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3 Alkaline complexes of the Kola peninsula

Cancelled!

Field guides:
Prof. Dr. Valery Smolkin, Vernadsky State Geological Museum, Russian Academy of  Sciences, Moscow
Prof. Dr. Andrei Arzamastsev, Geological Institute of Kola Scientific Center, Russian Academy of Sciences, Apatity

Post-conference fieldtrip: 17.8. -23.8.2008

Departure/Arrival: Murmansk / Murmansk
Participants should arrive to Murmansk airport on 17th  August  from which they will be taken to Apatity by bus (2.5 hours). Departure from Murmansk (Apatity) on August 23th.
The field trip will start and end in Murmansk, therefore travel costs to and from Murmansk are not included. Following routes from Frankfurt to Murmansk are being considered. Fly from Moscow to Murmansk (most preferable, flights daily).

Approximated costs: ca. 960 € (calculated for 13 participants)

Min. participants:         10
Max. participants:        16


Abstract

The Monchepluton: geology and ore deposits

The Monchepluton is a typical layered mafic–ultramafic intrusion that occupies an area of ~65 km2. The pluton belongs to the Paleoproterozoic peridotite–pyroxenite–gabbronorite association and serves as a host of Cu–Ni sulphide deposits and occurrences various in morphology, genesis, and ore composition. The Monchepluton was emplaced 2507–2493 Ma ago; the younger dikes are dated at 2506–2487 Ma.
The Monchepluton is horseshoe-shaped in plan and consists of two chambers previously called massifs, or branches. The NE-trending chamber 7 km in extent is expressed in topography as Mts. Nittis, Kumuzh’ya, and Travyanaya and denoted as the NKT chamber. The second, latitudinal chamber 9 km long extends from Mt. Sopcha to Mts. Nyud and Poaz and farther to the southeast toward the foothills of Mt. Vurechuaivench. Either chamber is a symmetric syncline with limbs dipping at angles 30o–40o (NKT) and from 40o–45o to 20o–25oat the limbs and 10o–15o in the axial part of the Sopcha–Nyud–Poaz chamber. As a result of the subsequent tectonic motions, the NKT chamber subsided at least by 300 m relative to the Sopcha–Nyud–Poaz chamber.
The vertical layering into zones combined with distinctly expressed lateral differentiation and occurrence of bottom zone enriched in quartz are specific features of the Monchepluton. The structure of this pluton is complicated by multifold supply of additional portions of hotter melt that were emplaced into the still crystallizing magma chamber (Mt. Sopcha).
The following zones are recognized in the summary section of the Monchepluton (from bottom to top): basal quartz norite–gabbronorite, harzburgite, harzburgite–orthopyroxenite, dunite, orthopyroxenite, norite, norite–gabbronorite, and gabbronorite–anorthosite. These zones are composed of the olivine–chromite, olivine–orthopyroxene–chromite, orthopyroxene, orthopyroxene–plagioclase, and plagioclase cumulates, the composition of which systematically changes in the vertical direction.
The monotonic variation in compositions of rocks and rock-forming minerals in the vertical section is disturbed in some cases by appearance of chromite-bearing dunite in the southwestern portion of the pluton (Dunite Block), ore-bearing dinite–harzburgite unit within orthopyroxenite zone at Mt. Sopcha, and a “critical” horizon in the middle part of Mt. Nyud, i.e., a unit enriched in xenoliths of pyroxene–plagioclase and high-alumina hornfels. The upper portion of the Monchepluton section was eroded in the early Paleoproterozoic before the volcanic eruptions in the Imandra–Varzuga Zone and in the Cenozoic as a result of glacial denudation.

