![](media/image1.pct){width="1.5in" height="0.5555555555555556in"}

U. S. DEPARTMENT OF THE INTERIOR

U. S. GEOLOGICAL SURVEY

**Petrology of Arkosic Sandstones, Pennsylvanian Minturn Formation and
Pennsylvanian and Permian Sangre de Cristo Formation, Sangre de Cristo
Range, Colorado\--Data and Preliminary Interpretations**

By David A. Lindsey^1^

**OPEN-FILE REPORT 00-0474**

![](media/image2.png){width="5.958333333333333in" height="4.5in"}

Potassic arkosic wacke with rounded quartz grains,Minturn Formation,
Marble Mountain section

This report is preliminary and has not been reviewed for conformity with
U. S. Geological Survey editorial standards or with the North American
Stratigraphic Code. Any use of trade, product, or firm names is for
descriptive purposes only and does not imply endorsement by the U. S.
Government.

^1^U. S. Geological Survey, Denver, Colo., 80225

**Table of Contents**

Abstract [1](#abstract)

Introduction [2](#introduction)

Sampling and methods [5](#sampling-and-methods)

Petrography and classification [17](#petrography-and-classification)

Mineral-chemical relationships [24](#mineral-chemical-relationships)

Stratigraphic variation [26](#stratigraphic-variation)

Petrogenetic models derived from factor analysis
[30](#petrogenetic-models-derived-from-factor-analysis)

Conclusions [33](#conclusions)

Acknowledgements [34](#acknowledgements)

References cited [34](#references-cited)

Appendix: Log-contrast principal components analysis and factor
interpretation\--a description of the method and tables summarizing two
experiments
[36](#appendix-log-contrast-principal-components-analysis-and-factor-interpretation--a-description-of-the-method-and-tables-summarizing-two-experiments)

**List of Figures**

Figure 1.\--Gneralized geologic map of study area in the Sangre de
Cristo Mountains, south-central Colorado (from Lindsey and Clark, 1995).

Figure 2.\--Topographic and geologic map of sampled stratigraphic
section of Minturn and lowermost Sangre de Cristo Formations at Marble
Mountain (from Lindsey, Johnson, and others, 1986).

Figure 3.\--Topographic and geologic map of sampled stratigraphic
section of Minturn Formation at Eureka Mountain (from Lindsey, Clark,
and Soulliere, 1985).

Figure 4.\--Topographic and geologic map of sampled stratigraphic
section of Sangre de Cristo Formation at Eureka Mountain (from Lindsey
and Schaefer, 1984).

Figure 5.\--Topographic and geologic map of sampled stratigraphic
section of upper Minturn and lower Sangre de Cristo Formation at Thirsty
Peak (from Lindsey, Soulliere, and Hafner, 1985).

Figure 6.\--Topographic and geologic map of sampled stratigraphic
section of Sangre de Cristo Formation at North Taylor Creek (from
Lindsey, Soulliere, and Hafner, 1985).

Figure 7.\--Triangular diagrams showing petrographic classification of
sandstones from the Minturn and Sangre de Cristo Formations: A) Q-F-L,
quartz-feldspar-lithic fragments, B) G-C-M, detrital grains-calcite
cement-matrix (\<0.03 mm), and C) Q-K-P, quartz-potassium
feldspar-plagioclase

Figure 8.\--Photomicrographs of sandstones in the Minturn and Sangre de
Cristo Formations: A) potassic arkosic wacke, Minturn Formation, Marble
Mountain section; B) sodic arkosic wacke, Minturn Formation, Marble
Mountain section; C) sodic arkosic metawacke, Sangre de Cristo
Formation, Thirsty Peak section; and D) potassic arkosic wacke, Sangre
de Cristo Formation, Eureka Mountain section.

Figure 9.\--Photomicrographs of quartz and other detrital grains, very
coarse sand to granule size, Minturn Formation: A) Minturn Formation,
Eureka Mountain section; B) Minturn Formation, Marble Mountain section;
and C) Minturn Formation, Marble Mountain section.

Figure 10.\--Photomicrographs of plutonic and metamorphic rock
fragments, granule size, Minturn Formation: A) Minturn Formation, Eureka
Mountain section; and B) Minturn Formation, near Eureka Mountain
section.

Figure 11.\--Diagrams showing chemical classification of sandstones from
the Minturn and Sangre de Cristo Formations: A) log (Fe~T~O~3~/K~2~O) vs
log (SiO~2~/Al~2~O~3~) (classification of Herron,1988), B) log
(SiO~2~/Al~2~O~3~) vs log (K~2~O/Na~2~O) (ratios of Pettijohn and
others, 1972), and C) Fe~T~O~3~+MgO vs Na~2~O vs K~2~O (classification
of Blatt and others, 1972).

