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Arkhangelsk District - Lomonosov, Arkhangelskaya, Karpinskogo, Karpinsky, Pionerskaya, Grib |
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Diamonds
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Super Porphyry Cu and Au
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The Lomonosov diamond mine, which exploits two kimberlite pipes, Arkhangelskaya and Karpinskogo-1 (2 km NW of the Arkhangelskaya pipe) and the Grib (20 km NW of the Arkhangelskaya pipe) kimberlite pipe are located within the Primorsky District of the Arkhangelsk Region, between 90 and ~110 km NNE of the city of Arkhangelsk. They are some of more than 50 kimberlite pipes found within the district, 15 of which are diamondiferous (#Location: Grib - 65° 30' 24" N, 41° 25' 21" E; Arkhangelsk - 65° 17' 26"N, 41° 1' 5"E).
Geological Setting
These pipes lie within the East European Platform, a collage of Archaean cratons and Palaeoproterozoic mobile belts, which underlie most of western Russia and the Baltic states. Late Neoproterozoic to Palaeozoic sediments cover most of the platform to the south and east of Scandinavia. In its eastern part there are two Archaean cratons, the Kola and Karelia to the north and south respectively, separated by the NW-SE trending Palaeoproterozoic Belomorian mobile belt. These cratons are made up of Early Archaean tonalitic gneisses and granulites, surrounded by narrow greenstone belts, containing both sedimentary and volcanic rocks. These rocks were reworked in the Belomorian belt, to produce amphibolite-facies metamorphism, granite emplacement and crustal thickening. The southeast-ward extensions of both cratons and the Belomorian belt are hidden beneath a Vendian to Palaeozoic sedimentary cover, in the Arkhangelsk area.
Subsequently the Baltic Shield underwent extension to produce the Mesoproterozoic (Riphean) Kola-Belomorian graben system, part of larger rift system that affected the entire East European Platform (Bogdanova et al., 1996). This extension influenced both the siting and nature of the subsequent Devonian alkaline magmatism, and fragmented the uniformly thick lithosphere of the Baltic Shield in the Kola-Arkhangelsk area into thick (>200 km) blocks that were separated by a network of Mesoproterozoic rifts with significantly thinner (<100 km) underlying lithosphere. These rifts were mainly within the Belomorian and other former Palaeoproterozoic mobile belts, although a few (e.g., Leshukonskiy) were on the margins of the cratons (Mahotkin et al., 1999).
These rifts contain red-bed dominated sedimentary infilling, with accompanying tholeiitic basalts and ferrobasalts (K-Ar age 1300 Ma; Staritskiy, 1981; Sinitsin et al., 1982). Later Vendian sediments complete the infilling and overlap the graben shoulders. Further Riphean tholeiitic basalt dykes and sills cut the NE margin of the Kola craton, adjacent to another Riphean graben (Staritskiy, 1981; Berkovsky & Platunova, 1989). Within the Kola and Karelia cratons, Riphean magmatism is represented by lamproitic dykes (Proskuriykov et al., 1992). Some of these have been recently reclassified as kimberlites (Mahotkin, 1998).
In the Arckhangel area, which is part of the East European Platform, the SE extremity of the exposed Kola Craton is overlian by a shallowly eastward dipping 800 to 3500 m thick sequence of Vendian (Late Neoproterozoic 650 to 543 Ma), Middle to Upper Carboniferous and Permian rocks. The Neoproterozoic sedimentary sequence is intruded by, and the Carboniferous carbonate-terriginous and Permian rocks overlie, the small volume Arkhangelsk igneous activity, which comprised a short intense, widespread phase of Late Devonian (~380 to 360 Ma) mafic, alkaline-ultramafic and carbonatitic magmatism immediately following large-scale lithospheric doming of the East European Platform (Mahotkin et al., 2000). In the Kola-Arkhangelsk-Timan area, it was associated with further localised doming, centred on the Kola Peninsula (Nikishin et al., 1996). The style of magmatism varied from the eruption of tholeiitic basalts to the emplacement of large alkaline igneous and carbonatite complexes and relatively small-volume ultramafic alkaline sub-volcanic pipes (diatremes) pipes and sills (Mahotkin et al., 1999).