 


Day-to-day:

17 August. Flight Moscow – Murmansk, transfer to Apatity by car.
18 August. Trip to Monchegorsk (60 km of Apatity). Excursion to the layered Monchepluton. Examination of sulphide ore and rocks from the lower part of the pluton, bottom zone and disseminated ore of the Mt. Travyanaya, the layered zone of Mt. Kumuzh’ya, ore veins of Mt. Nittis, system of ore-controlling dikes, and to the Sopchozero chromite deposit.
19 August. Excursion to the middle part of the Monchepluton. Examination of ore layer 330 at Mt. Sopcha, sulphide ore stockwork of the Nyud-II deposit, critical horizon and Terrace ore occurrence at Mt. Nyud.
20 Augusty. Trip to Kirovsk (25 km of Apatity). Geology of the Khibiny pluton of alkali syenite
21Augusty. Excursion to the Koashva open pit (50 km of Apatity). Examination of apatite – nepheline ore.
22 Augusty. Trip to Revda (200 km of Apatity). Geology and mineralization of the Lovozero pluton. Visit to the Karnasurt mountain outcrops and open pits.
23 August. Transfer from Apatity to airport. Flight from Murmansk to Moscow.  

 

18 August. Excursion to the layered Monchepluton and ore deposits

Stop 1. The Sopcheozero chromite deposit.
The Sopcheozero chromite deposit located in the southwestern Monchepluton is a complex combination of ore lenses and layers disturbed by steep faults. Its projection on the horizontal plan looks as a tract 1200 m long and 80–240 m wide. The Main orebody gently plunge to the southeast reaching an elevation mark of – 70 m, where it splits into several bodies that rise to the south. The thickness of the Main orebody varies from 1.6 to 40.6 m (commonly 7–17 m and 14.7 m on average). The thickness of ore layers and lenses in the southeastern part of the deposit also varies in a range from 10 to 56 m.
The inner structure of the ore unit is characterized by lenticular layering caused by alternation of ores with variable contents of chromite disseminations. The high-grade densely impregnated and massive ores with spotty and banded structure amount to 33% of the bulk ore; 62.5% fall on the ordinary disseminated ore, and 4.5%, on the low-grade ore. The weighted average Cr2O3 content in the high-grade ore is 38.76%, in the ordinary ore, 16.65%, and 23.5% in the ore layer as whole.
The high-grade banded ore and the host ultramafic rocks, as well as crosscutting gabbroic and microgranitic dikes may be examined in the Sopcheozero open pit, where the head portion of ore layer is exposed. Samples of various ore types are available in dumps.          

 The participants of the international excursion in Monchegorsk area in 2005.

Stop 2. Sulphide ore deposit in the NKT bottom zone, Mt. Travyanaya.
The NKT Bottom Lode deposit is distinguished by extremely complex geological structure. The orebody is crescent-shaped in section, being conformable with overlying rocks. The lode mimics the contour of the massif sole, however, does not overlie it directly, being separated by quartz gabbronorite layer 5–10 m thick. The ore lode varies in thickness from 5 to 50 m and extends for more than 3 km along the strike. This thickness is correlated with thickness of bottom rocks, and the Ni content is correlated with content of sulphides. The thickness of ore lode and Ni grade increase inward the magmatic chamber. The ore mineralization reveals extremely variable structural pattern controlled by the primary structural elements of the pluton, including taxitic character of host rocks, gradual transition between different rocks, complex intercalation, and development of pegmatoid varieties. The bottom rocks comprise plagioclase-bearing olivine and olivine-free orthopyroxenites, olivine norite, norite, gabbronorite, quartz–biotite gabbronorite, and xenoliths of country gneiss as well.
In the Mt. Travyanaya area, one may examine the dumps of old mine and the host intrusive rocks of the bottom zone.

