Isotopic evidence on the origin and age of the Blind River uranium deposits

Abstract

Isotopic analyses of lead extracted from a variety of minerals from Blind River, Ontario, are reported. The detrital minerals monazite and zircon both give lead‐ratio ages of 2500 million years. The uraninite ore gives a lead‐ratio age of 1700 m y. Other isotopic evidence is quoted to suggest that the age of the sediment in which the uranium is found may also be approximately 1700 m y, or older. The lead found in pyrite, pyrrhotite, sericite, and feldspar has anomalous isotopic ratios which can be explained by the hypothesis that they received additions of radiogenic lead from the uraninites (presumed to be 1700 m y old) 1200 to 1300 m y ago. In any case the age of these minerals, in the sense of time of last chemical alteration, is not greater than 1450±150 m y. All our measurements can be interpreted without assuming a major period of mineralization more recent than 1000 m y ago, although we are unable to rule out such a possibility from our evidence.

The isotopic composition of lead in microclines from the Llano uplift, Texas

“…They were able to demonstrate that the isotopic composition of these leads had evolved very similarly to that of galena ores [Russell and Farquhar, 1960]. Investigations by Mair et al [1960], Murthy and Patterson [1961], Doe [1962], and Doe and Hart [1963] have used the lead isotopic composition of feldspars to study certain igneous and metamorphic processes. The present investigation is an attempt to ß Now with the U.S. Geological Survey, Denver, Colorado. use microclines from various plutonit and metasedimentary rocks that represent a single teetonic episode in order to study the interrelationship of the lead isotopes in the rock.…”

Sediment Transport in a Precambrian Ice Age: The Huronian Gowganda Formation

“…It is part of the thick sequence of sediments designated Huronian and shown by radiometric dating to be about 2 billion years old (4). Along the north shore of Lake Huron, it rests on older Huronian sediments; but between Sudbury and Quebec, it directly overlies the Archean basement.…”