Porphyry-epithermal Cu-Mo-Au–Ag mineralization in the Nakhodka ore field, Baimka Trend, Chukotka, Russia: a geological, mineralogical, and geochemical perspectiveстатья
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Аннотация:The Nakhodka ore field (NOF) is situated in the Baimka Trend, Chukotka, Russia, and comprises the Vesenny epithermalAu–Ag, and Malysh, Nakhodka, Vesenny III, and Pryamoy porphyry Cu-Au±Mo deposits. Porphyry and epithermal mineralization of the NOF are hosted by Early Cretaceous diorite and monzonite intrusions, which are dated at 139–141 Ma(U–Pb zircon). The NOF mineralization is structurally controlled. The prevailing stress field during the evolution in theBaimka dextral shear zone (also known as Baimka Trend) has led to the formation of extensional and strike-slip structuresthat control distinct zones with strong quartz-sericite alteration and sheeted high-grade quartz–sulfide veining; characteristics that are similar to the world-class Peschanka porphyry Cu-Au deposit located about 20 km to the NW of the NOF.Four types of hydrothermal alteration are documented in the NOF: (1) potassic, (2) propylitic, (3) quartz-sericite, and morerarely (4) argillic. Two phases of porphyry-style mineralization are distinguished: (1) early-stage quartz-magnetite veiningassociated with potassic alteration and (2) sheeted quartz-sulfide (bornite, chalcopyrite, molybdenite, pyrite) veining thatis spatially associated with a strong quartz-sericite alteration assemblage. Epithermal Au–Ag mineralization belongs to theintermediate-sulfidation type and consists of gold-bearing polymetallic quartz-dolomite±rhodochrosite veins and veinlets.The NOF is defined by a distinct geochemical zonation. Geophysical data show that the high-grade stockwork zones atthe Vesenny III porphyry Cu-Au deposit are defined by pronounced magnetic anomalies reflecting abundant hydrothermalmagnetite veining, while the Vesenny epithermal Au–Ag deposit is defined by a strong negative magnetic anomaly due tostrong silicification and magnetite-destructive quartz-sericite to argillic alteration.