The Rogerley Mine - Weardale, County Durham, England, Part I
By Jesse Fisher and Lindsay Greenbank

This article was originally published in the January/February 2000 issue of
Rocks and Minerals, Vol. 75, No. 1, pp. 54‹61. Copyright © 2000, Helen
Dwight Reid Educational Foundation. www.heldref.org

Beautiful green fluorite specimens from this classic locality are once again on the collector market, thanks to a new find in the summer of 1999.

The Northern Pennine orefield has been an important source of lead, fluorspar (commercial fluorite), and other metallic and nonmetallic ores for many centuries. The earliest records of mining date from the twelfth century, with the high point of lead mining occurring in the eighteenth and nineteenth centuries, followed by a rise in fluorspar production during the late nineteenth through mid-twentieth centuries (Dunham 1990). Mineral specimens have long been a byproduct of these mining operations, and the area around Weardale is particularly noted for the production of many exquisite, well-crystallized specimens of fluorite that exhibit a strong daylight fluorescence unique to fluorite from this region. Mines such as the Heights, Boltsburn, Blackdene, Cambokeels, and Frazers’ Hush are famous among mineralogists and collectors, and specimens from these locations now grace most major mineral collections worldwide.
In recent years, however, large-scale commercial mining has seen a serious decline throughout the Weardale area, along with the rest of the United Kingdom. As a result, the supply of crystallized mineral specimens for the collector’s market as a byproduct of mining for lead and fluorite ores has largely ceased. Those specimens that do make it to market these days are, for the most part, recycled out of old collections. The one exception to this has been specimens from the Rogerley mine, which was worked by partners Lindsay Greenbank and Mick Sutcliffe (operating as Cumbria Mining and Mineral Company) on a part-time basis between its discovery in the early 1970s and 1996. The Rogerley is, to date, the only mine in the United Kingdom that has been operated specifically for the recovery of mineral specimens on a commercial basis, and during this time the mine produced a limited but steady stream of high-quality fluorite specimens, most of which are an attractive emerald-green color.

By 1996 the partners had decided to retire from mining and generously offered to assist in transferring the operation of the mine to a group of interested Americans. After completing the re-negotiation of all lease agreements, the current operators (a partnership of Cal Graeber, Paul Geffner, the lead author [JF], and the mining crew of Byron Weege, Otto Komerak, and Jonina and Bill Pogue), operating as UK Mining Ventures, began full-time operations at the Rogerley in May 1999. After spending approximately six weeks rehabilitating the mine, they began drifting and almost immediately encountered a large cavity lined with green fluorite. Excavation of this pocket lasted throughout the summer and produced literally hundreds of specimens of finely crystallized fluorite. This find shows that, despite centuries of mining activity, the Weardale area still has the potential to produce large amounts of high-quality fluorite specimens; it also demonstrates the viability of commercial mining aimed at specimen recovery in this historic district.

Location and Geography

The Weardale district of the Northern Pennine orefield is located in the largely rural northwestern portion of County Durham, not far south of Hadrian’s Wall in northern England. The Wear Valley runs east-west, following the course of the River Wear, beginning near the town of Wolsingham in the east and continuing westward for more than 20 miles. Although at one time heavily forested, much of this area was cleared centuries ago, and the region is now predominantly open moorland, divided by stone walls and the occasional stone cottage. Inhabited towns and villages, for the most part, occupy the valley floor, and Stanhope is the center of commercial activity for the valley. A few miles north of Stanhope is the picturesque village of Rookhope, formerly the center of much of the local mining. A number of the most productive mines in the Weardale district, including the Boltsburn, Stotsfieldburn, Groverake, and Frazer’s Hush, were located at or near Rookhope, but with the closure of these mines, the village is now fairly quiet. With the decline of mining, tourism and the raising of sheep and cattle are now the mainstays of the local economy. Evidence of past mining abounds, however, and the hills surrounding the valley are covered with numerous long-abandoned quarries, pits, and mine dumps, the names and histories of which are mostly lost in antiquity. Mineral specimens brought from the mines as curiosities by miners can still occasionally be seen as decorations in yards and along walls surrounding cottages in the dale. On rare occasions specimens can be found that have actually survived the vicissitudes of time in reasonable shape, and though the owners are usually aware of their value, purchases can sometimes be negotiated.