Stop 3. The NKT vein ore field, Mt. Kumuzh’ya and Mt. Nittis
The systems of near-vertical ore veins that fill tectonic fractures are localized in axial zones of both chambers and are clustered into the NKT and Mt. Sopcha ore fields (Fig. 9). The veins’ strike varies from 0o to 20o NE in NKT and from 20o to 50o on Mt. Sopcha. Most veins occur in the layered zone of alternating harzburgite and olivine clinopyroxneite; some veins extend above this zone.
Sulphide ore of the NKT field may be examined on the northeastern slope of Mt. Kumuzh’ya and on the northern slope of Mt. Nittis. Crosscutting relationships of dikes may be observed at the top of Mt. Nittis.

 

19 August. Excursion to the layered Monchepluton

Stop 1. Ore layer 330 on Mt. Sopcha.
The unique ore layer 330, one of the first discovered but remaining yet undeveloped deposit of the disseminated Cu–Ni sulphide ore, crops out on the slope of Mt. Sopcha 800 m above its foot. The origin of this layer is a most interesting enigma of the Monchepluton.
The ore layer represents an extended key horizon—a unit 4–5 m thick on average hosted in homogeneous orthopyroxenite. Its outcrops are discontinuously traced on slopes of Mt. Sopcha along its entire perimeter at a height of 330 m; the layer was also penetrated by boreholes at a depth. The ore layer is often displaced by normal and reverse faults for a distance of a few meters. The fine rhythmic alternation of laminas enriched and depleted in olivine is a characteristic feature of the ore layer in its lower part. Segregations of coarse-grained pegmatoid rocks are abundant in the upper part of the section.
The complete section of the ore layer and its contacts may be examined at the western slope of Mt. Sopcha; samples of sulphide and PGE ores are available.

Stop. 2. The Critical Horizon, Mt. Nyud (Terrace).
The so-called Critical Horizon as a unit that hosts the Terrace deposit of the disseminated and pocket–disseminated ore discovered by A.E. Fersman and his colleagues in the 1930s occurs on the western and northwestern slopes of Mt. Nyud.
The unit is confined to the transition from the underlying olivine norite to the olivine-free norite and consists of the complex, irregular alternation of meso- and melanocratic norites, plagioclase-bearing orthopyroxenite, gabbronorite, and harzburgite. The plicated xenoliths of high-alumina schists and fine-grained hornfels, as well as products of their melting as micronorite and microgabbronorite segregations are the characteristic feature of the Critical Unit that reaches its greatest thickness (~50 m) close to the Terrace deposit; the thickness diminishes to 20 m and less in the northeastern direction. At a depth, the unit is pinched out to the east at a short distance.
The Terrace deposit is hosted in norite and olivine norite that mainly occur below the Critical Horizon and are not exposed at the surface. The thickness of irregularly lenticular ore zone amounts to 20 m. The disseminated, stringer–disseminated, and pocket ores reveal a wide range of sulphide contents.

Stop 3. The Nyud II deposit of sulphide ore.
The deposit is located in the southwestern Nyud–Poaz massif and hosted in melanocratic norite.
The cup-shaped orebody is 40 m thick. Its geological boundary is determined by occurrence of the Critical Horizon. The ore is composed of massive sulphide schlieren and discontinuous veins, veinlets, and disseminations. The schlieren are 5–7 m long and surrounded by a complex systems of offsets, veins, and disseminations. The norite-hosted deposits (Terrace, Nyud II) are characterized by a high variability of ore that consists of fragmentary layers and stocks associated with rocks of the Critical Unit, nonuniform disseminations, veinlets, and large sulphide pockets and schlieren from 0.5 to 7.0 m in size. No structural control of ore distribution and metal contents in ore is noted within deposits. Combination of syn- and epigenetic types of ore mineralization and its Cu–Ni specialization are also characteristic.
The participants of excursion may examine rocks of the Critical Unit and its structure on the southwestern slope of Mt. Nyud, as well as various types of ore from the Terrace and Nyud II deposit are available from the open pit and dumps of older adit.

