Comparison of the epithermal gold deposits in the Mesozoic tectonic and magmatic activation zones of Transbaikalia and North Caucasus (as example Baley and Radujnoe deposits)

Kaigorodova E.N.

The Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry RAS, Moscow, Russia

katmsu@mail.ru

Baley-type epithermal deposits are known in all fold belts, which were subjected to activation. In 1976, a similar Baley-type object was discovered in the North Caucasus at Hulam-Bezengi Gorge in Kabardino-Balkaria. Au-Ag deposit Radujnoe is localized in the North Jurassic depression related to the Mesozoic tectonic-magmatic activation (TMA) and processes of riftogenesis. A number of autors suppose that there is a direct relationship between the riftogenesis and formation of Au-ore deposits. For example, the Baley deposit is localized in Undine-Dain depression. However, scale of expression of TMA in the North Caucasus and Trans-Baikal is differed. In the North Caucasus TMA has led to the formation of Chegem-Uruh volcano-plutonic belt, extending through the mountainous part of the republics of Kabardino-Balkaria and North Ossetia, while in the Transbaikal TMA covered huge territory (virtually all of Transbaikalia, North-East Mongolia and North-West China). Therefore, the scale of the Mesozoic productive mineralization in the Caucasus is much more less.

North Jurassic depression was formed on the basement of PR-PZ rocks. In the Radujnoe deposit area the basement is composed of Paleozoic granites (belorechensk granites). Jurassic sedimentary rocks are presented by sandstones, siltstones and mudstones. Here is widely distributed the formations of volcanic necks, extrusive domes, lava flows (two phase of volcanism - consistently differentiated basalt-rhyolite formation and contrast-differentiated trachybasalt-trachyrhyolite one). Baley-type does not characterized by such intense development of volcanic processes. In this respect the deposit Radujnoe is similar to the Au-Ag deposits of northeastern Russia. It should be also noted that in the Baley ore field are marked deep facies of igneous rocks associated with later mezozoic TMA (micro/middle-grainy leucocratic granites). At the Radujnoe deposit area were described only the volcanic facies. There are widespread dissemination of the injection-explosive breccias with quartz cement (chalcedony often).

We note other classification aspects of Radujnoe field to Baley-type: the role of intersection of steeply dipping faults in the formation of ore pillars; near-surface typical mineralization is disseminated (epithermal typomorphic minerals) - calcite, adularia, clay minerals; intensive argillization of rocks of the crystallic basement; the intensive silicification of host sedimentary rocks until to form monomineralic quartz metasomatic rocks; Au is in native form and dispersed in sulfides. However, there are features that distinguish Radujnoe from Baley types: quartz-sulfide thin veins form a network of "injection", their thickness is less than 5 cm; in the apical parts of the volcanic bodies barite and gypsum are developed; Au-Ag mineralization is combined spatially with silver-barite-polymetallic mineralization, which is also associated with volcanic processes and is localized in the sedimentary rocks, forming stratum body. We can concluded that the Radujnoe deposit represents the first stage of Baley-type mineralization - adularia-carbonate-quartz with Au (second stage of Au-pyrargyrite-miargyrite-carbonate-quartz-mineralization is not developed at the Radujnoe deposit) with the imposition of the silver-barite-polymetallic mineralization Sadon-type.

References:

1. Krivosheev V.G. (2006) Score prospects of Au-Ag ore-mineralization and associated barite-polymetallic mineralization in Chegem Uruh-volcanic-plutonic belt. Nalchik.

2. Spiridonov A.M., Zorina L.D., Kitaev N.A. (2006) Gold-bearing ore-magmatic system of Transbaikalia, Novosibirsk Academic Publishing House "Geo".