A complicated heavily faulted intrusion section with some mineralisation. BGS: Unnamed Igneous Intrusion, Ordovician - Diorite And Gabbro. Igneous Bedrock formed approximately 444 to 488 million years ago in the Ordovician Period. Local environment previously dominated by intrusions of silica-poor magma. Setting: intrusions of silica-poor magma. These rocks were formed from silica-poor magma intruded into the Earth's crust. It cooled to form intrusions ranging from large, coarse-crystalline, often gabbroic, plutons at depth to smaller, fine to medium crystalline, often basaltic dykes and sills.