Structural corridors in Landsat lineament interpretation

In plots of symbolised geo-data which have variations in density of symbol population, structural corridors are defined by relatively narrow belts in which the density of symbol population is in marked contrast to that of surrounding areas. Some corridors are of high population density (HPD), some of low population density (LPD), whilst others are serial composites. In geology, corridors are to be seen in ancillary plots of gravimetrics, magnetics, photolineaments, Landsat lineaments and allied data. Those related to ore deposits are commonly 100–200 km in length, with aspect ratios (length/breadth) from 20 to 40. They are distinguished from conventional anomaly trends by not necessarily defining absolute highs or lows in individual symbol measurements. Rather do they reflect dislocations in the pattern of material distributions which the symbols represent, and are therefore related more to gradient functions. They must be distinguished from random trends which pervade ordinary patterns of material distributions. Corridors defined for the one area by different sets of geo-data frequently do not coincide, and this is anticipated by differences in the particular qualities measured, and the geological times at which these qualities were established. Field observations show structural corridors to correspond to subsurface dislocations, and, depending on the type of geological environment, either edges or centres of corridors are significantly related to mineral and oil deposits. In airphoto and Landsat lineament plots, the best data for revealing corridors are the smaller features at the high frequency end of the symbol dimensional range. In such cases, structural corridors are hard to preconceive, and emerge only after the assembly of data is complete. This greatly reduces the problem of subjectivity of the interpreter. Photolineament corridors in the Kalgoorlie goldfield of Western Australia are discussed and compared with Landsat corridors related to metal and oil occurrences in North America.