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Motivated by the need for megapixel high definition trace element imaging to capture intricate detail in natural material, together with faster acquisition and improved counting statistics in elemental imaging, a large energydispersive detector array called Maia has been developed by CSIRO and BNL for SXRF imaging on the XFM beamline at the Australian Synchrotron. A 96 detector prototype demonstrated the capacity of the system for real-time deconvolution of complex spectral data using an embedded implementation of the Dynamic Analysis method and acquiring highly detailed images up to 77M pixels spanning large areas of complex mineral sample sections.

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Many ore deposits are hosted by metamorphic rocks, and metamorphic fluids have been invoked as a source for various deposits, especially gold deposits. Metamorphic fluid compositions reflect original sedimentary environment: continental shelf sequences yield saline metamorphic fluids with little dissolved gas while metasediments from accretionary and oceanic settings host less saline fluids with significant CO 2 contents.The principal difficulty in reconciling ore deposits with a metamorphic origin is that many form quickly (c. 1 Ma), whereas metamorphic heating is slow (c. 10-208/Ma). Gravitational instability means that fluid cannot be retained. Metamorphic ores may nevertheless form by: (a) segregation leading to enrichment of pre-existing concentrations; (b) infiltration of water-rich fluids from schists into marbles at high temperature overstepping decarbonation reactions and allowing fast reaction that locally draws down temperature; and (c) rapid uplift driving dehydration reactions owing to pressure drop.Some orogenic lode gold deposits fit well with a purely metamorphic origin during rapid uplift, but others are problematic. At Sunrise Dam, Western Australia, anomalies in Sr-isotope ratios and in apatite compositions indicate a partial mantle/magmatic source. Low salinity, H 2 O-CO 2 fluids commonly associated with hydrothermal gold reflect the effect of salt on gas solubility, not the origin of the fluid.Gold Open Access: This article is published under the terms of the CC-BY 3.0 license.Many hydrothermal ore deposits are hosted by metamorphic rocks, and so the possibility that ore deposits may form from metamorphic fluids has been discussed for many years. In this paper we will review what is known about metamorphic fluids from a chemical perspective, and the implications that this may have for their ore-forming potential, and then put this in the context of the history of regional metamorphism and the physical supply of fluid to possible ore systems. Possible natural examples of metamorphic fluids giving rise to ore deposits are also discussed with an emphasis on gold mineralization, because this is the type of mineralization for which metamorphic fluids have been most widely invoked.The term metamorphic fluid is used here in the strict sense to denote fluids present during prograde metamorphism. They will commonly include a component of pre-metamorphic formation waters as well as fluid released by breakdown of volatilebearing minerals, all modified by ongoing interactions with host rock. This definition is much more restrictive than that often used in stable isotope studies, which embraces all fluids that have isotopically equilibrated with metamorphic rocks, irrespective of their origin.Despite some clear evidence to the contrary (e.g. Roedder 1972), until recently crustal fluids were generally assumed to carry only small amounts of potential ore metal in solution. Thus the problem of understanding ore deposits was seen as one of accounting for extensive focussing of fluid flow. With the ...

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The source and transport regions of fluidized (transported) breccias outcrop in the Cloncurry Fe-oxide-Cu-Au district. Discordant dykes and pipes with rounded clasts of metasedimentary calc-silicate rocks and minor felsic and mafic intrusions extend several kilometres upwards and outwards from the contact aureole of the 1530 Ma Williams Batholith into overlying schists and amphibolites. We used analytical equations for particle transport to estimate clast velocities ( ‡20 m sec )1 ), approaching volcanic ejecta rates. An abrupt release of overpressured magmatic-hydrothermal fluid is suggested by the localization of the base of the breccias in intensely veined contact aureoles (at around 10 km, constrained by mineral equilibria), incorporation of juvenile magmatic clasts, the scale and discordancy of the bodies, and the wide range of pressure variation (up to 150 MPa) inferred from CO 2 fluid inclusion densities and related decrepitation textures. The abundance of clasts derived from depth, rather than from the adjacent wallrocks, suggests that the pressure in the pipes was sufficient to restrict the inwards spalling of fragments from breccia walls; that is, the breccias were explosive rather than implosive, and some may have vented to the surface. At these depths, such extreme behaviour may have been achieved by release of dissolved fluids from crystallizing magma, in combination with a strongly fractured and fluid-laden carapace, sitting under a strong, low permeability barrier. The relationship of these breccias to the Ernest Henry iron-oxide-Cu-Au deposit suggests they may have been sources of fluids or mechanical energy for ore genesis, or alternately provided permeable pathways for later ore fluids.