Application of the Visman method to the design of a soil sampling campaign in the mining district of Linares (Spain)

The Visman method is an efficient tool in environmental geochemistry. The present study concerns the application of the Visman method in a pilot sampling exercise for the design and subsequent implementation of a tactical campaign in geochemical soil prospection. The aim of this study is to solve the problem of the support of the sampling unit by planning for an optimum combination of the mass and number of sampling increments. The areas selected for the pilot study were in the traditional mining district of Linares (province of Jaén, Southern Spain). The conclusions drawn from this study have enabled, for the first time, a tactical campaign to be carried out in this mining locality, over a surface area of 126 km2 occupying virtually the whole of the granite batholite. The large surface area, the different geological substrates and the variety of human activities have given rise to a large degree of geochemical variability. Aluminium and lead were taken as reference elements to estimate the evolution of the variance and the precision, with respect to the mass and number of sampling increments. Three mapping units with a surface area of 1 km2 were taken as representative of the geochemical reality of the study area; in one of these, mining and metallurgic activities took place, and in another, mining and mineral-extraction activities, while in the third, lying outside the batholite, there were no mining activities. The sampling programme for tactical prospection (reconnaissance) was designed according to the Visman method, on the basis of the variance and precision to be accepted, the budget available and the objectives laid down. The elements that presented a high degree of variability (i.e. a high distribution variance) were identified as those related to former mining activities.