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Granular aggregates of fine-grained graftonite (Fe,Mn,Ca)3(PO4)2and intergrown wolfeite (Fe,Mn)2(PO4)(OH) occur in amphibolite-facies metamorphosed iron formations associated with the Gamsberg Zn-Pb deposit, South Africa. To date, these minerals were believed to have limited parageneses, being essentially restricted to granitic pegmatites and iron meteorites. This paper is the first report of the occurrence of graftonite and wolfeite in a regionally metamorphosed, iron formation-hosted setting. The aggregates are found together with Mn- and Pb-rich apatite and calcian pyromorphite in a pristine unit of almost pure chemical precipitates, the origin of which is intimately linked to the base-metal mineralizing process. Evidence from Gamsberg supports previous studies conducted on pegmatite-hosted graftonites that a simple host rock mineralogy and geochemical prerequisites, such as high activities of Fe, Mn, Ca and a deficiency in F, exert a dominant control on the stabilization of these minerals. However, in a marine sedimentary environment, significant concentrations of phosphorus have to be precipitated to prevent stabilization of all the phosphorus as fluorapatite. The paucity of graftonite in such settings suggests that the combination of these requirements is only rarely achieved.

The first units of the Sequential Combustion System gas turbine family are in commercial operation. The first gas turbine GT24 (60Hz, 165MW-class) started the commercial operation, while the first GT26 (50Hz, 265MW-class) demonstrates its performance at the GT test facility. More engines are presently in the commissioning phase or will be in the near future. These turbines are designed to offer increased output at high GT efficiency. To acheive this, the sequential combustion system, a reheat process with two combustors, has been developed. Whereas the first combustor is based on the proven EV-combustor technology, extensive research and development efforts have been carried out in developing the lean premixed self-igniting second combustor (SEV). This paper is a follow-up of the ASME paper 96-GT-315, which described the basic research work concerning the lean premixing SEV-burners with self-ignition. The present paper reports the experience gained during commissioning of the first engines. The performance of the two combustors, as well as the measured emissions, are discussed and compared with the expected values and rig test results. Finally, the potential of the sequential combustion system to reach low NOx levels is demonstrated by unveiling the results of the extensive testing program during the commissioning phase.

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Calderite-rich garnet and franklinite-jacobsite-rich spinel occur in amphibolite-facies hydrothermal metasedimentary rocks that stratigraphically overlie the Proterozoic Gamsberg Zn-Pb deposit, South Africa. The minerals are restricted in occurrence to an irregularly developed Mn-Fe-rich unit at the top of the ore-bearing horizon (the Gams Formation), which is interpreted to be genetically related to the underlying sulfide mineralization. The rocks are well laminated on a centimeter to decimeter scale and consist of alternating layers of garnet, pyroxenoid, Mn-rich clinopyroxene and Fe oxide (Zn-Mn-rich ferrite spinel, magnetite, hematite). The garnet contains up to 36% of the calderite component in solid solution with andradite and spessartine, whereas the spinel reaches a maximum franklinite component of 39% in solid solution with magnetite and jacobsite. Associated minor to accessory minerals include manganoan calcite, manganoan and zincian tremolite, Sr-rich epidote, hyalophane, pyrophanite, melanotekite and mimetite. The occurrence and spatial distribution of calderitic garnet, Zn-Mn-rich spinel and hematite constrain oxygen fugacities during metamorphism to conditions close to the HM buffer for the uppermost part of the Gams Formation, and indicate that considerable gradients in f(O 2) and f(S 2) existed within this specific horizon. The preserved assemblages are products of complex reduction and decarbonation reactions of protoliths composed of Mn-Ca-rich carbonate, Fe-Mn oxides and hydroxides, silica and aluminous clay. Under the observed conditions of P, T and f(O 2), the contrasting parageneses are a function of delicate variations in the bulk composition of the precursor sediments. The Mn-Fe-rich and Zn-S-poor nature of these metahydrothermal rocks indicates that they represent a dispersion halo of low-temperature and oxidized fluids that postdated base-metal mineralization. Collectively, the unusual mineralogical and chemical composition of these rocks provides an indication of the spectrum of rock types that may be associated with metamorphosed deposits of base-metal sulfides.