Plumbotectonics IIA, Precambrian massive sulfide deposits

Abstract

Professor Tugarinov has long recognized the importance of common lead in rocks and ore deposits as an age indicator. The paper he authored with L. K. Gavrilova and V. P. Bedrinov in 1963, and the work of Cantanzaro and Gast (1960), are two of the most extensive studies of the evolution of lead isotopes in feldspars. Such studies are very important to our understanding of crustal evolution because of our ability to calibrate feldspar ages by other means. The pioneer paper by Stanton and Russell (1959) opened the way for dating certain deposits submarine volcanic exhalative massive sulfide deposits in the orogene. It is now generally accepted that these deposits formed during volcanism or shortly thereafter (Hutchinson, 1973). Therefore their lead isotope evolution may be correlated with time by dating the enclosing rocks. Over the last eight years, investigators have gradually realized that lead isotopic analyses, coupled with geochronologic studies, may yield much additional information about ore deposits and their origins. This paper evaluates the lead isotopic characteristics of Precambrian massive sulfide deposits of all types. The treatment here will be similar to that used by Doe and Zartman (1976) in their "plumbotectonics" model for Phanerozoic deposits of this type. The submarine volcanic exhalative ores were chosen for emphasis because they are the type class for "conformable" or "stratiform" leads used in lead isotope model theory. We suggest that any deviation from a strictly average isotopic composition for a given age of deposit can often be explained by differences in the tectonic settings in which the ores were formed. This paper is a "state-of-knowledge" discussion of that thesis.