Centre for Russian and Central EurAsian Mineral Studies (CERCAMS)
Recent publications resulting from CERCAMS-hosted research (Abstracts of peer-reviewed papers)
D.Konopelko 1,4, G. Biske1, B. Belyatsky2, O. Eklund3 and R. Seltmann4 (2003): Hercynian post-collisional magmatism of the SE Tien Shan, Kyrgyzstan: Timing and metallogenic potential. Extended abstract for the IGCP-473 workshop in Urumqi, China, 9-22 August 2003
1 Geological Faculty, St. Petersburg State University, 7/9
University Embankment, St. Petersburg, 199034, Russia. E-mail: konopelk@dk2032.spb.edu
2 Institute of Precambrian Geology and Geochronology RAS,
2 Makarova Embankment, St. Petersburg 199034, Russia
3 Department of Geology, University of Turku, FIN-20014, Turku,
Finland
4 Centre for Russian and Central EurAsian Mineral Studies, Department
of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD,
UK
Abstract
Four post-collisional intrusions of the Kokshaal range in the SE Tien Shan, Kyrgyzstan formed as a result of two regional magmatic pulses at 296 Ma and 280 Ma. The intrusions crosscut folded Late Palaeozoic rocks and post-date the main stage of deformations in the region. The ages of the two magmatic pulses bracket with the ages of the "orogenic" gold deposits of the Southern Tien Shan and define specific post-collisional stage of magmaism and mineralization.
X.C. Zhang 1, B. Spiro2, C.Halls3, C.J. Stanley2 and K.Y. Yang4 (2003): Sediment-hosted disseminated gold deposits in SW Guizhou, PRC: Their geological setting and origin in relation to mineralogical, fluid inclusion and stable isotope characteristics International Geology Review Vol 45.
1 Department of Earth Science and Engineering, Royal School of Mines, Imperial College, London SW7 2BP, UK and Institutte of Geochemistry Chinese Academy of Sciences, Guiyang 550002, P.R.. China
2 Department of Mineralogy, The Natural History Museum, London SW7 5BD, UK
3 Department of Earth Science and Engineering, Royal School of Mines, Imperial College, London SW7 2BP, UK, and Department of Mineralogy, The Natural History Museum, London SW7 5BD, UK
4 Institutte of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, P.R.. China
Abstract
The sediment-hosted disseminated gold deposits
in Southwest Guizhou, People's Republic of China (PRC) are located in
faults on the flanks of anticlines or domes in clastic sedimentary rocks
of Late Permian to Middle Triassic age on the southwestern edge of the
Yangtze Paraplatform. Lamprophyres crop out in the vicinity of the gold
deposits. Mineralization in the area coincides with belts of weak Bouguer
gravity and magnetic anomalies. The Lannigou and Yata deposits, described
in detail in the present study, together with Baidi, are situated in
the southeastern domain where mineralization was emplaced in fine turbidites
of basinal facies of Middle Triassic age. The structures guiding this
mineralization are high-angle reverse faults on domes or anticlines.
To the northwest, the Getang deposit is one of a group of deposits,
including Zimudang, Sanchahe, Dayakou, and Xiongwu, which were emplaced
in silicified breccias in impure carbonates or marls of Upper Permian
to Lower Triassic platform facies. They are controlled by low-angle
and bedding-parallel faults on anticlines.
The clastic sedimentary host rocks are rich in illite and organic matter.
Mineralization takes the forms of pervasive silicification, veinlets
of quartz and disseminated auriferous arsenic-bearing pyrite and arsenopyrite,
veins of quartz and calcite, and veinlets of realgar, cinnabar and stibnite.
Gold is mainly associated with arsenic-rich pyrite. The main stage gold
mineralization in pyrite is accompanied by pervasive silicification
of host rocks. The Permian Emeishan basalts, widely distributed in the
northwestern area, contain high average gold contents and may have been
the primary source of the gold in the sediment-hosted deposits in SW
Guizhou. Arsenic, antimony and mercury show a pattern of distribution
similar to that of gold in country rocksand host rocks. Gold is found
mainly in pyrite and partly in illite. Analysis of samples from the
Lannigou deposit by high-resolution electron-probe microanalysis (EPMA)
revealed that gold occurs in zones of intermediate arsenic content (3-5
wt%) on pyrite rims. It is deduced that gold probably occurs as discrete
submicron-sized particles rather than as a charged Au species in a coupled
diadochic substitution with arsenic in the pyrite structure.
The auriferous fluids at the Lannigou and Yata deposits are shown to
be CO2-rich (Xco2>0.05)
and of low salinity (<5 wt% equiv. NaCl) with relatively high homogenization
temperatures (mainly 240 to 300 0C)
and were probably trapped under high confining pressures (1.5 to 2.3
kb). They are not typical epithermal fluids. At Lannigou, the d34SVCDT
values of sulphides range from +8.4 to +12.5‰, the d13CVPDB
of carbon in calcite ranges from -0.1 to -3.6‰, and the d18OVSMOW
of quartz and calcite are mainly around +17.6 and around +25.8‰ respectively.
