Abstracts of International conference Geochemistry of magmatic rocks-2009 . School ซGeochemistry of Alkaline rocksป

š๓ollision granitoides and sienites of the Urals: Conditions of location, geochemical and metallogenic specializationš and practical significance

Sazonov V.N**^* ,Ogorodnikov V.N*^* Polenov Yu.A**

^* Institute of geology geochemistry, Urals branch of RAS, Ekaterinburg, Russia

^** Urals State Mining University, Ekaterinburg, Russia

ššš

ššššš A collision process in the Urals took place in two time interval: 375 – 320 and 320 – 240 Ma.

In early stage quartz diorite, granodiorites, adamellites and granites (Berezovsk, Kochkar, Aidirla, Verkh-Isetsk and others ore fields), specialized on Au, W, As at least measure Mo and fluid phase – on CO₂, F-Cl, S, were formed. In late stage were formed biotite (normal) granites, leucogranites (Murzinka-Aduy, Djabic, Adamov plutons and s.o.), specialized on rare metals and big spectrum of non metallic mineralizations (asbestos, talc, mica, quartz etc.) and fluid phase – on F; gabbro-granite-sienite complexes (Magnitogorsk ore region), specialized on Fe, at least measure Mo, Pb and fluid phase – on Cl – F; alkaline granites and sienites of theš Gumbeysky,

šStepnoy complexes and sienites of the Berzovsk gold field (Fershtater, 1987; Sazonov et al., 2007_1,2; Kholodnov, 2007).

In the Magnitogorsk gabbro-alkaline granite pluton there zones in vertical section are recognized: 1) upper alkaline granitic and sienitic, 2) transitional gabbro-granitic and 3) lower gabbroic. In the pluton’s origin the main role the main role took place intrachamber fractionation. We can see in a low pluton’s level skarns with magnetite mineralization, but in a upper level – a week Mo and Pb mineralization (Kholodnov, 2007). The chemical compositions of Magnitogorsk plutonites, a trend of distribution REE, Fe, Ti and Nb, Zr, P and some other elementsš in them are typical for continental rifts. According to (Sazonov et al., 2007₁), a substan’s source for formation rocks of the Magnitogorsk rifts was a boundary between mantle reservoirs EM1 and EM2. Position like this we can find in [Kholodnov, 2006] who consider that the rocks of the Magnitogorsk pluton are the result of inter action of mantle substance with slab’s pattern. In this situation it is stand clearly why gabbro of Magnitogorsk pluton specialized on Fe and Cl but alkaline granites and sienites on Mo, Pb and F-Cl.

ššššš The Gumbeisk alkaline complex. This complex include some massifs-stocks subalkaline group (boundary between C and P) which consist of sienite-diorite, sienite, quartz sienite, granosienite which controlled by diagonal fault – element of suture zone of a duplex character. The massif’s host rocks are volcanites and sedimentary formations (D₂). In the stocks there are two deposits and some manifestation of W (stockworcš and skarn nature). A mineralization besides W include Mo and Au (rare). Complex was formed with participation of mantle substance (Sazonov et al., 2007₁).

šššššš Granitiid massifsš of tonalite-granodiorite formation (I-type). They submitted batholiths or batholith like bodies and consist of tonalities and granodiorites (prevail), rare gabbro and gabbrodiorites (may be absence), adamellites and granites. Massifs are controlled by fault’s zones (they are duplexes often). In an endocontact of massifs there many henoliths including gabbroic. In big massifs we can find granitoid’s, diorites’ and lamprophiry’s dykes and products of hydrothermal activity. The last conclude quartz veins mainly. They fixed big (up to 1,5 km) shearing and breaking fractures. These veins are not productive. The productive ones are more younger, in them native gold and sulfides especially pyrite spread. I-type granitoids were formed thanks to earth crust and mantle substances.

šššššš Granite massifs of granite formation (S-type). These granites’ nature is crust. They were formed because silic substratš (gneissic block , R) was partly melting. F-type hydrothermal fluid was formed with such granites. Pegmatites and quartz veins were formed in connection with them. The main value of both formations are rare metals and granulate quartz. And may be mention emeralds and crystals.

šššš Sienite of the Stepnoy complex. Monzodiorites are the main rocks of this complex. Many dykes (granites, granosienites, sienites, sienodiorites) fixed in them. Construction? Composition and metallogeny specialization of these massifs and massifs of Gumbeyka complex (see above)š are analogous.

ššššš Alkaline rocks of the Berezovsk ore field. These rocks distinguished by M.B.Borodaevskaya (1951year) in the contact of collision granitoid-porphiry dykes with antigorite serpentinite. There following zonation wasš picket out: granite-porphiry – albite quartz-bearing sienite – albite sienite (without quartz) albitite – serpentinite. In formation of metasomatites a mantle fluid (T > 400 ^OC, P>2 kbar, specialization on Na, CI – F) and components of granitoids and serpentinites took place.š

ššššš Today metallogenic and geochemistry (including such volatile elements as F, Cl, CO₂, S) specializationš of complexes rocks of different geodynamic environments are known. So this caused a possibility to pick out in boundaries of structure-formation spots perspective on ore and non ore deposits. Besides a fluid specialization jf collision patterns is important criteria of magmatic specialization and potential ore-bearing. It pre-determine by: spot of melt’s generation (mantle, crust), nature of substrate and geodynamic regime. A fluid specializationš (F, Cl an example) is characteristic for all parts of ore-magmatic system – magmatites, ore bodies and associate metasomatites. Thas fluid specialization is a base for formation analyses of magmatites, associated metasomatites and metallogeny.

