The mafic complex of El Cajon Mountain is composed of lamprophyre, mafic breccia, syenite, and a sulfide-rich hypersthene gabbro which intruded a suite of granitic rocks as a pipe-like structure. Sulfides were deposited by metasomatic replacement of the silicates and in fracture following the last mafic intrusion. The chaotic nature of the stoping of large amounts of rock from the conduit walls and apparent small size of the structure indicate that the sulfides and associated mafic breccia were emplaced as a fluidized solid-gas system along the inter-section of major joint sets.
