Metamorphism (greenschist facia down) of terrigenous rocks in the northern part of the Kularsky gold-bearing district, Yakutia: mineral ratios with cleavage

Abstract

In the Kularsky gold-bearing area, where 170 tons of gold were extracted from placers, primary gold deposits have not been well studied; therefore, their development requires detailed geological analysis including the study of rock metamorphism. A large Ulakhan-Sis anticline composed of Permian carbonaceous-terrigenous rocks is found on the northwestern flank of the Kular-Nersky folded belt of the Verkhoyano-Kolyma orogenic region. In this article we describe the material composition of carbonaceous-terrigenous rocks prevalent in the northern part of the Kularsky district. The degree of their postdiagenetic transformations varies from metagenesis in Triassic rocks to muscovite-chlorite and biotite subfacies of the greenschist facia of metamorphism in Permian rocks of the Ulakhan-Sis anticline. As the transition from metagenesis to muscovite-chlorite and biotite subfacies of metamorphism the degree of recrystallization of rocks, the grain sizes of the recrystallization of clastic quartz and the width of newly formed muscovite flakes are increasing, monazite, ilmenite, biotite flakes appear in rocks. These changes occur before the completion of formation in the rocks of the S1 slate cleavage.After the formation of the latter, mainly before the appearance of a later crenulation cleavage S2, crystallization of pyrite occurs in the rocks. Porphyroblasts of biotite and magnesiosiderite appear during the formation of a crenulation cleavage S2. The appearance of biotite during the formation of the S1 and S2 cleavages may correspond to the theories about the two-stage metamorphism of the rocks of the area. Thus, further metamorphism studies in this region are required.