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1 2Dmitry Zozulya , Nelson Eby1Geological Institute, Kola Science Centre, Apatity, Russia
2University of Massachusetts Lowell, USA
Rare-metal ore occurrences, related to the Late Archean A-type alkali granites from the Keivy zone (NE Fennoscandian shield)
Typology, geology, mineralogy and geochemical specialization of Keivy alkali granite rare-metal occurrences
syn-COLG
VAG ORG
WPG
Y+Nb
Rb
1 10 100 1000
10
100
1000
Y1 10 100 1000
ORG
VAG +syn-COLG
WPG
Nb
10
100
1000
Nb
A
MI
S
Y
10
100
M
M
A
Zr
IS
1000
100
A
SI
M
100
1010
1 10
10000Ga/Al20
0,1
1
10
100
0,1 1 10
Y/Nb
Yb
/Ta
graniteanorthosite
OIB
IAB
nepheline syenite
0,1
1
10
100
0,1 1 10
Y/Nb
Ce/
Nb
graniteanorthosite
IAB
OIB
nepheline syenite
Geochemistry of the rocks from the Keivy complex and tectonic discriminant diagrams
The rocks of the Keivy complex are extremely enriched in Zr (300-5000 ppm), Y (40-500 ppm), Nb (20-600 ppm), Rb (160-900 ppm), REE (100-1000 times chondrites), have associated Zr-REE ore occurrences, are very low in Sc (0.3-1.3 ppm) and Sr (10-30 ppm), and high Ga/Al ratios. On standard trace element discriminant diagrams of Whalen et al. (1987), Pearce et al. (1984), Eby (1990) the Keivy peralkaline granites plot as within-plate or post-collisional A-type granitoids. The low Y/Nb and Yb/Ta ratios for the associated nepheline syenite indicate an OIB affinity. The anorthosites show high compatible element (Sc, 25-40 ppm and Sr, 460-670 ppm) abundances and very low incompatible elements (Zr, 60-100 ppm, Y, 4-15 ppm, Nb, 8-12 ppm, Rb, 15-30 ppm), but the same Y/Nb, Ce/Nb, Yb/Nb ratios as the granites. The enriched source for the Keivy anorthosites has low eNd (-0.15 to -0.24) and low Y/Nb ratios (0.6-1.3). The least evolved syenogranites plot in the EM2-field on the eSr - e Nd diagram.
1
2
3
4
57
0 500 1000 1500 2000 2500 3000
R1= 4Si - 11(Na+K) - 2(Fe+Ti)
500
1000
1500
2000
1 - mantle fractionates2 - pre-plate collision3 - post collision4 - late orogenic5 - anorogenic6 - syn-collision7 - post orogenic
R2=
6C
a +
2M
g +
Al
6
A suite of peralkaline granites and associated syenite and of massif-type anorthosites is found in the Archean Keivy terrane of the NE Baltic shield. The Keivy peralkaline granite complex consists of 2650-2660 Ma aegirine-arfvedsonite granites (six massifs of a few hundred meters thicknesses and with the total exposure area of ca.
22500 km ), 2670 Ma lepidomelane-ferrohastingsite syenogranites in margins of some massifs, and 2680 Ma lepidomelane-ferrohastingsite syenite dykes cutting the TTG basement. Small dike-like bodies of 2610 Ma nepheline syenite cut the West Keivy peralkaline granite massif. The Keivy anorthosite complex consists
2of several large (up to the 170 km ) lopoliths composed mainly of anorthosite and gabbro-anorthosite and spatially confined to granite
White Tundra West Keivy
343+/-342 Ma 1
4
5
3 2
2560
2640
2600
2680
2674+/-6 MaMSWD=0.94
Pike&Bear Lake
2
1
3
4
2663+/-7 MaMSWD=0.49
793+/-354 Ma
2600
2660
2640
2620
Tsaga
3
2
1
18-2
18-42640
2620
2600
2580
2668+/-10 MaMSWD=0.045
0
18-3
18-5
0
2659+/-3 MaMSWD=0.90
4
3
2
1
466+/-28 Ma
2654+/-5 MaMSWD=0.32
2000
2600
2500
2400
2300
2200
2100
Sakharjok
1400
1600
1800
2000
2200
2400
2600
42
1
3
2613+/-35 MaMSWD=1.1
1467+/-22 Ma
3
42
1
1700
1900
2100
2300
2500
1709+/-49 Ma
2682+/-10 MaMSWD=0.44
Sakharjok
A B
F
C D
E18-1
206 Pb238 U A -
207Pb 235 Pb D - alkaline syenite; E - F - gabbro-anorthosites
peralkaline granite; B - syenogranite; C - nepheline syenite;
040038036034
032030
068
066
KANDALAKSHA BAY
B A R E N T S S E A
0 40 km
F i n
l a
n
d K e i v y
Khibiny & Lovozeromassifs
0 10 km
Gabbro-anorthosite(Tsaga & Pike Bear Lake)
Nepheline syenites(Sakharyok intrusion)
Metasediments(Chervurt Fm.)
Metavolcanics(Lebyazha Fm.)
Amphibolite
Gabbro-norite(Fyodorov-Pana intr.)
Peralkaline granite
Latite - monzonite(Mar'yok River suite)
TTG gneisses
Imandra-Varzuga Belt
A
A
B
CD
E
Peralkaline granite massifs: A - West Keivy; B - White Tundra. Gabbro-anorthosite massifs: C - Tsaga; D - Pike and Bear. E - Sakharjok nepheline syenite massif.
