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Abra is a blind, sedimentary rock-hosted polymetallic Fe–Pb–Zn–Ba–Cu ± Au ± Ag ± Bi ± W deposit, discovered in 1981, located within the easterly trending Jillawarra rift sub-basin of the Mesoproterozoic Edmund Basin, Capricorn Orogen, Western Australia. The Edmund Basin contains a 4–10 km thick succession of siltstone, sandstone, dolomitic siltstone, and stromatolitic dolomite. The age of the Edmund Group is between 1.66 and 1.46 Ga. The Abra polymetallic deposit is hosted in siltstone, dolostone, sandstone and conglomerate of the Irregully and Kiangi Creek Formations, but the mineralised zones do not extend above an erosion surface marking the change from fluvial to marine facies in the lower part of the Kiangi Creek Formation. The Abra deposit is characterised by a funnel-shaped brecciated zone, interpreted as a feeder pipe, overlain by stratiform–stratabound mineralisation. The stratiform–stratabound mineralisation includes a Red Zone and an underlying Black Zone. The Red Zone is characterised by banded jaspilite, hematite, galena, pyrite, quartz, barite, and siderite. The jaspilite and hematite cause the predominant red colouration. The Black Zone consists of veins and rhythmically banded sulphides, laminated and/or brecciated hematite, magnetite, Fe-rich carbonate and scheelite. In both zones, laminations and bands of sulphide minerals, Fe oxides, barite and quartz commonly exhibit colloform textures. The feeder pipe (Stringer Zone) merges with Black Zone and consists of a stockwork of Fe-carbonate-quartz, barite, pyrite, magnetite and chalcopyrite, exhibiting fluidised and/or jigsaw textures. The Abra mineral system is characterised by several overprinting phases of hydrothermal activity, from several stages of brecciation and fluidisation, barite and sulphide veining to barren low-temperature chalcedonic (epithermal regime) veining. Hydrothermal alteration minerals include multi-stage quartz, chlorite, prehnite, Fe-rich carbonate and albite. Albite (Na metasomatism) is an early alteration phase, whereas Fe-rich carbonate is a late phase. Fluid inclusion studies indicate that the ore fluids had temperatures ranging from 162 to 250 °C, with salinities ranging from 5.8 to about 20 wt.% NaCl. In the course of our studies, microthermometric and Raman microprobe analyses were performed on fluid inclusions in carbonate, quartz and barite grains. Fluid inclusions in quartz show homogenisation temperatures ranging from 150 to 170 °C with calculated salinities of between 3.7 and 13.8 wt.% NaCl. The sulphur isotopic system shows δ 34 S values ranging from 19.4 to 26.6‰ for sulphides and from 37.4 to 41.9‰ for barite ( Vogt and Stumpfl, 1987; Austen, 2007 ). Sulphur isotope thermometry between sulphides and sulphide–barite pairs yields values ranging from 219 to 336 °C ( Austen, 2007 ). Galena samples were analysed for Pb isotope ratios, which have been compared with previous Pb isotopic data. The new Pb isotope systematics show model ages of 1650–1628 Ma, consistent with the formation of the host Edmund Basin. Re–Os dating of euhedral pyrite from the Black Zone yielded an age of ~ 1255 Ma. This age corresponds to the 1320–1170 Ma Mutherbukin tectonic event in the Gascoyne Complex. This event is manifested primarily along a WNW-trending structural corridor of amphibolite facies rocks, about 250 km to the northwest of the Abra area. It is possible that the Re–Os age represents a younger re-activation event of an earlier SEDEX style system with a possible age range of 1640–1590 Ma. A genetic model for Abra is proposed based on the above data. The model involves two end-members ore-forming stages: the first is the formation of the SEDEX style mineral systems, followed by a second multi-phase stage during which there was repeated re-working of the mineral system, guided by seismic activity along major regional faults. [ABSTRACT FROM AUTHOR]

The study of fluid inclusions can help constrain the conditions at which diagenetic minerals precipitated, leading to a better understanding of the geologic controls and relative timing of changes in porosity and/or mineralising events. Many of the diagenetic minerals are easily deformed and it is important to check for any post-entrapment changes to the inclusions. Possible post-entrapment changes include reaction with the host crystal, necking down, nucleation metastability and thermal re-equilibration. The recommended method of detecting these problems is to examine individual fluid inclusion assemblages (FIAs) and report data for each individual FIA. These studies have been enhanced by the development of new micro-analytical techniques such as micro-fluorescence spectroscopy, micro-infrared spectroscopy, nuclear magnetic resonance, various mass spectrometry techniques and the analysis of individual fluid inclusions using laser ablation/decrepitation methods. Special techniques have been developed for hydrocarbon-bearing inclusions such as the Grains containing Oil Inclusions (GOI), Fluid Inclusion Stratigraphy (FIS), and the Molecular Composition of Inclusions (MCI) techniques. The fluid inclusions that form in some minerals during diagenesis provide the only direct means of examining the fluids present in these systems. They provide useful temperature, pressure, and fluid composition data that cannot be obtained by other means. [ABSTRACT FROM AUTHOR]