Figure 12.\--Diagrams showing effect of mineral abundance (detrital
grains) versus total oxide content: A) quartz vs SiO~2~, B) potassium
feldspar + mica vs K~2~O, C) plagioclase vs Na~2~O, and C) loss on
ignition (LOI) vs total (detrital) mica.

Figure 13.\--Diagrams showing effects of mixing on abundance of major
oxides, detrital grains, and cement in the Minturn and Sangre de Cristo
Formations: A) Al~2~O~3~ vs SiO~2~, B) silicates except quartz vs
quartz, C) CaO vs SiO~2~, D) MnO vs SiO~2~, and E) P~2~O~5~ vs SiO~2~.

Figure 14.\--Stratigraphic variation of major oxides and minerals at
three sections in the Minturn and Sangre de Cristo Formations: A)
SiO~2~, B) Al~2~O~3~, C) Na~2~O, D) quartz, E) total silicates except
quartz, and F) plagioclase.

Figure 15.\-- Stratigraphic variation of major oxides and heavy minerals
at three sections in the Minturn and Sangre de Cristo Formations: A) log
CaO, B) P~2~O~5~, C) MnO, and D) detrital heavy minerals.

Figure 16.\-- Stratigraphic variation of major oxide log ratios at three
sections in the Minturn and Sangre de Cristo Formations: A) log
(SiO~2~/Al~2~O~3~), B) log (K~2~O/Na~2~O), and C) log (Fe~T~O~3~/K~2~O).

**List of Tables**

Table 1.\--Chemical composition (major oxides, loss on ignition, and
trace elements) of sandstones, Minturn and Sangre de Cristo Formations.

Table 2.\--Mineral composition of sandstones, Minturn and Sangre de
Cristo Formations.

Table 3.\--Summary of factor interpretations based on log-contrast
principal components analysis.

Table 4.\--17X17 centered log-ratio correlation matrix, log ratio data,
Minturn and Sangre de Cristo Formations.

Table 5.\--Eigenvalues (roots) of 17X17 log-ratio correlation matrix.

Table 6.\--Communalities for orthogonal rotations, 6 principal
components, 17 variables.

**T**able 7.\--Six-factor orthogonal solution, 17 variables, Varimax
rotation.

Table 8.\--29X29 centered log-ratio correlation matrix, log ratio data,
Minturn and Sangre de Cristo Formations.

Table 9.\--Eigenvalues (roots) of 29X29 log-ratio correlation matrix.

Table 10.\--Communalities for orthogonal rotation, 5-7 principal
components, 29 variables.

Table 11.\--Six-factor orthogonal solution, 29 variables, Varimax
rotation.

**Petrology of Arkosic Sandstones, Pennsylvanian Minturn Formation and
Pennsylvanian and Permian Sangre de Cristo Formation, Sangre de Cristo
Range, Colorado\--Data and Preliminary Interpretations**

By David A. Lindsey

# Abstract

This report describes the mineral and chemical composition of immature,
arkosic sandstones of the Pennsylvanian Minturn and Pennsylvanian and
Permian Sangre de Cristo Formations, which were derived from the
Ancestral Rocky Mountains. Located in the Sangre de Cristo Range of
southern Colorado, the Minturn and Sangre de Cristo Formations contain
some of the most immature, sodic arkoses shed from the Ancestral Rocky
Mountains. The Minturn Formation was deposited as fan deltas in marine
and alluvial environments; the Sangre de Cristo Formation was deposited
as alluvial fans.

Arkoses of the Minturn and Sangre de Cristo Formations are matrix-rich
and thus may be properly considered arkosic wackes in the terminology of
Gilbert (Williams and others, 1954). In general, potassium feldspar and
plagioclase are subequal in abundance. Arkose of the Sangre de Cristo
Formation is consistently plagioclase-rich; arkose from the Minturn
Formation is more variable. Quartz and feldspar grains are accompanied
by a few percent rock fragments, consisting mostly of intermediate to
granitic plutonic rocks, gneiss, and schist. All of the rock fragments
seen in sandstone are present in interbedded conglomerate, consistent
with derivation from a Precambrian terrane of gneiss and plutonic rocks
much like that exposed in the present Sangre de Cristo Range.

Comparison of mineral and major oxide abundances reveals a strong
association of detrital quartz with SiO~2~, all other detrital minerals
(totaled) with Al~2~O~3~, potassium feldspar plus mica with K~2~O, and
plagioclase with Na~2~O. Thus, major oxide content is a good predictor
of detrital mineralogy, although contributions from matrix and cement
make these relationships less than perfect.

Detrital minerals and major oxides tend to form inverse relationships
that reflect mixtures of varying quantities of minerals; when one
mineral is abundant, the abundance of others declines by dilution. In
arkose of the Minturn and Sangre de Cristo Formations, the abundance of
quartz (and SiO~2~) is enhanced by weathering and transport, which
destroys feldspar and rock fragments. Weathering also preferentially
destroys plagioclase (and removes Na~2~O) over potassium feldspar. Thus,
as fresh sodic arkose detritus is weathered and transported in the
fluvial environment, it becomes potassic and quartz-rich. Stratigraphic
profiles of mineral and major oxide abundance reveal that weathering and
transport, including reworking by marine currents, was most effective in
reducing plagioclase and enhancing quartz content of arkosic sediment in
the Minturn Formation near Marble Mountain. In general, the quartz-poor,
sodic arkoses of the Sangre de Cristo Formation indicate little
weathering in the source area or during transport.

