ИСТИНА

The Kapelka prospect related to the Upper Cretaceous volcanic rocks of the Okhotsk-Chukotka Volcanic Belt is located in the central part of the large Pucheveem volcano-tectonic depression. Propylite, argillic rocks, and hydrothermal quartzite are predominant altered wall-rock, whereas potassium and phyllic (quartz-sericite) alterations are minor. The metasomatic zones reach 200-300 m in thickness. Propylite is composed of epidote, chlorite, potassium feldspar and quartz with minor sericite, albite, titanite, rutile and carbonate. Chlorite-smectite, montmorillonite, dickite, and quartz are the major minerals of argillic alteration; minor minerals are chlorite, sericite, adularia, carbonate, and fluorite. The temperature of formation of propylite and argillic rocks estimated from thermometer of Cathelineau (1988) is 330-365 and 110-300°С, respectively. The LS type of ore mineralization is predominant at the Kapelka prospect. Pyrite-arsenopyrite, base metal (galena, sphalerite, chalcopyrite, bornite) and gold-silver-sulfosalt (electrum, polybasite, pearceite, acantite and Zn-rich tetrahedrite and tennantite) assemblages are distinguished. Native silver, acantite, anilite, brochantite, anglesite, cerussite, malachite, azurite and wulfenite are resulted from supergene alteration of primary mineral assemblages. Native silver is related to the oxidized segregations of the polybasite-pearceite solid solution and is characterized by the low content of Cu and Au up to 0.3 and 0.2 wt %, respectively. The segregations of early sulfides are rimmed by acantite, anilite and coveline, which are resulted from enrichment in the cementation zone. The major carriers of Au and Ag at the prospect are electrum, polibasite and pearceite, while acantite, native silver and tetrahedritess are minor. The fineness of electrum (Au/(Au+Ag+Cu)*1000) ranges from 614 to 493. Cu is the most characteristic admixture in the minerals of the polybasite-pearceite series; its concentration in pearceite reaches 12 wt %. The Kapelka prospect is similar in mineralogy to the large Valunisty Au-Ag LS deposit in the eastern Chukchi Peninsula.