JAROSITE PRECIPITATION ALONG LARAMIDE AND BASIN AND RANGE MIGRATION PATHWAYS IN JURASSIC AZTEC SANDSTONE, VALLEY OF FIRE, NV, USA

The Aztec Sandstone in and around Valley of Fire State Park is known for dramatic diagenetic coloration patterns including unusual jarosite cements. This research documents the association of jarosite cements and specific diagenetic facies, along with orientation of faults and joints to determine a relative timing of infiltration of the jarosite-precipitating fluid. Field research recorded the strikes of joints and the associated cement mineralogy using a handheld field Vnir reflectance spectrometer. Samples were collected and returned to the lab for bulk mineralogy and microscopy. Iron oxides and calcite are common, and jarosite is restricted to pockets of bleached or purple and yellow facies of Eichhubl et al. (2004). These pockets occur along fractures suggesting that the fractures were migration pathways for the jarosite precipitating fluids. The fractures strike mostly north, rather than NE (Laramide), which implies that the migration path for the jarosite was Basin and Range and therefore, the latest stage alteration. The stability of jarosite on geologic time scales is unusual because jarosite is unstable in the lab and becomes hematite in a matter of weeks when exposed to circumneutral water. This has implications for a new understanding of jarosite stability and has potential impacts on the interpretation of jarosite in sedimentary environments on Mars.