Geometrical features can appear in variographic studies and usually they affect, or hide, grade distribution structures. The presence of a series of nearly homogeneous kaolin areas, linked together in "zones", creates a mosaic effect. This phenomenon is due to the existence of periodical settling regimes of the rivers. The size of these "zones" can affect the form of the variogram and increase the nugget effect due to high differences of values in the edge of the "zones". A hole effect is one the other known phenomena caused by the presence of two or more separated lenses with low difference in grade and shape. The distance between these lenses can thus be estimated.