Sm-Nd dating of the giant Sullivan Pb-Zn-Ag deposit, British Columbia

We report here Sm and Nd isotope data for hydrothermal tourmalinites and su lfide ores from the giant Sullivan Pb-Zn-Ag deposit, which occurs in the lo wer part of the Mesoproterozoic Purcell (Belt) Supergroup. Whole-rock sampl es of quartz-tourmaline tourmalinite from the footwall alteration pipe yiel d a Sm-Kd isochron age of 1470 +/- 59 Ma, recording synsedimentary B metaso matism of elastic sediments during early evolution of the Sullivan hydrothe rmal system. Data for variably altered (chloritized and/or albitized) tourm alinites from the hanging wall of the deposit, which are believed to have f ormed originally ca. 1470 Ma, define a younger 1076 +/- 77 Ma isochron beca use of resetting of Sm and Nd isotopes during Grenvillian metamorphism. HCl leachates of bedded Pb-Zn ore yield a Sm-Nd isochron age of 1451 +/- 46 Ma , which is consistent with syngenetic-exhalative mineralization ca. 1470 Ma ; this age could also reflect a slightly younger, epigenetic hydrothermal e vent. Results obtained for the Sullivan deposit indicate that the Sm-Nd geo chronometer has the potential to directly date mineralization and alteratio n in stratabound sulfide deposits that are not amenable to dating by other isotope methods.