Abstract: The Maldon gold deposit in central Victoria has geological, geochronological and fluid chemistry characteristics that distinguish it from typical vein-hosted, ‘orogenic’ gold deposits in this region. The deposit lies within the thermal aureole of the Late Devonian Harcourt Granite and associated granitic dykes that postdate regional metamorphism (~445Ma) and large gold deposits such as Bendigo. The fluid inclusions are characterised by the presence of non-aqueous (i.e. carbonic) fluids, which exhibit complex freezing and heating behaviour, as well as mixed CO2–low-salinity aqueous fluids (mostly ≤10wt.% NaCl eq.). Raman analysis indicates that carbonic inclusions can vary from CO2-rich to CH4 +N2-rich. Furthermore, higher-salinity fluid inclusions, containing 20–22wt.% NaCl eq., occur locally. Overall, fluid inclusions in the K-feldspar zone are much less abundant by volume than those in the cordierite zone probably due to recrystallisation, suggesting limited magmatic fluid input. The Harcourt Granite is a moderately reduced, I-type granite and it is suggested that the ‘retrograde’, reduced fluids (e.g. CH4 +N2-rich), formed within the thermal aureole of the granite and associated dykes during contact metamorphism, are not part of the regional mineralising fluid system, which was dominated by deeply derived CO2–low-salinity aqueous fluids of metamorphic origin. Thus, the Maldon deposit is an ‘orogenic’ gold deposit that was metamorphosed and/or remobilised during the emplacement of post-orogenic intrusions. [Copyright &y& Elsevier]

Solid, vapor, and fluid inclusions in transparent gem rhodonite crystals from Broken Hill, New South Wales, Australia, have been identified for the first time using Raman spectroscopy and gemological/ petrographic techniques. Among the solid inclusions are sphalerite, galena, quartz, and fluorite. The rhodonite also contained hollow needle-like tubes and negative rhodonite crystals. Three-phase inclusions were found to contain a saline liquid, a gaseous mixture of nitrogen (N2) and methane (CH4), and ilmenite crystals. [ABSTRACT FROM AUTHOR]

• Grasberg contains low salinity, hypersaline liquid and multi-solid inclusions. • Inclusion data indicate a single phase fluid input at >700 °C and 5 wt% NaCl salinity. • Phase separation from the magmatic fluid produces a two phase fluid mixture containing <2 vol% liquid. • The amount of metal fractionated to liquid is low relative to that in the vapor phase. • The disparity between pressures from inclusion and geologic estimates is resolved. • Fluid flux data from Grasberg shows that it formed in only a few thousand years. Fluid inclusion data provide a unique insight into the behaviour of magmatic fluids as they expand from source to surface to form porphyry copper deposits. For example, saline, liquid phase inclusions in combination with vapor phase inclusions help to define the environment of mineralization in terms of large scale, two-phase fluid flow within a magmatic vapor plume. However, the pressure at which ore formation occurs within the plume is controversial because inclusion-based estimates are commonly much higher than those based on geological estimates. Uniquely, the Grasberg supergiant porphyry copper deposit occupies the breccia-filled diatreme underlying the crater of a maar volcano and preserved a lacustrine-volcaniclastic sequence that marks the paleo-surface to within a few hundred meters. Interpreting fluid inclusion data with respect to this paleo-surface shows that porphyry mineralization extended from a paleo-depth of about 500 m to over 1500 m depth, as defined by drilling. The Grasberg deposit has three distinct populations of fluid inclusions (low salinity, hypersaline liquid and multi-solid inclusions) that are strongly clustered with respect to salinity and trapping temperature. Similar clusters of co-existing liquid- and vapor-rich inclusions are also common to porphyry copper deposits worldwide. Applying the principles of energy and mass conservation, a simple model of isenthalpic phase separation by condensation may be derived to account for these data clusters and how they are related. Vapor- and liquid-rich hypersaline inclusions may be shown quantitatively to be the consequence of expansion of a continuum low salinity, low density magmatic vapor phase to a two-phase fluid where the liquid fraction is minor (<2 vol%) and is best considered to be an aerosol or fog. The clustering of the inclusion data is the product of the different ranges of pressures that fluids encountered from the initiation of individual stockwork fractures through to their resealing. The application of mass and energy conservation principles also shows that, even though metal partitioning to the liquid phase may be favored, the proportion of total metal fractionated to the small mass of liquid is low relative to that remaining in the vapor phase. Therefore, while partitioning of metals between liquid and vapor phases may be a contributing process for metal deposition in porphyry copper deposits, other vapor-phase processes are required to efficiently deposit these major metal resources. [ABSTRACT FROM AUTHOR]

