U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2015–1025

Geochemical Maps of Stream Sediments in Central Colorado, 

from New Mexico to Wyoming
Cover: Overlooking North Fork Lake Creek and Colorado highway 82 east of Independence Pass, with Star Mountain (12,920 ft) in the background. Photograph by Stuart A. Giles.
Geochemical Maps of Stream Sediments in Central Colorado, 

from New Mexico to Wyoming

By Robert G. Eppinger, Stuart A. Giles, and Terry L. Klein

Open-File Report 2015–1025

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2015

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Suggested citation:

Eppinger, R.G., Giles, S.A., and Klein, T.L., 2015, Geochemical maps of stream sediments in central Colorado, from New Mexico to Wyoming: U.S. Geological Survey Open-File Report 2015–1025, 120 p., 

http://dx.doi.org/10.3133/ofr20151025.

ISSN 2331-1258 (online)
iii

Contents

Introduction....................................................................................................................................................................................................................................................................................1

Stream-Sediment Sampling and Analytical Methods ............................................................................................................................................................................................................1

Geologic Setting of Central Colorado........................................................................................................................................................................................................................................2

Mineral Deposits of Central Colorado.......................................................................................................................................................................................................................................2

Geographic Information System and Spatial Analysis of Geochemistry Data...................................................................................................................................................................5

Geochemistry Maps and Discussions.......................................................................................................................................................................................................................................5

References Cited.......................................................................................................................................................................................................................................................................119

Figures

1. Generalized rock types of central Colorado, and mining districts and mineralized areas of central Colorado..........................................................................................3

2. Maps of central Colorado stream-sediment geochemistry—aluminum (Al) ....................................................................................................................................................7

3. Geologic formations associated with the element aluminum in stream sediments in central Colorado .....................................................................................................8

4. Maps of central Colorado stream-sediment geochemistry—antimony (Sb) ....................................................................................................................................................9

5. Mining districts and geologic formations associated with the element antimony in stream sediments in central Colorado................................................................10

6. Maps of central Colorado stream-sediment geochemistry—arsenic (As) .....................................................................................................................................................11

7. Mining districts and rock units associated with the element arsenic in stream sediments in central Colorado.....................................................................................12

8. Maps of central Colorado stream-sediment geochemistry—barium (Ba)......................................................................................................................................................13

9. Mining districts and rock units associated with the element barium in stream sediments in central Colorado......................................................................................14

10. Maps of central Colorado stream-sediment geochemistry—beryllium (Be)..................................................................................................................................................15

11. Mining districts and rock units associated with the element beryllium in stream sediments in central Colorado..................................................................................16

12. Maps of central Colorado stream-sediment geochemistry—bismuth (Bi)......................................................................................................................................................17

13. Mining districts associated with the element bismuth in stream sediments in central Colorado...............................................................................................................18

14. Maps of central Colorado stream-sediment geochemistry—cadmium (Cd) ..................................................................................................................................................19

15. Mining districts and rock units associated with the element cadmium in stream sediments in central Colorado..................................................................................20

16. Maps of central Colorado stream-sediment geochemistry—calcium (Ca).....................................................................................................................................................21

17. Mining districts and rock units associated with the element calcium in stream sediments in central Colorado. ...................................................................................22

18. Maps of central Colorado stream-sediment geochemistry—cerium (Ce) ......................................................................................................................................................23

19. Mining districts and rock units associated with the element cerium in stream sediments in central Colorado......................................................................................24

20. Maps of central Colorado stream-sediment geochemistry—cesium (Cs)......................................................................................................................................................25

21. Mining districts and rock units associated with the element cesium in stream sediments in central Colorado......................................................................................26
iv

22. Maps of central Colorado stream-sediment geochemistry—chromium (Cr)..................................................................................................................................................27

23. Mining districts and rock units associated with the element chromium in stream sediments in central Colorado.................................................................................28

24. Maps of central Colorado stream-sediment geochemistry—cobalt (Co)........................................................................................................................................................29

25. Mining districts and rock units associated with the element cobalt in stream sediments of central Colorado.......................................................................................30

26. Maps of central Colorado stream-sediment geochemistry—copper (Cu)......................................................................................................................................................31

27. Mining districts and rock unit associated with the element copper in stream sediments of central Colorado........................................................................................32

28. Maps of central Colorado stream-sediment geochemistry—europium (Eu)..................................................................................................................................................33

29. Mining district associated with the element europium in stream sediments of central Colorado..............................................................................................................34

30. Maps of central Colorado stream-sediment geochemistry—gallium (Ga)......................................................................................................................................................35

31. Rock units associated with the element gallium in stream sediments of central Colorado.........................................................................................................................36

32. Maps of central Colorado stream-sediment geochemistry—holmium (Ho) ...................................................................................................................................................37

33. Rock units associated with the element holmium in stream sediments of central Colorado.......................................................................................................................38

34. Maps of central Colorado stream-sediment geochemistry—indium (In)........................................................................................................................................................39

35. Mining districts and rock unit associated with the element indium in stream sediments of central Colorado ........................................................................................40

36. Maps of central Colorado stream-sediment geochemistry—iron (Fe) ............................................................................................................................................................41

37. Mining districts and rock units associated with the element iron in stream sediments of central Colorado ...........................................................................................42

38. Maps of central Colorado stream-sediment geochemistry—lanthanum (La) ................................................................................................................................................43

39. Mining districts and rock units associated with the element lanthanum in stream sediments of central Colorado ...............................................................................44

40. Maps of central Colorado stream-sediment geochemistry—lead (Pb)...........................................................................................................................................................45

41. Mining districts associated with the element lead in stream sediments of central Colorado.....................................................................................................................46

42. Maps of central Colorado stream-sediment geochemistry—lithium (Li).........................................................................................................................................................47

43. Rock units associated with the element lithium in stream sediments of central Colorado..........................................................................................................................48

44. Maps of central Colorado stream-sediment geochemistry—magnesium (Mg).............................................................................................................................................49

45. Rock units associated with the element magnesium in stream sediments of central Colorado .................................................................................................................50

46. Maps of central Colorado stream-sediment geochemistry—manganese (Mn).............................................................................................................................................51

47. Mining districts and rock unit associated with the element manganese in stream sediments of central Colorado ...............................................................................52

48. Maps of central Colorado stream-sediment geochemistry—mercury (Hg)....................................................................................................................................................53

49. Mining districts associated with the element mercury in stream sediments of central Colorado..............................................................................................................54

50. Maps of central Colorado stream-sediment geochemistry—molybdenum (Mo)...........................................................................................................................................55

51. Mining districts and rock unit associated with the element molybdenum in stream sediments of central Colorado .............................................................................56

52. Maps of central Colorado stream-sediment geochemistry—neodymium (Nd)..............................................................................................................................................57

53. Mining districts and rock units associated with the element neodymium in stream sediments of central Colorado..............................................................................58

54. Maps of central Colorado stream-sediment geochemistry—nickel (Ni).........................................................................................................................................................59

55. Mining districts and rock units associated with the element nickel in stream sediments of central Colorado........................................................................................60

56. Maps of central Colorado stream-sediment geochemistry—niobium (Nb)....................................................................................................................................................61
v

57. Rock units associated with the element niobium in stream sediments of central Colorado........................................................................................................................62

58. Maps of central Colorado stream-sediment geochemistry—phosphorus (P)................................................................................................................................................63

59. Mining districts and rock unit associated with the element phosphorus in stream sediments of central Colorado...............................................................................64

60. Maps of central Colorado stream-sediment geochemistry—potassium (K)...................................................................................................................................................65

61. Mining districts and rock units associated with the element potassium in stream sediments of central Colorado................................................................................66

62. Maps of central Colorado stream-sediment geochemistry—rubidium (Rb)...................................................................................................................................................67

63. Mining districts and rock unit associated with the element rubidium in stream sediments of central Colorado.....................................................................................68

64. Maps of central Colorado stream-sediment geochemistry—scandium (Sc) .................................................................................................................................................69

65. Rock units associated with the element scandium in stream sediments of central Colorado.....................................................................................................................70

66. Maps of central Colorado stream-sediment geochemistry—selenium (Se)...................................................................................................................................................71

67. Rock units associated with the element selenium in stream sediments of central Colorado......................................................................................................................72

68. Maps of central Colorado stream-sediment geochemistry—silver (Ag).........................................................................................................................................................73

69. Mining districts associated with the element silver in stream sediments of central Colorado...................................................................................................................74

70. Maps of central Colorado stream-sediment geochemistry—sodium (Na) .....................................................................................................................................................75

71. Rock units associated with the element sodium in stream sediments of central Colorado.........................................................................................................................76

72. Maps of central Colorado stream-sediment geochemistry—strontium (Sr)...................................................................................................................................................77

73. Rock units associated with the element strontium in stream sediments of central Colorado.....................................................................................................................78

74. Maps of central Colorado stream-sediment geochemistry—sulfur (S)...........................................................................................................................................................79

75. Mining districts associated with the element sulfur in stream sediments of central Colorado...................................................................................................................80

76. Maps of central Colorado stream-sediment geochemistry—tellurium (Te)....................................................................................................................................................81

77. Mining districts associated with the element tellurium in stream sediments of central Colorado.............................................................................................................82

78. Maps of central Colorado stream-sediment geochemistry—thallium (Tl)......................................................................................................................................................83

79. Mining districts and rock unit associated with the element thallium in stream sediments of central Colorado......................................................................................84

80. Maps of central Colorado stream-sediment geochemistry—thorium (Th) .....................................................................................................................................................85

81. Rock units associated with the element thorium in stream sediments of central Colorado ........................................................................................................................86

82. Maps of central Colorado stream-sediment geochemistry—tin (Sn) ..............................................................................................................................................................87

83. Mining districts and rock units associated with the element tin in stream sediments of central Colorado..............................................................................................88

84. Maps of central Colorado stream-sediment geochemistry—titanium (Ti)......................................................................................................................................................89

85. Rock units associated with the element titanium in stream sediments of central Colorado........................................................................................................................90

86. Maps of central Colorado stream-sediment geochemistry—tungsten (W)....................................................................................................................................................91

87. Mining districts and rock unit associated with the element tungsten in stream sediments of central Colorado.....................................................................................92

88. Maps of central Colorado stream-sediment geochemistry—uranium (U)......................................................................................................................................................93

89. Mining districts and rock units associated with the element uranium in stream sediments of central Colorado....................................................................................94

90. Maps of central Colorado stream-sediment geochemistry—vanadium (V)....................................................................................................................................................95

91. Mining districts and rock units associated with the element vanadium in stream sediments of central Colorado.................................................................................96
vi

92. Maps of central Colorado stream-sediment geochemistry—ytterbium (Yb)..................................................................................................................................................97

93. Rock units associated with the element ytterbium in stream sediments of central Colorado.....................................................................................................................98

94. Maps of central Colorado stream-sediment geochemistry—yttrium (Y).........................................................................................................................................................99

95. Rock units associated with the element yttrium in stream sediments of central Colorado........................................................................................................................100

96. Maps of central Colorado stream-sediment geochemistry—zinc (Zn)..........................................................................................................................................................101

97. Mining districts and rock unit associated with the element zinc in stream sediments of central Colorado...........................................................................................102

98. Maps of central Colorado stream-sediment geochemistry—Factor 1: Ce-La-Y-Th-Nb-Ti-(Be-Fe-P).......................................................................................................103

99. Mining districts and rock units associated with Factor 1 elements in stream sediments of central Colorado.......................................................................................104

100. Maps of central Colorado stream-sediment geochemistry—Factor 2: Ni-Cr-V-Mg-Co-(Fe) .....................................................................................................................105

101. Mining districts associated with Factor 2 elements in stream sediments of central Colorado.................................................................................................................106

102. Maps of central Colorado stream-sediment geochemistry—Factor 3: Zn-Pb-Cu-As-(Mo) .......................................................................................................................107

103. Mining districts associated with Factor 3 elements in stream sediments of central Colorado.................................................................................................................108

104. Maps of central Colorado stream-sediment geochemistry—Factor 4: Al-Sr-Na-Ba ..................................................................................................................................109

105. Mining districts and rock units associated with Factor 4 elements in stream sediments of central Colorado.......................................................................................110

106. Maps of central Colorado stream-sediment geochemistry—Factor 5: K-Li-Al-(Be)-(-Ca)-(-Fe)-(-V) .......................................................................................................111

107. Mining districts and rock units associated with Factor 5 elements in stream sediments of central Colorado.......................................................................................112

108. Maps of central Colorado stream water geochemistry—pH...........................................................................................................................................................................113

109. Mining districts and rock unit associated with high or low pH in stream water at sediment collection sites of central Colorado ....................................................114

110. Maps of central Colorado stream-sediment geochemistry—Scintillometry ................................................................................................................................................115

111. Rock units associated with high scintillometry values in stream sediments of central Colorado.............................................................................................................116

112. Maps of central Colorado stream water geochemistry—Specific Conductance........................................................................................................................................117

113. Mining districts and rock units associated with high specific conductance in stream water at sediment collection sites of central Colorado ....................................118

Table

1. Characteristics of the principal mineral deposit types found in central Colorado...........................................................................................................................................4
vii

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square foot (ft

2

) 0.09290 square meter (m

2

)

square mile (mi

2

) 2.590 square kilometer (km

2

)

SI to Inch/Pound

Multiply By To obtain

Length

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

Area

square meter (m

2

) 10.76 square foot (ft

2

)

square kilometer (km

2

) 0.3861 square mile (mi

2

)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F = (1.8 × °C) + 32

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C = (°F - 32)/1.8

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 (NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1927 (NAD 27).

Altitude, as used in this report, refers to distance above the vertical datum.

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 25 °C).
viii
Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

By Robert G. Eppinger, Stuart A. Giles, and Terry L. Klein

Introduction

The U.S. Geological Survey (USGS) recently completed a series of geologic, mineral resource, and environmental assessment studies in the Rocky Mountains of central Colorado, from Leadville eastward to the range front 

and from New Mexico to the Wyoming border. Regional stream-sediment geochemical maps, useful for assessing 

mineral resources and environmental effects of historical mining activities, were produced as part of the study. 

The data portrayed in this 56-parameter portfolio of landscape geochemical maps serve as a geochemical baseline 

for the region, indicate element abundances characteristic of various lithologic terranes, and identify gross anthropogenic effects of historical mining. However, although reanalyzed in this study by modern, sensitive methods, 

the majority of the stream-sediment samples were collected in the 1970s. Thus, metal concentrations portrayed in 

these maps represent stream-sediment geochemistry at the time of collection.

Stream-Sediment Sampling and Analytical Methods

Nearly 1,200 sediment samples collected in the late 1970s by the National Uranium Resource Evaluation 

(NURE) program were retrieved from the USGS sample archive and resubmitted for geochemical analysis by 

42-element inductively coupled plasma emission and mass spectrometry using the methods described in Taggart 

(2002). These new data were combined with similar new data from recently collected USGS samples (Church 

and others, 2012) and with a subset of previously reanalyzed NURE samples (Grossman, 1998) to create a 

geospatial dataset of 1,479 stream-sediment samples and the associated suite of 56 geochemical landscape maps 

presented here. Mapped elements are Ag, Al, As, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cs, Cu, Eu, Fe, Ga, Hg, Ho, 

In, K, La, Li, Mg, Mn, Mo, Na, Nb, Nd, Ni, P, Pb, Rb, S, Sb, Sc, Se, Sn, Sr, Te, Th, Ti, Tl, U, V, W, Y, Yb, and 

Zn. Other mapped parameters are pH and specific conductance (both measured on stream waters at the sediment 

sample site), the results of multielement R-mode factor analysis (discussed below), and scintillometry measurements that estimate radioactive element content. The latter were taken at sediment sample sites during the 

original NURE program. A history and details of the NURE program are found in Smith (2006).

The 48 major, minor, and trace elements were determined either by inductively coupled plasma–atomic 

emission spectrometry (ICP–AES) or inductively coupled plasma–mass spectrometry (ICP–MS), except for Hg 

and Se, which were analyzed by cold-vapor atomic absorption and decomposed by using hydride-generation 

atomic absorption, respectively. For the ICP methods, each sample was decomposed by using a mixture of 

hydrochloric, nitric, perchloric, and hydrofluoric acids at low temperature, followed by analysis by ICP–AES 

and ICP–MS. Although the four-acid digestion technique may not completely digest some oxide minerals 

that contain elements such as Cr, Sn, and the rare-earth elements, resulting data still are useful for identifying 

samples that have high concentrations of those elements. The ICP–AES technique begins with calibration by 

standardizing with digested rock reference materials and multielement solution standards. The ICP–MS technique begins with calibration with aqueous standards, and internal standards are used to compensate for matrix 

effects and internal drifts. Data reproducibility for all 48 elements is ±15 percent at five times the lower limit of 

determination, and the calculated relative standard deviation of duplicate samples is no greater than 15 percent. 

Details on all techniques used appear in Taggart (2002).

The five-factor analysis maps represent factor scores generated using R-mode factor analysis, a multivariate statistical procedure based on a linear correlation matrix of the analyzed data and used to generate multielement “factors” that may describe geologic processes (Howarth and Sinding-Larsen, 1983; Tabachnick and 

Fidell, 2007). An orthogonal varimax rotation and five-factor model were chosen and used on a log-normalized 

dataset after removing highly censored elements (those with 20 percent or more of the analytical values lying 

below the lower determination limit). Elements within a given factor behave similarly in their gross spatial distributions. Factor 1 explains the most variance for elements within the dataset, and each of the subsequent four 

factors (in numerical sequence) explains progressively less variance.
2 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Geologic Setting of Central Colorado

The study area in Colorado is in the central Rocky Mountains and includes prominent mountain ranges, 

such as the Front Range, the Sawatch Range, the Wet Mountains, the Mosquito Range, and the Sangre de Cristo 

Mountains. Intermontane parks interspersed between the ranges include North, Middle, and South Parks, 

and the San Luis Valley. Figure 1 shows major lithologies and mining districts within the study area. Similar 

lithologies of various ages are combined in the figure rather than a traditional geologic map display, where 

lithologies are differentiated by age, since the geochemical element-distribution maps that follow are more 

a reflection of rock type than rock age. A brief discussion follows of the various rock units combined in the 

lithologic map shown in figure 1 (modified from Church and others, 2012).

Major rock types range from late Paleoproterozoic crystalline rocks to Paleozoic and Mesozoic sedimentary rocks and thence to Laramide to mid-Tertiary plutonic rocks. The Paleoproterozoic basement rocks 

are composed of metamorphosed and deformed 1.75–1.73 giga-annum (Ga) island-arc volcanic rocks in the 

south-central part of the study area (Bickford and others, 1989a; Van Schmus and others, 1993). Those rocks are 

intruded by intermediate-composition plutonic rocks of similar age (Reed and others, 1987). Throughout much 

of the rest of the area, the basement rocks are composed of 1.73–1.71 Ga metasedimentary rocks derived from 

erosion of the Archean Wyoming craton to the north or from retreating Paleoproterozoic arc complexes to the 

southeast. Plutonic rocks of 1.72–1.68 Ga intruded all of the older rocks in the area. Mesoproterozoic plutonic 

rocks (1.44–1.39 Ga) of intermediate to felsic composition are abundant throughout the area (Anderson, 1983). 

The 1.1-Ga Pikes Peak batholith is the youngest and largest of all the Proterozoic granitoid bodies in central 

Colorado (Barker and others, 1975; Smith and others, 1999).

Paleozoic carbonate sedimentary rocks formed a thin cover (less than 2 kilometers (km) thick) on basement rocks from Cambrian to Pennsylvanian time (DeVoto, 1990). Late Cambrian plutonic rocks and carbonatites were emplaced in the south-central part of the area and are related to rifting of the continental margin 

to the southeast in Oklahoma (Bickford and others, 1989b). In Pennsylvanian and Permian time, parts of the 

area covered by Paleozoic formations were uplifted and the sedimentary and basement rocks were eroded into 

adjacent basins, creating locally thick accumulations (3–4 km) of conglomerate and red beds (Lindsey and 

others, 1986). The region stabilized during the remainder of Mesozoic time as marine shale and limestone 

were deposited in seaways throughout the region (in units as much as 3 km thick). In latest Cretaceous time, 

the region was deformed by the Laramide orogeny, which created monoclinal uplifts and adjacent depositional 

basins (Dickinson and Snyder, 1978).

From Cretaceous to early Tertiary time, plutons ranging from mafic to intermediate composition intruded the 

basement rocks and created sills and laccoliths in the Paleozoic and Mesozoic strata (Simmons and Hedge, 1978). 

Hydrothermal alteration accompanied some of those plutons, and some plutons contain mineral deposits of base 

and precious metals that were mined beginning in the mid-1800s (Sims and others, 1963; Rice and others, 1985). 

The superposition and localization of Cretaceous-Tertiary magmatism and concurrent hydrothermal mineralization within preexisting Proterozoic basement structures define the Colorado Mineral Belt (Tweto and Sims, 1963; 

Wilson and Sims, 2003; fig. 1). Volcanoes erupted and formed calderas across the southern part of the study 

area during middle Tertiary time and formed large volcanic fields such as those in the San Juan Mountains to the 

southwest of the study area (Steven and Lipman, 1976). Silica-undersaturated subvolcanic rocks were emplaced 

in the east-central part of the study area (Lindgren and Ransome, 1906; Kelley and Ludington, 2002). Plutons of 

predominantly felsic composition were emplaced during middle Tertiary time (Mutschler and others, 1981).

During late Tertiary time, extensional faulting related to development of the Rio Grande Rift disrupted 

much of the area, creating block-faulted mountain ranges and basins. Pleistocene glaciation followed that 

sculpted modern valleys and mountain peaks. Quaternary sedimentary deposits blanket the modern valleys.

Mineral Deposits of Central Colorado

The Colorado Mineral Belt (CMB; Tweto and Sims, 1963) is a northeast-trending structure that crosses 

the central part of the state. The CMB contains most of the state’s metal producing areas, both in terms of the 

volume of metal produced and the number of producing mines. The metal producing areas are spatially associated with Late Cretaceous to latest Paleogene epizonal plutons, dikes, and sills that generally range in composition 

from intermediate to felsic. Those rocks intrude Proterozoic igneous and metamorphic rocks (metasedimentary and 

metavolcanic) and Phanerozoic clastic and carbonate sedimentary rocks that are as young as Late Cretaceous. In 

the study area, plutons related to the CMB range in age from 70 mega-annum (Ma) to about 25 Ma (Bookstrom 

and others, 1987; Cunningham and others, 1994). Mineral deposits within the CMB consist of precious-metal and 

polymetallic vein deposits (Ag, Au, Cu, Pb, and Zn), carbonate replacement deposits (Ag, Cu, Pb, and Zn), baseand precious-metal skarn deposits (Ag, Au, Cu, Pb, and Zn), and porphyry molybdenum and copper-molybdenum 

deposits (Cu and Mo). Most historical mines exploited polymetallic veins of limited areal extent, producing gold, 

silver, copper, lead, and zinc (Lovering and Goddard, 1950; Pearson, 1980). Mining district boundaries shown in 

figure 1 and on subsequent maps largely are taken from Wilson (2003), although some boundaries were modified 

by combining districts for simplicity during this study.

Mineral deposits in the study area are classified by mineral deposit type (Cox and Singer, 1986). Table 1 

shows characteristics of these mineral deposits, such as exploited metals, gangue mineralogy, and hydrothermal 

alteration type. In sampled catchments, polymetallic veins were the deposit type most commonly found. 

Polymetallic veins may constitute a surface expression of, and overlie, many larger mineral deposit types, 

such as porphyry systems that occur within the study area (Cox, 1986a, 1986b; Ludington, 1986; Cox and 
Mineral Deposits of Central Colorado 3

Figure 1. (A) Generalized rock types of central Colorado, and 

(B) mining districts and mineralized areas of central Colorado. 

Modified from Church and others (2012).

50250 KILOMETERS

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#

#

^

Cañon

City

Aspen

Pueblo

Salida

Alamosa

Boulder

Gunnison

Leadville

Georgetown

Buena

Vista

Breckenridge

Fort Collins

Central

City

Idaho

Springs

Colorado

Springs

Steamboat

Springs

Denver

Golden

Walsenburg

Pikes Peak

 Mt.

Princeton

South Park

North Park

Middle Park

Luis

San

Valley

FRONT RANGE

WET MOUNTAINS

SANGRE DE CRISTO MOUNTAINS

SAWATCH RANGE

MOSQUITO RANGE

–107° –106° –105°

41°

40°

39°

38°

37°

Low : 4,250

High : 14,433

Elevation (feet)

Mineralized area

Mining district

# Summit

B. MINING DISTRICTS AND MINERALIZED AREAS

EXPLANATION

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

–107° –106° –105°

41°

40°

39°

38°

37°

Major fault

Plutonic rock of mafic composition

Plutonic rock of intermediate composition

Plutonic rock of felsic composition in the Pikes Peak batholith

Plutonic rock of felsic composition

Volcanic rock of mafic composition

Volcanic rock of intermediate composition

Volcanic rock of felsic composition

Metamorphic rock of intermediate to mafic composition

Metamorphic rock of pelitic to siliceous composition

Sedimentary and metasedimentary rock of quartzite composition

Sedimentary rock of shale composition

Sedimentary rock of shale to sandstone composition

Sedimentary rock of sandstone composition

Sedimentary rock of carbonate to sandstone composition

Sedimentary rock of carbonate composition

Sedimentary rock of carbonate to shale composition

Sedimentary rock containing evaporite and red-bed deposits

Unconsolidated deposit, artificial fill, water or snow

Study area boundary

EXPLANATION

A. GENERALIZED LITHOLOGIES

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
4 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Table 1. Characteristics of the principal mineral deposit types found in central Colorado.

