Geochemistry of rare earth elements in the Baba Ali magnetite skarn deposit, western Iran – a key to determine conditions of mineralisation
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Date
2016-04
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Instytut Geologii UAM
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Abstract
The Baba Ali skarn deposit, situated 39 km to the northwest of Hamadan (Iran), is the result of a syenitic pluton that
intruded and metamorphosed the diorite host rock. Rare earth element (REE) values in the quartz syenite and diorite
range between 35.4 and 560 ppm. Although the distribution pattern of REEs is more and less flat and smooth, light REEs
(LREEs) in general show higher concentrations than heavy REEs (HREEs) in different lithounits. The skarn zone reveals
the highest REE-enriched pattern, while the ore zone shows the maximum depletion pattern. A comparison of the concentration
variations of LREEs (La–Nd), middle REEs (MREEs; Sm–Ho) and HREEs (Er–Lu) of the ore zone samples to
the other zones elucidates two important points for the distribution of REEs: 1) the distribution patterns of LREEs and
MREEs show a distinct depletion in the ore zone while representing a great enrichment in the skarn facies neighbouring
the ore body border and decreasing towards the altered diorite host rock; 2) HREEs show the same pattern, but in the
exoskarn do not reveal any distinct increase as observed for LREEs and MREEs. The ratio of La/Y in the Baba Ali skarn
ranges from 0.37 to 2.89. The ore zone has the highest La/Y ratio. In this regard the skarn zones exhibit two distinctive
portions: 1) one that has La/Y >1 beingadjacent to the ore body and; 2) another one with La/Y < 1 neighbouring altered
diorite. Accordingly, the Baba Ali profile, from the quartz syenite to the middle part of the exoskarn, demonstrates
chiefly alkaline conditions of formation, with a gradual change to acidic towards the altered diorite host rocks. Utilising
three parameters, Ce/Ce*, Eu/Eu* and (Pr/Yb)n, in different minerals implies that the hydrothermal fluids responsible
for epidote and garnet were mostly of magmatic origin and for magnetite, actinolite and phlogopite these were of magmatic
origin with low REE concentration or meteoric water involved.
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Keywords
Almoughlagh, Ce/Ce* ratio, Eu/Eu* ratio, La/Y ratio
Citation
Geologos, 2016, 22, 1, pp.33-47.
ISBN
ISBN 978-83-232187-4-6