Composition of fluid inclusions from the cave-in-rock bedded-replacement fluorite deposits in the Illinois-Kentucky district

Title from PDF of title page (University of Missouri--Columbia, viewed on May 23, 2012).The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file.Thesis advisor: Dr. Martin AppoldIncludes bibliographical references."July 2011"The stable mid-continent platform of North America hosts some of the greatest known concentrations of Mississippi Valley-type (MVT) mineralization in the world. Most of the mineralization occurs between two major physiographic regions, the Ozark Plateau and the Interior Low Plateau. The Illinois-Kentucky district is one of three principal MVT districts in the Interior Low Plateau and is distinct from other North American mid-continent MVT deposits in that its ore mineral assemblage is dominated by fluorite instead of sulfide minerals or barite. However, like these other MVT deposits, the Illinois-Kentucky deposits were probably precipitated from northward flowing sedimentary brines set in motion by topographic gradients created by the Alleghanian-Ouachita orogeny during the Late Paleozoic. The primary objective of the current study was to quantify the chemical composition of the mineralizing fluids through in situ fluid inclusion analysis using microthermometry, laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), and laser Raman spectroscopy in order to try to gain insights into the ore formation process. Results show that the fluids that formed the Illinois-Kentucky district are chemically distinct from the fluids that formed MVT deposits in the Ozark Plateau. These differences can be attributed to interaction of the mineralizing sedimentary brines with ultramafic, rift-related igneous rocks present in the Illinois-Kentucky district but not in any of the Ozark Plateau districts. Fluid inclusion homogenization temperature and salinity relationships suggest that MVT mineralization in the Illinois-Kentucky district was produced from a mixture of at least three brines, two of which had relatively high salinities and temperatures and the third of which was cooler and more dilute. Mixing among at least three fluids is supported by the elemental concentration data, which tend not to correlate with one another or with the microthermometry data, but rather plot as two-dimensional arrays. The compositions of the end member fluids could not be pinpointed from the available data, however it appears that at least one of the fluids had elevated concentrations of the ore metals, Pb, Zn, Cu, and Fe as high as on the order of 1000's of ppm

Do Domain Knowledge and Retrieval Practice Predict Students’ Study Order Decisions?

Learning complex concepts is necessary for student success, but it is often challenging. Learning such concepts can be influenced by students’ study order choices during learning to switch to a new category (interleaved study order) or stay within the same category (blocked study order). Students often prefer stay decisions during learning and make relatively few switch decisions; however, an open question is whether students’ switch decisions are related to their level of prior knowledge in the domain and the learning strategy they use (retrieval practice versus study). To examine these relationships, we recruited undergraduate students from an introductory geology course. Prior to the course modules on rock classification, students self-rated their knowledge, took a prior knowledge test, classified rock exemplars by completing study or retrieval practice trials, and made study order choices. Students then completed assignments and attended lectures in their geology course on igneous, sedimentary, and metamorphic rocks. Next, students self-rated their knowledge, took a new prior knowledge test, completed study or retrieval practice trials, made study order decisions, took final classification tests, and self-reported beliefs about study order choices. Even though students’ knowledge increased after course modules on rock identification, and most students believed that domain knowledge impacts study decisions, prior knowledge did not predict students’ switch decisions. In contrast, students who completed retrieval practice trials made substantially more switch decisions (i.e., interleaved study) than did students who completed study trials