Iron-titanium oxides and other heavy minerals, notably zircon and
sphene, tend to be most abundant in the Sangre de Cristo Formation.
Although concentrated locally as fluvial placers, the overall abundance
of heavy minerals probably reflects lack of weathering and proximity to
source.

The degree of weathering and destruction of unstable grains (feldspar
and rock fragments) in the Minturn and Sangre de Cristo Formations of
the Sangre de Cristo Range was dependent on rates of uplift and erosion
as much as climate (wet versus dry). Reworking by marine currents
further reduced the proportion of unstable grains during Minturn time.
Sodic (plagioclase-rich), quartz-poor arkose in the coarse,
conglomeratic Sangre de Cristo Formation is the product of rapid uplift
and erosion.

# Introduction

The tectonic and climatic environment of the Ancestral Rocky Mountains
have long been of interest to geologists. The general paleogeography of
the Ancestral Rocky Mountains has been identified by regional
compilations (Mallory, 1972; McKee and others, 1975), which reveal a
group of ranges and lower emergent areas in the present region of
western Colorado, New Mexico, and part of Oklahoma, north of the coeval
Ouachita-Marathon fold belt. The highest, most tectonically active
ranges were bordered by alluvial fans and fan deltas that accumulated
coarse, arkosic detritus in the surrounding seas. Interpretations of
climate have relied in part on petrologic studies of the sediments
eroded from the Ancestral Rocky Mountains (e.g., Suttner and Dutta,
1986; Van de Kamp and Leake, 1994). The paleoclimate of the early
Ancestral Rockies is interpreted as humid in the Front Range of Colorado
and dry to the west, with dry climate prevailing throughout the region
by the end of the uplift of the Ancestral Rockies.

This report describes the chemical and mineral composition of sandstones
derived from one part of the Ancestral Rocky Mountains. The data
reported here are from sandstone samples collected from the
Pennsylvanian Minturn Formation (mixed marine-alluvial fan delta
deposits) and the Pennsylvanian and Permian Sangre de Cristo Formation
(alluvial fan deposits) in the northern Sangre de Cristo Range of
Colorado (Fig. 1). The samples were collected during stratigraphic and
sedimentologic studies of the Minturn and Sangre de Cristo Formations
(Lindsey, Clark, and Soulliere, 1986) and were first used to determine
background geochemical values for mineral resource appraisal of the
Sangre de Cristo Wilderness Study Area (Johnson and others, 1984) and
study of copper-uranium mineralized rocks (Lindsey and Clark, 1995).
Data on these samples fill a geographic gap for arkoses derived from the
Ancestral Rocky Mountains; they represent immature, arkosic sandstones
derived from the adjacent San Luis-Uncompahgre uplift of the Ancestral
Rocky Mountains (Lindsey, Clark, and Soulliere, 1986).

![](media/image3.pct){width="5.997222222222222in"
height="7.2444444444444445in"}

**Figure 1.**\--Generalized geologic map of study area in the Sangre de
Cristo Mountains, south-central Colorado (from Lindsey and Clark, 1995).
RAS, Rito Alto stock; TP, Thirsty Peak (section); NTC, North Taylor
Creek (section); EM, Eureka Mountain (section); CN, Crestone Needle; MM,
Marble Mountain (section).

Data sets on the chemical and mineralogical composition of arkosic
sandstone from other parts of the Ancestral Rocky Mountains have been
published and interpreted (Hubert, 1960; Suttner and Dutta, 1986;
Cullers and Stone, 1991; Van de Kamp and Leake, 1994). Van de Kamp and
Leake (1994) and Suttner and Dutta (1986) found regional differences
among arkoses, with the most feldspathic and plagioclase-rich (sodic)
arkoses present in the Pennsylvanian and Permian Cutler Formation and
the Minturn Formation of western and central Colorado, respectively. In
contrast, potassium feldspar-rich (potassic) arkoses dominate the
Fountain Formation of the Front Range (Van de Kamp and Leake, 1994) and
the Wet Mountains (Cullers and Stone, 1991). Van de Kamp and Leake
(1994) ascribe the regional variation in the composition of
Pennsylvanian and Permian arkoses to variable weathering before
deposition of Ancestral Rockies sediment. Detailed petrologic studies of
stratigraphic sections in the Cutler Formation and the Fountain
Formation show no temporal trend in relative abundance of quartz types,
feldspar, or rock fragments in the Cutler, but major enrichment of total
quartz and polycrystalline quartz in the lower part of the Fountain
Formation (Suttner and Dutta, 1986). Suttner and Dutta (1986)
interpreted variation in arkose composition as a climatic effect, with
humid climate during early uplift of the Front Range, dry climate during
late uplift of the Front Range, and dry climate throughout uplift of the
Uncompahgre highland (western Colorado). Climatic interpretations for
Pennsylvanian and Permian time are supported by the distribution of
humid-climate plant fossils and coals and by arid-climate paleosols
(Suttner and Dutta, 1986).

