Abstract

Different models have been presented by Lovering (1930) and Tweto and Sims (1963) to explain the distribution of epithermal ore deposits in Colorado. GIS analyses using the outlines of mining districts and data from the Mineral Resource Data System of the USGS provided tests of the two models. The results reveal that the Colorado Mineral Belt of Tweto and Sims (1963) does not provide the best correlation with Colorado’s mining districts and known metallic mineral resources (gold, silver, copper, lead, molybdenum, zinc, tellurium, and bismuth).

Components of Lovering’s (1930) model for the Front Range, when applied statewide, provide the most robust correlations — even more so than the correlations with Tweto and Sims’ (1963) “maximum extent” Colorado Mineral Belt. The statewide application of Lovering’s (1930) model accounts for the “anomalous” mining districts of Rosita-Westcliffe, Cripple Creek-Victor, Rito Seco, and Hahns Peak; all of which are excluded from Tweto and Sims’ (1963) “maximum extent” of the Colorado Mineral Belt. The results of this study are also consistent with the detailed work of Caine (2007, 2008), Klein et al. (2008), and Wessel and Ridley (2010) showing that the Proterozoic shear zones are not the primary control for ore deposits in the Front Range.

The results of this study demonstrate that the Proterozoic metamorphic rocks in Colorado provided the first-order, geologic control for the upward migration of Laramide and post-Laramide magmas and ore-forming fluids. Additionally, the analysis confirms Lovering’s (1930) conclusion that Proterozoic granitic plutons acted as barriers to upward migration of magmas and ore-forming fluids during the Tertiary. Moreover, our analysis indicates that the Proterozoic granitic barriers probably diverted and concentrated the ascending fluids near the pluton margins because a high percentage of known mining districts and metallic mineral resources in Colorado occur within one mile of these pluton margins.