1.3 APPLIED SEDIMENTOLOGY
15
1.3.2.4 Ores in Sediments: Conclusion
The preceding account shows that many ore bodies occur intimately associated with
sedimentary rocks. They originated as detrital placers, syngenetically by direct precipitation, and epigenetically by diagenetic precipitation and replacement from fluids of
diverse and uncertain origins. Sedimentology throws considerable light on these problems of ore genesis, notably by utilizing its geochemical and petrophysical aspects. It
can be argued that these problems of ore genesis are peripheral to the actual business
of locating workable deposits. But if one believes, for example, that lead-zinc sulfide
mineralization is an inherent feature of reef limestones, then the search can be extended
beyond areas of known hydrothermal mineralization. Theories of metallogenesis thus
play a part in deciding which areas may be prospective for a particular mineral.
Regardless of prevailing prejudices of metallogenesis, however, sedimentology can
still be used as a searching tool. Facies analysis can map a complex of mineralized reefs,
define a minette iron ore shoreline, or locate permeability barriers in carnotite-rich alluvium. Sedimentologic surveys can be carried out at the same time as direct geochemical and geophysical methods and should form an integral part of the total exploration
effort.
Finally, Table 1.3 shows the wide range of sedimentary environments in which mineral
Table 1.3
Occurrence of Mineral Deposits in Various Sedimentary Environments a
Main lithology
Environment
Mineralization
Fluvial
Sandstones
Deltas
Carbonates
Lakes
Placers
Uranium roll-front ores
Cu-Fe red bed ores
Coal
Sideritic ironstones
Oil shales
Evaporites
Coal
"Bog" iron ores
Beaches
Placers
Continental shelves
Reefs
Shale and chert
Pelagic
Phosphates
Sedimentary iron ores
Evaporites
Pb-Zn Mississippi
Valley ores
Cu-Zn sulfides
Manganese nodules
Barytes
a Examples are discussed at appropriate places in the ensuing text, principally in Chapter 6.
15
1.3.2.4 Ores in Sediments: Conclusion
The preceding account shows that many ore bodies occur intimately associated with
sedimentary rocks. They originated as detrital placers, syngenetically by direct precipitation, and epigenetically by diagenetic precipitation and replacement from fluids of
diverse and uncertain origins. Sedimentology throws considerable light on these problems of ore genesis, notably by utilizing its geochemical and petrophysical aspects. It
can be argued that these problems of ore genesis are peripheral to the actual business
of locating workable deposits. But if one believes, for example, that lead-zinc sulfide
mineralization is an inherent feature of reef limestones, then the search can be extended
beyond areas of known hydrothermal mineralization. Theories of metallogenesis thus
play a part in deciding which areas may be prospective for a particular mineral.
Regardless of prevailing prejudices of metallogenesis, however, sedimentology can
still be used as a searching tool. Facies analysis can map a complex of mineralized reefs,
define a minette iron ore shoreline, or locate permeability barriers in carnotite-rich alluvium. Sedimentologic surveys can be carried out at the same time as direct geochemical and geophysical methods and should form an integral part of the total exploration
effort.
Finally, Table 1.3 shows the wide range of sedimentary environments in which mineral
Table 1.3
Occurrence of Mineral Deposits in Various Sedimentary Environments a
Main lithology
Environment
Mineralization
Fluvial
Sandstones
Deltas
Carbonates
Lakes
Placers
Uranium roll-front ores
Cu-Fe red bed ores
Coal
Sideritic ironstones
Oil shales
Evaporites
Coal
"Bog" iron ores
Beaches
Placers
Continental shelves
Reefs
Shale and chert
Pelagic
Phosphates
Sedimentary iron ores
Evaporites
Pb-Zn Mississippi
Valley ores
Cu-Zn sulfides
Manganese nodules
Barytes
a Examples are discussed at appropriate places in the ensuing text, principally in Chapter 6.