In addition to this intrusive activity on the East European Platform, a 300 m thick, NW-SE trending Frasnian (Late Devonian) volcano-sedimentary succession of tholeiitic lavas and tuffs (Staritskiy, 1981) outcrops over an area of 2500 km2 along the northeastern margin of the platform, extending from the Kanin Peninsula to Middle Timan, 300 km to the NE of the Arkhangelsk area. Other occurrences of Late Devonian magmatism are found throughout the region and along the Murmansk coast of the Kola Peninsula (Staritskiy, 1981; Ishmail-Zadeh et al., 1997). These extensive tholeiitic lavas are associated with a major tholeiitic dyke swarm (Berkovsky and Platunova, 1989) that extends ∼2500 km north-south and links Late Devonian magmatism throughout the East European Platform into a single igneous mega-province (Wilson & Lyashkevich, 1996).
This Late Devonian magmatism across and on the margin of the East European Platform of the Kola region forms a large intrusive and sub-volcanic alkaline provinces, the Kola Alkaline Province, which outcrops over an area of ~100 000 km2 and comprises 24 igneous complexes (Dudkin and Mitrofanov, 1993; Kogarko et al., 1995). Most of these were intruded during the same short Late Devonian 380 to 360 Ma interval (Kramm et al., 1993; Beard et al., 1996, 1998). Three types of intrusion have been recognise: i). nepheline syenite complexes; ii). alkaline-ultramafic complexes predominantly composed of peridotites, pyroxenites and ijolites; and iii). complexes containing significant carbonatite. The largest alkaline intrusive complexes were emplaced on the Kola Peninsula. Lithospheric extension and sedimentation associated with this major NW-trending rift zone are estimated to have begun at ~375 Ma (Nikishin et al., 1996). The relatively small-volume carbonatite bearing complexes have a more scattered distribution across the Kola craton (Kramm et al., 1993). Apart from the Arkhangelsk area kimberlite diatremes and dykes, kimberlite-like rock-types are also known along the Terskii Coast field, across the White Sea on the south coast of the Kola Peninsula (Beard et al., 1998).
The small-volume Arkhangelsk igneous activity, which comprises the Arkhangelsk Alkaline Igneous Province, mostly has the form of sub-volcanic pipes (diatremes) and some sills (Sinitsin and Grib, 1995). These diatremes form several clusters or igneous fields, each with distinctive petrological characteristics. They occur in two groups on the SE side of the White Sea: i). along and up to 100 km inland from the Zimniy Bereg (i.e. Winter Coast to the north of the city of Arkhangel and opposite the nose of the Kola Peninsula) which include the diamondiferous Arkhangelsk and Grib pipes; ii). on the NE side of the Onega Peninsula, to the southwest of Arkhangel, separated from the Zimniy Bereg by the Gulf of Dvina (Mahotkin et al., 1999).
A belt of NE-SW trending normal faults extends throughout the Arkhangelsk Alkaline Igneous Province, mostly concealed beneath Upper Palaeozoic sedimentary rocks, and with the evidence of limited crustal thinning and remnants of Upper Devonian to Lower Carboniferous sedimentary rocks preserved along this zone are considered to be evidence for weak Devonian extension (Grib et al., 1987; Nikishin et al., 1996). The Arkhangelsk Alkaline Igneous Province diatremes are thought to be mostly sited at the intersection of NE-SW faults and the shoulders of former Mesoproterozoic (Riphean) grabens. Specifically, most of the kimberlites, lamproites and alkaline picrites of the main Zimniy Bereg fields of Zolotitsa, Mela, Kepino-Pachuga and Verkhotina-Soyana are emplaced in Late Neoproterozoic (Vendian) sequences (Erinchek et al., 1998) that are believed to overlie the margins of several north-south to NW-SE aligned grabens and intervening Archaean Kola cratonic basement horsts (Sinitsin and Grib, 1995).