Although climate can be interpreted from petrology in carefully
controlled cases (Suttner and Dutta, 1986), the link between
pre-depositional weathering and climate is not simple. The degree of
weathering before deposition depends upon the rate of uplift, erosion,
and transport to the ultimate site of deposition (Devaney and Ingersoll,
1993). Rapid uplift and erosion of source areas produces arkose that
resembles the composition of its source. Slow uplift of source areas
allows other factors such as climate and depositional environment to
influence arkose composition. Rapid uplift and erosion followed by
burial should produce immature sediment, even in humid climates.

The Minturn and Sangre de Cristo Formations of the Sangre de Cristo
Range are not ideal for petrologic interpretation of paleoclimate from
arkose composition. Two processes, reworking on marine shelves and
alteration after deposition, may have affected arkose composition.

Much of the Minturn Formation of the Sangre de Cristo Range was
deposited along a fan-delta coast ((Lindsey, Clark, and Soulliere,
1986). Effects of reworking on the maturity of arkosic detritus on
fan-deltas can be complex. Feldspar and rock fragments are exposed to
destruction when fluvial sediment is discharged onto marine shelves.
Quartz grains are likely to be reduced to single crystals and rounded in
shallow seas. Falling sea level can re-entrain reworked marine sand as
fluvial sand. In contrast, turbidite fans offshore from deltas can allow
fluvial sand to bypass marine shelves, and thus avoid reworking.
Although it is desirable to limit samples for petrologic studies of
paleoclimate to fluvial sands (Suttner and Dutta, 1986), such control of
sampling was not possible in the mixed marine-fluvial depositional
environment of the Minturn Formation. Complex depositional histories of
individual sandstone beds can not be recognized from field study alone
and, thus, sampling populations can not be restricted with confidence.

Much of Minturn and Sangre de Cristo Formations of the Sangre de Cristo
Range has been affected by weak to moderate greenschist metamorphism at
\~200°-300°C (Lindsey, Andriessen, and Wardlaw, 1986). The effects of
metamorphism in the range are similar to those expected from burial
diagenesis, in that unstable rock fragments and feldspar, especially
plagioclase, were altered to chlorite and sericite. Burial under
Laramide thrust plates and high heat flow during later Rio Grande
rifting promoted mineral alteration. Contact metamorphism was limited to
the vicinity of the Oligocene Rito Alto stock, which includes the
sampled section near Thirsty Peak. Some areas along the east side of the
range, including the sampled section near Marble Mountain, escaped the
most intense heat; conodonts there have low alteration indices,
indicating temperatures of \<70°C. Thus, much of the data reported here
are not readily amenable to paleoclimate interpretation. Interpretations
of paleoclimate from arkose composition assume that chemical and
mineralogical variation is pre-depositional in origin and not the result
of diagenesis (or metamorphism) (Velbel and Saad, 1991).

Although petrologic data on arkose from the Sangre de Cristo Range
appear to have little value for paleoclimatic interpretation, the data
are useful for understanding other processes that affect arkose
formation. The preliminary interpretations explored here, and the
methods used to arrive at interpretation, are the focus of this report.
This report is part of the author\'s investigation of the chemical
composition of sandstone, with emphasis on statistical analyses of
existing data (for another example, see Lindsey, 1999).

# Sampling and methods

Arkosic sandstones from four measured sections at Marble Mountain (Fig.
2), Eureka Mountain (Figs. 3 and 4), Thirsty Peak (Fig. 5), and North
Taylor Creek (Fig. 6) were collected for petrographic and chemical
analysis. Measured sections at Marble Mountain and Eureka Mountain are
composites of several sections connected by tracing beds along strike.
The section at Eureka Mountain extends from the east side of the range
west to the head of Groundhog basin; it forms the basis for descriptions
of reference sections for the Minturn and Sangre de Cristo Formations in
this part of Colorado (Lindsey and Schaefer, 1984; Lindsey and others,
1985). The other sections are unpublished, but are available for
inspection at U. S. Geological Survey field-record archives at the
Federal Center, Lakewood, Colo. The section at Marble Mountain is
believed to represent a nearly complete interval of the Minturn
Formation; only the lowermost part of the Sangre de Cristo Formation
(near Crestone Needle) was studied. The section east of Thirsty Peak is
within 2 kilometers of the mineralized (molybdenum) Rito Alto stock.
Some rocks of the Thirsty Peak section show obvious evidence of contact
metamorphism and mineralization, including recrystallized limestone and
epidote-rich nodules, metamorphic biotite, and anomalous concentrations
of trace metals. The section on North Taylor Creek represents about 400
m of Sangre de Cristo Formation of uncertain stratigraphic position, but
probably located at least 1000 m above the base.

