The West Primorye noble-rare metal zone: A new Cenozoic metallogenic taxon in the Russian Far East

Abstract

The majority of the explored germanium reserves of the World are localized in the Cenozoic coal-bearing structures of Primorye. However, the metallogeny of this period remains poorly studied and individual Cenozoic metallogenic zones have not yet been distinguished in Primorye. It is believed that all Cenozoic ore belts and zones of the Russian Far East are confined only to Kamchatka and the Kurils [1]. The present paper substantiates the identification of a new taxon for the Russian Far East, namely the West Primorye noble‐rare metal metallogenic zone, which coincides with the synonymous Cenozoic riftogenic structure. The main features of its structure, evolution, and ore potential are considered. It is concluded that this zone is promising for a wide spectrum of mineral resources, which are located both in the riftogenic suprachamber grabens and in the adjacent framing structures related to fluid‐hydrothermal activity in the course of the Cenozoic bimodal and basic‐alkali basic volcanism. The Primorye region includes about 50 Cenozoic depressions, most of which are filled with coal-bearing sediments (Fig. 1) mainly represented by fault-related (often one-sided) grabens from n to 10‐20 km long and from 100 n m to n km wide. The thickness of the Cenozoic cover is typically no more than 100 n m and reaches 1‐1.5 km only in the central parts of the largest structures. Only three small NW- and EW-oriented depressions are located in the Sikhote Alin mountainous area east of the Central Sikhote Alin fault. Most of the Cenozoic NNE- and NE-oriented depressions are concentrated in a zone (100‐200 km wide and 750 km long) between the Arsen’evka fault and the Russian‐Chinese border. This area was considered as a single (Cenozoic) West Primorye riftogenic zone, which intersects all ancient terranes of the region [3]. This zone represents a fragment of the larger Ussuri‐Amur rift system (in a wider aspect, Tan Lu‐ Okhotsk rift system), which extends from the Lower Amur region to the adjacent areas of Korea and China [4]. This riftogenic structure (a scattered rifting zone in terms of morphology) was produced by the oblique collision of the Eurasian and Okhotsk Sea plates [4]. The latter plate migrated in the southwestern direction and produced a system of NS- and NNE-oriented dextral strike-slip faults along plate boundaries. The dextral displacement also took place along older faults characterized by sinistral dislocations in the Cretaceous. The localization of most Cenozoic coal-bearing depressions at the regional strike-slip faults and auxiliary NE-oriented faults, which are extensional structures during dextral strike-slip dislocations, indicates an important role of synkinematic tectonics in the Cenozoic destruction of the Earth’s upper crust [5, 6]. This process was accompanied by repeated outbursts of volcanic activity, which was mainly restricted to the areas of most intense graben formation. In many depressions, the felsic and basic extrusions and dikes crosscut coal-bearing sequences, while beds of lavas, tuffs, and tuffites are widespread in the entire Cenozoic sequence. Geophysical data indicate that some negative structures are correlated with subsurface magma chambers [7]. Suprachamber coal-bearing depressions are the most ore-bearing structures. In particular, the Lower Bikin suprachamber structure contains one of the world’s largest germanium‐coal deposit with inferred Ge reserves of more than 2000 t and a series of gold‐ silver (with PGE) occurrences localized in both coals and host rocks [3].