Hi, Analogueman:

Here is a brief description of the mining term "NSR" for your perusal:

The Gross, or Net Smelter Return (NSR) Royalty, is characterized by royalty payments that are a fixed or variable percentage of the sales price, or gross revenue, the mining operator receives from the sale of mineral product from the property. The mining operator's gross revenue, in metal mines, is often referred to as Net Smelter Return because it is common for the mining operator to sell the mineral product in a form that requires further processing by a smelter or refinery. The Net Smelter Return is the amount of money which the smelter or refinery pays the mining operator for the mineral product and is usually based on a spot, or current price of the mineral, with deductions for the costs associated with further processing. In non-metal mines the selling price is usually 'fob mine site' because of the transportation costs involved in delivering the mineral product to the buyer.

Source: http://www.minval.com/royalty_mineral.html

This is an abridged definition only, further information is available from the above source, or Wikipedia, etc.

Best regards,