Arsenopyrite in Fluorite

Mineral inclusions have long been a popular category among collectors. While most inclusion collectors (include myself) tend to focus on quartz, fluorite has received less attention. This may be due to its lower production volume, fragile nature (due to well-developed cleavage), and often dark body color that makes inclusions harder to see. However, when a clear inclusion is found in fluorite, it becomes desirable.

The Yaogangxian Mine (YGX), the largest tungsten mine in the Nanling region of South China, is also one of the world’s most important localities for producing top-quality fluorite specimens. (For more background on fluorite from this locality, please refer to my earlier posts.) At YGX, most ore veins are located along the northern contact between granite and sedimentary rocks, often cutting across both lithologies.

Among the ore minerals, arsenopyrite, although present in minor amounts, is key to understanding the formation of ore deposits such as gold, and tungsten (herein). Arsenic is typically concentrated in sedimentary rocks, which likely served as the source reservoir at YGX. Oxidized magmatic-hydrothermal fluids (possibly the source of sulfur?) leached arsenic from these sedimentary rocks, and arsenopyrite precipitated under conditions of redox disequilibrium. Fluorite formed either simultaneously with or slightly after arsenopyrite and, under slow cooling conditions (less fractures), sometimes preserved sharply defined arsenopyrite crystals as inclusions.

I’ve seen a few similar specimens before, but most fluorites aren’t nearly as gemmy as this one. The fluorite here also displays a beautiful bluish-purple color, and with the added mineral and fluid inclusions, it almost looks like an animated sky.

Fluorite with arsenopyrite, dolomite and muscovite inclusion, 6.1cm, Yaogangxian Mine, Yaogangxian W-Sn ore field, Yizhang Co., Chenzhou, Hunan, China

Jingnan (Tom) Zhang Coll & Photo