Highly altered felsic metavolcanics associated with the Kidd Creek, Ontario, Cu-Zn massive sulfide deposit show a large range of Sm/Nd ratios and yield a Sm-Nd isochron of 2674 ± 40 Ma (initial ratio ϵNd = 1.55 ± 0.30), which represents the time of rare-earth-element redistribution during intense hydrothennal alteration. That the Sm-Nd age is consistent with age constraints on ore deposition provided by precise U-Pb zircon data indicates contemporaneity of ore deposition, hydrothennal alteration, and rare-earth mobility. The age is therefore interpreted as a minimum age of ore deposition. In contrast, the Rb-Sr age of the altered rocks, as well as the metavolcanic rocks outside the alteration zone, has been reset at 2576 ±26 Ma, most likely as a result of widespread low-temperature metasomatism unrelated to ore deposition. Our results suggest that Sm-Nd dating could be a useful tool in the study of ore deposits and, potentially, in the study of a wide range of mineralizations.
Initial ϵNd(T) values for massive ore, altered felsic volcanics, and their weakly altered precursors are identical, indicating derivation and redistribution of light rare-earth elements within the altered footwall volcanics. These data suggest that the footwall volcanics have also supplied part of the base metals to the stratiform ore.