The phlogopite peridotite unit of the Finero Complex is a restitic harzburgite that records two metasomatic events. The first event is related to the intrusion of basaltic magma, which reacted with the pyroxene of the host harzburgite to produce chromitite pods with dunite haloes. It also produced secondary clinopyroxene and amphibole in the harzburgite and enriched harzburgite in Na and the light rare earth elements. The second metasomatic event is related to the later intrusion of clinopyroxenitic dykes. During this event, water-rich vapour penetrated the harzburgite along fractures and reacted with it to form phlogopite, thus enriching the rock in K. Chromitites host zircons that yield an age for the first metasomatic event of 207·9 + 1·7/−1·3 Ma, during which time extensional tectonics prevailed in the Southern Alps.

Metamorphism of primary manganese deposits changes the oxi-hydroxide assemblage into a braunite-rich paragenesis. Braunite magnetic properties, together with the increase in grain size during metamorphism, can allow magnetic enrichment at gravel-sand grain size. Samples were collected from a manganese deposit in the Eskişehir region of Turkey, where a metamorphic event changed mineralogy from an original Manganese (Mn) oxi-hydroxide and chert assemblage to a braunite-rich quartzite and also showed an increase in grain size as a result of metamorphism. These samples were first crushed to a fine grain size and braunite was collected using a magnetic separator. Results show that metamorphic braunite-rich manganese deposits can be successfully enriched at high Mn recovery with the best results in the +1–10 mm grain size range.

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 study of Mg–Fe²⁺ subsolidus exchange between olivine and spinel is a powerful tool to unravel the thermal history of ultramafic rocks. We have implemented such a study using olivine–spinel diffusivity patterns in fresh mineralogical samples from the Finero mafic-ultramafic Complex in the Ivrea-Verbano zone of Northern Italy. Our analytical suite includes chromitites and dunites of the Phlogopite-Peridotite Unit from the core of the Complex. Primary and re-equilibrated olivine and spinel compositions were derived from diffusivity curves calculated by fitting data via an exponential function. Resulting XMg (Mg/(Mg + Fe²⁺) values were then used for geothermometry. Samples are found to demonstrate a maximum temperature of 849 °C and a minimum temperature of 656 °C; these temperatures coincide with the limits of elemental exchange in this mineralogic system. We were unable to identify primary olivine/spinel compositions related to the original formation of the dunite–chromitite suite during Early Permian metasomatic activity. Temperature of 849 °C is ascribed to the Late Triassic re-heating event dated at 208 ± 2 Ma. Continuous cooling followed this event at rates of 10⁻⁴ and 10⁻² °C/yr until cessation of elemental exchange activity at ~656 °C. A rapid cooling rate is associated with the uplift and subsequent decrease of geothermal gradient during the early stages of the opening of the Piemont ocean basin.

Mg-Fe²⁺ diffusion patterns in olivine and chromite are useful tools for the study of the thermal history of ultramafic massifs. In the present contribution, we applied the exponential modeling of diffusion patterns to geothermometry and geospeedometry of chromitite ores from two different ophiolite contexts. The Iballe ophiolite (Northern Albania) hosts several chromitite pods within dunites. Primary and re-equilibrated Mg#, estimated by using an exponential function, provided re-equilibration and primary temperatures ranging between 677 and 996 °C for chromitites and between 527 and 806 °C for dunites. Cooling rates for chromitites are higher than for dunites, suggesting a different genesis for the two lithologies, confirmed also by spinel mineral chemistry. Chromitites with MORB affinity formed in a SSZ setting at a proto-forearc early stage, explaining the higher cooling rates, while dunites, with boninitic affinity, were formed deeper in the mantle in a more mature subduction setting. At the Nea Roda ophiolite (Northern Greece) olivine in chromitites do not show Mg-Fe variations, and transformation into ferrian chromite produced “fake” diffusion patterns within chromite. The absence of diffusion patterns and the low estimated temperatures (550–656 °C) suggest that Nea Roda chromitites were completely re-equilibrated during an amphibolite-facies metamorphic event that obliterated all primary features.