METALLOGENICAL PARTICULARITIES OF GRANITOID MASSIFS ON

NORTHERN AND CENTRAL CHUKOTKA

Sushkin L.B.

«Projectinvest» Co. Ltd, Ekaterinburg, Russia, sushkin@email.kht.ru

Uranium occurences are widespread in various volcanotectonic and volcanoplutonic structures of Okhotsk-Chukotka volcanogenic belt and Verkhoyan-Chukotka fold area.They are restricted primarily to outmost parts of median masses, where were intensively developed processes of tectono-magmatic reactivation and granitization. The most of them localized in U-bearing acid intrusive rocks and lavas or clothely genetically related to acid granitoid magmatism (Van-Van-E, 1996).

The most of uranium occurences discovered within the fold systems of Northern and Central Chukotka are related genetically to massifs of highly radioactive granites. For example, the uranium mineralization of the most known Severnoe deposit is localized mainly in the porphiry-like grаnites, which contain 20-25 ppm of uranium with radioactivity 80 mcR/ h.

The most important features of the uranium ore occurences in highly radioactive granites are as fallows:

a) The ore–bearing granite massifs were greizenized with rare-metal polysulfide mineralization, prior to uranium ore deposition. The commercial tin-sulfide mineralization and the uranium ore-bodies are localized in differentfaults and blocks and originated in different times.

b) The uranium-bearing zones contain the products of silification, sericitization, albitization, chloritization, fluoritization and zeolitization.

c) The uranium orebodies are localized in steeply dipping shutter zones, mostly stringing NW and almost N. They are often associated with numerous dikes of andesite porphiry and microdiorite.

Uranium ore occurences of this type (Severnoe, Yanranayskoe, Kukeneyskoe, Katumskoe and others) can be classified as uranium-rare-metal ore association. They show a high correlation between uranium and Nb, Sn, Pb and Zn.

Deposits of this type are widespread in French Massif Central and uranium ores is utilized by France nuclear industry. In fact, the discovery of these deposits in Russian North-East made an impuls to carry out a systematyc syrvey of granite massifs in other regions of the USSR. As a result, some large deposits of this kind have been explored in Mesozoic granites of East Transbaikalie (Gornoe, Beryozovoe, Durulguevskoe). Besides that, few years earlier there were discovered unique and large uranium deposits in in volcanic rocks (Tulukuevskaya, Streltsovskaya, Dornotskaya VTD) (Ishukova, 2005).

Uraniumferous metallogenic zones of the Central and Eastern Chukotka districts correspond to volcanic-plutonic depressions fillid with volcanics of some volcanic-plutonic assemblages. Ore-bearing VTDs are made up of effusive and intrusive rocks. Plutonogenic compaund of this assemblages form group of dome-like and sill-like bodies developed at the basement of VTD, as well, as inside them, at various stratigraphic levels (Ishukova, 2005; Konstantinov, 2005). The Cretaceous tectonic-magmatic activation was preceded by prolonged regimes of Triassic pericrattonal downwarping with the intens sedimentation.

All intrusions, including the ore-bearing ones are always accompanied by multy-element geochemical aureoles of U, Sn, Bi, Pb and Zn. Circum – intrusion aureoles are only reliably identifiable in sedimentary host rocks. In volcanics, aureoles of this sort are very hard to destinguish due to high background levels of the essential aureole-forming elements and the presence of petrogenic anomalies both within the intrusions and the host rocks.

One of the major problems in prediction and exploration of uranium deposits is to determine whether or not the newly discovered are ore-bearing. Reliable criteria for a selection of this sort are yet unavalable.

Some problems of the intrusions origion and its menallogeny are still unresolved. Serious attention needs in particular a question about relationship of uranium with gold. The definitive answer on this principle question requires undertaking special more deep studies of the ore material.

Broad development in region gilded, rare metal mineralization and multiple manifestations of the uranium occurences alongside with broad development as highradioactive granitoids, so and highproductive black schist complexes of the thick masses, intensive processes of tectono-magmatic reactivation is indicative of possibility of the discovery here large uranium and complex ore object ( Konstantinov, 2005; Sushkin, 2007).