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Chemical composition and evolution of the garnets in the Astamal Fe-LREE distal skarn deposit, Qara-Dagh-Sabalan metallogenic belt, Lesser Caucasus, NW Iran

Citation

Baghban, S and Hosseinzadeh, MR and Moayyed, M and Mokhtari, MAA and Gregory, DD and Mahmoudi Nia, H, Chemical composition and evolution of the garnets in the Astamal Fe-LREE distal skarn deposit, Qara-Dagh-Sabalan metallogenic belt, Lesser Caucasus, NW Iran, Ore Geology Reviews, 78 pp. 166-175. ISSN 0169-1368 (2016) [Refereed Article]

Copyright Statement

Copyright 2016 Elsevier B.V.

DOI: doi:10.1016/j.oregeorev.2016.02.020

Abstract

The chemistry of garnet can provide clues to the formation of skarn deposits. The chemical analyses of garnets from the Astamal Fe-LREE distal skarn deposit were completed using an electron probe micro-analyzer. The three types of garnet were identified in the Astamal skarn are: (I) euhedral coarse-grained isotropic garnets (10–30 mm across), which are strongly altered to epidote, calcite and quartz in their rim and core, with intense pervasive retrograde alteration and little variation in the overall composition (Adr94.3–84.4 Grs8.5–2.7 Alm1.9–0.2) (garnet I); (II) anhedral to subhedral brecciated isotropic garnets (5–10 mm across) with minor alteration, a narrow compositional range along the growth lines (Adr82–65.4 Grs21.9–11.7 Alm11.1–2.4) and relatively high Cu (up to 1997 ppm) and Ni (up to 1283 ppm) (garnet II); and (III) subhedral coarser grained garnets (> 30 mm across) with moderate alteration, weak diffusion and irregular zoning of discrete grossular-almandine-rich domains (Adr84.2–48.8 Grs32.4–7.6 Alm19.9–3.5) (garnet III). In the third type, the almandine content increases with increasing grossular/andradite ratio and increasing substitutions of Al for Fe3 +.

Almost all three garnet types have been replaced by fine-grained, dark-brown allanite that is typically disseminated and has the same relief as andradite. The Cu content increases while Ni content decreases slightly towards the rim of garnet II and garnet III. Copper in garnet II is positively correlated with increasing almandine content and decreasing andradite content, indicating that the almandine structure, containing relatively more Fe2 +, is more suitable than andradite and grossular to host divalent cations such as Cu2 +. Nickel in garnet II is positively correlated with increasing andradite content, total Fe, and decreasing almandine content. This is because Ni2 + substitutes for Fe3 + in the Y (octahedral) position. There are unusual discrete grossular-almandine rich domains within andraditic garnet III, indicating the low diffusivity of Ca compared to Fe at high temperatures.

Item Details

Item Type:Refereed Article
Keywords:NW Iran, Astamal, Distal skarn, Garnet, Chemical zoning, Discrete grossular-almandine-rich domains, Mineral chemistry
Research Division:Earth Sciences
Research Group:Geology
Research Field:Mineralogy and Crystallography
Objective Division:Expanding Knowledge
Objective Group:Expanding Knowledge
Objective Field:Expanding Knowledge in the Earth Sciences
Author:Gregory, DD (Dr Daniel Gregory)
ID Code:115052
Year Published:2016
Web of Science® Times Cited:1
Deposited By:CODES ARC
Deposited On:2017-03-06
Last Modified:2017-09-11
Downloads:0

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