Geochemical dispersions of Rb and Sr in granitic wall rocks of the Bethlehem JA and Valley Copper porphyry-type deposits are reported. Values of Rb and Rb/Sr ratios increase progressively from the periphery of the deposits to the central portion where intense potassic and phyllic alteration coincide with a large part of the orebodies. In contrast, Sr levels decrease from the outer margins, where propylitic and argillic alteration are dominant, to the core of intense alteration. Distribution of Rb and Sr are controlled by the abundances of K and Ca, respectively. Geochemical contrast between regional background and anomalous levels of Rb and Sr are similar to those reported for porphyry copper deposits in mafic and intermediate volcanic rocks.On the basis of these results, primary dispersion of Rb and Sr in conjunction with alteration studies could be a useful guide in defining areas most suitable for detailed exploration.

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