Weathering of a copper stratiform deposit (schist) at Salobo, Brazil, has produced two distinct Cu-bearing minerals from a biotite parent: vermiculite and a manganese oxide containing as much as 13% and 25% CuO, respectively. Manganiferous products were formed as the result of an interhorizon transfer of solutions through a fissure system. Thus, the structural orientation of the schists was a major factor in controlling the supergene concentration of Cu. The Cu-vermiculite formed by the weathering of Fe-biotite, although the unweathered biotites in the parent rocks were found to contain no copper, suggesting that Cu was supplied by weathering solutions. X-ray powder diffraction (XRD) and cationexchange capacity data for the Cu-vermiculite differ from those of typical Mg-vermiculite and are similar to those of hydroxy- Al-vermiculite. A comparison of the XRD pattern of the Cu-vermiculite with that of a Cu-free vermiculite indicates that Cu atoms are located in interlayer sites. Cu probably occurs in a brucite-like layer. The position and structure of the Cu K-absorption spectrum suggest that the Cu is divalent and exists in 6-fold coordination.

Highly tectonized contact between serpentinite and younger pegmatite in the magnesite mine of Wiry contains various layer silicates. Vermiculite, chlorite, smectite, and interstratified mica-vermiculite were recognized by means of routine XRD examination. Two three component interstratifications of mica-vermiculite-chlorite and chlorite-swelling chlorite-smectite were identified by a combined procedure of deconvolution of the XRD patterns and simulation of XRD tracings. A mineral with large diffraction maxima, displaying “chlorite intergrade” characteristics, appeared to be a mixture of chlorite, mixed layer chlorite-smectite, and vermiculite. Polytypes of phyllosilicates were determined by the X-ray transmission method. Due to the heritage of parent mineral polytype structure by transitional products of alteration, two distinct sequences of layer silicates were observed: one formed from trioctahedral mica (vermiculite, mixed layer mica-vermiculite); and one evolved from chlorite (e.g., mixed layer chlorite-swelling chloritesmectite). A tentative scheme of the primary contact zone structure, not obscured by subsequent brittle tectonics either by transformation of layer silicates, is proposed.