THE UDOKAN-CHINEY ORE-MAGMANIC SYSTEM

IN THE NORTHTRANSBAIKALIA, SIBERIA, RUSSIA

Gongalsky Bronislav¹ (gon@igem.ru)), Krivolutskaya Nadezhda² (nakriv@mail.ru)

¹ Institute of Geology of Ore Deposits, Russian Academy of Sciences, Moscow, Russia

² Vernadsky Institute of Geochemistry and Analytical Chemistry, RAS, Moscow, Russia

 

The North Transbaikalia is a unique ore region containing extra large deposits of different metals and genetic types. Copper deposits of different scale representing the most importance unique including the Udokan deposit of copper sandstones, a lot of satellite deposits of the same type around it (the Sakinsky, the Pravoingamakitsky, the Unkur etc.) and the Chiney copper magmatic deposit with noble metals. They all were formed during Early Proterozoic epoch which was very productive in terms of Cu. For the first time magmatic, hydrothermal and sedimentary copper ores in the North Transbaikalia are regarded as different parts of common the Udokan-Chiney ore-magmatic system. But up to now the relationships and origin of numerous deposits and ore manifestations are not yet established. The Udokan deposit of copper sandstones is situated ═in the central part of the ore region. It is framed by the croppingouts of the gabbroides of the Chiney, the Mylove, the Luktur massifs, the Main Dyke of Udokan and small bodies with copper (essentially chalcopyrite) of sulfide ores, enriched in noble metals.═ Inside the intermediate zone (between the Udokan sedimentary and the Chiney magmatic deposits), numerous ore manifestations and deposits having signs of the both genetic types are situated. Firstly, the Pravoingamakitsky, the Unkur and the Sakinsky deposits belong to this group. All these deposits have very close chemical (Cu, Ag, Au) and mineralogical (bornite-chalcocite and chalcopyrite) composition.

Sulfide ores located in different heteroabyssal blocks of lithosphere represent═ parts of a common ore-magmatic system. They are a result of fractional crystallization of basic-ultrabasic melts. There were consecutively formed the following types: magmatic ores in inner parts of layered intrusions, magmato-hydrothermal ores in exocontacts of massifs, hydrothermal═ and═ hydrothermal-sedimentary ones in sandstones. Hydrothermal fluids play very important role in the origin of copper ores in the Kodaro-Udokan region. Copper precipitated from fluids in submarine conditions in the Udokan═ deposit. This observation is not in contrast with the sedimantary genesis of the deposit. ══

 

Introduction. The North Transbaikalia is a unique ore region containing extra large deposits of different metals and genetic types concentrated within very small area (1500═ km²). They are the Katugin rare elements metasomatic deposit, the Sulumat ferriginous quartzite deposit, the Golevskoe synnyrite ═deposit etc. Especially copper deposits of different scale represent the most importance: the unique Udokan deposit of copper sandstones and a lot of satellite deposits of this type around it (the Sakinsky, the Pravoingamakitsky, the Unkur etc.) and so the Chiney copper magmatic deposit with noble metals and extra large reserves of Fe-Ti-V ores. They were all formed during Early Proterozoic epoch which was very productive in terms of Cu. But up to now the relationships and origin of numerous deposits and ore manifestations are not yet established. A question about genetic relations between different types of copper deposits is not very important for theory, but for practice. It helps finding new perspective ore objects.═

Geological background. ══For the first time magmatic, hydrothermal and sedimentary copper ores in the North Transbaikalia are regarded as different parts of common the Udokan-Chiney ore-magmatic system. Many kilometers of country-rock displacements along the deep faults exposed to heterogeneous components of this system that allowed to study these different fragments.════════

On the modern surface the Udokan deposit of copper sandstones is eposed within transaction zone of two cycle structures (Kemenskaya and Ingamakitskaya) fixed by geophysical data and results of interpretation (Gongalsky, Krivolutskaya, 2004). It is situated ═in the central part of the region. It is framed by the cropping outs of the gabbroides of the Chiney, the Mylove, the Luktur massifs, the Main Dyke of Udokan and small bodies with copper (especially chalcopyrite) of sulfide ores, enriched in noble metals.═ Inside the intermediate zone (between the Udokan sedimentary and the Chiney magmatic deposits), numerous ore manifestations and deposits having signs of the both genetic types are situated.

Firstly, the Pravoingamakitsky, the Unkur and the Sakinsky deposits belong to this group.

 

 

Fig.1. Schematic geological map of the the Kodaro-Udokan region:═ 1) Quaternary deposits; 2) volcanic rocks ( N-Q ); 3) sedimentary Vend-Cambrian deposits; 4) Lower Proterozoic carbonate-terrigenous rocks of the Udokan seria;═ 5) granite, Ingamakitsky complex; 6) gabbro, Chiney complex═ (massifs: 1-Chiney, 2 √Mylove, 3 √ Luktur); 7) granite, Kodarsky complex;═ 8)═ granite, Kuandinsky complex ;═ 9) Main Dyke of the Udokan deposit;═ ═10) Cu sandstone horizon in the Udokan deposit; 11) faults; 12) deposits: 1- Pravoingamakitskoe, 2 - Sakinskoe, 3 -Klukvennoe, 4 -Unkur, 5 -Krasnoe, 6 -Magnitnoe, 7-Etyrko, 8 -Rudnoe, 9 -Kontaktovoe, 10 -Skvoznoe; 13) railway station.

The authors have studied geological structure, mineralogical and chemical composition of copper ores of different genetic types. The Udokan and the Chiney deposits are characterized here briefly because they had been discribed (Arkhangelskaya et al., 2004; Gongalsky, Krivolutskaya, 1993). The main attention will be paid to, where such features of typical hydrothermal origin are found at the first time.

