2.Determine the distribution of the minerals on the outcrop, hand specimen and thin section scales. Ask the following questions: (i) Do the minerals occur as the fill to vrins or vugs? (ii) Do they replace sprcific primary minerals, secondary minerals or clasts (selective alteration)? (iii) Do they replace the whole rock and contained minerals in restricted areas, suck as the envelopes around vrins (selectively pervasive)? (iv) Do they replace the whole rock at the outcrop scale (pervasive)? (v) Do they occur in sprcific zones around veins or fractures, and if so, what is the relationship to other zones? In some cases, it may be possible to quantify the intensity of alteration in terms of the extent to which the rock is replaced by hydrothermal minerals. This provides an indication of the premeability in the protolith and the fluid rock ratio during alteration.