Five Largest Gold Mines in China are all UndergroundThe reason is obvious as it is elsewhere .
Open pit deposits are the uplifted portion of dessiminated gold that becomes oxidized through the weathering process .
The source of this gold is the basement motherlodes which can extend to depths in excess of 1000 m below the base of the open pit and whose grades are doubles or more of the surface pit oxide gold.
With 2.5 million ounces exposed todate by the Songj open pit mine, it's a highly probable bet that the underground gold resource at Songi will be in excess of 5 million ounces once underground mining replaces open pit mining in a decade or so.
So, potential mine life here including the inevitable transit to underground mining will be well over 40 years ....
https://www.mining-technology.com/marketdata/five-largest-gold-mines-china-2020/