At Getang, the isotopic compositions of hydrothermal minerals are in
the range d34SVCDT
of -14.3 to +4.4‰ for sulphides, d13CVPDB
of -3.2 to -0.6‰ for calcite and d18OVSMOW
of +14.0 to +15.3‰ for calcite and quartz. These isotope analyses show
that sulphur was probably derived mostly via the marine reservoir from
the sedimentary country rocks, though part of the sulphur in the Getang
deposit could be from altered or weathered basalt. Most of the carbon
in the hydrothermal fluids was probably derived from the dissolution
of carbonates in sedimentary rocks, though decarbonation reactions caused
by low-grade metamorphism at deeper levels could have contributed some
of the CO2. The original hydrothermal
fluids responsible for the gold mineralization are deduced to have formed
by burial metamorphism at depths of 6-8 km with addition of meteoric
water through deep fractures. Mineralization probably took place when
fluids concentrated at near lithostatic pressures in permeable clastic
horizons deconpressed as they were released along structural channelways
during the Yanshanian tectonic cycle when impermeable shale cover sequences
were breached. Mixing between evolved formation water/burial metamorphic
water and meteoric waters was an important process during the late stage
of the hydrothermal evolution. The tectonic setting, structural control,
hydrothermal alteration, and ore and gangue mineral assemblages of the
deposits in SW Guizhou show many features in common with those of the
Carlin-type gold deposits in Nevada, USA, though the host rocks, relationship
to igneous rocks and the timing of mineralization are different.
Frances Wall (2004): Kola Peninsula: minerals and mines. Geology Today vol. 19, No. 6, November-December 2003, 206-211.
Department of Mineralogy, The Natural History Museum, London, UK; E-mail: f.wall@nhm.ac.uk
Abstract
Numerous world class mineral deposits made the Kola Peninsula a 'Mecca' for mineralogists and key economic deposits make it one of Russia's most important industrial area. For geologists there is the challenge of explaining how this situation has come about.
R.J. Herrington1, M. Smith2, V.V. Maslennikov3, E. Belogub3 and R.N. Armstrong1 (2002): A short review of Palaeozoic hydrothermal magnetite iron-oxide deposits of the South and Central Urals and their geological setting. In: Porter T.M. (ed.), Hydrothermal Iron Oxide Copper-Gold & Related Deposits: A Global Perspective, Vol. 2, pp. 243-253, PGC Publishing, South Australia, ISBN 0-9580574-1-9.
1 Department of Mineralogy, The Natural History Museum, London,
UK; E-mail: rmh@nhm.ac.uk
2 The School of the Environment, University of Brighton, UK;
3 Institute of Mineralogy, Russian Academy of Sciences, Miass,
Russia.
Abstract
The Urals orogen represents the site of Palaeozoic ocean development which developed into a zone of arc development, arc-continent collision, continent-continent collision and post-orogenic collapse. The orogen is host to a number of world-class VMS deposits in the Silurian to Devonian arc sequences but in addition is host to highly significant iron oxide deposits of both hydrothermal and orthomagmatic origin. The hydrothermal ores are developed in Palaeozoic belts associated with rift-related dominantly mafic, largely subaerial alkaline volcanism intruded by comagmatic stocks a varying ages from the Late Silurian to Early Carboniferous. Volcanism, sedimentation and mineralisation all seem to be controlled by major N to NNE trending structures. Much of the mafic volcanic sequence shows hematisation, evidence of early oxidation of the lava-tuff packages. Mineralisation comprises massive and disseminated magnetite bodies with elevated REE and ubiquitous accessory apatite. The deposits can be huge, in the case of the Carboniferous Kachar deposit in Kazakhstan reserves of over a billion tonnes of >45% Fe are defined. Some of the bodies are true contact skarns developed at the contact between intrusive bodies and volcano-sediments which include limestones. Other bodies, including the giant Kachar deposit are distal to any possible related intrusions and are developed within regionally extensive scapolite alteration zones. A regionally consistent pattern of early feldspar+-biotite alteration followed by ore-stage pyroxene-garnet-scapolite followed by late hydrous silicate-carbonate alteration is repeated throughout the Urals. Regionally extensive scapolitisation is common in most of the belts. Base metals are common in the deposits, often appearing late in the paragenetic sequence, with some bodies having almost economic copper grades (0.6% Cu) with significant precious metals.
V.V. Zaykov, V.V. Maslennikov, E.V. Zaykova and R.J. Herrington (2001): Ore formation and ore-facies analysis of massive sulphide deposits of the Urals paleoocean. Miass: Urals Branch of the Russian Academy of Sciences 315pp ISBN 5-7691-1234-4 (in Russian with English abstract).
