Alteration Mineralogy and Geochemistry at Swansea, Arizona: A Potential Analog for Brine-Basalt Interaction on Mars

In this study, we use thermal infrared spectroscopy and petrographic and chemical analyses to understand the alteration mineralogy and geochemistry at Swansea, Arizona. The goals of the study are to: 1) understand the alteration and mineralization history of the Swansea area, 2) determine the relationship of alteration at Swansea to regional tectonism, 3) model the geochemistry of the mineralizing fluid and its relationship to fluids that altered the adjacent Harcuvar Mountains, and 4) establish a relationship between field observations, geochemical and mineralogical studies, and remote sensing of hydrothermal alteration of basalt as a planetary analog. Swansea is located in the Buckskin Mountains of western Arizona. The various host rocks at Swansea has been largely hydrothermally altered, and have undergone Cu-Fe-Mn mineralization. Bulk mineralogies of samples of basalt, limestone, and basin fill conglomerate, were determined from deconvolution of thermal infrared spectra. Mineralogy recovered from spectral deconvolution was confirmed by X-ray diffraction. Basalt has been completely metasomatized to calcite, clay, hematite, and potassium feldspar. Conglomerate, which originally consisted of clasts of felsic and intermediate crystalline rocks, has been altered to clay, potassium feldspar, and calcite. Limestone was altered to mostly calcite with minor clay, potassium feldspar, and hematite. Mineral mapping using Landsat TM ratios and deconvolution of Thermal Infrared Multispectral Scanner (TIMS) data show that: 1) mineralogies of field samples are representative of the sampled rock units, and 2) alteration was pervasive throughout the Swansea area. Similar alteration has been documented in the Harcuvar Mountains to the east, where deep (~10 km) crustal brines that migrated along the Tertiary Buckskin-Rawhide detachment fault metasomatized various host rocks. However, alteration mineralogy in the Harcuvar Mountains includes abundant quartz and is calcite-poor. The fluids that altered each locality are likely genetically related, but their chemistry may reflect evolution of the fluid through time and space. Future work will include the development of a model for alteration of basalt by brine on the Earth and Mars. Although some of the variables between terrestrial analogs and Martian conditions are obviously different, this study may lead to models of alteration or albitization of basalt by brines on Mars.