MINERALOGICAL STUDY OF VOLCANIC SUBLIMATES FROM HALEMA UMA U CRATER, KILAUEA VOLCANO

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1 MINERALOGICAL STUDY OF VOLCANIC SUBLIMATES FROM HALEMA UMA U CRATER, KILAUEA VOLCANO Liliana G. DeSmither Department of Geology University of Hawai i at Hilo Hilo, HI ABSTRACT Anatase and silica-rich deposits found around Halema uma u Crater, within the Kilauea Caldera, are thought to be similar to those that have been found at Home Plate on Mars. The deposits found at Halema uma u Crater on Kilauea Volcano have been altered by acid sulfate steam leaching around the fumaroles. These fumarole deposits at Kilauea have been used as an analog site for the deposits at Home Plate, but there is also recent suggestion that the deposits are hotsprings-related silica sinter (Ruff et al., 2011). Comparison of altered and unaltered deposits around Halema uma u crater show that the only elemental oxides left in the rocks are silica (as opal-a) and titanium (as poorly crystalline anatase). Both Si and Ti are mobile in this environment and show a strong zoning. In the outer zone, the rock is largely replaced by opal, but retains its original vesicular texture. Comparison of major element chemistry suggests that titanium was lost from this zone. In the inner zone, the rock has broken down into loosely consolidated, friable material high in Si and Ti that also frequently contains scattered native sulfur crystals. The concentrations of Ti in these deposits is roughly double the amount that should be present if all elements other than Si and Ti were leached from the rock. The decomposed state of the rocks suggest that silica was also leached from the central altered zones, leaving titanium enriched in these samples. The outer silica-rich zone appears to be a good analog for the Si-rich Gertrude Weise deposits near Homeplate, whereas the Ti- and S-rich deposits in the core of the alteration are analogs for the S-rich Tyrone soils found nearby. The zonation of the acid sulfate deposits at Halema uma u Crater seems similar INTRODUCTION Kilauea Volcano on the Island of Hawai i has been used as a terrestrial analog for the Home Plate deposits found on Mars. Morris et al. (2009) discussed how silica rich materials at Home Plate tend to also have titanium enrichment. Other elements have been significantly leached from the area because they more soluble than SiO2 and TiO2. They interpreted that the system had undergone acid sulfate leaching. Two types of deposits in particular that have been found at Home Plate, sulfur-rich Tyrone soils and silica-rich Gertrude Weise soils, are believed to have formed during the same process (Wang et al., 2008). Both soils deposits are found in an area that is topographically low, and contain other Si-rich outcrops within them. They believe the two soils are both end members of the same hydrothermal process and that they had been sorted chemically, transported by water and then deposited at some point during this process. However, Ruff et al. (2011) noted that a hydrothermal hotsprings also form deposits with high opal-a concentrations, and may show enrichments in titanium. Ruff et al suggest that the absence of sulfur in the Home Plate soils, suggesting this chemical signature is not unique to one 24

2 hydrothermal system over the other, and the lack of sulfur enriched deposits contrast with the idea of acid sulfate leaching. SUBLIMATE SAMPLES In May of 2009 Ken Hon and Lopaka Lee collected 73 samples from around the rim of Halema uma u Crater under a National Park Service research permit. Ryan Bishop chose 10 sublimates and one ejecta sample from the 2008 eruption for this mineralogical study. Samples from the most intensely altered zones, HM-15 and HM-18, were found to be composed primarily of opaline silica with variable amounts of anatase. These samples appear similar to silica-rich materials at Home Plate by the MER Spirit (Chemtob, 2010). I have expanded Ryan Bishop s work by looking at the core of 3 additional fumarolic alteration zones. The goal was to find altered materials that have similar silica and anatase alteration, and to look at the surrounding materials. Analyses of the samples illustrates a better image of what the area surrounding Halema uma u crater looks like on a larger scale, so it can be compared to Home Plate deposits. During the course of this project a large number of samples were looked at from four principal alteration sites around Halema uma u crater. The main samples being analyzed for this project due to the anatase and silica content were: HM-15, HM-18, HM-24, HM-45, HM-51, HM-52, HM-54, and HM-56. Minerals and other phases were identified by X-ray diffraction on the UH-Hilo Pharmacy Bruker D-8 diffractometer and on the Hitachi S3400 Scanning Electron Microscope with an Oxford EDS detector. X-ray Fluorescence (XRF) for major elements has been used for bulk analysis of four samples consisting of pairs of altered and unaltered spatter, and an additional four samples of altered powdery materials all collected from sites around Halema uma u. These analyses were run by the Washington State University GeoAnalytical Lab. The major element XRF analyses allow us to evaluate how Si and Ti have been transported in the environment and to determine whether or not they are immobile residues. Loss On Ignition (LOI) analysis has also been done on the samples and measures the weight of the material that has been lost during the heating process. Many samples contain significant amounts of native sulfur and water-rich opal. Both compounds have low vaporization points and are lost during the during heating and contributed to the LOI. Samples were also analyzed for S and SO 3 which can be subtracted from the LOI to determine the amount of water in the samples. The samples that were selected to compare the composition of fresh and altered spatter. The samples are: HM-15 unaltered spatter, HM-15 altered spatter, HM-18, HM-51, HM-52, HM-54 unaltered spatter, HM-54 altered spatter, and HM-56. All of samples were recalculated with only SiO 2 and TiO 2, as these were the only elements left above trace levels in the altered samples. Comparison of the recalculated analyses for fresh and altered samples allows the assessment of leaching versus precipitation during alteration. 25

