Determining the Effect of Calculus, Hypocalcification, and Stain on Using Optical Coherence Tomography and Polarized Raman Spectroscopy for Detecting White Spot Lesions

Optical coherence tomography (OCT) and polarized Raman spectroscopy (PRS) have been shown as useful methods for distinguishing sound enamel from carious lesions ex vivo. However, factors in the oral environment such as calculus, hypocalcification, and stain could lead to false-positive results. OCT and PRS were used to investigate extracted human teeth clinically examined for sound enamel, white spot lesion (WSL), calculus, hypocalcification, and stain to determine whether these factors would confound WSL detection with these optical methods. Results indicate that OCT allowed differentiating caries from sound enamel, hypocalcification, and stain, with calculus deposits recognizable on OCT images. ANOVA and post-hoc unequal N HSD analyses to compare the mean Raman depolarization ratios from the various groups showed that the mean values were statistically significant at P < .05, except for several comparison pairs. With the current PRS analysis method, the mean depolarization ratios of stained enamel and caries are not significantly different due to the sloping background in the stained enamel spectra. Overall, calculus and hypocalcification are not confounding factors affecting WSL detection using OCT and PRS. Stain does not influence WSL detection with OCT. Improved PRS analysis methods are needed to differentiate carious from stained enamel

Paradoxical co-existing base metal sulphides in the mantle: The multi-event record preserved in Loch Roag peridotite xenoliths, North Atlantic Craton

The role of the subcontinental lithospheric mantle as a source of precious metals for mafic magmas is contentious and, given the chalcophile (and siderophile) character of metals such as the platinum-group elements (PGE), Se, Te, Re, Cu and Au, the mobility of these metals is intimately linked with that of sulphur. Hence the nature of the host phase(s), and their age and stability in the subcontinental lithospheric mantle may be of critical importance. We investigate the sulphide mineralogy and sulphide in situ trace element compositions in base metal sulphides (BMS) in a suite of spinel lherzolite mantle xenoliths from northwest Scotland (Loch Roag, Isle of Lewis). This area is situated on the margin of the North Atlantic Craton which has been overprinted by a Palaeoproterozoic orogenic belt, and occurs in a region which has undergone magmatic events from the Palaeoproterozoic to the Eocene. We identify two populations of co-existing BMS within a single spinel lherzolite xenolith (LR80) and which can also be recognised in the peridotite xenolith suite as a whole. Both populations consist of a mixture of Fe-Ni-Cu sulphide minerals, and we distinguished between these according to BMS texture, petrographic setting (i.e., location within the xenolith in terms of ‘interstitial’ or within feldspar-spinel symplectites, as demonstrated by X-ray Computed Microtomography) and in situ trace element composition. Group A BMS are coarse, metasomatic, have low concentrations of total PGE (&lt; 40 ppm) and high (Re/Os)N (ranging 1 to 400). Group B BMS strictly occur within symplectites of spinel and feldspar, are finer-grained rounded droplets, with micron-scale PtS (cooperite), high overall total PGE concentrations (15–800 ppm) and low (Re/Os)N ranging 0.04 to 2. Group B BMS sometimes coexist with apatite, and both the Group B BMS and apatite can preserve rounded micron-scale Ca-carbonate inclusions indicative of sulphide-carbonate-phosphate immiscibility. This carbonate-phosphate metasomatic association appears to be important in forming PGE-rich sulphide liquids, although the precise mechanism for this remains obscure. As a consequence of their position within the symplectites, Group B BMS are particularly vulnerable to being incorporated in ascending mantle-derived magmas (either by melting or physical entrainment). Based on the cross-cutting relationships of the symplectites, it is possible to infer the relative ages of each metasomatic BMS population. We tally these with major tectono-magmatic events for the North Atlantic region by making comparisons to carbonatite events recorded in crustal and mantle rocks, and we suggest that the Pt-enrichment was associated with a pre-Carboniferous carbonatite episode. This method of mantle xenolith base metal sulphide documentation may ultimately permit the temporal and spatial mapping of the chalcophile metallogenic budget of the lithospheric mantle, providing a blueprint for assessing regional metallogenic potential. Abbreviations: NAC, North Atlantic Craton; GGF, Great Glen Fault; NAIP, North Atlantic Igneous Province; BPIP, British Palaeogene Igneous Province; SCLM, subcontinental lithospheric mantle; PGE, platinum-group elements; HSE, highly siderophile elements; BMS, base metal sulphid

A comprehensive geological, petrological, and geochemical evaluation of the Voisey's Bay NI-CU-CO sulfide deposit: an integration of empirical data and process mechanics

