THE DUKAT GOLD-SILVER DEPOSIT, RUSSIA

The Dukat gold-silver deposit is located within the continental margin Okhotsk-Chukot volcano-genic belt, northeastern Russia. The ore field represents a long-developing volcano-intrusive cupola structure that is composed of rock associations of the following ages: (1) late Trias sic gray marine terrigene molasse (Verkhoyan complex); (2) early Creta ceous rhyolite association; (3) coal-bearing molasse; (4) early - late Cretaceous andesite; (5) diorite-granodiorite associations; (6) late Cretaceous rhyolite and leucogranite; and (7) Paleogene basalt associa tions. The cupola incorporates a large subvolcanic body surrounded by sheets and smaller satellite subvolcanic and neck bodies. At the deepe r levels, the structure is revealed by the gravimetric anomaly as a gr anitoid massif uplift. The volcano-intrusive cupola is crosscut by a s eries of northeastern and subordinate northwestern echelon faults. The deposit is represented as submeridional and northwestern ore zones an d veins that are concentrated in the northern segment of the ore field . Rhyolites of the volcano-cupola structure at the deposit plunge unde r the overlying coaly pelite rocks. The deposit is confined of a tecto nic block restricted by northeastern and northwestern faults. The intr icate ore zones consist of one or several brecciated veins within a st ringer-disseminated mineralization halo. These ore veins belong to the open cavity-filling type. Hydrothermal-metasomatic alterations are re gistered by preore chlorite-hydromica-quartz, syn-ore adular- and albi te-bearing, and postore skarnoid assemblages. Ore bodies formed as a r esult of successive deposition of the following mineral assemblages: q uartz-chlorite, quartz-sulfides, quartz-chlorite-adular, quartz-rhodon ite, comb-textured and drusy amethyst-type quartz, quartz-tourmaline, sulfide-tourmaline, sulfide-chlorite, and coarse quartz-chlorite. The Au : Ag ratio in the productive quartz-chlorite-adular and quartz-rhod onite assemblages is 1 : 340 and 1 : 550, respectively. Major ore mine rals are acanthite, kustelite, electrum, and native silver. Supergene processes led to the development of a wide spectrum of oxidation zone minerals, as well as the neomorphs of acanthite and supergenous silver . The mineralization belongs to a shallow (0.5 - 1 lan) type, but it i s characterized by relatively high temperatures (320 - 450 degrees C) and arejuvenation of the ore process. In general, the mineralization i s paragenetically associated with the ultrapotassic rhyolite-granite c omplex that is characterized by a successive replacement of the volcan ic and plutonic phases within the long-developing central volcano-intr usive cupola structure.