ore facies suggests anoxic to locally suboxic event for the host basin. delta S-34((V-CDT)) values of pyrite, sphalerite, and galena range from +10.9 to +29.8 aEuro degrees. The highest delta S-34 values correspond to the bedded ore (+28.6 to +29.8 aEuro degrees), and the lowest to the massive ore (+10.9 to +14.7 aEuro degrees) and the feeder zone (+11.3 and +12.1 aEuro degrees). The overall range of delta S-34 is consistent with a sedimentary environment where sulfide sulfur was derived from two sources. One of them was corresponding to early ore-stage sulfides in bedded ore and distal facies, consistent with bacterial reduction from coeval seawater sulfate in a closed or semiclosed basin. However, the delta S-34 values of late ore-stage sulfides, observed mainly in massive ore, interpreted as a hydrothermal sulfur component, leached from the lower part of the ECVSS. Sulfur isotopes, along with the sedimentological, textural, mineralogical, fluid inclusion, and geochemical characteristics of the Chahmir deposit are in agreement with a vent-proximal (Selwyn type) SEDEX ore deposit model. Peer Reviewed Postprint (author's final draft)