The Fengjiashan mine: Daye District, Ezhou Prefecture, Hubei Province, China.
During the past three years there has been a considerable increase in the number of collector-oriented publications concerning the minerals and mineral occurrences of China. One of these (among many others) was the article by Hawthorne et al. in vol. 33, no. 6 of the Mineralogical Record (November-December 2002) describing the new mineral species hubeite, recently approved by the International Mineralogical Association. With great precision and thoroughness the article presented all relevant mineralogical data; however, only sketchy information on the purported locality was given, and a full description of the deposit was conspicuously absent. At the time, specimens of the new mineral were being brought onto the market solely by Chinese mineral dealers, who were selling them to American and European dealers and collectors. The locality itself had not yet been visited by any professional mineralogist or by any dealers seriously interested in mineralogy. Thus it is not surprising that since the first appearance of hubeite, it has commonly been misidentified as manganbabingtonite, and specimens have been attributed to various incorrect localities.
With a view to obtaining accurate information on hubeite and on its occurrence, I decided to visit the locality early in 2002, accompanied on the trip by the Chinese dealer Yunfu Gao, of Changsha, and the German collector J. Backhauss.
In Hawthorne et al. (2002) the "Daye mine," in Hubei province, was cited as the type locality for hubeite. In fact, the mineral comes from the Fengjiashan wollastonite mine in the Daye district, sometimes also known as the "Daye copper mine." This locality should not be confused with the nearby Daye iron mine, a large opencast mine which has yielded no specimens of note. Therefore it is preferable to use the name Fengjiashan.
Since the initial appearance of hubeite on the market, other, associated minerals have aroused great interest (for example, inesite, Japan-law twinned quartz, and unusually formed amethyst), and so I published detailed reports on Fengjiashan mine minerals in the German mineral magazine Lapis (vol. 28, no. 9; September 2003) as well as in ExtraLapis (26/27, 2004, p. 134-137).
The Middle-Lower Yangtze Metallogenic Belt, extending from Wuhan in Hubei Province in the west to Zhenjiang in Jiangsu Province in the east, contains more than 200 polymetallic (Cu-Fe-Au, Mo, Zn, Pb, Ag) deposits and is one of the most important metallogenic belts of China (Yu Sheng Zhau et al., 1996). This belt is controlled by faults and aulacogens (sediment-filled tectonic troughs in cratons) in the continental plate. In the Early Yanshan Epoch (Jurassic Period), the dominant west-northwest and east-west lithospheric faults controlled the distribution of Cu, Mo and Au mineralization, whereas in the Late Yanshan Epoch (Cretaceous Period) the north-northeast and northeast lithospheric faults controlled Cu-Fe mineralization. The ore deposits are quite diverse in their types, including Fe and Cu skarns, Cu porphyries, Fe magma injections, Fe hydrothermal deposits and remobilized sedimentary Fe and/or Cu deposits. The major orebodies include the iron-copper deposits of Tieshan, Chengchao, Tonglushan and Tongshankou in the Daye area; Chengmenshan, Wushan and Yangjishan in the Jiurui area; Tonguanshan, Shizihshan (Dongguashan), Fengjuangqiao and Xinqiao in the Tongling area; and the deposits in the Ningwu-Luzong area.
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The skarn-type Fe and Cu deposits are major contributors to China's copper reserves and significant contributors to its iron reserves.
These deposits developed in the contact zones between felsic intrusions and carbonate country rocks. At the Tonglushan deposit, a typical representative of this type, quartz diorite porphyries have intruded gypsum-bearing limestones of the Triassic-age Daye Formation.
The porphyry copper deposits of the Metallogenic Belt are similar to those in the western United States; important examples include the Chengmenshan deposit in Jiujiang prefecture, Jiangxi province; the Fengsandong deposit in Hubei province; and the Shaxi deposit in Anhui province.
There are a number of vein-type Cu-Fe-Mo-Au deposits. Even though they are small compared with the skarn and porphyry deposits, they contain higher percentages of Cu than these do. The Tongniujing deposit, Anhui, is typical.
