Mineral Resource Derivative Maps
Mineral Evaluations and Maps by John W. Keller; Map viewers by F. Scot Fitzgerald
Mineral resource derivative maps were constructed by the CGS using 7.5 minute quadrangles published under the current CGS STATEMAP geologic mapping program. Derivative maps are qualitative generalizations of detailed geological information that are used to assist in evaluating complex geological information. These maps were created from digital geologic map data and historical mine locations to provide information on the general distribution of select potential mineral resources. They may be used as a general guide: a more detailed analysis is required to determine the economic viability of these units.
The derivative maps were produced for the following three general resource types:
1) Construction aggregate materials;
2) Industrial minerals; and
3) Placer gold
These resources were further subdivided into the categories presented in Table 1 (see below). Ratings were assigned to geological units based on their potential to contain economically viable mineral resources. The rating system, criteria, and general notes are presented in Table 2 (see below). Certain mineral resources were not evaluated because they were not conducive to derivative mapping of surface units (e.g. uranium, coal, oil and gas, bedrock-hosted lode gold/silver, gold/silver/base metal, molybdenum/tungsten, and sediment-hosted copper). For example, these deposits may be deep and unrelated to the units mapped at the surface.
Table 1. Resource Categories used in the derivative maps
|GENERAL RESOURCE TYPE||CATEGORY AND DESCRIPTION / NOTES|
Construction Aggregate Materials (AGG)
|Sand and Gravel – Construction aggregate; may also include rip-rap and landscaping material. Does not include fill or borrow material.|
|Decomposed Granite – Rated only for bedrock units such as Pikes Peak Granite (in-place but friable due to partial weathering). Only rated in the region of the Pikes Peak batholith.|
|Crushed Stone – Construction aggregate; may also include rip-rap and landscaping material.|
Industrial Minerals (IM)
|Clay, Claystone, and/or Shale – May include any of the following: ball clay, bentonite, common clay, fire clay, Fuller’s earth, and kaolin. Also, claystone/shale for lightweight aggregate (see the United States Geological Survey [USGS] commodity reports for clays at http://minerals.usgs.gov/minerals/pubs/commodity/clays/).|
|Fluorite/Fluorspar – In Colorado, usually in vein deposits too narrow to show on 1:24,000 scale geologic maps.|
|Limestone and/or Dolomite – Non-aggregate industrial uses may include any of the following: cement manufacturing, lime manufacturing, fluxing agent, soil conditioning, water, waste treatment, and other miscellaneous uses (see the USGS commodity reports for crushed stone at http://minerals.usgs.gov/minerals/pubs/commodity/stone_crushed/).|
|Peat – Includes unconsolidated organic material.|
|Pegmatite – Pegmatite-hosted minerals, undivided; principally feldspar, mica, quartz, beryl, and locally lithium in Colorado. May also locally contain small resources of rare earth elements (REE’s) (e.g. niobium) as well as columbite-tantalite, garnet, and other minerals.|
|Perlite – Lightweight aggregate, soil conditioner, filtration, and fillers.|
|Evaporite Salts – Includes potential halite and sylvite (a potash source).|
|Silica – May include silica sand, quartzite, and high-silica sand/sandstone.|
|Dimension Stone – Building construction, flagstone, paver stone, countertops, monuments, ornaments, etc.|
|Volcanic Ash – May also include pumice and scoria.|
|Metals (MET)||Placer Gold|
|Rare Earth Elements (REEs)|
Table 2. Mineral potential numeric rating system used in the derivative maps
|Mineral Potential Numeric Rating||Numeric Rating System Description and General Criteria|
|HIGH POTENTIAL (Red) – Area of mapped geological unit(s) as described has a high potential to contain economically viable mineral resources and units with similar characteristics have produced mineral resources locally. Area (e.g. ArcGIS polygon) may contain active or inactive mines. May include “mine waste” areas (e.g. Fairplay, Colorado area placer gold). In exceptional cases, new areas (e.g. ArcGIS polygons) were created where original geologic mapping did not adequately differentiate between a larger host unit and where a mineral deposit of mappable areal extent exists (e.g. the Homestake Pegmatite in the Cameron Mountain quadrangle).|
