The Pingtouling mine: Liannan County, Guangdong Province, China.
Large and fine mimetite crystals have come from few places in the world, the most prominent being the Tsumeb mine in Namibia, Hat Yai province in Thailand, and the Mt. Bonnie mine in Australia. In all cases the number of specimens produced was quite small. In August 2002 a zone containing brilliant crystallized mimetite was encountered in the Pingtouling lead-zinc mine, Liannan Yao Autonomous County, Guangdong province, China. Some of the specimens found their way to the Tucson Show in January 2003 and caused great excitement in the mineral world.
As is typical in China, the locality was at first concealed by dealers or by their suppliers; it was identified variously as "near Bapu, Guangdong," and the "Wu Chuan mine, Guangxi" (Moore, 2003). However, the true source was eventually revealed as the Pingtouling ("flat-topped mountain") mine about 200 meters from Pingtouling village, about 10 km southwest of the town of Zhaigang in Liannan, Guangdong province. An unpaved 12-km road connects the mine area to the regional highway from the town of Zhaigang.
The beautiful, sub-tropical, forested mountainous area in which the mine is located is populated mainly by the Yao people, one of 11 ethnic groups in Liannan County. The Yao are a unique people with their own culture and language, though most of them also speak Mandarin Chinese. The Yao homeland is rich in spectacular vistas and relatively undeveloped natural resources such as timber, hydroelectric power and more than 20 exploitable mineral deposits (mainly lead, zinc, iron and copper, but also gold, tin, tungsten, manganese and bismuth). Though formerly operated by the government, most of the small mines are now being worked by private owners and township cooperatives.
The occurrence was admirably described in an article by Guanghua Liu (2005), from which much of the information here is taken. Specimens have also been pictured in Liu (2006), Moore (2003) and Moore (2004), as well as on the cover of the May-June 2003 issue of the Mineralogical Record.
Mining has been carried on in the area for at least the last 2,000 years. The Pingtouling lead-zinc deposit was discovered accidentally by a local farmer in 1952. Ore cropped out in a river bed where the farmer had been "fishing" with explosives. Between 1952 and 1954 he extracted about 5,000 tons of high-grade oxide ore averaging more than 40% metal content. In 1956 a drilling company owned by the provincial government completed a drilling project on the site and delineated the orebody, much of which lies under the riverbed. Large-scale mining by the Damaishan Copper Mining Company (owned by the county government) did not begin until 1967, following diversion of the riverbed in order to make possible a hand-dug open pit operation. About 30 miners were employed in the pit, but as the excavation deepened, water-pumping began to cause surface subsidence in the surrounding area. Mining ceased in 1970, the workings were abandoned, and the mine pit was allowed to flood. The local people eventually forgot that the excavation had been officially named the Pingtouling mine, and began referring to it simply as the Dashuihu ("big water pool") mine.
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By 1999 the Damaishan Copper Mining Company had gone bankrupt. A former miner named Li Yutang purchased the rights to the mine for 80,000 yuan (about $9,750) and began working it again. The flooded open pit seemed beyond reclamation, so he sank three inclined shafts in an attempt to intercept the heavily oxidized portion of the orebody that was not under the riverbed. Despite investing close to another $100,000, he failed to find the ore. In 2001 he leased the mining rights to a Mr. Zhou, a miner from Yunnan province, who sank two additional shafts and recovered a few hundred tons of oxidized lead ore, but lost money in the process. Several pockets of beautiful mimetite were encountered in 2001 and early 2002, but were crushed as ore.
In 2002 the mining rights were leased to Jiang Zemin. He opened a narrow adit (called the Dashuihu adit), just 1.2 X 1.8 meters across, at the margin of the old open pit and succeeded in reaching the orebody. Employing just six miners, he began extracting arsenic-rich ore (locally up to 30% As).
In August of 2002, more crystallized mimetite was encountered, but the crystals were of rather poor quality and a dirty brown color. These were given away free to some mineral dealers from Guilin, who later sold them to several European dealers. In October 2002 another pocket was encountered, consisting of better-quality specimens with brightly colored crystals from 1 to 10 mm in size. These crystals are rather varied in color, ranging from a deep yellow resembling mimetite to a red or red-orange resembling vanadinite to dark brown and brown-green resembling pyromorphite; some of the crystals are bi-colored. Berthold Ottens (personal communication) puchased some of these in Changsha in late 2002.