Geology and age of the Keivy anorogenic complex in the Kola Peninsula, NW Russia
Apatity
1951
SC RK I ASG
Genetic type Geological position
Geological structure Main rock-forming minerals Rare-metal mineralization Geochemical specialisation and type by Cherny (1991)
Occurrence' symbol on the map
Mineralised granites-I
Apical parts of massifs
Lens-like bodies of few tens m thickness and up to 5 km length
Quartz, albite, microcline, magnetite, aegirine
Zircon, thorite, chevkinite, allanite,fergusonite, britholite-(Y), bastnäsite
Zr, Y, HREE, Th, Nb (Nb/Ta>15) NYF-type
Mineralised granites-II
Bottom parts of massifs
Bodies of irregular shape (10-2100km ), confined to tectonically
fractured zones
Quartz, microcline, magnetite, chlorite, ±hematite
Zircon, thorite, fluorite, cassiterite, pyrochlore
Zr, REE, Th, Nb (Nb/Ta=8-10), Sn, Li, FNYF-LCT-type
Albitites Exocontact zones
Isometric and irregular-shaped 2bodies (tens m ) with gradual
transition to country rocks; zonal structure: quartz core and albite outer zone
Quartz, albite, aegirine, arfvedsonite
Zircon, thorite, titanite, aeshynite-(Y), thalenite, britholite-(Y)
Zr, Y, HREE, Th, Nb (Nb/Ta=20), Ti NYF-type
Microclinites Bottom and inner parts of massifs
2Irregular-shaped bodies (tens m ) with gradual transition to country rocks with rare quartz cores
Microcline, quartz, protolithionite
Zircon, thorite, pyrochlore-(W), cassiterite
Zr, REE, Th, Nb (Nb/Ta=8), Sn, W, LiNYF-LCT-type
Apobasic metasomatite
Contact zones of granites with basic rocks
Small irregular-shaped bodies of inhomogeneous structure; bear restites of mafic rocks
Quartz, albite, microcline, aegirine, arfvedsonite, ferrohastingsite, lepidomelane
Zircon, thorite, epidote-(REE), fergusonite, chevkinite, gadolinite, pyrochlore, fluorite, cassiterite, danalite, monacite
Zr, REE, Th, Nb (Nb/Ta=10 -24), Sn, F, Be, W NYF-LCT or NYF type
Silexites-I Exocontact zones
Small irregular-shaped bodies and veins (1-2 m); sharp contact to country rock; taxitic structure
Quartz, arfvedsonite, aegirine, ilmenite, lepidomelane, magnetite, albite
Zircon, fergusonite, britholite-(Y), chevkinite, bastnäsite, thorite, fluorite
Zr, Y, HREE, Nb (Nb/Ta=15 -20), Th, Ti, FNYF-type
Silexites-II Endocontact zones
Small isometric and irregular-shaped bodies (up to 1 m); gradual transition to country granite; taxitic structure
Quartz, aegirine, arfvedsonite, magnetite, ilmenite, ±microcline
Zircon, fergusonite, britholite-(Y), chevkinite, yttrialite, thorite,
Zr, Y, HREE, Nb (Nb/Ta> 20), Th, TiNYF-type
Quartz-feldspar-astrophylite pegmatites
Apical and inner parts of massifs
Vein-like bodies up to 10 m length with chambers; zonal pegmatitic structure
Quartz, microcline, arfvedsonite, ±albite
Astrophyllite, gadolinite Y, HREE, Ti, BeNYF-type
Quartz-microcline pegmatites
Contact zones Vein-like bodies up to 30x10 m length of zonal pegmatitic structure
Quartz, microcline, magnetite, ±albite, ±aegirine
Fergusonite, chevkinite, britholite-(Y), aeshynite-(Y), gadolinite
Y, Nb (HREE, Be)NYF-type
Amazonite pegmatites
Roof country rocks (gneiss of Keivy complex)
Large vein-like bodies up to few 100 m length of zonal pegmatitic structure
Amazonite, quartz, albite, lepidomelane
Microlite, betafite, pyrochlore-(W), keyviite, fluorite-(Y), xenotime, gadolinite, genthelvite, polylithionite, kainosite, cassiterite, galena, molybdenite
Y, Yb, Nb, Ta, F, Li, Sn (Pb, W, Mo)NYF-LCT-type
Hydrothermal veins
Apical parts of massifs and roof country rocks
Veins of up to several tens m length and 0.5 m thickness; sharp contact to country rocks
Quartz, riebeckite, ±microcline Zircon, ilmenite, fluorite, astrophyllite (Zr, Ti, F)NYF-type
Mineralised nepheline syenites
Linear zones in magmatic body
Several steeply dipping linear zones of 200-1350 m length and of 3-30 m thickness
Nepheline, aegirine, microcline, albite, lepidomelane
Zircon, britholite-(Y), pyrochlore, fluorite, meliphanite, behoite
Zr, Y, REE, Nb, F, Be
Zircon in mineralised granite-I (image width 0.4 cm)
Aeshyinite-(Y) and zircon in albitite(image width 0.5 cm)
Britholite-(Y) in silexite-I(image width 1.0 cm)
Fergusonite and zircon in silexite-I(image width 0.8 cm)
Chevkinite and zircon in silexite-II(image width 0.5 cm)
Britholite-(Y) in silexite-I(image width 1.2 cm)