MINERALOGY OF THE TOLSONA MUD VOLCANOES IN THE COPPER RIVER BASIN, ALASKA

Our study identifies the primary minerals in the sediments that compose the Tolsona mud volcanoes, which are located within the western part of the Copper River basin, Alaska. This region is poorly drained due to extensive glacial lake sediments and is characterized by saline groundwater that seeps from springs and mud volcanoes. The Tolsona cones appear to have grown following the retreat of glacial ice, based on stratigraphic relationships with Pleistocene sediments and fossil assemblages. Blocks of underlying sedimentary rocks are absent at the surface, which suggests at least the later stages of cone growth were characterized by the accretion of muddy water rather than the typical explosive growth of mud volcanoes (Grantz et al., 1962). Gases emitted from the volcanoes are hypothesized to aid in the mud reaching the surface. The chemistry of the volcanoes’ water and gases have been extensively studied (e.g. Motyka et al., 1989); however, the mineralogy of the mud has not. The purpose of this research is to identify the primary minerals present in the mud at the surface of two of the Tolsona mud volcanoes. A total of 15 samples were collected including 7 from the first mud volcano (TolMV-1), 7 from the second mud volcano (TolMV-2), and 1 sample of lake sediment near TolMV-1 for comparison. Analysis of the mineral composition is being completed using a Miniflex x-ray diffractometer (XRD) with a Cu radiation source. Prior to analysis, each sample was dried and sieved to a particle size <63 mm. Diffraction patterns generated for each of the samples have indicated nearly identical mineral composition with only minor differences in a few of the smaller peaks throughout the transected areas within each mud volcano. In addition, a comparison of mineral compositions between volcanoes yields similar XRD patterns. Interpretation of the diffraction patterns is based on peak analysis and reduction in comparison with powder diffraction files for known minerals. Current analyses and data reduction have shown low quartz as the prominent mineral present in the Tolsona mud volcano samples. Other possible minerals include albite, oligoclase, and illite-montmorillanite based on minor peak analysis of the diffraction patterns. Diffraction patterns are being modeled for mixtures of different mineralogical modes for comparison.