Silver Mineralization in Deep Magmatogenic Systems of Ancient Island Arcs: The Ildeus Ultrabasic Massif, Stanovoy Mobile Belt (Russian Far East)

Iron–Titanium Oxide–Apatite–Sulfide–Sulfate Microinclusions in Gabbro and Adakite from the Russian Far East Indicate Possible Magmatic Links to Iron Oxide–Apatite and Iron Oxide–Copper–Gold Deposits

“…Primarily, amphibole in the segregations contains elevated Al content (~5-6 wt.%). In comparison, all secondary amphiboles (actinolite, tremolite) with clear replacement textures in the Ildeus complex are characterized by low Al (<2 wt.%) content [55,[60][61][62]]. An isolated microinclusion of ilmenite was also observed immediately adjacent to the larger inclusion clusters (Figure 4a), although it is unclear from the textural data if this minute ilmenite could, at some point, have been considered an integral part of the larger ITOASS segregation in Figure 4a.…”

“…The Central Asian Orogenic Belt is composed of various metamorphic, ophiolitic (both MORB and SSZ-types) and arc-related terranes [56][57][58], some of which were either accreted or subducted along the SSZ in Early Mesozoic [59]. The northward subduction of the Mongol-Okhotsk ocean floor beneath the SSZ is marked, in particular, by mineralized ultramafic-mafic plutonic complexes, which form a linear belt roughly parallel to the southern edge of the Siberian continent [55,[60][61][62]. One of the best developed and certainly most studied (including drilling) intrusions in this magmatic belt is the Ildeus mafic-ultramafic complex, which carries multi-stage polymetallic Ni-Co-Cu-Pt-Pd-Au-Ag mineralization [55,[60][61][62].…”

“…Some core-related ultramafic cumulates and pyroxenitic dikes were locally subjected to several episodes of metasomatism, resulting in hydrated (talc + serpentine + chlorite ± carbonate) and alkali-rich (quartz + albite + potassic feldspar + biotite + sericite ± muscovite) assemblages. Ultramafic rocks display exotic disseminated sulfide-native metal-alloy mineralization [60][61][62] summarized in Table 1. Ildeus maficultramafic rocks follow a calc-alkaline differentiation trend in AFM diagrams and display prominent high-field-strength element depletions coupled with large-ion lithophile and light rare earth element enrichments characteristic of subduction zone magmas [61,62].…”

“…Ultramafic rocks display exotic disseminated sulfide-native metal-alloy mineralization [60][61][62] summarized in Table 1. Ildeus maficultramafic rocks follow a calc-alkaline differentiation trend in AFM diagrams and display prominent high-field-strength element depletions coupled with large-ion lithophile and light rare earth element enrichments characteristic of subduction zone magmas [61,62]. Granodiorites display very low Y concentrations (<10 ppm) and high Sr/Y ratios (50-400) typical of adakites [63][64][65].…”

“…Besides pyrite, acanthite and barite, amphibole and plagioclase phenocrysts and groundmass phases in the adakitic lava also contain spongylike grains and aggregates of non-stoichiometric silver chloride (Figure 8e,f). We have previously shown that the non-stoichiometric ratio of Ag to Cl in the halide microinclusions in magmatic rocks is due to their exposure to light during sample preparation and to electron beams during SEM-EDA studies [61].…”