پترولوژی (Jan 2018)
Geochemical-metallogenic evolution of Agh-Daragh igneous rocks (north of Ahar) links to Cu-Au±W occurrences
Abstract
The Agh-Daragh study area in the north of Ahar is located in Ahar-Arasbaran zone. The area is distinguished by W, Cu and Au metal endowment and has been explored during stream sediment and heavy mineral exploration. At least, three mineral occurrences are detected in Agh-Daragh area including Cu stockwork-disseminated mineralization in Chupanlar (occurred in Omz quartz-monzonite), Cu-Au±W vein-type mineralization in Ayran Goli (occurred in Og granodiorite), and Fe±Cu skarn in Gowdal (occurred between quartz-monzonite unit and crystallized carbonate). Chemically, Agh-Daragh mineralization-related metaluminous granitoids belong to oxidized, I-type and high-K calc-alkaline to shoshonitic series. They have SiO2 = 63.5–67.6 wt%, Al2O3 = 14–16.5 wt%, and K2O/Na2O = 0.5–1.8. Moreover, LILE enrichment relative to HFSE depletion and HREE in the granitoids and the dikes occurred due to fluid-melt interaction, which are characteristics of subduction tectonic environment. In their magmatic evolution, the Agh-Daragh intrusive rocks underwent a transition from the early intrusive phases belonging to granodiorite (Og unit) with low K/Na and Fe2O3/FeO ratios and to the late intrusive phases belonging to quartz-monzonite (Omz unit) enriched in K (K/Na >1) and oxidized (Fe2O3/FeO >1). It seems that high content of volatiles in high-K and oxygenate magmas occurs due to saturation of magmatic melt in water under a lower degree of quartz-monzonite crystallization immediately preceding Cu-Au±W mineralization at Agh-Daragh intrusive suite. Combining our field geology and geochemical-metallogenic evidences, we conclude that the mineralization in Agh-Daragh area mostly occurred in accompany with late quartz-monzonite stocks; as a result, identification of high-K intrusive rocks and related dikes have important implications for proceeding exploration planning specially indicating of drilling points, and further refines the basis for mineral exploration in Sheyviar Dagh intrusive suite and subsequently in Ahar-Arasbaran metallogenic zone.
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