|MEDIUM POTENTIAL (Yellow) – Area of mapped geologic unit(s) as described has a moderate potential to contain economically viable mineral resources based on geologic unit description, other publications specific to the area or formation, and/or past regional resource use patterns. Lithological descriptions indicate that portions of the mapped geologic unit may contain mineral resources and similar geological formations may have been productive elsewhere in Colorado.|
|LOW POTENTIAL (Blue) – Area of mapped geologic unit(s) as described has a low potential to contain economically viable mineral resources of this type in the mapped area.|
|NO POTENTIAL (Light Grey) – Area of mapped geologic unit(s) as described has no potential to host mineral resources in the mapped area. For example, crystalline bedrock units have no potential to contain sand and gravel resources. Also includes areas mapped as water, artificial fill, and landfill.|
|Notes and Additional Criteria|
|(1) Ratings for construction aggregate materials may vary between different areas/polygons of the same formation/lithology on the same quadrangle based on the interpretation of variables associated with economic potential including steepness of terrain, altitude, remoteness (e.g. absence of access roads), and the potential for the material to be adversely affected by hydrothermal alteration and/or excessive fracturing. For example, some igneous intrusions may often be rated a “3” for crushed stone aggregate; however, the presence of numerous metal mines in the vicinity indicates the high likelihood that hydrothermal alteration has greatly softened the rock imparting a high degree of physical heterogeneity making it less suitable for use as “Construction Aggregate”. Therefore, it may receive a rating of “2” or “1” due to these factors and the areas/polygons have not been split.|
|(2) In general, construction aggregate material resources (e.g. sand and gravel, crushed stone, etc.) areas/polygons should be at least 3 acres in size and have a minimum estimated average exposed width of about 250 feet to qualify for a rating of “2” or above. Small polygons may have high ratings if they are mapped adjacent to a larger units with similar physical characteristics and higher resource potential.|
|(3) Ratings for areas/polygons of some surficial units, particularly Qa (alluvium), Qf (fan deposits), and Qac (alluvium and colluvium), are often rated differently within the same quadrangle map due to differences in clast composition and quality inferred from bedrock mapped in the source area drainages, differences in morphology, size or width of unit, remoteness, and steepness.|
|(4) In general, mapped geologic areas/polygons have not been split during this evaluation. The mineral potential rating for areas/polygons is based on the highest rating for any part of the polygon. Portions of the same polygon will in reality have different actual mineral economic potential than other parts. For example, a single mapped area/polygon of Quaternary alluvium may be broad/thick in a low valley area (high potential) and thin/narrow in an upland area (low or medium potential). In this example, the area/polygon will be rated high potential (“3”). In rare cases, new areas/polygons were created where original geological mapping did not adequately differentiate between a larger “host” unit and where a mineral deposit of mappable areal extent exists (e.g. Homestake pegmatite, Cameron Mountain quadrangle).|
|(5) In the Keystone quadrangle, all Proterozoic units were given only a moderate rating (“2”) for crushed stone due to abundant shearing, faulting, brecciation and alteration in the hanging wall of the Williams Range thrust fault and numerous other major faults. Additionally, hydrothermal alteration associated with igneous intrusions and “mineral belt” shear zones reduces aggregate potential.|
The mineral derivative maps are subdivided into four geographic regions shown in the figure above: Front Range, Central Mountain, West-Central, and South-Southwest. Each region includes several USGS 7.5-minute quadrangles as shown below.
CLICK the region of interest in the map below to view the derivative maps for that area. Please be patient while the map loads.
