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| Titel |
On the origin of zebra textures in Mississippi Valley-Type Pb-Zn Deposits with a special emphasis on the San Vicente Mine, Peru |
| VerfasserIn |
Ulrich Kelka, Daniel Koehn |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250091041
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| Publikation (Nr.) |
 EGU/EGU2014-5307.pdf |
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| Zusammenfassung |
| Alternating dark and white bands are common features of ore hosting dolostones which are
generally termed zebra textures. Worldwide these structures occur in ore deposits of
the Mississippi Valley-Type (MVT). This type of deposit frequently develops in
hydrothermal systems located in the flanks of foreland basins. In most MVT ore
deposits it is possible to distinguish between different stages which occur during the
formation of the zebra textures and the precipitation of the ore-minerals (mostly
Sphalerite and Galena). As the dark and white bands consist nearly completely of
dolomite, despite the colour, the only clearly recognisable difference is the grain
size.
Today there are several theories which try to explain the formation of this kind of structure,
for example by dissolution-precipitation (FONTBONTé et al., 1993) or by displacive vein
growth (MERINO et al., 2006).
Based on these theories and additional analytical findings, we want to develop a numerical
model to study the banding and mineralisation. This model should include all processes from
dolomitization, to the development of the zebra textures and finally the precipitation of
Sphalerite and Galena.
Using optical microscope and SEM, we found, that there are also differences in the
shapes of the grain boundaries of the fine grained dark (lobate) and coarse grained
white bands (polygonal). Furthermore, there is a large number of second-phase
particles, namely apatite, iron oxides and organic matter, present in the dark bands.
Often these particles are lined up at the grain boundaries. These insights lead to
the hypothesis that the grain growth in the dark bands is influenced by obstacles
that reduce the growth rate and therefore lead to a bifurcation of this rate in the
system.
For the modelling the microdynamic simulation software ELLE is used to perform a
2D-simulation at the scale of a thin section. This simulation uses a boundary-model coupled
with a lattice-particle-code (BONS et al. 2001). The grain boundaries move according to a
rate law based on dissolution-precipitation processes as a function of differences
in surface energy. Layered distributions of particle densities are initially set as a
background.
With this simple simulation of grain growth influenced by particle distributions we show, that
this process is able to develop structural patterns that are very similar to those present in the
natural samples from the San Vicente Mine in Peru.
References
BONS P D, KOEHN D, and JESSELL W (2008) Microdynamic Simulation. Springer-Verlag Berlin
Heidelberg
FONTBONTé L (1993) Self-organization fabrics in carbonate-hosted ore deposits: the example of
diagenetic crystallization rhythmites (DCRs), In: Current research in geology applied to ore
deposits. Proceedings of the Second Biennial SGA Meeting, Granada, Spain, p. 11
-14
MERINO E, CANALS A, and FLECHTER R C (2006) Genesis of self-organized zebra textures in burial
dolomites: Displacive veins, induced stress, and dolomitization. Geologica Acta, Vol. 4 No. 3, p.
383-393 |
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