Many closely spaced kimberlite diatremes are characterized by major differences in mineral composition of their assemblages (both kimberlite and inclusions). Although some of this variation clearly is a function of local differences of host rock through which the upward moving magma passed during emplacement of the respective pipes, variations in type and intensity of alteration are probably more significant to an understanding of emplacement history. The Sloan 1 and 2 pipes in the northern Colorado-southern Wyoming kimberlitic diatreme field are approximately 150 m apart and contain substantially different assemblages especially of nodular material. These pipes are evaluated in terms of emplacement related alteration processes. Intensity and type of secondary reaction may be a function of time, magnitude, and/or level of intrusive activity. Pipes that fail to penetrate uppermost crustal levels would approximate roofed dikes of similar composition in which fresh upper mantle and lower crustal materials ...