Behavior of some elements at weatheringof granites of the Melechov massif

Geoscience Research Reports 42, 2009 (GRR for 2008), pages 189–194

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Abstract

Relatively early stages of chemical weathering in granites of the Melechov massif are evaluated mainly by comparison of fresh samples from boreholes with weathered samples from soil cap (collected from depth close to 2 m). Weathered granites are depleted in SiO2, whereas their Al2O3 and loss of ignition (LOI) increase; there are two very different processes of feldspars decomposition, which usually results in the formation of two groups with contrasting Al2O3 at similar LOI. In the Lipnice granite, removal of Ca and partly of Na, Sr and Ba from the rock begins at relatively early stages of weathering. In coarse-grained Melechov granite, however, this process is much slower, perhaps due to the sorption or precipitation of secondary phases. Europium is not affected by weathering, though it was originally concentrated mainly in feldspars in contrast to the trivalent REE. The elements primarily concentrated in biotite (including Rb, Cs and most of trace metals of environmental interest) are passively concentrated in weathered rocks thanks to the sorption, mainly on vermiculite which forms from biotite (presence of vermiculite was proven by X-ray powder diffraction of biotite concentrates).