GRADE AND TONNAGE MODEL OF HOT-SPRING GOLD-SILVER

by Byron R. Berger and Donald A. Singer

COMMENTS This model applies to the descriptive model for Hot-spring Au-Ag, number 25a, by Berger (1986a). It is a modified version of a previously published report (Berger and Singer, 1987). Estimated pre-mining tonnages and grades from the deposits listed below were used to construct the model. Where several different estimates were available for a deposit, the estimated tonnage associated with lowest cutoff grades was used.

The grade-tonnage model is presented in a graphical format to make it easy to compare this type with other deposit types (Cox and Singer,1986), and to display the data. The plots (figures 1-3) 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 gold and silver grade. Each dot represents an individual deposit and the deposits are cumulated in ascending grade or tonnage. 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 lognormal distributions are constructed.

No significant correlations between grades and tonnages were observed.

Table X. Grades and tonnages of hot-spring Au-Ag deposits

[ tonnage in million metric tonnes; gold and silver grades in grams per metric ton.]