 |
| Deep blue sapphires were discovered in southern Baffin Island, Canada, in 2002. One of the original prospectors, Seemeega Aqpik, is shown with a matrix specimen containing a sapphire crystal that measures 7.7 cm long. Photo by William Rohtert. |
In 2002, local prospectors Seemeega and Nowdla Aqpik discovered gem-quality sapphires in an outcrop southwest of the community of Kimmirut on the south coast of Baffin Island, Nunavut, northern Canada (see figure). To date, six corundum occurrences have been discovered over a distance of 390 m.
The original occurrence, called “Beluga,” contains deep blue sapphires with violet overtones. Individual crystals up to 7.7 × 2.1 cm have been recovered (again, see figure), although most are in the range of 15 × 4 mm. Some of the sapphires are color-zoned (especially larger crystals), and may display concentric, irregular, or end-to-end variations in hue. The smaller crystals are generally free of inclusions, whereas the larger ones are often fractured and, in most cases, included with calcite and/or apatite. Needles of thomsonite, a zeolite mineral, coat grain boundaries and penetrate deeply into some of the crystals.
Most of the Beluga sapphire crystals exhibit spectacular zoning in cathodoluminescence which corresponds to the color zoning. Very faint compositional zoning was sometimes seen in backscattered-electron images obtained with a scanning electron microscope. Electron-microprobe analysis of 10 sapphire samples yielded maximum TiO2 and FeO values of 0.13 and 0.30 wt.%, respectively.
In August 2004, fragments of yellow, colorless, and light blue sapphires were discovered at another occurrence located 50 m from the Beluga lens, over an area about 0.5 × 0.5 m. Called “Beluga South,” this locality also contains weathered fragments of a corundum-bearing plagioclase-muscovite-calcite rock. Microprobe analyses of the yellow and colorless sapphires (one sample of each) showed that the dominant chromophore in the yellow material was iron, with up to 0.04 wt.% FeO; all other potential chromophores were below the detection limit.
Two yellow sapphires from the Beluga South occurrence were loaned to GIA for examination (1.09 and 1.47 ct). The following properties were recorded by one of us (EPQ): color—yellow to orangy yellow, with no pleochroism observed; diaphaneity—transparent; R.I.—1.758–1.766; birefringence—0.008; S.G.—3.99 and 4.01; Chelsea filter reaction—none; and fluorescence—moderate orange to long-wave and very weak orange to short-wave UV radiation. No absorption features were visible with a desk-model spectroscope. Microscopic examination revealed that both stones contained a few long white needles, and the oval sapphire also had a single “fingerprint.” No evidence of heat treatment was seen.
The Baffin Island sapphires are hosted by calc-silicate lenses in a marble unit of the metasedimentary Lake Harbour Group, near a major terrane boundary within the Paleoproterozoic Trans-Hudson Orogen. Silica-poor (i.e., syenitic or ijolitic) magmas may have played a role in the initial formation of the calc-silicate lenses. The Beluga sapphires occur with plagioclase, clinopyroxene, phlogopite, muscovite, calcite, graphite, nepheline and scapolite. Apatite, rutile, titanite, and zircon are common in the host rock, and rare phases include chlorite, tourmaline (dravite), monazite, sanbornite, thorianite, and uraninite (identified by energy-dispersive spectroscopy). Petrographic studies suggest that this diverse mineral suite formed during retrograde metamorphism accompanied by infiltration of CO2-bearing fluids. The area also hosts other gem varieties in complexly deformed, high-grade metamorphic rocks. These include diopside, pargasite, garnet, spinel, scapolite, tourmaline, apatite, zircon, moonstone, and lapis lazuli. The continental collision setting of southern Baffin is analogous to gem-producing areas within the India-Asia collision zone (i.e., from Afghanistan to Vietnam).
In late 2003, the mineral rights to the sapphire-bearing area of southern Baffin Island were acquired by True North Gems Inc. So far, True North has polished 137 sapphires from the Beluga lens, with a total weight of 19.33 carats. The largest stone is a 0.66 ct trilliant. In addition, 67 yellow and colorless sapphires have been cut from the Beluga South occurrence, with a total weight of 10.62 carats. The largest yellow sapphire is a 1.47 ct oval. All of the color varieties have been cut as calibrated round brilliants in sizes down to 1 mm, with most stones measuring 3 mm in diameter.
Anthony N. LeCheminant (tony_lecheminant@rogers.com)
Petrogen Consultants
Manotick, Ontario, Canada
Lee A. Groat, Gregory M. Dipple, James K. Mortensen
University of British Columbia
Vancouver, British Columbia, Canada
Paul Gertzbein
Department of Indian Affairs and Northern Development
Iqaluit, Nunavut, Canada
William Rohtert
True North Gems Inc.
Vancouver, British Columbia, Canada
Elizabeth P. Quinn
|
