Cherkashov, G. A.

Ivanova, A. M.

Smirnov, A. N.

Ushakov, V. I.

English

Electronic Publication Information Center

Polarforschung 69, 163 - 167, 1999 (erschienen 2001)Placer Minerals of the Russian Arctic Shelf.By Anastasiya M. Ivanova', Vadim 1. Ushakov', Georgy A. Cherkashov' and Alexander N. Smirnov'THEME 10: Metallogenetie Provinees in the Circum-ArcticRegionSummary: Placer concentrations of tin, gold, diamonds, amber and otherminerals form an important part in the mineral resource potential of theRussian Arctic shelves. These concentrations occur within the nine majorzones which include 20 smaller regions differing in the type of placer mine-rals. Of primary interest are the gold and tin placers. More than 30 goldplacers have been discovered at the Bol'shevik Island (Severnaya Zemlya) andon the northern Taymyr Peninsula. Placer concentrations of tin minerals aretraced from the Malyi and Bol'shoi Lyakhov Islands (New Siberian Islands) tothe mainland. The Lyakhov region is unique in the scope of tin resources; 13placers of cassiterite were reported both from onshore and offshore.The East Siberian-Chukchi bimetal zone includes the major Chaun tin-bearingregion and the Val'karai region is known for a combination of tin placers inthe Cape Billings area and a unique placer gold occurrence at Ryveem.PIacer concentrations of titanium, iron and rare earth elements, as weil aspIacer shows of diamonds occur around the periphery of the White andBarents Seas.The coastal areas of West and East Siberia are considered to be prospective inrespect of amber placers; in some areas there are significant accumulations offossil ivory.The Cenozoic paleoenvironments on the Arctic continental margin were onthe whole quite favorable for the formation and conservation of sizable placerconcentrations of valuable minerals. Long duration (since Eocene to Recent)and low sedimentation rates along with relatively stable tectonic environ-ments, multiple alternations of transgressive and regressive cycles facilitatedthe formation of major and unique placers with polygenetic productive hori-zons.VNIIOkeangeologia has developed and currently operates the data base whichcontains characteristics of 500 placer concentrations located in the Arctic;they are classified according to their dimension and mineralogy.GENERAL DESCRIPTION AND REGIONALDISTRIBUTIONThe shelves of the Aretie seas within the Russian Federationextend from the Kola to the Chukehi Peninsula for a distaneeof more than 8000 km. The geology of the margins representsthe alternation of aneient pre-Cambrian massifs with Paleo-zoic-Mesozoic fold and aetivation zones with vast gentledepressions (littoral lowlands) involving Mesozoic-Cenozoicsedimentary eomplexes. The latter form offshore a thiek coverwithin marginal-continental basins. Different mineral re-sourees; coal, oil, gas and eondensate, phosphorites are accu-mulated in the sedimentary cover, with plaeers of differentminerals in its upper part.Minerogenie zoning has allowed, as applied to plaeers, to, All-Russia Research Institute for Geology and Mineral Resourees ofthe World Oeean(VNIIOkeangeologia), 1 Anglisky pr., I, 190121 SI. Petersburg, Russia.Manuseript reeeived 13 Oetober 1999, aeeepted 15 May 2001diseern several taxonomie units. A large unit, a placer zone, islinear or ring-wise in plan with the area of several ten thou-sands km", Placer areas involved in the zone are slightlyelongated (or close to isometrie) with an area of several thou-sands of km2 (loeally up to 10000-15000 km-), Loeal units,placer clusters (l00-1000 km', loeally up to 2000-3000 km'),eontain eertain plaeers or, more often, their groups. Smallerareas of plaeer mineralization loeated within the areas andzones present a poorly studied unit. Plaeer clusters and smallerareas are monomineralie, while plaeer areas ean be eithermonomineralie or eontaining two or three kinds of minerals.Prineiples and proeedures of minerogenie zoning of shelfareas were developed, in ease of plaeers, in the All RussiaResearch Institute for Geology and Mineral Resourees of theWorld Oeean (VNIIOkeangeologia; 1980-1985) as a basis foreompiling different-scale maps, estimating mineral resoureesand developing data base.Nine plaeer zones with different minerals are located along theshelf zone of the Russian Aretie (Fig.l). These zones are:Severnaya