The Marble Mountain and Eureka Mountain sections are located in separate
thrusted blocks, whereas the Thirsty Peak and North Fork Taylor Creek
sections are located in autochthonous terrane. The autochthonous terrane
has been folded and faulted, but is not believed to have been thrusted.
The Marble Mountain and Eureka Mountain sections are located in the
Marble Mountain and Spread Eagle Peak thrust plates (or blocks) that are
believed to have been transported a significant distance laterally.
Thus, stratigraphic sections of Minturn and Sangre de Cristo Formations
differ radically from one thrust block to another and from the
autochthonous terrane east of the thrusts.

A total of 50 samples were collected for analysis. All are sandstones
except two, which consisted of the sandy matrix of diamictite beds from
the Sangre de Cristo Formation. Detrital grains range in size from
coarse sand to granules. All samples are single hand specimens weighing
about 200-300 g and were collected from outcrops. All samples were
analyzed for major oxides, loss on ignition (LOI), and the trace
elements Cu, Mo, Pb, Th, U, and Zn. In addition, semi-quantitative
analyses of numerous other trace elements were made. Mineral abundance
was determined from thin sections of all but five samples\--one from the
Thirsty Peak section and four from the North Taylor Creek section.

All samples were analyzed for major oxides by wavelength dispersive
X-ray fluorescence spectrometry (Taggart and others, 1987). The trace
elements Cu, Mo, Pb, and Zn were analyzed by inductively coupled
plasma-atomic absorption emission spectroscopy (Lichte and others,
1987). Thorium and uranium were determined by the delayed-neutron method
(McKown and Millard, 1987). All other trace elements were determined by
the six-step semi-quantitative spectrographic method (Golightly and
others, 1987). Semi-quantitative values are reported in six logarithmic
classes per decimal place in the series 1, 1.5, 2, 3, 5, 7, 10, etc.
Estimates of mineral abundance among grains and cement were made by
counting 300 points in thin sections. Thin sections were cut from the
same hand specimens as those used for chemical analysis, prior to
grinding for chemical analysis. All grains larger than 0.03 mm were
identified; the rest were classified as matrix. Rock fragments were
identified and tallied as such, not by the mineral encountered at points
on the counting traverse. Potassium feldspar was identified by
cobaltinitrite stain. For the most part, identification of plagioclase
grains could be confirmed by polysynthetic twinning and alteration. In a
few cases, the alteration of feldspars was too severe to permit separate
identification of potassium feldspar and plagioclase.

Chemical and mineralogical data, with values below limits of detection
already replaced, is given in Tables 1 and 2. Lower limits of detection
were encountered during semi-quantitative analyses for a few trace
elements; for graphing and statistical analysis, these were replaced by
arbitrary values. Detection limits and replacement values are included
in the caption of Table 1.

**Table 1.**\--Chemical composition (major oxides, loss on ignition, and
trace elements) of sandstones, Minturn and Sangre de Cristo Formations.
Stratigraphic level given in meters (m) above (+) or below (-) the
Minturn-Sangre de Cristo contact. Major oxides determined by wavelength
dispersive X-ray fluorescence spectrometry by J. S. Mee and D. F. Siems;
loss on ignition (LOI) by heating to 900°C by Mee and Siems; trace
elements Cu, Mo, Pb, and Zn by inductively-coupled plasma-atomic
absorption emission spectroscopy by J. M. Motooka; thorium and uranium
by the delayed-neutron method by R. J. Knight; and all other trace
elements by the six-step semi-quantitative spectrographic method by E.
F. Cooley. The lower limit of detection was encountered for Co (5 ppm),
Mo (.05 ppm), and Sr (100 ppm) for a few samples; such \"less than\"
values were replaced with 3, .05, and 70, respectively. Fe~T~O~3~, total
iron as Fe~2~O~3~; LOI, loss on ignition. Blank values (\--), not
determined.

  --------- --------- --------------- ------------- ------- ----------------
  Sample    Lab. No.  Section         Formation     Color   Stratigraphic
  No.                                                       Level (m)

  7A        EKS440    Marble Mountain Sangre de     Red     115
                                      Cristo                

