Comparative Mineralogical and Geochemical Characteristics and Ore Potential of the Ikchuka and Dukaly Mafic–Ultramafic Massifs (Khabarovsk Krai)

   Research subject. The mafic–ultramafic massifs of Ikchuka (~16 km²) and Dukaly (~30 km²) located in the Central Sikhote-Alin (Khabarovsk Krai) formed under accretion–collision tectonic conditions.

   Aim. To compare the mineralogical and geochemical characteristics of the massifs, determine their formational affiliation, and identify factors controlling the formation of different types of ore mineralization.

   Materials and methods. Over 4600 lithogeochemical samples were analyzed (ICP–MS/AES after four-acid digestion). Microscopy, X-ray diffraction, FTIR spectroscopy, and scanning electron microscopy with EDS were carried out. Nonparametric statistical tests (Mann–Whitney), discriminant and factor analyses (Statistica), and geothermobarometry based on antigorite composition were applied.

   Results. The ultramafic part of the Ikchuka massif represents a tectonic slab of mantle restite exhumed to the surface during accretion–collision events. In contrast, the Dukaly massif formed as a product of magmatic differentiation, where local hybridization of ultramafic and gabbroic melts in contact zones triggered sulfide liquid immiscibility and primary PGE concentration. Epigenetic Ni–Bi–Pb mineralization (parkerite, maucherite, cobaltite) against the background of Cu–Fe sulfides dominates in Ikchuka, whereas Dukaly hosts low-sulfide PGE assemblages (cabriite, irarsite, tomamaeite, potarite, tatianaite, stannopalladinite, sperrylite). In PGE-enriched zones of the Dukaly massif, Cr/Ni = 4.16–5.0 and Pt/Pd = 1.94–2.25, indicating hybridization between ultramafic and gabbroic melts in contact zones. The formation of PGE-bearing assemblages occurred via a two-stage process: (1) extraction of platinum-group elements from a highly evolved basaltic melt at
T ~ 1000–1200°C and P = 3–20 kbar; and (2) their redeposition during a pneumatolytic–hydrothermal stage as temperatures decreased from 480–650 °C to ~250 °C. The critical involvement of Cl-bearing fluids (Cl-apatite, phlogopite, chlorite) is demonstrated.

   Conclusions. The massifs represent two geochemically distinct systems. The Dukaly massif exhibits the highest ore potential, as its low-sulfide PGE mineralization is genetically linked to contact plagioperidotites and followed by pneumatolytic–hydrothermal reworking.

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