DESCRIPTIVE MODEL OF SANDSTONE-HOSTED Pb-Zn
By Joseph A. Briskey
DESCRIPTION Stratabound to stratiform galena and sphalerite in multiple, thin, sheetlike ore bodies in arenaceous sedimentary rocks.
GENERAL REFERENCES Bjørlykke and Sangster (1981), Briskey (1982).
Rock Types Continental, terrigenous, and marine quartzitic and arkosic sandstone, conglomerate, grit, and siltstone. Local evaporates.
Textures Bedding, crossbedding, paleochannels, liquification structures, and intraformational slump breccias. Quartz and subordinate calcite cement.
Age Range Proterozoic to Cretaceous host rocks.
Depositional Environment Host rocks deposited in combined continental and marine environments including piedmont, fluvial, lagoonal-lacustrine, lagoonal-deltaic, lagoonal-beach, and tidal channel-sand bar environments. Commonly succeeded by marine transgressions.
Tectonic Setting(s) Deep weathering and regional peneplanation during stable tectonic conditions, accompanied by marine platform or piedmont sedimentation associated with at least some orogenic uplift. Sialic basement, mainly "granites" or granitic gneisses.
Associated Deposit Types Sediment-hosted Cu.
Mineralogy Fine- to medium-crystalline galena with sporadic smaller amounts of sphalerite, pyrite, barite, and fluorite. Minor chalcopyrite, marcasite, pyrrhotite, tetrahedrite-tennantite, chalcocite, freibergite, bournonite, jamesonite, bornite, linnaeite, bravoite, and millerite. Quartz and calcite are usual gangue minerals, and organic debris occurs in some deposits.
Texture/Structure Clots of galena 0.5 to several centimeters in diameter; disseminations 0.1-1.0 mm in diameter; locally massive. Ore and gangue minerals are intergranular. Galena bands locally highlight crossbedding, and other sedimentary structures in sandstone. Laisvall has crosscutting curvilinear features resembling roll fronts.
Alteration "Sericite" (white mica?) reported in some deposits; but may only be recrystallized sedimentary illite.
Ore Controls Intergranular porosity. Ore may be massive where localized by porous sedimentary structures (above), impermeable barriers, faults, joints, and fractures. Within or immediately above paleochannels, or less commonly, paleoridges.
Weathering Surface oxidation of galena to cerussite, minor anglesite and pyromorphite, chalcopyrite to malachite, azurite, covellite, and chalcocite and (or) sphalerite to smithsonite, hemimorphite, hydrozincite, and goslarite.
Geochemical Signature Anomalous amounts of Pb and Zn in host rocks and derivative soils; Ba, F, and Ag are enriched in lowermost parts of some deposits. Zinc tends to increase upward in the deposits. Sialic basement may contain anomalous lead concentrations. Background in sandstone: Pb = 7 ppm; Zn = 16 ppm.
Laisvall, SWDN (Rickard and others, 1979)
Vassbo and Guttusjo, SWDN (Chrisofferson and others, 1979)
Largentiere, FRNC (Samama, 1976; Michaud, 1980)
Zeida-Bou Mia, MRCO (Schmitt and Thiry, 1977)
Bou-Sellam, MRCO (Caia, 1976)
Yava (Salmon R.), CNNS (Hornbrook, 1967; Scott, 1980a, b)
George Lake, CNSK (Karup-Moller and Brummer, 1970; Sangster and Kirkham, 1974)
Mechernich-Maubach, GRMY (Bjørlykke and Sangster, 1981)