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The chemistry of brine, vapor, and low-salinity fluid inclusions measured by proton-induced X-ray emission from the Bismark skarn deposit, Mexico, is consistent with an evolving magmatic-hydrothermal system with no evidence for external fluid inputs. The results support a model that invokes early phase separation of magmatic fluids into brine and vapor (two-phase field) at high temperature and lithostatic pressure, followed by the entrapment of a low-salinity magmatic fluid (one-phase field) at lower temperature and hydrostatic pressure. The early brine and vapor inclusions contain high Pb and Zn concentrations and low Cu; however, the vapor contains significantly more Cu than the brine and was likely transported as a sulfur complex. The fluid phase changes observed and behavior of Cu are comparable to those of porphyry Cu systems. The later, low-salinity fluid at Bismark represents a distinct pulse of magmatic fluid with a high K/Ca ratio in which base metals, including Cu, were transported by chloride complexes. Paragenetic relationships and variations in the relative concentrations of Cu, Pb, and Zn suggest that this fluid was primarily responsible for ore deposition. The relative Cu, Pb, and Zn concentrations in fluid inclusions at Bismark are consistent with those measured from base-metal ores in high-temperature carbonate-replacement deposits throughout Mexico, and suggest that the bulk-metal budget of these deposits is primarily controlled by magmatic-hydrothermal fluids deficient in Cu. Keywords: Mexico, skarn, fluid inclusions, proton-induced X-ray emission, base metals.

Quenched carbonate-silicate inclusions in lherzolitic clinopyroxene macrocrysts, derived from 200 km beneath the Slave craton in northern Canada, are interpreted as natural samples of mantle carbonatites. Oxygen, carbon, and strontium isotope data provide evidence for the involvement of subducted crustal material in the origin of these carbonatites, supporting suggestions that carbon recycling by subduction is an important prerequisite for carbonatite magmatism. The compositional range of the inclusions suggests that the parent melt was decreasing in silica content as it was trapped in the host crystal, a trend that is predicted experimentally. Isotopic disequilibrium between the carbonatitic inclusions and the host clinopyroxene indicates that they were trapped shortly before kimberlite eruption, suggesting a temporal link between the entrapment of the carbonatite in the host and the Paleocene eruption of the kimberlite. Keywords: carbonatites, isotopes, subduction, Slave province, mantle melts, xenoliths.

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.

Geologic samples are extremely diverse and share a tendency for both heterogeneity and complexity. This is especially true for ores, which commonly result from a complex interplay of processes in highly dynamic environments. In recent years, a number of tools allowing the chemical mapping of major (e.g., mineral liberation analysis, MLA), minor (e.g., electron microprobe, EPMA), and trace (e.g., laser ablation-inductively coupled plasma-mass spectrometry, LA-ICP-MS) elements in geologic samples at ~1- to 50-µm resolution and over mm2 areas have seen rapid development and have become readily available. To date, the application of synchrotron-based X-ray fluorescence (SXRF) mapping has been limited to addressing key questions because of low availability and high cost. This paper demonstrates how recent advances in X-ray fluorescence detector technology are bringing new possibilities to ore petrology. Millisecond dwell times allow collection of thin section size maps at resolutions of a few µm in hours, while improvements in data analysis software simplify the production of quantitative elemental maps. Based on the imaging of six samples representative of different commodities (Pt, U, Cu, Ge) and different geologic contexts (PGE deposit; sandstone-hosted U deposit; vein-type polymetallic hydrothermal deposit; iron oxide-copper-gold (IOCG) deposit), we demonstrate that megapixel SXRF (MSXRF) can efficiently provide the information necessary to understand metal speciation in the context of thin section-scale textural complexity. Image analysis revealed a number of new results for the studied deposits, for example, (1) the distribution of micrometer-sized Pt-rich grains and Ti mobility during the formation of schistosity at the Fifield Point prospect (New South Wales, Australia); (2) the presence of Ge contained in organic matter and of Hg minerals associated within quartzite clasts in the Lake Frome U ores (South Australia); (3) confirmation of the two-stage Ge enrichment in the Barrigão deposit, with demonstration of the presence of Ge in solid solution in the early chalcopyrite (Portuguese Iberian pyrite belt); and (4) the enrichment of U during late dissolution-reprecipitation reactions in the bornite ores of the Moonta and Wallaroo IOCG deposits (South Australia). These results illustrate that MSXRF is a powerful technique for locating nano- to microparticles of precious metals (Pt) and trace contaminants (e.g., Hg) that form distinct (micro) minerals. In addition, it is a powerful tool for understanding commodities with relatively low ore grades and complex distribution (100-1,000 ppm; e.g., U, Ge). [ABSTRACT FROM AUTHOR]