Abstract: Quantitative Determination of Minerals in Australian Tertiary Oil Shales

Andrew Mandile, Adrian Hutton

A standardless quantitative x-ray diffraction phase analysis program, using Rietveld refinement parameters, accurately determined the mineralogy of claystone, oil shale and carbonate-rich rocks in Australian Tertiary oil shale sequences. The program produces full-pattern analyses and overcomes problems such as reproducible intensities and overlapping profiles. It also accounts for absorption contrast and preferred orientation of powder crystallites. Bragg-Brentano calibration data are calculated for the different rock types of the oil shale sequences to correct for diffractometer and sample transparency intensity aberrations. These intensity correction curves are particularly important in the quantification of clay minerals. As clay minerals have ill-defined crystal structures and are commonly poorly crystalline, observed and modified (hkl) data sets of the appropriate clay minerals are used.

Australian Tertiary oil shales contain up to 11 mineral phases including dominantly interstratified illite-smectite, illite, kaolinite and quartz; locally important minerals include calcite, dolomite, siderite, analcite and other silicates including buddingtonite. Samples are divided into 12 groups where each group consists of samples with similar mineralogy. This allows easier refinement of the Rietveld parameters. Once these groups have been set for one sequence, they can be used for other sequences with similar rock types.

Oil shales produce traces that are characterized by an amorphous hump between the 15 and 33 degrees 2(^THgr). The area of the hump is a function of the organic content and can be used to quantify the organic matter content.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994