Front Range – Mineral Derivative Maps
The Front Range mineral derivative map areas are listed below and include the following quadrangles:
|Cabin Gulch||Eastonville||Mount Deception|
|Castle Rock North||Elizabeth||Palmer Lake|
|Castle Rock South||Elsmere||Pikeview|
|Cherry Valley School||Falcon||Ponderosa Park|
|Cheyenne Mountain||Falcon NW||Russelville Gulch|
|Dakan Mountain||Larkspur||Watkins SE|
|Dawson Butte||Manitou Springs|
Central Mountains – Mineral Derivative Maps
The Central Mountain mineral derivative map areas are listed below and include the following quadrangles:
|Antero Reservoir||Copper Mountain||Keystone|
|Breckenridge||Fairplay East||Leadville South|
|Buena Vista East||Fairplay West||Marmot Peak|
|Buena Vista West||Garo||Maysville|
|Castle Rock Gulch||Gribbles Park||Salida East|
|Jack Hall Mountain|
West Central Mountains – Mineral Derivative Maps
The West-Central Mountain mineral derivative map areas are listed below and include the following quadrangles:
South-Southwest – Mineral Derivative Maps
The South-Southwest mineral derivative map areas are listed below and include the following quadrangles:
|Culebra Peak (southern half)||La Valley|
|Durango East||Ludwig Mountain|
|Durango West||Rules Hill|
|Electra Lake||Taylor Ranch|
|Fort Garland SW||Vellecito Reservoir|
Notes about the Mineral Derivative Map links and the Mapviewer
After you click on the link to the mapviewer, perform the following to view the mineral derivative maps:
1.) Check one of the commodities you would like to view (NOTE: only one commodity can be viewed clearly at one time, the map viewer will only show the top commodity that is turned on in the Layer List tab);
2.) Zoom in to the quadrangle or region you would like to view (NOTE: the mineral derivative mapping is visible only when zoomed into the map. If you look at the scale in the bottom left of the map, when you get to the “2 Mile” zoom, the polygons will start to populate);
3.) If you wish to view another mineral derivative map commodity, deselect the current one, and then select another commodity further down the list. Just note that the topmost one turned on will be the only one to show);
4.) The “Basemap” feature at the top of the mapviewer allows the user to include recent satellite/aerial imagery, Topographic maps, terrain, etc.
Water features are colored a light cyan color.
Black lines within each area are the boundaries of geological formations/units. Geologic formation/unit codes can be displayed by clicking on the area of interest with the “i” button. These geological codes and areas are described in each individual geologic quadrangle map and are included for reference purposes only. The individual geologic quadrangle maps are also available for free download on the CGS Bookstore. Use the SEARCH bar and type in the quadrangle name.
The polygon ratings for mineral resource potential were interpreted for each CGS geologic quadrangle maps using the following methods:
- Each CGS STATEMAP geologic map quadrangle, including the accompanying report for the quadrangle and the detailed descriptions of map units, was carefully studied. Many of the map reports contain sections on known mineral resources located in and near the quadrangle, and descriptions of map units often contain the map author’s opinion regarding the mineral potential of map units, particularly for use as construction aggregate.
- An ArcMap 10.1 project was created for each quadrangle, beginning with the ESRI shapefiles or geodatabases that contain the polygons for each mapped geologic unit. Shapefiles were quality-checked with the published .PDF versions of the map to ensure that shapefile polygons corresponded to the final published map product.
- Statewide and regional mineral resource and mining publications and public databases in GIS format were imported into the ArcMap projects and compared to mapped geological units.
- Georeferenced USDA NAIP aerial composite orthoimages from 2011 were imported and used to help determine the actual locations of historic and current mines, quarries, and gravel pits in relation to mapped geological units.
- Numerous non-GIS publications relating to Colorado mineral resources were reviewed.
