Abstract

The Murgul ore deposit belongs to the East Pontic metallogenetic province and is related to a subvolcanic formation of an Upper Cretaceous island-arc volcanism. The deposit is linked to a 250-m-thick felsic pyroclastic member of Senonian age.The Murgul deposit consists of (1) a widespread disseminated ore with varying Cu contents ranging from 0.2 to 0.7 percent, (2) a stockworklike ore with average Cu contents between 1.0 and 2.5 percent, and (3) small ore lodes with Cu contents from 5.0 to 10.0 percent.The mineralization is spatially associated with an intense two-stage alteration of the host rock: an initial stage of phyllic and argillic alteration, and a late stage characterized by silicification. The continuation of the volcanic activity with ascending hydrothermal solutions caused an intense remobilization of the disseminated ore producing the stockworklike and vein mineralizations. They consist of pyrite and chalcopyrite with minor contents of sphalerite, galena, and fahlore.The study of the rare earth element distribution in the alteration zones supports the distinction between the two stages and reveals a close correlation between increasing wall-rock alteration and depletion of the rare earth elements. Petrographic data indicate that the rare earth element patterns of the altered host rocks are predominantly controlled by the abundance of sericite, illite, montimorillonite, kaolinite, and dickite. The formation of the two main orebodies must have been completed before an intense subaerial or intertidal erosion and weathering took place. This phase is indicated by a relatively thin layer of transgressive kaolinized weathering products which are overlain by barren felsic volcanics.

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