U–Pb Isotope Age of Zircon (LA–ICP–MS Method) from Magmatic Rocks and Some Aspects of the Genesis of the Tyrnyauz Mo–W Deposit (North Caucasus)

The authors' determinations of the U–Pb isotopic age of zircon (LA–ICP–MS method) in the main types of igneous rocks emphasize the presence of both Neogene and older (up to Late Paleozoic) intrusions at the deposit. The earliest are rocks of the “trondhjemite” massif, which were emplaced in the Late Paleozoic. This age of the rocks of the trondhjemite massif, confirmed by the U–Pb isotopic method (302 ± 4 Ma) for zircon from rocks of its main intrusive phase (tonalites–granodiorites), is consistent with manifestation of Late Paleozoic tungsten-bearing magmatism and associated W mineralization in the North Caucasus (in the Peredevoi Range) and allows a possible Late Paleozoic age of large bodies of altered skarns with W mineralization at the Tyrnyauz deposit. At the next, Neogene stage, the intrusion of leucocratic granites took place with the formation of bodies of igneous breccias, the emplacement of an accompanying aplite dike formation, and the development of intense molybdenum (with subordinate W) mineralization in large vein–veinlet, stockwork systems. The U–Pb isotopic age of zircon in leucocratic granites is 2.67 ± 0.04 Ma. Later, a large massif of biotite (Eldzhurt) granites and associated formation of aplite and alaskite dikes were formed. Emplacement of subvolcanic rhyolite bodies followed. The U–Pb isotopic age of zircon in the Eldzhurt granites is 2.10 ± 0.08 Ma, and in rhyolites, 2.05 ± 0.04 Ma. Intrusion of these rocks was accompanied by the formation of Mo–W–Bi–Te–Au mineralization.