Activities in mineral deposit modeling have continued to develop on several fronts since the publication of "Mineral Deposit Models," edited by Cox and Singer (1986). That bulletin is a collection of 87 descriptive deposit models and 60 grade and tonnage models prepared by many authors both from within and outside of the U.S. Geological Survey. The present bulletin continues that effort with the addition of new or revised models. Before these models are introduced, a review of modeling as used here is provided as well as an overview of mineral deposit modeling since the publication of Cox and Singer (1986).
Explanation of Descriptive and Grade and Tonnage Models
A general definition of a mineral deposit model as found in Cox and Singer (1986, p. 2) is "the systematically arranged information describing the essential attributes (properties) of a class of mineral deposits. The model may be empirical (descriptive), in which instance the various attributes are recognized as essential even though their relationships are unknown; or it may be theoretical (genetic), in which instance the attributes are interrelated through some fundamental concept."
With a descriptive model in hand, member deposits can be recognized and their size and grades can be used to develop a grade and tonnage model. Ideally, the data should be the estimated premining tonnages and grades. Estimates should be for the tonnage at the lowest cut-off grades. The grade and tonnage model is presented in a graphical format in order to make it easy to display the data and to compare this type of deposit with other deposit types (Cox and Singer, 1986). The plots show either grade or tonnage on the horizontal axis, whereas the vertical axis is always the cumulative proportion of deposits. The units are all metric, and a logarithmic scale is used for tonnage and most grades. Each dot represents an individual deposit, and the deposits are cumulated in ascending grade or tonnage.
Due to limitations in the plot route, a point will not be shown on the plot if it has exactly the same value as the vertical axis (e.g., the Keystone-Union deposit is not displayed in figure 12). On rare occasion, values less than the value of the vertical axis are not shown as well (e.g., Hog Ranch is not displayed in figure 16). Smoothed curves, representing percentiles of a lognormal distribution that has the same mean and standard deviation as the observed data are plotted through the points. Intercepts for the 90th, 50th, and 10th percentiles of the log-normal distributions are constructed.
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