Two metallogenic series occur in the Middle-Lower Yangtze Metallogenic Belt: sedimentary and magmatic-hydrothermal. The sedimentary series were generated primarily during the development of sedimentary cover on the Yangtze Craton during late Paleozoic and Triassic times. The environments for sedimentation were commonly littoral to shallow-marine. Carbonate rocks, with minor siliceous and clastic rocks, were the dominant types deposited. The magmatic-hydrothermal series were formed during the Mesozoic. The genetic styles of the magmatic-hydrothermal deposits are numerous, but they are commonly characterized by the following traits:
(1) They are products of magmatic evolution during the Yanshan Epoch and are intimately associated with magmatic bodies.
(2) Although the ore-forming materials are thought to have been supplied mainly by magmas, in some deposits they were supplied by alkaline metasomatism caused by intrusive bodies, and in others they were supplied by remobilization of sedimentary or volcanic-sedimentary proto-ore.
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(3) The mechanisms of ore formation include hydrothermal alteration and vein filling, ore magma injection, and remobilization of sedimentary proto-ore by magmatic-hydrothermal activity.
MINES OF THE DAYE DISTRICT
The County of Daye lies in the southern part of the middle reaches of the Yangtze River, in southeastern Hubei province, between east longitude 114[degrees]31" to 115[degrees]21", and north latitude 29[degrees]40" to 30[degrees]15". Daye County belongs to Huangshi prefecture, which is comprised of one county-grade city (Daye), one county (Yangxin), and four districts (Huangshi Port, Shihuiyao, Xialu and Tieshan), as well as 19 subdistricts, 51 towns, 247 neighborhood commissions and 1,026 village commissions. Daye County (alternatively, the city of Daye) manages six rural areas, 12 towns and 494 administrative villages; it has an area of 1593 square kilometers and a population of 840,000. The climate is subtropical, with an average yearly temperature of 17[degrees]C.
Daye County is rich in natural resources, including a great variety of metallic and non-metallic mineral deposits. It is one of China's ten major centers of iron production, an important center of coal production, and one of China's six most important cities for the manufacture of bronze. Gold and silver production is the first-ranking revenue source for Hubei province. It is important to point out that there is a considerable number of mines, mining camps and quarries in the Daye region; among these are many specimen-producing localities, especially for calcite, which often are impossible to specify precisely. Exact locality data may confidently be provided only in cases of major discoveries, or when there is a distinctive suite of associated species.
Huangshi prefecture, including Daye county, is one of the birthplaces of Chinese bronze-age culture. Thousands of years ago the ancestors of the present inhabitants created the Yangtze River culture, which produced China's earliest artworks in bronze. During the Yin Dynasty, copper mining began in the Daye area; the ancient ruins of the Tonglushan copper mines and smelters were discovered in 1973. Iron mining and smelting at Tieshan, near Daye, also dates to ancient times: Zhan Zhidong began the Daye iron mine at Tieshan during the Qing Dynasty.
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THE FENGJIASHAN MINE
Of all the mines of the Middle-Lower Yangtze Metallogenic Belt, it is the Fengjiashan wollastonite mine (also known as the Daye copper mine) which has become most significant to mineral collectors during the past ten years.
Begun by the government in 1966 as a copper mine exploiting chalcopyrite ore, the Fengjiashan mine proved only marginally profitable, and so in the early 1980's, at which time it was employing 200 workers, it was converted to a privately operated wollastonite mine. The operating company describes the mine as follows:
Huangshi Jinshan Wollastonite Co., Ltd. is a wollastonite manufacturer integrating extraction, sizing, processing and marketing. It is a large enterprise with the most advanced equipment and richest mining resources in the middle region of China. The wollastonite produced by this company under the brand name "Fengjiashan" is world-renowned for its unique filamentary structure and fine physical and chemical performance, and is competitive with the wollastonite produced in India and the U.S. Located in the southern suburb of Daye city, the world-reputed "Capital of Copper," the company plant is accessed conveniently by land or water.
