A series of papers on manganese metallogenesis appeared in a journal
issue edited by Frakes and Bolton [1992]. They also reviewed the
mode of origin of Phanerozoic sedimentary manganese deposits and
correlated their occurrences with variations in ocean chemistry, sea level
and paleoclimate. They concluded that extensive Mn carbonate and
oxide precipitation occurred during periods of regression; these periods
promote oxidation of seafloor organic matter, release of CO
and
global greenhouse warming.
Some unusual Ni-Mo-PGE-bearing black shales in China were studied by
Murowchick et al. [1994], who concluded that they formed via
venting of metalliferous hydrothermal fluids into an anoxic,
phosphogenic basin. Large variations in ion microprobe 
S/
S
values for pyrite implied that bacteriogenic seawater sulfate reduction
associated with organic matter decomposition was an important
mechanism for ore deposition.
Most of our domestic uranium resources occur in Tertiary non-marine sandstone deposits that are thought to have formed by groundwater transport and deposition. Sanford [1994] developed a four-layer finite difference model for the formation of tabular sandstone uranium deposits. His results indicated that regional fluid flow was gravity-driven, with discharge concentrated at lake shorelines or playa margins. Inferred zones of mixed local and regional groundwater discharge were associated with the ore zones; these data support a fluid interface mixing mechanism for ore deposition.
Precambrian conglomerates rich in detrital pyrite, uraninite and quartz
continue to challenge economic geologists as well as paleoclimatologists,
because such a combination of minerals cannot survive fluvial transport
in our present oxygen-rich atmosphere. Vennemann et al. [1992]
found variable 
O values in adjacent quartz pebbles and their
contained fluid inclusions in Archean conglomerates from the
Witwatersrand (South Africa) and Huronian (Canada) districts. They
concluded that the pebbles preserved their predepositional oxygen
isotopic compositions and fluid inclusion chemistry. Both areas exhibited
quartz pebble 
O modes consistent with derivation from erosion of
Archean granites and pegmatites. However, the Witwatersrand pebbles
exhibited a broader, heavier range in 
O values, suggesting an
additional source of quartz from erosion of Archean greenstone belt lode
gold deposits. This provenance difference may explain the presence of
both Au and U in the Witwatersrand ores, but only Au in the Huronian
ores. The 
O values and fluid inclusion characteristics of
the quartz pebbles were inconsistent with previous proposals for their
derivation from Archean exhalative deposits.