PB AND CU ISOTOPE TRACERS OF FLUID FLOW AT BINGHAM CANYON PORPHYRY COPPER DEPOSIT

The Bingham Canyon deposit, one of the largest Cu-Au-Mo porphyry ore bodies in the world, is located southwest of Salt Lake City, Utah. The molar tooth shape of the ore body is thought to be lithologically controlled at depth. High temperature isotopic variation can be seen in copper throughout the Bingham Canyon Porphyry Copper Mine. Copper isotope ratios in the giant Bingham Canyon porphyry range from -0.4 to 1.3 per mil in bornite and -0.3 to 2.0 per mil in chalcopyrite. The copper isotope values show a loose pattern of decreasing δ⁶⁵Cu away from the quartz monzonite porphyry (QMP) intrusion. This pattern may mean that the copper isotope values are changed as the fluids in the main mineralizing pulse cooled. Previous studies have shown that the change in isotopic fractionation in copper can be explained by precipitation of the sulfides during cooling and/or phase change in the mineralizing fluid. The isotopic patterns seen in the copper ratios do not correlate to what is seen in the lead isotope patterns. Lead values have small variability in each of the ratios. ²⁰⁶Pb/²⁰⁴Pb initial isotopic values average 17.56 ± 0.13, ²⁰⁷Pb/²⁰⁴Pb average 15.224 ± 0.01 and ²⁰⁸Pb/²⁰⁴Pb average 38.331 ± 0.23. Lead values can give insight into the orogenesis of the deposit.