Presently the mine produces about 50,000 tons of wollastonite per year, the major share of production being exported to Japan. Wollastonite is a versatile raw material, with many industrial uses; it is widely used in ceramics as a bond between the earthenware base and the glazing of wall tiles. In 2002 the mine workings consisted of a 140-meter-deep shaft and three tunnels. In May 2006 it could be seen that this shaft, called Fengjiashan I, had been closed, and that about 500 meters from it a second shaft, 50 meters deeper, called Fengjiashan II, had been activated. Meanwhile, near the old shaft a complete ore-preparation facility for wollastonite had been built; here the wollastonite ore was being broken down, ground up, and packed for shipment. A further 500 meters away, another company was operating a still deeper working called Fengjiashan III: this is not a shaft but a tunnel which accesses the ore directly.
The orebody is a typical skarn deposit, with zones of very pure wollastonite reaching 1 meter thick, lying along a contact between marble and intrusive diorite. The wollastonite is never found as free crystals in pockets; rather, elongated wollastonite crystals to 20 cm form compact radial aggregates. Green andradite crystals to several centimeters across may be seen in direct contact with chalcopyrite crystals. The famous and attractive inesite specimens, as well as amethyst specimens showing long-prismatic crystals and a distinctive color zoning, came from the Fengjiashan I shaft. Inesite has only rarely been found in Fengjiashan II, and the specimens are unattractive. Amethyst crystals from Fengjiashan II are short-prismatic and are associated with calcite. Fengjiashan III primarily produces chalcopyrite and molybdenite, with minor amounts of wollastonite. Hubeite has been found in all three workings, but is especially common in Fengjiashan III, where it is associated with pyrite and chalcopyrite.
Occasionally the Fengsangdong mine, near Yangxin, has been given as a locality for inesite and hubeite, but this attribution has turned out to be false: these minerals occur only in the Fengjiashan mine. Mineral specimens for collectors are not recovered by the Haungshi Jinshan Wollastonite Company, Ltd., but rather through a Mr. Cao, who employs up to 15 people as specimen-miners. Of first importance among the types of specimens gathered are inesite, amethyst and Japan-law twins of quartz.
The Cao family has also collected and marketed mineral specimens from other localities; for example, they were first to market the azurite from Guichi. From their headquarters in Daye, the Cao family members have extended their operations to the east and to the west. It is thanks to them that many localities throughout Hubei province and in the southeastern part of Sichuan province have been developed.
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Apophyllite Group K[Ca.sub.4][Si.sub.8][O.sub.20](F,OH).8[H.sub.2]O
Apophyllite is distributed widely in the Fengjiashan mine. It is a late-forming mineral, occurring as overgrowths on quartz, calcite, inesite and hubeite. Unfortunately the beauty of many potentially very fine specimens of these species is often compromised by coatings of apophyllite which cannot be chemically removed. According to Hawthorne et al. (2002), this apophyllite is compositionally zoned, with inner regions of natroapophyllite ([Na.sub.0.8][K.sub.0.2]) and outer rims of fluorapophyllite ([K.sub.1.0]); it is unknown whether these relations remain constant with varying crystal size. The colorless apophyllite crystals display a thin-tabular habit and reach considerable sizes: to 10 cm along an edge. Specimens in which apophyllite crystals to 1 cm have grown over pale violet amethyst can be quite attractive.
Calcite is encountered very frequently in the Fengjiashan mine, a first generation occurring as squat rhombohedrons and a second generation as steep scalenohedrons. For the most part the crystals are opaque and colorless, and only rarely are they transparent and yellow.
Chalcopyrite was the ore mineral originally mined at Fengjiashan. The crystals reach several centimeters across, but usually have weathered surfaces and consequently a blackish blue color.
Datolite is found extremely rarely at the Fengjiashan mine, as greenish, translucent to transparent crystals reaching 7 cm.
Early in 2005, a dealer in Changsha offered a specimen, presumably of heulandite, from a new discovery at Fengjiashan. After the sheaf-shaped crystal aggregates had been cleaned, however, they were seen to be transparent and of an olive-green color--clearly not heulandite. Analysis showed that the species in question is epidote, a skarn mineral. The crystals are rough-surfaced but reach 4 cm long
Fluorite is very rare at Fengjiashan. Crystals thus far observed are bluish and reach 2 cm; they are tightly intergrown and do not have clearly recognizable forms.
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Tabular hematite crystals to about 1 mm are occasionally seen scattered on quartz.
