GEOLOGY OF THE PICHER FIELD IN OKLAHOMA

The rock formations exposed at the surface in the Picher mining field include Mississippian and Pennsylvanian units that are nearly flat, with a low regional northwest dip of about 20-25 ft/mi. At a few places, sharply defined structural features are accompanied by appreciable dips (up to 70 degrees). The Miami Trough, Bendelari Monocline, and Rialto Basin are three prominent structures that dominate the main part of the Picher Field.

Mississippian rocks units, principally the Boone Formation, are host for most ore deposits. The Boone is composed of fossiliferous limestone and thick beds of nodular chert. This formation, which is 350-400 ft thick in the Picher area, is subdivided into seven members (in ascending order): St. Joe Limestone, Reeds Spring, Grand Falls Chert, Joplin, Short Creek Oolite, Baxter Springs, and Moccasin Bend. Beginning with B near the top of the Moccasin Bend and ending with R in the Reeds Spring, 16 beds are distinguished. The Quapaw Limestone (Meramecian) locally overlies the Boone. The Chesterian Series, represented by the Hindsville Limestone, Batesville Sandstone, and Fayetteville Shale, forms a disconformable contact with the Boone and/or Quapaw Limestone. Both the Hindsville and Batesville are mineralized locally.

Pennsylvanian formations of the Krebs Subgroup (lower division of the Cherokee Group) were deposited on a post-Mississippian erosion surface. The formations consist of alternating terrestrial fine-grained sandstone, shale, and thin coal beds and include the McAlester Formation, the Savanna Formation, and the basal Bluejacket Sandstone Member of the Boggy Formation.

Ore deposits in the Picher Field occur mainly in the upper half of the Boone Formation. A majority of the mine workings are within the M bed. Other important ore zones occurred within the K, G, H, and E and Chesterian beds; and sheet ground (or low-grade blanket deposits) occur within the Grand Falls Chert Member. Stope heights varied from 10-20 ft. to over 100 ft. The main ore minerals were sphalerite and galena; the zinc to lead ratio for the ore, based on total production from the field, was about 4.1:1.