Table 4. Reconnaissance U in The Tumbarumba Basaltic Gem Field, New South Wales: In Relation to Sapphire-Ruby Deposits of Eastern Australia

Table 4. Reconnaissance U-Pb isotope dating, zircon megacryst, Tumbarumba gemfield. graincolourU (ppm)Th (ppm)206Pb/238 U±1age±1 (Ma)Pb*%cPbB2orange brown174460500.00362±1823.3±1.2122.4 206 Pb/ 238 U refers to radiogenic 206 Pb which was estimated by correcting the measured 207 Pb/ 206 Pb in each case by the amount required to yield concordant Pb/U ages, using an assumed common 207 Pb/ 206 Pb of 0.9618 (Broken Hill ore Pb). Pb* refers to the total radiogenic Pb as measured (in ppm). %c Pb refers to the percentage of common (non radiogenic) 206 Pb in the total measured 206 Pb. Analyst P.D. Kinny, SHRIMP facility, Australian National University.