Mineralogical and geochemical characteristics of noble and rare-metal intergrowths from ore-placer occurrences, Anabar anteclise, Siberian platform

Intergrowths of platinum group minerals (PGM) with gold, silver, rare metals and semimetals (Bi, Pb, Sn, Sb, Te,As)from the Anabar River basin placers (northeastern Siberian Platform) were analyzed for their chemical composition and structure. While magmatogenic Au and PGE mineralization is recognized in sulfide and oxide ores of differentiated mafic-ultramafic intrusions, these metals typically reside as isomorphic impurities or as microscopic, dispersedinclusions, making them unsuitable for forming large placer grains. Recent discoveries of complex magmatogenicdeposits reveal geochemical signatures in precious and rare metals indicative of both granitoid and mafic-ultramaficmagmatism. The long-term evolution of these ore-magmatic systems spans stages from early magmatic and transitional fluid-magmatogenic to late hydrothermal-metasomatic. Consequently, rare discoveries of large polymineralintergrowths of noble and rare metals are invaluable for constraining the physicochemical parameters of such paragenetic ore associations and for guiding the exploration for nearby sources of precious metals. We demonstrate that themicrostructures of these natural precious-metal intergrowths resemble those of synthetic and metallurgical alloys. Byanalyzing compositional variations and structural forms, we discuss potential crystallization trends of these polymineral natural alloys using Pd-Au-Cu and Pd-Au-Te phase diagrams, which constitutes the core scientific contribution ofthis work. This study indicates that the sources of complex noble-rare metal mineralization in the northeastern Siberian Platform are primarily fluid-magmatic ore systems of diverse ages, related to Phanerozoic, differentiated maficultramafic platform intrusions. Furthermore, a genetic association with ancient metamorphosed granitoids and basiccrystalline schists is supported.