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The Sillver Bow Creek Sapphire Deposit


Photograph of the Silver Bow Creek sapphire deposit showing a portion of the debris flows which has been reworked into fluvial channel deposits. Within the channel deposits, the sapphire grade is approximately 10 g/m3 which is 20% of that within the debris flows. However, within the channel deposits, gold grades have been increased by a factor of 3 to approximately 3 g/m3.


Photograph of a silliminite schist pebble recovered from the sapphire bearing debris flows at the Silver Bow Creek deposit. In total, thirty-two schist pebbles were recovered during this study, of which two were found to contain corundum / sapphires during thin-section examination. These metamorphic pebbles are interpreted to be xenoliths weathering out of the surrounding Lowland Creek volcanics.


Photomicrograph of a sillimanite schist pebble containing sapphire porphyroblasts recovered from the sapphire bearing debris flows at the Silver Bow Creek deposit. The presence of highly aluminous xenoliths containing corundum within the sapphire-bearing debris flows cannot be a coincidence. We believe that the sapphires recovered from the Silver Bow Deposit represent refractory porphyroblasts which are the remnants of otherwise completely assimilated corundum-bearing biotite-sillimanite schist.


Photomicrograph of an igneous pebble containing dark-blue sapphire phenocrysts recovered from the sapphire bearing debris flows at the Silver Bow Creek deposit. It is hypothesized that this sample represents a melt which formed as a result of the host magma becoming locally under saturated with respect to silica proximal to an assimilating aluminous rock such as the sillimanite schist pebble shown above.



Photograph of a selected number of gem grade sapphires recovered from the debris flows at the Silver Bow Creek sapphire deposit. Some of these sapphires have thin rinds of both spinel and opal adhering to their surfaces and all exhibit etched surface morphologies which are interpreted to be the result of magmatic resorbtion.

Photograph of the numerous spinel grains recovered from the Silver Bow Creek sapphire deposit. Like the sapphires, the spinel grains are also believed to represent refractory porphyroblasts which are the remnants of the biotite-sillimanite schist represented above after it was completely assimilated.