Metalliferous sediments of the Triassic cherty formation in the Ol’ga ore district of primorye: Tin-noble metal ores of a new genetic type

Abstract

The Triassic cherty formation of Sikhote Alin [1] hosts metalliferous deposits. They are commonly represented by siliceous‐rhodochrosite rocks and their metamorphosed analogues (primarily, consisting of Mn-silicates and aluminosilicates) with high concentrations of Ga, Au, Pt, Pd, and other metals [3]. In the Ol’ga district, the metalliferous deposits are also represented by chocolate-brown siliceous rocks (hereafter, brown cherts) and tin‐iron ores. The metalliferous deposits occur in the Middle‐ Late Triassic siliceous‐clayey sequence. They make up at least one ore-bearing unit (thickness of 5 m or more) represented by brown cherts with a manganese rock bed near the upper contact. The overlying tin‐iron ore bed varies from tens of centimeters to a few meters in thickness. Judging from locations of native exposures, talus, and alluvial fragments, the ore-bearing unit is developed over an area of no less than 20 km 2 (Fig. 1). The manganese rocks are composed of rhodonite, pyroxmangite, and spessartine with a maximum V 2 O 3 content of 0.20 wt % [2, 4]. The rocks contain kanoite, tephroite, manganactinolite, dannemorite, tirodite, pyrosmalite, pyrophanite, hubnerite, scheelite, native silver, native gold, minerals of the cobaltite‐ gersdorffite series, pentlandite, millerite, violarite, tetradymite, tellurobismuthite, and other minerals. The manganese rocks also include Au (up to 35 g/t), Pt (0.08‐ 0.33 g/t), Zn (up to 5.97 wt %), Cu (up to 0.64 wt %), Ni (up to 0.14 wt %), and Co (up to 0.10 wt %) [3]. Nearly all polished samples contain native silver dissemination up to 20 µ m in diameter. Gold grains ( n mm in size) extracted by the acid treatment of manganese rocks are characterized by a high grade of fineness