NDLI: New constraints on fluid sources in orogenic gold deposits, Victoria, Australia

Content Provider	Springer Nature Link
Author	Fu, Bin Kendrick, Mark A. Fairmaid, Alison M. Phillips, David Wilson, Christopher J. L. Mernagh, Terrence P.
Copyright Year	2011
Abstract	Fluid inclusion microthermometry, Raman spectroscopy and noble gas plus halogen geochemistry, complemented by published stable isotope data, have been used to assess the origin of gold-rich fluids in the Lachlan Fold Belt of central Victoria, south-eastern Australia. Victorian gold deposits vary from large turbidite-hosted ‘orogenic’ lode and disseminated-stockwork gold-only deposits, formed close to the metamorphic peak, to smaller polymetallic gold deposits, temporally associated with later post-orogenic granite intrusions. Despite the differences in relative timing, metal association and the size of these deposits, fluid inclusion microthermometry indicates that all deposits are genetically associated with similar low-salinity aqueous, CO2-bearing fluids. The majority of these fluid inclusions also have similar 40Ar/36Ar values of less than 1500 and 36Ar concentrations of 2.6–58 ppb (by mass) that are equal to or much greater than air-saturation levels (1.3–2.7 ppb). Limited amounts of nitrogen-rich fluids are present at a local scale and have the highest measured 40Ar/36Ar values of up to 5,700, suggesting an external or distinct source compared to the aqueous fluids. The predominance of low-salinity aqueous–carbonic fluids with low 40Ar/36Ar values, in both ‘orogenic’ and ‘intrusion-related’ gold deposits, is attributed to fluid production from common basement volcano-sedimentary sequences and fluid interaction with sedimentary cover rocks (turbidites). Aqueous fluid inclusions in the Stawell–Magdala deposit of western Victoria (including those associated with N2) preserve mantle-like Br/Cl and I/Cl values. In contrast, fluid inclusions in deposits in the eastern structural zones, which contain more abundant shales, have elevated molar I/Cl ratios with maximum values of 5,170 × 10−6 in the Melbourne Zone. Br/I ratios in this zone range from 0.5 to 3.0 that are characteristic of fluid interaction with organic-rich sediments. The maximum I/Cl and characteristic Br/I ratios provide evidence for organic Br and I released during metamorphism of the shales. Therefore, the regional data provide strong evidence for the involvement of sedimentary components in gold mineralisation, but are consistent with deeper metamorphic fluid sources from basement volcano-sedimentary rocks. The overlying sediments are probably involved in gold mineralisation via fluid–rock interaction.
Starting Page	427
Ending Page	447
Page Count	21
File Format	PDF
ISSN	00107999
Journal	Contributions to Mineralogy and Petrology
Volume Number	163
Issue Number	3
e-ISSN	14320967
Language	English
Publisher	Springer-Verlag
Publisher Date	2011-08-28
Publisher Place	Berlin/Heidelberg
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Fluid inclusions Noble gas Halogen Gold mineralisation Central Victoria Orogeny Geology Mineral Resources Mineralogy
Content Type	Text
Resource Type	Article
Subject	Geochemistry and Petrology Geophysics

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