Abstract: A Quasi-ductile fractures is a new type of fractures which is different from either the brittle ruptures or the ductile shear zone.It occurs mainly at the centre of a ductile shear zone and may develop later from a further, shearing of the rocks.Such fractures are often Characterized by breccias composed of mylonites and by vertical and horizontal zoning of mineralization at high temperatures and pressures.Fluid carrying Pb.S etc may partly come from the mylonites.There are decrease or loss of some elements in the wall rocks at the both sides of mineralized belts.Microfissures, cataclastic flows and strain localization are found in them.