Tri-State Lead-Zinc Ore Illustrating Open Space Filling Textures



Galena (Gn; white) deposited on sphalerite (Sl; grey) in Tri-State lead-zinc ores. The ores exhibit open space filling textures in which sphalerite was deposited first forming euhedral crystals upward into open space, and galena was subsequently deposited on sphalerite with its base taking the shape of the underlying sphalerite. The sphalerite crystal on the left is typical of the euhedral shape of crystalline sphalerite; it exhibits a rotund shape (section through your thumb). A single quartz crystal is present at the boundary between galena and sphalerite. Quartz may have been deposited on sphalerite and partly replaced the underlying sphalerite, or the quartz crystal may have been deposited after both sphalerite and galena preferentially replacing galena. Picher field, Tri-State District, Missouri, Oklahoma, and Kansas. Ore microscopy, reflected light, medium magnification.



Pyrite (Py; white) and marcasite (Mc; whitish yellow) deposited on sphalerite (Sl; grey). Pyrite and marcasite have formed euhedral crystals upward into open space, and take the shape of the underlying rotund sphalerite. Pyrite has formed cubes and marcasite formed more elongate prismatic crystals upward into open space. Plastic (P) fills the former open space. Picher field, Tri-State Lead-Zinc District, Missouri, Oklahoma, and Kansas. Ore microscopy, reflected light, medium magnification.



Pyrite (Py; white) deposited on sphalerite (Sl; grey) taking the shape of the earlier deposited sphalerite and forming it own euhedral cubic shape upward into former open space. Chalcopyrite (Cp; deep yellow) was subsequently deposited on the top of pyrite and sphalerite. Picher field, Tri-State Lead-Zinc District, Missouri, Oklahoma, and Kansas. Ore microscopy, reflected light, medium magnification.



Pyrite (Py; white) deposited on sphalerite (Sl; grey) taking the shape of the earlier deposited sphalerite and forming it own euhedral cubic shape upward into former open space. Chalcopyrite (Cp; deep yellow) was subsequently deposited on the top of pyrite and sphalerite. In contrast to those three minerals that were deposited in open space, enargite (En; brownish grey) was deposited by replacement. Enargite preferentially replaced chalcopyrite but also partly replaced the margins of the pyrite cube to give a ragged appearance typical of replacement. The late fluids that deposited enargite probably found ease of travel along the crystal boundary between sphalerite and chalcopyrite, and obtained the copper for enargite from the replacement of the copper mineral chalcopyrite. Two NE trending scratches (black) illustrate their use in determining the hardness of ore minerals. The scratches are widest in chalcopyrite, the softest of the ore minerals in the photomicrograph, become narrower in harder enargite, are barely perceptible in the very hard pyrite, and become broader in the softer sphalerite. Picher field, Tri-State Lead-Zinc District, Missouri, Oklahoma, and Kansas. Ore microscopy, reflected light, medium magnification.