Chalcocites and other new finds from China

Chalcocite and other sulfides from a 2013 discovery at the Tongshan Copper-Iron Mine, Daye, Huangshi County, Hubei Province China Robert Lavinsky The Arkenstone XiaoJun Chen The Arkenstone China Hexiong Yang University of Arizona Bob Downs University of Arizona A few strange specimens of a colorful metallic mineral were first brought to the Arkenstone’s buying office in Shanghai around the end of 2012. They were labeled as “copper” at the time. By January, emails had been received with pictures of a bewildering variety of habits, all clearly of the same material.

It was time to see in person! Before the 2013 Tucson Show, Arkenstone representatives visited the specimen market in Chenzhou in Hunan Province, and tracked down the source.

A friend of ours made contact with the mine manager and was allowed to visit the mine twice during the productive period of this deposit/vein, once at the start and once at the end, after

it was mined out.

After seeing photos of specimens in place on heavy rock faces, Arkenstone helped funding a US-made diamond chain saw of the kind so often used in specimen recovery projects these days, but unfortunately the saw would not cut through the matrix—perhaps because of the high content of copper and iron in the matrix. Consequently very few large specimens were recovered, because of the difficulty of chopping them out of the solid walls. Only at the end of this open pocket were attempts made to extract larger specimens which could be sent to a lab in the US for trimming.

The occurrence consisted of one long open pocket (perhaps a watercourse) that wound for at least a dozen meters, and was so big that men could sit in it. Thousands of small pieces came out, including many fine thumbnails which, sadly, were scraped off the wall into containers, damaging many of them. Of the larger pieces, many were damaged, especially in the early days, and are now just a “colorful crust” on rock. The miners simply did not have the tools, training or patience to collect specimens properly. So there are few matrix pieces. However, on the specimens that do include matrix, there is sometimes a beautiful mix of copper mineralization and calcite crystals. Probably a few hundred pieces of well-collected material of miniature size and larger were recovered, and only a few dozen truly outstanding larger pieces. The last large pocket was collected in April of 2013, from the original channel. We are not aware of any new pocket found since that time, although some material continues

Figure 40. Chalcopyrite-coated chalcocite and djurleite in situ, at the Tongshan mine, Daye, Huangshi County, Hubei Province, China. Xiaojun Chen photo.

116

The Mineralogical Record, volume 45, January–February, 2014

Figure 41 (above left). Main shaft of the Tongshan mine.

Xiaojun Chen photo.

Figure 42 (above). Chalcopyritecoated chalcocite and djurleite, 4 cm, from the Tongshan mine, Daye, Huangshi County, Hubei Province, China. John Veevaert specimen and photo.

Figure 43 (left). Chalcopyritecoated chalcocite and djurleite, 6 cm, from the Tongshan mine, Daye, Huangshi County, Hubei Province, China. Rob Lavinsky (The Arkenstone) specimen and photo. to trickle out to the market from the original find.

This is certainly one of the more exciting finds from China in recent times, and because there are so many specimens, there should be plenty available in every size and price range at the 2014 Tucson show.

Eight samples of different habits were provided by Arkenstone for analysis. Two of us (Hexiong Yang and Bob Downs) at the University of Arizona’s Mineralogy Department ran analyses on these strange specimens. Chinese dealers who obtained them were labeling them variously as “bornite,” “copper,” or “chalcocite” by September of 2013 when the last stragglers came to market. Eight samples were given for analysis, each showing a slightly different habit or style of crystallization.

In general, sulfides and sulfosalts do not produce useful Raman spectra, so X-ray diffraction was employed for identification. From the X-ray diffraction data, the unit-cell parameters can be determined and the species identified. All analyses were conducted using a Bruker X8 APEX2 CCD X-ray diffractometer equipped with graphite-monochromatized MoKα radiation.

The Mineralogical Record, volume 45, January–February, 2014

The results were interesting. All of the colorful outside patina of these specimens, of any type or habit, is chalcopyrite (we had guessed that it was bornite). Additionally there are primary elongated crystals of chalcopyrite that look like narrow, extruded straws, which erupt from masses of djurleite of a bubbly habit.

Larger, more massive crystals with three-dimensional form (to 2 cm) proved to be chalcocite covered with chalcopyrite, and this chalcocite occurs in both an elongated habit and a platy habit similar to that of specimens from Cornwall or Connecticut.

The matrix on which the chalcocite grows is typically a bubbly mass of colorful djurleite; small, sharp, thin and fragile crystals up to 2 cm are also djurleite. Some djurleite crystals are thin, elongated, flat blades with multiple pointed terminations like fingers. The chalcocite crystals are all much thicker and of a stout to platy habit. So habit can be used to identify which sulfide is underneath the protective layer of chalcopyrite.

Upon analysis, the chalcocite crystals yielded such ideal results that samples from this find are clearly among the most pure known, and have been added to the repository of mineralogical standards housed at the University of Arizona (the RRUFF project).

117