Petrology and geochemistry of alkaline lavas Holzun ore district of Gorny Altay

*Gusev A.I., **Gusev N.I.

*Biisky pedagogical state univercity, Biisk, Russia; Federal State Unitary Enterprise «A.P. Karpinsky Russian geological research institute», Saint Petersburg, Russia

Holzun apatite-magnetite with REE deposit  locate on the border of Republic Altay and Kaxahstan on the divide of rivers Haidun and Talovy Turgusun. The ore country rocks of Holzun deposit exhibit by volcanogenic-sedimentary Korgon suit  (D₁-₂ krg). The two sequences derive in composite of Holzun ore horizon: low sedimentary-volcanogenic with lavas and tuffs of trachytes, pantellerites, rhyolites, seldom trachyandesite and trachybasalt composites and upper volcanogenic-sedimentary with lavas and tuffs of middle-alkaline rhyolite composite with seldom comendites.

The ore horizon extend in ore district more 9 km and it located to more deflect of  Korgon trough that it is elongate on N-N-W direction on 70 km. An all  lavas on diagram TAS produce trend from phonotephrite to  trachyandesite,  trachyte, tracydacite and rhyolite, felsite and attribute to high- K suite (fig. 1).

Figure 1. Diagram (Na₂O+K₂O) – SiO₂ after (Peccerillo, Taylor, 1996) for lavas deposit Holzun

1- trachybasalt, 2- trachyandezibasalt, 3- trachyte, 4- tracydacite and trachyandesite, 5- felsite, 6- pantellerites, 7- comendite.

In lavas of deposit Holzun observe maximum of Rb, K₂O, Be, Nb, Ta and F and minimum of B, Pb, H₂O and S, that these characterize to mantle oceanic plumes. The model chondrit-normalized REE pattern show on figure 2.

Figure 2. Rare earth element patterns for rock types of Holzun areal Other legend on fig. 1.

The values of tetrad effect fractionation elements in all rocks for exclusion felsites (1, 12) are not reaching considerably level. The tetrad effect fractionation in ribbon felsites classify to M-type. As is known, tetrad-effect M-type detect in high evolutionary granitoid systems and volcanic series on late stages  of differentiation (Masuda, Ikeuchi, 1979). In consequence the mechanism of forming lavas Holzun deposit followed fractionation REE at the most acid lavas differentiates – ribbon felsites.

High-K lavas of deposit Holzun form close trend to line regress of  continental intraplate settings and mantle of cjntinental plums on diagram of ratio tantalium to niobium. (fig. 3).

Figure 3. Diagram ratio concentrations Ta – Nb for lavas deposit Holzun

Lines equations regression after (Kovalenko et al., 2007): I - for magmas MОR и DM (depleted mantle); II – for oceanic island and mantle oceanic plums; III – continental intraplate settings and mantle continental plums. Other

legend on fig.1.

Close position of trend for lavas Holzun observe and on diagram of ratio uranium to niobium. The principal distinct confine in appreciably more high concentrations of uranium in rocks of Holzun deposit and trend for rocks types is perpendicular to line of regress intraplate settings and mantle continental plums.

High-K lavas of Holzun form common trend from trachyte and trachyriodacite to felsites and comendite on diagram Th/Yb – Ta/Yb and confine in field intraplate mamgatism (fig. 4).  There are confined wholly in field of basalt association of archipelago Kergelen and partially in field of alkaline basalts and partially in field of  alkaline basalts of Baykal rift zone and gravitate to average composition alkaline basalts of oceanic islands (OIB).

Figure 4. Diagram Th/Yb – Ta/Yb for high-K lavas Holzun deposit.

Digital show fields of compositions: 1- tholeiites volcano Mauna Kea, Hawaii (Frey et al., 1991); 2- basalts association archipelago Kergelen; 3- alkali basalts of Baykal rift zone; 4- traps of Deccan and Parana (Wilson, 1989).

The ratio of isotopes 87Sr/86Sr и 143Nd/144Nd for volcanogenic rocks of Holzun areal adjust influence mantle source type PM in mantle array and evolution compositions to direction mantle source type EM 2, that it is typically interpret how result of enriching mantle reservoir by subduction continental sediments. The evolution of basalt magmatizm obey trends batch melting of mantle source type PM and influence subduction fluids with localization composites volcanic rocks near boundary of plums and nonplums sources.

References

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