DESCRIPTIVE MODEL OF BEDDED BARITE

MODEL 31b

By Greta J. Orris

APPROXIMATE SYNONYM Stratiform barite.

DESCRIPTION Stratiform deposits of barite interbedded with dark-colored cherty and calcareous sedimentary rocks.

GEOLOGICAL ENVIRONMENT

Rock Types Generally dark-colored chert, shale, mudstone, limestone or dolostone. Also with quartzite, argillite, and greenstone.

Age Range Proterozoic and Paleozoic.

Depositional Environment Epicratonic marine basins or embayments (often with smaller local restricted basins).

Tectonic Setting(s) Some deposits associated with hinge zones controlled by synsedimentary faults.

Associated Deposit Types Sedimentary exhalative Zn-Pb (see fig. 158).

DEPOSIT DESCRIPTION

Mineralogy Barite ± minor witherite ± minor pyrite, galena, or sphalerite. Barite typically contains several percent organic matter plus some H2S in fluid inclusions.

Texture/Structure Stratiform, commonly lensoid to poddy; ore laminated to massive with associated layers of barite nodules or rosettes; barite may exhibit primary sedimentary features. Small country rock inclusions may show partial replacement by barite.

Alteration Secondary barite veining; weak to moderate sericitization has been reported in or near some deposits in Nevada.

Ore Controls Deposits are localized in second- and third-order basins.

Weathering Indistinct, generally resembling limestone or dolostone; occasionally weathered-out rosettes or nodules.

Geochemical Signature Ba; where peripheral to sediment-hosted Zn-Pb, may have lateral (Cu)-Pb-Zn-Ba zoning or regional manganese haloes. High organic C content.

EXAMPLES

Meggen, GRMY (Krebs, 1981)

Magnet Cove, USAR (Scull, 1958)

Northumberland, USNV (Shawe and others, 1969)