USE OF RB-SR RATIOS AS A GUIDE TO MINERALIZATION

Rb is incorporated in K minerals and Sr in Ca minerals and hence the Rb/Sr ratio amplifies any increase in K or loss of Ca in hydrothermal alteration zones. Submarine exhalative deposits, which have no recognizable alteration zones in the Broken Hill district and in southeastern New South Wales display an increase in the Rb/Sr ratio of the wall rocks due primarily to Sr depletion in the ore zone. Granites associated with mineralization commonly have a high Rb/Sr ratio as a result of fractionation. Associated with eastern Australian W-Mo-Bi deposits, this ratio increases towards mineralization as a result of replacement of plagioclase by K-mica in the altered granitic rocks. An increase in Rb/Sr values from the periphery to the core of a porphyry copper deposit has been documented. We conclude that the ratios may be useful as a guide to different types of mineralization in rocks that either display alteration or have no recognizable alteration. © 1979.