Kimberlite and Alkaline Picrite Pipes
The diamondiferous-kimberlite diatremes of the Zolotitsa cluster (which include the Arkhangelsk pipe, discovered in 1980) and the alkaline picrite pipe at Chidvia (further S towards the city of Arkhangelsk) are typical examples of the Zimniy Bereg pipes. The vent deposits comprise either one or two phases of breccia, the first of which is composed of diverse polylithic tuffs and breccias, often layered with rounded fragments (lapilli) of kimberlites or alkaline picrites, olivine pseudomorphs, xenoliths of country rocks and quartz sand, cut by later dykes (Sablukov, 1987). Various proportions of these fragments are present, producing a range of clastic rock-types, ranging from autolithic tuffs to sandstones and sedimentary breccias. Subhorizontal micro-lamination, fragment size-sorting, plant remains (Lower Frasnian) and xenoliths of Early and Middle Palaeozoic sedimentary rocks are encountered to a depth of 600 m (Sablukov, 1987). Polylithic breccias and tuffs are intruded by kimberlite or alkaline picrite breccia composed of lapilli and altered olivines, cemented by a serpentine-saponite mixture, with additional minor talc, richteritic amphibole and diverse carbonates, whilst the relative proportion of polylithic and autolithic igneous breccias vary between pipes and within each (Mahotkin et al., 1999).
Most diatremes have well-developed infill craters that have apparently undergone little erosion, occurring as trough-like or saucer-shaped depressions infilled by flat-lying tuffs and interbedded tuffaceous sediments, sandstones and sedimentary breccias that include zones of cross-laminated, fine-grained accretionary lapilli tuff (Sablukov, 1987). In addition to the main pipes, several 0.5 to 3 m thick sills of kimberlite, with local carbonate facies, are locallyexposed within Vendian arenites (Mahotkin et al., 1999).
Kimberlites are the predominant rock-type in the Zimniy Bereg fields, and have been divided into a predominantly mica-poor Eastern Group and a predominantly micaceous Western Group (Parsadanyan et al., 1996). However, Mahotkin et al., 1999) emphasises the Arkhangelsk Alkaline Igneous Province kimberlites are mostly fragmented and drastically overprinted by post-magmatic alteration, with only the Pionerskaya pipe having a possible massive facies encountered in drilling at depth, although these may also instead be either exceptionally large clasts or post-breccia dykes.
The Western Group kimberlites are predominantly micaceous, and include most of the diamond-rich diatremes of the province. The are characterised by a groundmass of Ti chromites (>70%), Cr-ulvospinel and titanite, and absence of ilmenite and rutile. Indicator minerals include chromite, with picroilmenite absent and garnet and Cr-diopside rare (Garanin et al., 2001).
The least altered examples come from the Pionerskaya pipe massive facies principally comprise macrocrysts and phenocrysts of fresh olivine, together with microphenocrysts of phlogopite. Anhedral to subhedral olivine macrocrysts form 25 to 30 modal % of the rock, ranging from 2 to 12 mm across, with high mg-numbers (MgO/[FeOt+MgO] x 100) of 92.3 to 92.6 and Ni contents, and low Ca contents (Sobolev et al., 1989), and olivine inclusions in diamonds (Hervig et al., 1980). Up to 25% of the rock is composed of euhedral olivine phenocrysts that are 0.01 to 1.2 mm long that have less-magnesian cores (mg-number of 89.9 to 90.6), and are Ni depleted and Ca enriched, relative to the olivine macrocrysts. These phenocrysts are zoned, with mg-numbers increasing and Ni decreasing outwards. The smallest crystals are partly or totally altered to serpentine and saponite (Mahotkin et al., 1999).
Phlogopite has a modal abundance that varies from 15 to 35% of the rock, but very rarely may reach up to 60%. Sparse, up to 0.3 mm magnesian phlogopite microphenocrysts with mg-numbers of 92 to 93 and low Ti contents, surround the olivine grains. Phlogopite may also occur as <1.5 mm poikilitic anhedral plates enclosing olivine phenocrysts, perovskite and small crystals of a phase that has been entirely replaced by pectolite and hydroandradite. Groundmass phlogopite crystals have mg-numbers that vary in from 91.2 to 77 (Mahotkin et al., 1999).
