Uralian-Alaskan-type mafic–ultramafic complexes are recognized as a distinct class of intrusions regarding lithologic assemblage, mineral chemistry and petrogenetic setting. In the present study, we discuss new data on the distribution of major elements in minerals of the spinel group in rocks from Uralian-Alaskan-type complexes in the Ural Mountains, Russia. Cr-rich spinel (Cr2O3 = 20–53 wt%) in dunite with interstitial clinopyroxene and in wehrlite cumulates indicate that it reacted with interstitial liquid resulting in the progressive substitution of Al2O2 and Cr2O3 by Fe2O3 and TiO2. A distinct change in the spinel chemistry in dunite (Cr2O3 = 47–53 wt%), towards Al2O3- and Cr2O3-poor but Fe2O3-rich compositions monitors the onset of clinopyroxene fractionation in wehrlite (Cr2O3 = 15–35 wt%, Al2O3 = 1–8 wt%, Fe2O3 = 25–55 wt%). In more fractionated mafic rocks, the calculated initial composition of exsolved spinel traces the sustained crystallization of clinopyroxene by decreasing Cr2O3 and increasing FeO, Fe2O3 and fO2. Finally, the initiation of feldspar crystallization buffers the Al2O3 content in most of the spinels in mafic rocks at very low Cr2O3 contents (<5 wt%). The fractionation path all along and the reaction with interstitial liquid are accompanied by increasing Fe2O3 contents in the spinel. This likely is caused by a significant increase in the oxygen fugacity, which suggests closed system fractionation processes. Spinel with Cr2O3 < 27 wt% is exsolved into a Fe2O3-rich and an Al2O3-rich phase forming a variety of textures. Remarkably, exsolved spinel in different lithologies from complexes 200 km apart follows one distinct solvus line defining a temperature of ca. 600°C. This indicates that the parental magmas were emplaced and eventually cooled at similar levels in the lithosphere, likely near the crust–mantle boundary. Eventually, these 600°C hot bodies were rapidly transported into colder regions of the upper crust during a regional tectonic event, probably during the major active phase of the Main Uralian Fault.