Metasomatism in the Whin Sill of the North of England. Part I: Metasomatism by Lead Vein Solutions

The products of the metasomatism of igneous rocks are found for the most part only in small quantities since diffusion through a solid rock of the solutions responsible for metasomatic changes is a slow process. In the Whin Sill there are two types of metasomatic alteration product which though insignificant in total amount are nevertheless widely distributed. The first type, which was formed along the walls of an early joint system by the action of juvenile solutions, is part of the history of the cooling down of the Whin Sill and will be described in a subsequent paper. The second type was produced by the action of lead vein solutions. Although unconnected with any stage in the cooling down of the Whin Sill, this type has an important bearing on the general mechanism of replacement and especially on the part played by diffusion, whose effects may be seen in both types as an extended transition between altered and unaltered dolerite.