When searching in Google:

"In a polymetallic mine, the cut-off may be expressed as an 'equivalent grade' of the primary metal, or by the net smelter return (NSR) value of the mineralized material. That cut-off will be whatever grade is needed to recover enough metal or mineral to pay the cash costs of production"

In other words, my understanding is that the NSR cut off value might be a good indication of the C1 cash cost. 

It was reported in January 2021 that the NSR cut off value used for the new RE is US$4.31/t.

Per year, SC is expected to generate: 133 000 tpd x 365 days x 0.92 (availability) = 44.7M tonnes.

This result in 385 000 tonnes of concentrate that would translate in approx. 350Mlbs of CuEq.

350Mlbs of CuEq / 44.7M tonnes per year = 7.83 lbs of CuEq produced per tonne.

US$ 4.31/t divided by 7.83 lbs of CuEq per tonne = US$0.55 per pound of copper (possible LOM C1 cost)

If we refer to the 2013 FS, we could assume that production might be higher in the initial years, which would lower the C1 cost.

Example:

• 410Mlbs CuEq years 1 to 7 should lower the cost from US$0.55 to US$0.47
• 325Mlbs CuEq years 8 to 21 should increase the cost from US$0.55 to US $0.59

Higher production and lower cost in the initial years = higher NPV

Not sure if the above make total sense, but the numbers do seem to align...

IMO.

MoneyK