3 Table 1: Whole rock XRF analysis of altered materials (italicized) and unaltered materials (bold). 1 : 1919 average from Wright, 1971, 2 : 1974 average from Lockwood, Table 2: SiO 2 and TiO 2 recalculated to 100% to show the loss (-) and gain (+) of each and the mobility between them. Figure 1: Map of the Halema uma u Crater sampling sites. 26

4 Lava Flow Site: Samples HM1 A sample of gray crust, HM-1, is representative of most of the other crusts around Halema uma u crater. This sample contains sulfur, gypsum and opal-ct concentrated in a relatively thin (1 cm) layer Fissure Site: Sample HM13-HM20 Fresh black spatter (HM15) and altered white spatter (HM-15 alt) were collected from the 1971 fissure rampart (Table 1). The altered sample is nearly pure opal and has very high silica contents. There is very little sulfur in the altered sample and most of the LOI can be attributed to water within the opal Shelly Pahoehoe Channel Site: Samples HM18-HM29 Sample HM-18, analyzed by Ryan Bishop, was a salmon colored soft material that was altered to form silica spheres mostly consisting of opal with some anatase. XRF analysis (Table 1) shows that the altered material has highly leached all of the elements it contained in the unaltered analysis except for SiO 2 and TiO 2. The crust above HM-18, HM-19, was a white and yellow sulfur crust that was found to have an abundance of opal-ct along with some anatase. HM-24, a very soft and porous sample found filled with sulfur, was found beneath a gray crust. XRD analysis on the sample identified opal and sulfur peaks. Small amounts of anatase were detecting using the SEM. North Pit Area: Samples HM31-HM36 From the samples taken in the North Pit Area, three crust samples were analyzed with the XRD. HM-31, white crust that forms over 10-20% of the area, HM-34 yellowish orange crust that surrounds lithic bombs, and HM-36, a gray hardpan crust that coats much of the area all contain both anatase and opal CT., Samples HM-31 and HM-36 also contain sulfur, whereas gypsum was found in HM-34 and HM-36. Figure 2: SEM image of an opal sphere at 20 microns. Figure 3: HM-51 pinkish opal and anatase. 27

5 Fissure SW of Halema uma u: Samples HM45-HM52 Covering about 80% of the area south of the 1974 fissure is a grayish green hardpan crust, HM-45. The crust has opal-ct and anatase with some sulfur and iron as well, and an SEM image shows the form of the opal spheres (Figure 2). The other crust in the area south of the fissure was HM-47, which was comprised of opal-ct and gypsum. The sulfur crusts around the active fumaroles, HM-50, also had opal-ct, gypsum and anatase. Beneath this sulfur crust was pink-salmon altered clay material, HM-51, which looks very similar to the other anatase rich deposits found (Figure 3). Looking at the XRF data found on table 1, the TiO 2 increased over seven and a half times from the unaltered data, and the SiO 2 slightly increased as well while everything else was significantly leached from the sample. Just above the pink-salmon clays was a layer of white material that was abundant in sulfur, HM-52. After removing as much of the sulfur as possible from the sample, XRD and SEM results showed that Opal-CT, anatase and gypsum were also in the sample. XRF analyses (Table 1) show that all of the elements have been leached almost to zero, except for SiO 2 and TiO 2 which increased slightly in the sample 1971 Fissure E of Halema uma u: Samples HM54 and HM-56 Fresh and completely altered spatter found on the 1971 rampart show differences in composition similar to HM-15 altered and fresh spatter with a gain in silica and a loss of titanium. All other elements were almost completely leached out. White totally replaced spatter, HM-54, found on the west end of the 1971 fissure system contains opal, anatase and sulfur. SEM results found olive shaped spheres made up of anatase and silica with the inside being almost entirely anatase (Figure 4). HM-56, white-pink soft material found under crust, also has abundance of opal-ct and anatase. SiO 2 is highly concentrated in this sample, where as TiO 2 is roughly equivalent to the fresh sample, and everything else has been leached out (Table 1). Figure 4: SEM image showing the anatase (Ti) within opalized vesicular spatter. 28

