Timing of the Pine Creek tungsten skarn and the causative Morgan Creek pluton, California: Implications for ore genesis and regional geology

Eleven new Re-Os molybdenite ages from six samples from the Pine Creek tungsten
skarn near Bishop, California, and seven new laser ablation multicollector inductively
coupled plasma mass spectrometry (LA MC-ICP-MS) U-Pb zircon ages from
the adjacent Morgan Creek pluton, have been determined in order to examine the timing
and duration of the magmatic-hydrothermal system. The Re-Os analyses show
ages of 91.0, ~94, 104.6, and 107.2 Ma, over an apparent 16 M.y. period of mineralization.
Ages for three of the six samples are identical within error (±0.5 Ma) at ~94 Ma.
Ages of 91.0 and ~94Malikely represent distinct mineralizing events, whereas the oldest
two ages (104.6 and 107.2 Ma) from disseminated molybdenite in skarn may indicate
disturbance of the Re-Os system. Two of the three ages in the main 94 Ma group
were from quartz pods or veins that could have sheltered the molybdenite from late
fluid flow that might have disturbed the Re-Os isotopic system in the disseminated
molybdenite.