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UBC Theses and Dissertations

Low-temperature thermochronology of the northern Carlin Trend : evidence for Late Cretaceous exhumation of northern central Nevada and short duration of Carlin ore-forming hydrothermal systems Cruickshanks, Moira


Samples were collected from Jurassic intrusions in the northern Carlin Trend to determine the thermal history of the region that was strongly affected by Late Cretaceous exhumation and Eocene hydrothermal fluid flow. Low-temperature apatite fission track and apatite and zircon (U-Th)/He thermochronology of the northern Carlin Trend records 3-4 km exhumation since the Late Jurassic. At least 1-2 km exhumation occurred during a phase of rapid exhumation between 85-60 Ma that is coincident with extensional collapse of the overthickened hinterland of the Sevier orogeny. Late Cretaceous exhumation ages provide a background against which ~40 Ma thermal anomalies associated with the formation of the Carlin-type Au deposits can be observed. In the northern Carlin Trend, a thermal halo defined by apatite fission track resetting was observed up to 400 m out from major fluid flow conduits around the Goldstrike Stock that is immediately south of the multi-million ounce Betze-Post deposit. A lack of hydrothermal alteration within the stock shows that Eocene hydrothermal fluid flow was concentrated around its edge, and that heating of the stock was predominantly conductive. Finite element modelling and forward modelling of time-temperature paths constrain the duration of a hydrothermal fluid event to on order of 10 kyr. Multiple phases of this duration of fluid flow are possible, but were either thermally isolated or were shorter-lived. The high rates of fluid flux associated with short fluid flow durations are similar to those observed in hydrothermal systems driven by forced convection or pressure-driven flow, suggesting fluid flow responsible for the formation of Carlin-type Au deposits was driven by a magmatic source or seismicity rather than free convection.

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