Mode of occurrence of titanium and zirconium in laterites

Untersuchungen zur geochemischen Verteilung des Zirkoniums in der Lithosphäre

SUMMARY
Zircons have been studied in the sedimentary rocks of the Sparagmite Group (Eocambrian) and their metamorphic associates from the Trondheim area and the adjacent regions in Norway and Sweden. The majority of zircon population (type B) has been formed in the sediments by authigenesis. Another authigenic associate is rutile. The authigenic zircons have irregular, round and ellipsoidal habits. In metamorphic rocks the same grains show a greater tendency of euhedrism, forming drum-like crystals with acute (331) pyramids and short prisms. Authigenic zircons are usually clear and transparent but some grains may show cloudy appearance. A few other grains (type A) with different habit and many inclusions appear to be of detritai nature.

Dissolution of a metamictized zircon population in the source rock is possible in many ways. An important possibility is the dissolution of zircons in alkaline solution. Carbonated lime-rich waters or other acidic solutions could be equally effective. Zirconates, so formed, are transported to the basin of deposition as colloidal particles or as ionic complexes. The authigenic process is visualized as a deposition of the zirconates by adsorption or by precipitation as zirconium hydroxide, possibly due to change in the Eh and pH in the environment. The hydrated oxide subsequently reacts with silica to form metastable hydrozircon. In course of time hydrozircon dehydrates and becomes a normal zircon.

Numerous growths have been noted and are classified genetically into (l) late authigenic growths, and (2) growths syngenetic with metamorphism. The shape of the host grain usually controls the final shape of the overgrown grain.

There is some effect of metamorphism on the morphology of the authigenic zircons. In view of the characters of the newly generated zircons, the use of shape, size, zoning and such other parameters of zircons in petrogenetic problems, has to be retested to ensure its reliability.

Rather than being a mineral of igneous derivation only, zircon is from three parentages: igneous, authigenic and metamorphic. It is argued that the persistence of the authigenic zircons should be greatest because of very low concentration of radioactive elements.

Evolution of zircons in sedimentary and metamorphic rocks

............................................ Introduction...................................... Acknowledgments............................. Historical background..................... Geologic setting................................ Stratigraphic resume...................... Niobrara Formation................ Pierre Shale ...... ................... Sharon Springs Member. Weskan Member............... Lake Creek Member......... Salt Grass Member.......... Unnamed member............ Beecher Island Member... Sharon Springs Member................. Dark soft shale unit................. Organic-rich shale unit........... Phosphatic shale unit. ... Rate of sedimentation.............. 1 1 3 3 5 6 6 7 7 7 9 10 10 10 10 11 11 14 16 Composition.......... ................................................................ Previous studies..... ............ .......... . ............... Mineralogy .............................................................. Niobrara Formation........................................... Sharon Springs Member of the Pierre Shale. Upper members of the Pierre Shale. Bentonites............................................................. Basaluminite and hydrobasaluminite. .......... Potassium feldspar....................... ................... Barite and apatite.............................................. Chemical composition................................................. Mode of occurrence of elements.----------. -----Leaching of surface samples...... ... ........... Bentonites............................................................. Comparison with other shales...... .. Major elements . Minor and trace elements.......................... Measured sections...-.-.--------............. ........ . . References cited.................... ....... .............. . Index.......... ........................................ ... Page 20 20 22 23 23 24 24 26 30 30 31 34 37 37 37 37 38 39 45 49

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Mode of occurrence of titanium and zirconium in laterites

Citations

Untersuchungen zur geochemischen Verteilung des Zirkoniums in der Lithosphäre

Evolution of zircons in sedimentary and metamorphic rocks

Stratigraphy and composition of the Sharon Springs Member of the Pierre Shale in western Kansas

Zirconium mobility in bauxites of Southern Brazil

Iron and titanium oxides in soil clays and silts

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