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    James Mungall & James Brenan


    James Mungall was born in Ottawa in 1960, where he lived until he began his studies at the University of Waterloo in 1978. Nine years later, having spent more time dirtbagging, baking bagels, tanning hides, and pumping dirty water than he had in school, he graduated with a B.Sc. in geology and headed for Montreal. There he did his M.Sc. and Ph.D. in igneous petrology under Robert Martin/'s guidance, studying the petrogenesis first of shoshonitic intrusions in the Grenville Province and later of peralkaline ocean island rhyolites in the Azores. Six years of attempting to answer questions about magmatic processes by looking at old rocks convinced him that he should try to understand magma chemistry and physics in the laboratory. After two years of experimental investigations of the transport properties of silicate melts at the Bayerisches Geoinstitut in Germany, Jim found himself back in Canada in the summer of 1996, looking for nickel deposits and communing with the affectionate mosquitoes of northern Quebec. In 1999, Jim found a place where he could combine a passion for field work with the possibility of doing experimental petrology and teaching at the University of Toronto, where he has remained ever since.

    James Brenan is a petrologist and geochemist who simulates rock-forming conditions in the laboratory to understand the processes responsible for element distribution in the Earth and terrestrial planets. James was born in Needham, Massachusetts, in 1963. He entered McGill University on 1981, took Introduction to Geology and became hooked on the subject by the inspired teaching of A.E. "Willy" Williams-Jones. James acquired a severe bias for the "dark-coloured" igneous rocks under the influence of Don Francis, and it was Don who suggested further graduate studies. James received a B.Sc.(Hon.) from McGill University in 1985, then enrolled in the Ph.D. program at Rensselaer Polytechnic Institute (Troy, NY). Under the guidance of Bruce Watson, James conducted experiments to better establish the role of aqueous fluids in trace-element recycling through subduction zones. For this work, he received a Ph.D. in 1990. James was a post-doctoral researcher at the Geophysical Laboratory (1990-1992) and Lawrence Livermore National Laboratory (1992-1996) before taking a faculty position at the University of Toronto.


    The paper is based on the observation that unusual abundances of halogen-rich minerals are found in close spatial association with base-metal and precious-metal sulfide mineralization cogenetic with igneous rocks in several localities worldwide.? Mungall and Brenan?s investigation of the partitioning of fluorine, chlorine, bromine, and iodine between coexisting silicate and sulfide liquids established that chlorine, bromine, and iodine have significant solubilities in sulfide liquids but that fluorine does not. In associated experiments on chlorine in Fe-Cu sulfide melts, they found that chlorine substantially lowers the melting point of monosulfide solid-solution, is moderately incompatible in monosulfide solid-solution, and thus is enriched in the residual melt. These results led to the conclusions that ?....sulfide melts are capable of dissolving and transporting significant concentrations of halogens in the absence of an aqueous fluid? and that ?...observed enrichments in halogens in some mineralized environments are consistent with ore deposition by purely magmatic processes.? These are major changes in our understanding and interpretation of base-metal and precious-metal sulfide mineralization.

    Although the authors pointed out that this is a reconnaissance study, the preliminary results lead to implications and speculations in a number of areas. The previously observed elevated ratio of Cl/Br in alteration halos around sulfide ore bodies in the Sudbury igneous complex can be explained by the results in this paper, thus confirming that high Cl/Br ratios are a useful exploration guide. The presence of lawrencite [(Fe,Ni)Cl2] in grains of Fe-Ni alloy in lunar basalts and iron-nickel meteorites now can be explained. The possibility that halogens may have been preferentially differentiated into the core of the early Earth has implications for dating events in the formation of the Earth.

    The results presented in this paper will have a profound impact on research in many areas of the Earth sciences. Mungall and Brenan?s findings on the solubilities of halogens in sulfide melts are factors that must be considered in any research program on sulfides.

    © 2006 Mineralogical Association of CanadaLast update 2014-02-05