A very few of the clasts in the Karpinskiy-I diatreme at depths of between 370 and 395 m have been classified as olivine lamproites by Mahotkin et al. (1995), characterised by the same abundant olivine macrocrysts and phenocrysts as the associated kimberlites. These clasts are set in a fine-grained groundmass of red-brown phlogopite, light brown richteritic amphibole and clinopyroxene, lacking both perovskite and hydrogarnet. The Mela sills on the northern margin of the Western Group kimberlites are composed of a carbonate-rich variant of kimberlite, comprising serpentinised olivine grains and phlogopite flakes, set in abundant calcite, and locally grades into a carbonatite.
The Eastern Group kimberlites of the Kepino-Pachuga and Verkhotina-Soyana fields are mica poor, relative to those in the Western Group, with phlogopite generally only forming 1 to 7% of the rock rarely reaching 20%. Perovskite, rutile and Fe-Ti oxides are found as accessory phases in the serpentinized groundmass. The kimberlites of this group are characterised by the presence of Ti-chromite, Mg-ulvospinel, titanomagnetite, picroilmenite, rutile and perovskite in the groundmass. Picroilmenite, pyrope and Cr-diopside are among the heavy fraction indicator minerals (Garanin et al., 2001).
The richly diamondiferous Grib kimberlite pipe (also known as Anomaly 441) which was discovered in 1996 lies within the Eastern Group kimberlites. All of the kimberlites of the Eastern Group are closely associated with neighbouring diatremes of alkaline picrites.
Rock interpreted by Mahotkin et al. (1999) as Alkaline picrites comprise many of the intrusions of the Verkhotina-Soyana, Kepino-Pachuga and Chidvia groups of diatremes in both the Western and Eastern groups of intrusions of the Arkhangelsk Alkaline Igneous Province. In contrast to the typical Arkhangelsk Alkaline Igneous Province kimberlites, which dominantly contain rounded olivine macrocrysts, together with other kimberlite indicator minerals, these diatremes contain MgO-rich rock-types that are also rich in euhedral or subhedral phenocrysts but poor in rounded macrocrysts. However, they also contain substantial amounts (up to ~40%) of a former euhedral microphenocryst and groundmass phase that resembles melilite in morphology but has been entirely replaced by aggregates of hydroandradite (±pectolite).
The Grib Kimberlite Pipe is masked by 52 to 83, but averaging 66 m, of glacio-lacustrine sands and carbonaceous carbonates and sandstones. The maximum dimensions of the pipe below overburden are ~410 x 450 m with an area of 14.25 ha, reducing to 12.4 ha at a depth of 100 m below the base of cover, 8.5 ha of which has the form of a truncated, inverted cone which flares outwards from a depth of about 200 m to the base of overburden.
Four main geological units have been recognized in the upper part of the pipe, underlain by two other varieties of crater facies kimberlite.
Rb-Sr dating of phlogopite from the kimberlite gives dates of 372±8 Ma, which is approximately coeval with that of the Arkhangelskaya pipe (Shchukina et al., 2012)
Published grades and tonnages for different mining cases include:
Open Pit - 73.5 Mt @ 70 carats per hundred tonnes (cpht) for 51.2 million carats (Mct),
Block Cave - 58.9 Mt @ 65 cpht for 38.4 Mct,
High Grade Block Cave Tonnes - 42.8 Mt @ 82 cpht, for 35.2 Mct.
The Lomonosov mine exploits two of the six kimberlite pipes in the immediate area, the Arkhangelskaya and Karpinskogo-1. The other four are Karpinsky-2, Pionerskaya, Pomorskaya and Lomonosov. The six pipes are arranged in the form of a NNE trending, near-linear chain with a total length of 9.5 km, with individual pipes spaced at from 0.13 to 2.15 km. At the base of overburden, individual pipes cover areas varying from 10.25 to 36.88 ha.
The interiors of the pipes are composed of four main types of kimberlites with drastically different conditions of occurrence, composition and diamond content. The tuffogenic-sedimentary and tufforganic rocks of the crater facies have not been affected by erosion and form sub-horizontal tabular bodies in the top of the downward tapering conical form of the Pionerskaya, Karpinsky and Arkhangelskaya pipes. In addition, autolithic breccia and xenotuff breccias of the vent facies occur as steeply inclined columns in the diatreme sections of all the pipes. Autolithic breccias in the Arkhangelskaya pipe form a steep shoot dipping at ~85° NE. This shoot covers an area of 405 x 395 m at a depth of 159.5.