  8B        EKS441    Marble Mountain Minturn       Gray    -400

  8C        EKS442    Marble Mountain Minturn       Red     -499

  8E        EKS443    Marble Mountain Minturn       Red     -724

  8F        EKS444    Marble Mountain Minturn       Gray    -772

  8G        EKS445    Marble Mountain Minturn       Gray    -826

  8I        EKS446    Marble Mountain Minturn       Gray    -952

  8J        EKS447    Marble Mountain Minturn       Gray    -1018

  8K        EKS448    Marble Mountain Minturn       Gray    -1102

  8N        EKS449    Marble Mountain Minturn       Gray    -1164

  8O        EKS450    Marble Mountain Minturn       Gray    -1174

  8R        EKS451    Marble Mountain Minturn       Gray    -1261

  12B       EKS452    Thirsty Peak    Minturn       Red     -402

  12D       EKS453    Thirsty Peak    Minturn       Red     -267

  12H       EKS454    Thirsty Peak    Minturn       Red     -132

  12L       EKS456    Thirsty Peak    Sangre de     Red     30
                                      Cristo                

  12M       EKS457    Thirsty Peak    Sangre de     Red     264
                                      Cristo                

  12N       EKS458    Thirsty Peak    Sangre de     Red     390
                                      Cristo                

  12O       EKS459    Thirsty Peak    Sangre de     Red     594
                                      Cristo                

  12P       EKS460    Thirsty Peak    Sangre de     Gray    651
                                      Cristo                

  21A       EKS461    Eureka Mountain Sangre de     Red     425
                                      Cristo                

  21B       EKS462    Eureka Mountain Sangre de     Red     583
                                      Cristo                

  21C       EKS463    Eureka Mountain Sangre de     Red     671
                                      Cristo                

  21D       EKS464    Eureka Mountain Sangre de     Red     855
                                      Cristo                

  21G       EKS466    Eureka Mountain Sangre de     Red     1611
                                      Cristo                

  31G       EKS467    Marble Mountain Minturn       Gray    -1181

  31J       EKS469    Marble Mountain Minturn       Gray    -1049

  31M       EKS416    Marble Mountain Minturn       Gray    -665

  125A      EKS417    Eureka Mountain Minturn       Gray    -1950

  125B      EKS418    Eureka Mountain Minturn       Gray    -1824

  125C      EKS419    Eureka Mountain Minturn       Gray    -1733

  125D      EKS420    Eureka Mountain Minturn       Gray    -1578

  125F      EKS421    Eureka Mountain Minturn       Gray    -1093

  126A      EKS422    Eureka Mountain Minturn       Gray    -787

  126B      EKS423    Eureka Mountain Minturn       Gray    -627

  126C      EKS424    Eureka Mountain Minturn       Gray    -486

  127A      EKS425    Eureka Mountain Minturn       Red     -335

  127B      EKS426    Eureka Mountain Minturn       Gray    -248

  127D      EKS427    Eureka Mountain Minturn       Red     -107

  127G      EKS428    Eureka Mountain Sangre de     Red     122
                                      Cristo                

  127H      EKS429    Eureka Mountain Sangre de     Red     254
                                      Cristo                

  129D      EKS430    Eureka Mountain Minturn       Gray    -85

  129J      EKS432    Eureka Mountain Minturn       Gray    -45

  129K      EKS433    Eureka Mountain Minturn       Red     -40

  129M      EKS434    Eureka Mountain Minturn       Gray    -15

  129O      EKS435    Eureka Mountain Sangre de     Red     15
                                      Cristo                

  9A        EKS436    North Taylor    Sangre de     Red     \--
                      Creek           Cristo                

  9B        EKS437    North Taylor    Sangre de     Red     \--
                      Creek           Cristo                

  9C        EKS438    North Taylor    Sangre de     Red     \--
                      Creek           Cristo                

  9D        EKS439    North Taylor    Sangre de     Red     \--
                      Creek           Cristo                
  --------- --------- --------------- ------------- ------- ----------------

  -------- --------- ------- ------- ------ ------ ------ ------ ------ ------- ------
  Sample   SiO2      Al2O3   FeTO3   MgO    CaO    Na2O   K2O    TiO2   P2O5    MnO
  No.                                                                           

           Weight                                                               
           Percent                                                              
           (Pct)                                                                

