Extensive Copper, page-54

snakepit
Well one of the worlds biggest new mines Oyu Tolgoi in Mongolia was a BHP cast off after they had dome 3 drilling programs they pulled out. And this was first mined by early humans.:
A minor amount of copper was recovered at the Southern Oyu area during the Bronze Age, as indicated by small circular pits and minor copper smelting slag.

During the 1980s the district was investigated by joint Mongolian-Russian regional geochemical surveys which reported the Central Oyu area as a molybdenum anomaly. In 1996, Mr. Garamjav (now a senior geologist at Turquoise Hill Resources), who first visited the Oyu Tolgoi region in 1983 and noted evidence of alteration and copper staining, guided Magma Copper to the Oyu Tolgoi area. Following the visit exploration tenements were secured by Magma Copper.

BHP Billiton (BHP, which acquired Magma Copper in late 1996) began exploration at Oyu Tolgoi as part of a regional reconnaissance program of the South Gobi desert during the 1997 field season. After geological mapping, stream and soil sediment surveys, magnetic and induced polarization surveys, BHP completed six diamond core holes totalling 1,100 metres in September and October of 1997. With encouraging results a second phase of drilling began. Commencing in April 1998, BHP completed an additional 13 core holes totalling 2,000 metres with positive results obtained in four of the holes. A third phase of drilling was then conducted in August and September, 1998, completing four holes totalling 800 metres. These holes failed to return significant mineralization and the project was suspended pending a review.

In 1999, additional drilling and exploration was recommended; however, further exploration at Oyu Tolgoi by BHP was discontinued due to cut-backs in BHP's exploration budgets. At this time BHP's exploration tenements in Mongolia, including the Oyu Tolgoi exploration concession, were offered for joint venture.

Ivanhoe Mines signed an option agreement with BHP to earn 100% interest in the Oyu Tolgoi Concession in May 2000. A reverse circulation (RC) drill program was initiated by Ivanhoe in June, 2000, completing 109 holes totalling 8,828 metres by September. The program targeted the supergene-enriched, chalcocite blanket discovered in BHP's drill hole OT-3. The results from Ivanhoe's drilling were encouraging, including the discovery of additional high-grade supergene copper mineralization.