Hubeite, the recently describeded manganese-iron silicate (Hawthorne et al., 2002), forms bladed, wedge-terminated, dark brown to black crystals averaging 5 mm long. The crystals cluster in small fan-shaped aggregates and in radial sprays perching typically on rose-pink inesite or quartz crystals, with apophyllite, calcite, pyrite and ilvaite. This new mineral species was named for the province of Hubei (pronounced "Hoo-bay"). Actually the name should not have been spelled "hubeite" but rather "hubei-ite"--retaining the "i" in "Hubei" for proper pronounciation, apart from the "-ite" ending.
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The calcium-iron silicate ilvaite is commonly seen as black microcrystals on quartz or calcite. The crystals, reaching about 2 mm long, show dipyramid faces but no prism faces. (Jordi Fabre reports that the ilvaite from Fengjiashan is actually manganoilvaite.)
Inesite from the Fengjiashan mine displays a characteristic raspberry-red or reddish orange coloration. Individual crystals are only a few millimeters long as a rule, exceptionally reaching 1.5 or 2 cm long. The crystals are thin-tabular, greatly elongated and very brittle, aggregating in drusy crusts and in sheaves to radiating spherical clusters. In many cases the druses of inesite are fully or partly encrusted (unfortunately) by tiny blackish hubeite crystals or apophyllite crystals, rendering the specimens less attractive. On the other hand, specimens with sheaves or spherical clusters of inesite on prismatic quartz crystals are very attractive. For top specimens of this type, high prices in U.S. dollars are asked in China.
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The cleaning and preparation of inesite/hubeite specimens presents a problem. Unfortunately, Chinese dealers treat many specimens with hydrochloric acid, which turns crystal faces dull. To refresh their colors the crystals are then oiled. When acquiring specimens from Fengjiashan one should exercise due caution.
Irregular, tarnished, striated, blocky to platy or bladed marcasite crystals to about 1.5 cm have been found with colorless scaleno-hedral calcite crystals.
Pyrite occurs in cubic crystals to 6 cm. Pyrite pseudomorphs after chalcopyrite crystals are also known.
Colorless to milky quartz occurs in the Fengjiashan mine as crystals commonly measuring 10 cm long, but exceptionally reaching 30 cm. A specialty of the mine is the common occurrence of Japan-law twinned quartz crystals, which reach 10 cm along one "arm." Very few of these crystals are lustrous or wholly transparent; as a rule they are cloudy, with dull surfaces.
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Pale violet amethyst crystals to 15 cm long are also found. For a few of the pocket discoveries it has been observed that only the lower parts of the crystals have a violet color, while the upper parts are largely colorless; in other cases the crystals are a uniform lavender color. Deep violet-colored amethyst crystals were found for the first time in 2001; they measure up to 5 cm long. In 2002, deep violet Japan-law twins measuring 4 cm along an arm were discovered.
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Scheelite crystals to 1 cm associated with quartz and pyrite are among the rarer specimens from Fengjiashan. It is interesting that good crystals of scheelite have been observed to occur in so many mines in southern and central China: a clear indication that the magmas which intruded during the Yanshan Epoch, giving rise to most of the region's endogenetic ore deposits, had a common origin.
Sheaf-shaped aggregates of yellowish to cream-colored stilbite/stellerite crystals, the sheaves reaching 4 cm, have been observed rarely in the mine. Whether the species is stilbite or stellerite has not yet been determined.
Wollastonite is not found as free crystals in pockets but, rather, as typical aggregates of elongated crystals to 20 cm.
To date, only four mines in the area of the Middle-Lower Yangtze Metallogenic Belt have supplied mineral specimens to the market, although about 30 named deposits and many individual workings are registered. These include not only copper and iron deposits, but a great number of polymetallic ones. In the future, with closer monitoring of individual mines and further training of mine workers, we may expect more interesting mineral discoveries. One such new occurrence worthy of mention is the Huangtun lead-silver mine, which lies not far from Tongling at Lujiang. This is the source of the remarkable wire silver specimens first offered on the mineral market in 2005.
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|Publication:||The Mineralogical Record|
|Date:||Jan 1, 2007|
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