The Gumeshevo skarn-porphyry copper deposits in the Central Urals, Russia: Evolution of the ore-magmatic system as deduced from isotope geochemistry (Sr, Nd, C, O, H)

The Early Devonian Gumeshevo deposit is one of the largest ore objects pertaining to the dioritic model of the porphyry copper system paragenetically related to the low-K quartz diorite island-arc complex. The ((87)Sr/(86)Sr)(t) and (E >(Nd))(t) of quartz diorite calculated for t = 390 Ma are 0.7038-0.7045 and 5.0-5.1, respectively, testifying to a large contribution of the mantle component to the composition of this rock. The contents of typomorphic trace elements (ppm) are as follows: 30-48 REE sum, 5-10 Rb, 9-15 Y, and 1-2 Nb. The REE pattern is devoid of Eu anomaly. Endoskarn of low-temperature and highly oxidized amphibole-epidote-garnet facies is surrounded by the outer epidosite zone. Widespread retrograde metasomatism is expressed in replacement of exoskarn and marble with silicate (chlorite, talc, tremolite)-magnetite-quartz-carbonate mineral assemblage. The (87)Sr/(86)Sr ratios of epidote in endoskarn and carbonate in retrograde metasomatic rocks (0.7054-0.7058 and 0.7053-0.7065, respectively) are intermediate between the Sr isotope ratios of quartz dioritic rocks and marble ((87)Sr/(86)Sr = 0.70784 +/- 2). Isotopic parameters of the fluid equilibrated with silicates of skarn and retrograde metasomatic rocks replacing exoskarn at 400A degrees C are delta(18)O = +7.4 to +8.5aEuro degrees and delta D = -49 to -61aEuro degrees (relative to SMOW). The delta(13)C and delta(18)O of carbonates in retrograde metasomatic rocks after marble are -5.3 to +0.6 (relative to PDB) and +13.0 to +20.2% (relative to SMOW), respectively. Sulfidation completes metasomatism, nonuniformly superimposed on all metasomatic rocks and marbles with formation of orebodies, including massive sulfide ore. The delta(34)S of sulfides is 0 to 2aEuro degrees (relative to CDT);(87)Sr/(86)Sr of calcite from the late calcite-pyrite assemblage replacing marble is 0.704134 +/- 6. The delta(13)C and (87)Sr/(86)Sr of postore veined carbonates correlate positively (r = 0.98; n = 6). The regression line extends to the marble field. Its opposite end corresponds to magmatic (in terms of Bowman, 1998b) calcite with minimal delta(13)C, delta(18)O, and (87)Sr/(86)Sr values (-6.9 aEuro degrees, +6.7aEuro degrees, and 0.70378 +/- 4, respectively). The aforementioned isotopic data show that magmatic fluid was supplied during all stages of mineral formation and interacted with marble and other rocks, changing its Sr, C, and O isotopic compositions. This confirms the earlier established redistribution of major elements and REE in the process of metasomatism. A contribution of meteoric and metamorphic water is often established in quartz from postore veins.