At current prices, that would give the Cononish project a rate of return of about 37% before tax and see the initial investment repaid within 26 months of the start of production.

BBC: Falling gold prices delay plans to reopen Cononish mine

When you invest in a project your primary concern is that your rate of return exceed the rate of interest that you are paying.

FORBES: Interest Rates and the Consumer

In turn, that lower interest rate should help Kilroy realize a return on the project of about 7%, better than the below-5% return that many investors are getting by acquiring existing buildings.

WSJ: Hooray for Hollywood! Columbia Square Redevelopment Is Slated

He expects an internal rate of return of between 15% and 20% over the project's lifetime.

ECONOMIST: Urban regeneration