A previously unrecorded group of stratiform and stratabound-type magnetite beds (IOCG) has been found at the southeastern border of the Ossa Morena Zone (Variscan Massif of Spain). These mineralizations, hosted in Upper Precambrian-Lower Cambrian rocks, are located in a transpressive belt, and were strongly deformed by the Variscan Orogeny, thus showing polyphase noncoaxial folding. This folding has been recognized by the interference patterns observed in magnetite beds outcropping in old mine workings. A detailed mapping of several adits shows a Ramsay type 1 ‘egg box’ or dome-and-basin interference pattern which arises when both D1 (NW-SE trending) and D2 (NE-SW trending) fold axes and axial planes are orthogonal or at a high angle to each other. An analysis of the magnetitic layers using orthogonal thickness and conic functions has been carried out to characterize fold profiles geometry.
Deformation is also accommodated by oblique WNW-ESE trending thrust faults which produce centimetric to metric displacements of the magnetite beds. A 22% shortening in the NE-SW direction and 24% in the NW-SE direction has been estimated. Finally, as polyphase folding and thrust structures in three dimensions have a complex geometry, a 3D geological modelling has been carried out to obtain a better insight into the geometry of mineralized magnetite bodies. Copyright © 2010 John Wiley & Sons, Ltd.