Early mesozoic carbonatites in folded formations of the Taimyr Peninsula

ISSN 1028�334X, Doklady Earth Sciences, 2010, Vol. 435, Part 2, pp. 1592–1595. © Pleiades Publishing, Ltd., 2010.Original Russian Text © O.V. Petrov, V.F. Proskurin, 2010, published in Doklady Akademii Nauk, 2010, Vol. 435, No. 6, pp. 776–779.

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A small�scale (1 : 1 000 000) and medium�scale(1 : 200 000) geological survey revealed a family ofinjection carbonatite bodies with gold�bearing cop�per–polymetallic sulfide and fluorite–barite mineral�ization in the western, central, and eastern areas of theTaimyr Peninsula (Fig. 1). Previously [2], these bodieswere defined as Devonian sedimentary rocks outcrop�ping in cores of anticlinal structures among Carbonif�erous–Permian terrigenous formations. In centralTaimyr, they were considered as injection carbonatitetectonites and high�temperature metasomatites [3, 7].

Three rock groups are recognized among carbon�atites: sedimentary carbonate rocks, fluidal–explosivecarbonate breccias, and carbonatites (intrusive, lava�like and vein–veinlet) [8].

The fluidal–explosive rocks are characterized bybreccia structures consisting of size�variable rock frag�ments, blocks included. Rock fragments in carbonatebreccia are cemented by the “fluid” carbonate mass ofseveral generations. In each subsequent generation,the preceding breccia occurs in the form of fragments.The youngest generation is healed by veinlets of fluo�rite–calcite and siderite compositions. There are alsocarbonate breccias with oval�shaped fragments ofaltered gabbro–dolerites and syenites. At the exocon�tact of carbonate breccias with Permian terrigenousrocks, thin carbonate injections form a system of retic�ulate–comb structures with altered “fused” flattenedunidirectional fragments (3–10 cm across) of silt�stones and shales.

Carbonatites display near�vertical tectonic andcrossing injection contacts, and their bodies, whichare a few tens to hundreds of meters across, are lentic�ular–elongated to rounded in shape and form beadedchains 50–60 km long. Some bodies (dike–vein stock�works) up to 2 km long alternate with small stocks and

necks (a few tens of meters in diameter) with injec�tions into host rocks). The exocontact zones of apicalparts of intrusive carbonatite bodies exhibit brecciatedmetadolerites saturated with albite–carbonate mate�rial. Metadolerite xenoliths ranging in size from a fewto >10–15 cm, sometimes up to 20 m, are angular�rounded in shape, with distinct crusts of contact trans�formations.

The intrusive and lavalike carbonatites are charac�terized by “saccharoidal” massive to, locally, fluidaland ataxite structures. Some rock varieties containlarge euhedral dolomite phenocrysts (1–5 cm across)in the fine�grained substantially calcite–dolomitegroundmass, which form the large�porphyric oligo�phyric texture of effusive rocks. Carbonatites are com�posed of dolomite, ferruginous dolomite, ankerite,and calcite accompanied by accessory periclase,hydrodolomite, apatite, monazite, sodalite, sphene,rutile, fluorite, zircon, baddeleytte, xenotime, cli�nochlore, cristobalite, sergeevite, and sassolite. Sili�cate minerals constitute 5–10% of the rock volumeand are represented by xenomorphic grains of albite,nepheline with embedded acicular aegerine crystals,arfedsonite, rare chrome spinelid, garnet, augite, andpigeonite. Another remarkable feature of carbonatitesis the presence of boron�bearing minerals (inyoite andberborite). Secondary alterations of carbonatites arereflected in the different recrystallization degree,deformations of different carbonatite generations, andwide development of exsolution and porphyroblastictextures.

The vein–veinlet carbonatites with sulfide mineral�ization are composed of calcite with Sr�bearing barite,subordinate Sb calcite, siderite, Fe–Ca carbonate ofintermediate composition, epidote, hematite, chlorite,alkali amphibole, and axinite. Ore minerals are repre�sented by pyrite, pyrrhotite, magnetite, hematite, goet�hite, maghemite, sphalerite, galenite, scheelite, chal�copyrite, subordinate cleiophane, arsenopyrite, gers�dorffite, cinnabar, and bornite. The pyrite contentlocally amounts to 30–40% up to the formation ofpure sulfide ores. Sphalerite mineralization is locally

Early Mesozoic Carbonatites in Folded Formations of the Taimyr Peninsula

O. V. Petrov and V. F. ProskurinPresented by Academician N.S. Bortnikov May 12, 2010

Received May 17, 2010

DOI: 10.1134/S1028334X10120081

Karpinskii All�Russia Research Institute of Geology (VSEGEI), Srednii pr. 74, St. Petersburg, 199106 Russiae�mail: vsgdir@vsegei.ru

GEOLOGY

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as high as 40%. Galenite and chalcopyrite occur assingle grains. Scheelite is developed in sphalerite alongfissures, in nests, and along crystal facets. Fluorite isusually represented by dark violet antozonite.

Sulfidized carbonatites contain the following ele�ments: Au 0.1–0.4 g/t; Ag up to 40 g/t; Hg 40 ppm;Pt 0.04 ppm; Pd 0.024 ppm; Pb 7.17%; Zn up to7.94%; Cu up to 0.39%; Ni 0.02%; Cd 0.03%, Ge >0.03%. The microprobe study of gold revealed its con�centrations in ore minerals (pyrite, pyrrhotite, Co andNi arsenides, sphalerite) ranging from 0.6 to 4.9 g/t.

