1_Readme Title: Assessment method for epithermal gold deposits in northeast Washington State using weights-of-evidence GIS modeling By D.E. Boleneus, G.L. Raines, J.D. Causey, A.A. Bookstrom, T.P. Frost, and P.C. Hyndman Open-File Report 01-501 Manuscript approved December 31, 2001 Prepared in cooperation with the USDA Forest Service, Pacific Northwest Region, Okanogan and Colville National Forests This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although these programs have been used by the US Geological Survey, no warranty, expressed or implied, is made by the USGS as to the accuracy and functioning of the programs and related program material, nor shall the fact of distribution constitute any such warranty, and no responsibility is assumed by the USGS in connection therewith. U.S. DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY Contents: Abstract Introduction Weights of Evidence Training sites Analysis of geologic patterns for epithermal model Measures of mineral activity Assessment of future mineral industry activity Conclusions References Cited Appendix I. Databases II. Glossary 12 Figures 9 Tables Digital data and files: Text and data from this report can be found on the internet at the USGS website: http://pubs.usgs.gov/of/2001/of01-501/ Text and other files accompanying this report are listed below: [txt -- ascii text document, PDF -- Adobe Acrobat Portable Document Format, doc -- MS Microsoft Word document, JPEG -- raster image compression format] Name of file Name of folder Type Description 1_readme.txt root txt General information of01-501 root doc Report text and tables fig1, fig4ab, fig6, fig9, fig10, fig12 jpg JPEG Figures 1, 4, 6, 9, 10, 12 fig1, fig4ab, fig6, fig9, fig10, fig12 pdf PDF Figures 1, 4, 6, 9, 10, 12 (600 dpi) JPEG and PDF files--These files are provided in event that user has need for the figures in different formats. ArcView shapefiles may be obtained from the author on an informal basis, but are not a part of this publication. ABSTRACT--The weights-of-evidence analysis, a quantitative mineral resource mapping tool, is used to delineate favorable areas for epithermal gold deposits and to predict future exploration activity of the mineral industry for similar deposits in a four-county area (222 km x 277 km), including the Okanogan and Colville National Forests of northeastern Washington. Modeling is applied in six steps: (1) building a spatial digital database, (2) extracting predictive evidence for a particular deposit, based on an exploration model, (3) calculating relative weights for each predictive map, (4) combining the geologic evidence maps to predict the location of undiscovered mineral resources and (5) measuring the intensity of recent exploration activity by use of mining claims on federal lands, and (6) combining mineral resource and exploration activity into an assessment model of future mining activity. The analysis is accomplished on a personal computer using ArcView GIS platform with Spatial Analyst and Weights-of-Evidence software. In accord with the descriptive model for epithermal gold deposits, digital geologic evidential themes assembled include lithologic map units, thrust faults, normal faults, and igneous dikes. Similarly, geochemical evidential themes include placer gold deposits and gold and silver analyses from stream sediment (silt) samples from National Forest lands. Fifty mines, prospects, or occurrences of epithermal gold deposits, the training set, define the appropriate areally-associated terrane. The areal (or spatial) correlation of each evidential theme with the training set yield predictor theme maps for lithology, placer sites and normal faults. The weights-of-evidence analysis disqualified the thrust fault, dike, and gold and silver silt analyses evidential themes because they lacked spatial correlation with the training set. The decision to accept or reject evidential themes as predictors is assisted by considering probabilistic data consisting of weights and contrast values calculated for themes according to areal correlation with the training sites. Predictor themes having acceptable weights and contrast values are combined into a preliminary model to predict the locations of undiscovered epithermal gold deposits. This model facilitates ranking of tracts as non-permissive, permissive or favorable categories based on exclusionary, passive, and active criteria through evaluation of probabilistic data provided by interaction of predictor themes. The method is very similar to the visual inspection method of drawing conclusions from anomalies on a manually overlain system of maps. This method serves as a model for future mineral assessment procedures because of its objective nature. To develop a model to predict future exploration activity, the locations of lode mining claims were summarized for 1980, 1985, 1990, and 1996. Land parcels containing historic claims were identified either as those with mining claims present in 1980 or valid claims present in 1985. Current claim parcels were identified as those containing valid lode claims in either 1990 or 1996. A consistent parcel contains both historic and current claims. The epithermal gold and mining claim activity models were combined into an assessment (or mineral resource-activity) model to assist in land use decisions by providing a prediction of mineral exploration activity on federal land in the next decade. Ranks in the assessment model are: (1) no activity, (2) low activity, (3) low to moderate activity, (4) moderate activity and (5) high activity. Primary author current address: email dboleneu1@juno.com