Calcite with Marcasite

specimen number:
1655509

location:
Parc Mine, Llanrwst, Gwynedd, Wales, UK

description:
Colorless rhombohedral crystals of calcite across the top of matrix with crystallized marcasite. In good condition.

The Parc Mine, located near Llanrwst in the Gwydir Forest of North Wales, was the largest and most productive lead and zinc operation in the Llanrwst mining district. Geologically, the deposit consists of fissure veins hosted within Ordovician-aged sedimentary and volcanic rocks, specifically siltstones and tuffs of the Nant Ffrancon Subgroup. The mineralization was formed by hydrothermal fluids that deposited galena and sphalerite, often accompanied by quartz and pyrite, along steeply dipping faults. Historically, while mining in the Gwydir Forest area has roots stretching back to the 17th century or earlier, the Parc Mine reached its industrial peak in the 20th century. Major development occurred between 1855 and 1920, with a notable period of modernization and expansion during and after World War II under various owners, including the Johannesburg Consolidated Investment Company. Large-scale commercial extraction finally ended in 1954, though the site was later used for significant metallurgical and environmental research, particularly the Parc Mine Project in the 1960s. Today, the remains of the processing mill and the deep adits serve as important landmarks of the Welsh industrial heritage.

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