Argon and SHRIMP-RG Data for Magmatic Steam Alunite, Sericite, and Zircon from Alunite Ridge and Deer Trail Mountain, Marysvale, Utah

Samples of vein-type magmatic-steam alunite were collected over several field seasons from five mines and prospects (L&N, Mt. Edna, Christmas, upper Mineral Products, and Close In) in the Alunite Ridge and Deer Trail Mountain area, Marysvale, Utah, as well as a sample from the Deer Trail mine workings from which sericite was separated. The magmatic-steam alunite and sericite were analyzed by the 40Ar/39Ar method to constrain the timing and duration of magmatic activity associated with the intrusion of two porphyry stocks beneath Alunite Ridge and Deer Trail Mountain. In addition, a sample of a highly altered rhyolitic quartz porphyry dike was collected from the upper Mineral Products mine, from which zircons were separated and analyzed using a sensitive high resolution ion microprobe reverse geometry (SHRIMP-RG) to determine a U/Pb date and quantify trace element concentrations. The rhyolitic dike is Oligocene in age (ca. 30.7 Ma), and our results indicate additional work is needed to refine the chronology of the Bullion Canyon Volcanics which are cut by the dike. Our magmatic-steam alunite and sericite results indicate there where two spatially and temporally distinct periods of episodic magmatic hydrothermal activity in the Miocene from ca. 15.7–15.1 Ma and from ca. 14.7–13.8 Ma. These results refine the chronology of hydrothermal activity associated with concealed porphyry stocks, and demonstrates the utility of high precision geochronology as an exploration tool for locating and characterizing deeply concealed porphyry systems.