Gouache painting of mineralizing fluids. This painting shows how mineral veins in the North Pennines were formed. Mineral-rich waters (represented by the arrows), heated by the Weardale Granite intrusion circulated through cracks and faults in the overlying rocks (a sequence of Carboniferous limestones, shales and sandstones), depositing minerals as they cooled. The mineral veins in the North Pennines area were formed from deep saline water solutions which contained dissolved minerals. These contained iron, lead and copper minerals which were dissolved from surrounding rocks, including the Weardale Granite. The granite acted as a 'heat engine', warming the water and causing it to flow in a convection circuit along faults and fissures. As the fluids cooled, the dissolved minerals crystallized as crusts on the fissure walls. The North Pennines area in northern England has been designated an Area of Outstanding Natural Beauty and is also the site of Britain's first 'European Geopark'. The area is one of high fells, open moorland and wide dales. The unique character of the area owes much to human activity over hundreds of years, especially in relation to mining of the mineral deposits in the rocks.
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