Resume:
This monograph contains the compiled results of the Russian perspective of joint NHM-IMIN (Russian partners) research since 1995 into the massive sulphide deposits of the south Urals. The book documents characteristics of the deposits and host rocks within the Uralide orogen, proposing models for the environment of formation, early diagenesis and subsequent preservation of the deposits.
R.J. Herrington1, R.N. Armstrong1, V.V. Zaykov2, V.V. Maslennikov2, S.G. Tessalina1,2, J-J. Orgeval3, and R.N.A. Taylor4 (2002): Massive sulfide deposits in the south Urals: Geological setting within the framework of the Uralide orogen. In: Mountain building in the Uralides: Pangea to Present, Geophysical Monograph 132, American Geophysical Union, pp 155-182.
1 Department of Mineralogy, The Natural History Museum, London,
UK; E-mail: rmh@nhm.ac.uk
2 Institute of Mineralogy, Russian Academy of Sciences Miass,
Russia;
3 BRGM, Orleans, France;
4 Southampton Oceanography Centre, Southampton, UK.
Abstract
The south Urals is host to more than 80 Paleozoic volcanic-hosted massive sulfide (VMS) deposits developed in four distinct metallogenic zones. From west to east these are: the Sakmara zone, Main Uralian fault zone, and the east and west Magnitogorsk zones. In the Sakmara zone, the chemistry of host volcanic suites is consistent with development of the zone in a Silurian oceanic arc. The Main Uralian fault marks a line of paleosubduction and contains VMS deposits similar to those formed in modern mid-ocean ridge settings. The Magnitogorsk zones contain VMS deposits formed in a Devonian fore-arc, arc and inter-arc or proto-back arc setting. The earliest volcanics of the Magnitogorsk zone, the Baimak-Buribai formation, form a boninitic fore-arc sequence, evolving later to more calc-alkalic volcanics with evidence for a contribution from subducted slab to the volcanics. Later, and farther east of the subduction suture, a rifted, more mature arc setting formed where the Karamalytash formation volcanics developed in an inter-arc or proto-back arc setting. The Karamalytash formation shows little evidence of contribution from subducted sediment to the melt. Stratigraphically overlying the Baimak-Buribai formation, and partly time equivalent to the Karamalytash formation, is the Irendyk formation. The Irendyk formation is VMS-poor, but contains abundant epiclastic volcanosediments and epithermal-like gold-barite deposits, indicative of shallower sea conditions. The Irendyk formation appears to form a long linear geographic feature, perhaps marking the line of an emerging arc sequence behind which the Karamalytash formation developed in a rift. Previous authors suggest that the west and eastern Magnitogorsk zones developed as separate arcs, but the arc-like volcanics in the east Magnitogorsk zone may simply indicate the migration of the volcanic arc eastwards as the East European craton approached the Main Uralian fault.
Jingwen Mao1,2, Andao Du3, R. Seltmann4, and Jinjie Yu2 (2003): Re-Os ages for the Shameika porphyry Mo deposit and the Lipovy Log rare metal pegmatite, central Urals, Russia. Mineralium Deposita, SPRINGER Online First (Published online: 9 Nov. 2002) DOI 10.1007/s00126-002-0331-2. Contact E-mail: jingwenmao@263.net
SpringerLink article1
Faculty of Geosciences and Resources, China
University of Geosciences, Beijing China;
2 Institute of Mineral Resources, Chinese
Academy of Geological Sciences, Beijing, China;
3 National Research Center of Geoanalysis, Chinese Academy of Geological
Sciences, Beijing, China;
4 Department of Mineralogy, Natural History Museum, Cromwell Road, London,
UK.
Abstract
The ages for pegmatite rare metal and beryl (emerald) deposits, as well as porphyry Mo deposits in the Hercynian Uralide orogen, are not well known. Five molybdenite samples from the Lipovy Log pegmatite Ta-Nb-Mo deposit and 11 molybdenite samples from the Shameika porphyry Mo deposit were selected for Re-Os dating. Both mineral occurrences are spatial-temporally associated with the Adui composite granite pluton, a well-known rare metal-related granite intrusion. A Re-Os isochron age of 262.0±7.3 Ma was obtained for the Lipovy Log pegmatite Ta-Nb-Mo deposit. The Shameika porphyry Mo deposit, associated with the Malyshevo leucogranitic stock and surrounding hornfels, provided isochron ages of 273±5 and 282±6 Ma, for two groups of molybdenite (within stock and within hornfels). All of these Re-Os ages are consistent with presumed Hercynian ages for the granite intrusions, formed in a post-collisional setting within the Uralide orogen.
A.S. Yakubchuk, R. Seltmann, V.V. Shatov and A. Cole (2001):The Altaids: Tectonic Evolution and Metallogeny. SEG Newsletter, no. 46, pp. 1, 7-14.
