Abstract
This study combines historic geological and mining data, modern GIS mapping, fieldwork and sample analysis to produce a model for Cornish crosscourse faulting. Several crosscourse fault zones on the north Cornwall coast, between Hell's Mouth and Holywell Bay, have been investigated. Key data include fault orientation, kinematics, fault rock types, damage zone width and relative chronology. Faults typically strike NW–SE and their development may be influenced by earlier late-Variscan shear zones. Many faults indicate extensional kinematics and precipitation of vein quartz that is presumed to reflect Triassic ENE-WSW regional extension and the wider occurrence of crosscourse mineralisation (Gleeson et al. 2000; Scrivener et al. 1994; Shail and Alexander 1997). These are variably overprinted by oblique to strike-slip reactivation episode(s) of late Jurassic-Neogene age.
GIS analysis was carried out on a range of data sets to map prospective faults of significant strike trace length SE from the coastal area, towards the Carnmenellis Granite. In addition, offshore bathymetric data was used to extend fault traces to the NW. The integration of mapped lineaments allowed key structures to be identified and correlated with those observed during fieldwork and those recorded in historical mining records (Collins 1912; Dines 1956; Henwood 1843).
A preliminary crosscourse classification has been produced and the potential factors influencing prospectivity for the extraction of lithium-enriched geothermal fluids evaluated. The post-Triassic reactivation episodes play a significant role in enhancing intrinsic fault zone permeability. In addition, the contemporary in situ stress regime may enhance dilatancy along these fault zones and allow significant permeability to be maintained at depth.
Footnotes
Disclosure statement
No potential conflict of interest was reported by the authors.