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Causes of variation in crystal morphology in metamorphogenic pyrite deposits of the Cameros Basin (N Spain)

Alonso Azcárate, Jacinto and Rodas , Magdalena and Fernández Díaz, Lourdes and Bottrell, S.H. and Mas, J.R. and López Andrés, Sol (2001) Causes of variation in crystal morphology in metamorphogenic pyrite deposits of the Cameros Basin (N Spain). Geological Journal, 36 (2). pp. 159-170. ISSN 0072-1050

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Abstract

The low-grade metasediments of lthe Cameros Basin, northem Spain, host a number of deposits of spectacular quality pyrite
mineralization. These formed during regional metamorphism and the pyrite crystals exhibit a wide range of morphologies. On
the basis of pyrite crystal habit, the deposits can be classified into two groups: Group 1 comprises deposits with cubic, elongated
or platy crystals; Group 11 comprises deposits charactenzed by pyntohedra and cubo-pyritohedra with striated faces, along with
blocky crystals and he-grained aggregates. Group 1 deposits are formed in sequences dorninated by meandriform fluviatile
sediments, while Group 11 is hosted by deltaic plain and lacustrine metasediments.
Temperature differences between deposits and As content are possible causes of the different pynte morphologies in the
deposits, but no significant variation exists between the two groups for either factor. Comparison with experimentally grown
pyrite crystals suggests that Group 1 deposits have morphologies indicative of lower degrees of pyrite supersaturation than
pyrite crystals in Group 11 deposits. The sedimentary facies hosting Group 11 deposits provides a greater availability of
sedimentary sulphur (pyrite and sulphates). Moreover, reactions involving sulphate during metamorphism may have modified
fluid chernistry, which would also act to produce higher degrees of pynte saturation in fluids derived from the sulphate-rich
deltaic plain and lacustrine metasediments hosting the Group 11 deposits. This hypothesis is confirmed by sulphur isotope data
on the pyrites, which show a larger component of 34S-Enriched sulphate-derived sulphur in these deposits.


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Uncontrolled Keywords:Pyrite; Crystal morphology; Sulphur isotopes; Supersaturation; Sulphur availability; Fluid chemistry; Cameros Basin; Spain
Subjects:Sciences > Geology > Crystallography
ID Code:10586
Deposited On:03 May 2010 12:11
Last Modified:03 May 2010 12:11

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