Contact:
aley@nhm.ac.uk
The review paper comprises the first publication
from the NHM Mineralogy Department's Centre for Russian and Central
Asian Mineral Studies. The Altaids are one of the largest and most
economically important of the crustal blocks of the Eurasian landmass.
They host large numbers of ore deposits, many of world class, including
gold, copper-molybdenum, lead-zinc, and nickel. The rich metal endowment
of the Altaids is a result of a prolonged and complex history of crustal
growth and deformation. The paper describes the development of the
Altaids in relation to the diverse and widespread mineralisation they
contain.Abstract
A.S. Yakubchuk1, A. Cole2, R. Seltmann1 and V.V. Shatov3
(2002):Tectonic setting, characteristics, and regional exploration
criteria for gold mineralization in the Altaid orogenic collage: The
Tien Shan province as a key example. Society of Economic Geologists,
Special Publication 9, p. 177-201. Contact: aley@nhm.ac.uk
1 Department of Mineralogy, Natural History Museum, Cromwell Road, London,
United Kingdom
2 Metal Bulletin Research, London, United Kingdom
3 All-Russia Geological Institute VSEGEI, St. Petersburg, Russia
Abstract
The richest gold province in central Eurasia, containing about two-thirds of the region’s gold reserves, occurs in the late Paleozoic fold and thrust belts of the Tien Shan, a component of the giant Altaid orogenic collage. Extending through Uzbekistan, Tajikistan, Kyrgyzstan and continuing into western China, the Tien Shan hosts an array of world-class gold deposits. Principally, these include late Paleozoic orogenic-type gold deposits, such as Muruntau and Kumtor, two of the world’s ten biggest gold resources. Such deposits are often temporally and spacially associated with syntectonic granitoid intrusions that were emplaced into a terrain of metamorphosed terrigenous carbonaceous rocks of Late Proterozoic to middle Paleozoic age. In addition, many gold deposits are also related to world-class Cu-porphyry, epithermal and skarn systems formed earlier during early-middle Carboniferous magmatic arc activity. Similar, but smaller and older deposit types occur throughout the entire Altaids.This orogenic collage consists of several Vendian to late Paleozoic magmatic arcs, which were first rifted off the East European and Siberian cratons. The clockwise rotation of Siberia relative to Eastern Europe during middle and late Paleozoic caused several collisional episodes of these arcs, both with each other and with the cratons, as well as their gradual oroclinal bending. The formation of porphyry and epithermal deposits in the magmatic arcs coincides with the episodes of their oroclinal bending, whereas each collisional episode coincides with the formation of orogenic gold deposits. The giant gold deposits, however, formed during the final amalgamation of the collage in the Tien Shan province.
Although the Tien Shan has been actively studied during the Soviet era, it remains relatively under-explored, and the regionally extensive gold mineralization indicates that considerable potential for major new discoveries still exists in the province. It is a highly prospective terrain for orogenic gold deposits especially, but also for skarn, Carlin-like, and epithermal gold occurrences, which may represent a broad-scale telescoping of hydrothermal systems. Conceptual models of orogenic gold mineralization in the belt invoke interaction between imbricated thrusts, deep-seated high-angle reverse and strike-slip faults, synorogenic granitoid intrusions and metalliferous black shales during late Paleozoic arc-continent collision and deformation. These factors represent the main geological criteria that provide the maximum potential for the formation of gold deposits in the Tien Shan, and can be extrapolated to assist exploration elsewhere in the Altaids.R. Seltmann, A. Yakubchuk and V. Shatov (2002): Mineral Potential of Central Asia: What Do We Know? In: Mineral Potential of Asia – An MMAJ Forum. CD-Rom with Power Point Presentations and Proceedings abstract publication. Metal Mining Agency of Japan. http://www.mmaj.go.jp/mric_web/MMAJ_FORUM/MMAJForum.html E-mail: rs@nhm.ac.uk
Abstract
The Central Asian republics of Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan and Uzbekistan intend to redefine their role both in the CIS and Asian markets, developing the mineral and energy resource potential of their national economies. The landlocked location of the Central Asian mineral provinces causes high infrastructure costs. Most transport routes are traditionally through Russia. One possible alternative is a Silky Way railroad project.The mining industry in these five transition-economy countries plays an important role. In the past, the region served as a major metal provider for the FSU. Mineral products account for 1/3 to 1/2 of national GDPs from exports of gold (3.4 percent of the world’s production in Uzbekistan (1996) and significant amount in Kyrgyzstan), ferrochrome (20 percent of the world’s production in Kazakhstan), copper, lead, zinc, molybdenum, tungsten, niobium, tantalum, uranium, mercury, and antimony. In Turkmenistan, which focuses on the energy sector, and Tajikistan, processing imported bauxite with cheap hydroelectric power means that the mining industry plays a subordinate role. This is despite significant mineral resources of gold, silver, and copper in the Tajik Tien Shan and the Pamirs.