6 RESULTS AND CONCLUSIONS All of the lava flows originally had very similar chemical compositions (Table 1). The XRF analyses show that almost all of the major and trace elements, with the exception of SiO2 and TiO2,have been depleted in the altered samples compared to the fresh ones. The variable contents of SiO2 and TiO2 indicate that they are relatively insoluble and cannot easily be leached out of their environments. Throughout the samples taken around the crater, most of the crust samples, unless otherwise specified as a sulfur crust, were largely made up of opal-ct. Beneath these crusts is white clay-like material. Samples of this material, HM-52 and HM-56, have gained about the same amount of SiO2 and TiO2 as the fresh samples when recalculated (Table 2). Directly below the white material are the pink/salmon colored soft material, HM-18 and HM- 51. These deposits have gained the highest concentrations of TiO2 out of the samples with respective gains of 4% and 18%. HM-15 and HM-54 are the only XRF samples that actually show a loss TiO2, and they are both samples of altered spatter found on the ground surface. They also have the highest concentrations of SiO2 and have been able to maintain their original structure, unlike the soft materials. This information suggests that the Ti and Si are mobile during the acid sulfate leaching process, because the Si is concentrated in the upper crusts and ground spatter, whereas the Ti becomes increasingly more concentrated in the layers under the surface crust. The powdery material found in samples HM-18 and HM-51, fit the description of the Gertrude Weise soils found at Home Plate being that they are both light-toned and have high concentrations of Si and Ti. With the Ti and Si becoming mobile in the system and the other elements being highly depleted, the process of acid sulfate leaching caused by fumaroles seems to be a reasonable explanation for the formation of the deposits found at Home Plate on Mars. ACKNOWLEDGEMENTS I would like to thank Dr. Ken Morris for all of his help, and allowing me the time I needed using the XRD, John Coney for all of his help assisting me with the SEM and the Washington State University GeoAnalytical Lab for completing XRF analysis on selected samples. I would also like to thank the NASA Space Grant Consortium for giving me the opportunity to work on this research project. I would like to thank my advisor Dr. Ken Hon most of all, for all of his help and guidance throughout this project. REFERENCES Chemtob, S. M., B. L. Jolliff, G. R. Rossman, J. M. Eiler, and R. E. Arvidson (2010) Silica coatings in the Ka u Desert, Hawaii, a Mars analog terrain: a micro-morphological, spectral, chemical and isotopic study. JGR, 115, E04001, doi: /2009je Lockwood, J. P., Tilling, R. I., Holcomb, R. T., Klein, F., Okamura, A. T., Peterson, D. W. (1999), Magma Migration and Resupply During the 1974 Summit Eruptions of Kilauea Volcano, Hawai i, U.S. Geological Survey Professional Paper Morris, R. V., Ming, D.W. (2009), Chemical and Mineralogical Constraints for Modeling Hydrous Environments on Mars from the Mars Exploration Rovers, Workshop on Modeling Martian Hydrous Environments, NASA Johnson Space Center, Houston TX. 29

7 Ruff, S. W., et al. (2011), Characteristics, distribution, origin, and significance of opaline silica observed by the Spirit rover in Gusev crater, Mars, J. Geophys. Res., 116, E00F23, doi: /2010je Wang, A., and 14 colleagues, Light-toned salty soils and coexisting Si-rich species discovered by the Mars Exploration Rover Spirit in the Columbia Hills. J. Geophys. Res. 113, E12S40. doi: /2008je Wright, T. L. (1971), Kilauea and Mauna Loa in Space and Time, Geological Survey Professional Paper