This thesis consists of three manuscripts, which report results on: 1) methodologies for systematic ore characterization utilizing the Voisey's Bay Ni-Cu-Co magmatic sulfide Ovoid deposit of northern Labrador as an example; 2) genesis of Voisey's Bay ores, focusing on the Ovoid deposit; and 3) discovery of a platinum-group element (PGE) occurrence in the vicinity of the Southeast Extension of the Voisey's Bay Ovoid deposit. -- The first manuscript defines, describes, and characterizes mineralogical and geochemical zonation of the Voisey's Bay massive sulfide Ovoid deposit to determine relationships between macroscopic ore textures, mineralogy, and chemical compositions of the sulfides. The emphasis is on development of algorithms to predict ore mineralogy derived from bulk chemical assays. A comparison to results from mineral liberation analysis indicates that the algorithms are very robust. The results show that the Ovoid deposit is strongly zoned from pyrrhotite-rich margins to a chalcopyrite-pentlandite-rich transitional zone and a magnetite-rich core. The TYPE I inner magnetite-rich ore has elevated Pb, Pt, and Pd relative to the remainder of the Ovoid (which correlate with high magnetite and moderate chalcopyrite) with the exception of a very central zone that has high chalcopyrite and Zn but lower Pb, Pt, and Pd relative to the remainder of the Ovoid. TYPE II ore is elevated in Pd and Zn, which corresponds to the chalcopyrite-pentlanditerich zone. Lead, Zn, Pt, and Pd are not enriched in the pyrrhotite-rich TYPE III outer ore zone relative to the remainder of the Ovoid. -- The second manuscript integrates mineralogical data and bulk assay data to quantitatively describe and model the emplacement (including physical/mechanical controls/processes) and crystallization history of the sulfide parent magmas of the Ovoid deposit and associated mineralized zones. Various models for ore upgrading (R, N, L factors) and crystallization (equilibrium, fractional, and partial fractional crystallization) were evaluated to determine which was involved in producing observed Ni and Cu tenors. Parental and derivative silicate magma compositions that may have been responsible for the ores were evaluated. The major conclusion is that the Ovoid deposit formed at an R factor of -150 from common basalt parent magmas and differentiated by partial fractional crystallization, trapping 30-40% residual liquid, mainly in the core of the ore body. Some of the residual liquid escaped to form disseminated mineralization. -- The third manuscript reports the first occurrence of platinum group-minerals (PGM) at Voisey's Bay, with grades of 1.95g/t Pt, 1.41g/t Pd, and 6.59g/t Au. Most of the PGE are present as discrete minerals hosted by disseminated base-metal sulfides in a hornblende gabbro dyke near the Southeast Extension of the Ovoid deposit. The PGM were determined to have a primary magmatic origin. Geological and geochemical relationships suggest that the dyke is associated with the main troctolite rocks that host the Ovoid, indicating a similar magma source. The PGM are related to a highly differentiated sulfide liquid that formed intermediate solid solution (ISS), which was derived by crystallization of monosulfide solid solution (MSS) from a sulfide melt. The sulfide melt was similar to that which formed the Ovoid deposit. The depletion of Pb and Pt in the center of the Ovoid may indicate loss of this material to the surroundings

Peisleyite an Unusual Mixed Anion Mineral - A Vibrational Spectroscopic Study

The mineral peisleyite has been studied using a combination of electron microscopy and vibrational spectroscopy. SEM photomicrographs reveal that the peisleyite morphology consists of an array of small needle like crystals of around 1 μm in length with a thickness of less than 0.1 μm. Raman spectroscopy in the hydroxyl stretching region shows an intense band at 3506 cm-1 assigned to the symmetric stretching mode of the OH units. Four bands are observed at 3564, 3404, 3250 and 3135 cm-1 in the infrared spectrum. These wavenumbers enable an estimation of the hydrogen bond distances 3.052(5), 2.801(0), 2.705(6) and 2.683(6) Å. Two intense Raman bands are observed at 1023 and 989 cm-1 and are assigned to the SO4 and PO4 symmetric stretching modes. Other bands are observed at 1356, 1252, 1235, 1152, 1128, 1098 and 1067 cm-1. The bands at 1067 is attributed to AlOH deformation vibrations. Bands in the low wavenumber region are assigned to the ν4 and ν2 out of plane bending modes of the SO4 and PO4 units. Raman spectroscopy is a useful tool in determining the vibrational spectroscopy of mixed hydrated multianion minerals such as peisleyite. Information on such a mineral would be difficult to obtain by other means