Mineralogy and Geochemistry of Ultramafic Rocks from Rachoni Magnesite Mine, Gerakini (Chalkidiki, Northern Greece)

Abstract

The importance of magnesite for the EU economy and industry is very high, making the understanding of their genesis for the exploration for new deposits a priority for the raw materials scientific community. In this direction, the study of the magnesite-hosting ultramafic rocks can be proved very useful. For the present study, ultramafic rock samples were collected from the magnesite ore-hosting ophiolite of the Gerakini mining area (Chalkidiki, Greece) to investigate the consecutive alteration events of the rocks which led to the metallogenesis of the significant magnesite ores of the area. All samples were subjected to a series of analytical methods for the determination of their mineralogical and geochemical characteristics: optical microscopy, XRD, SEM, EMPA, ICP–MS/OES and CIPW normalization. The results of these analyses revealed that the ultramafic rocks of the area have not only all been subjected to serpentinization, but these rocks have also undergone carbonation, silification and clay alteration. The latter events are attributed to the circulation of CO2-rich fluids responsible for the formation of the magnesite ores and locally, the further alteration of the serpentinites into listvenites. The current mineralogy of these rocks was found to be linked to one or more alteration event that took place, thus a significant contribution to the metallo- and petrogenetic history of the Gerakini ophiolite has been made. Furthermore, for the first time in literature, Fe inclusions in olivines from Greece were reported.

The Formation of Magnesite Ores by Reactivation of Dunite Channels as a Key to Their Spatial Association to Chromite Ores in Ophiolites: An Example from Northern Evia, Greece

“…Kymasi primary temperatures are consistent with other chromitite temperatures in ophiolite environments, such as Vourinos (Greece) [27,28], Iballe (Albania) [38,42], Kluchevskoy (Russia) [46], and Luobusa (China) [47]. [30,31], Vourinos high-Cr chromitites [28], Vourinos disseminated spinels in dunite [27] Gerakini disseminated spinels in dunite [11]; (b) Cr# vs. Mg# of chromite cores. Compositional fields are from [35,38]; (c) Cr# vs. TiO2 (wt%) of chromite cores.…”

“…High-Cr chromitites are similar to other ophiolite chromite ores within ultramafic rocks in Greece, such as Vourinos [27][28][29] and partially Gomati [30,31], while they are quite different from chromitites from the Othris ophiolite [32] (Figure 9a). Disseminated spinels within peridotites at Kymasi are similar to spinels within Vourinos peridotites [27] and Gerakini serpentinites and harzburgites [11].…”

“…Greece hosts exploitable ophiolite-related magnesite deposits in two areas: the Evia Island and the Chalkidiki peninsula [10,11]. The ore in Northern Evia consists of a shallow (200 m) stockwork of fracture-filling magnesite veins [12], hosted within peridotites (harzburgites and lherzolites) with various degrees of serpentinization.…”

“…(a) Cr 2 O 3 vs. MgO (wt%) of chromite cores. Compositional fields: Gomati high-Cr chromitites[30,31], Vourinos high-Cr chromitites[28], Vourinos disseminated spinels in dunite[27] Gerakini disseminated spinels in dunite[11]; (b) Cr# vs. Mg# of chromite cores. Compositional fields are from[35,38]; (c) Cr# vs. TiO 2 (wt%) of chromite cores.…”

Gemological Characterization of Peridot from Pyaung-Gaung in Mogok, Myanmar

“…The presence of serpentine is commonly referred to as a hydration reaction (serpentinization) that occurred when olivine was infiltrated by aqueous fluids, while talc and magnesite were produced through a carbonation reaction when carbon dioxide (CO 2 ) was present (Kelemen and Hirth, 2012;Lafay et al, 2018). The combined hydration and carbonation processes could be an indication of retrograde alteration in these Mogok peridot as the result of tectonic movements (Jan and Khan, 1996;Kelemen and Hirth, 2012;Bouilhol et al, 2015;Tzamos et al, 2020).…”