Chemical Weathering on the Carnmenellis Granite

C. M. Rice
Institute of Geological Sciences, London WC1X 8NG, England1
1Department of Geology and Mineralogy, University of Aberdeen.

Summary: The behaviour of 25 major and trace elements, together with mineral changes, has been examined in a deep weathering profile on the Carnmenellis granite, Cornwall. The bulk chemical and mineralogical composition of the regolith shows only minor changes from the parent rock indicating a low degree of chemical weathering. However, within the regolith marked differences occur between the fine fractions from the various horizons. Chlorite and degraded muscovite characterize the fines of horizons A+B and C whereas gibbsite and kaolinite characterize horizon D. Secondary minerals becoming base deficient with depth is the reverse of normal behaviour and two possible theories are advanced to explain this anomaly. Most of the trace elements are concentrated in the < 10 µm fraction of the various horizons, in part by an association with degraded muscovite. Tin and Zr occur in resistates and Be, Sr, and Co are mainly lost during weathering.

Mineralogical Magazine; December 1973 v. 39; no. 304; p. 429-447; DOI: 10.1180/minmag.1973.039.304.06
© 1973, The Mineralogical Society
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