  7A       59.2      15.40   7.33    4.53   3.71   2.66   3.00   0.56   0.180   0.19

  8B       65.9      14.90   3.38    3.85   1.75   3.14   2.50   0.40   0.140   0.07

  8C       64.0      14.80   6.22    3.69   0.51   3.29   3.55   0.51   0.150   0.07

  8E       69.4      13.60   4.22    2.59   0.66   3.58   3.03   0.39   0.160   0.05

  8F       65.8      14.30   4.34    2.99   1.58   3.47   3.13   0.51   0.240   0.12

  8G       64.6      14.90   5.49    3.72   0.74   3.33   2.76   0.67   0.260   0.05

  8I       70.9      11.70   4.90    2.73   0.55   1.70   2.68   0.57   0.110   0.04

  8J       80.1      9.35    1.91    1.41   0.08   0.58   4.45   0.18   0.050   0.02

  8K       71.8      12.00   4.89    2.68   0.14   1.56   3.63   0.54   0.090   0.03

  8N       76.5      11.10   3.41    1.90   0.10   0.93   3.18   0.34   0.070   0.03

  8O       66.4      13.20   6.54    4.03   0.50   1.39   2.99   0.85   0.120   0.05

  8R       74.4      12.00   3.36    1.61   0.25   1.73   3.30   0.35   0.100   0.06

  12B      69.3      13.70   4.27    2.64   1.08   4.35   2.15   0.36   0.130   0.03

  12D      65.0      14.90   4.22    3.29   2.97   4.46   2.62   0.43   0.140   0.05

  12H      67.6      14.20   4.62    3.13   1.83   4.01   1.47   0.57   0.170   0.06

  12L      67.9      13.90   2.94    1.85   3.39   3.62   3.06   0.41   0.160   0.14

  12M      68.6      13.60   4.52    1.94   2.07   3.44   3.10   0.53   0.150   0.08

  12N      64.6      13.50   4.01    1.82   6.50   4.43   2.67   0.64   0.200   0.18

  12O      63.7      13.40   7.75    1.58   1.90   3.49   4.13   1.30   0.200   0.12

  12P      69.9      13.80   4.01    1.88   1.08   4.11   2.95   0.46   0.130   0.12

  21A      66.6      14.10   5.47    2.81   0.75   3.16   3.11   0.51   0.150   0.15

  21B      67.6      14.20   5.60    1.39   0.38   4.27   3.53   0.62   0.160   0.09

  21C      64.1      14.00   6.29    2.00   2.38   3.04   3.55   0.74   0.160   0.14

  21D      64.0      14.00   7.50    1.81   1.18   3.10   3.90   0.88   0.270   0.09

  21G      72.1      13.30   3.35    0.27   1.07   3.98   4.15   0.31   0.110   0.06

  31G      74.8      10.70   3.63    1.67   0.28   1.51   3.79   0.48   0.090   0.09

  31J      74.3      11.10   3.21    2.20   0.33   1.04   4.70   0.28   0.090   0.05

  31M      68.0      13.60   3.42    2.29   1.35   3.14   4.09   0.33   0.150   0.08

  125A     66.2      13.70   6.22    3.85   0.37   2.56   3.34   0.64   0.150   0.04

  125B     62.9      14.70   6.52    3.82   0.70   3.06   3.15   0.80   0.280   0.04

  125C     72.8      11.60   4.22    2.09   0.36   2.02   3.49   0.42   0.080   0.04

  125D     67.2      12.70   6.10    3.41   0.67   2.38   2.37   0.96   0.320   0.03

  125F     68.3      12.10   5.87    3.37   0.72   2.00   2.73   0.98   0.280   0.05

  126A     62.6      14.40   5.09    3.43   1.81   3.35   3.43   0.65   0.190   0.06

  126B     65.2      15.40   5.98    3.11   0.46   2.28   3.52   0.63   0.230   0.07

  126C     65.4      15.20   4.79    2.87   0.96   2.95   3.28   0.75   0.250   0.09

  127A     63.3      16.20   5.41    3.37   0.50   2.37   4.49   0.64   0.220   0.09

  127B     67.6      14.00   5.67    2.96   0.44   3.18   2.42   0.47   0.160   0.14

  127D     62.0      15.50   6.69    3.61   0.98   3.31   3.41   1.06   0.510   0.13

  127G     67.3      13.10   5.20    2.72   1.60   2.78   2.87   0.64   0.170   0.14

  127H     69.4      13.60   4.08    1.89   1.02   3.02   3.15   0.56   0.170   0.10

  129D     64.7      13.80   7.95    2.74   0.57   2.81   3.43   0.82   0.190   0.10

  129J     69.1      13.60   4.03    2.71   0.48   2.49   3.61   0.48   0.140   0.11

  129K     68.6      12.40   4.54    2.98   1.44   1.84   3.85   0.41   0.120   0.12

  129M     62.0      15.30   6.65    4.64   0.53   2.40   3.16   0.75   0.260   0.15

  129O     64.0      13.20   7.31    2.52   1.97   2.25   3.41   0.74   0.190   0.22

  9A       62.9      12.20   2.85    1.25   6.95   3.46   2.97   0.52   0.140   0.12

  9B       69.9      13.40   3.43    1.40   1.30   4.06   3.28   0.41   0.120   0.12

  9C       64.4      15.00   4.83    2.21   1.85   3.40   4.30   0.59   0.200   0.08

  9D       67.0      14.20   5.17    2.57   0.53   3.76   3.25   0.65   0.200   0.08
  -------- --------- ------- ------- ------ ------ ------ ------ ------ ------- ------

  -------- ------ --------- ------ ------ ------ ------ ------ ------ ------ ------
  Sample   LOI    B         Ba     Be     Co     Cr     Cu     La     Mo     Ni
  No.                                                                        

           Pct    Parts per                                                  
                  million                                                    
                  (ppm)                                                      

