Abstract

Qualitative and quantitative mineralogical studies of the Chattanooga Shale are in progress. Problems of separation and analysis of mineral and organic components are difficult because the rock is fine-grained. However, the application of light and electron microscopy, X-ray diffraction, nuclear-track study, and other methods has provided data of interest.

Megascopically, the shale is a massive chocolate-brown sediment which displays faint indications of lamination. Some pyrite lenses, nodules, and crystals and a few mica flakes are large enough to be seen with a hand lens.

In thin section the rock is seen to consist of grains of quartz and feldspar in a matrix of yellow to red-brown organic material, which incorporates shreds of mica and probably clay particles and is dotted by small clusters of pyrite. Larger organic fragments with associated pyrite are common and take various forms. Individual mineral particles range from pyrite cubes less than 0.15 micron on a side to quartz and feldspar grains as large as 0.10 mm.

X-ray studies show the clay minerals to be illite, kaolinite, and chlorite in decreasing order of abundance. Tourmaline, zircon, and apatite are the characteristic heavy minerals of the sediment.

Quantitative studies, accomplished by a combination of chemical and mineralogical methods, have shown the composition of a batch sample of this rock to be approximately: 22% quartz, 9% feldspar, 31% illite and kaolinite, 22% organic matter, 11% pyrite and marcasite, 2% chlorite, 2% iron oxides, and 1% tourmaline, zircon, and apatite.

Alpha-track studies of emulsion-covered thin sections indicate that no uranium mineral is present. Approximately 70% of the uranium atoms is randomly distributed throughout the fine-grained matrix of the rock, whereas another 25% is concentrated in organic-pyrite-clay complexes such as pyrite nodules and discrete organic bodies. In unweathered samples there is no relationship between uranium distribution and textural features such as bedding.

The data indicate that the uranium was precipitated from sea water under reducing conditions and has not been redistributed following compaction of the sediment.

This content is PDF only. Please click on the PDF icon to access.

First Page Preview

First page PDF preview
You do not currently have access to this article.