Zemlya and Kara gold-bearing, East Laptev tin-bearing, East Siberian-Chukchi and Chukchi-Anadyr bimetal(tin and gold), South Laptev gold- and diamond-bearing, andthree zones in the western sector of the Aretie, speeialized fordiamonds, minerals of titanium, iron, zireonium and rare earthelements (IVANOVA et al. 1998), Of primary interest are thegold and tin plaeers.Gold placersAlong the shoreline of the Taimyr Peninsula, on SevernayaZemlya and the adjaeent shelf, there are the following gold-bearing areas (GRAMBERG & USHAKOV 2000): BolshevikIsland, Chelyuskin and North Taimyr included into theTaimyr-Severnaya Zemlya gold-bearing provinee (SevernayaZemlya and Kara plaeer zones). Clusters with plaeer mineralsare prominent within these areas. There are formations in-cluding alluvial Pleistocene-Holocene near-surface plaeers(dominating on Bolshevik Island) and those eontaining littoralor polygenetie produetive beds ranging in age from Oligoeeneto Holoeene. The latter are most eommon in clusters of theChelyuskin area where gold plaeers oeeur in vast paleodepres-sions (Fig. 2). Gold-bearing beds of high thiekness and lengthare buried beneath the cover of soft sediments 5-10 to 50-60 mthiek. The underlying waste mantle and Mesozoie conglo-merates are also gold-bearing, The near-surface Pleistoeenegold-bearing horizons are extended along the seafloor.An unique Ryveem cluster of the Valkarai area near the EastSiberian Sea shoreline is eharaeterized by a combination oftwo types of gold plaeers (alluvial plaeers normal to the163ARe T C o C E A NA _ B • EFig. 1: Distribution of placers and some other deposits in Russian Arctic.A: placer areas, 1-4: minerals of Ti, Fe, Zr, REE and diamonds, I: Tersk - Kandalaksha, 2: Onega, 3: Kuloi, 4: Kanin - Timan; 5-9: gold, 5: North Taimyr, 6:Chelyuskin, 7: Bol'shevik Island; 8-9: gold and diamonds, 8: Anabar - Khatanga, 9: Ust' Lena; 10-13: tin, 10: Lyakhov, 11: Chokurdakh - Svyatoi Nos, 12:Prikolym-Rauchuan, 13: Chaun; 14: tin and gold - Valkarai; 15-16: gold, 15: WrangeIlsland, 16: Amguem-Vankarem; 17: gold and tin - East Chukchi.B - Novaya Zemlya deposits, I & 3: manganese, I: Sul'rneneva, 3: Rogachev - Tainin; 2: polymetals - Bezymyannyi and Pavlov. C: onshore diamond deposits inArkhangel'sk region. D: area offossil ivory accumulations. E: shelf zonepresent shoreline and littoral placers striking concordant withancient and recent beaches). The gold placers are of a verywide age range (Eocene to Holocene) there, being commonlyburied beneath the cover of loose deposits up to 40-50 m thick.Gold dispersion haloes occur in Pleistocene-Holocene sedi-ments at the seafloor of the De Long Strait (northern flank ofRyveem Cluster). The placers are associated with primarysources (ore showings) and ancient (late Cretaceous - Danian)waste mantle. Similar features in distribution and formation ofplacers are most likely typical of the Chelyuskin gold-bearingarea, where discovery of large formations is expected.Wrangel Island shows certain prospects for placer gold, butgeological exploration at the territory of its national reserve isprohibited. Deep-seated gold placers are typical of littorallowlands in the Amguem-Vankarem area.Tin placersTin placers are associated with the East Arctic margins of theEurasian continent and with the adjacent shelf. The EastLaptev placer zone involving two areas extends along theboundary between the Laptev and East Siberian seas (DORO-FEEV et al. 1999). The Lyakhov placer area (Bolshoi and MalyiLyakhov Islands of New Siberian Islands, in Eterikan Strait) isunique in its scope of tin reserves. Thirteen p1acer formations164are known there, three of them are large and two are mediumin size. Productive polygenetic horizons of great thicknessvary in age from Eocene-Oligocene to Holocene and arecommonly buried (Fig. 3). Three placer formations lie on theseafloor. A submarine Chokurdakh cassiterite placer (Vari'kinaBay in Laptev Sea) with a thick Miocene-Holocene productivebed is located in the same Chokurdakh-Svyatoi Nos area.The Chaun area is the second largest tin-bearing district, Itstretches along the shoreline and on the seafloor of the ChaunBay and is part of the East Siberian-Chukchi placer zone. Fivemainly submarine placers with the Miocene-Holocene produc-tive horizons have been discovered there. Small cassiteriteplacers and gold placer shows are known further east nearIchatka and Billings Capes (Prikolym-Rauchuan area). Showsof placer gold and cassiterite are common in the East Chukchiarea, easternmost part of the region.Diamond placersThe shoreline and littoral zones of the Arctic seas show realprospects for placer diamonds. Within the Kola-Belomorsk-Tyman zone, placer shows of diamonds and dispersion haloesof associated minerals are closely related to primary sources.These sources are diamond-bearing kimberlite bodies in theFig. 