Between October and November of 2002 the main pocket was apparently encountered and even better specimens were brought out; these are primarily yellow in color, with crystals up to nearly 2 cm. A total of around 3,000 specimens were collected from this find with amazingly professional care, and a significant percentage of them were preserved in a relatively undamaged state, including approximately 300 pieces of good quality and a few dozen of top quality. Most of these were purchased by one dealer in Changsha, for the remarkable price of around $250 per ton--the same as the ore value! He sold about half of the find to New York mineral dealer Daniel Trinchillo. Berthold Ottens and other European dealers obtained lots as well, which they sold in Europe. Trinchillo and others brought specimens to the following Tucson Show (Moore, 2003). Through Trinchillo, Rob Lavinsky of The Arkenstone acquired a major portion of the find. Mike Bergmann and a handful of other dealers also acquired lots for resale. Lower-end specimens were also marketed in Tucson by a number of Chinese dealers.
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A period of furious collecting ensued at the mine, but apparently nothing more was found after November 2002. It was later said (Moore, 2004; Liu, 2005) that additional pockets were discovered as late as September 2003. At least four more lots of specimens came on the market, including some top-quality pieces. This material may have been from newly found pockets or may simply have been the second half of the big lot of specimens found in the original October-November 2002 pocket. (Chinese dealers like to speculate in specimens, waiting for prices to go higher.) In any case, nothing has been found there since 2003. Jiang Zemin, however, continued to mine the deposit for ore, and by May of 2004 he had extracted more than 10,000 tons of high-grade oxide ore, but by 2005 mining had penetrated into the unoxidized ore.
Bryan Lees of Collector's Edge Minerals hired a contract crew of Chinese miners to work the mine from April to December of 2005, part of that time under the direction of Bryan's mining supervisor, Graham Sutton. They concentrated on the zone about 20 meters down the 80-meter inclined shaft where the original mimetite pockets had been encountered. Despite driving over 20 meters of exploratory drifts they unfortunately found virtually nothing except traces of white pyromorphite and scraps of bad brown mimetite--not even worth exporting. The original miners, it seems, had been meticulously thorough in removing any trace or hint of good mineralization. It is now relatively certain (as anything can be in the mining world) that the occurrence is exhausted.
According to Liu (2005), the Pingtouling orebody is a hydrothermal deposit genetically related to the emplacement of nearby granitic plutons. The presence of iron, copper and arsenic deposits elsewhere in the local area suggests the existence of a polymetallic belt. The orebody is heavily oxidized in the surface zone, down to a level about 2 meters below the level of the river, below which unoxidized lead ore predominates.
The first specimens found in 2002 range in color from bright red (at first assumed to be vanadinite) to orange, yellow and brownish green (thought perhaps to be pyromorphite); some crystals are elongated, tapered, and bi-colored orange-red and yellow. Subsequent finds proved to be of higher quality and primarily yellow to yellow-orange in color. So spectacular are the crystals, and so surprising the quantity (for mimetite), that when they first reached the American market in 2003 suspicion immediately arose that the yellow crystals were pyromorphite instead of mimetite. However, analyses conducted at the University of Arizona (Marcus Origlieri, personal communication) soon confirmed their identity as mimetite, and those results were later repeated by analysts in China and Germany. The red crystals and the green crystals were analyzed at the University of Stuttgart and, amazingly, both were found to be pure end-member mimetite, with hardly a trace of vanadium or phosphorus (Berthold Ottens, personal communications).
The vast majority of the mimetite crystals are simple, blocky, hexagonal prisms with large, smooth pinacoid faces. All of the faces generally have a mirror-bright, adamantine luster and very sharp edges. The crystals are beautifully translucent to gemmy in places (though no large, completely water-clear crystals like those from Tsumeb were found). Most crystals are 1 cm or less, but single crystals up to over 2 cm were recovered, in thick crusts and intergrown clusters on a blackish to ochre-colored limonitic gossan matrix. The exposed terminations tend to be perfect, whereas the end attached to matrix tends to taper down irregularly, as is often seen with large vanadinite crystals. In other cases the prism sides and even the pinacoid face are broken up into striated or terraced surfaces that grade into parallel crystal aggregates.
