Skarn-greisen deposits of the lost river and mount ear ore field,Seward Peninsula,Alaska, United States

The boron, tin, tungsten, beryllium, and fluorite deposits of the York Range, Seward Peninsula, represent the continuation of the Asian segment of the Pacific ore belt and are globally conjugate with the Verkhoyan-Chukotka ore province of Northeastern Russia. They are localized in the alteration aureoles of dolomites and limestones of the Paleozoic Port Clarence Formation at the contact with the Mesozoic leucocratic granites and genetically belong to the magnesian-skan ore formation. Ore-generating process developed in marbles, skarns, and greisens under hypabyssal conditions in several stages and was accompanied by sequential formation of polymineral assemblages. Early mineralization is represented by magnetite in prograde pyroxene skarns after dolomites. Postmagmatic ore stage is represented by formation of endogenous borates, including their tin-bearing Mg-Fe species, in the magnesian skarns, superposition of calcareousskarn assemblages containing calcium borates, borosilicates, and scheelite, formation of cassiterite and wolrframite in the greisenized granites, and precipitation of sulfides, chrysoberyl, and fluorite. The mineral composition of the rocks and ores was formed under the influence of F-bearing hydrothermal solutions, which caused the presence of fluorine in borates, rock-forming silicates, and the replacement of calcite by fluorite. Boron, tin, beryllium, and fluorine participate at all the stages of endogenous process, but the mineral modes of their occurrence are varied, which is confirmed by data on their chemical composition. The results of studying the skarns and ores of the Alaska deposits are of great applied and scientific significance, and can be used for study of skarn-greisen deposits localized at the contacts of carbonate rocks with granite intrusions of the Pacific ore belt and other world’s regions.