Extract
The correlation of isolated outcrops of igneous rocks where two or more similar intrusions are exposed is a difficult problem which is not always solved by thin sections or field studies. Such a problem was encountered in mapping the closely related Pikes Peak and Silver Plume granites of pre-Cambrian age in the Sawatch Range of central Colorado (Fig. 1). A comparison of the heavy minerals of the isolated outcrops with those of known granites was undertaken; and for this purpose large samples, suitable for crushing and heavy mineral analysis, were collected from various points within the areas of each batholith, and from the small outcrops whose age was in question. It was hoped that sufficient similarities in the heavy mineral assemblages might be established to be of value in making correlations. Furthermore, as work on the heavy minerals in igneous rocks is still in the experimental stage, a series of analyses from various parts of a given batholith should throw some light on the question of whether heavy minerals may be distinct and constant enough to be characteristic and so give a reliable means of correlation of isolated exposures.