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Russian Geology and Geophysics

2002 year, number 10

GEOCHEMICAL FEATURES OF ROCKS OF VOLCANOPLUTONIC ASSOCIATIONS OF THE DUKAT GOLD-SILVER DEPOSIT

M. N. Zakharov, R. G. Kravtsova, and L. A. Pavlova
Keywords: geochemistry, petrochemistry, REE and trace elements, igneous rocks
Pages: 929-939

Abstract

Study was given to the rocks of volcanoplutonic association of the Dukat gold-silver deposit, northeastern Russia. The Dukat plutonic uplift, with which the deposit is associated, is a result of intrusion of a two-phase pluton into a series of Lower Cretaceous ignimbrites. It consists of early-phase monzogranites and late-phase leucogranites. The Rb-Sr age of radiodacite ignimbrites is estimated at 99.1 1.4 Ma, and that of leucogranites of the second phase, at 80 2 Ma. All magmatic formations of the uplift belong to the petrochemical calc-alkalic series. Two groups of rocks which differ in the magnitude of serial index () have been recognized: monzo- and leucogranitic. The first group contains monzogranites (-2.41), diorites, amphibolic diorite porphyrites, and postmineral Na-basalts. The second group contains leucogranites (-2.02), Lower Cretaceous ignimbrites, and subalkalint K-basalts.
The monzogranites and leucogranites of the Dukat plutonic uplift are geochemically specialized for Ag, Sn, B, and REE. As a rule, there is no correlation between these and rock-forming elements. The index of accumulation of concentrations, IAC, is 17.9 in mozongranites and 19.7 in leucogranites. Carrier minerals and concentrators of ore elements and REE are accessory minerals (orthite, tourmaline, and ore minerals). The highest contents of volatiles (F, B, Cl, S), REE, Ag, Sn, and, to a lesser extent, Pb and Zn are recorded in ignimbrites and explosive breccias of rhyodacite composition, occurring at the top of the intrusion. Ignimbrite IAC is 69.5. Maximum concentrations of Au are noticed in explosive breccias of diorite porphyrites. Data on distribution of volatiles and REE in rocks of volcanoplutonic associations of the Dukat Au-Ag deposits are reported for the first time.
It is supposed that mineralization formed under the effect of a deep-seated fluid containing F, B, Cl, S, and other gas mineralizers. The most probable source of ore-bearing fluids is a long-lived local chamber of basaltic magma far from the granitoid pluton.