Mineral resources versus geologic diversity in small areas

Abstract

There is a simple linear relationship between geologic diversity ( = the number of rock types — 1) and the mineral-resource diversity ( = the number of commodities produced — 1) which may be used to predict the number of commodities produced from a given number of geologic rock types in a region. In addition it is shown that the geologic and mineral-resource diversities are related positively to size (expressed as log A km 2) of sampling unit. It is of some interest to determine whether these relationships hold for sample units the size of counties. 182 counties from six states, Maine (16), New Hamshire (10), Vermont (14), Pennsylvania (67), Nevada (17), and California (58) are used to investigate these relationships. The regression of geologic diversity ( s g − 1) on size (log A) is positive, linear, and about r 2 = 41.0% determining. Similarly, the regression of mineral-resource diversity ( s m − 1) on size (log A) is positive, linear, and r 2 = 39.6% determining. The regression of mineral resource on geologic diversity also is similarly linear and positive with r 2 = 54% determining. The regression of geologic diversity on size for a larger global population ( n = 413; where sample units are countries and states) is similar to that for the 182 counties with r 2 = 48% determining. Evidently, the relationships hold for sample units the size of counties with a similar slope but a smaller intercept. It then is shown that for sample units the size of states and countries (i.e. log A from 3.0 to 6.5) the intercept is about 12. In other words, given a sample unit the size of states or countries with a geologic diversity of zero, the region is geologically homogeneous, one would expect it to produce some 12 commodities; on the other hand if the sample unit is the size of counties with the same value of zero for geologic diversity, then it would likely produce from 3 to 5 commodities.