ABSTRACT

Lead isotope ratios are measured for five ores, five Paleozoic sedimentary rocks, and six Miocene igneous rocks from the Hokuroku Basin, northern Honshu, to see if any genetic link exists between the kuroko mineralization and its immediate basement. The ore lead data show no significant variation and are within analytical uncertainties of the previous analyses of kuroko deposits from northeast Japan. The rock lead data have a large spread relative to the data available for kuroko deposits from northeast Japan. Certain Paleozoic sediments, which are thought to be the most representative of the basement underlying the mineralization, are significantly more radiogenic than the kuroko ores. The data for igneous rocks, on the other hand, fall in a narrow range, though their rock type ranges from mafic to fairly felsic in composition, and are all similar to the available kuroko ore data. The kuroko lead, therefore, is likely to come mainly from the igneous rocks rather than from the immediate basement, although some lead contribution from the basement rocks is also suggested.