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| Titel |
The physical hydrology of magmatic-hydrothermal systems: High-resolution 18O records of magmatic-meteoric water interaction from the Yankee Lode tin deposit (Mole Granite, Australia) |
| VerfasserIn |
Szandra Fekete, Philipp Weis, Thomas Driesner, Christoph A. Heinrich, Lukas Baumgartner, Anne-Sophie Bouvier |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250133697
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| Publikation (Nr.) |
 EGU/EGU2016-14338.pdf |
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| Zusammenfassung |
| Magmatic-hydrothermal ore deposits are important economic Cu, Au, Mo and Sn
resources (Sillitoe, 2010, Kesler, 1994). The ore formation is a result of
superimposed enrichment processes and metals can precipitate due to
fluid-rock interaction and/or temperature drop caused by convection or
mixing with meteoric fluid (Heinrich and Candela 2014).
Microthermometry and LA-ICP MS trace element analyses of fluid inclusions of
a well-characterized quartz sample from the Yankee Lode quartz-cassiterite
vein deposit (Mole Granite, Australia) suggest that tin precipitation was
driven by dilution of hot magmatic water by meteoric fluids (Aud\'{e}tat et
al.1998). High resolution in situ oxygen isotope measurements of quartz have
the potential to detect changing fluid sources during the evolution of a
hydrothermal system. We analyzed the euhedral growth zones of this
previously well-studied quartz sample. Growth temperatures are provided by
Aud\'{e}tat et al. (1998) and Aud\'{e}tat (1999). Calculated $\delta
^{18}$O values of the quartz- and/or cassiterite-precipitating fluid show
significant variability through the zoned crystal. The first and second
quartz generations (Q1 and Q2) were precipitated from a fluid of magmatic
isotopic composition with $\delta ^{18}$O values of $\sim $8 -- 10
\permil\. $\delta ^{18}$O values of Q3- and
tourmaline-precipitating fluids show a transition from magmatic $\delta
^{18}$O values of $\sim $ 8 \permil\ to $\sim $ -5
\permil\. The outermost quartz-chlorite-muscovite zone was
precipitated from a fluid with a significant meteoric water component
reflected by very light $\delta ^{18}$O values of about -15
\permil\, which is consistent with values found by previous
studies (Sun and Eadington, 1987) using conventional O-isotope analysis of
veins in the distal halo of the granite intrusion. Intense incursion of
meteoric water during Q3 precipitation (light $\delta ^{18}$O values)
agrees with the main ore formation event, though the first occurrence of
cassiterite is linked to Q2 precipitating fluid with magmatic-like isotope
signature. This apparent discrepancy can be explained by the presence of a
fluid of meteoric origin that was isotopically equilibrated with a hot, but
already solidified and fractured granitic intrusion under rock-dominated
conditions prior their transfer to the cold ore deposition site (Heinrich,
1990).
Conversely, in porphyry copper systems meteoric fluid incursion has been
assumed to participate in formation of peripheral or post-mineralization
processes (Bowman et al., 1987; Sillitoe, 2010; Williams-Jones and Migdisov,
2014). However, recent numerical simulations of porphyry copper systems
identify a significant role of meteoric fluids for the enrichment process,
providing a cooling mechanism for metal-rich fluids expelled from an upper
crustal magma chamber (Weis et al. 2012, Weis 2015). Furthermore, new
petrographic and fluid inclusion work of ore-mineralized quartz veins
(Landtwing et al., 2010; Stefanova et al., 2014) indicates lower ($\sim
$450\r{ }C) than magmatic fluid temperatures for copper precipitation. Given
that the Yankee Lode study validated the capability of high resolution, in
situ $\delta ^{18}$O analysis to trace meteoric water incursion, we will
apply this method to hydrothermal quartz samples from two significant
porphyry copper deposits (Bingham Canyon, USA and Elatsite, Bulgaria). By
this we intend to better constrain a potential role of meteoric water
incursion in porphyry copper ore precipitation.
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