Excelsior Mining (TSXV:MIN) is working on developing the Gunnison project, located in the copper porphyry belt in Arizona. At first glance, developing a copper project in Arizona might not turn many heads. However, add low-cost production, a pre-tax net present value of $1.24 billion (discount rate of 7.5 percent) and a 59.7-percent pre-tax internal rate of return (IRR), all while using a copper selling price of $2.75 per pound, and you've got something to talk about. When Excelsior released its prefeasibility study on January 17, the market paid attention, shooting the company's share price up an impressive 358 percent. While some of that hype has calmed, the fact remains that Excelsior holds one of the lowest-cost copper projects in North America. According to Excelsior's study for the Gunnison project, the "acid plant" option indicates that with an annual production rate of 110 million pounds of copper for the first 14 years of a 20-year mine life, and a total of 1.683 billion pounds of copper produced, the company is looking at an average life-of-mine operating cost of $0.68 per pound. The initial capital costs for the project (excluding sustaining capital) are expected to be $284.74 million. One of the features that has resulted in such positive economics for Gunnison is its amenability to in-situ recovery (ISR). Investors are most familiar with ISR when it comes to mining uranium or potash deposits. However, while this type of mining is not common practice when it comes to copper, it has been done before. To learn more about ISR and how it relates to copper, Copper Investing News (CIN) spoke with Excelsior's CEO, Stephen Twyerould. CIN: Excelsior plans to mine its copper using ISR techniques, which are more well known for uranium and potash mining. How do theses techniques apply to copper mining?ST: The main point that I like to get across is that it's not a science experiment; it's not new technology. Basically, what we're doing is the same thing that you find in the uranium space; it's all off-the-shelf technology. You drill a central injection well that's surrounded by recovery wells. Using your central injection well, you feed in a weak acidic solution that dissolves the copper underground. As an example, in South Australia they mine uranium using ISR by injecting a very weak sulfuric acid solution. We would use a similar solution at our copper project. When people hear about this process, people tend to think that the acid is going to spread everywhere; however, it's not that aggressive. To get an idea of the process, imagine you have a glass of cola and it's filled with ice. If you use a straw to drink the cola, then the cola will move through the ice cubes to the straw. This is what it is like with the recovery well in the ground, when we start pumping; it draws the water that's underground towards the recovery well. If in a nearby well we supply the weak acid solution, then it is also drawn through the ground to the recovery well.