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Clara Mine, Oberwolfach, Freiburg Region
The Clara Mine is located in Oberwolfach, in the Black Forest region of Baden-Württemberg, Germany. The mine is situated within the Friedrich Christian Herrensegen Fault Zone, which is part of the larger Black Forest Gneiss Complex. This geological setting has played a crucial role in the formation of the mineral-rich veins exploited by the mine.
The primary rock types in the area include gneiss and Triassic sandstone, which host numerous baryte and fluorite veins. These veins are the result of hydrothermal activity associated with the regional tectonic events that shaped the Black Forest. The deposit has undergone four distinct mineralisation episodes, each contributing different elements and creating new minerals. This complex geological history has resulted in an exceptionally diverse mineral assemblage.
Mineral Paragenesis and Sequencing
The mineral assemblage at Clara Mine reflects a complex paragenetic sequence influenced by multiple mineralisation events. Based on the extensive list provided in Mindat, we can identify several key stages of mineral formation:
- Primary Sulphide Stage: This early stage is characterised by the formation of sulphide minerals such as pyrite, chalcopyrite, galena, and sphalerite.
- Baryte-Fluorite Stage: The main ore-forming stage, resulting in the deposition of baryte and fluorite, which are the primary economic minerals of the mine.
- Copper-Arsenic Stage: This stage is marked by the formation of various copper and arsenic minerals, including enargite, tennantite, and arsenopyrite.
- Secondary Mineral Stage: This involves the alteration of primary minerals, leading to the formation of numerous secondary minerals, particularly copper and arsenic species like malachite, azurite, and scorodite.
- Supergene Alteration Stage: The final stage, characterised by the formation of various oxide, hydroxide, and hydrated minerals due to weathering processes.
The sequence of mineral deposition is influenced by factors such as changing temperature, pressure, and fluid composition over time. For example, the early sulphide minerals likely formed at higher temperatures, while the later secondary and supergene minerals formed under cooler, more oxidising conditions near the surface.
Associated Minerals
The Clara Mine is renowned for its mineral diversity. Some of the most notable associated minerals include:
- Copper minerals: Azurite, malachite, chrysocolla, and cuprite
- Arsenic minerals: Scorodite, arsenopyrite, and various arsenates
- Lead minerals: Pyromorphite, mimetite, and cerussite
- Silver minerals: Native silver, argentite, and various silver sulfosalts
- Rare earth minerals: Bastnäsite, monazite, and xenotime
These associated minerals play significant roles in the paragenetic sequence, often forming as a result of alteration or replacement of primary minerals. For instance, malachite and azurite commonly form from the alteration of primary copper sulphides, while scorodite may result from the oxidation of arsenopyrite.
Mineral Diversity
According to Mindat, the Clara Mine boasts an impressive 457 different mineral species. This exceptional diversity reflects the complex geological history of the site and the various mineralisation events that have occurred over time.
Type Locality Minerals
Clara Mine is the type locality for several minerals, highlighting its geological significance. Based on Mindat, the following 17 minerals are listed as type locality (TL) specimens:
- Agardite-(Ce)
- Arsenbrackebuschite
- Arsenocrandallite
- Arsenogorceixite
- Arsenogoyazite
- Bariopharmacosiderite
- Benauite
- Claraite
- Cualstibite
- Nollmotzite
- Oberwolfachite
- Phosphofibrite
- Phyllotungstite
- Rankachite
- Slottaite
- Tungstibite
- Uranotungstite
These type locality minerals represent unique or first-discovered species at Clara Mine, further emphasising the exceptional mineral diversity of this deposit.
The unusual mineral diversity at Clara Mine can be attributed to its complex geological history, involving multiple mineralisation events and a wide range of physicochemical conditions. The interplay between primary hydrothermal deposition and subsequent alteration processes has created an environment conducive to the formation of numerous rare and interesting mineral species.
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