Abstract-The metallogenic aspects, tectonic setting, magmatism, structure, and composition of Au-and Ag-bearing porphyry copper deposits in the Buchim-Damjan-Borov Dol ore district and their genetic fea tures are considered and compared with earlier published data. Special attention is paid to supergene gold in heavy concentrate halos of the Borov Dol deposit. The total Cu reserves ofthe deposits discussed in this paper do not exceed 150 kt. The Buchim deposit likely is the world's smallest deposit of this type currently involved in mining. A comprehensive study ofthese dwarf porphyry copper deposits is undertaken to answer questions on the conditions of their formation . How do they differ from formation conditions of giant deposits?
The Okhotsk-Chukotka volcanic belt (OChVB) formed over 25 Ma from the middle Albian to the Cenomanian at the boundary of the continental Verkhoyansk-Chukotka and the Koryak-Kamchatka collages of terranes as a special tectonic unit of the Earth's crust composed of subaerial volcanic rocks extending for 3000 km. In regard to the oceanic margin, the inner, outer, and flank zones of the OChVB have been recognized. The complex structure of terranes in the basement and the OChVB itself resulted in the formation of diverse epithermal deposits. Porphyry copper-molybdenum deposits are concentrated in the inner zone. The outer zone is characterized by gold-silver ore mineralization and a variety of tin deposits. Silver-base-metal deposits (Dukat, Lunny, Arylakh, etc.) are confined to the rift-related volcanic trough that complicates the OChVB between the Yana-Kolyma and Omolon terranes.
The Shkol'noe deposit is localized in a small granitoid stock, the root portion of which is traced using geophysical data to a depth of 5-8 km. The high grade gold ore (33 gpt Au) is enriched in silver and principally differs in ore composition from the previously studied mesothermal gold-quartz and epithermal gold-silver deposits in the Russian Northeast. The main reserves of the Shkol'noe deposit concentrate in bonanzas (20% of the total volume of orebodies). The internal deformation is related to the rearrangement of matter in freibergite; exsolution structures in fahlore and native gold are related to postmineral metamor phism. It is suggested that the ore of the Shkol'noe deposit occupies a transitional position between porphyry type and epithermal levels of ore deposition.
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