The richest ores, include autolithic breccias and toffoganic rocks, at the Arkhangelskaya and Karpinsky pipes, while the leanest is the Pomorskaya pipe, which is principally composed of xenotuff breccias.
The Arkhangelskaya pipe has a pear-shaped form in plan, with a dyke-like extension on its southeastern margin. The pipe has dimensions of 550 x 490 m, and covers an area of 14.993 ha at the base of overburden at a depth of near 110 m below surface. In vertical section it has a downward tapering cone shape. The Internal structure of the pipe is complex, both in plan and in vertical section, with heterogeneous distribution of diamond content directly related to its attitude, peculiarities of its internal structure and lithologic composition.
Lehtonen et al. (2009) have calculated that the Arkhangelskaya pipe seems to have sampled the bulk of its diamonds from the deepest portion of the diamond stability field, between 190 and 210 km. In contrast, the neighbouring Lomonosova and Pionerskaya pipes are known to have collected their diamonds from depths of 130 to 160 km.
JORC compliant remaining resources at ALROSA's Lomonosov diamond mines as of 1 July 2013 were (Independent experts report to ALROSA by Micon International, 2013):
Arkhangelskaya Pipe
Probable reserve - 57.087 Mt @ 0.76 c/t, for 43.189 Mct,
Karpinskogo-1 Pipe
Probable reserve - 18.438 Mt @ 1.13 c/t, for 20.918 Mct.
In 2015, the ALROSA website quoted the following statistics:
Arkhangelskaya Pipe
Diamond production in 2014 - 1.373 Mct,
Ore resources inclusive of reserves - 95.634 Mt @ 0.86 c/t,
Karpinskogo-1 Pipe
Diamond production in 2014 - 0.266 Mct, (mining started during 2014)
Ore resources inclusive of reserves - 30.156 Mt @ 1.11 c/t.
This summary is drawn from references listed below, particularly Mahotkin et al., 1999, and a series of other abstracts and websites.
The most recent source geological information used to prepare this decription was dated: 2013.
Record last updated: 8/2/2016
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
Arkhangelsk Grib
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Selected References:
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Kostrovitsky S I, Malkovets V G, Verichev E M, Garanin V K and Suvorova L V 2004 - Megacrysts from the Grib kimberlite pipe (Arkhangelsk Province, Russia): in Lithos v77 pp 511-523
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Lehtonen, M., O Brien, H., Peltonen, P., Kukkonen, I., Ustinov, V. and Verzhak, V., 2009 - Mantle xenocrysts from the Arkhangelskaya kimberlite (Lomonosov mine, NW Russia): Constraints on the composition and thermal state of the diamondiferous lithospheric mantle: in Lithos v.112, pp. 924-933
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Mahotkin, I. L., Gibson, S.A., Thompson, R.N., Zhuravlev, D. Z. and Zherdev, P. U., 1999 - Late Devonian Diamondiferous Kimberlite and Alkaline Picrite (Proto-kimberlite?) Magmatism in the Arkhangelsk Region, NW Russia: in J. of Petrology v.41, pp. 201-227,
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Malkovets V, Taylor L, Griffin W , O Reilly S, Pearson N, Pokhilenko N, Verichev E, Golovin N and Litasov K 2003 - Cratonic conditions beneath Arkhangelsk, Russia: garnet peridotites from the Grib kimberlite: in 8th International Kimberlite Conference, Selected Papers Mitchell R H, Grutter H S, Heamann L M, Scott Smith B H and Stachel T 5p
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Malkovets V, Taylor L, Griffin W, O Reilly S, Pokhilenko N, Verichev E, Golovin N, Litasov K, Valley J and Spicuzza M, 2003 - Eclogites from the Grib kimberlite pipe, Arkhangelsk, Russia: in Mitchell R H, Grutter H S, Heamann L M, Scott Smith B H and Stachel T 8th International Kimberlite Conference, Selected Papers Elsevier Science 5p.
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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