Burakovskii-Aganozero layered complex: Composition and petrologic applications

The paper considers the structure of the Burakovskii-Aganozero layered comp lex, which was formed at 2449 Ma. Petrographic and geochemical characterist ics of rocks making up the layered series of the Aganozero and Shalozero bl ocks were studied in detail. New isotopic and geochemical data are presente d and previous results on isotopic characteristics are generalized. It was concluded that the Burakovskii-Aganozero layered intrusion was a polyphase complex. The main phases correspond to the emplacement of "Aganozero" (epsi lon (Nd) = -0.4 to +0.9 and Sr-87/Sr-86(T) = 0.7021-0.7035) and "Shalozero" (epsilon (Nd) = -3.31 and Sr-87/Sr-86(T) = 0.7020) magmas, which formed th e intrusion. There is evidence for the presence of other small-volume intru sion phases. The Aganozero and Burakovskii-Shalozero blocks are two subcham bers. According to geophysical data, each of them has its magma conduit. Th e Aganozero portion of the layered complex was formed earlier as the first intrusion phase. The Aganozero magma of this phase differed from the magma of the second intrusion phase, which produced the Burakovskii-Shalozero por tion of the layered complex, both in isotopic characteristics and chemical composition (lower silica and iron contents). This is suggested by the petr ography of the layered series rocks, compositions of rock-forming minerals, and geochemical characteristics of rocks composing blocks of the layered c omplex. This allows us to suppose that the initial magmas of these blocks w ere genetically different and represented successive intrusions of evolving magmas from a single magma chamber or from two independent chambers. Our d ata provide a new insight into the problem of ore potential of the layered complex, in particular, its platinum-bearing capacity (Korneev et at, 1999a , 1999b).