Fields in Bangarpet Taluk, Kolar District of Karnataka state, India, gold was first mined prior to the 2nd and 3rd century AD by digging small pits. (Golden objects found in Harappa and Mohenjo-daro have been traced to Kolar through the analysis of impuritiesthe impurities include 11% silver concentration, found only in KGF ore.) The Champion reef at the Kolar gold fields was mined to a depth of during the Gupta period in the fifth century AD. During the Chola period in the 9th and 10th century AD, the scale of the operation grew. The metal continued to be mined by the eleventh century kings of South India, the Vijayanagara Empire from 1336 to 1560, and later by Tipu Sultan, the king of Mysore state and the British. It is estimated that the total gold production in Karnataka to date is 1000 tons. The mining of the Hungarian deposit (present-day Slovakia) primarily around Kremnica was the largest of the Medieval period in Europe. During the 19th century, numerous gold rushes in remote regions around the globe caused large migrations of miners, such as the California Gold Rush of 1849, the Victorian Gold Rush, and the Klondike Gold Rush. The discovery of gold in the Witwatersrand led to the Second Boer War and ultimately the founding of South Africa. Gold-bearing reefs in the neighbouring Free State province were found shortly thereafter, driving significant development in the region with the establishment of the Free State goldfields. The Carlin Trend of Nevada, U.S., was discovered in 1961. Official estimates indicate that total world gold production since the beginning of civilization has been around and total gold production in Nevada is 1.1% of that, ranking Nevada as one of the Earth's primary gold producing regions. As of 2020, the world's largest gold producer was China with 368.3 tonnes of gold mined in that year. The second-largest producer of gold was Russia where 331.1 tonnes was mined in the same year, followed by Australia with 327.8 tonnes. Statistics Despite its decreasing content in ores, gold production is increasing. This increase can be achieved through ever larger-scale industrial installations as well as innovations, especially in hydrometallurgy. Methods Hard rock mining Hard rock gold mining extracts gold encased in rock, rather than fragments in loose sediment, and produces most of the world's gold. Sometimes open-pit mining is used, such as at the Fort Knox Mine in central Alaska.