Typomorphic features of placer gold from Bolshevik island of the Severnaya Zemlya Archipelago (Russia)

This paper presents the morphologic, chemical and other typomorphic characteristics of native gold from four placer deposits (basins of the Lev. Nora, Skalistaya and Golysheva rivers, and Loginova brook), four placer occurrences (basins of the Lagernaya, Nizh. Litke and Prokhodimaya rivers, and Tikhiy brook), and the alluvial deposit of cape Mordovin on Bolshevik island of the Severnaya Zemlya archipelago (Russia). Optical microscopy, scanning electron microscopy and electron-probe microanalysis were used in this study.Placer gold from the Lagernaya, Golysheva, Nizh. Litke and Skalistaya rivers, Tikhiy brook and cape Mordovin is characterized by a very high fineness (> 988‰) in the rims and a lower fineness (860‰–970‰) in the center. Gold particles from the placers of the Lev. Nora and Prokhodimaya rivers and Loginova brook are low fineness and widely vary in the center (from 647‰ to 920‰) and are high fineness (950‰–980‰) in the rims. In some gold particles from the placers of the Lev. Nora and Skalistaya rivers, zones with Cu up to 1.2 wt.% and Hg up to 2.6 wt.% are observed. Titanite, monazite, cobaltite, ulmannite, brannerite, rutile, zircon, Y-xenotime, bismuthite, native bismuth and bismuthinite, garnet (almandine), Cu- or Ni-pyrrhotite were found in the native gold from the Skalistaya and Lev. Nora placers. Native gold from the Skalistaya river placer contains mineral micro-inclusions of cobaltite, Cu,Cd-bearing sphalerite and Fe,Cu-ullmannite. Native gold from the Lev. Nora river placer differs in the presence of brannerite and bismuth minerals.On the basis of the obtained results, available metallogenic characteristics of Bolshevik island and literature data, the following types of primary sources are predicted for these locations: (1) Lev. Nora river deposits of gold-copper rare metal and porphyry gold-copper formations; (2) Skalistaya river deposits of porphyry gold-copper and gold-quartz formation; (3) all the other locations: deposits of gold-quartz and gold-sulfide-quartz formations (hosted in terrigenous carbonaceous complexes). The presence of intermediate reservoirs near some of these locations is probable.