ИСТИНА

We have studied tetrahedritess (ttss) from the Peschanka and Nakhodka porphyry Cu deposits, which are located in the western Chukchi Peninsula and related to the Early Cretaceous quartz monzodiorite porphyry. Ttss was found to replace copper and base-metal sulfides. The first type ttss replaces enargite, bornite and chalcopyrite. It is classified as tennantite (sb = Sb / (Sb + As) up to 0.05) with the high fe [Fetotal /(Fetotal + Zn)] value ranging from 0.65 to 1.0 and a high Cuexcess (up to 1.43 apfu). The second type ttss replaces sphalerite and overgrows galena. The fe and sb value ranges from 0.0 to 0.27 and from 0.04 to 1.0, respectively. Te bearing ttss (apfu Te) filling intersitces between grains of base-metal sulfides was identified. It has high Cuexcess (up to 1.08 apfu), with the sb and fe value 0.04-0.08 and 0.18-0.19, respectively. This ttss is classified as an intermediate member of the tennantite-goldfieldite series. Ttss of the porphyry Cu deposits replacing enargite and bornite typical HS minerals evolves from Fe-rich tennantite to Zn-rich tetrahedrite testifying to the increasing fH2S and decreasing temperature of crystallization. Ttss replacing base-metal sulfides typical IS minerals evolves from Zn-rich tennantite to Zn-rich tetrahedrite, indicating decreasing temperature of the hydrothermal fluid. Our data on the chemical composition of ttss at Peschanka and Nakhodka are consistent with literature. Trudu and Knittel (1998) referred Te-rich tetrahedritess to HS assemblage. At Peschanka and Nakhodka, Te-rich tennantite is associated with galena and sphalerite, which are typical of IS mineralization. The literature data (e.g. Knittel, 1989) indicates that tennantite-goldfieldite series is characteristic of epithermal mineralization at the porphyry copper deposits. At the same time, at the LS type epithermal deposits, Te-rich ttss belongs to the tetrahedrite-goldfieldite series. Thus, ttss at the porphyry Cu deposits shows 2 trends of evolution: from Cuexcess Fe-rich tennantite to Zn-rich tetrahedrite and from Zn-rich tennantite to Zn-rich tetrahedrite. Te-bearing ttss at the porphyry Cu deposits is an intermediate member of the tennantite-goldfieldite series found in both HS and IS assemblages, whereas at the LS-type deposits it is an intermediate member of the tetrahedrite-goldfieldite series. According to Silitoe and Hedenquist (2003), HS mineralization is always related to the porphyry system, IS type is related or not to the porphyry system, and LS type never relates to this system. Therefore, referring Te-bearing fahlores to different isomorphic series is a criterion to determine type of epithermal mineralization and subsequently relation to porphyry system.