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Microtraces
in columbites according to LA-ICP-MS data
Vasilyev
N.V.*, Udoratina O.V. **, Sitnikova M.A. ***
*FSUC IMGRE,
Moscow, Russia,
**IG Komi SC
UB RAS, Syktyvkar, Russia
***BGR
Geozentrum, Hannover, Germany
udoratina@geo.komisc.ru
In recent years mineralogical investigations actively have been using
local methods to study isotope and microtrace mineral composition (LA-ICP-MS,
SIMS). These methods allowed studying microcomposition of zircons,
sheelites, columbites and other minerals from various genetic
environments. Federal Agency for geosciences and resources (BGR,
Hannover, Germany) supports program «Fingerprinting
of conflict minerals: columbitetantalite (‘‘coltan’’) ores»
for the study of microtrace composition of columbites and database is
being developed. Within the framework of this program the certification
of columbite-tantalum mineral ore Coltan is carried out to observe
trading chains. This program plans to characterize the behavior of
microtraces in columbites and tantalites from various pegmatites of
Africa, and the results have been presented in a number of articles (for
example Graupner et al., 2010).
We studied the behavior of columbites from deposits Ulug-Tanzek and
Taikeu with -MS Element XR and laser ablation system New Wave UP193-FX
with locality 10-80 mcm.
The greatest homogeneity was determined for 1k columbite, and it was
chosen as reference sample for the second stage of investigations. At
the second stage the microtraces in columbites from deposits Ulug-Tanzek,
Zashikhinskoe, Novobobrovskoe ore field were studied in IMGRE with the
use of ICP-MS Elan 6100 DRC and laser ablation system LSX-200 with
locality 50 mcm.
The columbites from various genetic environments are characterized by
considerable changes in Y, REE, Ta, Ti, Sn, W, Th, U contents. The
behavior of rare earths is the most indicative regarding geochemical
information about the microtrace composition.
The contents of rare earths were normalized by khondrites, and
indicative Eu/Eu*, Ce/Ce*, La/Lu ratios were calculated.
The columbites from deposits in alkaline granites and metasomatites
Ulug-Tanzek (eatern Tuva), Zashikhinskoe (Novoudin district of Irkutsk
region), Taikey (Polar Urals) were studied. All the studied fractions of
columbites from these objects are characterized by a pronounced negative
europium anomaly, which is common for granite parageneses. The depth of
the anomaly from early generations to the latest is not consistent.
Columbite REE distribution is generally characterized by a sharp
enrichment of heavy lantanoids La/Lu <<1. The columbites of the latest,
possibly metasomatic generation, differ sharply from the early
columbites by greater activity of light and medium lantanoids, and
accordingly, equal-arm spectrum La/Lu ≈1, which is usual for minerals of
late hydrothermal stage.
The columbites from Novobobrovsky ore field (Middle Timan) are also
characterized by the enrichment of heavy REE, and the europium anomaly
is not distinct. Fraction 460 was studied from melanocratic phenites,
and also 10-A-1 from quartz-goethite vein. Both fractions are similar by
microtrace composition.
The studies of microtrace composition in columbites give a certain
genetic information about the genesis and evolution of rare metal
mineralization. We characterized a number of fetures of the columbite
mineralization connected with alkaline granites and phenites.
The studies are supported by the Program of RAS Presidium 12-П-5-1015
(block 4).
References
Graupner T., Melcher F., Gabler H.E., Sitnikova M., Bratz H. Rare earth
element geochemistry of columbite-group minerals: LA-ICP-MS data //
Mineralogical Magazine, 2010, Vol. 74(4), pp. 691–713. |