ELEMENT MOBILITY IN PARAGNEISSES AND METABASITES OF THE CONTINENTAL DEEP DRILLING PROJECT (KTB GERMANY)/

Leaching experiments (pH = 3. T = 70 degrees C) have been performed on paragneisses and metabasites from the KTB drill cores. The experiment s yielded the fraction of total element content that is easily availab le to acidic aqueous fluids. The intensity of mineralogic alteration i n the studied samples is expressed in terms of easily leachable fracti ons of K or Ba. Its reliability is shown by correlation with a petrogr aphically determined alteration index. For the paragneisses, the easil y available fractions of Fe, Mg, Mn. Ca, Na. K, Ba. Co, Cr. Ni. Sr. V. and Y together with the variables whole-rock content and depth of sam ples were subjected to a factor analysis, the results of which are pre sented as a five-factor model. Correlation plots of easily leachable e lement fraction and whole-rock content vs an alteration index (percent age of leachable K reveal the changes in leachability as a function of intensity of alteration In a cataclastic boundary between paragneisse s and metabasites at 1610 m depth. the changes in whole-rock content a nd leachability of elements are studied in detail and compared with th e general trends in alteration. The results point to considerable inte rcrystalline element redistribution during retrograde metamorphism, wi th only insignificant element transport on a meter scale. Although con siderable fractions of many elements were easily available to acidic f luids (3 < pH < 4) in the experiments. the whole-rock element content was maintained during retrogression. suggesting that water-rock ratio and fluid flow were low. During alteration K. Ba, Fe, Co, Ni, Cr, and V are immobilized in situ. whereas Sr. Ca. and Y become more leachable . Across the studied, strongly altered. lithologic contact, element tr ansport up to 7 m normal to foliation can be traced. Here. Ca, Sr, Mg, Co, Ni. and Cr are slightly enriched. whereas It, Bal Fe, and hill ar e slightly depleted.