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| Titel |
Multifractal magnetic susceptibility distribution models of hydrothermally altered rocks in the Needle Creek Igneous Center of the Absaroka Mountains, Wyoming |
| VerfasserIn |
M. E. Gettings |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1023-5809
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| Digitales Dokument |
URL |
| Erschienen |
In: Nonlinear Processes in Geophysics ; 12, no. 5 ; Nr. 12, no. 5 (2005-06-10), S.587-601 |
| Datensatznummer |
250010770
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| Publikation (Nr.) |
 copernicus.org/npg-12-587-2005.pdf |
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| Zusammenfassung |
| Magnetic susceptibility was measured for 700 samples of drill core from
thirteen drill holes in the porphyry copper-molybdenum deposit of the
Stinkingwater mining district in the Absaroka Mountains, Wyoming. The
magnetic susceptibility measurements, chemical analyses, and alteration
class provided a database for study of magnetic susceptibility in these
altered rocks. The distribution of the magnetic
susceptibilities for all samples is multi-modal, with overlapping peaked
distributions for samples in the propylitic and phyllic alteration class, a
tail of higher susceptibilities for potassic alteration, and an
approximately uniform distribution over a narrow range at the highest
susceptibilities for unaltered rocks. Samples from all alteration and
mineralization classes show susceptibilities across a wide range of values.
Samples with secondary (supergene) alteration due to oxidation or enrichment
show lower susceptibilities than primary (hypogene) alteration rock. Observed magnetic susceptibility variations and the monolithological
character of the host rock suggest that the variations are due to varying
degrees of alteration of blocks of rock between fractures that conducted
hydrothermal fluids. Alteration of rock from the fractures inward
progressively reduces the bulk magnetic susceptibility of the rock. The model
introduced in this paper consists of a simulation of the fracture pattern
and a simulation of the alteration of the rock between fractures. A multifractal
model generated from multiplicative cascades with unequal ratios produces
distributions statistically similar to the observed distributions. The reduction
in susceptibility in the altered rocks was modelled as a diffusion process operating
on the fracture distribution support. The average magnetic susceptibility was then computed for each
block. For the purpose of comparing the model results with observation, the
simulated magnetic susceptibilities were then averaged over the same
interval as the measured data. Comparisons of the model and data from
drillholes show good but not perfect agreement. |
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