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The Miocene low-sulphidation epithermal deposits of the Omu camp in northeastern Hokkaido are small past-producers of precious metals and represent significant exploration targets for high-grade Au and Ag ores. The quartz textures of ore samples and the distribution of ore minerals within quartz veins were studied to identify the processes that resulted in the bonanza-grade precious metal enrichment in these deposits. In the high-grade vein samples, which are crustiform or brecciated in hand specimen, ore minerals exclusively occur within colloform quartz bands. High-magnification microscopy reveals that ore-bearing colloform bands consist of fine-grained quartz exhibiting relic microsphere textures and quartz having a mosaic texture that formed through recrystallisation of the microspheres. The presence of relic microspheres is evidence that the microcrystalline quartz hosting the ore minerals formed through recrystallisation of a noncrystalline silica precursor phase. The ore-hosting colloform bands composed of agglomerated microspheres alternate with barren colloform quartz bands that are composed of fibrous chalcedonic quartz and mosaic quartz formed through recrystallisation of the chalcedony. The findings of this study are consistent with previous models linking bonanza-grade precious metal enrichment and the formation of bands of noncrystalline silica in low-sulphidation epithermal veins to episodic vigorous boiling or flashing of the hydrothermal system in the near-surface environment., The Miocene low-sulphidation epithermal deposits of the Omu camp in northeastern Hokkaido are small past-producers of precious metals and represent significant exploration targets for high-grade Au and Ag ores. The quartz textures of ore samples and the distribution of ore minerals within quartz veins were studied to identify the processes that resulted in the bonanza-grade precious metal enrichment in these deposits. In the high-grade vein samples, which are crustiform or brecciated in hand specimen, ore minerals exclusively occur within colloform quartz bands. High-magnification microscopy reveals that ore-bearing colloform bands consist of fine-grained quartz exhibiting relic microsphere textures and quartz having a mosaic texture that formed through recrystallisation of the microspheres. The presence of relic microspheres is evidence that the microcrystalline quartz hosting the ore minerals formed through recrystallisation of a noncrystalline silica precursor phase. The ore-hosting colloform bands composed of agglomerated microspheres alternate with barren colloform quartz bands that are composed of fibrous chalcedonic quartz and mosaic quartz formed through recrystallisation of the chalcedony. The findings of this study are consistent with previous models linking bonanza-grade precious metal enrichment and the formation of bands of noncrystalline silica in low-sulphidation epithermal veins to episodic vigorous boiling or flashing of the hydrothermal system in the near-surface environment.

Combinatorial chemistry allows the synthesis of libraries of compounds by combination of building blocks or by combinatorial elaboration of a central scaffold.([1,2]) Carbohydrates hold great promise as scaffolds due to their high degree of functionalization, relative conformational rigidity, commercial availability of many stereoisomeric forms, and their well-described chemistry. Hirschmann, Nicolaou, Smith, and their coworkers pioneered the use of carbohydrates as scaffolds in their design and synthesis Of beta-D-glucose derived non-peptide peptidomimetics of the peptide hormone somatostatin (SRIF).([3,4]) However, only relatively few examples on the application of carbohydrates as scaffolds in combinatorial chemistry have been described.([5-11]) For example, Brill et al. anchored a 1,6-anhydro-beta-D-glucopyranoside (levoglucosan) derived epoxide to a solid support and introduced diversity by opening of the support-bound 2,3-epoxide.([9]) Hirschmann et al. employed the opening of a D-glucose derived 1,2-epoxide with a thiol in one of the initial steps towards the synthesis of a library of D-glucose derived compounds. ([10])We reasoned that introduction of all substituents by O-acylation or carbamoylation would give final products with too high a degree of conformational freedom. To introduce substituents directly on the carbohydrate ring and to keep protecting group manipulations on the resin-bound carbohydrate scaffold to a minimum, we decided to prepare a scaffold in which diversity would be introduced by opening of an epoxide. Also, it was a requirement that the scaffold should contain nitrogen, as amines are found in many pharmacologically relevant molecules, e.g., CNS active compounds. We chose inexpensive D-glucosamine as starting material, to prepare a 3,4-epoxide, and to block the C-1 as the methyl glycoside (Scheme 1). Both solution and solid-phase strategies were envisioned; for the solid-phase strategy, the amine could serve as a convenient point for a

