Abstract
Microscopic, non-gem quality, grains of blue sapphire (corundum) have been identified in a small (1–2 cm wide), discontinuous, dike of nelsonite hosted by aluminous feldspathic gneiss. The gneiss was excavated during the construction of a hydroelectric plant on the Black River at Port Leyden, NY (western Adirondack Highlands). The sapphire location is 250 m NE of the Port Leyden nelsonite deposit. The small dike may represent a separate intrusion of nelsonite or one sheared from the main nelsonite orebody during Ottawan (circa 1050 Ma) deformation and metamorphism. The sapphires range in size from 0.1 to 2.0 mm, and commonly show parting, pleochroism, and hexagonal oscillatory zoning (from deep blue to clear). Electron microprobe analysis shows comparable levels of Fe in both clear (0.71–0.75 wt. %) and blue (0.38–0.77 wt. %) portions of grains, but clear sections have significantly lower TiO2 levels (0.002–0.011 wt.%) compared to blue sections (0.219–0.470 wt. %). Cr2O3 abundances range from 0.006 to 0.079 wt. % whereas V2O3 abundances range from 0.010 to 0.077 wt. % in blue sapphires. Small amounts of MgO were detected in one of the clear corundum grains (0.013 wt. %) and two of the six blue grains (0.001–0.015 wt. %), but the remaining five grains were below the limit of detection. Ga2O3, however, was detected in five out of six blue-colored grains (0.026–0.097 wt. %) but was below the limits of detection for clear grains. Optical spectroscopic data collected on the blue sapphire grains show broad absorbance in the yellow, orange, and red part of the spectrum (~565–740 nm) consistent with intervalence charge transfer between the next nearest neighbor Fe2+ and Ti4+. A magmatic origin of the sapphire grains is supported by petrologic and trace element data from the blue sapphires, but Cr abundances are inconsistent with this interpretation. Sapphire in a nelsonite host rock represents a new type of occurrence.
Highlights
Gem corundum deposits worldwide are generally associated with quartz-free rocks of both igneous and metamorphic origin
Optical spectroscopic data collected on the blue sapphire grains show broad absorbance in the yellow, orange, and red part of the spectrum (~565–740 nm) consistent with intervalence charge transfer between the nearest neighbor Fe2+ and Ti4+
A magmatic origin of the sapphire grains is supported by petrologic and trace element data from the blue sapphires, but Cr abundances are inconsistent with this interpretation
Summary
Gem corundum deposits worldwide are generally associated with quartz-free rocks of both igneous and metamorphic origin. We report a new type of occurrence of strongly blue-colored, microscopic, corundum (blue sapphire) from a small nelsonite dike hosted by aluminous gneiss in the western. We discuss the petrography, mineral description of sapphire from a nelsonite. We discuss the petrography, mineral chemistry, chemistry, optical spectroscopy, and inferred origin of this sapphire occurrence. The sapphire location is location is 250 m northeast of the Port Leyden nelsonite (Figure 1b; [8]). It is unclear how the small, 250 m northeast of the Port Leyden nelsonite (Figure 1b; [8]) It is unclear how the small, sapphire-bearing, sapphire-bearing, nelsonite dike is related to the larger, nelsonite orebody. Map of the eastern part of the village upstate New York and the village of Port Leyden.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
