RUBY AND SAPPHIRE FROM MULING , NORTHEASTERN CHINA

Rubies and sapphires from alluvial deposits in Muling area of northeastern Heilongjiang Province, China received revitalized interests as colored stones became widely embraced on the China gem markets in recent years.

Rough rubies and sapphires we acquired from local miners commonly exhibited well-formed tabular hexagonal crystals while some sapphires showed tumbled appearance in broken pieces. These materials generally showed abraded features resembling unhealed fissures, but some stones were predominantly clean and large enough (ranged about 1-15 ct) to be faceted.

The ruby and pink sapphire production mostly appeared purplish red, while sapphire production exhibited a range of colors in violetish blue, light to deep blue, yellow and colorless. Among these samples, only deep blue sapphires showed hexagonal dark blue color zoning in the center of crystals.

Trace element analysis from LA-ICP-MS showed that the pink to purplish red series were dominated by chromium (173-636ppma) with noticeable level of iron (1650-2510ppma) and titanium (36-70ppma). Yellow sapphires contained highest iron content (4480-4800ppma) while iron content (1580-2260ppma) was much lower in blue sapphires along with appreciable amount of titanium (75-610 ppma) as blue chromophore. Magnesium content ranged from 10 to 80 ppma and did not show clear correlation to color while gallium content (10-100 ppma) fell into the range of natural corundum.

Internal features of rubies and sapphires from Muling consisted of fluid inclusions, mineral inclusions, twining and whitish needles which formed 3-dimensional skeleton network. Mineral inclusions were identified by Raman as feldspar and sillimanite.

Based on mining and geological information and our current analysis of rubies and sapphires from Muling, authors inferred that rubies and sapphires from Muling might have originated from an earlier volcanic eruption and experienced subsequent high-pressure geological processes. They could not be defined as a classic igneous deposit. Ruby and sapphire deposits from Muling are likely non-classic alkali basalt deposits.

Considering color saturation, transparency and size, the gem quality and variety of rubies and sapphires from Muling are competitive and deposits are highly promising among well-known global sources of gem corundum.