[Metals, minerals, and alteration types are listed in approximate order of abundance]

Deposit type Metals Major ore minerals Minor ore minerals Gangue minerals Alteration type and style

Cenozoic

Polymetallic veins Ag, Au, Pb, Zn, 

Cu

Pyrite, galena, sphalerite, tetrahedrite, 

chalcopyrite 

Argentite, ruby silver Quartz, calcite, siderite, dolomite Argillization, sericitization, silicification, propylitization

Porphyry Mo or Cu-Mo Mo, Cu, Sn, W Molybdenite, chalcopyrite, pyrite Cassiterite, huebnerite, Quartz, fluorite, sericite, topaz Silicification, sericitization, potassium feldspar, propylitization

Polymetallic replacement 

and skarn

Ag, Pb, Zn, Cu Galena, sphalerite, tetrahedrite, pyrite Chalcopyrite, pyrrhotite Dolomite, barite, siderite, fluorite Regional dolomitization, local silicification

Fluorite veins F Fluorite Base metal sulfides, pyrite Quartz, calcite, barite, manganese oxide Argillization, sericitization, silicification

Tungsten veins W Ferberite Pyrite, sphalerite, tetrahedrite,

scheelite

Quartz, calcite, siderite, barite Silicification, argillization, sericitization, potassium feldspar,

propylitization

Uranium veins U, Th, V Uraninite, torbernite, coffinite Base-metal sulfides, pyrite Calcite, ankerite, quartz Argillization, sericitization

Alkaline Au-telluride veins Au, Ag, Te Gold, silver, and base metal telluride 

minerals, native gold

Pyrite Quartz, chalcedony, fluorite, calcite, dolomite, 

hematite, apatite

Argillization, silicification, sericitization, potassium feldspar,

biotitization 

Cambrian

Thorium veins Th, Pb, Zn, Ba Thorite, galena, sphalerite Pyrite Calcite, quartz, barite Fenitization

Proterozoic

Stratabound Cu-Zn Cu, Zn Chalcopyrite, sphalerite, pyrrhotite, pyrite,

gahnite

Galena, arsenopyrite Amphiboles, chlorite, garnet, sillimanite, epidote,

anthophyllite, pyroxene

Argillization (metamorphosed to high temperature 

aluminosilicates minerals)

Pegmatite minerals various Feldspar, mica, beryl, quartz None
Geochemistry Maps and Discussions 5

Singer, 1986). These polymetallic vein deposits were the target of historical mining for gold, silver, and lead 

in the latter 19th and early 20th centuries in Colorado (Henderson, 1926). The areal extent and abundance of 

polymetallic vein deposits reflect the exploration history, level of erosion, and exposure in the study area. Gold 

is the dominant economic metal in the polymetallic vein deposits, with minor silver and some molybdenite. 

Porphyry molybdenum and copper-molybdenum deposits are known in the study area, but only at the Climax 

and Henderson mines have the porphyry molybdenum deposits been exploited. Limestone replacement and 

skarn deposits also have been exploited in the western and southwestern part of the study area, producing a 

large amount of silver, lead, and zinc in the Leadville and Gilman areas. Thorium-rich vein deposits are associated with the Cambrian mafic and ultramafic Wet Mountains alkaline igneous complex in the northern and 

central Wet Mountains (Armbrustmacher, 1984). Those deposits also contain minor amounts of base metals 

and barium. A relatively small number of uranium vein deposits and fluorite vein deposits occur throughout the study area. Relatively small stratabound copper-zinc deposits also occur throughout the study area in 

Proterozoic metasedimentary rocks. Granite pegmatite deposits, widely scattered within the northern two-thirds 

of the study area, have been exploited locally and are associated with large Proterozoic plutons.

Geographic Information System and Spatial Analysis 

of Geochemistry Data

The stream-sediment geochemical data used in this study were acquired from multiple sources in diverse 

formats, mainly as Microsoft (MS) Excel spreadsheets or in MS Access databases. The data were prepared for 

inclusion in a geographic information system (GIS) by normalizing all field names and consolidating the data into 

a single MS Access database, then by using that database as the source for generating shapefiles (and later geodatabase feature classes) by using Esri ArcGIS 10.0 software. Owing to the point-source nature of geochemical data, 

the initial shapefiles were point-based features, with fields for various sample identification labels (IDs) and source 

reference information, dates of collection and analysis, geographic coordinates, analytical method and censored 

data information, and the results of field measurements and laboratory analyses. Factor analysis was conducted 

outside of the GIS on the same data, and the results then were imported into the GIS as a separate table.

Once all the data were assembled within the GIS, each element and factor was classified by percentiles, 

because percentiles are reproducible and resistant to skewing effects from statistical outliers. The data then 

were symbolized using color-coded, proportionally scaled circles to emphasize high values (or low values in the 

case of pH), and saved as symbol layer files. Once all elements, factors, and field measurements were classified 

and symbolized, the Geostatistical Analyst extension in ArcGIS was used to generate raster prediction surfaces 

and statistics using the inverse distance weighting (IDW) interpolation method. The IDW method was chosen 

because it assumes that relations in elemental concentrations decrease with increasing distance between the 

sampled points and also because it is exact; widely differing concentrations in close proximity do not generate false extremes, because minimum and maximum concentrations occur only at sample points. The resulting 

raster surfaces then were classified and colored identically to the matching element point layers. Due to dynamic 

association with the active GIS analytical data, each prediction raster was converted into a polygon shapefile in 

order to preserve predicted class divisions as filled contours.

The geochemical GIS files used to make the symbolized layers, to conduct the IDW analysis, and to construct each map are available with this report, available for download at http://dx.doi.org/10.3133/ofr20151025. 

The IDW prediction surface shapefiles themselves are not included due to changes in GIS software that allow 

a more accurate spatial analysis of the geochemistry data since those shapefiles were first produced. Also 

included is a shapefile of the study area boundary (108 samples lie outside the boundary but are included 

in the prediction analysis). The relevant GIS files also are provided at the URL above as feature classes in 

an ESRI ArcGIS 10.0 geodatabase.

Geochemistry Maps and Discussions

Each map includes a histogram, summary statistics, a symbolized point layer of the stream-sediment 

sample distribution, and a prediction surface calculated from the point-source concentrations. Each summary 

statistics graph displays a frequency histogram and a cumulative frequency curve. The graph’s left axis is 

labeled frequency, the right axis is labeled cumulative frequency, the bottom axis is labeled concentration, and 

both top and bottom axes show units of measure, unless otherwise noted. A boxplot on the top axis identifies the 

10th, 25th, 50th, 75th, and 90th percentiles, calculated on the respective number of samples. For some elements 

with a high percentage of analytical results below the detection limit (“nondetects”), the left side of the boxplot may be truncated because nondetects cluster on the far left side of the frequency histogram (for example, 

bismuth, fig. 12). Each map is accompanied by a short description of the geochemical and areal distribution of 

the mapped constituent, including observations concerning the geologic association, nearby mining districts, 

crustal abundances, and geochemical characteristics of the respective element, the latter two based on information in Rankama and Sahama (1950), Wedepohl (1969–1978), Rose and others (1979), Levinson (1980), and 

Reimann and de Caritat (1998). Several first-order geologic features are apparent in the geochemical maps. 

These include (1) the northeast-trending CMB (highlighted by the elements Ag, As, Bi, Cd, Cu, Hg, In, Mo, 

Pb, Sb, Te, Tl, and Zn); (2) the Mesoproterozoic Pikes Peak batholith (Be, Th, and the rare-earth elements); 

(3) gabbros and mafic metavolcanic rocks in northern and central Colorado (Cr, Ni, and V); (4) the Thirtynine 

Mile volcanic field (Ba and Sr); and (5) the Boulder County tungsten district (W).
6 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming
Geographic Information System and Spatial Analysis of Geochemistry Data 7

Figure 2. Maps of central Colorado stream-sediment geochemistry—aluminum (Al).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

Central Colorado Stream-Sediment

Geochemistry—Aluminum

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

A B

1.7–4.2% (<2.5th percentile)

4.3–5.4% (2.5–10th percentile)

5.5–6.2% (10–25th percentile)

6.3–7.3% (25–75th percentile)

7.4–7.9% (75–90th percentile)

8.0–8.5% (90–97.5th percentile)

8.6–9.5% (>97.5th percentile)

Aluminum (weight percent)

Crustal abundance = 8.36%

Limit of detection = not applicable

1.7 10

0

125

250

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1479

 1.7000

 9.5000

 6.7114

 6.6138

 6.8000

 7.2000

 1.045

 0.02718

–0.9274

 2.326

Al

weight percent (wt%)

EXPLANATION

Colorado state border

Study area boundary

Colorado Mineral Belt

Frequency

Cumulative Frequency

Concentration, in weight percent

2 3 4 5 6 7 8 9
8 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Figure 3. Geologic formations associated 

with the element aluminum in stream 

sediments in central Colorado.

Aluminum (Al) content in igneous rocks generally is proportional to feldspar content. In sedimentary rocks, aluminum is the result of weathering of silicate minerals, in particular feldspar, and 

their aluminum content is directly proportional to their clay mineral content.

Stream-sediment samples with high aluminum concentrations (>90th percentile) in the study 

area (fig. 2) are associated with source areas containing abundant feldspar, such as coarse-grained 

Proterozoic felsic and intermediate-composition plutons, intermediate volcanic rocks, Pennsylvanian 

and Permian arkosic, clastic sedimentary rocks, immature basin-filling sediments of Tertiary and 

Quaternary age, and alluvial fan and some periglacial deposits with proximal source units predominantly composed of the previously mentioned Proterozoic and Phanerozoic rocks (fig. 3). Samples 

with the lowest concentrations (<25th percentile) are associated with Phanerozoic carbonate-rich and 

mature clastic sedimentary rock units.

^Denver

Coalmont

Formation

Middle Park

Formation

Boulder

Creek

pluton

Kenosha Pass

pluton

Madera

Formation

Farisita

Conglomerate

Sangre de

Cristo Formation

Sangre de

Cristo Formation

–107° –106° –105°

41°

40°

39°

38°

37°

Elevation (feet)

Low : 4,250

High : 14,433

EXPLANATION

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Generalized formation boundary

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Rock units from Church and others (2012).

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
Geochemistry Maps and Discussions 9

Figure 4. Maps of central Colorado stream-sediment geochemistry—antimony (Sb).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

Central Colorado Stream-Sediment

Geochemistry—Antimony

EXPLANATION

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Colorado state border

Study area boundary

Colorado Mineral Belt

A B

<0.15 ppm (<2.5th percentile)

0.15–0.20 ppm (2.5–10th percentile)

0.21–0.27 ppm (10–25th percentile)

0.28–0.62 ppm (25–75th percentile)

0.63–1.3 ppm (75–90th percentile)

1.4–7.2 ppm (90–97.5th percentile)

7.3–59 ppm (>97.5th percentile)

Antimony (parts per million)

Crustal abundance = 0.20 ppm

Limit of detection = 0.080 ppm

0.08 60

0

60

120

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1064

 0.0800

 59.0000

 1.0288

 0.4627

 0.3800

 0.2800

 3.358

 0.103

 10.3

 137

Sb

parts per million (ppm)

Frequency

Cumulative Frequency

Concentration, in parts per million

0.1 1 10
10 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Antimony (Sb) is a strongly chalcophile element, is associated primarily with hydrothermal 

base- and precious-metal deposits, and commonly is found as a syngenetic or diagenetic component 

in organic-rich (black) shales. It is contained primarily in stibnite in low-temperature hydrothermal 

deposits and in tetrahedrite and sulfosalt minerals at higher temperatures. It is relatively mobile in 

fresh water, and iron-oxyhydroxide precipitates are commonly enriched in antimony.

High concentrations of antimony (>90th percentile) are found in stream-sediment samples within 

the Colorado Mineral Belt (figs. 4 and 5). The largest cluster of samples with high concentrations is 

around the Blackhawk and Central City–Idaho Springs districts and reveals downstream dispersion 

eastward along Clear Creek to the range front. Within the Colorado Mineral Belt, there are also clusters around the Argentine, Gold Brick, Tincup–Cumberland Pass, Whitepine, and Monarch districts. 

Other areas yielding high concentrations of antimony include the Boulder-Tungsten, Dumont, Gold 

Hill, Leadville, and Silver Plume–Georgetown districts. Just outside the study area boundary in the 

southern part of the mineral belt, a single sample containing anomalous antimony and several other 

metals came from the Bonanza district (see copper discussion, fig. 27). A large cluster of samples with 

high antimony concentrations (90 to 97.5th percentile) in the northwestern part of the study area is 

underlain largely by the Late Cretaceous Niobrara Formation and the Pierre Shale. A similar cluster of 

samples with high concentrations (90 to 97.5th percentile) occurs along the southeastern edge of study 

area in an area underlain by varied Proterozoic plutons and metasedimentary rocks and Cretaceous 

sedimentary rocks.

Figure 5. Mining districts and geologic 

formations associated with the element 

antimony in stream sediments in 

central Colorado.

^ Clear Ck.

Denver

ARGENTINE

LEADVILLE

GOLD HILL

BOULDER–

TUNGSTEN

DUMONT

MONARCH

TINCUP–

CUMBERLAND

PASS

BLACKHAWK

GOLD

BRICK

SILVER PLUME–

GEORGETOWN

CENTRAL CITY–

IDAHO SPRINGS

WHITEPINE

BONANZA

–107° –106° –105°

41°

40°

39°

38°

37°

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

Pierre Shale or Niobrara Formation, undivided, boundary

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Mining districts from Wilson (2003), 

rock units from Church and others (2012).

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
Geochemistry Maps and Discussions 11

Figure 6. Maps of central Colorado stream-sediment geochemistry—arsenic (As).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

Central Colorado Stream-Sediment

Geochemistry—Arsenic

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Colorado state border

Study area boundary

Colorado Mineral Belt

A B

<1 ppm (undetected) (<2.5th percentile)

1.0–1.5 ppm (2.5–10th percentile)

1.6–2.0 ppm (10–25th percentile)

2.1–5.5 ppm (25–75th percentile)

5.6–11 ppm (75–90th percentile)

12–38 ppm (90–97.5th percentile)

39–730 ppm (>97.5th percentile)

Arsenic (parts per million)

Crustal abundance = 1.8 ppm

Limit of detection = 1 ppm

0.211 800

0

175

350

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1479

 <1

 730.0000

 7.4957

 3.4622

 3.0000

 2.0000

 28.2

 0.7332

 17.86

 397.3

As

parts per million (ppm)

EXPLANATION

1 10 100

Frequency

Cumulative Frequency

Concentration, in parts per million
12 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Arsenic (As) is a strongly chalcophile element associated primarily with hydrothermal deposits 

and as a syngenetic or diagenetic component in many organic-rich (black) shales. It is contained in 

various sulfide and sulfarsenide minerals and commonly coprecipitates with iron oxyhydroxides in 

streams.

High concentrations (>90th percentile) of arsenic are found in stream-sediment samples within 

the Colorado Mineral Belt (figs. 6 and 7). The largest cluster of samples with high concentrations is 

around the Blackhawk and Central City–Idaho Springs districts and reveals downstream dispersion 

eastward along Clear Creek to the range front. Elsewhere in the Colorado Mineral Belt, samples having high arsenic concentrations (>90th percentile) are associated with the Argentine, Breckenridge, 

Dumont, Gold Hill, Henderson, Leadville, Lincoln Gulch, Montezuma–Geneva Creek, Red Mountain, 

Tenmile-Kokomo, and Silver Plume–Georgetown districts. South of the mineral belt, clusters occur 

around the Lake George, Cripple Creek–Victor, and Rosita Hills districts. Clusters of samples having lower-level (90 to 97.5th percentile) arsenic concentrations in the northern part of the study area 

are underlain by diverse sedimentary and igneous rock types. Many such samples are underlain by 

Cretaceous sedimentary rock units that contain substantial amounts of organic-rich shales, such as the 

Belden and Pierre Shales. Just outside the study area boundary in the southern part of the mineral belt, 

a single sample containing anomalously high arsenic and several other metals represents the Bonanza 

district (see copper discussion on fig. 27). A small cluster of samples near Cañon City that contains 

anomalous As concentrations in stream sediments might reflect anthropogenic contamination related 

to several historic smelters that operated in the Cañon City–Florence area in the late 19th and early 

20th centuries (Henderson, 1926). While few in number, these samples also contain anomalous concentrations of several ore-related elements, including Ag, As, Cd, Co, Cr, Cu, In, Mn, Pb, S, W, and 

Zn. Maps for those elements show the same small cluster near Cañon City. Isolated samples obtained 

near Denver that contain elevated arsenic concentrations are described in the discussion of copper 

(figs. 26 and 27).

Figure 7. Mining districts and rock units

associated with the element arsenic in stream 

sediments in central Colorado.

^ Clear Ck.

Denver

BONANZA

ARGENTINE

LEADVILLE

GOLD HILL

DUMONT

BRECKENRIDGE

ROSITA HILLS

BLACKHAWK

LAKE GEORGE

CRIPPLE CREEK–VICTOR

TENMILE–

KOKOMO

RED MT.

MONTEZUMA–GENEVA CK.

SILVER PLUME–

GEORGETOWN

CENTRAL CITY–

IDAHO SPRINGS

HENDERSON

LINCOLN

GULCH

Cañon City

–107° –106° –105°

41°

40°

39°

38°

37°

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

Pierre Shale boundary

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Mining districts from Wilson (2003),

rock units from Church and others (2012).

Belden Shale boundary

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt
Geochemistry Maps and Discussions 13

Figure 8. Maps of central Colorado stream-sediment geochemistry—barium (Ba).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

Central Colorado Stream-Sediment

Geochemistry—Barium

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Colorado state border

Study area boundary

Colorado Mineral Belt

A B

130–376 ppm (<2.5th percentile)

377–495 ppm (2.5–10th percentile)

496–580 ppm (10–25th percentile)

581–800 ppm (25–75th percentile)

801–970 ppm (75–90th percentile)

971–1,300 ppm (90–97.5th percentile)

1,310–6,100 ppm (>97.5th percentile)

Barium (parts per million)

Crustal abundance = 390 ppm

Limit of detection = not applicable

130 7,000

0

125

250

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1479

 130.0000

 6100.0000

 727.5930

 688.3731

 690.0000

 710.0000

 313.9

 8.162

 6.817

 86.21

Ba

parts per million (ppm)

 1,000

EXPLANATION

Frequency

Cumulative Frequency

Concentration, in parts per million
14 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Barium (Ba) in igneous rocks is present mainly where it substitutes chemically for potassium 

in potassium feldspar, muscovite, and biotite. However, the barium content of those minerals in 

end-stage differentiates (such as granite pegmatites) generally is relatively low compared to that 

of less-evolved rocks. Barium also may occur as barite in hydrothermal vein systems and in some 

stratabound deposits. Barium is variably mobile during weathering and may be concentrated in clay 

minerals.

Stream-sediment samples with high barium concentrations (>90th percentile) highlight the 

northeastern Colorado Mineral Belt, particularly the Argentine, Boulder-Tungsten, Halls Gulch, 

Montezuma–Geneva Creek, and North Gilpin districts (figs. 8 and 9). Along the west-central edge 

of the study area within the mineral belt, samples with high barium concentrations (>90th percentile) 

also are associated with the Independence, Lincoln Gulch, and Red Mountain districts surrounding 

the Grizzly Peak caldera. Isolated samples with high concentrations of barium (>97.5th percentile) 

are associated with the Cripple Creek–Victor and Rosita Hills districts. These high concentrations 

likely are related to the occurrence of barite or barium substituting for potassium in alteration minerals such as muscovite in these epithermal, precious-metal and base-metal hydrothermal systems. In 

the northern part of the study area, a large, diffuse anomaly (>90th percentile) is underlain largely by 

basin-filling sedimentary rocks of the Coalmont and Middle Park Formations, where the anomaly may 

be related to high content of feldspar or clay minerals. In the southern part of the study area, diffuse 

clusters (90 to 97.5th percentile) are underlain by rocks of the alkali-calcic, intermediate-composition 

Thirtynine Mile volcanic field. Diffuse clusters also are found in and around the Wet Mountains 

and the Wet Mountain Valley. In the southern part of the area, a large diffuse cluster of high-barium 

samples (90 to 97.5th percentile) is underlain by varied Cretaceous and younger sedimentary rocks 

and basin-fill deposits where barium may be associated with clay minerals.

Figure 9. Mining districts and rock units

associated with the element barium in stream 

sediments in central Colorado.

^Denver

Thirtynine Mile

volcanic field

Coalmont Formation

Middle Park

Formation

Grizzly Peak caldera

WET MOUNTAINS

Wet

Mountain

Valley

NORTH GILPIN

ARGENTINE

BOULDER–TUNGSTEN

ROSITA

HILLS

MONTEZUMA–

HALL'S GULCH GENEVA CK.

INDEPENDENCE

RED MT.

LINCOLN

GULCH

CRIPPLE CREEK–

VICTOR

–107° –106° –105°

41°

40°

39°

38°

37°

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Mining district

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Mining districts from Wilson (2003),

rock units from Church and others (2012).

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Generalized formation boundary
Geochemistry Maps and Discussions 15

Figure 10. Maps of central Colorado stream-sediment geochemistry—beryllium (Be).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Beryllium

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Colorado state border

Study area boundary

Colorado Mineral Belt

A B

<1 ppm (<10th percentile)

1.001–1.600 ppm (10–25th percentile)

1.601–2.600 ppm (25–75th percentile)

2.601–3.300 ppm (75–90th percentile)

3.301–7.200 ppm (90–97.5th percentile)

7.201–200.1 ppm (>97.5th percentile)

Beryllium (parts per million)

Crustal abundance = 2.00 ppm

Limit of detection = 1 ppm

0.211 220

0

200

400

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1479

 <1

 200.1111

 2.5468

 2.0379

 2.0000

 2.0000

 5.673

 0.1475

 29.41

 998

Be

parts per million (ppm)

Frequency

Cumulative Frequency

Concentration, in parts per million

1 10 100
16 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Beryllium (Be) is most abundant in late-stage igneous differentiates, especially in rocks of alkaline compositions such as alkali granite and nepheline syenites where Be commonly occurs in alkali 

feldspars, mica, and beryl. Beryllium is relatively immobile during weathering when present as beryl.

The largest cluster of stream-sediment samples with high (>90th percentile) beryllium concentrations is underlain by the Mesoproterozoic Pikes Peak batholith in the east-central part of the study 

area (figs. 10 and 11). The Eocene Mount Princeton pluton in the Sawatch Range contains many 

beryl occurrences that may explain the presence of multiple samples with high barium concentrations 

(>90th percentile). The Mount Antero stock, which intrudes the Mount Princeton pluton, also may 

contribute to the high beryllium concentrations (>90th percentile) in nearby samples. In the Colorado 

Mineral Belt, small clusters of samples with high concentrations (>97.5th percentile) occur over and 

downstream of the Oligocene Henderson porphyry-Mo deposit and in the Alma and Chalk Creek districts. Within the northeast part of the mineral belt, lower level clusters (90 to 97.5th percentile) also 

are found around the Argentine, Boulder-Tungsten, Breckenridge, Climax, Consolidated Montgomery, 

Gold Hill, Tenmile-Kokomo, Tennessee Pass, and Upper Blue River districts. In the western part of 

the study area within the mineral belt, samples with high beryllium concentrations (90 to 97.5th percentile) are associated with the Independence, Monarch, Red Mountain, Marshall Pass, and Winfield 

districts. Near the Lake George district, one sample (>97.5th percentile) overlies a greisen deposit in 

the Redskin stock within the west-central part of the Mesoproterozoic Pikes Peak batholith.

Figure 11. Mining districts and rock units

associated with the element beryllium in stream 

sediments in central Colorado.

Mount Antero stock

Mount

Princeton

pluton

^ Clear Ck.

Denver

Pikes Peak

batholith

ARGENTINE

GOLD HILL

BOULDER–TUNGSTEN

BRECKENRIDGE

MARSHALL PASS

MONARCH

WINFIELD

CONSOLIDATED MONTGOMERY

LAKE GEORGE

CHALK

CREEK

INDEPENDENCE ALMA

UPPER BLUE RIVER

TENMILE–KOKOMO

HENDERSON

CLIMAX

RED MT.

TN PASS

–107° –106° –105°

41°

40°

39°

38°

37°

Mining district

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Mining districts from Wilson (2003),

rock units from Church and others (2012).

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Generalized intrusion boundary
Geochemistry Maps and Discussions 17

Figure 12. Maps of central Colorado stream-sediment geochemistry—bismuth (Bi).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Bismuth

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Colorado state border

Study area boundary

Colorado Mineral Belt

A B

<0.04 ppm (<10th percentile)

0.04–0.070 ppm (10–25th percentile)

0.071–0.31 ppm (25–75th percentile)

0.32–0.61 ppm (75–90th percentile)

0.62–3.7 ppm (90–97.5th percentile)

3.8–21 ppm (>97.5th percentile)

Bismuth (parts per million)

Crustal abundance = 0.0082 ppm

Limit of detection = 0.04 ppm

0.00811 25

0

200

400

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1403

 <0.04

 21.0000

 0.5008

 0.1234

 0.1900

 0.0082

 1.711

 0.04567

 8.019

 74.54

Bi

parts per million (ppm)

0.1 1 10

Frequency

Cumulative Frequency

Concentration, in parts per million
18 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Bismuth (Bi) is strongly chalcophile in its geochemistry and is similar to antimony in its behavior. Bismuth, probably in bismuthinite or sulfosalt and telluride minerals, commonly is associated 

with lead-rich minerals in hydrothermal deposits. It is relatively immobile during weathering.

Samples having high (>90th percentile) bismuth concentrations correlate well with areas of 

hydrothermal metal deposits in the entire Colorado Mineral Belt within the study area (figs. 12 and 

13). Stream-sediment samples with high bismuth concentrations (>90th percentile) are found in a 

well-defined dispersion train along Clear Creek below the Blackhawk and Central City–Idaho Springs 

districts eastward to the range front. Other areas having samples with high (>90th percentile) bismuth concentrations in the mineral belt include the Alma, Argentine, Bonanza, Boulder-Tungsten, 

Breckenridge, Browns Canyon, Chalk Creek, Consolidated Montgomery, Dumont, Gold Brick, 

Henderson, Jamestown, Lake Albion, Leadville, Lincoln Gulch, Monarch, Montezuma–Geneva 

Creek, North Gilpin, Red Mountain, Silver Plume–Georgetown, Tenmile–Kokomo, Ward, Whitepine, 

and Winfield districts. Outside the mineral belt, samples with high (>97.5th percentile) bismuth concentrations are found in the vicinity of the Lake George and Manhattan districts.