The Enterprise nickel deposit (40 Mt of 1.07% Ni) is located on the eastern edge of the Kabompo dome. Nickel sulphides are hosted within a sequence of quartz-, carbonate-, and carbon-rich metasedimentary rocks that interfinger with and overlie siliciclastic metasedimentary rocks. The host rocks contain significant kyanite, talc, and magnesian chlorite. Silicification and magnesian metasomatism occurred prior to or concurrent with a regional metamorphic event (590-500 Ma). Mineralisation resulted in the precipitation of Ni and Fe-Ni sulphides in veins and as semimassive replacements of the host rocks. Ni sulphides precipitated in two main stages. The deposit contains minor Cu and trace amounts of Co and platinum group elements. A discrete zone of Cu sulphides underlies a portion of the Ni sulphide zone. Re-Os geochronology on molybdenite yields a 540.6 ± 1.8 Ma age for mineralisation at Enterprise, the approximate age of metamorphism. Sulphur isotope results indicate that S was derived largely from Neoproterozoic marine sulphate by thermochemical sulphate reduction. Significant volumes of mafic igneous rocks are not present in the immediate area of the Enterprise deposit. No evidence of prealteration concentrations of nickel exists within the sedimentary rock sequence at the deposit. The alteration and mineralisation style is similar to the much less metamorphosed nickel-bearing Shinkolobwe uranium deposit in the Democratic Republic of Congo, though the Enterprise deposit does not contain significant uranium. The sediment-hosted Ni-rich deposits of Central African Copperbelt exemplified by Enterprise appear to represent a new style of hydrothermal nickel mineralisation., The Enterprise nickel deposit (40 Mt of 1.07% Ni) is located on the eastern edge of the Kabompo dome. Nickel sulphides are hosted within a sequence of quartz-, carbonate-, and carbon-rich metasedimentary rocks that interfinger with and overlie siliciclastic metasedimentary rocks. The host rocks contain significant kyanite, talc, and magnesian chlorite. Silicification and magnesian metasomatism occurred prior to or concurrent with a regional metamorphic event (590-500 Ma). Mineralisation resulted in the precipitation of Ni and Fe-Ni sulphides in veins and as semimassive replacements of the host rocks. Ni sulphides precipitated in two main stages. The deposit contains minor Cu and trace amounts of Co and platinum group elements. A discrete zone of Cu sulphides underlies a portion of the Ni sulphide zone. Re-Os geochronology on molybdenite yields a 540.6 ± 1.8 Ma age for mineralisation at Enterprise, the approximate age of metamorphism. Sulphur isotope results indicate that S was derived largely from Neoproterozoic marine sulphate by thermochemical sulphate reduction. Significant volumes of mafic igneous rocks are not present in the immediate area of the Enterprise deposit. No evidence of prealteration concentrations of nickel exists within the sedimentary rock sequence at the deposit. The alteration and mineralisation style is similar to the much less metamorphosed nickel-bearing Shinkolobwe uranium deposit in the Democratic Republic of Congo, though the Enterprise deposit does not contain significant uranium. The sediment-hosted Ni-rich deposits of Central African Copperbelt exemplified by Enterprise appear to represent a new style of hydrothermal nickel mineralisation.

The Grass Valley orogenic gold district in the Sierra Nevada foothills province, the largest historic gold producer of the North American Cordillera, comprises both steeply dipping E-W veins located along lithological contacts in accreted c.300 and 200 Ma oceanic rocks and shallowly dipping N-S veins hosted by the Grass Valley granodiorite; the latter have yielded about 70% of the 13 000 000 ounces of historic lode gold production in the district. The oceanic host rocks were accreted to the western margin of North America between 200 and 170 Ma, metamorphosed to greenschist and amphibolite facies, and uplifted between 175 and 160 Ma. Large-scale magmatism in the Sierra Nevada occurred between 170-140 Ma and 120-80 Ma, with the Grass Valley granodiorite being emplaced during the older episode of magmatism. U-Pb isotope dating of hydrothermal xenotime yielded the first absolute age of 162 ± 5 Ma for the economically more significant N-S veins. The vein-hosted xenotime and associated monazite are unequivocally of hydrothermal origin as indicated by textural and chemical characteristics, including grain shape, lack of truncated growth banding, lack of an Eu anomaly, and low U and Th concentrations. The N-S veins are temporally distinct from a younger 153-151 Ma gold event that was previously reported for the E-W veins. The geochemistry of the Grass Valley granodiorite is consistent with it being the product of arc magmatism but it is has no direct genetic relationship to gold mineralisation., The Grass Valley orogenic gold district in the Sierra Nevada foothills province, the largest historic gold producer of the North American Cordillera, comprises both steeply dipping E-W veins located along lithological contacts in accreted c.300 and 200 Ma oceanic rocks and shallowly dipping N-S veins hosted by the Grass Valley granodiorite; the latter have yielded about 70% of the 13 000 000 ounces of historic lode gold production in the district. The oceanic host rocks were accreted to the western margin of North America between 200 and 170 Ma, metamorphosed to greenschist and amphibolite facies, and uplifted between 175 and 160 Ma. Large-scale magmatism in the Sierra Nevada occurred between 170-140 Ma and 120-80 Ma, with the Grass Valley granodiorite being emplaced during the older episode of magmatism. U-Pb isotope dating of hydrothermal xenotime yielded the first absolute age of 162 ± 5 Ma for the economically more significant N-S veins. The vein-hosted xenotime and associated monazite are unequivocally of hydrothermal origin as indicated by textural and chemical characteristics, including grain shape, lack of truncated growth banding, lack of an Eu anomaly, and low U and Th concentrations. The N-S veins are temporally distinct from a younger 153-151 Ma gold event that was previously reported for the E-W veins. The geochemistry of the Grass Valley granodiorite is consistent with it being the product of arc magmatism but it is has no direct genetic relationship to gold mineralisation.