History of Mining in the Northern Pennines

There is considerable evidence of mining in southern England during the Roman occupation, but there is no direct evidence that mining was conducted in the northern Pennines during that time. It may or may not be coincidental, however, that Hadrian’s Wall (built A.D. 112) was constructed along a line marking the northern limits of the Northern Pennine orefield. The first documented evidence of mining in the area dates from the twelfth century and records the presence of silver mines in the areas of what are now Alston Moor, just west of Weardale, and Northumberland. Weardale was at this time a forested area that belonged to the Bishops of Durham, who used it as a hunting preserve. The villages of Eastgate and Westgate mark the former entrances to this forest preserve (King 1982).

Lead mining in Weardale reached its greatest levels during the eighteenth and nineteenth centuries. The London Lead Company acquired its first leases in the area in 1692 and continued mining and smelting activities until 1882. The Beaumont Company had its beginnings around the same time and was active until 1884. Oxidized near-surface deposits of siderite and ankerite provided economic deposits of iron ore in some mines and were exploited by the Weardale Iron Company from 1842 until around 1920, with the majority of activity occurring prior to 1880. During the 1880s the declining prices for lead forced both the Beaumont and the London Lead Companies to give up their leases in the area. Some of these were picked up by the Weardale Lead Company, which continued lead mining and smelting until 1931. According to Dunham (1990), twenty-eight separate lead-smelting operations were active in the region during the height of mining in the nineteenth century, but by 1919 the last one had closed.

The mining of nonmetallic ores–fluorspar, witherite, and barytes (commercial barite ore) in the northern Pennines began about the time lead and iron mining were in decline. Fluorspar mining was begun in 1882 by the Weardale Iron Company, which continued operations until being taken over in 1964 by Imperial Chemical Industries, which was, in turn, taken over in 1977 by Swiss Aluminum Mining (UK), Ltd. Shortly after the Second World War, British Steel Corporation was also actively mining fluorspar in the region. By the early 1990s the area’s fluorspar mining was in serious decline, largely due to competition from overseas sources, and during the summer of 1999 the last ore-producing mines in Weardale–Frazer’s Hush and Groverake–had closed.
Total production values for lead and fluorspar from the Weardale district over the years are impressive. According to Dunham (1990), almost 1 million tons of lead were produced from 1666 through 1985. Almost 2 million tons of fluorspar were produced between 1850 and 1984. For more information on the history and production of the many individual mines in the Weardale area, the reader is referred to the recently published monograph by Fairbairn (1996).

Geology and Mineralogy of Ore Deposits

The Northern Pennine orefield is a fault-bounded block covering an area of approximately 550 square miles. A series of Paleozoic faults that were reactivated during the Tertiary form the southern and northwestern margins of the block, tilting it eastward with a maximum displacement along the fault margins of up to 3,000 meters (Sawkins 1966). The Pennine block can be further divided into northern and southern portions by the east-west trending Stainmore syncline. The northern portion, containing the Weardale district, is known as the Alston block, while the southern portion is known as the Askrigg block (Dunham 1990). The ore-bearing deposits of the Pennine block are hosted by a series of Lower to Upper Carboniferous sedimentary units–sandstones, limestones, shales, and coal beds. These sediments form rhythmic sequences, or cyclothems, that were deposited during repeated marine transgressions. The ideal transgressional sequence, indicating a progression from deep marine to shallow marine to terrestrial, would be limestone Æ shale Æ sandstone Æ coal, but this sequence is often incomplete.

The Carboniferous sedimentary sequence rests unconformably on the Weardale Granite, which has a K/Ar age of 362 ± 6 m.y. (Dunham 1990). This granite is not exposed at the surface, but its existence was proposed because of a negative gravity anomaly in the region and was later confirmed by borehole. Though the Weardale Granite is not believed to be genetically related to mineralization in the northern Pennines, its location is coincident with the later fluorite/galena deposits, and King (1982) suggests that its presence may have exerted a structural control on the emplacement of orebodies. Dunham (1990) describes the Weardale Granite as having an anomolously high heat flow and suggests a mantle source for the heat. Though the Weardale Granite had been intruded, exposed by erosion, and reburied prior to the emplacement of the Northern Pennine orefield, it is probable that the granite acted as a localizing conduit for the heat driving the mineralizing process. Several igneous dikes and sills have been intruded into the Carboniferous sedimentary sequence, the largest of which is the Great Whin Sill, a quartz-orthopyroxene diabase (dolerite in British usage) of Late Carboniferous age.