Figure 13. Mining districts associated with 

the element bismuth in stream sediments in 

central Colorado.

^ Clear Ck.

Denver

NORTH GILPIN

ARGENTINE

LEADVILLE

BOULDER–TUNGSTEN

DUMONT

BRECKENRIDGE

WHITEPINE

JAMESTOWN

GOLD

BRICK

WINFIELD

CHALK

CREEK

HENDERSON

BROWN'S

CANYON

RED MT

MONARCH

WARD

MONTEZUMA–GENEVA CREEK

BLACKHAWK

SILVER PLUME–GEORGETOWN

CENTRAL CITY–IDAHO SPRINGS

ALMA

CONSOLIDATED MONTGOMERY

TENMILE–

KOKOMO

LINCOLN

GULCH

LAKE ALBION

LAKE GEORGE

MANHATTAN

BONANZA

–107° –106° –105°

41°

40°

39°

38°

37°

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Mining districts from Wilson (2003).

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt
Geochemistry Maps and Discussions 19

Figure 14. Maps of central Colorado stream-sediment geochemistry—cadmium (Cd).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° V106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Cadmium

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Colorado state border

Study area boundary

Colorado Mineral Belt

A B

<0.1ppm (<25th percentile)

0.101–0.500 ppm (25–75th percentile)

0.501–2.60 ppm (75–90th percentile)

2.61–10.8 ppm (90–97.5th percentile)

10.9–84.0 ppm (>97.5th percentile)

Cadmium (parts per million)

Crustal abundance = 0.16 ppm

Limit of detection = <0.1 ppm

0.0211 90

0

200

400

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1479

 <0.1

 84.0000

 1.2462

 0.2223

 0.2000

 0.0222

 4.647

 0.1208

 9.882

 130.3

Cd

parts per million (ppm)

Frequency

Cumulative Frequency

Concentration, in parts per million

0.1 1 10
20 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Cadmium (Cd) is strongly chalcophile in its geochemistry and is similar to zinc and bismuth 

in its behavior. Cadmium commonly substitutes for zinc in sphalerite. It is relatively mobile during 

weathering and may be adsorbed on manganese- and iron-hydroxide precipitates or be present in 

organic matter. Organic-rich shales or carbonate rocks commonly are enriched in cadmium.

Stream-sediment samples containing cadmium (>90th percentile) identify the entire Colorado 

Mineral Belt (figs. 14 and 15). The presence of cadmium indicates occurrence of sphalerite or 

complex sulfide minerals in polymetallic veins and replacement deposits that constitute the majority of deposits in the mineral belt. A lower-level (90 to 97.5th percentile) dispersion train is evident below the Blackhawk and Central City–Idaho Springs districts along Clear Creek eastward 

to the range front. Other districts in the mineral belt associated with high cadmium concentrations 

(>90th percentile) are the Alma, Argentine, Bonanza, Boulder-Tungsten, Breckenridge, Browns 

Canyon, Chalk Creek, Climax, Daily, Dumont, Empire, Gold Brick, Gold Hill, Henderson, Lake 

Albion, Leadville, Monarch, Montezuma–Geneva Creek, Sedalia, Silver Plume–Georgetown, 

St. Kevin–Sugarloaf, Tenmile-Kokomo, Upper Blue River, Whitepine, and Winfield districts. Outside the mineral belt, low-level clusters or single samples of high cadmium concentrations (90 to 

97.5th percentile) are found around the Cotopaxi, Guffey, Lake George, Thirtyone Mile Creek, and 

Rosita Hills districts and downstream of the Grape Creek district. A number of samples with high concentrations (90th to 97.5th percentile) are underlain by the organic-rich Pierre Shale in the southeastern and northwestern parts of the study area.

Figure 15. Mining districts and rock units 

associated with the element cadmium in 

stream sediments in central Colorado.

ARGENTINE

LEADVILLE

GOLD HILL

BOULDER–TUNGSTEN

DUMONT

BRECKENRIDGE

WHITEPINE

ROSITA HILLS

BLACKHAWK

DAILY

GOLD

BRICK

WINFIELD

ST. KEVIN–

SUGARLOAF

LAKE GEORGE

UPPER BLUE RIVER

CHALK

CREEK

COTOPAXI

GUFFEY

GRAPE

CREEK

BROWN'S CANYON

LAKE ALBION

MONARCH

MONTEZUMA–

GENEVA CREEK

SILVER PLUME–GEORGETOWN

CENTRAL CITY–IDAHO SPRINGS

ALMA

TENMILE–

KOKOMO

HENDERSON

EMPIRE

CLIMAX

SEDALIA

THIRTYONE

MILE CREEK

BONANZA

^ Clear Ck.

Denver

Cañon City

–107° –106° –105°

41°

40°

39°

38°

37°

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

Pierre Shale boundary

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Mining districts from Wilson (2003), 

rock units from Church and others (2012).

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt
Geochemistry Maps and Discussions 21

Figure 16. Maps of central Colorado stream-sediment geochemistry—calcium (Ca).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

Colorado state border

Study area boundary

Colorado Mineral Belt

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Calcium

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

A B

0.1200–0.5200% (<2.5th percentile)

0.5200–0.8100% (2.5–10th percentile)

0.8100–1.100% (10–25th percentile)

1.100–2.478% (25–75th percentile)

2.478–3.300% (75–90th percentile)

3.300–6.000% (90–97.5th percentile)

6.000–15.50% (>97.5th percentile)

Calcium (weight percent)

Crustal abundance = 4.66% (46,600 ppm)

Limit of detection = not applicable

0.12 16

0

70

140

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1479

 0.1200

 15.5000

 2.0187

 1.6729

 1.7000

 1.1000

 1.512

 0.03932

 3.534

 19.51

Ca

weight percent (wt%)

Frequency

Cumulative Frequency

Concentration, in parts per million

1 10
22 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Calcium (Ca) is the principal cation in the common minerals calcium plagioclase, calcite, 

dolomite, and gypsum. Calcium concentrations are highest in intermediate to mafic igneous rocks, 

carbonate-rich sedimentary rocks, and in evaporites. It is mobile during weathering and primarily is 

precipitated in carbonates.

Stream-sediment samples having high calcium concentrations (>90th percentile) in the study 

area are associated with four diverse groups of bedrock units (figs. 16 and 17). These units are 

(1) Pennsylvanian to Cretaceous carbonate-bearing sedimentary rocks such as the Chugwater, 

Niobrara, and Morrison Formations; (2) Paleozoic limestone-, dolomite- and dolomitic limestonebearing units, such as the Madera, Manitou, Leadville, and Minturn Formations; (3) evaporite-bearing 

units such as the Eagle Valley and Minturn Formations; and (4) mafic and ultramafic metavolcanic 

rocks that are part of the Proterozoic volcanic-arc rocks of the Green Mountain arc in the far northern part of the study area plus the eastern Gunnison arc near Salida and extending into the northern Wet Mountains. Also in this last group are mafic metavolcanic and metagabbroic rocks east of 

Breckenridge. Within the Colorado Mineral Belt, calcium concentrations generally fall below the 

90th percentile, with the exception of high calcium concentrations associated with samples from the 

Monarch (>97.5th percentile), Henderson, and Jamestown (both 90–97.5th percentile) districts. Low 

Ca concentrations are evident in samples underlain by the Pikes Peak batholith, reflecting predominance of potassium feldspar relative to plagioclase in that batholith.

Figure 17. Mining districts and rock units

associated with the element calcium in stream 

sediments in central Colorado.

^Denver

Green

Mountain

volcanic arc

JAMESTOWN

MONARCH

COTOPAXI

HENDERSON

Salida

Breckenridge

WET MOUNTAINS

Pikes Peak

batholith

Gunnison

volcanic arc

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

Igneous rock boundary

EXPLANATION

Carbonate-bearing rock boundary

Evaporite-bearing rock boundary

Limestone-, dolomite-, and dolomitic-

 limestone–bearing rock boundary

Mining districts from Wilson (2003),

rock units from Church and others (2012).

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt
Geochemistry Maps and Discussions 23

Figure 18. Maps of central Colorado stream-sediment geochemistry—cerium (Ce).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° 105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Cerium

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Colorado state border

Study area boundary

Colorado Mineral Belt

A B

19.0–48.0 ppm (<2.5th percentile)

48.1–67.0 ppm (2.5–10th percentile)

67.1–86.0 ppm (10–25th percentile)

86.1–210 ppm (25–75th percentile)

211–369 ppm (75–90th percentile)

370–678 ppm (90–97.5th percentile)

679–4,520 ppm (>97.5th percentile)

Cerium (parts per million)

Crustal abundance = 66.4 ppm

Limit of detection = not applicable

19 5,000

0

70

140

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1479

 19.0000

 4520.0000

 190.3342

 141.3132

 128.0000

 110.0000

 228.9

 5.951

 7.639

 104.2

Ce

parts per million (ppm)

Frequency

Cumulative Frequency

Concentration, in parts per million

100 1,000
24 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Cerium (Ce) is one of 15 metallic elements called rare earth elements (REEs). The REEs include 

cerium, dysprosium, erbium, europium, gadolinium, holmium, lanthanum, lutetium, neodymium, 

praseodymium, promethium, samarium, terbium, thulium, and ytterbium. Yttrium is very similar 

to and commonly grouped with the REEs. The report contains geochemical maps of elements shown 

in bold in the previous sentences. All of these elements are similar geochemically and typically are 

found together, although in different elemental abundances. Despite their name, the REEs are relatively plentiful in the Earth’s crust. The REEs are strongly lithophile in igneous rocks and typically 

are concentrated in the most evolved rocks, such as granites and granite pegmatites. The REEs content 

generally is highest in alkaline rocks and carbonatites. With exception of europium, REEs (with their 

large ionic radii and trivalent charge) are concentrated in residual liquids during differentiation and 

commonly are concentrated in late trace minerals, such as fluorite, apatite, zircon, sphene, garnet, 

epidote-group minerals, monazite, xenotime, allanite, and thorite. The REE-bearing minerals typically 

are resistant to weathering. In sediments and sedimentary rocks, REEs are concentrated in heavymineral residual or alluvial placer deposits, in highly weathered deposits such as karst (for example, 

bauxite), and in phosphorite.

Highest concentrations of cerium (>90th percentile) are found in stream-sediment samples 

eroded from felsic igneous intrusions of various ages from Precambrian to Tertiary (figs. 18 and 19). 

Samples from areas underlain by Mesoproterozoic felsic igneous bodies in the northern two-thirds 

of the study area, including the Pikes Peak and Sherman batholiths and the Kenosha Pass, St. Vrain, 

St. Kevin, and Log Cabin plutons, consistently show the highest concentrations of cerium. Samples 

obtained over or near plutons of similar age and composition in the southern one-third show moderate concentrations of Ce, generally in the 90th to 97.5th percentile. Mining districts having spatial 

associations with high (>90th percentile) cerium values all are located in the Colorado Mineral Belt 

and include the Argentine, Boulder-Tungsten, Central City–Idaho Springs, Daily, Eldora, Gold Hill, 

Granite, Henderson, Independence, Jamestown, Silver Plume–Georgetown, and Tincup–Cumberland 

Pass districts.

Figure 19. Mining districts and rock units

associated with the element cerium in stream 

sediments in central Colorado.

Kenosha Pass

pluton

St. Kevin pluton

Sherman

batholith

St.

Vrain

pluton

Log Cabin

pluton

^ Clear Ck.

Denver

Pikes Peak

batholith

ARGENTINE

BOULDER–TUNGSTEN GOLD HILL

JAMESTOWN

TINCUP–

CUMBERLAND PASS

SILVER PLUME–

GEORGETOWN

CENTRAL CITY–

IDAHO SPRINGS

GRANITE

INDEPENDENCE

DAILY

ELDORA

HENDERSON

–107° –106° –105°

41°

40°

39°

38°

37°

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Mining districts from Wilson (2003),

rock units from Church and others (2012).

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Generalized intrusion boundary
Geochemistry Maps and Discussions 25

Figure 20. Maps of central Colorado stream-sediment geochemistry—cesium (Cs).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Cesium

A B

Colorado state border

Study area boundary

Colorado Mineral Belt

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

<0.05 ppm (<2.5th percentile)

0.05–1.80 ppm (2.5–10th percentile)

1.81–2.60 ppm (10–25th percentile)

2.61–6.00 ppm (25–75th percentile)

6.01–8.30 ppm (75–90th percentile)

8.31–12.0 ppm (90–97.5th percentile)

Cesium (parts per million)

Crustal abundance = 2.6 ppm

Limit of detection = 0.05 ppm

0.0111 30

0

70

140

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1064

 <0.05

 28.0000

 4.7043

 3.3523

 4.2000

 <0.05

 3.183

 0.09758

 2.095

 7.867

Cs

parts per million (ppm)

Frequency

Cumulative Frequency

Concentration, in parts per million

0.1 1 10
26 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Cesium (Cs) typically is concentrated in highly evolved igneous rocks (such as granite pegmatites) in silica-undersaturated rocks, and in hydrothermal potassium feldspar. It is found primarily in 

the minerals leucite, mica, potassium feldspar, and beryl. During weathering, cesium is mobile and 

clay minerals can become enriched.

A strong cluster of stream-sediment samples with high cesium concentrations (>90th percentile) 

identifies varied felsic igneous rocks within the northern end of the Colorado Mineral Belt (figs. 20 

and 21). Mining districts having samples associated with high cesium concentrations (>97.5th percentile) in the mineral belt include the Alicante, Alma, Argentine, Breckenridge, Boulder-Tungsten, 

Central City–Idaho Springs, Gold Hill, Montezuma–Geneva Creek, Silver Plume–Georgetown, and 

Upper Blue River districts, with several of the highest concentrations (20–23 ppm) from samples 

within and just downstream of the Henderson district. Outside the mineral belt, high cesium concentrations were found in a few samples near the Lake George district. Scattered sample locations with 

high cesium concentrations (>90th percentile) in the northern part of the study area also are underlain 

by various felsic igneous rocks.

Figure 21. Mining districts and rock units

associated with the element cesium in stream 

sediments in central Colorado.

^ Clear Ck.

Denver

ARGENTINE

GOLD HILL

BOULDER–TUNGSTEN

BRECKENRIDGE

ALMA

LAKE GEORGE

UPPER BLUE RIVER

HENDERSON

MONTEZUMA–GENEVA CREEK

SILVER PLUME–GEORGETOWN

CENTRAL CITY–IDAHO SPRINGS

ALICANTE

Silver Plume

pluton

Boulder

Creek

pluton

–107° –106° –105°

41°

40°

39°

38°

37°

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Mining districts from Wilson (2003),

rock units from Church and others (2012).

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Generalized intrusion boundary
Geochemistry Maps and Discussions 27

Figure 22. Maps of central Colorado stream-sediment geochemistry—chromium (Cr).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Chromium

A B

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Colorado state border

Study area boundary

Colorado Mineral Belt

<9.1 ppm (<2.5th percentile)

9.1–17 ppm (2.5–10th percentile)

18–27 ppm (10–25th percentile)

28–65 ppm (25–75th percentile)

66–93 ppm (75–90th percentile)

94–130 ppm (90–97.5th percentile)

140–410 ppm (>97.5th percentile)

Chromium (parts per million)

Crustal abundance = 122 ppm

Limit of detection = 1 ppm

0.211 450

0

80

160

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1479

 <1

 410.0000

 50.2031

 39.9724

 43.0000

 35.0000

 33.87

 0.8806

 2.299

 12.57

Cr

parts per million (ppm)

Frequency

Cumulative Frequency

Concentration, in parts per million

1 10 100
28 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Chromium (Cr) is most abundant in igneous rocks of ultramafic and mafic compositions, where 

it typically resides in the minerals chromite, olivine, pyroxene, and some garnets. The abundance of 

chromium in most other rocks is very low. Chromite is insoluble during weathering and may be concentrated in residual, alluvial, and marine placer deposits.

High chromium concentrations (90th to >97th percentile) in stream-sediment samples correspond 

roughly with the occurrence of early Proterozoic and Cambrian mafic and ultramafic rocks (figs. 22 

and 23). These types include the Proterozoic Green Mountain volcanic-arc rocks in the northern part 

of the Colorado Mineral Belt area and the Gunnison arc rocks of the west-central part of the area, 

and the mafic metavolcanic and gabbroic rocks in the western Front Range just east of Breckenridge. 

Several high-chromium samples also occur near the Cambrian mafic and ultramafic rocks in the 

northern Wet Mountains. Within and around the mineral belt, however, many samples with concentrations in the upper percentile ranges (>90th percentile) were taken from areas with bedrock compositions typically low in chromium (such as felsic igneous and sedimentary rocks); nevertheless, samples 

with high chromium concentrations likely are related to volumetrically minor mafic dikes. Clusters 

of stream-sediment samples with high chromium concentrations (>97.5th percentile) are present in 

the northern end of the mineral belt in the Boulder-Tungsten, Gold Hill, Magnolia, Blackhawk, and 

Central City–Idaho Springs districts, as well as farther southwest in the mineral belt in the Argentine, 

Halls Gulch, and Montezuma–Geneva Creek districts. The Mesoproterozoic Pikes Peak batholith is 

noticeably depleted in chromium, reflecting the evolved granitic composition of the batholith.

Figure 23. Mining districts and rock units

associated with the element chromium in stream 

sediments in central Colorado.

^Denver

Gunnison volcanic arc

Green Mountain

volcanic arc

Breckenridge

WET MOUNTAINS

Cañon City

Pikes Peak

batholith

ARGENTINE

GOLD HILL BOULDER-TUNGSTEN

BLACKHAWK

MONTEZUMAGENEVA CREEK

CENTRAL CITYIDAHO SPRINGS

MAGNOLIA

HALL’S GULCH

–107° –106° –105°

41°

40°

39°

38°

37°

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Mining districts from Wilson (2003),

rock units from Church and others (2012).

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Generalized igneous rock boundary
Geochemistry Maps and Discussions 29

Figure 24. Maps of central Colorado stream-sediment geochemistry—cobalt (Co).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Cobalt

A B

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Colorado state border

Study area boundary

Colorado Mineral Belt

<4.4 ppm (<2.5th percentile)

4.4–6.6 ppm (2.5–10th percentile)

6.7–8.7 ppm (10–25th percentile)

8.8–16 ppm (25–75th percentile)

17–20 ppm (75–90th percentile)

21–27 ppm (90–97.5th percentile)

28–110 ppm (>97.5th percentile)

Cobalt (parts per million)

Crustal abundance = 29.0 ppm

Limit of detection = 1 ppm

0.211 120

0

125

250

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1479

 <1

 110.0000

 12.9870

 11.5653

 12.0000

 13.0000

 7.074

 0.1839

 4.005

 37.27

Co

parts per million (ppm)

Frequency

Cumulative Frequency

Concentration, in parts per million

1 10 100
30 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Cobalt (Co) is most abundant in ultramafic to mafic igneous rocks, where it is present in the 

minerals olivine and pyroxene, in related serpentinitic alteration products, and in magmatic sulfide 

minerals. Cobalt also is concentrated in some hydrothermal sulfide deposits, in some bog iron and 

siderite deposits, and in pyritic shales. Cobalt is moderately mobile during weathering and may be 

concentrated in manganese- and iron-oxyhydroxide minerals in the aqueous environment, particularly 

in areas of natural or anthropogenic acid-rock drainage.

Within the Colorado Mineral Belt, a prominent cluster of stream-sediment samples with high 

cobalt concentrations (>97.5th percentile) identifies mafic to intermediate igneous rock types within 

the Argentine, Halls Gulch, and Montezuma–Geneva Creek districts (figs. 24 and 25). Samples 

from the northeastern end of the mineral belt have slightly lower cobalt concentrations (90 to 

97.5th percentile) and highlight the Blackhawk, Boulder-Tungsten, Central City–Idaho Springs, 

Chicago Creek–Freeland, Dumont, Eldora, Gold Hill, Magnolia, and North Gilpin districts. Outside the mineral belt, high cobalt concentrations (>90th percentile) are found in samples from areas 

overlying or near intermediate and mafic volcanic and subvolcanic intrusive rocks of the Thirtynine 

Mile volcanic field, as well as throughout the northern Wet Mountains, where Cambrian alkaline 

mafic and ultramafic plutons and dikes are present. Samples with high cobalt concentrations in 

districts outside the mineral belt arise from Mesoproterozoic stratabound base-metal deposits in the 

Cotopaxi, Grape Creek, Guffey, Oak Creek, Rosita Hills, and Silver Cliff districts. Other scattered 

samples with high cobalt concentrations may indicate volumetrically minor mafic to intermediate 

igneous rocks. The Mesoproterozoic Pikes Peak batholith is depleted noticeably in cobalt, reflecting 

the evolved granitic composition of that batholith.

Figure 25. Mining districts and rock units

associated with the element cobalt in stream 

sediments of central Colorado.

^Denver

NORTH GILPIN

ARGENTINE

GOLD HILL

BOULDER–TUNGSTEN

DUMONT

ROSITA HILLS

MONTEZUMA–GENEVA CREEK

SILVER CLIFF

HALL'S GULCH

COTOPAXI

GUFFEY

CHICAGO CREEK–

FREELAND

BLACKHAWK

CENTRAL CITY–

IDAHO SPRINGS

ELDORA

GRAPE

CREEK

OAK CREEK 

NORTH/SOUTH

Thirtynine Mile

volcanic field

MAGNOLIA

WET MOUNTAINS

Cañon City

Pikes Peak

batholith

–107° –106° –105°

41°

40°

39°

38°

37°

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Mining districts from Wilson (2003),

rock units from Church and others (2012).

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Igneous rock boundary
Geochemistry Maps and Discussions 31

Figure 26. Maps of central Colorado stream-sediment geochemistry—copper (Cu).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Copper

A B

Colorado state border

Study area boundary

Colorado Mineral Belt

<4.4 ppm (<2.5th percentile)

4.4–8.5 ppm (2.5–10th percentile)

8.6–13 ppm (10–25th percentile)

14–31 ppm (25–75th percentile)

32–54 ppm (75–90th percentile)

55–220 ppm (90–97.5th percentile)

230–2,600 ppm (>97.5th percentile)

Copper (parts per million)

Crustal abundance = 68.0 ppm

Limit of detection = 2 ppm

0.411 3,000

0

100

200

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1479

 <2

 2600.0000

 39.5433

 21.0740

 20.0000

 12.0000

 113.4

 2.948

 12.48

 216.6

Cu

parts per million (ppm)

Frequency

Cumulative Frequency

Concentration, in parts per million

1 10 100 1,000

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
32 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Copper (Cu) is abundant in mafic igneous rocks where it is present in the minerals pyroxene, 

amphibole, biotite, and chalcopyrite. Copper can be highly concentrated in hydrothermal sulfide 

deposits, in bog iron and siderite deposits, pyritic shales, and stratabound sulfide deposits in sedimentary rocks. Copper is mobile during weathering and may be concentrated in manganese- and ironoxyhydroxide minerals in streams.

Stream-sediment samples with high concentrations of copper (>90th percentile) strongly identify 

mineralized areas within the entire CMB (figs. 26 and 27). A well-defined dispersion train of samples 

with high copper concentrations along Clear Creek extends downstream from the Blackhawk and 

Central City–Idaho Springs districts eastward to the range front. Other mining districts within the 

Colorado Mineral Belt from which samples bearing high concentrations of copper (>90th percentile) were obtained include the Alma, Argentine, Boulder-Tungsten, Breckenridge, Chalk Creek, 

Consolidated Montgomery, Dumont, Empire, Gilman-Redcliff, Gold Brick, Gold Hill, Halls Gulch, 

Henderson, Jamestown, Leadville, Lincoln Gulch, Monarch, Montezuma–Geneva Creek, North 

Gilpin, Red Mountain, Silver Plume–Georgetown, Tarryall Creek, Tenmile-Kokomo, Ward, and 

Whitepine districts. South of the mineral belt, high copper concentrations are found in samples from 

the Blanca, Lake George, Oak Creek, and the Rosita Hills districts. Conversely, stream sediments 

from samples collected over and near the Pikes Peak batholith are uniformly lower in copper content. 

Just outside the study area boundary in the southern part of the mineral belt, a single sample containing anomalous copper was obtained from the Bonanza district, where a variety of base-metal ores 

were mined (Knepper and Marrs, 1971). The same sample is anomalous in Ag, As, Bi, Cd, Cu, Hg, 

In, Pb, S, Sb, Sn, Te, Tl, W, and Zn. Also, outside the study area and just north of Denver, a sample 

contains anomalous copper. That sample and a few adjacent samples contain variously anomalous 

concentrations of As, Bi, Cd, Cu, Hg, Mo, Pb, Sb, and Zn, the same suite of metals found in an indepth soil study around Denver by Smith and others (2011), who attributed the metals to historical 

anthropogenic mining-related activities.

Figure 27. Mining districts and rock unit

associated with the element copper in stream 

sediments of central Colorado.

Pikes Peak

batholith

^ Clear Ck.

Denver

NORTH GILPIN

ARGENTINE

LEADVILLE

GOLD HILL

BOULDER–TUNGSTEN

DUMONT

BRECKENRIDGE

WHITEPINE

JAMESTOWN

ALMA

GOLD

BRICK

BLANCA

GILMAN–

REDCLIFF

LAKE GEORGE

HENDERSON

TARRYALL CREEK

RED MT

MONARCH

WARD

BLACKHAWK

CENTRAL CITY–IDAHO SPRINGS

CONSOLIDATED MONTGOMERY

HALL'S GULCH TENMILE–

KOKOMO

EMPIRE

CHALK

CREEK

LINCOLN

GULCH

OAK CREEK

NORTH/SOUTH

ROSITA HILLS

Cañon City

SILVER PLUME–GEORGETOWN

MONTEZUMA–

GENEVA CK.

BONANZA

–107° –106° –105°

41°

40°

39°

38°

37°

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Mining districts from Wilson (2003),

rock units from Church and others (2012).

