Rb-Sr systematics in drill core samples of the Eye-Dashwa Lakes pluton at the whole rock and mineral scale

Twenty-one whole-rock samples from boreholes ATK-1 and ATK-6 define a precise Rb-Sr isochron with an age of 2637 ± 33 Ma and initial 87Sr/86Sr intercept, IR(Sr), of 0.70144 ± 0.00006. An internal mineral isochron for ATC-1 (991-997) and biotites from ATK-1 (35.63) and ATK-1 (3.84) give younger ages of 2541 ± 14 Ma 2574 ± 25 Ma, and 2534 ± 25 Ma, respectively. Data for samples from fracture zones scatter but correlate around an isochron of 2281 ± 153 Ma. The internal isochron and biotite ages record cooling below about 300 C due to uplift and erosion. The younger age, 2281 ± 153 Ma, records an episode or episodes of brittle failure at relatively high crustal levels. These fractures provided pathways for infiltration of water, which facilitated the mineralogical alteration