• Some Australian gold deposits are either orogenic or intrusion-related deposits. • We compared highly mineralised and weakly mineralised goldfields in north Australia. • Three chemically distinct types of quartz occur in the well-endowed Tanami goldfield. • LA-ICPMS shows that the deposits in both goldfields are intrusion-related deposits. • Multiple mineralisation events are associated with higher gold endowment. Gold deposits in the Tanami and Kurundi-Kurinelli goldfields of the Northern Territory, Australia, have geological and geochemical characteristics that distinguish them from the typical vein-hosted, orogenic gold deposits that occur in other parts of Australia. This study used cathodoluminescence (CL) and laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) analyses of fluid inclusions to investigate the source of mineralising fluids from both the highly mineralised Tanami goldfield and weakly mineralised Kurundi-Kurinelli goldfields in northern Australia. Cathodoluminescence showed three generations of quartz in fractured and mineralised veins from the Groundrush deposit in the Tanami goldfield but the remaining deposits had uniform dark CL images. The LA-ICPMS trace element data indicate an evolution from B-As–enriched, magmatic fluid to a highly Sr-Ba-enriched fluid which results from interaction with sedimentary rocks. The fluids from both regions have chlorinity normalised Zn and Pb concentrations at the magmatic end of the metamorphic – magmatic mixing trend for these elements. This is in agreement with previous studies showing that gold mineralisation is coeval with magmatism in the Tanami region. The relatively high salinity of the fluids in both the Tanami and Kurundi – Kurinelli goldfields, and their trace element contents indicates that the deposits in both regions are intrusion-related gold deposits. The higher gold endowment of the Tanami region may result from the multiple gold-mineralisation events in this region whereas fluid flow associated with mineralisation in the Kurundi – Kurinelli goldfields appears to be of limited extent. [ABSTRACT FROM AUTHOR]

Kiruna-type iron oxide-apatite (IOA) deposits, an important source of iron, show close associations with andesitic subvolcanic intrusions. However, the processes of ore formation and the mechanism controlling iron concentration remain uncertain. Here, we report the widespread presence of high-temperature (>800°C) water-poor multisolid hydrosaline liquid inclusions in pre-and syn-ore minerals from IOA deposits of eastern China. These inclusions consistently homogenize to a liquid phase by vapor disappearance and mostly contain 3 to 10 wt % Fe, signifying a substantial capacity for iron transportation by such hydrosaline liquids. We propose that the hydrosaline liquids were likely immiscible from the dioritic magmas with high Cl/H2O in subvolcanic settings. Subsequent reaction with host rocks and/or decompression and cooling of the hydrosaline liquids is deemed responsible for the simultaneous formation of high-temperature alteration and magnetite ores, thereby providing important insights into the distinctive characteristics of IOA deposits in shallow magmatic-hydrothermal systems. [ABSTRACT FROM AUTHOR]

• BQ-, A 2 -, and B-veins, showing irregular walls formed under lithostatic pressure. • Straight-walled D 1 -type veins formed under hydrostatic pressure. • The Zefreh prospect formed from magmatic and hypersaline liquids, and vapors. • eterogeous δ34S‰ values of sulfides a • The Zefreh prospect would be a relatively poor target for further exploration. The Zefreh porphyry Cu–Mo prospect is located in the central part of the NW-trending Cenozoic Urumieh–Dokhtar Metallogenic Belt, 75 km NE of Isfahan city, central Iran. Chalcopyrite and molybdenite mainly occur as disseminated sulfides in the host rocks and, to a lesser extent, in the surrounding volcanic rocks. Four types of fluid inclusions were identified in quartz-rich veins: i.e., two-phase liquid-rich, two-phase vapor-rich, simple brine, and multi-phase brine inclusions. Liquid-rich inclusions in ore-bearing, A-type quartz veins homogenized between 350° and 370 °C, suggesting that fluids trapped in these inclusions were derived from magmatic fluids at high temperatures. Simple and multi-phase brine inclusions exhibited homogenization or partial homogenization over a wide range from 350° to 1209 °C. The very high homogenization temperatures and the presence of up to six solid phases in multi-phase brine inclusions indicate heterogeneous trapping of melt, fluid, and vapor. The Zefreh porphyry prospect is thought to have formed from hypersaline liquids and vapors that exsolved from a magmatic intrusion assembled in the shallow crust. The δ34S values of sulfides from the Zefreh porphyry prospect range from +0.8‰ to +10.7‰. This indicates that the early, ore-bearing quartz veins dominated by high-δ34S pyrites may have interacted with later hydrothermal fluids, or alternatively, the pyrites are paragenetically late products of propylitic and K-feldspar-dominated potassic alteration assemblages. Another plausible explanation for significantly enriched δ34S values of sulfides may be mixing of hydrothermal fluids of magmatic origin with the Cenozoic seawater (δ34S ≈ +22‰). It is suggested that the Zefreh prospect likely would be a poor target for further exploration. [ABSTRACT FROM AUTHOR]