Copper mines in the Sierra de Tharsis or Sierra de Tarse, north of the port of Huelva in Southern Spain, were rediscovered by a French engineer in 1853 . Ernest Deligny staked his claim in an area which bore the marks of a succession of older copper workings from the sixteenth century, from the period of Roman occupation and, even earlier, from a period of Phoenician colonisation. In 1855 , Deligny managed to persuade a fellow Frenchman, Eugene Duclerc to form a new company known as the C'ie des Mines de Cuivre d'Huelva and, with Duclerc as general manager and Deligny as engineer, they set about mining for pyrites, from which to extract the copper. Unfortunately Deligny and Duclerc proved to be less than effective as engineer and manager and, in 1860 , the directors of the company replaced them with Victor Mercier. Beset with difficulties, particularly in relation to transport, Mercier came into contact with a group of British alkali makers, headed by Charles Tennant ( 1823-1906 ) of Glasgow, Scotland.
The British alkali makers were primarily interested in Mercier's business as a means of obtaining sulphur, a by-product of the process whereby copper is extracted from pyrites. Sulphur was in increasing demand as an important raw material in the manufacture of soap, glassware and in the bleaching and dyeing of textiles. Charles Tennant had become a partner in the family business of Charles Tennant & Co in 1850 . The firm, by that time, was highly successful and was located at the St. Rollox chemical works in Glasgow. It also had interests in sulphur mines in Sicily and sugar estates in Trinidad. Charles Tennant's father, John ( 1796-1878 ), had organised a close alliance between the alkali makers in Britain, which became the basis for the Tharsis Sulphur & Copper Co Ltd , incorporated in Edinburgh, Scotland, in 1862 , which took over the copper mines in the Sierra de Tharsis.
One of the first activities of the new company was to build a railway from the mines to the port of Huelva, a distance of about 30 miles. The company became a major world trader in sulphur and was even able to make some impact on the markets for copper. A final by-product of the process of copper extraction was iron. Tennant set up the Steel Company of Scotland in 1872 in the hopes that a means might be discovered for processing the "billy blue" iron ore that was left once copper and sulphur had been removed. Unfortunately this proved too difficult although the Steel Company of Scotland carried on in to the 1890s, using the more conventional raw material of pig iron and scrap, producing mild steel, particularly for the ship-building industry.
In 1871 , Tharsis Sulphur & Copper Co Ltd had works at St Rollox and offices at 136 West George Street, Glasgow. At that date the resident manager at the St Rollox Works was James Dryburgh and the secretary in West George Street was Jonathan Thomson. Tennant resigned from the chairmanship of the company in 1906 . In 1960 , the chairman and managing director of the company was W P Rutherford, and it was supplying sulphur products, essential in the manufacture of man-made fibres, dye-stuffs and fertilisers. Around 1981 , the Company became Tharsis plc . In 1991 , Tharsis plc , still located at 136 West George Street, were describing themselves as pyrites merchants. In 1998 , the company's head offices moved to 48 West Regent Street, Glasgow.