, California State University (San Bernardino)
The third year of this project saw the completion of a major project milestone with the publication of our work on revision of the lead carbonate (cerussite) oxygen stable isotope thermometer. In this work, the reason for discrepancy between experimental and empirical geothermometers was examined. It was determined, using detailed SEM/EDS studies, that previous work on this thermometer utilized rapid precipitation experiments that yielded hydrocerussite cores on some grains. This in turn produced incorrect fractionation determinations for the cerussite-water system. This article presents this new work, reviews other recent work on lead carbonate isotope systematics, and establishes new oxygen stable isotope thermometers for both the cerussite-water and hydroserussite-water systems. This work bears directly upon studies of secondary lead deposits, and interpretation of lead carbonate isotope values on archeological artifacts.
Another aspect of our work has been completed, with publication of an article that details the work that was done on fluid flow through porous media. In this project, causes and pathways for acid mine drainage were investigated for coal mine waste “gob” in central Indiana. Primary among these findings were the role of chemosynthetic Archea in dissolution and precipitation of minerals in these coal mine wastes. Significantly, this work suggests that reduction of acid mine drainage may be accomplished through modification of the waste pile biology, namely through reduction of Acidithiobacillus ferrooxidans and promotion of Leptospirillum ferrooxidans.
Our nitrogen isotope work on samples collected from the Atacama Desert of Chile has proceeded during the year, and another season of field work is scheduled for September of 2011. This field work will involve undergraduate student participation for senior research projects. Nitrogen and oxygen stable isotope analyses of these materials were hindered by the presence of high levels of other salts in the samples. As a result, a more complex extraction was required, with samples undergoing leaching, followed by nitrate stripping using selective ion resin columns. The collected nitrate was then eluted for final sample preparation and isotopic analysis.
The preliminary results of this nitrate mineral work are to be presented at the Society for Geology Applied to Mineral Deposits (SGA) annual meeting in Antofagasta, Chile in September 2011. Our results suggest that the caliche nitrate beds of the Atacama Desert have a distinct nitrogen isotope stratigraphy. In addition to this intriguing new result, which we will test at additional sites during the coming field season, we have determined the nitrogen isotope values of copper nitrate (Gerhardtite) from three copper deposits in the Atacama Desert. The interpretation of nitrogen isotope values of the copper nitrate within the context of the isotope stratigraphy of the main caliche beds suggest that copper nitrate formed exclusively during an isotopically distinct late event. This work will prove useful in understanding genesis of secondary “exotic” oxidation zone copper deposits of the Atacama Desert. It may also assist with interpretation of genesis of the enigmatic caliche deposits themselves.
A key component of our work has been undergraduate student experiential learning. The third year of this work saw a significant increase in participation by undergraduate students, and in particular students from groups traditionally underrepresented in the sciences. This was achieved through participation in several workshops geared towards minority participation, and the implementation of these methods.