The laboratory thermobarogeochemical investiga�tion of carbonatites at VSEGEI showed that withrespect to fluid inclusions they are distinctly divisibleinto primary sedimentary and magmatic varieties. It isestablished that carbonatites were formed from “boil�ing” fluids at temperatures of at least 420°C and underpressures of approximately 2.5 kbar. According to theSHRIMP–II local analysis of zircons, injection car�bonatite bodies were formed at the Middle–Late Tri�assic transition. The sedimentary carbonatites appearto contain only Precambrian detrital zircons. Themaximal chondrite C1�normalized REE concentra�tions are registered in intrusive and lavalike carbon�atites (Fig. 2). Crinoid limestones are characterized by

typical (for sediments) low REE concentrations. High87Sr/86Sr values (0.7072–0.7098) typical for sedimen�tary rocks indicate the significant contribution oforganogenic carbonate rocks to the formation ormigration of carbonatite magma.

The study of the carbon and oxygen isotope com�positions in carbonate rocks of different lithology andgenesis revealed the conditional evolutionary trend ofTaimyr carbonatites (Fig. 3). The latter may beexplained by (1) mixing of “crustal” carbonatites(fields 2 and 3 correspond to isotope ratios character�istic of carbonatite massifs in folded regions that wereformed from the enriched mantle EM�2 owing torecycling of upper continental crust material in sub�duction zones [1]) with sedimentary carbonate rocksduring upward magma migration and (2) by fluid–metamorphic transformation of sedimentary carbon�ate rocks under high pressures and temperatures, for�mation of fluid–explosive breccias and intrusions, andformation of lavalike “near�surface” carbonatites dur�ing further magma movement. The exotic field of thetrend of carbonatite (6) attributed to the lavalike varietyis, probably, explained by mixing of the erupted carbon�atite magma with the methane (with isotopically lightcarbon) fluid, which could originate from carbonates

Fig. 1. Schematic location of injection carbonatite bodies in the Taimyr province. (1) Carbonatite massifs; (2) distribution areasof carbonatite massifs and their numbers: (1) East Taimyr, (2) Central Taimyr, (3) West Taimyr; (3) Late Hercynian–Early Cim�merian fold–thrust zones: South Byrranga (SB) with upper Paleozoic–Lower Mesozoic (a) and North Byrranga (NB) withLower–Middle Paleozoic (b) formations; (4) North Kara Early–Late Hercynian heterogeneous uplift with Proterozoic andLower to Middle Paleozoic formations; (5) principal faults: proven (a) and hypothetical (b): Main Taimyr (MT), Diabazovyi(DZ), Pyasino–Faddeevskii (PF), Pogranichnyi (P), Central Taimyr (CT).

78° 96° 114°

76°

74°

108°96°84°240 km16060400

1 2 3 4 51

1

2

3

76°

74°

PF

MT

CT

PF

MT

DZ

P

P

KARA SEA

Yenisei–Khatanga

Trough

SB

NB

SB

NB

CTa b ab

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PETROV, PROSKURIN

1

La0.1

Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

12345

10

100

1000Rock/Chondrite C1

Fig. 2. REE distribution spectra in carbonates from carbonatite rocks of the Eastern Taimyr Peninsula normalized to chondriteC1. Carbonatites: (1) intrusive, (2) lavalike, (3) vein–veinlet, (4) carbonate breccias, (5) limestones.

–40

50 10 15 20 25 30 35δ

18O (SMOW)

–45

–35

–30

–25

–20

–15

–10

–5

0

5

1

23

4

5

1

7 23

8

4

6

5

δ13C (PDB)

Isotopicfractionation

Assumed evolutionary trendof Taimyr carbonate rocks

Mixingwith low�temperature

water fluid

Trends of mixingwith methanogenic

carbonates

Fig. 3. Carbon and oxygen isotope compositions in carbonates from carbonatite rocks of the Eastern Taimyr Peninsula. (1–5)see Fig. 2. Composition fields after [1, 5, 6, 10]: (1) rare metal carbonatites, (2) “crustal” carbonatites, (3) altered sedimentaryrocks, (4) sedimentary carbonatites, (5) magmatogenic and soil carbonates, (6) carbonate with the exotic isotope compositionfrom the Taimyr Peninsula, (7, 8) sodium carbonatites from Ol Doinyo Lengai Volcano, Tanzania: (7) unaltered carbonates fromlavas, (8) altered carbonates from lava.

similar to their soil varieties, biomass, or carbonatesdeveloping on the sea bottom in areas of the present�day discharge of fluids with biogenic methane [9].

The mineralogical and isotopic–geochemicalproperties of injection carbonatite bodies from the

western, central, and eastern Taimyr Peninsula, the Sr,Ba, C, and O concentrations included, imply theirformation owing to melting of the sedimentary car�bonate substrate. According to schematic zonality in[4], Taimyr carbonatites occupy the highest position

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corresponding to syenite rocks with various carbon�atites of late formation stages with gold�bearing, chal�copyrite–pyrite, galenite–sphalerite, hematite–sid�erite, and fluorite–barite mineralization.

ACKNOWLEDGMENTS

This work was supported by the Federal Agency forManagement of Mineral Resources of the RussianFederation (state contacts no. 2 of September 30,2004, and no. 44 of March 30, 2006).

REFERENCES

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