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Article Dans Une Revue Ore Geology Reviews Année : 2015

Geology, timing, and genesis of the high sulfidation Au (–Cu) deposit of Touzlar, NW Iran

Résumé

The Touzlar Au (–Cu) deposit in northwestern Iran is hosted by pyroclastics and lavas of andesitic to trachytic composition and by the coeval microdiorite stocks. The EW to NW trending host volcano-plutonic complex is part of the Cenozoic Urumieh–Dokhtar Magmatic Arc (UDMA) of the Zagros orogenic belt, a stratovolcano formed within the shallow marine environment of the Oligo-Miocene Red Beds of northwestern Iran that overlay a metamorphic core complex in an extensional regime. The zircon U–Pb ages of the host volcanic and subvolcanic rocks are 18.1 ± 1.0 to 19.3 ± 0.3 Ma. The deposit with an estimated reserve of 1.5 Mt of ore @ 2.2 g/t gold and 0.3% Cu consists of a number of sub-parallel, massive silicified zones and breccia quartz veins within a hydrothermal alteration zone that follows the E-W trending extensional structures. The hydrothermal alteration assemblages consist of extensive propylitic and argillic alteration, advanced argillic alteration, silicification and sulfidation in the core zone, and of phyllic alteration. The multi-stage mineralization consists of disseminations, veins–veinlets and open space fillings. Advanced argillic alteration and silicification associated with different degrees of Cu-rich sulfidation occurred in phases (A) and (B). Phase (C) is characterized by hydrothermal brecciation and precipitation of sulfides in open spaces that was followed by the precipitation of barite in phase (D). Gold is found as free grains associated with quartz (phase B) and as overgrowth on pyrite grains in phase (C). Supergene Fe-oxyhydroxides formed with minor amounts of azurite and malachite, as well as gypsum, and is associated with enrichment in mineable gold grades of up to 5 ppm. Homogenization temperatures of the (LV) fluid inclusion from the mineralized quartz veins range from 211 to 310 °C and salinities from 0.3 to 8 wt.% NaCl equiv. These fluid inclusions coexist with low-density, CO2-bearing fluid inclusions suggesting low-pressures, dilation associated with the precipitation of gold at these lower temperatures. Isotope compositions of quartz and barite are similar and vary within a short range of δ18OH2O 5.58 to 8.95‰ and 6.8 to 8.77‰ respectively suggesting that the ore fluids formed from mixing of magmatic fluids with meteoric waters. Calculated δ34SH2S composition (− 2.68 to 15.59‰) of the sulfides indicate an igneous source for the sulfur that highly exchanged with a sedimentary source. The Touzlar deposit shows characteristic alteration assemblages and ore minerals of high sulfidation deposits. It has been formed in relation with the lower Miocene, high-level magmatic–hydrothermal activity within an extensional regime at the last stages of the UDMA activity of northwestern Iran.

Dates et versions

hal-01172208 , version 1 (07-07-2015)

Identifiants

Citer

Seyed Mehran Heidari, Farahnaz Daliran, Jean-Louis Paquette, Dominique Gasquet. Geology, timing, and genesis of the high sulfidation Au (–Cu) deposit of Touzlar, NW Iran. Ore Geology Reviews, 2015, 65, pp.460-486. ⟨10.1016/j.oregeorev.2014.05.013⟩. ⟨hal-01172208⟩
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