Petrology and hydrothermal mineralogy of US Geological Survey Newberry 2 drill core from Newberry Caldera, Oregon

USGS Newberry 2 was drilled to a depth of 932 m within Newberry caldera. The bottom-hole temperature of 265??C is the highest reported temperature of any drill hole in the Cascades region of the US. The upper part of the stratigraphic section penetrated by Newberry 2 consists of caldera fill below which are increasingly more mafic lavas ranging from rhyodacite at 501 m to basalt at 932 m. Measured temperatures shallower than 300 m are less than 35??C, and rock alteration consists of hydration of glass and local palagonitization of basaltic tuffs. Incipient zeolitization and partial smectite replacement of ash and pumice occurred of basaltic tuffs. Incipient zeolitization and partial smectite replacement of ash and pumice occurred throughout the pumiceous lithic tuffs from 300 to 500 m. Higher-temperature alteration of the tuffs to chlorite and mordenite occurs adjacent to a rhyodacite sill at 460-470 m; alteration minerals within the sill consist of pyrrhotite, pyrite, quartz, calcite, and siderite. Below 697 m the rocks are progressively more altered with depth mainly because of increased temperature along a conductive gradient from 100??C at 697 m to 265??C at 930 m. -from Authors