Tectonic history of the Urals as stored in molybdenites of porphyry and greisen deposits

Geological characteristics, trace element geochemistry, and Re-Os dating of molybdenite are presented and discussed for seven Cu and Mo porphyry, one Cu skarn-porphyry and two Mo and Mo-W greisen deposits. Re contents in molybdenite are discussed versus ore mineralogy, molybdenite polytypes, formation temperature, and whole rock chemistry of parental rocks. They are also evaluated in the light of the geotectonic settings of these deposits and tectonic history of the Urals.Re-Os dating of molybdenite evidences that the porphyry deposits studied are confined to four volcanic arc terranes of the Urals and are linked to four subduction events: Tomino and Birgilda (ca. 430 Ma) and Zeleny Dol (ca. 420 Ma) porphyry deposits linked to the East Uralian volcanic arc; Voznesenskoe porphyry (ca. 395 Ma) and Verkhneuralskoe porphyry (ca. 365 Ma) deposits linked to the Magnitogorsk arc and its collision to the East European continent respectively; Mikheevskoe porphyry and Tarutino skarn-porphyry deposits (ca. 360 Ma) linked to subduction under the East Uralian microcontinent; Benkala porphyry deposit (ca. 335 Ma) linked to the activity of the Valerianovka Andean-type arc. The Talitsa Mo porphyry deposit (ca. 300 Ma) as well as YuzhnoShameiskoe (ca. 280 Ma) and Koklanovskoe (ca. 255 Ma) greisen Mo-W deposits are linked to collision between East European and Kazakh continents.Electron microprobe analysis and laser ablation inductively coupled mass-spectrometry of molybdenite demonstrate an extremely irregular distribution of all trace elements on both grain-scale and deposit-scale levels. Most trace elements (Fe, Co, Cu, Zn, As, Se, Ag, Sb, Te, Pb, Bi, etc.) form mineral inclusions within molybdenite while Re and W are commonly incorporated into molybdenite lattice. Re contents and distribution in molybdenite are indicative for tectonic setting of the deposits. Molybdenite from deposits formed within intra-oceanic arcs (Mikheevskoe, Tomino, and Voznesenskoe porphyry Cu deposits) is featured by high Re contents (1000-5000 ppm) and low W contents (<10 ppm). Molybdenite from Verkhneuralskoe (arc-continent collision stage) and Benkala (Andean-type arc) deposits is featured by lower Re contents (mainly 400-900 ppm) and higher W contents (30-120 ppm). Molybdenite from Talitsa Mo-porphyry, and Yuzhno-Shameiskoe and Koklanovskoe greisen deposits (continent-continent collision) is featured by the lowest Re contents (<10 ppm to 370 ppm) and the highest W contents (10 to 150 ppm). Geometrical mean Re content in molybdenite for all ten deposits studied has positive correlation with average Cu/Mo ratio in ore implying mass balance was one of the key controls of Re incorporation in molybdenite. In addition, Re content has a negative correlation with SiO2 and total REE contents in ore-bearing intrusive rocks as well as with the absolute age of the deposits which correlates with the general evolution of porphyry- and greisen-type deposits of the Urals. For subduction-related porphyrydeposits magma composition was generated with strong influence of the shallow subduction component. Fluid -mobile elements and various degrees of partial melting of the mantle wedge strongly depend on Re contents. Collision tectonic settings are marked by low Re concentrations in molybdenite.