2: Gold placers of Bol'shevik Island. 1: tectonic scarps along Mesozoic-Cenozoic riftogenic structures; 2: graben valleys; 3: abrasion scarps; 4:showings of gold; 5: gold placersMalyi LyakhovIsland. .1 ~~-,B~ol~'s=h~oiLyakhov· •I-----J[;-----Island-----:;..;::...a,.-=------:-'I....:.-=t"'-a bC§tFig. 3: Tin plaeers of Bol'shoi Lyakhov Island. Ia: uplifted blocks of aneient denudation relief, 1b: aneient compensated basins; 2: remnant highs; 3: loeallow-amplitude uplifts; 4: struetural-teetonie scarps of arehed-bloeky uplifts; 5: erosion-teetonic depressions; 6: boundaries of plaeer clusters: NL: North Lyakhov,WL: West Lyakhov; 7a: polygenie placers, 7b: littoral plaeers, 7e: alluvial placers; 8: shore line.165Tersk-Kandalaksha, Onega and Kuloi areas, and intermediatecollectors (sedimentary Silurian, Devonian and probablyLower Triassie and Jurassie beds) in the Kanin-Timan area.Diamond crystals and satellite minerals associate with gold inPleistocene-Holocene sediments (beaches, alluvium) of theAnabar-Khatanga and Ust' Lena placer areas (South Laptevzone). Jurassie and Cretaceous conglomerates are the mainsources of the mineralization. Accumulations of titanium, zir-conium and iron (occasionally REE) minerals are observed onbeaches in every area of rhe Kola-Belomorsk-Tyrnan zone.Amber placersPlacer shows of amber are very common along the shorelineof Russian Arctic seas from the Kola Peninsula to the LowerIndigirka River. The West-Arctic Region of the Baltic-Dniepersubprovince of the Eurasian amber-bearing province, knownby its unique amber deposits near the city of Kaliningrad, isconsidered as the most prospective in terms of high-qualityamber.Fossil ivory accumulationsThe coasts and islands of the Laptev and East Siberian Seasform part of the vast area of fossil ivory accumulations(SMIRNOV 1998). Russia is a monopolist for this kind ofmineral raw material. At the close of the XIX century, pro-duction of mammoth tusks in Russia was one-third of theivory world trade. The world-wide prohibition for productionof ivory is causing a rebirth of interest in fossil ivory. Sizeableindustrial accumulations of fossil ivory are known in northernYakutia and New Siberian Islands (recent beaches, drainageareas, terraces and river beds). These areas are unique in massburial and conservation of fossil ivory in permafrost by loessand glacial late Pleistocene sediments. Subsequent processesof fluvial erosion and thermoabrasion were responsible forcontinuing exposure of fossil ivory accumulations fairly clas-sified as placer deposits.PLACER FORMING CONDITIONSThe study of placers on Russian Arctic shelves, conductedover the last 30 years made it possible to infer the main regula-rities in their distribution and formation.Closely associated with structural framework of the region isthe main feature of lateral distribution of the placers, theirrestriction to transition zones located in the marginal parts ofsedimentary basins along orogenie structures of the continen-tal frame and also along the periphery of insular structures.The transition zones are characterized by accumulative anddenudation-accumulative relief, by morphostructures of mod-erate downwarpings and uplifts (total effect of neotectonicmovements varies from +200 m up to -200m) and by theCenozoic sedimentary cover of several meters up to 100-150rn thick.The presence of source ore formations (both primary andintermediate collectors) is aprerequisite for placer formation.Concentrations of minerals in placers are controlled by distri-166bution and nature of traps. They involve the recent and ancientdepressions, levelling planes, river valleys, beach and terracesystems, and foot of slopes. The shore and the adjacent shelfare known to have been an area for multiple alternations oftransgressive and regressive cycles during the Cenozoic. Thisis