ABSTRACT

The size frequency distributions of heavy minerals can be expressed in terms of the size separation between the modes of each heavy mineral and that of the light minerals (quartz plus feldspar). The modal separation is = log₂(Z_H/Z_L)^[1]/[3] ( H/L)^[2]/[3]). Z_L and Z_H are shape factors for the light and heavy minerals, respectively, = (M - F)/F, where is specific gravity and the subscript M is for mineral and F is for fluid.

A test of this theoretical distribution function was made for heavy minerals in four Tertiary formations in Huerfano Park, Colorado, whose age, mode of deposition, direction of transport, and local source areas are already well-known. A careful sampling and laboratory procedure was used to obtain weight frequencies of the minerals in an open statistical system, so that tests could be made to determine usefulness of the heavy mineral frequencies for correlation and provenance studies.

The measured modal separations (_meas.) deviate considerably from the theoretical modal separations based on specific gravity and shape. The size frequency modes of most of the minerals are smaller than expected. Minerals having similar _meas. can be used to correlate beds, since correlation is done by mineral grains having hydraulic properties which appear equivalent to the streams that deposited the grains.

The provenances for the heavy minerals can be specifically identified as being Precambrian crystalline and Pennsylvanian-Permian sediments by means of analysis of the mineral correlation matrix. Visual clustering by mineral associations, and by the more formal factor analysis give essentially the same results. Principal component factoring and Varimax Rotation are objective methods for identifying independent mineral provenances.