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Generalized intrusion boundary
Geochemistry Maps and Discussions 33

Figure 28. Maps of central Colorado stream-sediment geochemistry—europium (Eu).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

Central Colorado Stream-Sediment

Geochemistry—Europium

A B

EXPLANATION

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Colorado state border

Study area boundary

Colorado Mineral Belt

<2 ppm (<25th percentile)

2.0–3.0 ppm (25–75th percentile)

3.1–4.0 ppm (75–90th percentile)

4.1–5.0 ppm (90–97.5th percentile)

5.1–14 ppm (>97.5th percentile)

Europium (parts per million)

Crustal abundance = 2.14 ppm

Limit of detection = 2 ppm

0.411 16

0

90

180

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

369

 <2

 14.0000

 1.8708

 1.2366

 2.0000

 0.4111

 1.574

 0.08196

 1.784

 9.01

Eu

parts per million (ppm)

Frequency

Cumulative Frequency

Concentration, in parts per million

1 10
34 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Europium (Eu) is one of 15 metallic elements called rare earth elements (REEs). The REEs, 

including europium, are strongly lithophile in igneous rocks. Most REEs, with their large ionic radii 

and trivalent charge, are concentrated in residual liquids during differentiation and crystallize in 

trace minerals in evolved rocks. However, because of its divalent rather than trivalent charge and its 

suitable (smaller) ionic size, europium preferentially substitutes for calcium in early-crystallizing 

plagioclase. Thus, the remaining REE-bearing melt may be relatively depleted in europium as it crystallizes. See the cerium map (fig. 19) for further discussion on the geochemical behavior of the REEs.

In this study, only a small subset of samples (369 out of 1,479) from the Grossman (1998) and 

the Church and others (2012) studies were analyzed for europium. Concentrations of europium in 

the study area (fig. 28) are low overall. The limited number of analyses and the narrow concentration 

range for europium (2–8 parts per million, single outlier at 14 parts per million) results in this element 

being a poor discriminator of rock associations. Within the Colorado Mineral Belt, only the Argentine 

district is associated spatially with samples containing relatively high europium concentrations 

(figs. 28 and 29). Both within and outside the mineral belt, samples with relatively high europium 

concentrations also are enriched in Ce, La, and Y. These REE patterns and related geologic associations are better elucidated by maps of Ce, La, and Y, because many more samples (n = 1,479) were 

analyzed for those elements.

Figure 29. Mining district associated with 

the element europium in stream sediments 

of central Colorado.

^Denver

ARGENTINE

–107° –106° –105°

41°

40°

39°

38°

37°

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Mining districts from Wilson (2003).

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt
Geochemistry Maps and Discussions 35

Figure 30. Maps of central Colorado stream-sediment geochemistry—gallium (Ga).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Gallium

A B

Colorado state border

Study area boundary

Colorado Mineral Belt

<8.5 ppm (<2.5th percentile)

8.5–13 ppm (2.5–10th percentile)

14–15 ppm (10–25th percentile)

16–20 ppm (25–75th percentile)

21–24 ppm (75–90th percentile)

25–30 ppm (90–97.5th percentile)

31–55 ppm (<97.5th percentile)

Gallium (parts per million)

Crustal abundance = 19.0 ppm

Limit of detection = 4 ppm

0.811 60

0

175

350

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1433

 <4

 55.0000

 18.0087

 17.0550

 18.0000

 17.0000

 5.118

 0.1352

 0.747

 5.027

Ga

parts per million (ppm)

Frequency

Cumulative Frequency

Concentration, in parts per million

1 10

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
36 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Gallium (Ga) in igneous rocks substitutes for aluminum in silicate mineral structures. The highest proportion of aluminum and therefore gallium is found in alkaline and alkali-calcic intermediate 

rocks. Gallium also may be concentrated in late-stage granite pegmatites. During weathering gallium 

is concentrated with aluminum in clay minerals.

A general but tenuous correlation links samples containing high gallium concentrations with 

felsic and intermediate plutonic rocks (figs. 1 and 30). The highest gallium concentrations (90th to 

>97th percentile) in the study area are associated with stream-sediment samples derived from rocks of 

the Mesoproterozoic Pikes Peak batholith and many other middle and early Proterozoic granitic and 

intermediate plutons (figs. 30 and 31). Samples from areas near and overlying the alkali-calcic to alkaline, intermediate to mafic volcanic rocks of the Thirtynine Mile volcanic field, the eastern San Juan 

volcanic field (just southwest of the study area), and Middle Park show similar gallium concentrations. Those gallium concentrations generally are low to moderate (75th percentile and below) in most 

sedimentary rocks and associated unconsolidated sediments in the study area.

Figure 31. Rock units associated with 

the element gallium in stream sediments 

of central Colorado.

^Denver

Pikes Peak

batholith

Middle Park

Formation

Thirtynine Mile

volcanic field

San

Juan

volcanic

field

–107° –106° –105°

41°

40°

39°

38°

37°

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Rock units from Church and others (2012).

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Rock unit boundary
Geochemistry Maps and Discussions 37

Figure 32. Maps of central Colorado stream-sediment geochemistry—holmium (Ho).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Holmium

A B

Colorado state border

Study area boundary

Colorado Mineral Belt

<4 ppm (<75th percentile)

4.0–6.0 ppm (75–90th percentile)

6.1–10 ppm (90–97.5th percentile)

11–27 ppm (>97.5th percentile)

Holmium (parts per million)

Crustal abundance = 1.26 ppm

Limit of detection = <4 ppm

0.811 30

0

125

250

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

293

 <4

 27.0000

 2.1576

 1.2529

 <4

 <4

 3.254

 0.1901

 3.571

 17.15

Ho

parts per million (ppm)

Frequency

Cumulative Frequency

Concentration, in parts per million

1 10

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
38 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Holmium (Ho) is one of 15 metallic elements called rare earth elements (REEs). The REEs, 

including holmium, are strongly lithophile in igneous rocks. See the cerium map (fig. 19) for further 

discussion on the geochemical behavior of the REEs.

In this study, only a small subset of samples (293 out of 1,479) from the Grossman (1998) study 

were analyzed for holmium (fig. 32). The highest concentrations of holmium (>90th percentile) are 

found in samples from the main phase of the Mesoproterozoic Pikes Peak batholith, and in samples 

overlying the Mesoproterozoic Yankee Boy and Shawnee plutons immediately north of the Pikes 

Peak batholith; and in addition in one sample from the Paleoproterozoic Service Creek pluton in the 

Park Range (figs. 32 and 33). Map patterns of samples having relatively high holmium concentrations 

agree fairly well with patterns for Ce, La, and Y. The REE patterns and related geologic associations 

are better elucidated by maps of Ce, La, and Y, however, because many more samples (n = 1,479) 

were analyzed for those elements.

Figure 33. Rock units associated with

the element holmium in stream sediments 

of central Colorado.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Rock units from Church and others (2012).

Pikes Peak

batholith

Yankee Boy pluton

Shawnee

pluton

Service

Creek

pluton

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Generalized intrusion boundary
Geochemistry Maps and Discussions 39

Figure 34. Maps of central Colorado stream-sediment geochemistry—indium (In).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Indium

A B

Colorado state border

Study area boundary

Colorado Mineral Belt

<0.02 ppm (<2.5th percentile)

0.02–0.040 ppm (2.5–10th percentile)

0.041–0.050 ppm (10–25th percentile)

0.051–0.10 ppm (25–75th percentile)

0.11–0.17 ppm (75–90th percentile)

0.18–0.63 ppm (90–97.5th percentile)

0.64–5.5 ppm (>97.5th percentile)

Indium (parts per million)

Crustal abundance = 0.24 ppm

Limit of detection = 0.02 ppm

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1072

 <0.02

 5.5000

 0.1219

 0.0784

 0.070

 0.060

 0.2777

 0.0084

 10.7967

 161.1304

ln,

parts per million (ppm)

0.01 0.1 1 8

40

80

120

160

0

40%

80%

20%

60%

Concentration, parts per million

Frequency

Cumulative Frequency

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
40 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Indium (In) is concentrated in late-stage igneous differentiates such as granite pegmatites and 

greisens and may be concentrated in hydrothermal deposits, primarily in sphalerite. It is also concentrated in some pyritic marine shales. During weathering indium is moderately mobile and may 

be concentrated in iron and manganese oxyhydroxides and in iron carbonates.

The highest indium (>97.5th percentile) concentrations in the study area are largely confined 

to stream-sediment samples within the Colorado Mineral Belt and, in general, anomalous indium 

(90th to 97.5th percentile) either was found in samples from within the mineral belt or in samples 

overlying the Mesoproterozoic Pikes Peak batholith (figs. 34 and 35). A single sample (>97.5th percentile) from the Lake George district on the western side of the Pikes Peak pluton may be related to 

a greisen deposit there. A dispersion train of indium from the Blackhawk district down Clear Creek 

to the range front is evident. Within the mineral belt, clusters of samples with high indium concentrations (>97.5th percentile) also are found in the Alma, Argentine, Breckenridge, Henderson, Leadville, 

Monarch, Montezuma–Geneva Creek, Tenmile-Kokomo, and Whitepine districts. Just outside the 

study area boundary in the southern part of the mineral belt, a single sample containing anomalous 

indium and several other metals came from the Bonanza district (see copper discussion, fig. 27).

Figure 35. Mining districts and rock unit

associated with the element indium in stream 

sediments of central Colorado.

^ Clear Ck.

Denver

Pikes Peak

batholith

ARGENTINE

LEADVILLE

BRECKENRIDGE

WHITEPINE

BLACKHAWK

ALMA

MONARCH

MONTEZUMA–GENEVA CREEK

TENMILE–

KOKOMO

HENDERSON

LAKE GEORGE

Cañon City

BONANZA

–107° –106° –105°

41°

40°

39°

38°

37°

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Mining districts from Wilson (2003),

rock units from Church and others (2012).

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Generalized intrusion boundary
Geochemistry Maps and Discussions 41

Figure 36. Maps of central Colorado stream-sediment geochemistry—iron (Fe).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Iron

A B

Colorado state border

Study area boundary

Colorado Mineral Belt

0.790–1.80% (<2.5th percentile)

1.81–2.36% (2.5–10th percentile)

2.37–3.00% (10–25th percentile)

3.01–5.10% (25–75th percentile)

5.11–6.73% (75–90th percentile)

6.74–11.1% (90–97.5th percentile)

11.2–38.0% (>97.5th percentile)

Iron (weight percent)

Crustal abundance = 6.22%

Limit of detection = not applicable

0.79 40

0

70

140

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1479

 0.7900

 38.0000

 4.5267

 4.0168

 3.9000

 3.3000

 2.947

 0.07663

 4.884

 36.66

Fe

weight percent (wt%)

Frequency

Cumulative Frequency

Concentration, in weight percent

1 10

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
42 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Iron (Fe) content of rocks is highest in mafic and ultramafic igneous rocks, iron formations, and 

ironstone. In the secondary environment, iron is weathered easily from many silicate and sulfide minerals and is readily transported in acidic, reduced groundwater and in surface water. It is precipitated 

from groundwater and surface water by oxidation.

High iron concentrations (>90th percentile) identify scattered stream-sediment samples obtained 

throughout the Colorado Mineral Belt; four strong clusters (>97.5th percentile) of samples lie over the 

Blackhawk, Browns Canyon, Central City–Idaho Springs, Montezuma–Geneva Creek, Red Mountain, 

and Sedalia districts (figs. 36 and 37). Samples having lower iron concentrations (75th to >97.5th percentile) are common in the mafic and ultramafic metavolcanic rocks that are part of the Proterozoic 

volcanic rocks of the Gunnison volcanic arc and the northern Wet Mountains in the central part of the 

study area, in the Green Mountain volcanic arc in the far northern part of the study area, and in the mafic 

metavolcanic and metagabbroic enclave near Swandyke (east of Breckenridge).

Figure 37. Mining districts and rock units

associated with the element iron in stream 

sediments of central Colorado.

^Denver

MONTEZUMA–

GENEVA CREEK

BLACKHAWK

RED MT

BROWN'S

CANYON

CENTRAL CITY–

IDAHO SPRINGS

SEDALIA

Gunnison volcanic arc

Breckenridge

WET MOUNTAINS

Green Mountain

volcanic arc

–107° –106° –105°

41°

40°

39°

38°

37°

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Mining districts from Wilson (2003),

rock units from Church and others (2012).

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Igneous rock boundary
Geochemistry Maps and Discussions 43

Figure 38. Maps of central Colorado stream-sediment geochemistry—lanthanum (La).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Lanthanum

A B

Colorado state border

Study area boundary

Colorado Mineral Belt

13–26 ppm (<2.5th percentile)

27–33 ppm (2.5–10th percentile)

34–43 ppm (10–25th percentile)

44–110 ppm (25–75th percentile)

120–180 ppm (75–90th percentile)

190–340 ppm (90–97.5th percentile)

350–2,140 ppm (>97.5th percentile)

Lanthanum (parts per million)

Crustal abundance = 34.6 ppm

Limit of detection = not applicable

13 2,500

0

60

120

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1479

 13.0000

 2140.0000

 94.6524

 71.2369

 65.0000

 110.0000

 109.5

 2.846

 7.486

 100.7

La

parts per million (ppm)

Frequency

Cumulative Frequency

Concentration, in parts per million

100 1,000

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
44 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Lanthanum (La) is one of 15 metallic elements called rare earth elements (REEs). The REEs, 

including lanthanum, are strongly lithophile in igneous rocks. See the cerium map (fig. 19) for further 

discussion on the geochemical behavior of the REEs.

Highest concentrations of lanthanum (>90th percentile) are found in stream-sediment samples 

obtained from over the main phase of the Mesoproterozoic Pikes Peak batholith and in samples from 

sites underlain by various felsic igneous intrusions from Precambrian to Tertiary in age (figs. 38 and 39). 

Samples from over Mesoproterozoic felsic igneous rocks in the northern two-thirds of the study area, 

including the Pikes Peak and Sherman batholiths and the Kenosha Pass, St. Vrain, St. Kevin, and Log 

Cabin plutons show consistently high La concentrations. In contrast, samples derived from plutons of 

similar age and composition in the southern one-third have relatively lower La concentrations, generally 

in the 25th to 75th percentile range. Mining districts spatially associated with samples having high concentrations of lanthanum (>90th percentile) all are located in the Colorado Mineral Belt and include the 

Argentine, Boulder-Tungsten, Daily, Eldora, Gold Hill, Granite, Henderson, Jamestown, Silver Plume–

Georgetown, and Tincup–Cumberland Pass districts.

Figure 39. Mining districts and rock units

associated with the element lanthanum in 

stream sediments of central Colorado.

^Denver

ARGENTINE

BOULDER–TUNGSTEN GOLD HILL

JAMESTOWN

TINCUP–

CUMBERLAND PASS

SILVER PLUME–

GEORGETOWN

GRANITE

DAILY

ELDORA

HENDERSON

Sherman

batholith

Saint Vrain

pluton

Log Cabin

pluton

Pikes Peak

batholith Kenosha Pass

pluton

St. Kevin pluton

–107° –106° –105°

41°

40°

39°

38°

37°

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Mining districts from Wilson (2003),

rock units from Church and others (2012).

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Generalized intrusion boundary
Geochemistry Maps and Discussions 45

Figure 40. Maps of central Colorado stream-sediment geochemistry—lead (Pb).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Lead

A B

Colorado state border

Study area boundary

Colorado Mineral Belt

6.3–13 ppm (<2.5th percentile)

14–17 ppm (2.5–10th percentile)

18–20 ppm (10–25th percentile)

21–45 ppm (25–75th percentile)

46–100 ppm (75–90th percentile)

110–600 ppm (90–97.5th percentile)

610–12,000 ppm (>97.5th percentile)

Lead (parts per million)

Crustal abundance = 13.0 ppm

Limit of detection = not applicable

6.3 14,000

0

100

200

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1479

 6.3000

12000.0000

 97.8688

 36.1246

 29.0000

 19.0000

 513.4

 13.35

 16.88

 345.2

Pb

parts per million (ppm)

Frequency

Cumulative Frequency

Concentration, in parts per million

10 100 1,000 10,000

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
46 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Lead (Pb) substitutions are common in potassium feldspar, and lead is more abundant in granitic than in mafic rocks. Because lead substitutes for calcium and strontium at low temperatures, it 

becomes slightly more abundant in some carbonate rocks. Lead is found in many hydrothermal sulfide 

deposits as galena or with other base metals in complex sulfide minerals such as tetrahedrite. Weathering products, anglesite and cerussite, commonly are formed over primary hydrothermal deposits and 

are relatively insoluble.

Stream-sediment samples with high lead concentrations (>90th percentile) are almost exclusively 

confined to the Colorado Mineral Belt. Dispersion trains along Clear Creek from the Henderson district eastward to the range front are evident (figs. 40 and 41). Clusters of samples with high lead concentrations (>97.5th percentile) are associated with the Argentine, Leadville (two samples >1% Pb), 

and Montezuma–Geneva Creek districts. Isolated samples with high lead concentrations (>97.5th percentile) were obtained in the Blackhawk, Bonanza, Boulder-Tungsten, Breckenridge, Central City–

Idaho Springs, Chalk Creek, Gold Brick, Jamestown, Lake Albion, Lake George, Monarch, Oak 

Creek, Rosita Hills, Silver Plume–Georgetown, and Whitepine districts. Samples with moderate lead 

concentrations (75th to 90th percentile) commonly overlie many of the potassium feldspar–bearing 

granitic plutons in the study area, as seen in the southern Front Range and the Sawatch Range. 

Isolated samples obtained near Denver that contain elevated lead concentrations are described in the 

discussion of copper (figs. 26 and 27).

Figure 41. Mining districts associated with

the element lead in stream sediments of 

central Colorado.

^ Clear Ck.

Denver

ARGENTINE

LEADVILLE

BOULDER–TUNGSTEN

BRECKENRIDGE

WHITEPINE

ROSITA HILLS

JAMESTOWN

BLACKHAWK

GOLD

BRICK

LAKE GEORGE

LAKE ALBION

OAK CREEK

MONARCH

MONTEZUMA–GENEVA CREEK

SILVER PLUME–GEORGETOWN

CENTRAL CITY–

IDAHO SPRINGS

HENDERSON

CHALK

CREEK

BONANZA

SAWATCH RANGE

FRONT

RANGE

–107° –106° –105°

41°

40°

39°

38°

37°

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Mining districts from Wilson (2003).

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt
Geochemistry Maps and Discussions 47

Figure 42. Maps of central Colorado stream-sediment geochemistry—lithium (Li).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Lithium

A B

Colorado state border

Study area boundary

Colorado Mineral Belt

3.0–11 ppm (<2.5th percentile)

12–14 ppm (2.5–10th percentile)

15–18 ppm (10–25th percentile)

19–30 ppm (25–75th percentile)

31–38 ppm (75–90th percentile)

39–49 ppm (90–97.5th percentile)

50–290 ppm (>97.5th percentile)

Lithium (parts per million)

Crustal abundance = 18.0 ppm

Limit of detection = not applicable

3 300

0

100

200

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1479

 3.0000

 290.0000

 25.7312

 23.5844

 24.0000

 20.0000

 13.35

 0.3471

 7.151

 115.7

Li

parts per million (ppm)

Frequency

Cumulative Frequency

Concentration, in parts per million

10 100

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
48 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Lithium (Li) typically is concentrated in evolved igneous rocks (granites and granite pegmatites) 

in micas and accessory minerals, in evaporite-bearing sedimentary rock units, and in clay minerals. 

Lithium is moderately mobile in surface water.

In the central and northern parts of the study area, the distribution of stream-sediment samples 

with high (>90th percentile) concentrations of lithium is controlled strongly by Proterozoic granitic 

rocks and pegmatites, such as the Pikes Peak and Sherman batholiths and the St. Vrain, Kroenke, 

Silver Plume, and Mount Princeton plutons. To the south, lithium concentrations are relatively low 

(<75th percentile) in samples from Mesoproterozoic granitic rocks of the Wet Mountains and the 

Sangre de Cristo Mountains, suggesting that those rocks may have been derived from a magmatic 

source different from that of rocks of similar age and composition in the northern part of the study 

area (figs. 42 and 43). Samples derived from sedimentary rock units with high clay content, such 

as the Pierre Shale and the Minturn Formation, and from evaporite-bearing units such as the Eagle 

Valley Formation, also show relatively high lithium concentrations; many samples fall above the 

90th percentile.

Figure 43. Rock units associated with 

the element lithium in stream sediments 

of central Colorado.

^Denver Eagle

Valley

Fm.

Kroenke

pluton

Pikes Peak

batholith

Mount

Princeton

pluton

St.

Vrain

pluton

Sherman

batholith

Silver

Plume

pluton

WET MOUNTAINS

SANGRE DE CRISTO MOUNTAINS

–107° –106° –105°

41°

40°

39°

38°

37°

Low : 4,250

High : 14,433

Elevation (feet)

Pierre Shale or Minturn Formation boundary

EXPLANATION

Generalized intrusion boundary

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Rock units from Church and others (2012).

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt
Geochemistry Maps and Discussions 49

Figure 44. Maps of central Colorado stream-sediment geochemistry—magnesium (Mg).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Magnesium

A B

Colorado state border

Study area boundary

Colorado Mineral Belt

0.0400–0.2900% (<2.5th percentile)

0.2901–0.4350% (2.5–10th percentile)

0.4351–0.6160% (10–25th percentile)

0.6161–1.165% (25–75th percentile)

1.166–1.485% (75–90th percentile)

1.486–1.972% (90–97.5th percentile)

1.973–5.800% (>97.5th percentile)

Magnesium (weight percent)

Crustal abundance = 2.76%

Limit of detection = not applicable

0.04 6

0

100

200

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1479

 0.0400

 5.8000

 0.9135

 0.8129

 0.8300

 1.1000

 0.4559

 0.01186

 2.101

 13.26

Mg

weight percent (wt%)

Frequency

Cumulative Frequency

Concentration, in weight percent

0.1 1

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
50 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Magnesium (Mg) is the principal cation in the common igneous minerals olivine, pyroxene, 

some amphibole and serpentine minerals, chlorite, and dolomite. Magnesium concentrations are 

highest in ultramafic igneous rocks and in dolomitic carbonate-rich sedimentary rocks.

The distribution of stream-sediment samples with high magnesium concentrations (fig. 44) is 

similar to the distribution of samples with high calcium concentrations (fig. 16) in the study area. 

Samples having high magnesium concentrations (>90th percentile) are associated with two diverse 

groups of bedrock units: (1) Paleozoic dolomites, dolomitic limestone, and evaporite-bearing 

units such as the Madera, Manitou, Leadville, Minturn, and Eagle Valley Formations (fig. 45); 

and (2) mafic and ultramafic metavolcanic rocks that are part of the Proterozoic volcanic arc rocks 

of the eastern Gunnison arc, near Salida and extending into the northern Wet Mountains, and the 

Green Mountain volcanic arc in the far northern part of the study area. Also included are the mafic 

metavolcanic and metagabbroic rock enclaves in the western Front Range near Swandyke, east of 

Breckenridge. The Mesoproterozoic Pikes Peak batholith is depleted noticeably in magnesium, 

reflecting that batholith’s evolved granitic composition.

Figure 45. Rock units associated with the

element magnesium in stream sediments of 

central Colorado.

Pikes Peak

batholith

^

Salida

Breckenridge

WET MOUNTAINS

Denver Eagle

Valley

Formation

Gunnison volcanic arc

Madera

Formation

Minturn

Formation

Green Mountain

volcanic arc

FRONT RANGE

–107° –106° –105°

41°

40°

39°

38°

37°

Low : 4,250

High : 14,433

Elevation (feet)

Intrusion boundary

Volcanic arc boundary

EXPLANATION

Minturn Formation boundary

Eagle Valley Formation boundary

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Manitou and Leadville Formations are too small to show at this scale

Rock units from Church and others (2012).

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt
Geochemistry Maps and Discussions 51

Figure 46. Maps of central Colorado stream-sediment geochemistry—manganese (Mn).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Manganese

A B

Colorado state border

Study area boundary

Colorado Mineral Belt

68–260 ppm (<2.5th percentile)

261–407 ppm (2.5–10th percentile)

408–580 ppm (10–25th percentile)

581–1,250 ppm (25–75th percentile)

1,260–1,730 ppm (75–90th percentile)

1,740–3,580 ppm (90–97.5th percentile)

3,590–45,700 ppm (>97.5th percentile)

Manganese (parts per million)

Crustal abundance = 1,060 ppm

Limit of detection = not applicable

68 50,000

0

90

180

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1433

 68.0000

45700

 1170.5299

 876.1965

 880.0000

 1100.0000

 1974

 52.14

 14.04

 263.5

Mn

parts per million (ppm)

Frequency

Cumulative Frequency

Concentration, in parts per million

100 1,000 10,000

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
52 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Manganese (Mn) concentrations vary only slightly in igneous rocks relative to composition. In 

hydrothermal base- and precious-metal vein systems, manganese may be present as rhodochrosite and 

rhodonite and in calcite. Manganese is mobile in the weathering environment and is similar to iron in 

its behavior, where it is transported in the reduced state in surface water and groundwater and precipitated by oxidation.

Within the northern end of the Colorado Mineral Belt, clusters of stream-sediment samples 

with high manganese concentrations (>97.5th percentile) identify the Argentine, Blackhawk, Central 

City–Idaho Springs, Dumont, Henderson, and Montezuma–Geneva Creek districts (figs. 46 and 47). 

A possible dispersion train of manganese (>90th percentile) is evident along Clear Creek from the 

Henderson district eastward to the range front. Those high concentrations probably are related to 

weathering of exposures of hydrothermally mineralized rocks, as well as mine and mill waste from 

historical mining activities. Outside the mineral belt, a large cluster of samples with high manganese 

concentrations (>90th percentile) overlying the Mesoproterozoic Pikes Peak batholith probably is 

related to lithology. Similarly, a large, diffuse group of samples with high manganese concentrations 

(90th to 97.5th percentile) overlies many Cretaceous and younger sedimentary units north of the mineral belt and extends nearly to the Colorado–Wyoming border.