reflected in the vertical section of the sequences, in thestructural-formational complexes. The regular alternation ofmarine and continental facies has been responsible for poly-genetic composition of productive horizons which is the stri-king feature of shelf placer formation. Temporal periodicity,i.e. the existence of epochs most favorable for placer forma-tion is closely related to sedimentological stages. So, thehighest productivity belongs to the ancient (Eocene-Oligo-cene-Miocene) epochs and commonly following denudationand crust formation. The young Pleistocene-Holocene epochsin the Arctic regions are characterized by polar type of lithoge-nesis with the formation of permafrost strata and glaciers, byice-coverage of offshore zones and by relatively weak lithody-namic activity.The intrinsic feature of the Arctic placers, related to the recentposition of the shoreline, is the occurrence of most formationsand potential placers on the seafloor. The distribution of agreat number of minerogenic taxa (both placer and primary) inhigh latitudes is approximated by natural, geographie condi-tions. North of 69° 20', there are the Taimyr-SevernayaZemlya gold-bearing province, East Laptev tin-bearing zone,cassiterite placers in the Chaun Bay, Billings and Ryveyemtin- and gold-bearing clusters, and WrangelIsland promisingfor gold.The presence of placer metals within the Arctic shelves isdistinguished by a great number of large and unique forma-tions. The share of occurrences of gigantic placers (againsttotal number of formations) is abnormally high, about 10 %and 13 % for gold and tin placers, respectively. It is of interestthat similar (and much more contrast in terms of percentage)regularities are also typical of the Arctic hydrocarbon deposits.This common feature of different mineral types can probablybe explained by their similar structural position and evolutionof sedimentary basins. The crucial role was most likely playedby the duration of deposit emplacement of the occurrencesunder relatively stable subplatform environments and perma-nent downwarping. These long-lived occurrences haveproductive horizons of great thickness and wide age range.THE RESOURCE POTENTIAL OF THE RUSSIANARCTIC SHELVESSince 1981 VNIIOkeangeologia has been engaged in monitor-ing of minerogenic zonation and assessment of placer poten-tial of the Russian offshore areas, with development of thegeological surveys and exploration. The results are presentedon the map at ascale of 1:2,500,000 (latest version is of 1996).An information system of the offshore placer formations wasdeveloped in VNIIOkeangeologia in 1997. The geological database .Placer formations of the Russian offshore" intends toassess the placer potential based on all the mineral resourcesinvolved. Today the base holds data on 300 different-rankplacer formations located in the Arctic, with more detailedinformation on commercially important mineral resources(gold, tin, diamonds, minerals of iron, titaniurn, zirconium). Itshould be noted in eonclusion that the resourees of plaeerminerals are only part of the total mineral-raw potential of theRussian Aretie shelf zones. Along with large oil- and gas-bearing areas diseovered onshore and offshore, sizable aeeu-mulations of ore minerals (manganese and polymetals onNovaya Zemlya and diamond fields along the White Seashoreline; Fig.l) have been diseovered and studied for the lastdeeade. These diseoveries permit us to eonsider the Aretieoffshore areas as the most diverse and sizable in terms ofmineral resourees.ReferencesDorofeev, VK., Blagoveshchensky, M.G, Smirnov, A.N. & Ushakov, VI. (1999):New Siberian Islands. Geologieal strueture and metallogeny.- VNIIOke-angeologia, St.Petersburg, 130 pp. (in Russian).Gratnbergv 1.5. & Ushakov VI. (eds.). (2000): Severnaya Zemlya. Geologicalstrueture aud metallogeny.- VNIIOkeangeologia, St. Petersburg, 187 pp.(in Russian).Ivanova A.M., Suprunenko 0.1. & Ushakov VI. (1998): The mineral-rawpotential of Russian shelf areas.- VNIIOkeangeologia, St.Petersburg, 108pp.(in Russian).Sm/mol' A.N. (1998). Fossil ivory - a plaeer mineral resouree of the RussianAretie.- Mineral resources of Russia, Economics and management, ZAO"Geoinformmark" Moscow. N2, 16-20. (in Russian).167

Placer Minerals of the Russian Arctic Shelf

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