Stable isotope evidence for magmatic fluid input during large-scale Na–Ca alteration in the Cloncurry Fe oxide Cu–Au district, NW Queensland, Australia

Mark, Geordie, Foster, Damien R. W., Pollard, Peter J., Williams, Patrick J., Tolman, Justin, Darvall, Michael, and Blake, Kevin L. (2004) Stable isotope evidence for magmatic fluid input during large-scale Na–Ca alteration in the Cloncurry Fe oxide Cu–Au district, NW Queensland, Australia. Terra Nova Online, 16 (2). pp. 54-61.

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Abstract

Sodic–calcic alteration is common in mineralized hydrothermal systems, yet the relative importance of igneous vs. basinal fluid sources remains controversial. One of the most extensive volumes of sodic–calcic rocks occurs near Cloncurry, NW Queensland, and was formed by overlapping hydrothermal systems that were active synchronously with emplacement of mid-crustal batholithic granitoids (c. 1.55–1.50 Ga). Altered rocks contain albite–oligoclase, actinolite, diopside, titanite and magnetite. Alteration was localized by: (A) composite veins and breccias containing crystallized magma intimately intergrown with hydrothermal precipitates; (B) intrusions that host setting A veins and breccias; and (C) extensive breccia and vein systems linked to regional fault systems. Isotope analyses of actinolites in settings A and B indicate calculated δ18OH2O (+8.2 to +10.6‰) and variably depleted δDH2O (−130 to −54‰) compared with typical magmatic fluids, whereas those from setting C typically indicate calculated δ18OH2O (+8.0 to +12.8‰) and δDH2O (−29 to −99‰). The lowest δDH2O values are interpreted as representing residual fluids after significant (> 90%) open-system magmatic degassing. Overall the stable isotope, field, geochronological and geobarometric data suggest that these sodic–calcic alteration systems were formed by the episodic incursion of magmatic fluids that underwent minor isotopic modification as a result of varying degrees of interaction with country rocks.

Item ID: 4480
Item Type: Article (Refereed Research - C1)
ISSN: 0954-4879
Date Deposited: 10 Jun 2009 01:51
FoR Codes: 04 EARTH SCIENCES > 0403 Geology > 040307 Ore Deposit Petrology @ 100%
SEO Codes: 84 MINERAL RESOURCES (excl. Energy Resources) > 8401 Mineral Exploration > 840105 Precious (Noble) Metal Ore Exploration @ 100%
Citation Count from Web of Science Web of Science 28
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