Figure 47. Mining districts and rock unit

associated with the element manganese in 

stream sediments of central Colorado.

^ Clear Ck.

Denver

Pikes Peak

batholith

ARGENTINE DUMONT

MONTEZUMA–GENEVA CREEK

BLACKHAWK

HENDERSON

CENTRAL CITY–

IDAHO SPRINGS

–107° –106° –105°

41°

40°

39°

38°

37°

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Mining districts from Wilson (2003),

rock units from Church and others (2012).

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Generalized intrusion boundary
Geochemistry Maps and Discussions 53

Figure 48. Maps of central Colorado stream-sediment geochemistry—mercury (Hg).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Mercury

A B

Colorado state border

Study area boundary

Colorado Mineral Belt

<0.02 ppm (<2.5th percentile)

0.020 ppm (2.5–10th percentile)

0.021–0.030 ppm (10–25th percentile)

0.031–0.060 ppm (25–75th percentile)

0.061–0.11 ppm (75–90th percentile)

0.12–0.40 ppm (90–97.5th percentile)

0.41–6.3 ppm (>97.5th percentile)

Mercury (parts per million)

Crustal abundance = 0.086 ppm

Limit of detection = 0.02 ppm

0.00411 7

0

150

300

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1355

 <0.02

 6.3000

 0.0774

 0.0391

 0.0400

 0.0300

 0.2427

 0.006593

 16.42

 358.9

Hg

parts per million (ppm)

Frequency

Cumulative Frequency

Concentration, in parts per million

0.01 0.1 1

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
54 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Mercury (Hg) is strongly chalcophile in its geochemical association. It is found in sulfide minerals, as a native metal in some hydrothermal deposits, and from anthropogenic sources. Organic-rich 

shale and coal may be enriched in mercury. Low concentrations of mercury are produced in emissions 

from some coal-fired power plants. Mercury has a relatively low solubility as a native metal but is 

very soluble when oxidized, particularly as a chloride, and in some organic complexes.

The highest mercury concentrations (>97.5th percentile) arise from stream-sediment samples 

nearly exclusive to the Colorado Mineral Belt (figs. 48 and 49). The single highest concentration 

(6.3 parts per million, ppm) was determined from a sediment sample taken downstream of the Gold 

Brick district in the Sawatch Range. At the north end of the mineral belt, high mercury concentrations (>97.5th percentile) are found in samples from the Argentine, Blackhawk, Boulder-Tungsten, 

Breckenridge, Central City–Idaho Springs, Dumont, Gold Hill, Montezuma–Geneva Creek, North 

Gilpin, Silver Plume–Georgetown, and Ward districts. A strong dispersion train is evident from the 

Blackhawk and Central City–Idaho Springs districts eastward to the range front. These relatively 

high mercury concentrations likely are due largely to mercury’s use in amalgamation, a gold and 

silver extraction process common during ore milling in the late 1800s and early 1900s. Low concentrations of naturally occurring mercury also are possible in many of the hydrothermally mineralized 

areas. Outside of the mineral belt, sporadic and isolated moderately anomalous (90th to 97.5th percentile) mercury-bearing samples to the north and to the far south are underlain by varied rock types, 

generally are found distal to known mineral deposits, and have an undetermined origin. Isolated 

samples near Denver that contain elevated mercury concentrations are described in the discussion of 

copper (figs. 26 and 27).

Figure 49. Mining districts associated with 

the element mercury in stream sediments of 

central Colorado.

^ Clear Ck.

Denver

NORTH GILPIN

ARGENTINE

GOLD HILL BOULDER–TUNGSTEN

DUMONT

BRECKENRIDGE

GOLD BRICK

WARD

MONTEZUMA–

GENEVA CREEK

BLACKHAWK

SILVER PLUME–

GEORGETOWN

CENTRAL CITY–

IDAHO SPRINGS

–107° –106° –105°

41°

40°

39°

38°

37°

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Mining districts from Wilson (2003).

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt
Geochemistry Maps and Discussions 55

Figure 50. Maps of central Colorado stream-sediment geochemistry—molybdenum (Mo).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Molybdenum

A B

Colorado state border

Study area boundary

Colorado Mineral Belt

<0.113 ppm (<2.5th percentile)

0.113–0.310 ppm (2.5–10th percentile)

0.311–0.920 ppm (10–25th percentile)

0.921–3.60 ppm (25–75th percentile)

3.61–6.00 ppm (75–90th percentile)

6.01–14.0 ppm (90–97.5th percentile)

14.1–540 ppm (>97.5th percentile)

Molybdenum (parts per million)

Crustal abundance = 1.2 ppm

Limit of detection = 0.1 ppm

0.1 600

0

80

160

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1479

 <0.1

 540.0000

 4.0953

 1.5796

 1.6000

 0.1111

 20.05

 0.5214

 18.99

 430

Mo

parts per million (ppm)

Frequency

Cumulative Frequency

Concentration, in parts per million

1 10 100

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
56 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Molybdenum (Mo) is more abundant in highly evolved igneous rocks such as granites and granitic pegmatites and in organic-rich shales. It commonly is found in hydrothermal vein and disseminated deposits associated with felsic igneous intrusions and may be concentrated in some stratabound 

deposits such as uranium-vanadium sediment-hosted deposits. Molybdenum is mobile in the weathering environment and may be concentrated by adsorption onto iron oxyhydroxides, by formation of 

ferrimolybdite, and by precipitation in carbonate-rich environments. 

For unexplained reasons, the single highest molybdenum concentration (540 parts per million, 

ppm) is from an isolated sample taken within the Tertiary Coalmont Formation (figs. 50 and 51) in 

the northwest part of the study area. Anomalous molybdenum is found in numerous stream-sediment 

samples within the Colorado Mineral Belt. In the northern part of the mineral belt, a persistent 

dispersion pattern is evident from the Henderson district along Clear Creek to the range front. Three 

samples with high Mo concentrations (150–360 ppm) were obtained immediately downstream of 

the Henderson mine, a large porphyry molybdenum deposit. Another cluster of samples with high 

molybdenum concentrations (>97.5th percentile) surrounds the porphyry molybdenum deposit at the 

Climax mine, and the two highest-concentration samples from that deposit (190 ppm) were obtained 

immediately downstream. Also within the mineral belt, scattered samples with high concentrations 

(>97.5th percentile) occur in the Alma, Boulder-Tungsten, Holy Cross, Jamestown, Lake Albion, 

Leadville, Monarch, Red Mountain, Tenmile-Kokomo, and Winfield districts. A cluster of sample 

locations with lower molybdenum concentrations (90th to 97.5th percentile) is found downstream 

from the Argentine and Montezuma–Geneva Creek districts. South of the mineral belt, isolated 

samples with high molybdenum concentrations (>90th percentile) are present near the Lake George 

greisen deposit and the Cripple Creek–Victor gold-telluride deposits. Isolated samples near Denver 

that contain elevated molybdenum concentrations are described in the discussion of copper (figs. 26 

and 27).

Figure 51. Mining districts and rock unit

associated with the element molybdenum 

in stream sediments of central Colorado.

^ Clear Ck.

Denver

ARGENTINE

LEADVILLE

BOULDER–TUNGSTEN

JAMESTOWN

MONARCH

HOLY

CROSS MONTEZUMA–GENEVA CREEK

ALMA

WINFIELD

LAKE GEORGE

CRIPPLE CREEK–

VICTOR

RED MT

TENMILE–

KOKOMO

HENDERSON

LAKE ALBION

CLIMAX

Coalmont

Formation

–107° –106° –105°

41°

40°

39°

38°

37°

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Mining districts from Wilson (2003),

rock units from Church and others (2012).

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Generalized formation boundary
Geochemistry Maps and Discussions 57

Figure 52. Maps of central Colorado stream-sediment geochemistry—neodymium (Nd).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Neodymium

A B

Colorado state border

Study area boundary

Colorado Mineral Belt

14.0–25.0 ppm (<2.5th percentile)

25.1–31.0 ppm (2.5–10th percentile)

31.1–39.0 ppm (10–25th percentile)

39.1–104 ppm (25–75th percentile)

105–192 ppm (75–90th percentile)

193–396 ppm (90–97.5th percentile)

397–1,960 ppm (>97.5th percentile)

Neodymium (parts per million)

Crustal abundance = 39.6 ppm

Limit of detection = not applicable

14 2,000

0

17.5

35

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

369

 14.0000

 1960.0000

 98.4363

 68.1647

 59.0000

 32.0000

 142.2

 7.404

 7.532

 83

Nd

parts per million (ppm)

Frequency

Cumulative Frequency

Concentration, in parts per million

100 1,000

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
58 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Neodymium (Nd) is one of 15 metallic elements called rare earth elements (REEs). The REEs, 

including neodymium, are strongly lithophile in igneous rocks. See the cerium map (fig. 19) for further discussion of the geochemical behavior of the REEs.

In this study, only a small subset of samples (369 out of 1,479) from the Church and others 

(2012) and Grossman (1998) studies were analyzed for neodymium (fig. 52). The highest concentrations (>90th percentile) of neodymium in the study area are found in samples from the main phase 

of the Pikes Peak batholith and in samples obtained from areas underlain by felsic igneous intrusions 

of various ages from Precambrian to Tertiary, such as the Boulder Creek and Silver Plume plutons 

and the Montezuma stock (figs. 52 and 53). Mining districts spatially associated with high neodymium concentrations (>90th percentile) all are located in the Colorado Mineral Belt and include 

the Argentine, Daily, and Gold Hill districts. Both within and outside of the mineral belt, samples 

with relatively high neodymium concentrations also are enriched in Ce, La, and Y. The REE patterns 

and related geologic associations are better elucidated by maps of Ce, La, and Y, because many more 

samples (n = 1,479) were analyzed for those elements.

Figure 53. Mining districts and rock units

associated with the element neodymium in 

stream sediments of central Colorado.

^Denver

Pikes Peak

batholith

ARGENTINE

GOLD HILL

DAILY

Silver

Plume

pluton

Montezuma

stock

Boulder

Creek

pluton

–107° –106° –105°

41°

40°

39°

38°

37°

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Mining districts from Wilson (2003),

rock units from Church and others (2012).

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Generalized intrusion boundary
Geochemistry Maps and Discussions 59

Figure 54. Maps of central Colorado stream-sediment geochemistry—nickel (Ni).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Nickel

A B

Colorado state border

Study area boundary

Colorado Mineral Belt

<4.0 ppm (<2.5th percentile)

4.1–9.0 ppm (2.5–10th percentile)

9.1–13 ppm (10–25th percentile)

14–27 ppm (25–75th percentile)

28–36 ppm (75–90th percentile)

37–52 ppm (90–97.5th percentile)

53–180 ppm (<97.5th percentile)

Nickel (parts per million)

Crustal abundance = 99.0 ppm

Limit of detection = 2 ppm

0.411 200

0

90

180

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1479

 <2

 180.0000

 21.4429

 17.8532

 19.0000

 16.0000

 12.8

 0.3329

 2.719

 20.93

Ni

parts per million (ppm)

Frequency

Cumulative Frequency

Concentration, in parts per million

1 10 100

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
60 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Nickel (Ni) is most abundant in ultramafic to mafic igneous rocks where it is present in olivine 

and pyroxene, in common serpentine alteration products after olivine and pyroxene, and in magmatic 

sulfide minerals. Nickel is relatively immobile in the weathering environment.

Clusters of stream-sediment samples with high nickel concentrations (>97.5th percentile) 

in the northern end of the Colorado Mineral Belt surround the Boulder-Tungsten, Gold Hill, and 

Magnolia districts, flank the Blackhawk and Central City–Idaho Springs districts, and are found in 

the Argentine, Halls Gulch, and Montezuma–Geneva Creek districts (figs. 54 and 55). Anomalous 

nickel in the mineral belt probably is related to volumetrically minor Proterozoic mafic dikes present in much of the area. South of the mineral belt, a group of samples with high nickel concentrations (>97.5th percentile) characterizes the northern Wet Mountains and the Grape Creek district and 

may reflect Cambrian ultramafic and mafic alkaline complex rocks. Proterozoic metavolcanic and 

metagabbroic rocks of the Gunnison volcanic arc can be traced westward by a widely dispersed group 

of samples with nickel concentrations in the 90th to 97.5th percentile range. The Proterozoic Green 

Mountain volcanic arc rocks in the northern part of the area also are indicated by anomalous nickel. 

Other scattered samples north of the mineral belt that contain high nickel concentrations (>97.5th percentile) are of unknown rock association (perhaps mafic dikes?). A region of relatively low nickel 

concentrations (<10th percentile) highlights the evolved granitic rocks of the Pikes Peak batholith in 

the southern Front Range.

Figure 55. Mining districts and rock units

associated with the element nickel in stream 

sediments of central Colorado.

^Denver

ARGENTINE

GOLD HILL

BOULDER–TUNGSTEN

BLACKHAWK

GRAPE CREEK

MONTEZUMA–

GENEVA CREEK

CENTRAL CITY–

IDAHO SPRINGS

MAGNOLIA

HALL'S

GULCH

Pikes Peak

batholith

WET MOUNTAINS

Green Mountain

volcanic arc

FRONT RANGE

Gunnison

volcanic

arc

–107° –106° –105°

41°

40°

39°

38°

37°

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Mining districts from Wilson (2003),

rock units from Church and others (2012).

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Generalized igneous rock boundary
Geochemistry Maps and Discussions 61

Figure 56. Maps of central Colorado stream-sediment geochemistry—niobium (Nb).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Niobium

A B

Colorado state border

Study area boundary

Colorado Mineral Belt

<5.70 ppm (<2.5th percentile)

5.71–8.70 ppm (2.5–10th percentile)

8.71–12.0 ppm (10–25th percentile)

12.1–23.0 ppm (25–75th percentile)

23.1–35.0 ppm (75–90th percentile)

35.1–140 ppm (90–97.5th percentile)

141–914 ppm (>97.5th percentile)

Niobium (parts per million)

Crustal abundance = 20.0 ppm

Limit of detection = 4 ppm

0.811 1000

0

150

300

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric Mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1479

<4

 914.0000

 25.1574

 17.1755

 16.0000

 11.0000

 48.5

 1.261

 10.5

 150.1

Nb

parts per million (ppm)

Frequency

Cumulative Frequency

Concentration, in parts per million

10 100

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
62 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Niobium (Nb) is a lithophile element with its highest concentrations in some granite pegmatites, 

alkali granites and rhyolites, and alkaline intermediate to ultramafic igneous intrusive complexes. It is 

present as a trace element in biotite, rutile, sphene, and zircon. Sedimentary rocks generally contain 

relatively low niobium concentrations. Niobium distributions commonly mimic those of rare earth 

elements (REEs). Niobium is relatively immobile in the weathering environment.

In the study area, high niobium concentrations reflect underlying lithologies rather than mineral deposits. The highest niobium concentrations in the study area (>90th percentile) are found in 

stream-sediment samples that form a wide anomaly surrounding the Pikes Peak batholith (figs. 56 and 

57), similar in distribution to the heavy REEs yttrium and ytterbium. Niobium concentrations also 

generally are high (>90th to 97.5th percentile) in (1) alkalic-calcic to alkaline dikes and volcanic rocks 

of the Cenozoic Rabbit Ears volcanic complex and sediments in the Late Cretaceous to Paleocene 

Middle Park Formation, which contains material derived from alkaline Laramide volcanic rocks 

(Windy Gap volcanic series) in the northern part of the study area; (2) the granitic Log Cabin pluton 

and Sherman batholith near the Wyoming border; (3) the Eocene Montezuma stock in the central 

Front Range; (4) the alkalic granitic Mount Princeton pluton of the Sawatch Range; (5) some parts 

of the alkalic-calcic to alkaline Thirtynine Mile volcanic field in the central part of the study area; and 

(6) alkaline igneous rocks in the Wet Mountains.

Figure 57. Rock units associated with the 

element niobium in stream sediments of 

central Colorado.

^Denver

Sherman

batholith

Middle Park 

Formation

Rabbit

Ears

volcanic rock

Log Cabin

pluton

Mount

Princeton

pluton

Montezuma

stock

Thirtynine Mile

volcanic field Pikes Peak

batholith

WET MOUNTAINS

Middle Park 

Formation

Windy Gap

volcanic

rock

–107° –106° –105°

41°

40°

39°

38°

37°

Low : 4,250

High : 14,433

Elevation (feet)

Windy Gap volcanic rock

Generalized intrusion boundary

Rabbit Ears volcanic rock

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Rock units from Church and others (2012).

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt
Geochemistry Maps and Discussions 63

Figure 58. Maps of central Colorado stream-sediment geochemistry—phosphorus (P).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Phosphorus

A B

Colorado state border

Study area boundary

Colorado Mineral Belt

130–480 ppm (<2.5th percentile)

481–650 ppm (2.5–10th percentile)

651–840 ppm (10–25th percentile)

841–1,580 ppm (25–75th percentile)

1,590–2,300 ppm (75–90th percentile)

2,310–3,500 ppm (90–97.5th percentile)

3,510–6,300 ppm (>97.5th percentile)

Phosphorus (parts per million)

Crustal abundance = 1,120 ppm

Limit of detection = not applicable

130 7,000

0

70

140

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1479

 130.0000

 6300.0000

 1325.6387

 1160.0625

 1100.0000

 1100.0000

 782.6

 20.35

 2.249

 7.132

P

parts per million (ppm)

Frequency

Cumulative Frequency

Concentration, in parts per million

 1,000

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
64 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Phosphorus (P) is generally most abundant in mafic igneous rocks and in sedimentary rocks 

such as phosphorites and shales. Apatite, monazite, and xenotime are the most common phosphate 

minerals in all rock types, and these minerals are generally resistant to weathering. Phosphate in commercial fertilizers and in sewage effluent can contribute to phosphorus concentrations in downstream 

sediments and waters.

Within the Colorado Mineral Belt, high phosphorus concentrations (>90th percentile) are present in stream-sediment samples from the northeastern and west-central parts of the belt, including 

the Argentine, Boulder-Tungsten, Central City–Idaho Springs, Chicago Creek–Freeland, Gold Hill, 

Independence, Red Mountain, and Tincup–Cumberland Pass districts (figs. 58 and 59). A few scattered clusters occur in the south-central part of the study area and are associated mainly with the 

intermediate to mafic, alkaline to alkalic-calcic Thirtynine Mile volcanic field and probably with the 

Cambrian Wet Mountain alkaline complex. Several sample locations with high phosphorus concentrations (>97.5th percentile) lie over Mesoproterozoic granitic rocks in the southern Mosquito Range.

Figure 59. Mining districts and rock unit 

associated with the element phosphorus in 

stream sediments of central Colorado.

^Denver

ARGENTINE

GOLD HILL

BOULDER–TUNGSTEN

TINCUP–

CUMBERLAND PASS

CENTRAL CITY–

IDAHO SPRINGS

INDEPENDENCE

CHICAGO CREEK–

FREELAND

RED MT

ELDORA

Thirtynine Mile

volcanic field MOSQUITO RANGE

WET MOUNTAINS

–107° –106° –105°

41°

40°

39°

38°

37°

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Mining districts from Wilson (2003),

rock units from Church and others (2012).

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Generalized rock unit boundary
Geochemistry Maps and Discussions 65

Figure 60. Maps of central Colorado stream-sediment geochemistry—potassium (K).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Potassium

A B

Colorado state border

Study area boundary

Colorado Mineral Belt

0.260–1.30% (<2.5th percentile)

1.31–1.70% (2.5–10th percentile)

1.71–1.95% (10–25th percentile)

1.96–2.60% (25–75th percentile)

2.61–3.00% (75–90th percentile)

3.01–3.58% (90–97.5th percentile)

3.59–6.30% (>97.5th percentile)

Potassium (weight percent)

Crustal abundance = 1.84%

Limit of detection = not applicable

0.26 7

0

125

250

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1479

 0.2600

 6.3000

 2.3119

 2.2417

 2.3000

 2.2000

 0.5726

 0.01489

 0.9748

 4.075

K

weight percent (wt%)

Frequency

Cumulative Frequency

Concentration, in weight percent

1

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
66 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Potassium (K) in igneous rocks is most abundant in felsic rocks, where it is found primarily in 

potassium feldspar, muscovite, and biotite. Potassium concentrations are low in most sedimentary 

rocks with the exception of evaporites, immature sedimentary rocks, and illite-bearing rocks. Hydrothermally altered rocks containing sericite (muscovite), biotite, alunite, and jarosite have substantial 

amounts of potassium. Potassium feldspar is one of the first silicate minerals to dissolve during weathering, and potassium is very soluble (and mobile) in surface water.

North of the Colorado Mineral Belt, a cluster of stream-sediment samples with high potassium 

concentrations (>97.5th percentile) is associated with numerous Tertiary igneous dikes that intrude 

the Coalmont and Middle Park Formations and with rhyolitic ash-flow tuffs near the Never Summer 

Range (figs. 60 and 61). South of the mineral belt, samples with consistently high potassium concentrations (>90th percentile) lie over and surround the Pikes Peak batholith and likely are due 

to potassium feldspar in the stream sediment. Within the mineral belt, a cluster of high potassium 

concentrations (>97.5th percentile) is present in samples from the Henderson and Silver Plume–

Georgetown districts. Samples with lower level potassium concentrations (90th to 97.5th percentile) 

encompass a larger area including the Argentine, Central City–Idaho Springs, and Dumont districts. 

This relation may reflect potassically altered rocks. Another lower level cluster of potassium concentrations (90th to 97.5th percentile) appears in samples from the Boulder-Tungsten, Gold Hill, and 

Jamestown districts. Outside of the mineral belt, the Lake George and Rosita Hills districts also have 

samples that contain high potassium concentrations. Within the mining districts, the high potassium 

concentrations likely are due to hydrothermal alteration minerals or related weathering products in the 

stream sediment.

Figure 61. Mining districts and rock units

associated with the element potassium in 

stream sediments of central Colorado.

^Denver

ARGENTINE

GOLD HILL

BOULDER–

TUNGSTEN

DUMONT

JAMESTOWN

SILVER PLUME–

GEORGETOWN

CENTRAL CITY–

IDAHO SPRINGS

HENDERSON

Middle Park

Formation

Pikes Peak

batholith

ALMA

ROSITA HILLS

LAKE GEORGE

Coalmont

Formation

NEVER

SUMMER

RANGE

–107° –106° –105°

41°

40°

39°

38°

37°

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Mining districts from Wilson (2003),

rock units from Church and others (2012).

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Generalized rock unit boundary
Geochemistry Maps and Discussions 67

Figure 62. Maps of central Colorado stream-sediment geochemistry—rubidium (Rb).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Rubidium

A B

Colorado state border

Study area boundary

Colorado Mineral Belt

14–47 ppm (<2.5th percentile)

48–66 ppm (2.5–10th percentile)

67–81 ppm (10–25th percentile)

82–140 ppm (25–75th percentile)

141–170 ppm (75–90th percentile)

171–230 ppm (90–97.5th percentile)

231–850 ppm (>97.5th percentile)

Rubidium (parts per million)

Crustal abundance = 78.0 ppm

Limit of detection = not applicable

14 900

0

60

120

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1064

 14.0000

 850.0000

 113.3391

 104.2883

 100.0000

 110.0000

 54.76

 1.679

 5.14

 60.71

Rb

parts per million (ppm)

Frequency

Cumulative Frequency

Concentration, in parts per million

 100

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
68 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Rubidium (Rb) substitutes for potassium in igneous rocks and is most abundant in felsic rocks, 

especially those of alkaline composition. It is found primarily in potassium feldspar, muscovite, and 

biotite. In sedimentary rocks, immature sedimentary rocks, illite-rich rocks, and in some evaporates 

may be enriched in rubidium. The behavior of rubidium, in terms of solubility and mobility, is similar 

to that of potassium in the weathering environment.

Rubidium distribution likewise is similar to that of potassium. Within the Colorado Mineral Belt, 

a cluster of high rubidium concentrations (>97.5th percentile) is present in stream-sediment samples 

in and downstream from the Henderson district (figs. 62 and 63). Samples with smaller rubidium 

concentrations (90th to 97.5th percentile) identify the Alma, Argentine, Central City–Idaho Springs, 

Climax, Gold Hill, Jamestown, Silver Plume–Georgetown, and Tenmile-Kokomo districts. Those high 

concentrations are likely due to the presence of potassium-altered rocks in the hydrothermal systems 

and to the presence of felsic intrusive igneous rocks. In the south-central part of the study area, a large 

cluster of samples with high potassium concentrations (>90th percentile) lies over the Pikes Peak 

batholith, probably owing to unweathered potassium feldspar in stream sediments.

Figure 63. Mining districts and rock unit

associated with the element rubidium in stream 

sediments of central Colorado.

Mining districts from Wilson (2003),

rock units from Church and others (2012).

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

^ Clear Ck.

Denver

Pikes Peak

batholith

ARGENTINE

GOLD HILL

JAMESTOWN

SILVER PLUME–GEORGETOWN

CENTRAL CITY–

IDAHO SPRINGS

ALMA

TENMILEKOKOMO

HENDERSON

CLIMAX

–107° –106° –105°

41°

40°

39°

38°

37°

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Generalized intrusion boundary
Geochemistry Maps and Discussions 69

Figure 64. Maps of central Colorado stream-sediment geochemistry—scandium (Sc).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Scandium

A B

Colorado state border

Study area boundary

Colorado Mineral Belt

2.8–5.2 ppm (<2.5th percentile)

5.3–7.0 ppm (2.5–10th percentile)

7.1–8.8 ppm (10–25th percentile)

8.9–15 ppm (25–75th percentile)

16–19 ppm (75–90th percentile)

20–25 ppm (90–97.5th percentile)

26–36 ppm (>97.5th percentile)

Scandium (parts per million)

Crustal abundance = 25.0 ppm

Limit of detection = not applicable

2.8 40

0

80

160

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1433

 2.8000

 36.0000

 12.4864

 11.5278

 11.0000

 11.0000

 5.108

 0.1349

 1.055

 1.47

Sc

parts per million (ppm)

Frequency

Cumulative Frequency

Concentration, in parts per million

 10

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
70 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Scandium (Sc) concentrations are highest in mafic and ultramafic igneous rocks where the 

element is concentrated in minerals of the pyroxene and amphibole groups and in biotite. Scandium 

also may be concentrated by igneous differentiation into some granites and granite pegmatites in minerals of the garnet group, in tourmaline, and in beryl. Scandium concentrations in sedimentary rocks 

generally are quite low. It is a relatively immobile element in the weathering environment.

