Porphyry Copper Deposit Tract Definition – A Global Analysis Comparing Geologic Map Scales |
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Authors: | Gary L Raines Katherine A Connors Lesley B Chorlton |
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Institution: | (1) U.S. Geological Survey, c/o Mackay School of Earth Sciences, UNR, Reno, NV 89557, USA;(2) Geologic Data Systems, Denver, CO, USA;(3) Geological Survey of Canada, Ottawa, ON, Canada |
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Abstract: | Geologic maps are a fundamental data source used to define mineral-resource potential tracts for the first step of a mineral
resource assessment. Further, it is generally believed that the scale of the geologic map is a critical consideration. Previously
published research has demonstrated that the U.S. Geological Survey porphyry tracts identified for the United States, which
are based on 1:500,000-scale geology and larger scale data and published at 1:1,000,000 scale, can be approximated using a
more generalized 1:2,500,000-scale geologic map. Comparison of the USGS porphyry tracts for the United States with weights-of-evidence
models made using a 1:10,000,000-scale geologic map, which was made for petroleum applications, and a 1:35,000,000-scale geologic
map, which was created as context for the distribution of porphyry deposits, demonstrates that, again, the USGS US porphyry
tracts identified are similar to tracts defined on features from these small scale maps. In fact, the results using the 1:35,000,000-scale
map show a slightly higher correlation with the USGS US tract definition, probably because the conceptual context for this
small-scale map is more appropriate for porphyry tract definition than either of the other maps. This finding demonstrates
that geologic maps are conceptual maps. The map information shown in each map is selected and generalized for the map to display
the concepts deemed important for the map maker’s purpose. Some geologic maps of small scale prove to be useful for regional
mineral-resource tract definition, despite the decrease in spatial accuracy with decreasing scale. The utility of a particular
geologic map for a particular application is critically dependent on the alignment of the intention of the map maker with
the application. |
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Keywords: | Map scale weights-of-evidence porphyry deposits of world |
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