Although the archipelago was named in the 16th century for the fabled gold mines of King Solomon and had long-term mining potential, there have been insufficient high-quality mineral deposits to justify extensive mining investment. Mining was nevertheless the second-leading industry in 2002. Because of political and ethnic violence, mineral production in 2001 was limited to small quantities of common clays, crushed stone, and sand and gravel, and no gold or silver mining was reported (a minor amount of gold, and possibly associated silver, was obtained from primitive panning and sluicing by individuals); in 1999, production was 3,456 kg of gold and 2,138 of silver. The Gold Ridge Mine, at Mavu, which was closed from mid-2000 through the end of 2001, had undertaken a study to upgrade production from 3,100 kg per year to 4,500–4,700 kg per year, which could increase the mining sector's contribution to GDP from 1% to 15%. The country's main industrial prospects focused on its undeveloped mineral resources of gold-silver, lead-zinc, nickel, and phosphate. Deposits of bauxite, copper, chromite, and manganese ores have also been found.