Geochemical soil surveys as an aid to mapping and interpretation of the Lizard Complex

Abstract

The results of a geochemical soil survey have been used to refine the geological mapping and interpretation of the inland, poorly exposed part of the Lizard Complex. Using cluster analysis, six major groups were recognized within a data set comprising 619 samples analysed for Cr, Co, Ni, Cu, Zn and Pb. These represented ultrabasic rocks, gabbroic rocks, two distinct units of Landewednack hornblende schist, metalliferous mineralization, and soils dominated by exotic material such as löess. The geographical distribution of these groups indicates that a lower Landewednack unit can be recognized in the S and W, separated by a thin transition zone from the main Lizard peridotite. This contrasts with its NE contact which is marked by a wide transition zone of soils suggesting interdigitating gabbroic and ultrabasic compositions, corresponding to the Traboe cumulate complex (Leake & Styles 1984), and a sharp contact with an Upper Landewednack unit. Both soil and deep auger sampling indicate that ultrabasic rocks underlie much of the area previously mapped as a tongue-like SW extension of the Crousa Gabbro.