Khibina and Lovozero alkaline plutons: geology and unique mineralization

The two world biggest agpaitic intrusions are the key magmatic centers of the Paleozoic Kola Alkaline Province of the NE Fennoscandian Shield. In the Khibina pluton peralkaline K-Na and K nepheline syenites are intercalated with members of typical ultrabasic-alkaline and carbonatite series. In the Lovozero pluton agpaitic lujavrites (type locality) form rhythmic layered complex similar to that in Ilimaussaq, Greenland. Geophysical and geological data based on prospecting drilling program give evidence for significant difference in the internal structure of two giant polyphase magmatic bodies, and commercial mineralization enclosed in these intrusions. Participants will examine the main rock complexes of both massifs. In Khibina we will visit apatite-nepheline and titanite ore deposits. In the Lovozero field trip we will examine classical outcrops of lujavrite-foyaite-urtite rhythms with loparite (Nb, Ta) and eudialite (Zr, Hf) commercial mineralization.

Kalsilite nepheline syenites forming cliffs in the central part of the Khibina pluton.

The trip will ovide an opportunity for igneous petrologists and geochemists to ponder the role of plume-lithosphere interaction processes responsible for the origin of enormous amounts of agpaitic magmas and deciphering the circuitous routes of alkaline magma evolution. In the open pits of both plutons small pegmatite bodies with nice alkaline minerals, as well as dikes of alkaline lamprophyres and tinguaite are widespread. Khibina and Lovozero are famous for their unique mineralogy: over 550 mineral species are present here, more than 100 of them were discovered for the first time in the world. Most of rare minerals are sodium titano-, niobo- and zirconosilicates, which could be found in pegmatites and hydrothermal veins. Alteration of earlier minerals under hydrothermal and supergene conditions produces newly formed mineral phases, and this process continues up to present day. The trip will give you an opportunity to visit unique localities of these minerals and also to seе beautiful landscapes of Russian Laplandia.

20 Augusty. Excursion to the of the Khibiny pluton of alkali syenite.

Stop 1. Contact zone of intrusion. Massive coarse-grained nepheline syenites (massive khibinites) of the peripheric part of the massif. Contact eudialite-bearing pegmatiod zone. Xenoliths of Proterozoic green schists in alkaline rocks. Fenites.

Stop 2. Trachytoid coarse-grained nepheline syenites (trachytoid khibinites) of the peripheric part of the massif. Eudialite-bearing nepheline syenites.

Stop 3. K-rich massive nepheline and kalsilite syenites ("rischorrites"). Tinguaite dike.

Stop 4. Apatite-titanite mineralization zone. Layering in the ijolite-melteigite complex.

Stop 5. Irregular-grained nepheline syenite of the central part of Khibina pluton.

21 Augusty. Excursion to the Koashva open pit.

Stop 1.  Main types of apatite-nepheline ores, titanite-apatite ore, magmatic apatite breccia, massive juvite, pegmatite zones.

Stop 2. Ultra-alkaline veins within foidolites of Mt. Koashva. Koashva apatite deposit. Near the car.

 Phonolite (tinguaite) dike in agpaitic syenite.Khibina pluton, Small Vudyavr.

 

  Khibina apatite-nepheline deposit. Koashva open pit.

 

22 Augusty. Excursion to the Lovozero pluton

Stop 1. Karnasurt mountain outcrops and open pits. Differentiation of lujavrite-foyaite-urtite complex: rhythmic layering. Loparite ore bearing layers. Eudialite lujavrites. Poikilitic sodalite syenites.  

Stop 2. Alluaiv open pit. Pegmatite arfvedsonite-eudialyte-feldspar and arfvedsonite-ussingite-feldspar veins with ussingite, nepheline, mur­manite, mangan-neptunite, chkalovite, bornemanite, gmelinite, and steenstrupine.


 Eudialite-bearing pegmatite of the Lovozero pluton.

 

Stop 3. Old drill core storage in the Lovozero geological survey. Drill core of the eudilate lujavrite complex. Zr-Hf ores, containing up to 90% eudialite.