centuries had been a thorn in the side of the Dukes of Brunswick-Wolfenbüttel ruling over the adjacent Harz estates. In 1552 – after decades of legal proceedings, feuds and skirmishing – Duke Henry V took the occasion of the city's weakened position upon the Schmalkaldic War and seized ownership of the mines from the citizens. Mining operations were further promoted by Henry's son and successor Duke Julius of Brunswick-Wolfenbüttel from 1568. During the Thirty Years' War the Goslar citizens once again tried to regain the Rammelsberg mines distinguishing themselves as loyal supporters of the Imperial forces against the Protestant commander Christian the Younger of Brunswick; however, to no avail as his nephew Duke Augustus the Younger reconciled with Emperor Ferdinand in 1642. Under the Welf dukes, gold was also won from the 18th century onwards. With Goslar the Rammelsberg mines passed to the Kingdom of Hanover in 1814 and to the Kingdom of Prussia in 1866. Under the 1936/37 Rammelsbergprojekt, the mine was greatly expanded at the behest of the Nazi authorities as part of the Four-year plan. The Nazis saw the Rammelsberg with its metal ores as vital to their war efforts and the difficulty of mineral dressing the ore had been technically solved (using froth flotation). This led to the construction of the present-day surface installations including the hillside processing plant and Rammelsberg shaft. The architects were Fritz Schupp and Martin Kremmer, who designed other important industrial buildings (including the Zeche Zollverein in the Ruhr area, now also a UNESCO World Heritage Site). After more than 1000 years during which almost 30 million tonnes of ore were extracted, the mine was finally closed by the Preussag company on 30 June 1988 as the mineral deposits had been largely exhausted. A citizens' association argued forcefully against plans to demolish the surface installations and fill in the historic underground mine workings. Consequently, the disused mine was developed into a museum to preserve its heritage and display the history of the mine and its industrial equipment. Prospecting in 2009 In February 2009, the company, Scandinavian Highlands Holding A/S, published the results of geophysical investigations by its subsidiary, Harz Minerals GmbH, according to which hitherto unknown mineral deposits of the size of those at the Rammelsberg may be present, two kilometres west of the Rammelsberg ore deposits. In autumn 2009 several exploratory bores were sunk in the area of the Hessenkopf and