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A fluid inclusion and stable isotope study of the Moonta copper-gold deposits, South Australia: evidence for fluid immiscibility in a magmatic hydrothermal system
Ruano, S. M., Both, R. A. and Golding, S. D. (2002-12) A fluid inclusion and stable isotope study of the Moonta copper-gold deposits, South Australia: evidence for fluid immiscibility in a magmatic hydrothermal system. Chemical Geology, 192 3-4: 211-226.
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| Author(s) |
Ruano, S. M.
Both, R. A.
Golding, S. D.
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| Title |
A fluid inclusion and stable isotope study of the Moonta copper-gold deposits, South Australia: evidence for fluid immiscibility in a magmatic hydrothermal system
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| Journal name |
Chemical Geology
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| Publication date |
2002-12
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| Volume number |
192
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| Issue number |
3-4
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| ISSN |
0009-2541
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| Start page |
211
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| End page |
226
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| Total pages |
16
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| Editor(s) |
C. J. Allegre
P. Deines
S. L. Goldstein
E. H. Oelkers
R. L. Rudnick
L. M. Walter
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| Place of publication |
Netherlands
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| Publisher |
Elsevier Science BV
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| Collection year |
2002
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| Language |
eng
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| Subject |
C1
260301 Geochronology and Isotope Geochemistry
780104 Earth sciences
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| Abstract |
The copper-gold ores of the Moonta mineral field, in the eastern part of the Archaean-Mesoproterozoic Gawler Craton, South Australia, are vein deposits occupying fractures and shear zones within the Palaeoproterozoic Moonta Porphyry. The veins show a spatial relationship with Mesoproterozoic granites, equivalents of the Hiltaba Suite granites that are widespread in the Gawler Craton. The ores were deposited in four hydrothermal stages separated by episodes of fracturing; the first two stages were dominated by Fe oxides, the third by Fe sulfides and the final stage by a Cu-Fe-Co-Au-Zn-Pb-S assemblage. Three types of fluid inclusions are present in quartz associated with the oxide and sulfide minerals. Type I fluid inclusions are two-phase vapour-rich, with homogenization temperatures up to 473 T and low to moderate salinity (2 to 22 wt.% NaCl equivalent). Type 2 are two-phase liquid-rich with lower homogenization temperatures (up to 269 degreesC) and low to moderate salinities (0.7 to 22 wt.% NaCl equivalent), Type 3 are liquid-rich, solid(s)-beating with homogenization temperatures up to 467 degreesC and high salinities (28 to 55 wt.% NaCl equivalent). The coexistence of types 1 and 3 suggests that these fluid inclusions resulted either from trapping of boiling fluids or represent two immiscible fluids, most likely derived from a magma. The fluid history, reflected in fluid inclusion characteristics, was complex, involving variable amounts of boiling, cooling and mixing in the vein system. Salinity-homogenization temperature relationships indicate mixing of the hypersaline fluid and the vapour-rich fluid with a surface-derived fluid of low temperature and low to moderate salinity. deltaDH(2)O values (- 22parts per thousand to - 31 parts per thousand) and delta(18)O(H2O) values (2.9parts per thousand to 5.1 parts per thousand) calculated from analyses of chlorite and delta(18)O(H2O) values calculated from analyses of quartz (0.6 parts per thousand to 8.8 parts per thousand) on the basis of mean to maximum fluid inclusion homogenization temperatures are intermediate between magmatic water and surface-derived fluids (i.e. seawater or meteoric water), The narrow range of delta(18)O values of quartz (10.8 parts per thousand to 12.7 parts per thousand) may be explained by mixing of a magmatic fluid and either seawater or a low latitude, moderately evolved meteoric water, with a coupled decrease in fluid temperature and O-18 content. Similar ranges for delta(34)S values of ore sulfides (- 2.3 parts per thousand to 6.4 parts per thousand) and disseminated sulfides in the Moonta Porphyry and interdigitated Doora Schist (- 1.5 parts per thousand to 4.6 parts per thousand) suggest assimilation of crustal sulfur by the granitic magma or ore fluids.
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| Keyword(s) |
Fluid Inclusions
Stable Isotopes
Hydrothermal Copper - Gold
Gawler Craton
Moonta
Geochemistry & Geophysics
Hydrothermal Copper-gold
Geothermal Systems
Water
Nacl-cacl2-h2o
Fractionation
Chlorite
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