Most ore deposits are confined to the Altaid orogenic collage, located between the East European and Siberian cratons and smaller Precambrian slivers. Several generations of arc magmatism contributed primarily to the ore potential of the Stans: Vendian to Early Paleozoic, Middle Paleozoic to Early Carboniferous, Early Carboniferous to Permo-Triassic. In the Mesozoic, there were several post-collisional magmatic events. The resulting tectonic-metallogenic belts are confined to the Kipchak arc, Kazakh-Mongol arc and its back-arc rifts, Valerianov-Beltau-Kurama arc, South Tien Shan – East Urals – Irtysh-Zaissan suture, Mugodzhar-Rudny Altai arc, and Sakmara suture.
The region is among the world’s major Au producers. It hosts giant (>10 M oz) and medium to large orogenic (mesothermal) Au deposits of Muruntau, Kumtor, Bakyrchik, controlled by the South Tien Shan – East Urals – Irtysh Zaissan suture, granite-related Vasilkovskoe, Bestobe, Zholymbet deposits in the Kipchak arc, and Berezovskoe, Kochkar, Yubileinoe granite-related deposits in the Mugodzhar-Rudny Altai arc. Kochbulak, an important Au-Ag epithermal deposit, and low-grade hypogene Cu-porphyry deposits, with Au, Mo, and PGE by-products (Kounrad, Kalmakyr-Dalnee, Nurkazgan), are related to mid-late Paleozoic magmatic arcs of the region. The world-class Dzhezkazgan sediment-hosted Cu deposits are associated with Carboniferous red-bed aquifers. PGE mineralization occurs in black shale-hosted deposits (Muruntau) and in the porphyries (Bozshakol). Pb-Zn (Ag-Cu-Au) deposits (Maikain, Mizek, Tekeli, Shalkiya, Rudny Altai) are of different ages and types (VMS, sedex, sediment-hosted), with major production from Rudny Altai. Chromium deposits in Paleozoic ophiolites occur in the Kazakh Urals, related to the Sakmara suture (Kempirsai). Granite-related rare metal (Sn, W, Mo, Nb, Ta, REE) mineralization occurs in late-orogenic greisens, stockworks, skarns and pegmatites in Kazakhstan and Kyrgyzstan (Akchatau, Batystau, Verkhnee Kairakty, Aktiuz, Kalba). Significant U and V deposits of various types are present in Kazakhstan, Kyrgyzstan and Uzbekistan.
Regardless of the success of prospecting and exploration activities during Soviet time and since the 1990s, the region is still underexplored. This is a function of the complex geodynamic setting of this vast territory, exceeding the size of Europe, and is also related to continuing financial and legal difficulties. However, there are several operating mines with western investment. Despite the exploration maturity, this region is still able to generate new targets, especially in areas previously restricted or where attention is focussed under the Mesozoic-Cenozoic cover. Reassessing the conventional models of known deposits, such as mercury deposits of Kyrgyzstan or Fe-skarn deposits of the Torgai depression, can potentially lead to recognition of new deposit types. There is significant potential to develop known discoveries, such as lateritic nickel deposits in Kazakhstan.
D. Konopelko1, G. Biske1, B. Belyatsky2, R. Eklund3 and R. Seltmann4 (2002): Geochronology and geochemistry of Hercynian post-collisional granitoid complexes of the eastern part of the South Tien-Shan. In: F. Mitrofanov (ed.). Geology and geoecology - Proceedings XIIIth Young Scientist Conference, Apatity, Russia, 19-22 November 2002. Vol. 1: Geology, Petrology and Geochronology, Ecology; pp. 61-65.
1
St.Petersburg
State University, St. Petersburg, Russia; E-mail: konopelk@DK2032.spb.edu
2 Institute
of Precambrian Geology and Geochronology, St. Petersburg, Russia;
3 Turku
University, Finland;
4 Department
of Mineralogy, NHM, London, UK.
Abstract
The Tien-Shan belt formed during the late Paleozoic collision of Kazakhstan and Tarim paleocontinents. Shortly after the culmination of the collision voluminous post-collisional granitoid intrusions invaded the whole region regardless to the position of the Hercynian structural units. In the eastern Hercynian Tien-Shan some 25 intrusions with distinct A-type affinities have been formed.
Zircons from four major intrusions of the region were dated by U-Pb SIMS method utilizing ion microprobe Cameca 1270 in NHM, Stockholm and two magmatic pulses at 295 Ma and 280 Ma were established. When few discordant analyses were excluded from calculations the concordant ages for the four intrusions were calculated as following: Dzhangart 296.7±4.2 Ма, n=8, MSWD=0.69; Mudrjum 282.0±1.2 Ма, n=12, MSWD =4.1; Kok-Kiya 278.9±1.3 Ма, n=7, MSWD =0.08; Uchkoshkon 279±8.1 Ма, n=3, MSWD =4.9. All calculations were made using the program Isoplot/Ex v. 2.05 (Ludwig, 1999). Thus, it was established that the granitoids of the two age groups formed during two magmatic pulses with the age difference between the pulses outside the analytical error limits. eNd(315) values from seven samples representing granites of both age groups range between –2.39 and –5.62 indicating a significant input of Precambrian crustal component. This matches well the current knowledge of the eastern Tien-Shan as a collage of microcontinents with Precambrian basements.