ššššššš The spots of localization granitoids’ both groupsš are: a) suture zones, b) zones crossing and conjugated of suture zones with the faults of NW (diagonal) orientation, c) the Main granite axis of the Urals (there are some massifs located in the W fromš the Main suture zones). In the Urals granitoid batholites are located in such domains where a deep to the basalt strata consist of 21,5 km and thickness of the last is 30,6 km.

ššššš There are mach dykes (from acidic to basic composition) in the Uralian granitoid batholits. Dykes’ composition pre-determined by poly step anatexis on the basite (gabbro) base and crystallization differentiationš (Gold…, 2001; Fershtater et al., 2007; Kholodnov, 2007). More late granitoids accompanied more acidic dyke complexes. This was a reason for the next relations which everyone can see in the Shartash granite batholite (Central Urals): pegmatites cross lamprophyres, from the one hand andš lamprophires cross pegmatiotes from the other hand. Polystages granite massifs and associated mineralization was forming in time from 60 to 100 Ma (Gold…, 2001; Fershtater et al., 2007).

šššš Early granitoides are specialized on Au and W (see Korobeynikov, Mironov, 1992; Gold…, 2001; Fershtater et al., 2007). As a rule, there is more gold in more basic granitoides. The dykes complexes more auric then hosted granitoides. Dykes complexes are considerate as a fluid leader (Korobeynikov, Mironov,š 1992; Gold…, 2001). In apogranitoid fluid relatives F: Cl: S (perhaps and CO₂) is such which quite enoughš for extraction of Au, but of extraction chalkhophile elements and Fe in these conditions is not going on (Kholodnov, 2007).šššššš Late collision granites specialized on F (instead of Cl) and rare metals, they are nonauriferous.

šššššš Mostš gold deposits of quartz-veined type conjugated with a bererzite-listvenite formation. Its metasomatites are forming at high active of CO_2, low concentration Clš and relatively nigh F in the fluid. During process ofš berezitization-listvenitization F concentrated in muscovite, so content of F in the fluid increase. Cl take part in a transport Au, evidence – appear of this element and its in the nuggets of gold.

ššššš Hydroxide minerals of late collision granites poor of Cl (0,0-0,05 Wt.%). But they rich of F: in apatites 4,0, in biotites 1,5 Wt.% and more (Koroteev, Sazonov, 2005). Contents of F and K, Be, Ta, Nb, Li, Rb, Cs in late collision granites are correlated. Active of F in an apogranite fluid essential pre-determine of composition of rare metal (Be, Ta, Nb, Li, Rb, Cs) and W and W-Mo mineralization.ššš

ššššš The collision process played a dual role in the Urals. On the one hand, it caused transformation in the previous ore associations (chromites, Fe-quartzites, sulfide ores of massive sulfide deposits and other), on the other hand, in was the reason of formation of different types ofš mineralizations in suture zones (antigorite serpentnites, talc and talc-carbonate metasovatites, berezites, listvenites with quartz veins with native gold, and goldbearing sulfides).šš

ššššš Thus fluid specialization of collision granitoides is important criteria of magmatic specialization and potential ore-bearing. It pre-determine by: spot of melt’s generation (mantle, crust), nature of substrate andš geodynamic regime. A fluid specializationš (F and Cl an example)

is characteristic for all parts of ore-magmatic system -š magmatites, ore bodies and associatešš metasomatites. Thus, fluid specialization is a base for formation analyses of magmatites, associated metasomatites and metallogeny (Korobeynikov, Mironov 1992; Koroteev, Sazonov, 2005; Gold…, 2001; Kholodnov, 2007).

References:

Gold deposits of the Urals / Sazonov V.N., Ogorodnikov V.N., Koroteev V.A., Polenov Ju.A. Ekaterinburg, 2001. 622 p (in Russian).

Fershtater G.B. Petrology of the main intrusive associations. Moscow: Nauka, 1987. 276 p (in Russian).

šFershtater G.B., Krasnobaev A.A., Bea F. et al. Stages of Paleozoic intrusive magmatism of the Urals orogen and their geodynamic interpretation // Geodynamics, magmatism, metamorphism and ore-forming. Ekaterinburg, 2007. P. 89-120 (in Russian).

Kholodnov V.V. Halogens (F, Cl) – indicators of specialization of granitoids tonalite-granodiorite formation on the gold-sulfide-quartz mineralization // The same. P. 857-884 (in Russian).

Korobeinikov A.F., Mironov A.G. Gold’s geochemistry in endogenic process and gold deposits’ conditions of formation. Novosibirsk: Nauka, 1992. 217 p.

Koroteev V.A., Sazonov V.N. Geodinamics, ore-formation, prognosis. Ekterinburg, 2005. 258 p (in Russian).

Sazonov V.N., Nedosekova I.L., Ogorodnikov V.N., Polenov Ju.A. Sienite and sienite-miaskite complexes of the Urals // Geodynamics, magmatism, metamorphism and ore-forming. Ekaterinburg, 2007₁. P. 216-243 (in Rassian).

Sazonov V.N., Ogorodnikov V.N., Velikanov A.Ya. Formation and industrial-genetic types of gold deposits of the Urals // The same, 2007₂. P. 715-728 (in Russian).