## 2 Geologic Background and Samples  
The Stanovoy Suture Zone (SSZ) is located (Figure 1a) between the southern edge of the Aldan Shield (crystalline core of the Siberian craton) and accreted terranes of the Central Asian Chrogenic Belt (CAOB). The CAOB separates the East European craton to the west, Siberian Craton to the north and Tarim and North China crators to the south (Figure 1a). The CAOB is composed of Precambrian to Mesozoic oceanic, supra-subluction and back-arc ophiolites, fragments of accretionary prisms and oceanic plateaus as well as slivers of the ancient (pre-Phanerozoic) metamorphic crystalline basement intruded by Paleozoic to Mesozoic granitidis [43; 44; 45; 46]. The Stanovoy Suture Zone (SSZ) straddles the northeastern boundary between the CAOB and the Archean crystalline Aldan Shield of the Siberian craton (Figure 1a). The SSZ records a protracted history of Paleozoic to Early Mesozoic subduction and Late Jurassic-Early Cretaceous collision between Siberian and North Amur cratons [36]. The closure of the Mongol-Okhotsk ocean and formation of the SSZ was followed by Early Cretaceous postcollisional extension and adakitic/lamprophyric magmatism [36]. The central portion of the SSZ (the so-called Bryanta Block) is composed of Late Archean (2.86-2.75 Ga; [47]) presises, mafic schists and amphibolites, along with Late Proterozoic, Paleozoic and Mesozoic granitoid complexes (Figure 1b). Some mafic schists are characterized by igneous protoliths, crystallization ages of 1.93 Ga and the earliest metamorphic ages of 1.89 to 1.91 Ga [48]. Trace element geochemistry of these metabasalts suggests their derivation from subduction-type mantle sources in a Paleoproterozoic arc-continent collision zone along the southern edge of the Archean Aldan shield [47; 48]. The Early Cretaceous (115-117 Ma) volcanics and coeval granitoids (Figure 1b) with adakitic affinity represent late collisional and post-collisional magmatic pulses in the SSZ developed within the post-collisional extensional or transform-type continental margin environment [36]. The entire Precambrian to Mesozoic collision-related package in the central SSZ is intruded by Mesozoic ultramafic-mafic complexes associated with magmatic Au-PGE and base metal sulfide mineralization [36]. Late Triassic (232-233 Ma) Ildeus ultramafic-mafic intrusion was emplaced into the Precambrian amphibolite-genesis-schist terrane (Figure 1b) and is characterized by a tectonically distorted, concentrically zoned structure (Figure 1c). The inner core zones include plagioclase-bearing dunites, websterites and wehrlites, while the outer zones are predominantly composed of various pyroxenites and minor gabbros [36]. Both plutonic cores and outer zones are intruded by pyroxenites dikes, as well as numerous veinlets, veins and dikes of adakitic and lamprophyric composition [36]. Most rocks from the Ildeus ultramafic core are characterized by cumulate textures (locally nearly completely overprinted with low-temperature greenschist facies metamorphism) formed by variable proportions of olivine, clinopyroxene, orthopyroxene, Al-rich spinel and magnetite. Pyroxenites from the intrusion's margins are fine-grained and typically display allotriomorphic textures [36]. Intercumulus phases include amphibole and plagioclase with accessory apatite, zircon, ilmenite, magnetite and sulfide. Olivines in Ildeus ultramafic rocks exhibit some variations with respect to MgO, FeO, MnO and NiO. Olivines in dunites and plagioclase-bearing dunites exhibit very low levels of CaO, Al\({}_{2}\)O\({}_{3}\), TiO\({}_{2}\) and Cr\({}_{2}\)O\({}_{3}\), while FeO, MnO and TiO\({}_{2}\) are higher in websterites, wehrlites and pyroxenites [36].