The Influence of Cryptic Lineaments upon Patterns of Iron Mineralization, Appalachian Plateau, Western Pennsylvania

Coyle, Paul R.¹ and Anderson, Thomas H. ²

¹Coyle Geological Services, Pittsburgh, PA

²Department of Geology and Planetary Science, University of Pittsburgh, Pittsburgh, PA

In the Allegheny Plateau of west central Pennsylvania siliceous iron rich Buhrstone composes a thin irregular layer 1 to 50 cm thick at the top of the Pennsylvanian marine Vanport Limestone. The Buhrstone horizon that may include iron-oxide, siderite, clay or a combination of these, is restricted to the Vanport. However, the mineralized layer is not everywhere present, as shown by outcrops and 970 drill-holes throughout an area of 4700 km². Overlying strata consists, principally of shale and channels that locally cut through the Vanport and are filled with sandstone. Common Fe-stained strata, mineralized fossils and iron-filled fractures in and above the Vanport, indicate that the ore was precipitated. The occurrences of ore distinguish some elongate bodies that trend northwest and are parallel to a panel within which the channels are most extensively developed. The ore bodies, with the associated clay and siderite, and the sandstone channels delineate zones about 24 km wide. We interpret the margins of this zone to coincide with cryptic cross-strike discontinuities (CSD’s) with little or no surface expression.  Furthermore, changes in the generally northeasterly trend of folds, saddles located on anticlines and structural depressions in the Vanport Limestone occur at the intersection with the cryptic lineaments. The geological features recorded by the Vanport suggest that structural discontinuities control the distribution of the ore. Fluid flow-paths, parallel to lineaments striking N60^oW, are also influenced by the cryptic structures.