A. Fedkin1, *, R. Seltmann2, N. Bezmen1 and G. Zaraisky1 (2002): Experimental testing of line rocks in Li-F granites: evidence from superliquidus experiments with F and P added. Bulletin of the Czech Geological Survey, Vol. 77, 2, pp.113-125. ISSN 1210-3527.
1 Institute of Experimental Mineralogy RAS,
Chernogolovka, Moscow District, Russia
* Dept. of Geophysical Sciences, University of Chicago, Chicago, USA;
E-mail: avf@uchicago.edu
2 Department of Mineralogy, Natural History Museum, London, UK
Abstract
New experimental data on the simulation of layered textures typical of some highly evolved granites are presented. In the experiments, low-evolved and high-evolved granite systems were compared, both doped with F and F+P. Most of the runs exhibit zones of quartz crystallization within a chemically heterogeneous granite glass. The experiment using typical material from the Li-F-P-rich Podlesí granite stock (Krušné hory Mts., Czech Republic) as a starting charge, with added F and P, resulted in discrete microlayering. In the quenched glass, rhythmically alternating thin (5–10 µm) bands either enriched or depleted in alumina occurred. The experimental result simulates natural analogs of granitic line rocks, which occur locally in the Podlesí stock as well as in the Orlovka and Etyka granite massifs, Eastern Transbaikalia (Russia).M.A. Sitnikova, A.N. Zaitsev, F. Wall, A.R. Chakhmouradian & V.V. Subbotin (2001): Evolution of the chemical composition of rock-forming carbonates in Sallanlatvi Carbonatites, Kola Peninsula, Russia. Journal of African Earth Sciences 32:
A.N. Zaitsev, A. Demény, S. Sindern and F. Wall (2002): Burbankite group minerals and their alteration in rare earth carbonatites - source of elements and fluids (evidence from C-O and Sr-Nd isotopic data). Lithos, 62, 15-33. E-mail: fw@nhm.ac.uk
Abstract
Following from previous work in which burbankite carbonatites were described as transition environment pegmatites, this paper examines the source and evolution of the magma and fluids from which such carbonatites formed at Khibina and Vuoriyarvi. The work forms part of the recent INTAS-funded Kola project. It shows that REE-rich magmas and fluids are derived from the same carbonatitic source in each complex but that the complexes have different source signatures. In order to model the radiogenic isotopes in terms of mantle end members at least 3, possibly 4 components are now needed to produce the variation recorded on the Kola Peninsula.
L. E. Mordberg, C. J. Stanley and K. Germann (2001): Mineralogy and geochemistry of trace elements in bauxites: the Devonian Schugorsk deposit, Russia. Mineralogical Magazine, Vol. 65, 1, pp. 81-101. E-mail: cjs@nhm.ac.uk
Abstract
Processes of mineral alteration involving the mobilization and deposition of more than 30 chemical elements during bauxite formation and epigenesis have been studied on specimens from the Devonian Schugorsk bauxite deposit, Timan, Russia. Chemical analyses of the minerals were obtained by electron microprobe and element distribution in the minerals was studied by element mapping. Interpretation of these data also utilized high-resolution BSE and SE images. The main rock-forming minerals of the Vendian parent rock are calcite, dolomite, feldspar, aegirine, riebeckite, mica, chlorite and quartz; accessory minerals are pyrite, galena, apatite, ilmenite, monazite, xenotime, zircon, columbite, pyrochlore, chromite, bastnaesite and some others. Typically, the grain-size of the accessory minerals in both parent rock and bauxite is from 1 to 40 m. However, even within these rather small grains, the processes of crystal growth and alteration during weathering can be determined from the zonal distribution of the elements. The most widespread processes observed are: (1) Decomposition of Ti-bearing minerals such as ilmenite, aegirine and riebeckite with the formation of 'leucoxene', which is the main concentrator of Nb, Cr, V and W. Crystal growth can be traced from the zonal distribution of Nb (up to 16 wt.%). Vein-like 'leucoxene' is also observed in association with organics. (2) Weathering of columbite and pyrochlore: the source of Nb in 'leucoxene' is now strongly weathered columbite, while the alteration of pyrochlore is expressed in the growth of plumbopyrochlore rims around Ca-rich cores. (3) Dissolution of sulphide minerals and apatite and the formation of crandallite group minerals: 'crandallite' crystals of up to 40 m size show a very clear zonation. From the core to the rim of a crystal, the following sequence of elements is observed: CaBaCePbSrNd. Sulphur also shows a zoned but more complicated distribution, while the distribution of Fe is rather variable. A possible source of REE is bastnaesite from the parent rock. More than twelve crandallite type cells can be identified in a single 'crandallite' grain. (4) Alteration of stoichiometric zircon and xenotime with the formation of metamict solid solution of zircon and xenotime: altered zircon rims also bear large amounts of Sc (up to 3.5 wt.