THE UNIQUE CENTRAL ALDAN GOLD-URANIUM ORE DISTRICT (RUSSIA)

Abstract

In recent years, problems of the formation and distribution of ore deposits large and unique in their origin and scale have been discussed in publications and at international geological meetings. The aim of the present article is to show that not only individual deposits, but also ore districts may be unique. Such ore districts, for example, the Central Aldan gold-uranium ore district, contain deposits of various origins that belong to the same metallogenic epoch and were formed in similar geodynamic conditions. The Central Aldan gold-uranium ore district, with its resources of Au of 1000 t and U of 600000 t, is interpreted as a single unit. Its unique features are reflected at different levels: transregional, regional, and local. At the transregional level, its position is defined by the superposition of intense Mesozoic epicontinental tectonics, calc-alkaline-alkaline magmatism, and extensive hydrothermal ore mineralization on consolidated Early Precambrian structures of the Aldan Shield. In the Mesozoides of East Asia, An and U deposits are located separately from each other except for in the Central Aldan district, where these deposits occur jointly and possess unique features. The interrelation between the Early Precambrian and the ore-bearing Mesozoic structures is clearly manifested in the Aldan Shield itself. The Central Aldan ore district is situated at the conjunction of the two largest megablocks, the Aldan-Timpton and Timpton-Uchur, which 2 Ga ago were transformed into a gneiss-granulite terrane. The Central Aldan district is confined to the periphery of a giant dome made up of Early Precambrian rocks of the lengra complex. This district contains the largest and most varied subvolcanic calc-alkaline-alkaline intrusions. Finally, on the local scale, the Central Aldan magmatectonogen appears as the main ore-controlling factor. It consists of radial and ring faults cutting the crystalline basement and platform cover. It defines the distribution of Mesozoic magmatic rocks and various deposits in different radial blocks. The Central Aldan district contains three main types of ore deposits that form the following independent ore fields: the hydrothermal Au-U El'kon, the hydrothermal U Lebedinsk, and the polygenetic Au Kuranakh. The first and third deposits are unique not only in their scale, but in their origin as well. Deposits of the El'kon type are confined to rejuvenated faults of the crystalline basement and are characterized by exclusive extension of low-temperature Au-U mineralization. The third, Kuranakh type, in many respects enigmatic, is characterized by the presence of gold-bearing karst clays at the contact of platform limestones with Jurassic sandstones. The data presented in this article were accumulated during the 70-year history of the study and development of the Central Aldan district. Some deposits have been worked out and others preserved from operation due to different reasons. Many problems of the origin of ore deposits in the Central Aldan district have not yet been solved, and its total ore potential is far from being established.