Abstract

The tonnage-grade analysis presented in this paper is applied to North American porphyry copper deposits. The porphyry copper deposits in five regions are then compared using the tonnage-grade relationship. The analysis is comparable to that of Lasky (1950).The analytical technique that is presented can also be used to construct a metals budget for different types of deposits by region. Either geologically or politically defined regions may be used depending on the reasons for the analysis.A Monte Carlo simulation model that uses the tonnage-grade relationship for the porphyry copper deposits is used to construct metal distribution scenarios. A cumulative metal tonnage curve is constructed to display the simulation results. In addition, a cumulative-percent tonnage metal curve and a cumulative-percent tonnage ore curve are plotted on the same graph to show the relationship of ore to metal in the deposits.Although Lasky found that an inverse relationship exists for ore tonnage and grade within porphyry deposits, this does not appear to be true for metal tonnage and grade for the class as a whole. Deposits average 200 to 300 million tons of ore, and results of the analysis suggest that more metal is contained in the higher grade deposits. About 70 percent of the copper metal occurs in 50 percent of the deposits used for this analysis. These deposits are all above 0.7 percent copper; the remaining deposits in the sample are lower grade primary-sulfide-type deposits.Most deposits found since 1950 contain less than 2 million tons of copper metal. The majority of these deposits are lower grade, primary-sulfide-type deposits. Consequently, as the higher grade previously known deposits are exhausted, it will be necessary to utilize an increasingly large number of lower grade deposits.

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