In the study area, high scandium concentrations (>90th percentile) generally are related to the 

rock type and not related to mineral deposits. High scandium concentrations are found in streamsediment samples derived from several groups of Proterozoic igneous and meta-igneous rocks 

(figs. 64 and 65), such as a widespread group of mafic and ultramafic metavolcanic rocks that are part 

of the eastern Gunnison volcanic arc, near Salida and extending into the northern Wet Mountains; 

the Green Mountain arc in the far northern part of the study area; and mafic metavolcanic and 

metagabbroic rock enclaves near Swandyke, east of Breckenridge, and in the Front Range immediately west of Golden. Finally, samples from areas that lie over several Proterozoic granitic bodies 

also contain high concentrations, including the Kroenke pluton in the Sawatch Range, the San Isabel 

pluton in the southern Wet Mountains, and the main phase of the Pikes Peak batholith in the southern 

Front Range.

Figure 65. Rock units associated with the 

element scandium in stream sediments of 

central Colorado.

^Denver

Pikes Peak

batholith

San Isabel 

pluton

Kroenke

pluton

Salida

Breckenridge

Golden FRONT RANGE

WET MOUNTAINS

Gunnison

volcanic

arc

Green Mountain

volcanic arc

–107° –106° –105°

41°

40°

39°

38°

37°

Rock units from Church and others (2012).

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Generalized igneous rock boundary
Geochemistry Maps and Discussions 71

Figure 66. Maps of central Colorado stream-sediment geochemistry—selenium (Se).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Selenium

A B

Colorado state border

Study area boundary

Colorado Mineral Belt

<0.2 ppm (<10th percentile)

0.20–0.30 ppm (10–25th percentile)

0.31–0.70 ppm (25–75th percentile)

0.71–1.1 ppm (75–90th percentile)

1.2–2.0 ppm (90–97.5th percentile)

2.1–11 ppm (>97.5th percentile)

Selenium (parts per million)

Crustal abundance = 0.050 ppm

Limit of detection = 0.2 ppm

0.0411 12

0

125

250

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1334

 <0.2

 11.0000

 0.5692

 0.3523

 0.4000

 0.0411

 0.6579

 0.01801

 5.852

 63.77

Se

parts per million (ppm)

Frequency

Cumulative Frequency

Concentration, in parts per million

0.1 1 10

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
72 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Selenium (Se) is similar to sulfur in its geochemistry. Sulfide mineral-rich rocks and hydrothermal veins, especially those formed at low temperatures, may be enriched in selenium, as also may be 

organic-rich sedimentary rocks. During weathering, it is immobile in acidic conditions and concentrated in iron oxyhydroxides, clay minerals, and organic material. Under alkaline conditions, selenium 

is very mobile in surface water.

Stream-sediment samples having relatively high selenium concentrations are scattered throughout the study area and probably reflect various rock types rather than mineral deposits. The most 

consistent bedrock relation with selenium is shown by clusters of samples with high selenium concentrations (>90th percentile), which lie over Cretaceous sedimentary rock units that contain substantial 

amounts of organic-rich shales, such as the Benton and Pierre Shales (figs. 66 and 67). Such clusters 

lie in the northwestern, southeastern, and west-central parts of the study area. Other scattered samples 

with high selenium concentrations (>90th percentile) occur throughout the area with no clear relation 

either to bedrock or to mineral deposits.

Figure 67. Rock units associated with the 

element selenium in stream sediments of 

central Colorado.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

Rock units from Church and others (2012).

Low : 4,250

High : 14,433

Elevation (feet)

Pierre Shale boundary

EXPLANATION

Benton Group boundary

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt
Geochemistry Maps and Discussions 73

Figure 68. Maps of central Colorado stream-sediment geochemistry—silver (Ag).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Silver

A B

Colorado state border

Study area boundary

Colorado Mineral Belt

Silver (parts per million)

Crustal abundance = 0.080 ppm

Limit of detection = 0.2 ppm

0.0411 50

0

800

1,600

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1479

 <0.2

 48.0000

 0.6373

 0.0605

 <0.2

 <0.2

 3.463

 0.09006

 9.002

 96.45

Ag

parts per million (ppm)

<0.2 ppm (<90th percentile)

0.2–7 ppm (90–97.5th percentile)

7–48 ppm (>97.5th percentile) Frequency

Cumulative Frequency

Concentration, in parts per million

0.1 1 10

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
74 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Silver (Ag) is a strongly chalcophile element concentrated primarily in sulfide and telluride 

hydrothermal deposits. It is present primarily in sulfide, sulfosalt, and telluride minerals or as chloride 

or sulfate minerals following weathering of the primary minerals. Native silver is common in some 

deposits. Locally, silver is found in stratabound sediment-hosted deposits where it is deposited from 

percolating groundwater as silver chloride. Silver is mobile in surface water and may be adsorbed by 

manganese and iron oxyhydroxides and organic matter.

Silver was not detected in the majority of the stream-sediment samples (analyzed at 0.2 parts 

per million (ppm), the limit of detection), so discussion of silver distributions is limited to those 

samples in and above the 90th percentile. Stream-sediment samples having high silver concentrations (>90th percentile) strongly delineate the Colorado Mineral Belt (figs. 68 and 69). The highest 

concentrations (>97.5th percentile) are from samples that lie over known mining districts throughout 

the study area, including the Argentine, Boulder-Tungsten, Chalk Creek, Dumont, Goldbrick, Lake 

George, Leadville, Montezuma–Geneva Creek, Red Mountain, Rosita Hills, St. Kevin–Sugarloaf, 

and Tenmile-Kokomo districts. A lower-level (90th to 97.5th percentile) dispersion train of silver 

is evident in samples from the Silver Plume-Georgetown district downstream along Clear Creek to 

the range front. Just outside the study area boundary in the southern part of the mineral belt, a single 

sample containing anomalous silver and several other metals was obtained from the Bonanza district 

(see copper discussion, fig. 27).

Figure 69. Mining districts associated 

with the element silver in stream sediments 

of central Colorado.

^ Clear Ck.

Denver

ARGENTINE

LEADVILLE

BOULDER–TUNGSTEN

DUMONT

ROSITA HILLS

MONTEZUMA–

GENEVA CREEK

ST. KEVIN–

SUGARLOAF

LAKE GEORGE RED MT

SILVER PLUME–

GEORGETOWN

TENMILE–

KOKOMO

CHALK

CREEK

GOLD

BRICK

BONANZA

–107° –106° –105°

41°

40°

39°

38°

37°

Mining districts from Wilson (2003).

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt
Geochemistry Maps and Discussions 75

Figure 70. Maps of central Colorado stream-sediment geochemistry—sodium (Na).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Sodium

A B

0.0800–0.4500% (<2.5th percentile)

0.4501–0.8000% (2.5–10th percentile)

0.8001–1.175% (10–25th percentile)

1.176–1.790% (25–75th percentile)

1.791–2.200% (75–90th percentile)

2.201–2.600% (90–7.5th percentile)

2.601–3.600% (>97.5th percentile)

Sodium (weight percent)

Crustal abundance = 2.27%

Limit of detection = not applicable

0.08 0.1 1 4

0

90

180

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1479

 0.0800

 3.6000

 1.5218

 1.4049

 1.5000

 1.5000

 0.5452

 0.01418

 0.1052

 –0.05621

Na

weight percent (wt%)

Colorado state border

Study area boundary

Colorado Mineral Belt

Frequency

Cumulative Frequency

Concentration, in weight percent

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
76 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Sodium (Na) is most abundant in felsic igneous rocks where it is the principal cation in albite. 

Albite is one of the first silicate minerals to dissolve during weathering, and sodium is one of the 

elements most soluble in surface water. Sodium concentrations are low in most sedimentary rocks, 

with the exception of evaporites. Sodium is extremely mobile in the weathering environment. Under 

wet or humid conditions, sodium is extremely mobile and easily moved by streams. Sodium then is 

redistributed downstream as evaporation proceeds.

High sodium concentrations in the study area generally are related to bedrock type and particularly to weathering, rather than to mineral deposits. Sodium is most abundant (>75th percentile) over 

many granitic bodies, such as the Pikes Peak batholith, probably owing to the presence of variably 

weathering albite in immature sediment derived from the igneous rock (figs. 70 and 71). A diffuse 

cluster of stream-sediment samples with high sodium concentrations (>90th percentile) is associated with the Middle Park and Coalmont Formations in the north-central part of the study area. In 

the southern third of the study area, many samples with high sodium concentrations (>90th percentile) correlate with basin-fill deposits in the Wet Mountain Valley, the San Luis Valley, and the 

Sangre de Cristo Formation on the eastern flank of the Culebra Range. In many (perhaps most) cases, 

sodium may have been removed by streams from highland areas and concentrated by evaporation at 

lower elevations in basin-fill deposits.

Figure 71. Rock units associated with 

the element sodium in stream sediments 

of central Colorado.

^Denver

Coalmont

Formation

Middle Park

Formation

Sangre de

Cristo

Formation

Wet

Mountain

Valley

CULEBRA

RANGE

Pikes Peak

batholith

Luis

San

Valley

–107° –106° –105°

41°

40°

39°

38°

37°

Rock units from Church and others (2012).

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Generalized rock unit boundary

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
Geochemistry Maps and Discussions 77

Figure 72. Maps of central Colorado stream-sediment geochemistry—strontium (Sr).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Strontium

A B

Colorado state border

Study area boundary

Colorado Mineral Belt

9.00–91.0 ppm (<2.5th percentile)

91.1–130 ppm (2.5–10th percentile)

131–174 ppm (10–25th percentile)

175–336 ppm (25–75th percentile)

337–470 ppm (75–90th percentile)

471–790 ppm (90–97.5th percentile)

791–1,800 ppm (>97.5th percentile)

Strontium (parts per million)

Crustal abundance = 384 ppm

Limit of detection = not applicable

9 2,000

0

80

160

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1479

 9.0000

 1800.0000

 283.0230

 243.0534

 236.0000

 190.0000

 184.8

 4.806

 2.985

 14.23

Sr

parts per million (ppm)

Frequency

Cumulative Frequency

Concentration, in parts per million

10 100 1,000

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
78 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Strontium (Sr) is an alkali-earth element similar to calcium and barium in its geochemistry. In 

igneous rocks it is found mostly in plagioclase and is most abundant in feldspars of intermediate 

compositions. It also occurs to a limited extent in apatite, calcic pyroxenes and amphiboles, and in 

some potassium feldspars. In sedimentary rocks, carbonate and evaporite rocks may be enriched in 

strontium. It is relatively mobile during weathering. Like sodium, under wet or humid conditions, 

strontium is mobile and easily moved by streams. Strontium can then be redistributed downstream 

as evaporation proceeds.

High strontium concentrations in the study area generally are related to bedrock type and 

surface-water evaporation rather than to mineral deposits. A cluster of stream-sediment samples having high strontium concentrations (>90th percentile) in the northern part of the study area lies over 

rocks of the Coalmont and particularly the Middle Park Formations, and the alkalic-calcic to alkaline, 

intermediate to felsic composition Rabbit Ears volcanic sequence (figs. 72 and 73). Another cluster of 

samples with high strontium concentrations (>90th percentile) lies over the alkalic-calcic to alkaline, intermediate-composition volcanic and shallow intrusive rocks of the Thirtynine Mile volcanic 

field. In the southern part of the study area many samples with high strontium concentrations (in the 

90th to 97.5th percentile range) lie over alkalic-calcic, intermediate-composition volcanic rocks present in the Wet Mountains and the northern Culebra Range; adjacent Cenozoic basins containing rocks 

derived from similar intermediate-composition volcanic sources; and some Proterozoic intermediatecomposition units in the southern Sangre de Cristo Mountains. High strontium concentrations in 

stream sediments in basins, such as the Wet Mountain Valley, North Park, Middle Park, and South 

Park basins, might be related to near-surface redistribution as streams pick up strontium in adjacent 

highlands and deposit it in adjacent valleys by evaporation. Strontium distribution is similar to that 

of barium, except that many hydrothermal-vein systems in the Colorado Mineral Belt are enriched 

in barium.

Figure 73. Rock units associated with the 

element strontium in stream sediments of 

central Colorado.

^Denver

Coalmont

Formation

Middle Park

Formation

Thirtynine Mile

volcanic field

Rabbit

Ears

volcanic

rock

CULEBRA

RANGE

Luis

San

Valley

WET MOUNTAINS

SANGRE DE CRISTO MOUNTAINS

South Park

North

 Park

Middle

 Park

Wet Mountains Valley

–107° –106° –105°

41°

40°

39°

38°

37°

Rock units from Church and others (2012).

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Generalized rock unit boundary

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
Geochemistry Maps and Discussions 79

Figure 74. Maps of central Colorado stream-sediment geochemistry—sulfur (S).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Sulfur

A B

Colorado state border

Study area boundary

Colorado Mineral Belt

<0.011% (<2.5th percentile)

0.011–0.020% (2.5–10th percentile)

0.021–0.030% (10–25th percentile)

0.031–0.060% (25–75th percentile)

0.061–0.14% (75–90th percentile)

0.15–0.39% (90–97.5th percentile)

0.40–12% (>97.5th percentile)

Sulfur (weight percent)

Crustal abundance = 0.034%

Limit of detection = 0.01%

0.00211 14 0

125

250

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1064

<0.01

 12.0000

 0.1113

 0.0432

 0.0400

 0.0300

 0.6286

 0.01927

 15.69

 266.1

S

weight percent (wt%)

Frequency

Cumulative Frequency

Concentration, in weight percent

0.01 0.1 1 10

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
80 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

In ultramafic rocks, sulfur (S) is concentrated in magmatic sulfide minerals as part of the igneous 

differentiation process. Sulfur also is precipitated from hydrothermal fluids as various iron and basemetal sulfides common in hydrothermal mineral deposits. In addition, sulfur can precipitate from lowtemperature groundwater and seawater where reducing conditions, typically related to bacterial action, 

enable precipitation of sulfide minerals. During weathering of sulfide minerals, the sulfate anion is 

released and mobilized in surface water. Relatively insoluble or slightly soluble alkali-earth sulfate 

minerals, such as gypsum, barite, and anglesite, may form under evaporitic conditions.

A large cluster of stream-sediment samples with high sulfur content (>90th percentile) at the 

northern end of the Colorado Mineral Belt is associated with the Argentine, Boulder-Tungsten, 

Central City–Idaho Springs, Dumont, Gold Hill, Henderson, Jamestown, Montezuma–Geneva Creek, 

and Silver Plume–Georgetown districts (figs. 74 and 75). Two samples with the highest concentrations (11 and 12 percent) were obtained in the Blackhawk district. Isolated samples with high sulfur concentrations (>97.5th percentile) were taken near the Bonanza, Chalk Creek, Leadville, and 

Red Mountain districts. Dispersion trains are apparent in several stream reaches including from the 

Henderson district along Clear Creek to the range front, along Geneva Creek from the Montezuma–

Geneva Creek district to the North Fork of the South Platte River, and along Cripple Creek and 

Fourmile Creek below the Cripple Creek–Victor district.

Figure 75. Mining districts associated with 

the element sulfur in stream sediments of 

central Colorado.

^ Clear Ck.

Denver

Geneva Ck.

N. Fork S. Platte R.

Cripple

Ck. Fourmile Ck.

ARGENTINE

LEADVILLE

BOULDER–TUNGSTEN GOLD HILL

DUMONT

JAMESTOWN

MONTEZUMA–

GENEVA CREEK

BLACKHAWK

CHALK

CREEK

HENDERSON

RED MT

SILVER PLUME–GEORGETOWN

CENTRAL CITY–

IDAHO SPRINGS

CRIPPLE CREEK–

VICTOR

BONANZA

–107° –106° –105°

41°

40°

39°

38°

37°

Mining districts from Wilson (2003).

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
Geochemistry Maps and Discussions 81

Figure 76. Maps of central Colorado stream-sediment geochemistry—tellurium (Te).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry – Tellurium

A B

Colorado state border

Study area boundary

Colorado Mineral Belt

<0.1 ppm (<75th percentile)

0.1–0.2 ppm (75–90th percentile)

0.21–0.70 ppm (90–97.5th percentile)

0.71–7.9 ppm (>97.5th percentile)

Tellurium (parts per million)

Crustal abundance = 0.004 ppm

Limit of detection = <0.1 ppm

0.0211 8

0

450

900

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1064

 <0.1

 7.9000

 0.1141

 0.0382

 <0.1

 <0.1

 0.3943

 0.01209

 11.35

 176.7

Te

parts per million (ppm)

Frequency

Cumulative Frequency

Concentration, in parts per million

0.1 1

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
82 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Tellurium (Te) is similar to sulfur in its geochemistry, although it is much less soluble during 

weathering. Sulfide minerals in hydrothermal systems or in relatively low-sulfur, precious-metal telluride hydrothermal deposits may be enriched in tellurium.

Tellurium was not detected in the majority of stream-sediment samples from the study area 

(<75th percentile). Samples containing high tellurium (>97.5th percentile) are largely confined to the 

northern end of the Colorado Mineral Belt in the Argentine, Blackhawk, Boulder-Tungsten, Dumont, 

Gold Hill, Henderson, Jamestown, Montezuma–Geneva Creek, and Ward districts (figs. 76 and 77). A 

dispersion train may extend from the Henderson district eastward along Clear Creek to the range front. 

South of the mineral belt, samples from the Cripple Creek–Victor gold-silver telluride deposits contain 

some of the highest tellurium concentrations (1.9 to 4.7 parts per million, ppm). The single highest tellurium concentration (7.9 ppm) is from a sample obtained downstream of the Alma district. High tellurium 

concentrations (>97.5th percentile) are also present in samples taken near the Monarch and Whitepine 

districts. Just outside the study-area boundary in the southern part of the mineral belt, a single sample 

containing anomalous tellurium and several other metals is from the Bonanza district (see copper discussion with fig. 27).

Figure 77. Mining districts associated with 

the element tellurium in stream sediments of 

central Colorado.

^ Clear Ck.

Denver

ARGENTINE

GOLD HILL

BOULDER–TUNGSTEN

DUMONT

WHITEPINE

JAMESTOWN

BLACKHAWK

ALMA

CRIPPLE CREEK–

VICTOR

HENDERSON

MONARCH

WARD

MONTEZUMA–

GENEVA CREEK

BONANZA

–107° –106° –105°

41°

40°

39°

38°

37°

Mining districts from Wilson (2003).

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
Geochemistry Maps and Discussions 83

Figure 78. Maps of central Colorado stream-sediment geochemistry—thallium (Tl).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Thallium

A B

Colorado state border

Study area boundary

Colorado Mineral Belt

<0.31 ppm (<2.5th percentile)

0.31–0.40 ppm (2.5–10th percentile)

0.41–0.50 ppm (10–25th percentile)

0.51–0.80 ppm (25–75th percentile)

0.81–1.1 ppm (75–90th percentile)

1.2–1.6 ppm (90–97.5th percentile)

1.7–7.5 ppm (>97.5th percentile)

Thallium (parts per million)

Crustal abundance = 0.72 ppm

Limit of detection = 0.1 ppm

0.1 8

0

90

180

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1064

 0.1000

 7.5000

 0.7075

 0.6278

 0.6000

 0.5000

 0.4435

 0.01359

 5.767

 64.92

Tl

parts per million (ppm)

Frequency

Cumulative Frequency

Concentration, in parts per million

1

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
84 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Geochemically, thallium (Tl) has strong affinity for sulfur and most commonly is found as a trace 

constituent in the lead sulfide, galena. Thallium also is locally concentrated in organic-rich shales. It is 

relatively mobile in the weathering environment and can be concentrated in clay minerals and manganese oxides through adsorption.

Stream-sediment samples having the highest thallium concentrations (>97.5th percentile) are 

confined largely within the northern two-thirds of the Colorado Mineral Belt, with clusters around 

the Boulder-Tungsten, Breckenridge, Climax, Gold Hill, Henderson, Montezuma–Geneva Creek, and 

Tenmile-Kokomo districts (figs. 78 and 79). Lower concentrations (90th to 97.5th percentile) are found 

in samples from the Central City–Idaho Springs, Jamestown, and Silver Plume–Georgetown districts. 

Dispersion trains of thallium are evident along Clear Creek from the Henderson district eastward to 

the range front, and from the Montezuma–Geneva Creek district eastward along Geneva Creek to the 

North Fork of the South Platte River. South of the mineral belt, a single sample with a high Tl value 

(>97.5th percentile) was collected over the greisen deposit in the Proterozoic Redskin stock near the 

Lake George district, and a small sample cluster with high concentrations (>90th percentile) lies over the 

Cripple Creek–Victor alkaline gold-silver telluride deposits with dispersion downstream along Cripple 

Creek and Fourmile Creek.

Figure 79. Mining districts and rock unit

associated with the element thallium in stream 

sediments of central Colorado.

^ Clear Ck.

Denver

Geneva Ck.

Platte R.

N. Fork S.

Cripple

Ck. Fourmile Ck.

GOLD HILL BOULDER–TUNGSTEN

BRECKENRIDGE

JAMESTOWN

HENDERSON

MONTEZUMA–

GENEVA CREEK SILVER PLUME–GEORGETOWN

CENTRAL CITY–

IDAHO SPRINGS

TENMILE–

KOKOMO

CLIMAX

Redskin

stock

LAKE GEORGE

CRIPPLE CREEK–

VICTOR

–107° –106° –105°

41°

40°

39°

38°

37°

Mining districts from Wilson (2003),

rock units from Church and others (2012).

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Generalized intrusion boundary

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
Geochemistry Maps and Discussions 85

Figure 80. Maps of central Colorado stream-sediment geochemistry—thorium (Th).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Thorium

A B

<5.8 ppm (<2.5th percentile)

5.8–8.6 ppm (2.5–10th percentile)

8.7–12 ppm (10–25th percentile)

13–41 ppm (25–75th percentile)

42–77 ppm (75–90th percentile)

78–160 ppm (90–97.5th percentile)

170–1,100 ppm (>97.5th percentile)

Thorium (parts per million)

Crustal abundance = 8.10 ppm

Limit of detection = <4.0 ppm

0.811 1,200

0

80

160

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1479

<4.0

 1110.0000

 36.9252

 22.9170

 21.0000

 11.0000

 56.4

 1.467

 7.938

 109.8

Th

parts per million (ppm)

Colorado state border

Study area boundary

Colorado Mineral Belt

1 10 100 1,000

Frequency

Cumulative Frequency

Concentration, in parts per million

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
86 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Thorium (Th) in igneous rocks is strongly lithophile and is concentrated in evolved igneous 

rocks such as granites and granitic pegmatites. It is present most commonly in the minerals monazite, 

allanite, sphene, and zircon, although some pegmatites may contain the thorium minerals thorite and 

thorianite. Thorium-bearing minerals generally are resistant to weathering. Thorium generally accumulates with heavy minerals in sediments, where it may form placer deposits. It is much less mobile 

than uranium during weathering.

High thorium concentrations (>90th percentile) in stream-sediment samples are widely scattered 

in the northern two-thirds of the study area (figs. 80 and 81). These samples represent Proterozoic 

granitic rocks such as the Boulder Creek, Log Cabin, and St. Vrain plutons, the Pikes Peak batholith, 

and parts of the Eocene Mount Princeton pluton. Spatial overlap of several mining districts and samples with high thorium concentrations do occur, but the high thorium values are more likely related to 

accessory minerals in Proterozoic and younger felsic intrusive rocks than to mineralization.

Figure 81. Rock units associated with 

the element thorium in stream sediments 

of central Colorado.

^Denver

St. Vrain

pluton

Pikes Peak

batholith

Log Cabin

pluton

Mount

Princeton

pluton

Boulder Creek

pluton

–107° –106° –105°

41°

40°

39°

38°

37°

Rock units from Church and others (2012).

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Generalized intrusion boundary

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
Geochemistry Maps and Discussions 87

Figure 82. Maps of central Colorado stream-sediment geochemistry—tin (Sn).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Tin

A B

<0.112 ppm (<2.5th percentile)

0.112–0.122 ppm (2.5–10th percentile)

0.123–2.20 ppm (10–25th percentile)

2.21–3.40 ppm (25–75th percentile)

3.41–5.30 ppm (75–90th percentile)

5.31–11.0 ppm (90–97.5th percentile)

11.1–930 ppm (>97.5th percentile)

Tin (parts per million)

Crustal abundance = 2.10 ppm

Limit of detection = 0.1 ppm

<0.5 1,000

0

225

450

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1479

 <0.1

 930.0000

 3.6900

 1.2646

 2.2000

 0.1222

 25.57

 0.665

 32.77

 1165

Sn

parts per million (ppm)

Colorado state border

Study area boundary

Colorado Mineral Belt

1 10 100

Frequency

Cumulative Frequency

Concentration, in parts per million

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
88 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Figure 83. Mining districts and rock units

associated with the element tin in stream 

sediments of central Colorado.

Tin (Sn) is highly abundant in highly evolved igneous rocks such as granite and granite pegmatites, especially where those rocks are also fluorine rich. The most common tin-bearing mineral is 

cassiterite, which is insoluble during weathering. Because of its high density, cassiterite commonly 

becomes abundant in heavy-mineral placer deposits.

High tin concentrations (>97.5th percentile) are present in stream-sediment samples in the 

Colorado Mineral Belt near the Alma, Argentine, Breckenridge, Empire, Halls Gulch, Henderson, 

Leadville, Montezuma–Geneva Creek, and Silver Plume–Georgetown districts, as well as downstream from the Climax deposit (figs. 82 and 83). A dispersion train is evident along Clear Creek 

from the Henderson and Empire districts eastward to the range front. South of the Colorado Mineral 

Belt, samples with high tin concentrations (>90th percentile) overlie the Mesoproterozoic Pikes Peak 

batholith and a greisen deposit in the Redskin stock (Lake George district). Scattered throughout the 

study area are many other sample locations that have high tin concentrations (>90th percentile) but no 

apparent geologic source.