The Udokan deposit is located in the same-named overturned syncline (fig.1), 8 x 12 km, stretched along west-north-west direction. Ore horizon is of 350 m thickness and consists of disseminated and massive bornite-chalcocite bodies shaped in bands and lens among sandstones. All mineralogical types of ores have copper composition with Ag admixture (0.8 ppm). Parallel with the concordant position there are echelon-like small chalcocite-bornite and chalcopyrite lens and veins perpendicular to sedimantary rock stratification (fig.4). High Au concentrations have been discovered: in intersecting veinlets √ up to 0.3 ppm, in subconformable veins √ up to 0.1 ppm and in ore-free sandstones √ 0.03 ppm.

The main components of the Udokano-Chiney ore-magmatic system are mafic-ultramafic rocks of the chiney complex, including the Chiney, the Luktur and the Mylove massifs and subvolcanic rocks.

═(fig.1).The Mylove massif is situated nearby the Udokan deposit and the Chiney massif. It comprises some croppingouts of gabbro along the contact of the Lurbun granitic pluton and in the deep cuttings of rivers in its central parts. The Lurbun pluton brakes the rocks of the Chiney massif on the west dividing the existing earlier one large basic-ultrabasic pluton. Gabbro-diabas dykes including the Main Dyke of the the Udokan deposit (250 m ═thickness) are formed with massifs of one volcano-plutonic system. ═Comagmatic nature of all these bodies is determined by similarity of its rocks compositions and resembles distributions of rare-earths elements (fig.2). Sulfide and titanomagnetite mineralization are typical of all these rocks. Sulfide ores have almost pure copper composition. Main trace elements are Ag, Au, PGE. Ores consist mainly of chalcopyrite; rarely they are represented by chalcopyrite- pyrite variety.

The most important deposits are connected to the Chiney anorthosite-gabbronorite massif which value confronts with the one of the Udokan deposit. Internal structure of the Chiney massif is described in the following publications (Geological structure ┘, 2002; ═Gongalsky, Krivolutskaya, 1993). Three groups of rocks take part in its forming. Magmatic breccia with lamprophiric and gabbronorite cement finished are represent the last period of ═massif formation. They are closely associated with endo- and exocontact sulfide ores.

пХЯ. 2. Distribution of rare-earth elements in the rocks of the Chiney═ (1,2,3,5,6), Mylove (4)

and Luktur massifs══ (7) and Main Dyke of the Udokan (8)

Disseminated chalcopyrite-pirrotite ores dominate in endocontact of the massif. In contrast, the disseminated and veinlet ores are located in the exocontact, they are represented by chalcopyrite and bornite verities. Exocontact ores occur in sandstones and represent transitional type between essentially magmatic to sedimentary ones: parallel with chalcopyrite they are composed of chalcocite, millerite, PGE minerals.

The Chiney massif contains copper deposits: the Contaktovoe, the Skvoznoe, the Rudnoe located inside the contact zone of massif with surrounding terrigenous rocks.

The most part of satellite deposits of the Udokan located in the sedimentary rocks differ from this extra large deposit by essentially chalcopyrite ore composition and high Ag concentrations.

The Pravoingamakitsky deposit is one of the examples of hydrothermal type of deposits in the the Udokan-Chiney ore-magmatic system. There were found veins and breccia bodies with thickness up to 3 m and longitude with 5-7 m on the area of 2 km². They consist of pyrite-chalcopyrite ores which cement quarts fractions and sandstones. ═The limp of ore comprises of up to 370 ppm Ag, 1.2 - Au, 0.8 - Pd, 0.2 - Pt ppm.═ There are many rare minerals in veins likewise millerite (Ni_0.98Fe_0.03)_1.01S_0..99; pentlandite (Ni_5.69Fe_3.32)_9.01S_7.99; hessite Ag_1.98Te_1.02; clausthalite Pb_1.00(Se_0.78-0.85S_0.15-0.22)_1.0 and other Ag, Ni, Pb minerals of sulphosalt═ group.

 

Fig. 4. 1,2) Echelon-like position of ═chalcosine- bornite veinlets in the Udokan deposit 1) territory Zaozerny; 2) territory Zapadny, adit 9; 3,4) quartz √ pyrite - chalcopyrite of═ the ═Pravoingamakit deposit; 5) chalcopyrite lens of the Rudny deposit

Conclusions. Sulfide ores located in different heteroabyssal blocks of lithosphere represent═ parts of a common ore-magmatic system. They are a result of fractional crystallization of basic-ultrabasic melts. There were consecutively formed the following types: magmatic ores in inner parts of layered intrusions, magmato-hydrothermal ores in exocontacts of massifs, hydrothermal═ and═ hydrothermal-sedimentary ones in sandstones. Hydrothermal fluids played very important role in the origin of copper ores in the Kodaro-Udokan region. Copper precipitated from fluids in submarine conditions in the Udokan═ deposit. This observation is not in contrast with the sedimantary genesis of the deposit. ══

References

Archangelskaya V.V., Bykov═ Yu.V. Volodin R.N. et al. Copper Udokan and rare metals Katuginsky deposits in the Chita region, Russia. Chita. 2004. 520 p. (in Russian).

Geological structure and commercial minerals of the Chita region, BAM. Chita. 2002. 63 p. (in Russian).

Gongalsky B.I., Krivolutskaya N.A. Chiney layered pluton. Novosibirsk. Nauka., 1993. 184 p. (in Russian).

Gongalsky B.I., Krivolutskaya N.A. Unique copper metallogenic province of the North Transbaikalia (Siberia, Russia) // Metallogeny of the pacific Northwest: Tectonic, Magmatism and Metallogeny of active continental margins. Vladivostok, Dalnauka. 2004. P.443 √ 446.