Blackdene Mine, Weardale

Geological Context

The Blackdene Mine is situated in the Northern Pennine Orefield, a geologically significant region in England. It is located just north of the River Wear, between the villages of St. John's Chapel and Ireshopeburn. The mine's workings follow the Blackdene Vein, which runs northeastward from near the banks of the River Wear, intersecting with the Elmsford Mine's workings on the Slitt Vein.

Economic and Historical Significance

The Blackdene Mine has a rich history of mineral exploitation spanning several centuries:

Early History: Lead mining in this area dates back to at least the early 15th century, demonstrating the long-standing importance of its mineral wealth.

19th Century Development: The Beaumont Company developed the Blackdene Mine proper in the early 19th century, focusing on lead extraction.

20th Century Operations:

• Early 1900s: Fluorspar mining commenced from both the Blackdene and Slitt Veins.
• 1949: United Steel acquired the mine, which was abandoned at this time.
• 1950s: Extensive exploration and development occurred, concentrating on levels between the Three Yard Limestone to below the Scar Limestone.
• 1973: Commercial reserves on the Blackdene Vein were exhausted, leading to the development of a new incline to access unmined portions of the Slitt Vein.
• 1982: Ownership transferred to British Steel following nationalization but was later disposed of due to industry decline.
• 1982-1987: Weardale Mining and Processing operated the mine until its final closure in 1987.

Current Status: The majority of the mine is now inaccessible due to flooding, and accessible areas are badly understoped.

Mineral Assemblage

The Blackdene Mine hosts a diverse array of minerals, including:

1. Ankerite
2. Aragonite
3. Calcite
4. Chalcopyrite
5. Fluorite
6. Galena
7. Pyrite
8. Quartz
9. Siderite
10. Sphalerite

This mineral assemblage is characteristic of hydrothermal vein deposits in the Northern Pennine Orefield.

Mineral Paragenesis and Sequencing

The mineral assemblage at Blackdene Mine reveals a complex paragenetic sequence:

Primary Mineralisation: The sulphide minerals chalcopyrite, galena, pyrite, and sphalerite formed from metal-rich hydrothermal fluids circulating through the rock.

Gangue Minerals: Quartz and fluorite, common gangue minerals in hydrothermal vein deposits, formed alongside the sulphide minerals. The historical focus on fluorspar mining in the early 20th century confirms significant deposits of this mineral.

Carbonate Minerals: Ankerite, aragonite, calcite, and siderite represent multiple stages of carbonate mineralisation. These minerals formed during later stages of hydrothermal activity and subsequent alteration processes.

The mineral assemblage at Blackdene Mine reflects a series of mineralisation events, each contributing to the complex geological history of the site.

Conclusion

The Blackdene Mine in County Durham, England, stands as a significant mineralogical and historical site within the Northern Pennine Orefield. Its diverse mineral assemblage reflects the complex geological processes that shaped this region.

The mine's development history, including the shift from the Blackdene Vein to the Slitt Vein as reserves were depleted, demonstrates the adaptability required in long-term mining operations. This transition from lead mining to fluorspar extraction in the 20th century underscores the mine's economic importance and the evolving focus of mineral exploitation over time.

Specimens from Blackdene Mine are highly prized by collectors, particularly its fluorite. The fluorite from this locality is known for its exceptional fluorescence, displaying vibrant colours under ultraviolet light. This property, combined with the mine's rich history, makes Blackdene specimens especially desirable in the mineralogical community. The current inaccessibility of much of the mine due to flooding has only increased the value of existing specimens, as they represent a now-closed chapter in British mining history.