Some age measurements on micas from broken hill, Australia

Abstract

K‐Ar measurements were carried out on 24 mineral concentrates, mostly biotite, from rocks in the Broken Hill district of New South Wales; Rb‐Sr measurements were carried out for comparison on eight of these. The results range from 430 to 1360 m.y. for K‐Ar, and from 460 to 550 m.y. for Rb‐Sr. They indicate that the last event of sufficient intensity to affect the biotites of this area occurred in the Lower Palaeozoic. This may be correlated, as a first hypothesis, with the event which caused emplacement of the secondary “Thackaringa‐type” lead deposits.