%), Fe, Ca and Al in the form of as yet unidentified inclusions of 1-2 m. Monazite seems to be the least altered mineral of the profile. In the parent rock, an unknown mineral of the composition (wt.%): ThO2 - 54.8; FeO - 14.6; Y2O5 - 2.3; CaO - 2.0; REE - 1.8; SiO2 - 12.2; P2O5 - 2.8; total - 94.2 (average from ten analyses) was determined. In bauxite, another mineral was found, which has the composition (wt.%): ThO2 - 24.9; FeO - 20.5; Y2O5 - 6.7; CaO - 2.0; ZrO - 17.6; SiO2 8.8; P2O5 - 5.4; total - 89.3 (F was not analysed; average from nine analyses). Presumably, the second mineral is the result of weathering of the first one. Although the Th content is very high, the mineral is almost free of Pb. However, intergrowths of galena and pyrite are observed around the partially decomposed crystals of the mineral. Another generation of galena is enriched in chalcophile elements such as Cu, Cd, Bi etc., and is related to epigenetic alteration of the profile, as are secondary apatite and muscovite.
L.E. Mordberg, C.J. Stanley and K. Germann (2000): Rare earth element anomalies in crandallite group minerals from the Schugorsk bauxite deposit, Timan, Russia. European Journal of Mineralogy, 12, pp. 1229-1243. E-mail: cjs@nhm.ac.uk
Abstract
Two generations of crandallite [AB3(XO4)2(OH)6H0 or 1 - where A = Ca,Ba,Sc,Pb,Bi,REE,Th, B= Al,Fe,Ga, and X= P,As,S,Si,C] from the Schugorsk bauxite deposit were distinguished by electron probe microanalysis. The first formed under oxidizing conditions in a neutral to slightly alkaline environment and has significant cerium depletion. The second formed under reducing conditions and a more alkaline environment and is enriched in samarium. Crandallite minerals have a broad distribution in bauxitic and lateritic profiles of different origins and will have different REE profiles depending on the Eh-pH conditions during weathering. They can thus be used as environmental indicator minerals.
L.N. Kogarko, C.T. Williams and A.R. Woolley (2002). Chemical evolution of loparite through the layered, peralkaline Lovozero complex, Kola Peninsula, Russia. Mineralogy and Petrology, 74: 1-24. E-mail: ctw@nhm.ac.uk
Abstract
Lovozero, the largest of the world’s layered peralkaline intrusions, includes gigantic deposits of Nb + REE-loparite ore. Loparite became a cumulus phase after crystallisation of about 35% of the ‘Differentiated complex’, and its compositional evolution has been investigated through a 2.35km section of the intrusion. The composition of the cumulus loparite changes systematically upwards through the intrusion with an increase in Na, Sr, Nb and Th and decrease in REE and Ti. This main trend of loparite evolution records differentiation of the peralkaline magma through crystallisation of 1600m of the intrusion.
The formation of the loparite ores was the result of several factors including the chemical evolution of the highly alkaline magma and mechanical accumulation of loparite at the base of a convecting unit. At later stages of evolution, when concentrations of alkalis and volatiles reached very high levels, loparite reacted with the residual melt to form a variety of minerals including barytolamprophyllite, lomonosovite, steenstrupine-(Ce), vuonnemite, nordite, nenadkevichite, REE,Sr-rich apatite, vitusite-(Ce), mosandrite, monazite-(Ce), cerite and Ba,Si-rich belovite. The absence of loparite ore in the “Eudialyte complex” is likely to be a result of the wide crystallisation field of lamprophyllite, which here became a cumulus phase.
A. Yakubchuk (2002): The Baikalide-Altaid, Transbaikal-Mongolian and North Pacific orogenic collages: a similarity and diversity of structural patterns and metallogenic zoning. In: D. Blundell, F. Neubauer, A. von Quadt (eds) The Timing and Location of Major Ore Deposits in an Evolving Orogen, Geological Society Special Publication No. 204, 368 p.; E-mail: aley@nhm.ac.uk
Abstract
The Baikalides-Altaid, Transbaikal-Mongolians and North Pacific orogenic collages consist of several oroclinally bent magmatic arcs separated by accretionary complexes and ophiolitic sutures located between the major cratons. The tectonic patterns of these collages are principally similar as they were formed as a result of rotation of the surrounding cratons and strike-slip translation along the former convergent margins.