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Crystals vary in proportions from tablets that are two or three times as large across the pinacoid face as along the c axis, to primarily prismatic crystals where the elongation ratio is 4 or 5 to 1. The smallest crystals can be equant or nearly acicular, grading up to the largest crystals which are generally tabular. A few rare specimens show striated, elongated crystals tapering almost to a point. Some crystals show reflective, silky zones just below the prism surfaces indicative of micro-voids, exactly as seen on some large vanadinite crystals from Morocco.
Aside from the first few crystals found (which, as mentioned, range in color from red to orange, yellow and brownish green), the color of the mimetite specimens reaching the market ranges from colorless (very rare) to grayish yellow, but primarily pale yellow, canary-yellow, bright yellow-orange (exactly like the color of Old Yuma mine wulfenite) and darker yellow-orange (probably darkened by limonitic inclusions). Some crystals have selected faces rendered opaque brown by a thin layer of dirty inclusions. Most loose crystal clusters are around 2 to 5 cm in size, but fabulous cabinet specimens to over 17 centimeters were recovered, some of them heavily encrusted by large, superb crystals. Botryoidal mimetite was also found but was not considered to have sufficient specimen value and was generally not saved.
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Scorodite [Fe.sup.3+]As[O.sub.4] x 2[H.sub.2]O
According to mineral dealer Martin Jensen (Moore, 2005), a major zone of scorodite was encountered in the Pingtouling mine in November 2003. Apparently a whole ore car full of crystallized scorodite was mined but its specimen value was not recognized until most of it had been processed as ore; only about 30 specimens were saved. Martin purchased the specimens on behalf of his employer at the time, Collector's Edge Minerals in Golden, Colorado. Internet mineral dealer John Veevaert of Trinity Minerals purchased five of them. The lustrous scorodite crystals, up to 1 cm in size, are sharp and mirror-faced with light striations, and show a pronounced color change, from blue-green under incandescent lighting to purple-blue in daylight. The crystals line cavities to a few centimeters across in earthy brown limonite, associated with microcrystals of anglesite, arsenian siderite and beudantite. Some of the larger specimens with dense crystal pocket-linings are quite attractive.
Unlike the case with its mineral cousins, vanadinite and pyromorphite, discoveries of world-class crystallized mimetite have always been very limited in quantity and duration of production. Fine mimetite specimens from the Pingtouling mine were collected during only a few months in 2002. This was one of those cases where collectors had only a small window of time in which to obtain a high-quality specimen before the opportunity passed. Because mining in the small deposit has now passed through the oxidized zone, it is highly unlikely that any more specimens will be discovered. Like Kongsberg silver and Bolivian phosphophyllite, the specimens of Chinese mimetite now in collections will circulate among future generations of collectors as highly valued classics of mineralogy--among the first to come forth in the 21st century.
My thanks to Jeff Scovil for the use of his superb specimen photography; to Steve Behling and Graham Sutton of Collector's Edge Minerals for locality photos and information on their mining activities there; and to Berthold Ottens, Anthony Kampf and Guanghua Liu for reviewing the manuscript.
LIU, G., and OTTENS, B. (2004) Pyromorphit und Mimetesit, die farbigen Bleiminerale. In: ExtraLapis No. 26/27: China. Weise Verlag, Munchen. 26-31.
LIU, G. (2005) The mystic mimetite location of Liannan Yao Autonomous County. Rocks & Minerals, 80 (1), 24-31.
LIU, G. (2006) Fine Minerals of China. AAA Minerals AG, Zug, Switzerland, p. 64-73.
MOORE, T. (2003) What's new in minerals: Tucson Show 2003. Mineralogical Record, 34, 280, 283.
MOORE, T. (2004) What's new in minerals: Tucson Show 2004. Mineralogical Record, 35, 257.
MOORE, T. (2005) What's new in the mineral world. Posted 7/18/2005 on www.MineralogicalRecord.com.
Wendell E. Wilson
Tucson, Arizona 85750
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|Author:||Wilson, Wendell E.|
|Publication:||The Mineralogical Record|
|Date:||Jan 1, 2007|
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