Here’s another example of what I often argue — that mined out or decommissioned open pit mines should as much as possible be left as is, not covered with soil then reforested. Multiple purposes: (a) as man-made dam and lake to catch excess water and flash flood, (b) reduce flooding downstream during heavy rains, (c) use the lake water for fishery, irrigation, hydro-power, even possible drinking water source someday, (d) or simply for eco-tourism.
Nice story here from Sunstar Cebu.
AN OLD mining pit in western Cebu has turned into a popular site for social media-worthy selfies and groufies. Trees dot the slopes of the Biga Pit, providing a refreshing contrast to the barren, rocky slopes of two other open pits within the vast mines of Carmen Copper Corp. in Toledo City, Cebu. Visitors are greeted by, not a huge gaping hole with excavators and dump trucks at the bottom but, a stunning vista of a man-made lake with turquoise water.….
Biga Pit is one of three mining pits at the Toledo copper mines, currently the biggest in the country. The mines, sprawled across four villages, are situated about 50 kilometers west of Cebu City. The other two mining pits are Carmen and Lutopan. Only Carmen Pit is active, producing an average of 42,000 dry metric tons (DMT) of copper ore daily. Operations at Lutopan Pit, which still holds ore reserves of about 180 million metric tons, have been suspended and are expected to resume in 2021.
Biga Pit has been decommissioned and currently serves as the mine tailings storage facility, with an estimated operating life of 11 years. Underneath that turquoise water are tons of tailings, or the materials left after the valuable elements are extracted from the ores.
On its website, Carmen Copper said water at the Biga lake has a pH level of 7.5 to 8, which is within the normal range for surface water and safe enough for fish like tilapia to thrive in. In general, surface water with a pH level of more than 7 is considered basic while a pH level of less than 7 is considered acidic.