The Altaid and North Pacific collages have principally the same distribution of metallogenic belts. In particular, the middle-late Palaeozoic belts of porphyry and epithermal deposits in the Altaids occupy the same position as the Mesozoic-Cenozoic metallogenic belts of the North Pacific collage. The Ural platinum belt occupies similar position tothe belt of platinum-bearing intrusions in Alaska. Major mineralizing events producing world-class intrusion-related Au, Cu-(Mo)-porphyry and VMS deposits in the Altaids. Formation of major porphyry, epithermal and Alaska-type PGMdeposits took place simultaneously with oroclinal bending. The tectonic setting of the orogenic gold deposits in the Tien Shan and Verkhoyansk-Kolyma provinces, hosting world-class hardrock gold deposits, is also similar, especially the distribution of their gold endowments. Major orogenic gold deposits occur within the sutured backarc basins. The craton-facing passive margin rock sequences, initially formed within backarc basins and now entrapped within such oroclines, represent favorable locations for emplacement of orogenic gold deposits.
A. Yakubchuk (2002): Architecture and mineral deposit settings of the Altaid orogenic collage: a revised model. In: Bor-ming Jahn, N. Dobretsov and B. Natal'in (eds), Journal of Asian Earth Sciences, Special Issue (accepted for publication). E-mail: aley@nhm.ac.uk
Abstract
The Altaids are an orogenic collage of Neoproterozoic-Paleozoic rocks located between the East European, Siberian, North China and Tarim cratons, smaller Precambrian slivers of Mongolia and Late Proterozoic orogens. The basement structures of this collage consist of only three oroclinally bent Neoproterozoic-Early Paleozoic magmatic arcs (Kipchak, Tuva-Mongol, and Mugodzhar-Rudny Altai), separated by sutures of their former backarc basins, which were stitched by new generations of overlapping magmatic arcs. In addition the Altaids host accreted fragments of the Neoproterozoic to EarlyPaleozoic oceanic island chains and Neoproterozoic to Cenozoic plume-related magmatic rocks superimposed on the accreted fragments. All these assemblages host important, many world-class, Late Proterozoic to Early Mesozoic gold, copper-molybdenum, lead-zinc, nickel and other deposits of various types.
In the Late Proterozoic, during breakup of the supercontinent Rodinia the Kipchak and Tuva-Mongol magmatic arcs were rifted off Eastern Europe-Siberia and Laurentia to produce oceanic backarc basins. In the Late Ordovician, the Siberian craton began its clockwise rotation with respect to Eastern Europe and this coincides with the beginning of formation of the Mugodzhar-Rudny Altai arc behind the Kipchak arc.These earlier arcs produced mostly Cu-Pb-Zn VMS deposits, although some important intrusion-related orogenic Au deposits formed during arc-arc collision events in the Middle Cambrian and Late Ordovician.
The clockwise rotation of Siberia continued through the Paleozoic until the Early Permian producing several episodes of oroclinal bending, strike-slip duplication and reorganization of the magmatic arcs to produce the overlapping Kazakh-Mongoland Zharma-Saur-Valerianov-Beltau-Kurama arcs that welded the extinct Kipchak and Tuva-Mongol arcs. This resulted in amalgamation of the western portion of the Altaid orogenic collage in the Late Paleozoic. Its eastern portion amalgamated only in the early Mesozoic and was overlapped by the Transbaikal magmatic arc, which developed in response to subduction of the oceanic crust of the Paleo-Pacific Ocean. Several world-class Cu-(Mo)-porphyry, Cu-Pb-Zn VMS and intrusion-related Au mineral camps, which formed in the Altaids at this stage, coincided with the episodes of plate reorganization and oroclinal bending of magmatic arcs. Major Pb-Zn and Cu sedimentary rock-hosted deposits of Kazakhstan and Central Asia formed in backarc rifts, which developed on the earlier amalgamated fragments. Major orogenic gold deposits are intrusion-related deposits, often occurring within black shale-bearing sutured backarc basins with oceanic crust.
After amalgamation of the western Altaids, this part of the collage and adjacent cratons were affected by the Siberian superplume, which ascended at the Permian-Triassic transition. This plume-related magmatism produced various deposits, such as famous Ni-Cu-PGE deposits of Norilsk in the northwest of the Siberian craton.
In the early Mesozoic, the eastern Altaids were oroclinally bent together with the overlapping Transbaikal magmatic arc in response to the northward migration and anti-clockwise rotation of the North China craton. The following collision of the eastern portion of the Altaid collage with the Siberian craton formed the Mongol-Okhotsk suture zone, which still links the accretionary wedges of central Mongolia and Circum-Pacific belts. In the late Mesozoic, a system of continent-scale conjugate northwest-trending and northeast-trending strike-slip faults developed in response to the southward propagation of the Siberian craton with subsequent post-mineral offset of some metallogenic belts for as much as 70 to 400 km, possibly in response to spreading in the Canadian basin. India-Asia collision rejuvenated some of these faults and generated a system of impact rifts.