CONDITIONS OF THE HOST ROCKS METAMORPHISM OF THE BORZOVA RIVER GOLD ORE CLUSTER
(North Eastern Taimyr)
Y.V. Kiselnikov1, E.N. Perova2, V.F. Proskurnin1, А.G. Shneider1
1Karpinsky geological research Institute, Saint Petersburg, Russia
2Saint Petersburg State University, Saint Petersburg, Russia
Keywords: Central Taimyr accretionary belt, Borzova river gold ore cluster, contact metamorphism, spessartine, mineral geothermometry, K-Ar geochronology
Abstract
The metamorphic rocks in the North Eastern Taimyr region represent a consequential result of its complex geological history. Series of metamorphic processes were associated with the formation of lode copper and noble metals mineralization. The aim of this study is to investigate the type and degree of metamorphism experienced by the host basic volcanic rocks in the ore cluster. We have identified three stages of metamorphic process: the first stage led to formation of actinolite and sodium plagioclase paragenesis (with its chemical compositions corresponding to temperature about 400 °С) the second stage resulted in crystallization of hornblende, plagioclase, spessartine-almandine garnet, biotite, feldspars (oligoclase-andesine and K-Ba types) and various Fe-Ti phases (mineral geothermometers indicate the highest temperature range of 450-600 °С) and the final stage produced clinochlore, pyrite and fluorapatite (330-290°С with AlIV contents in chlorite). We interpret the studied rocks as hornfels on the basis of highly discordant contours of the aureole, the compositions of the garnet (spessartine is predominant component), and K-Ar ages of biotite (253 ± 5 Ma) and plagioclase (239 ± 8 Ma), which coincide with the time of Late Paleozoic-Mesozoic post-collisional granitoid magmatism. The absence of schistosity, disequilibrium assemblages, and abundance of volatile-rich minerals (containing F-, [OH]- and [SO4]2-) also indicate their contact origin. The discovered aureole includes the known Cu-Au-Ag veins and metasomatic occurrences, the age of which is therefore late- or post-metamorphic. We confirm our colleagues’ early suggested hypothesis about the impact of a hidden granitic massif on the host rocks and consider the high metamorphic grade to be a natural boundary for the ore cluster.
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