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Magma-derived fluids are important in geologic processes (e.g., metal sequestration and ore deposition) but are intrinsically transient. Samples of magmatic fluids represented by fluid inclusions in a single zoned quartz crystal from a miarolitic cavity within a porphyritic leucogranite hosting the Industrialnoe tin deposit, northeastern Russia, were studied by using modern in situ analytical methods (laser Raman spectroscopy, proton-induced X-ray emission). The fluid inclusions are either dominated by vapor or by complex multiphase brines. The inclusions within a given trapping plane have similar phase relationships; however, there are significant variations between inclusions in different healed fractures. Phase and chemical compositions of individual brine inclusions demonstrate significant compositional heterogeneity. (in terms of absolute element concentrations and ratios) of high-temperature magmatic fluids accumulated in the miarolitic cavity. This finding suggests that fluids leaving a crystallizing magma may have variable initial compositions that are subsequently modified by reactions with the rocks while the fluid is in transit to a miarolitic cavity, as well as by processes in the cavity, such as mixing, crystallization, and boiling. The inferred chemical diversity and fractionation of granite-derived fluids at near-magmatic conditions imply that fluids entering a cooler hydrothermal system are extremely complex and their metallogenic signature may differ from that of related ore deposits. Keywords: granite, fluid inclusions, ore deposit, PIXE, geochemistry.

Foid-bearing syenites and endoskarn xenoliths of the A.D. 472 Vesuvius eruption represent the magma chamber-carbonate wall-rock interface. Melt inclusions hosted in crystals from these rocks offer a rare opportunity to depict the formation and the composition of metasomatic skarn-forming fluids at the peripheral part of a growing K-alkaline magma chamber disrupted by an explosive eruption. Four principal types of melt inclusions represent highly differentiated phonolite (type 1), hydrosaline melt (type 3), unmixed silicatesalt melts (type 2), and a complex chloride-carbonate melt with minor sulfates (type 4). The high-temperature (700-800 [degrees] C) magmatic-derived hydrosaline melt is considered to be the main metasomatic agent for the skarn-forming reactions. The interaction between this melt (fluid) and carbonate wall rocks produces a Na-K-Ca carbonate-chloride melt that shows immiscibility between carbonate and chloride constituents at ~700 [degrees] C in 1 atm experiments. This unmixing can be viewed as a possible mechanism for the origin of carbonatites associated with intrusion-related skarn systems. Keywords: Vesuvius, skarn, melt inclusions, immiscibility.

Immiscible phases derived from degassing silicate magmas are considered to be precursors of metal-bearing hydrothermal fluids in porphyry deposits. The development of melt-inclusion techniques provides a window into this critical period of porphyry formation, when the cooling, decompression, and crystallization of silicate melts result in the formation of immiscible phases. The record of magmatic to hydrothermal evolution is presented using inclusions in clinopyroxene phenocrysts from the syenitic Balut dike, one of the host-rock lithologies for mineralization at the Dinkidi Cu-Au porphyry deposit, Philippines. Primary inclusions include silicate glass, multiphase aggregates comprising salts, silicates, sulfates, carbonates, sulfides and oxides, and highly saline aqueous fluids. Various analyses, including in situ laser ablation inductively coupled plasma-mass spectrometry of the multiphase inclusions, determined elevated concentrations of Cl, S, As, Tl, K, Na, and a number of metals, including those that form ore-grade deposits (e.g., Cu) and those that do not (e.g., Mo, Pb, Zn, and W) at the Dinkidi porphyry deposit. Silicate melt and multiphase salt-rich inclusions in clinopyroxene are interpreted as having originally formed as immiscible phases at magmatic temperatures.

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]