| Titre | Genetic model for Jurassic shale-hosted Zn-Pb deposits of the Arak Mining District, Malayer-Esfahan metallogenic belt: insight from sedimentological, textural, and stable isotope characteristics |
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| Auteur | Mahmoodi, P ;
Rastad, E; Rajabi, A; Alfonso, P; Canet, C; Peter, J M |
| Source | Ore Geology Reviews vol. 136, 104262, 2021 p. 1-24, https://doi.org/10.1016/j.oregeorev.2021.104262  Accès ouvert |
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| Année | 2021 |
| Séries alt. | Ressources naturelles Canada, Contribution externe 20210102 |
| Éditeur | Elsevier |
| Document | publication en série |
| Lang. | anglais |
| DOI | https://doi.org/10.1016/j.oregeorev.2021.104262 |
| Media | papier; en ligne; numérique |
| Formats | pdf; html |
| Lat/Long OENS | 49.3661 50.1014 34.0281 33.4514 |
| Sujets | modèles; gisements minéraux; gîtes sédimentaires; gîtes sulfureux; zinc; plomb; minéralisation; genèse des minerais; faciès; système hydrothermal; paléoenvironnement; roches hôtes; géologie du substratum
rocheux; lithologie; roches sédimentaires; schistes; analyses de textures; études des isotopes stables; géologie économique; sédimentologie; géochimie; Sciences et technologie; Nature et environnement; Phanérozoïque; Mésozoïque; Jurassique |
| Illustrations | cartes de localisation; diagrammes; photomicrographies; graphiques; tableaux; représentations graphiques combinées; coupes transversales |
| Programme | Initiative géoscientifique ciblée (IGC-5) Systèmes volcaniques et sédimentaires - systèmes minéralisés de sulfure massif volcanogénique |
| Diffusé | 2021 05 30 |
| Résumé | (disponible en anglais seulement)
The genetic model, including conditions under which mineralization formed, and relative timing of mineralization are critical questions for SEDEX deposits.
There is increasing awareness that sub-seafloor replacement is an important process in the formation of some SEDEX deposits. We have studied the Hossein-Abad and Western Haft-Savaran Zn-Pb SEDEX deposits are located in the Arak basin of the
Malayer-Esfahan Metallogenic Belt, Iran to address these questions of genesis. This metallotect formed in a back-arc paleotectonic setting as a result of the subduction of the Neo-Tethys oceanic plate beneath the Sanandaj-Sirjan Zone. The rocks that
host the mineralization are Jurassic organic matter-bearing, fine-grained sandstones, siltstones and shales. Asymmetric lenticular bedding, unidirectional flow (based on oblique silt lamination direction relative to horizontal bedding), graded
bedding and clay-rich interbeds indicate sediments were deposited from turbidity currents in a low-energy basin environment. There are three ore facies in the Hossein-Abad and Western Haft-Savaran Zn-Pb deposits: 1) bedded ore; 2) massive ore; 3)
feeder zone. Bedded ore contains pyrite framboids and polyframboidal clusters. The size range of the pyrite framboids (3 to 6 µm in diameter) indicates they formed in the water column and not in the subsurface. Characteristic structures in bedded ore
are: 1) sulfide-bearing silt injections into clay-filled burrows 2) injection of sulfide-bearing silt into flame structures of claystone laminae, and 3) organic matter in claystone oriented oblique relative to bedding. These structures are the result
of seismic deformation induced by synsedimentary earthquakes, whereby sulfides that formed in permeable unconsolidated sediment were injected into the organic matter-bearing claystone unit. The d18O and d13C values of siderite, calcite and dolomite
in veins from the feeder zone and massive ore range from 12.2 to 23.8 and -16.7 to 1.7 #0, respectively. These values indicate that formational water, seawater and organic matter oxidation-decomposition all played a role in hydrothermal carbonate
formation. Melting and homogenization temperatures for CO2 for CO2-bearing fluid inclusions range from -57.5 to -60 °C and 6.6 to 29.5 °C, respectively, and indicate the presence of <15 mol percent CH4. The CO2 homogenization temperature range
suggests the CO2-rich phase is a CO2-CH4 mixture. The CH4 and CO2 in the H2S-bearing fluid were likely generated by biodegradation and oxidation of organic matter via BSR and methanogenesis. The sulfur isotope compositions of pyrite, galena,
sphalerite and chalcopyrite from the feeder zone and the massive ores range from d34S -4.3 to +7.2 and display equilibrium fractionations, indicating that the sulfur originated from two processes: (a) bacterial reduction of seawater sulfate (BSR)
(distal from mineralization site), and (b) thermochemical reduction of seawater sulfate (TSR) (in both massive ore and feeder zone). Sulfur isotope geothermometric calculations ([galena-sphalerite) for two samples give temperatures in the range
209-224°C for the massive ore facies. Such high temperatures negate a contribution of sulfur from BSR. However, BSR likely occurred in sediments distal to the feeder zone, where seawater sulfate was bacterially reduced to H2S, and this H2S migrated
to the mineralization site during diagenesis. Collectively, the stable isotope data indicate mineralization formed in response to mixing occurred between ascending hot metalliferous hydrothermal fluid that rose up the fault and fracture network, with
H2S-bearing fluid and sulfate-bearing percolating seawater, triggering sulfide deposition. |
| Sommaire | (Résumé en langage clair et simple, non publié)
Cet article traite des contrôles génétiques sur la minéralisation de Pb-Zn hébergée dans les roches sédimentaires d'un important district minier
d'Iran. Les conclusions selon lesquelles la minéralisation s'est formée à l'intérieur et autour des failles qui ont amené des fluides au fond marin ont des implications d'exploration ailleurs, y compris au Canada. |
| GEOSCAN ID | 328367 |
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