Chromite compositional variability and associated enrichments in chromitites from the Gomati and Nea Roda ophiolite, Chalkidiki, Northern Greece
Articolo
Data di Pubblicazione:
2022
Citazione:
Chromite compositional variability and associated enrichments in chromitites from the Gomati and Nea Roda ophiolite, Chalkidiki, Northern Greece / M. Bussolesi, G. Grieco, F. Zaccarini, A. Cavallo, E. Tzamos, N. Storni. - In: MINERALIUM DEPOSITA. - ISSN 0026-4598. - 57:8(2022 Apr 06), pp. 1323-1342. [10.1007/s00126-022-01109-z]
Abstract:
The Gomati and Nea Roda ophiolites are located into the Serbo-Macedonian massif of the Chalkidiki peninsula (Northern
Greece). The present work focuses on the variability of platinum-group elements (PGEs), geochemistry, spinel mineral
chemistry, and platinum-group minerals (PGMs) — base metal minerals (BMMs) assemblage in chromitites of three Gomati
localities (St. George, Tripes, and Limonadika) and Nea Roda. The studied chromitites show variable textures and are heavily
altered. Primary silicates are almost completely replaced by chlorite, and chromite rims are altered into ferrian chromite.
The variability of spinel mineral chemistry in terms of Cr# [Cr/(Cr + Al)] and Mg# [Mg/(Mg + Fe2+)],
and the PGE contents,
argues for a genesis in a supra-subduction setting (SSZ), at different stratigraphic positions in the ophiolite section. Chromitites
from Tripes have the lowest Cr# (0.5–0.6) and the highest PGE contents (3516 ppb), similar to some chromitites formed
in small magma chambers in the cumulate sections above the Moho. The high PGE contents of Tripes chromitites are due
to an IPGEs-enriched melt derived from critical melting of mantle peridotites. Limonadika and St. George show the highest
Cr# (0.77–0.96 and 0.74–0.87, respectively) and variable PGE contents (175 ppb and 383 ppb on average respectively),
compatible with a genesis from boninitic magmas in the mantle section. Nea Roda chromitites have intermediate to high Cr#
(0.66–0.75) and low PGE contents (135 ppb on average) and show similarities to other intermediate chromitites formed from
evolving magma sources at subduction initiation. BMMs detected in both ophiolites are primary (pentlandite) and secondary
(mainly millerite and heazlewoodite) sulfides. All the detected PGMs are primary, crystallized from the melt, and entrapped
into chromite, and they are mainly laurites. In the studied chromitites, the absence of alloys indicates that the circulating fluids
during chloritization were at high fS2
and fO2,
and did not remobilize the PGEs. The same fluids are probably responsible
for the low-T crystallization of an uncommon suite of arsenides and antimonides at St. George.
Tipologia IRIS:
01 - Articolo su periodico
Keywords:
Platinum group elements; Supra-Moho; Chromitite; Greece; Ophiolites
Elenco autori:
M. Bussolesi, G. Grieco, F. Zaccarini, A. Cavallo, E. Tzamos, N. Storni
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