- Using the above information and other knowledge acquired through professional experience, each geologic polygon or group of polygons were given a rating of 0 (no potential) to 3 (high potential) for each mineral category evaluated. The highest ratings were given to geological units that have known current or historic mining activity within the quadrangle or adjacent quadrangles. Moderate ratings were applied to geologic units having had at least some statewide or regional mineral production, and whose detailed geologic description indicates the possibility that the unit contains useful mineral resources. Low ratings (1) were applied when the unit is unlikely to contain economically viable mineral resources under present circumstances. A rating of zero (0) was applied when there is no possibility of that mapped unit containing mineral resources in the category evaluated, or that by definition it cannot contain resources in the category. For example, all unconsolidated Quaternary surficial deposits received a rating of “0” for crushed stone aggregate because for the purposes of this project, crushed stone is defined only as material derived by crushing bedrock units.
- Ratings of polygons on adjacent quadrangles were compared, and any discrepancies between ratings were re-evaluated and made consistent across quadrangle boundaries.
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Argall, G.O., 1949, Industrial minerals of Colorado: Quarterly of the Colorado School of Mines, v. 44, no. 2, 477 p.
Butler, G.M., 1914, Clays of eastern Colorado: Colorado Geological Survey Bulletin 8, 353 p.
Bush, A.L., 1951, Sources of lightweight aggregate in Colorado: Colorado Scientific Society Proceedings, v. 15, no. 8, 368 p.
Cappa, J.A., and Bartos, P.J., 2007, Geology and Mineral Resources of Lake County: Colorado Geological Survey Resource Series 42, 59 p., plate, CD-ROM.
Colorado Geological Survey, numerous published 1:24,000 scale geologic maps, StateMap program: http://coloradogeologicalsurvey.org/geologic-mapping/statemap-program/completed-maps/
Colorado Division of Reclamation, Mining, and Safety, GIS mine permit data: http://mining.state.co.us/Reports/Pages/GISData.aspx
Courtney, P., 2014, Frac sand potential on selected State Trust lands in Colorado: Colorado State Land Board, Colorado Department of Natural Resources, 27 p.
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Hanley, J.B., Heinrich, E.W., and Page, L.R., 1950, Pegmatite investigations in Colorado, Wyoming, and Utah, 1942-1944: U.S. Geological Survey Professional Paper 227, 123 p.
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Langer, W.H., and Knepper, D.H. Jr., (1998) Geologic characterization of natural aggregate: A field geologist’s guide to natural aggregate resource assessment: U.S. Geological Survey Open-File Report 95-582, 32 p.
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Parker, B.H. Jr., 1974, Gold placers of Colorado: Quarterly of the Colorado School of Mines, v. 69, no. 3, 268 p.
Parker, B.H., Jr., 1992, Gold panning and placering in Colorado, how and where: Colorado Geological Survey Information Series 33, 83 p.
Schwochow, S.D., 1981, Inventory of nonmetallic mining and processing operations in Colorado: Colorado Geological Survey Map Series 17, 39 p.
Singewald, Q.D., 1950, Gold placers and their geologic environment in northwestern Park County, Colorado: U.S. Geological Survey Bulletin 955-D, 172 p.
Tweto, O., 1979, compiler, Geologic map of Colorado: U.S. Geological Survey, scale 1:500,000.
U.S. Geological Survey, Mineral Resources Data System (MRDS), GIS data: http://mrdata.usgs.gov/mrds/
U.S. Department of Agriculture Farm Service Agency, National Agriculture Imagery Program (NAIP), 2011 composite orthoimagery: http://www.fsa.usda.gov/programs-and-services/aerial-photography/imagery-programs/index
Vanderwilt, J.W., 1947, Mineral resources of Colorado: State of Colorado Mineral Resources Board, 547 p., 34 pl.
Van Gosen, B.S., Bush, A.L., 2001, Colorado vermiculite deposits: mines, prospects, and occurrences: U.S. Geological Survey Open-File Report OF-01-475, 10 p.
Waage, K.M., 1953, Refractory clay deposits of south-central Colorado: U.S. Geological Survey Bulletin 993, 104 p., 5 plates.