The ore deposits hosted by the Carboniferous sequence are of two types: near-vertical veins of hydrothermal origin and horizontal metasomatic flats. The ore-bearing veins have been intruded as open-space fillings along a series of regional fractures believed to have been created by regional doming at the end of the Carboniferous Period (Sawkins 1966). The main series of fractures trends east-northeast while a secondary set trends west-northwest. Ore minerals were preferentially deposited within the more competent stratigraphic units, typically limestones and hard sandstones. In less competent units such as shales, the ore-bearing veins usually break up into small, poorly mineralized stringers (Dunham 1990). Although the veins were often rich sources of ore, crystallized mineral specimens found in vein cavities were, with a few exceptions, not of the quality found in the flat cavities (King 1982).

The flats are sheetlike metasomatic mineral deposits emplaced along favorable horizons in limestones adjacent to veins. They appear to occur most frequently around the intersection of two or more veins (Dunham 1990). Although flats have been found in nine different limestone units, the majority occur within the Great Limestone, a thick unit forming the base of the Upper Carboniferous series. From studies made at the Boltsburn mine, Dunham (1990) further correlates the occurrence of flats in the Great Limestone with regions where the overlying Coal Sill Sandstone is thin and replaced by shale. Unlike the vein deposits, the metasomatic flats are frequently vuggy and are the source of most crystallized mineral specimens from the district.
The mineralogy of both the veins and flats in the Weardale region is relatively simple. Galena, fluorite, and quartz are common and widespread, and sphalerite, ankerite, siderite, and calcite may be locally abundant. Other sulfides, including pyrite, marcasite, chalcopyrite, and pyrrhotite, are occasionally found as well. Galena was the principal ore recovered from the Weardale mines until the late nineteenth century, and although the silver content of Weardale galena is generally low (averaging 4—8 ounces per ton [Dunham 1990]), some silver was recovered along with the lead. Local concentrations of sphalerite have been mined for zinc, and where sufficiently concentrated by oxidation processes, deposits of ankerite and siderite have proved economic as ores of iron. Fluorite was not an economic commodity until the advent of modern steel-making processes during the late nineteenth century created a demand for it as a fluxing agent. Before that, fluorite encountered in mining was considered waste (or "deads") and used as backfill or dumped. The rise in demand for fluorite coincided with a declining market for lead and helped extend the life of the mining district into the twentieth century.

Barite and witherite also occur in economic concentrations in the northern Pennines, but the distribution of barite-rich deposits is peripheral to the concentrations of fluorite; little, if any, has been mined in the Weardale district proper. Dunham (1937) states that there is a sharp boundary dividing fluorite and barite zones, and the two minerals do not overlap in distribution. Sawkins (1966) has shown that fluorite from the Northern Pennine orefield formed at higher temperatures than the barite, suggesting that a temperature gradient, along with the mixing of hydrothermal solutions with Ba-rich connate waters present in areas surrounding Weardale, resulted in this concentric pattern of mineral deposition.

Based on fluid-inclusion studies, Sawkins (1966) determined that, for the most part, fluorite, quartz, galena, and sphalerite from the Weardale area were deposited at temperatures between approximately 200° and 100°C. In addition, he determined that the Na/K ratios of the included fluids were low, suggesting that the minerals were deposited from hydrothermal solutions of meteoric rather than connate origin. The low temperature of deposition, the presence of meteoric hydrothermal solutions, along with the geographic and temporal relationship of ore deposition to regional doming, and a lack of apparent igneous source indicate that these deposits are genetically similar to the Mississippi Valley—type lead-zinc-fluorite deposits of the central United States. Moorbath (1962) reports a mean lead isotope age for northern Pennine galena of 280 ± 30 m.y., suggesting that regional mineralization occurred during the Permian Period and may be related to Hercynian orogenic activity (King 1982).

Continued in Part II