^ Clear Ck.

Denver

Pikes Peak

batholith

ARGENTINE

LEADVILLE

MONTEZUMA–

GENEVA CREEK

HALL'S

GULCH

HENDERSON

SILVER PLUME–GEORGETOWN

EMPIRE

Redskin

stock

BRECKENRIDGE

CLIMAX

ALMA

LAKE GEORGE

–107° –106° –105°

41°

40°

39°

38°

37°

Mining districts from Wilson (2003),

rock units from Church and others (2012).

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Generalized intrusion boundary
Geochemistry Maps and Discussions 89

Figure 84. Maps of central Colorado stream-sediment geochemistry—titanium (Ti).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Titanium

A B

0.020–0.15% (<2.5th percentile)

0.16–0.21% (2.5–10th percentile)

0.22–0.28% (10–25th percentile)

0.29–0.51% (25–75th percentile)

0.52–0.69% (75–90th percentile)

0.70–1.0% (90–97.5th percentile)

1.1–5.2% (>97.5th percentile)

Titanium (weight percent)

Crustal abundance = 0.632%

Limit of detection = not applicable

0.02 6

0

90

180

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1479

 0.0200

 5.2000

 0.4284

 0.3767

 0.3700

 0.3300

 0.276

 0.007177

 6.304

 83.4

Ti

weight percent (wt%)

Colorado state border

Study area boundary

Colorado Mineral Belt

0.1 1

Frequency

Cumulative Frequency

Concentration, in weight percent

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
90 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Figure 85. Rock units associated with the

element titanium in stream sediments of 

central Colorado.

Titanium (Ti) in igneous rocks is present most commonly in the minerals ilmenite, rutile, and 

sphene, as well as in titaniferous magnetite. It is also commonly incorporated to a limited extent into 

pyroxenes, amphiboles, and biotite. Titanium is most concentrated in mafic rocks, especially those 

of alkaline composition. Titanium minerals in sediments are commonly concentrated in placer and 

paleoplacer deposits because those minerals are resistant to weathering and have a high density.

In the study area, high titanium concentrations (>90th percentile) generally are associated 

with rock type and not related to mineral deposits. Stream-sediment samples showing high titanium 

concentrations (>90th percentile) are associated with Proterozoic mafic to ultramafic metavolcanic 

rocks and metagabbros in the Gunnison volcanic arc (in the central part of the Colorado Mineral 

Belt) and in the Green Mountain volcanic arc in the northwestern corner of the study area (figs. 84 

and 85). Samples with similar high concentrations represent areas containing mafic dikes and shallow intrusive rocks in the alkalic-calcic to alkaline Thirtynine Mile volcanic field, and a few sample 

sites are associated with the Rabbit Ears volcanic rocks. A cluster of sample locations with high Ti 

concentrations (90th to 97.5th percentile) lies near diverse alkaline mafic and ultramafic rocks in 

the Wet Mountains. Near the Colorado–New Mexico border, two samples with high concentrations 

(>97.5th percentile) appear to be related to mafic volcanic rocks in the Oligocene Hinsdale Formation. Sample locations with scattered high concentrations (>97.5th percentile) overlie parts of the 

Proterozoic granitic Pikes Peak batholith, Sherman batholith, and Pratt pluton and perhaps are related 

to late-stage pegmatite dikes.

^Denver

Gunnison volcanic

arc

Pikes Peak

batholith

Hinsdale

Formation

Thirtynine Mile

volcanic field

Pratt

pluton

Rabbit Ears

volcanic

field

WET MOUNTAINS

Sherman

batholith

Green

Mountain

volcanic arc

–107° –106° –105°

41°

40°

39°

38°

37°

Rock units from Church and others (2012).

Low : 4,250

High : 14,433

Elevation (feet)

Thirtynine Mile volcanic field boundary

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Pratt pluton boundary

Geochemistry sample site

Generalized igneous rock boundary

Study area boundary

Colorado Mineral Belt

Gunnison volcanic arc boundary

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
Geochemistry Maps and Discussions 91

Figure 86. Maps of central Colorado stream-sediment geochemistry—tungsten (W).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Tungsten

A B

0.3–0.5 ppm (<2.5th percentile)

0.51–0.70 ppm (2.5–10th percentile)

0.71–0.90 ppm (10–25th percentile)

0.91–2.0 ppm (25–75th percentile)

2.1–4.6 ppm (75–90th percentile)

4.7–24 ppm (90–97.5th percentile)

25–967 ppm (<97.5th percentile)

Tungsten (parts per million)

Crustal abundance = 1.20 ppm

Limit of detection = not applicable

0.3 1,000

0

90

180

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1064

 0.3000

 967.0000

 5.0836

 1.5546

 1.2000

 1.0000

 37.53

 1.151

 19.83

 455.3

W

parts per million (ppm)

Colorado state border

Study area boundary

Colorado Mineral Belt

1 10 100

Frequency

Cumulative Frequency

Concentration, in parts per million

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
92 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Figure 87. Mining districts and rock unit 

associated with the element tungsten in 

stream sediments of central Colorado.

Tungsten (W) is more abundant in highly evolved igneous rocks such as alkali granite and 

granite pegmatites, especially where they are enriched in fluorine. The most common tungstenbearing minerals are wolframite and scheelite, which are insoluble during weathering. Placer deposits 

commonly are enriched in these high-density minerals.

High tungsten concentrations (>90th percentile) are present in stream-sediment samples throughout much of the Colorado Mineral Belt and are highest (>97.5th percentile) at the northern end of the 

mineral belt (figs. 86 and 87). The highest concentrations (six samples, ranging from 170 to 970 parts 

per million (ppm) W) all represent sediments near the tungsten vein deposits in the Boulder-Tungsten 

district, where ferberite (the iron-rich end member of the wolframite mineral series) is common. 

Samples with lower tungsten concentrations (90th to 97.5th percentile) surround the BoulderTungsten district and extend into the Gold Hill, Jamestown, North Gilpin, and Ward districts. High 

tungsten concentrations (>90th percentile) are also found in samples from the Blackhawk, Central 

City–Idaho Springs, Chicago Creek–Freeland, Dumont, Henderson, and Silver Plume–Georgetown 

districts. A dispersion train is evident along Clear Creek from the Henderson district eastward to 

the range front. Within the mineral belt, scattered samples containing high tungsten concentrations 

(>90th percentile) were obtained in the Alma, Argentine, Bonanza, Breckenridge, Browns Canyon, 

Consolidated Montgomery, Eldora, Gold Brick, Holy Cross, Monarch, Twin Lakes, Upper Blue River, 

and Winfield districts. Scattered sample locations containing high tungsten concentrations (>90th percentile) lie north and south of the mineral belt, including the greisen deposit from the Redskin stock 

in the Lake George district. Many samples with high tungsten concentrations (>90th percentile) are 

scattered throughout the study area and may be related to trace amounts of disseminated scheelite in 

Proterozoic gneisses, particularly calc-silicate gneisses, in Colorado (Tweto, 1960).

^ Clear Ck.

Denver

NORTH GILPIN

ARGENTINE

BOULDER–TUNGSTEN GOLD HILL

DUMONT

BRECKENRIDGE

JAMESTOWN

MONARCH

HOLY CROSS

TWIN LAKES ALMA

GOLD BRICK

WINFIELD

CONSOLIDATED MONTGOMERY

LAKE GEORGE

CHICAGO CREEK–FREELAND

HENDERSON

BROWN'S CANYON

WARD

BLACKHAWK

SILVER PLUME–GEORGETOWN

CENTRAL CITY–

IDAHO SPRINGS

UPPER BLUE RIVER

Redskin

stock

ELDORA

BONANZA

–107° –106° –105°

41°

40°

39°

38°

37°

Mining districts from Wilson (2003),

rock units from Church and others (2012).

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Generalized intrusion boundary
Geochemistry Maps and Discussions 93

Figure 88. Maps of central Colorado stream-sediment geochemistry—uranium (U).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Uranium

A B

<0.2 ppm (<10th percentile)

0.2–1.8 ppm (10–25th percentile)

1.9–9.4 ppm (25–75th percentile)

9.5–17 ppm (75–90th percentile)

18–31 ppm (90–97.5th percentile)

32–500 ppm (>97.5th percentile)

Uranium (parts per million)

Crustal abundance = 2.3 ppm

Limit of detection = 0.2 ppm

0.0422 600

0

200

400

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geoometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1402

 <0.2

 500.0000

 7.4854

 2.0187

 4.5500

 0.0422

 15.86

 0.4235

 21.88

 662.3

U

parts per million (ppm)

Colorado state border

Study area boundary

Colorado Mineral Belt

0.1 1 10 100

Frequency

Cumulative Frequency

Concentration, in parts per million

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
94 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Figure 89. Mining districts and rock units 

associated with the element uranium in 

stream sediments of central Colorado.

Uranium (U) is a lithophile element concentrated in felsic igneous rocks and igneous rocks and 

residing in trace and accessory minerals such as zircon, xenotime, monazite, allanite, sphene and 

apatite. In sedimentary rocks, uranium concentrations are greatest in organic-rich shales, phosphorite, 

and immature clastic rocks derived from granitic and felsic-volcanic sources. Uranium deposits typically occur in sedimentary rocks, basin-fill deposits, fracture and fault zones, and in some tuffaceous 

volcanic rocks where groundwater or hydrothermal solutions encountered reducing conditions that 

caused uranium to precipitate.

High uranium concentrations (>97.5th percentile) are found in stream-sediment samples from 

many Mesoproterozoic granitic plutons (figs. 88 and 89). These deposits include some phases of the 

Pikes Peak batholith and the Kenosha Pass, Log Cabin, Monarch Pass, St. Vrain, and Silver Plume 

plutons. Sample locations over several Late Cretaceous to Oligocene plutons and stocks contain 

similar high concentrations, such as the Mount Antero stock, the Mount Princeton pluton, the felsic 

phase of the Twin Lakes pluton, and the Climax, Henderson, and Porphyry Mountain stocks. Several 

samples with high U concentrations (>90th percentile) also are associated with rhyolitic welded tuff 

units in the central part of the study area. Within the Colorado Mineral Belt, high uranium concentrations (>97.5th percentile) are found in samples from the Browns Canyon, Climax, Consolidated 

Montgomery, Halls Gulch, Henderson, Jamestown, Magnolia, Monarch, Montezuma–Geneva Creek, 

Silver Plume–Georgetown, and Upper Blue River districts, as well as very close to the range front 

from the Golden Gate Canyon area in the vicinity of the Schwarztwalder uranium mine.

^Denver

JAMESTOWN

MONARCH

MONTEZUMA–

GENEVA CREEK

MAGNOLIA

CONSOLIDATED

MONTGOMERY

BROWN'S

CANYON

UPPER

BLUE RIVER HALL'S GULCH

HENDERSON

CLIMAX

St. Vrain

pluton

Log Cabin

pluton

Silver Plume

pluton

Pikes Peak

batholith

Monarch

Pass

pluton

Mount

Princeton

pluton

Twin Lakes

pluton

Mount Antero stock

Kenosha Pass

pluton

Porphyry Mountain

stock

Golden Gate Canyon

SILVER PLUME–

GEORGETOWN

–107° –106° –105°

41°

40°

39°

38°

37°

Mining districts from Wilson (2003),

rock units from Church and others (2012).

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Some formations too small to show at this scale.

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Generalized intrusion boundary

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
Geochemistry Maps and Discussions 95

Figure 90. Maps of central Colorado stream-sediment geochemistry—vanadium (V).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Vanadium

A B

5.0–29 ppm (<2.5th percentile)

30–50 ppm (2.5–10th percentile)

51–68 ppm (10–25th percentile)

69–120 ppm (25–75th percentile)

130–160 ppm (75–90th percentile)

170–240 ppm (90–97.5th percentile)

250–1,000 ppm (>97.5th percentile)

Vanadium (parts per million)

Crustal abundance = 136 ppm

Limit of detection = not applicable

5 1,100

0

100

200

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1479

 5.0000

 1000.0000

 101.4408

 89.2303

 90.0000

 110.0000

 60.96

 1.585

 4.51

 44.38

V

parts per million (ppm)

Colorado state border

Study area boundary

Colorado Mineral Belt

10 100

Frequency

Cumulative Frequency

Concentration, in parts per million

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
96 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Figure 91. Mining districts and rock units 

associated with the element vanadium in 

stream sediments of central Colorado.

Vanadium (V) concentration in igneous rocks is related directly to abundance of the Fe-Ti minerals 

magnetite, ilmenite, and rutile and thus tends to be highest in mafic igneous rocks. Clay-rich sedimentary 

rocks also may show relatively high vanadium concentrations. Granites generally have low concentrations, as do mature clastic sedimentary rocks and carbonates. Vanadium, with its multiple oxidation 

states, characteristically is controlled by oxidation-reduction reactions in low-temperature aqueous solutions in the near-surface environment.

In the study area, most of the high vanadium concentrations probably are related to rock type. 

Stream-sediment samples with high vanadium concentrations in the >90th percentile range are scattered widely and associated with a variety of rock units (figs. 90 and 91). High concentrations are 

associated with mafic and ultramafic igneous rocks (such as those of the Thirtynine Mile volcanic 

field and the Gunnison volcanic arc), organic-rich shales such as the Pierre Shale, and with some 

basin-fill sedimentary units such as the Huerfano and northern Poison Canyon Formations in the 

southern part of the study area, where they may be related to small stratabound uranium-vanadium 

deposits (Vanderwilt, 1947). Similar to the distribution of samples containing cobalt, samples showing 

high (>90th percentile) vanadium concentrations south of the Colorado Mineral Belt may be related to 

Mesoproterozoic stratabound base-metal deposits in the Cotopaxi, Grape Creek, Guffey, Oak Creek, 

Rosita Hills, and Silver Cliff districts. Within the mineral belt, clusters of sample locations containing abundant vanadium are found in the Gold Hill, Magnolia, Boulder-Tungsten, and North Gilpin 

districts at the northeastern end, in the Halls Gulch and Montezuma–Geneva Creek districts, and at the 

southern end in the Browns Canyon, Whitepine, and Monarch districts. Concentrations of common 

accessory heavy minerals (such as magnetite, ilmenite, and rutile) in alluvial placers also may result in 

scattered, isolated samples showing high vanadium concentrations. The Mesoproterozoic Pikes Peak 

batholith is depleted noticeably in vanadium, reflecting that batholith’s strongly granitic composition.

Pikes Peak

batholith

^Denver

Huerfano

Formation

Poison

Canyon

Formation

Pierre

Shale

Pierre Shale

Pierre

Shale

Pierre

Shale

Thirtynine Mile

volcanic field

NORTH GILPIN

GOLD HILL

BOULDER–

TUNGSTEN

ROSITA

HILLS

WHITEPINE

MONTEZUMA–

GENEVA CREEK

SILVER

CLIFF

HALL’S GULCH

COTOPAXI

GUFFEY

GRAPE

CREEK

BROWN’S

CANYON

MONARCH

MAGNOLIA

OAK CK.

Gunnison volcanic arc

–107° –106° –105°

41°

40°

39°

38°

37°

Mining districts from Wilson (2003),

rock units from Church and others (2012).

Low : 4,250

High : 14,433

Elevation (feet)

Poison Canyon Formation boundary

Pierre Shale boundary

Gunnison volcanic arc boundary

Other igneous rock boundary

Huerfano Canyon Formation boundary

Mining district

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
Geochemistry Maps and Discussions 97

Figure 92. Maps of central Colorado stream-sediment geochemistry—ytterbium (Yb).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Ytterbium

A B

<1.0 ppm (<2.5th percentile)

1.1–2.0 ppm (2.5–25th percentile)

2.1–4.0 ppm (25–75th percentile)

4.1–6.0 ppm (75–90th percentile)

6.1–22 ppm (90–97.5th percentile)

23–51 ppm (>97.5th percentile)

Ytterbium (parts per million)

Crustal abundance = 3.10 ppm

Limit of detection = 1 ppm

0.211 60

0

80

160

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

369

 <1

 51.0000

 3.9695

 2.8891

 3.0000

 2.0000

 5.406

 0.2814

 5.381

 35.12

Yb

parts per million (ppm)

Colorado state border

Study area boundary

Colorado Mineral Belt

1 10

Frequency

Cumulative Frequency

Concentration, in parts per million

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
98 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Figure 93. Rock units associated with the 

element ytterbium in stream sediments of 

central Colorado.

Ytterbium (Yb) is one of 15 metallic elements called rare earth elements (REEs). The REEs, 

including ytterbium, are strongly lithophile in igneous rocks. See the cerium map (fig. 19) for further 

discussion of the geochemical behavior of the REEs.

In this study, only a small subset of samples (369 out of 1,479) from the Church and others 

(2012) and Grossman (1998) studies were analyzed for ytterbium (fig. 92). The highest concentrations 

of ytterbium (>90th percentile) were found in stream-sediment samples overlying the main phase 

of the Mesoproterozoic Pikes Peak batholith and from sample locations underlain by the San Isabel 

pluton in the Wet Mountains and the Kroenke pluton in the Sawatch Range, and in one sample downstream from the Tertiary Montezuma stock in the west-central Front Range (figs. 92 and 93). Several 

other REEs (Ce, Eu, Ho, La, and Nd) show spatial associations with felsic rocks in mining districts 

within the Colorado Mineral Belt (see respective pages, this report). The lack of this spatial association for ytterbium (and for yttrium as well) likely reflects the fact that the granitic rocks within the 

mineral belt are more enriched in light (La, Ce, Nd) and middle (Eu, Ho) REEs than in heavy REEs 

(Y, Yb). The overall map patterns for ytterbium mimic fairly well the patterns for yttrium, where 

many more samples (n = 1,479) were analyzed.

^Denver

Kroenke

pluton

Montezuma

stock

Pikes Peak

batholith

San Isabel

pluton

FRONT RANGE

WET MOUNTAINS

SAWATCH RANGE

–107° –106° –105°

41°

40°

39°

38°

37°

Rock units from Church and others (2012).

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Generalized intrusion boundary

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
Geochemistry Maps and Discussions 99

Figure 94. Maps of central Colorado stream-sediment geochemistry—yttrium (Y).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Yttrium

A B

<13.1 ppm (<2.5th percentile)

13.1–17.0 ppm (2.5–10th percentile)

17.1–22.0 ppm (10–25th percentile)

22.1–45.3 ppm (25–75th percentile)

45.4–69.0 ppm (75–90th percentile)

69.1–145 ppm (90–97.5th percentile)

146–453 ppm (>97.5th percentile)

Yttrium (parts per million)

Crustal abundance = 31.0 ppm

Limit of detection = 2 ppm

0.411 500

0

100

200

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geo.Mean:

Median:

Mode:

Std.Dev.:

Std.Err.:

Skew:

Kurtosis:

1479

 <2

 453.0000

 40.2749

 33.0884

 31.0000

 19.0000

 33.95

 0.8827

 4.184

 28.06

Y

parts per million (ppm)

Colorado state border

Study area boundary

Colorado Mineral Belt

1 10 100

Frequency

Cumulative Frequency

Concentration, in parts per million

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
100 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Figure 95. Rock units associated with 

the element yttrium in stream sediments 

of central Colorado.

Yttrium (Y) is one of 15 metallic elements called rare earth elements (REEs). The REEs, including yttrium, are strongly lithophile in igneous rocks. See the cerium map (fig. 19) for further discussion of the geochemical behavior of the REEs.

The highest concentrations of yttrium (>90th percentile) are found in stream-sediment samples 

obtained over and near the main phase of the Mesoproterozoic Pikes Peak batholith, with scattered 

lower concentrations (>90th to 97.5th percentile) from samples overlying several other, mainly 

Mesoproterozoic, granitic plutons in the study area (figs. 94 and 95). Plutons associated with high 

yttrium include the Kenosha Pass, Lone Rock, Shawnee, and Yankee Boy plutons in the Front Range, 

the southern portion of the Henry Mountain pluton, the Pratt and tectonized Mount Moriah plutons 

near the Wyoming border, and the Mesoproterozoic San Isabel pluton in the southern Wet Mountains. 

Other REEs (Ce, Eu, Ho, La, and Nd) show spatial associations with felsic rocks in mining districts 

within the Colorado Mineral Belt. The lack of this spatial association for yttrium (and for ytterbium, 

as well) likely reflects the fact that the granitic rocks within the mineral belt are more enriched in light 

(La, Ce, Nd) and middle (Eu, Ho) REEs than in heavy REEs (Y, Yb). ^Denver

Pikes Peak

batholith

San Isabel

pluton

Shawnee

pluton

Yankee Boy

pluton

Pratt and

Mount Moriah

plutons

Lone Rock

pluton

Henry

Mountain

pluton

Kenosha

Pass

pluton

FRONT RANGE

WET MOUNTAINS

–107° –106° –105°

41°

40°

39°

38°

37°

Rock units from Church and others (2012).

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Generalized intrusion boundary
Geochemistry Maps and Discussions 101

Figure 96. Maps of central Colorado stream-sediment geochemistry—zinc (Zn).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Zinc

A B

21.0–41.0 ppm (<2.5th percentile)

41.1–55.0 ppm (2.5–10th percentile)

55.1–73.0 ppm (10–25th percentile)

73.1–140 ppm (25–75th percentile)

141–280 ppm (75–90th percentile)

281–1,700 ppm (90–97.5th percentile)

1,710–96,000 ppm (>97.5th percentile)

Zinc (parts per million)

Crustal abundance = 76.0 ppm

Limit of detection = not applicable

21 100,000

0

150

300

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1479

 21.0000

96000.0000

 316.1394

 117.4226

 96.0000

 110.0000

 2677

 69.6

 31.67

 1108

Zn

parts per million (ppm)

Colorado state border

Study area boundary

Colorado Mineral Belt

100 1,000 10,000

Frequency

Cumulative Frequency

Concentration, in parts per million

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
102 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Figure 97. Mining districts and rock unit 

associated with the element zinc in stream 

sediments of central Colorado.

Zinc (Zn) is strongly chalcophile in its geochemistry, although it is locally present in some silicate minerals such as biotite. Zinc is commonly found in sphalerite and in other more complex sulfide 

minerals. It is relatively mobile during weathering and may be concentrated on manganese- and ironhydroxide precipitates and on organic matter. Organic-rich shales are commonly enriched in zinc.

The distribution of zinc in stream sediments is similar to that of cadmium and bismuth. 

Almost all concentrations are in the >97.5th percentile range; they occur in and help define the 

entire Colorado Mineral Belt (figs. 96 and 97). The single highest zinc concentration (96,000 parts 

per million, ppm) is from a sample obtained downstream of the Leadville district. Extremely high 

zinc concentrations (11,000 and 26,000 ppm, respectively) are found in two samples taken near the 

Chalk Creek district. Another sample with an extremely high zinc concentration of 13,000 ppm is 

from the Montezuma–Geneva Creek district. Elsewhere in the mineral belt, high zinc concentrations (>90th percentile) are found in numerous samples from many districts, including the Alma, 

Argentine, Blackhawk, Bonanza, Boulder-Tungsten, Breckenridge, Central City–Idaho Springs, 

Consolidated Montgomery, Daily, Dumont, Gold Brick, Gold Hill, Halls Gulch, Henderson, Holy 

Cross, Jamestown, Lincoln Gulch, Monarch, Red Mountain, Silver Plume–Georgetown, St. Kevin–

Sugarloaf, Tenmile-Kokomo, Upper Blue River, Whitepine, and Winfield districts. A zinc dispersion train is evident along Clear Creek from the Henderson district eastward to the range front. 

South of the mineral belt, high zinc concentrations (>90th percentile) are found in samples from the 

Cripple Creek–Victor, Lake George, and Rosita Hills districts and from scattered locations within the 

Mesoproterozoic Pikes Peak batholith.

^ Clear Ck.

Denver

ARGENTINE

LEADVILLE

MONTEZUMA–GENEVA CREEK

GOLD HILL

BOULDER–

TUNGSTEN

DUMONT

BRECKENRIDGE

WHITEPINE

ROSITA HILLS

JAMESTOWN

HOLY

CROSS

BLACKHAWK

ALMA

DAILY

GOLD

BRICK

WINFIELD

LAKE

GEORGE

CRIPPLE CREEK–

VICTOR

UPPER BLUE RIVER

CHALK

CREEK

RED MT

MONARCH

SILVER PLUME–GEORGETOWN

CENTRAL CITY–

IDAHO SPRINGS

ST. KEVIN–

SUGARLOAF

CONSOLIDATED MONTGOMERY

HALL'S GULCH

TENMILE–

KOKOMO

HENDERSON

LINCOLN

GULCH

Pikes Peak

batholith

BONANZA

–107° –106° –105°

41°

40°

39°

38°

37°

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Mining districts from Wilson (2003),

rock units from Church and others (2012).

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Generalized intrusion boundary
Geochemistry Maps and Discussions 103

Figure 98. Maps of central Colorado stream-sediment geochemistry—Factor 1: Ce-La-Y-Th-Nb-Ti-(Be-Fe-P). 

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado 

Stream-Sediment Geochemistry—

Factor 1: Ce-La-Y-Th-Nb-Ti-(Be-Fe-P)

A B

Parentheses indicate elements

of lesser significance in the factor

Colorado state border

Study area boundary

Colorado Mineral Belt

–2.768 to –1.561 (<2.5th percentile)

–1.561 to –1.069 (2.5–10th percentile)

–1.069 to –0.723 (10–25th percentile)

–0.723–0.549 (25–75th percentile)

0.549–1.323 (75–90th percentile)

1.323–2.223 (90–97.5th percentile)

2.223–5.733 (>97.5th percentile)

Factor 1: Ce-La-Y-Th-Nb-Ti-(Be-Fe-P)

Crustal abundance = Not applicable

Limit of detection = Not applicable

–3 6

0

70

140

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1479

 –2.7683

 5.7332

 0.0

 0.5201

–0.1197

–2.7683

 0.9888

 0.02571

 0.8882

 1.757

Factor 1

543210–1–2

Frequency

Cumulative Frequency

Factor Score

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
104 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Figure 99. Mining districts and rock units 

associated with Factor 1 elements in stream 

sediments of central Colorado.

