Myauchan Ore Field (Northeastern Asia), an Example of Weakly Eroded Ag–Pb–Zn Volcanoplutonic Mineralization

Abstract —The Myauchan ore field located in the Omsukchan zone of the Okhotsk–Chukotka Volcanic Belt is described. The Korennoe and Malyutka Ag–Pb–Zn ore occurrences forming this field are localized at the center of anticlinal fold of NW strike made up of Upper Triassic carbonate-terrigenous deposits intruded by stock-like bodies and dikes of Upper Cretaceous andesite, monzodiorite, granite-porphyry, and rhyolite-porphyry. Sulfide–carbonate–fluorite–quartz veins and vein–veinlet zones with arsenopyrite, pyrite, sphalerite, galena, chalcopyrite, and Ag-tetrahedrite are localized both in intrusions and in terrigenous strata. The field bears As–Sb–Ag–Pb–Au–Bi–Cu–Zn–W mineralization. Study of fluid inclusions and REE and ore element patterns show that the field ores formed from chloride solutions with the participation of surface waters in hydrothermal-magmatic system under epithermal conditions. The ores were deposited from solutions with TDS = 0.5–9.0 wt.% NaCl equiv. in the temperature range 106–287 ºC. The ores containing ca. 70 ppm Ag and up to 1.2% Pb formed through boiling-off of solutions enriched in iron salts. The ores with Ag < 7 ppm and Pb ≤ 25 ppm were generated from diluted hydrothermal solutions with predominant sodium salts and potassium admixture. Mineralization of the Myauchan ore field marks the upper level of the Ag–Pb–Zn ore system similar to the Gol’tsovoe deposit.