40Ar/39Ar Geochronology of Magmatic-Steam Alunite from Alunite Ridge and Deer Trail Mountain, Marysvale Volcanic Field, Utah: Timing and Duration of Miocene Hydrothermal Activity Associated with Concealed Intrusions

Porphyry and epithermal deposits are important sources of base precious metals. Most actively mined have been exhumed such that ore bodies relatively close to the surface therefore locatable economic extract. Identifying characterizing concealed deposits, particularly more deeply buried porphyry represents a far greater challenge for mineral exploration, will become progressively as near-surface resources gradually exhausted over time. We report high-precision 40Ar/39Ar dates coarsely crystalline alunite precipitated from magmatic steam in open fractures Oligocene dacitic volcanic rocks, SHRIMP 206Pb/238U zircon date one several rhyolite dikes present at Alunite Ridge Deer Trail Mountain, Utah. Both magmatic-steam related intrusions. The dike yielded an age 30.72 ± 0.36 Ma, which is older than commonly cited 27.1 Ma estimate Three Creeks Tuff Member Bullion Canyon Volcanics cut by dike. data samples sericite six mines prospects provide evidence least two periods episodic hydrothermal activity ca. 15.7–15.1 14.7–13.8 with younger pulses recorded eastern western sites, respectively. These consistent previous interpretations Mountain underlain stocks. analyses individual bands sample massive, centimeter-scale banded vein yield indistinguishable ages weighted mean 13.98 0.12 short-lived (≲250 ka) event vapor discharge recurring on short timescales (≲36 ka). geochronology valuable tool constrain timing duration associated unexposed intrusions potentially may be useful exploration.