The factor analysis maps presented in this report represent factor scores for a five-factor model 

generated using R-mode factor analysis, a multivariate statistical procedure.

Details on the factor analysis procedures used in this report are provided in the Methods section; 

elements within a given factor behave similarly in their gross distributions.

Factor 1, containing elements Ce-La-Y-Th-Nb-Ti-(Be-Fe-P), explains the most variance for 

elements within the dataset. It is a lithologic factor related to high concentrations of rare earth elements 

(REEs) and several other lithophile elements (that is, Be, Nb, and Th) in stream-sediment samples from 

certain granitic rocks. Here and in subsequent factor suites, elements in parentheses are weaker components of the respective factor. Titanium in this factor likely represents the presence of sphene (which 

also commonly contains REEs), rutile, or ilmenite (with iron) in sediments derived from granitic rocks. 

Phosphorus probably is incorporated into the REE-rich phosphate monazite. Factor 1 highlights many 

of the lithophile-element-rich granitic batholiths and plutons (mostly Mesoproterozoic) in the northern 

two-thirds of the study area. Those intrusions include the Pikes Peak and Sherman batholiths, and the 

Kroenke, Log Cabin, St. Vrain, and Silver Plume plutons (figs. 98 and 99). Mining districts indicated 

most strongly by Factor 1 (that is, falling above the 97.5th percentile) include the Browns Canyon, 

Cripple Creek–Victor, and St. Peters Dome districts. Mining districts indicated by Factor 1 at the 90th 

to 97.5th percentile include the Argentine, Boulder-Tungsten, Daily, Eldora, Gold Hill, Henderson, 

Jamestown, North Gilpin, and Silver Plume–Georgetown districts.

^Denver

NORTH GILPIN

ARGENTINE

GOLD HILL BOULDER–TUNGSTEN

JAMESTOWN

SILVER PLUME–GEORGETOWN

ST. PETERS

DOME

BROWN'S

CANYON

DAILY

ELDORA

CRIPPLE CREEK–

VICTOR

HENDERSON

Sherman

batholith

Kroenke

pluton

St. Vrain

pluton

Log Cabin

pluton

Silver Plume

pluton

Pikes Peak

batholith

–107° –106° –105°

41°

40°

39°

38°

37°

Mining districts from Wilson (2003),

rock units from Church and others (2012).

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Generalized intrusion boundary
Geochemistry Maps and Discussions 105

Figure 100. Maps of central Colorado stream-sediment geochemistry—Factor 2: Ni-Cr-V-Mg-Co-(Fe).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Factor 2: Ni-Cr-V-Mg-Co-(Fe)

A B

Parentheses indicate elements

of lesser significance in the factor

Colorado state border

Study area boundary

Colorado Mineral Belt

–5.447 to –2.211 (<2.5th percentile)

–2.211 to –1.098 (2.5–10th percentile)

–1.098 to –0.487 (10–25th percentile)

–0.487–0.609 (25–75th percentile)

0.609–1.097 (75–90th percentile)

1.097–1.555 (90–97.5th percentile)

1.555–2.697 (>97.5th percentile)

Factor 2: Ni-Cr-V-Mg-Co-(Fe)

Crustal abundance = Not applicable

Limit of detection = Not applicable

–6 3

0

80

160

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1479

 –5.4473

 2.6972

0.0

 0.4458

 0.0831

 –5.4473

 0.9568

 0.02488

 –1.1

 3.324

Factor 2

–5 –4 –3 210–1–2

Frequency

Cumulative Frequency

Factor Score

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
106 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Figure 101. Mining districts associated with 

Factor 2 elements in stream sediments of 

central Colorado.

Details on the factor analysis procedures used in this report are provided in the Methods section; 

elements within a given factor behave similarly in their gross spatial distributions.

Factor 2, containing elements Ni-Cr-V-Mg-Co-(Fe), explains the second-greatest variability for 

elements within the dataset and is a lithologic factor that indicates association with mafic rocks. Wide 

distribution of Factor 2 elements throughout the study area likely reflects sediments derived in part 

from mafic dikes, amphibolites, and other mafic igneous bodies of various ages present throughout 

the area (figs. 100 and 101). Although numerous stream-sediment samples with high values (above 

the 90th percentile) for Factor 2 were obtained in and around mining districts in the Colorado Mineral 

Belt, it is unlikely that such mineralization is related genetically to this factor. Mineral deposits 

containing high concentrations of this suite of mafic elements (Ni, Cr, V, Mg, and Co) are not present 

within the study area, although some deposits show enrichment in Co and V. The various rock and 

deposit types that might be indicated by the elements Co, Cr, Mg, Ni, and V are provided in more 

detail in individual element discussions associated with figures 23, 25, 45, 55, and 91, respectively.

^Denver

NORTH GILPIN

ARGENTINE

GOLD HILL

BOULDER–TUNGSTEN

BRECKENRIDGE

BLACKHAWK

MONTEZUMA–

GENEVA CREEK

CENTRAL CITY–

IDAHO SPRINGS

ELDORA

MAGNOLIA

HALL'S GULCH

–107° –106° –105°

41°

40°

39°

38°

37°

Mining districts from Wilson (2003).

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt
Geochemistry Maps and Discussions 107

Figure 102. Maps of central Colorado stream-sediment geochemistry—Factor 3: Zn-Pb-Cu-As-(Mo).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Factor 3: Zn-Pb-Cu-As-(Mo)

A B

Colorado state border

Study area boundary

Colorado Mineral Belt

–1.649 to –1.070 (<2.5th percentile)

–1.070 to –0.812 (2.5–10th percentile)

–0.812 to –0.534 (10–25th percentile)

–0.534–0.1667 (25–75th percentile)

0.167–1.110 (75–90th percentile)

1.110–2.831 (90–97.5th percentile)

2.831–7.504 (>97.5th percentile)

Factor 3: Zn-Pb-Cu-As-(Mo)

Crustal abundance = Not applicable

Limit of detection = Not applicable

–2 8

0

150

300

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1479

–1.6494

 7.5041

0.0

 0.3939

–0.2258

–1.6494

 0.9464

 0.02461

 2.368

 7.776

Factor 3

20 4 6

Frequency

Cumulative Frequency

Factor Score

Parentheses indicate elements

of lesser significance in the factor

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
108 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Figure 103. Mining districts associated with 

Factor 3 elements in stream sediments of 

central Colorado.

Details on the factor analysis procedures used in this report are provided in the Methods section; 

elements within a given factor behave similarly in their gross spatial distributions.

Factor 3, containing elements Zn-Pb-Cu-As-(Mo), explains the third-largest variability for elements within the dataset and reflects strong mineralization. The factor indicates areas of polymetallic 

and porphyry hydrothermal mineralization and related historical mining activity. Scores for this factor 

strongly highlight most metal-mining districts within and outside the Colorado Mineral Belt (figs. 102 

and 103), such as the Alicante, Alice–Yankee Hill, Alma, Argentine, Blackhawk, Boulder-Tungsten, 

Breckenridge, Central City–Idaho Springs, Chalk Creek, Chicago Creek–Freeland, Consolidated 

Montgomery, Cripple Creek–Victor, Daily, Dumont, Eldora, Empire, Fulford, Gilman-Redcliff, 

Gold Hill, Henderson, Independence, Jamestown, Lake Albion, Lake George, Leadville, Magnolia, 

Monarch, Montezuma–Geneva Creek, North Gilpin, Oak Creek North, Red Mountain, Rosita Hills, 

Silver Plume–Georgetown, St. Kevin–Sugarloaf, Tenmile-Kokomo, Twin Lakes, Upper Blue River, 

Ward, Whitepine, and Winfield districts. The factor effectively synthesizes geochemical patterns 

shown in single-element maps for the ore-related metals Zn, Pb, Cu, As, and Mo (figs. 96, 40, 26, 

6, and 50, respectively). An apparent dispersion train is present in Clear Creek from the Henderson 

and Daily districts eastward, downstream to the range front. Additional dispersion is seen in the 

Montezuma–Geneva Creek district eastward along Geneva Creek to the North Fork of the South 

Platte River. Historical mining and mineral processing activities around Denver and Cañon City 

(described in more detail in discussions of copper and arsenic, figs. 27 and 7, respectively) also are 

indicated by anomalous samples, although not as strongly as observed at sites within the mineral belt.

^ Clear Ck.

Denver

Geneva Ck.

N. Fork S.Platte R.

NORTH GILPIN

ARGENTINE

LEADVILLE

GOLD HILL

BOULDER–TUNGSTEN

DUMONT

BRECKENRIDGE

WHITEPINE

ROSITA HILLS

JAMESTOWN

DAILY

GOLD

BRICK

WINFIELD

GILMAN–

REDCLIFF

LAKE GEORGE

CRIPPLE CREEK–

VICTOR

UPPER BLUE RIVER

CHALK

CREEK

CHICAGO CREEK–FREELAND

MONARCH

WARD

MONTEZUMA–GENEVA CREEK

BLACKHAWK

SILVER PLUME–GEORGETOWN CENTRAL CITY–IDAHO SPRINGS

ELDORA

CONSOLIDATED MONTGOMERY

HALL'S GULCH

INDEPENDENCE

TENMILE–

KOKOMO

HENDERSON

Cañon City

BONANZA

LAKE ALBION

ALICE–YANKEE HILL

EMPIRE

MAGNOLIA

FULFORD

ST. KEVIN–

SUGARLOAF

ALMA

ALICANTE

TWIN

LAKES

RED MT.

OAK CREEK NORTH

–107° –106° –105°

41°

40°

39°

38°

37°

Mining districts from Wilson (2003).

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
Geochemistry Maps and Discussions 109

Figure 104. Maps of central Colorado stream-sediment geochemistry—Factor 4: Al-Sr-Na-Ba.

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Factor 4: Al-Sr-Na-Ba

A B

Colorado state border

Study area boundary

Colorado Mineral Belt

–4.988 to –1.931 (<2.5th percentile)

–1.931 to –1.081 (2.5–10th percentile)

–1.081 to –0.524 (10–25th percentile)

–0.524–0.604 (25–75th percentile)

0.604–1.134 (75–90th percentile)

1.134–1.755 (90–97.5th percentile)

1.755–2.982 (>97.5th percentile)

Factor 4: Al-Sr-Na-Ba

Crustal abundance = Not applicable

Limit of detection = Not applicable

–5 3

0

70

140

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1479

 –4.9876

 2.9821

 0.0

 0.4770

 –0.0003

 –4.9876

 0.9428

 0.02451

 –0.6469

 2.468

Factor 4

–4 –3 –1 0 1

Frequency

Cumulative Frequency

Factor Score

–2 2

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
110 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Details on the factor analysis procedures used in this report are provided in the Methods section; 

elements within a given factor behave similarly in their gross distributions.

Factor 4, consisting of elements Al-Sr-Na-Ba, explains the fourth-greatest variability for 

elements within the dataset, is most likely due to rock type, and perhaps reflects evaporative processes in basinal areas. The factor indicates the presence of plagioclase, a mineral highly abundant in 

intermediate-composition alkalic-calcic igneous rocks. Factor 4 highlights the Thirtynine Mile volcanic field and extrusive volcanic and plutonic rocks in much of the southern third of the study area, as 

well as the Rabbit Ears volcanic complex and the Middle Park Formation, which commonly contains 

volcanic debris (figs. 104 and 105). Even though stream-sediment samples showing high Factor 4 

scores (above the 90th percentile) were obtained near mining districts, Factor 4 probably is unrelated 

to mineralization.

Potassium feldspar is more abundant than plagioclase in granitic rocks within the Colorado 

Mineral Belt. A comparison of Factor 4 distribution and barium distribution (fig. 8), shows the general 

absence of anomalous samples within the northern end of the mineral belt on the Factor 4 map. That 

absence probably indicates that the barium contribution to Factor 4 is due to plagioclase, whereas high 

barium concentrations within the mineral belt (fig. 8) are due to barium’s substitution into potassium 

feldspar.

Factor 4 distributions are very similar to those of sodium and strontium alone (figs. 70 and 72, 

respectively). Anomalous samples in basins such as North Park, Middle Park, South Park, and the 

Wet Mountain Valley may reflect sediments affected by surface-water evaporation (Na and Sr) and 

containing associated fine clay minerals (Al and Ba).

Figure 105. Mining districts and rock units 

associated with Factor 4 elements in stream 

sediments of central Colorado.

^Denver

LIBERTY

ROSITA HILLS

MONTEZUMA–

GENEVA CREEK

BLACKHAWK

WINFIELD

GRAYBACK

CRIPPLE

CREEK–

VICTOR

HALL'S GULCH

CHICAGO CREEK–FREELAND

SEDALIA

GUFFEY NW

GUFFEY

Thirtynine Mile

volcanic field

Middle Park

Formation

Rabbit Ears

volcanic field

South Park

North Park

Middle

Wet Mountain Valley

Park

–107° –106° –105°

41°

40°

39°

38°

37°

Mining districts from Wilson (2003), 

rock units from Church and others (2012).

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Generalized rock unit boundary
Geochemistry Maps and Discussions 111

Figure 106. Maps of central Colorado stream-sediment geochemistry—Factor 5: K-Li-Al-(Be)-(–Ca)-(–Fe)-(–V).

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado

Stream-Sediment Geochemistry—

Factor 5: K-Li-Al-(Be)-(-Ca)-(-Fe)-(-V)

Parentheses indicate elements

of lesser significance in the factor

A B

Colorado state border

Study area boundary

Colorado Mineral Belt

–6.126 to –1.983 (<2.5th percentile)

–1.983 to –1.066 (2.5–10th percentile)

–1.066 to –0.497 (10–25th percentile)

–0.497–0.515 (25–75th percentile)

0.515–1.078 (75–90th percentile)

1.078–1.623 (90–97.5th percentile)

1.623–3.715 (>97.5th percentile)

Factor 5: K-Li-Al-(Be)-(-Ca)-(-Fe)-(-V)

Crustal abundance = Not applicable

Limit of detection = Not applicable

–7 4

0

90

180

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1479

 –6.1261

 3.7154

 0.0

 0.4281

 0.0441

 –6.1261

 0.9237

 0.02402

–0.8652

 3.845

Factor 5

–6 –4 0

Frequency

Cumulative Frequency

Factor Score

–2 2

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
112 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Details on the factor analysis procedures used in this report are provided in the Methods section; 

elements within a given factor behave similarly in their gross spatial distributions.

The group of elements in Factor 5, K-Li-Al-(Be)-(–Ca)-(–Fe)-(–V), explains the smallest variability for elements in the dataset. This factor likely reflects potassium feldspar or muscovite (or 

both) either in magmatically evolved igneous rocks of granitic composition or in altered rocks around 

porphyry systems. Potassium and aluminum, along with silicon, are the principal components in both 

minerals. Lithium may substitute for aluminum in micas, suggesting that this factor may be linked 

to lithium-bearing mica in highly evolved granitic rocks. Beryllium also is concentrated in similar 

granitic rocks. The negative loading of calcium, vanadium, and iron (indicated by the attached minus 

signs in the element list above) agrees with Factor 5 indicating evolved granites, as stream-sediment 

samples from such granites typically have low concentrations of those elements.

Factor 5 identifies various rocks within and outside of the Colorado Mineral Belt (figs. 106 and 

107). Clusters with high Factor 5 scores within the mineral belt are associated with two districts: the 

Argentine, Daily, Henderson, Montezuma–Geneva Creek, and Silver Plume–Georgetown districts; 

and the Alma, Climax, Consolidated Montgomery, Tenmile-Kokomo, and Upper Blue River districts. 

The anomalies centered on the Climax and Henderson districts (and perhaps others as well) may 

indicate potassically altered granitic rocks surrounding those porphyry centers. North and south of 

the mineral belt, two large clusters identify the Mesoproterozoic St. Vrain pluton and the Pikes Peak 

batholith, respectively.

Figure 107. Mining districts and rock units 

associated with Factor 5 elements in stream 

sediments of central Colorado.

^Denver

ARGENTINE

SILVER PLUME–

GEORGETOWN

ALMA CONSOLIDATED

MONTGOMERY

MONTEZUMA–

GENEVA CREEK

DAILY

UPPER

BLUE RIVER

TENMILE–

KOKOMO

HENDERSON

CLIMAX

Pikes Peak

batholith

St. Vrain

pluton

–107° –106° –105°

41°

40°

39°

38°

37°

Mining districts from Wilson (2003),

rock units from Church and others (2012).

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Generalized intrusion boundary
Geochemistry Maps and Discussions 113

Figure 108. Maps of central Colorado stream water geochemistry—pH.

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° V105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream Water

Geochemistry—pH

A B

Colorado state border

Study area boundary

Colorado Mineral Belt

2.85–3.0

3.1–4.0

4.1–5.0

5.1–6.0

6.1–7.0

7.1–8.0

8.1–9.0

9.1–10.0

10.1–10.5

pH

Crustal abundance = not applicable

Limit of detection = not applicable

2 11

0

70

140

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1104

 2.8500

 10.5000

 7.3417

 7.2834

 7.4000

 7.2000

 0.8697

 0.02618

 –0.9552

 3.019

pH

3 4 6

Frequency

Cumulative Frequency

pH

5 7 98 10

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
114 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

The pH and specific conductance were measured on waters at stream-sediment collection sites. 

Resulting pH data mostly reflect waters analyzed in the late 1970s under the National Uranium 

Resource Evaluation (NURE) study, but the data also include a smaller set of waters whose pH was 

measured during a more recent study by Church and others (2012). The pH measures the hydronium 

ion (H3

O+) content of water; the higher the hydronium-ion content, the lower the pH and the more 

acidic the water. Within the study area, many mining-affected riparian areas have been remediated 

since these water samples in the 1970s, and these areas now have less-acidic waters.

Data compiled in this study show that waters with pH values below 4.5 occur almost exclusively 

within the Colorado Mineral Belt and probably reflect historical acid-mine drainage and acid generated during weathering of exposed hydrothermal sulfide deposits (figs. 108 and 109). The lowest 

measured pH (2.85) is from a site downstream of the Red Mountain district along the western edge 

of the study area within the mineral belt. Other low-pH sites within the mineral belt (below 4.0) are 

from waters draining the Montezuma–Geneva Creek and the Central City–Idaho Springs districts. At 

the northern end of the study area is a large, diffuse cluster of sites with pH values of 5.1 to 6.0, all 

recorded by the 1970s NURE data (Smith, 2006). It is unclear whether that cluster is valid or is due 

to a meter-calibration error. Similarly, high pH values (above 9.1) from sites scattered throughout the 

study area also came from the 1970s NURE data and are poorly constrained. North and south of the 

mineral belt, sites with pH values of 8.1 and above are from areas commonly underlain by locally 

calcareous Cretaceous and younger sedimentary units such as the Pierre Shale.

Figure 109. Mining districts and rock unit 

associated with high or low pH in stream water 

at sediment collection sites of central Colorado.

^ Clear Ck.

Denver

MONTEZUMA–

GENEVA CREEK

RED MOUNTAIN

CENTRAL CITY–

IDAHO SPRINGS

Geneva Ck.

N. Fork S.Platte R.

–107° –106° –105°

41°

40°

39°

38°

37°

Mining districts from Wilson (2003), 

rock units from Church and others (2012).

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

Pierre Shale boundary

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt
Geochemistry Maps and Discussions 115

Figure 110. Maps of central Colorado stream-sediment geochemistry—Scintillometry.

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Stream-Sediment

Geochemistry—Scintillometry

A B

Colorado state border

Study area boundary

Colorado Mineral Belt

1.0–4.0 eq U (<2.5th percentile)

4.1–6.0 eq U (2.5–10th percentile)

6.1–9.0 eq U (10–25th percentile)

9.1–20 eq U (25–75th percentile)

21–28 eq U (75–90th percentile)

29–41 eq U (90–97.5th percentile)

42–1,759 eq U (>97.5th percentile)

Scintillometry (equivalent uranium (eq U) in parts per million)

Crustal abundance = not applicable

Limit of detection = not applicable

1 1,800

0

90

180

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1235

 1.0000

 1759.0000

 17.1822

 13.2966

 13.0000

 12.0000

 50.81

 1.446

 32.66

 1115

Scintillometry

parts per million (ppm)

Frequency

Cumulative Frequency

Concentration, in parts per million

10 100 1,000

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
116 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

A scintillometer measurement was taken onsite at stream-sediment sample locations during the 

1970s National Uranium Resource Evaluation (NURE) program. Scintillometry measures the total 

radiation (primarily gamma radiation) emitted by the decay of radioactive elements in minerals at the 

location of the sensor. Source minerals commonly are heavy resistate minerals such as zircon, monazite, sphene, thorite, and xenotime. The highest readings commonly occur at sites near granitic source 

rocks.

High scintillometry readings probably reflect rock type, rather than mineralization or relation 

to mineral deposits. The generally scattered high concentrations (>97.5th percentile) likely illustrate radioactive-element concentrations in felsic igneous rocks of various ages, such as the Pikes 

Peak batholith and the Monarch Pass, Mount Princeton, Rawah, St. Vrain, and Silver Plume plutons 

(figs. 110 and 111).

Figure 111. Rock units associated with high 

scintillometry values in stream sediments of 

central Colorado.

^Denver

Pikes Peak

batholith

St. Vrain

pluton

Rawah pluton

Silver Plume

pluton

Mount

Princeton

pluton

Monarch

Pass

pluton

–107° –106° –105°

41°

40°

39°

38°

37°

Rock units from Church and others (2012).

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Generalized intrusion boundary
Geochemistry Maps and Discussions 117

Figure 112. Maps of central Colorado stream water geochemistry—Specific Conductance.

(A) Sample site values as graduated symbols; (B) Filled-contour prediction surface.

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

^Denver

–107° –106° –105°

41°

40°

39°

38°

37°

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Low : 4,250

High : 14,433

Elevation (feet)

EXPLANATION

Central Colorado Water Geochemistry—

Specific Conductance

A B

Colorado state border

Study area boundary

Colorado Mineral Belt

10.0–24.0 μS/cm (<2.5th percentile)

24.1–38.0 μS/cm (2.5–10th percentile)

38.1–65.0 μS/cm (10–25th percentile)

65.1–240 μS/cm (25–75th percentile)

241–525 μS/cm (75–90th percentile)

526–1,600 μS/cm (90–97.5th percentile)

1,610–34,500 μS/cm (>97.5th percentile)

Conductivity (microsiemens per centimeter)

Crustal abundance = not applicable

Limit of detection = not applicable

10 35,000

0

45

90

10%

30%

50%

70%

90%

Samples:

Minimum:

Maximum:

Mean:

Geometric mean:

Median:

Mode:

Standard deviation:

Standard error:

Skew:

Kurtosis:

1108

 10.0000

34500.0000

 287.7286

 133.7170

 122.0000

 70.0000

 1138

 34.18

 25

 736.7

Conductivity

microsiemens per centimeter 

(μS/cm)

Frequency

Cumulative Frequency

Concentration, in microsiemens per centimeter

100 1,000 10,000

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO
118 Geochemical Maps of Stream Sediments in Central Colorado, from New Mexico to Wyoming

Specific conductance (conductivity) and pH were measured on waters at stream-sediment 

collection sites. Those data largely reflect waters measured in the late 1970s under the National 

Uranium Resource Evaluation (NURE) study and on a smaller number of waters measured during a 

more recent study by Church and others (2012). Specific conductance is the ability of a substance to 

conduct an electrical current. For water, it is a measure of dissolved ion content: the more ions in solution, the higher the conductivity. Marine and lacustrine shales and evaporitic rocks commonly produce 

waters with high specific conductance.

Within the study area, waters with higher specific conductance concentrations (>90th percentile) commonly are underlain by fine-grained Cretaceous sedimentary rocks (such as the Niobrara 

Formation and the Pierre Shale), and by younger unconsolidated or poorly consolidated basin-fill 

sedimentary units such as the Middle Park, South Park, and Cuchara Formations (figs. 112 and 113). 

The large regional cluster of sites with high specific conductance to the northeast of the study-area 

boundary (north of Denver) may reflect dissolved fertilizer loads in agricultural runoff. Similar, but 

less pronounced, anomalous clusters of sites also are present in lowland basin areas south of Pueblo, 

east of Cañon City, west of Walsenburg, in South Park, and in the San Luis Valley. Although some of 

those might be related to anthropogenic activities, natural causes, such as concentration of dissolved 

constituents by evaporation, also are possible. Along Clear Creek west of Golden, elevated specific 

conductance values might reflect higher dissolved-metal loads related to historical acid-mine drainage 

below mines of the Central City–Idaho Springs and Blackhawk districts, because those measurements 

were taken before clean-up efforts undertaken since the early 1990s.

Figure 113. Mining districts and rock units

associated with high specific conductance in 

stream water at sediment collection sites of 

central Colorado.

^ Clear Ck.

Denver

BLACKHAWK

CENTRAL CITY–

IDAHO SPRINGS

Middle Park

Formation

Cuchara Formation

South Park

Formation

Cañon

City

Pueblo

South

Park

Luis

San

Valley

Walsenburg

–107° –106° –105°

41°

40°

39°

38°

37°

Mining districts from Wilson (2003), 

rock units from Church and others (2012).

Low : 4,250

High : 14,433

Elevation (feet)

Mining district

EXPLANATION

0 20 40 60 80 100 MILES

0 20 40 60 80 KILOMETERS 100

Niobrara Formation or Pierre Shale, undivided, boundary

Other formation boundary

Geochemistry sample site

Study area boundary

Colorado Mineral Belt

Study

area

Map

area

WYOMING

NEW MEXICO

COLORADO

Golden
References Cited 119

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Publishing support provided by: 

Denver Publishing Service Center

For more information concerning this publication, contact:

Center Director, USGS Central Mineral and Environmental Resources Science Center

Box 25046, Mail Stop 973

Denver, CO 80225

(303) 236-1562

Or visit the Central Mineral and Environmental Resources Science Center Web site at: 

http://minerals.cr.usgs.gov/

This publication is available online at

http://dx.doi.org/10.3133/ofr20151025

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