  7A       2.71   700       500    10.0   50     300    4.3    50     0.07   50

  8B       3.71   200       700    2.0    20     100    4.5    50     0.11   30

  8C       2.48   100       1000   2.0    20     150    3.1    50     0.16   30

  8E       1.85   100       1000   1.5    15     50     18.0   50     0.10   20

  8F       2.70   100       1000   1.5    20     100    27.0   50     0.48   30

  8G       2.93   100       1000   1.5    15     100    7.2    200    0.05   30

  8I       2.82   100       5000   1.5    10     100    0.4    70     0.05   20

  8J       1.56   100       2000   1.5    3      30     0.5    50     0.05   10

  8K       2.31   100       1000   1.5    10     70     1.9    50     0.18   30

  8N       2.38   100       1000   1.5    15     50     5.7    50     0.68   20

  8O       3.52   150       1000   1.5    15     150    13.0   50     0.07   20

  8R       2.36   100       1500   1.5    10     50     6.6    50     0.25   20

  12B      1.24   20        1000   5.0    20     70     21.0   50     3.20   30

  12D      1.03   30        1000   2.0    15     100    5.5    50     1.50   30

  12H      1.90   50        700    2.0    10     50     2.2    70     0.24   20

  12L      1.99   50        2000   2.0    10     100    7.1    70     0.20   20

  12M      1.63   50        1500   2.0    15     150    3.0    70     0.17   20

  12N      0.91   20        1000   2.0    15     150    19.0   70     0.18   15

  12O      1.25   20        1500   2.0    15     100    27.0   200    0.43   10

  12P      0.99   20        1000   2.0    15     100    2.5    50     0.15   20

  21A      2.67   100       1000   2.0    20     100    8.6    50     0.14   20

  21B      1.64   10        1000   2.0    10     20     10.0   50     0.24   10

  21C      2.77   20        1500   2.0    20     70     13.0   70     0.17   20

  21D      2.64   20        1500   2.0    20     50     7.0    70     0.21   20

  21G      0.75   10        1000   3.0    5      7      7.1    200    0.20   5

  31G      2.46   50        1000   2.0    10     150    2.1    50     0.09   20

  31J      2.44   50        1500   1.5    5      50     2.1    50     0.05   20

  31M      2.54   30        2000   15.0   15     20     15.0   50     0.10   20

  125A     2.61   100       500    2.0    15     70     4.6    50     0.05   20

  125B     3.18   50        500    2.0    20     150    34.0   50     0.13   50

  125C     2.25   50        700    1.5    15     50     3.1    50     0.05   20

  125D     3.31   100       500    1.5    15     100    3.6    30     0.15   20

  125F     2.97   100       300    2.0    5      100    5.2    30     0.13   20

  126A     3.18   100       1000   1.5    20     100    6.5    50     0.10   20

  126B     2.76   200       700    2.0    10     70     1.9    50     0.07   20

  126C     2.72   100       700    1.5    10     50     7.4    50     0.11   20

  127A     2.87   150       1000   2.0    10     50     2.5    70     0.25   20

  127B     2.56   100       1000   2.0    10     70     4.2    50     0.05   20

  127D     2.66   70        700    2.0    15     30     9.8    50     0.41   20

  127G     3.06   50        500    2.0    15     50     24.0   50     0.22   20

  127H     2.37   100       700    2.0    10     30     6.6    50     0.15   10

  129D     2.60   100       700    2.0    15     100    4.2    50     0.12   20

  129J     2.52   100       700    2.0    15     50     5.8    30     0.13   20

  129K     3.11   50        700    3.0    10     70     0.8    70     0.09   20

  129M     3.61   70        1500   3.0    15     150    1.1    70     0.09   30

  129O     3.74   150       700    2.0    15     70     8.4    50     0.56   20

  9A       6.07   30        700    2.0    5      50     8.2    50     0.12   10

  9B       1.89   50        1000   2.0    10     30     7.8    50     0.13   10

  9C       2.91   70        1000   2.0    10     30     4.6    70     0.15   15

  9D       2.13   100       1000   2.0    20     50     7.6    50     0.17   30
  -------- ------ --------- ------ ------ ------ ------ ------ ------ ------ ------

  ---------- --------- ------ ------ ------- ------- ------ ------ ------ ------
  Sample No. Pb        Sc     Sr     Th      U       V      Y      Zn     Zr

             Parts per                                                    
             million                                                      
             (ppm)                                                        

  7A         5         30     500    7.04    5.10    200    50     49     100

  8B         3         20     100    5.73    2.63    100    30     39     150

  8C         4         20     100    10.40   3.96    200    300    55     300

  8E         1         20     300    4.84    1.32    100    50     42     150

  8F         21        20     300    6.79    4.07    100    50     46     300

  8G         2         20     200    10.60   3.55    100    50     42     300

  8I         1         20     300    6.99    1.73    150    50     31     300

  8J         1         7      100    4.85    0.83    100    10     13     100

  8K         3         20     100    7.42    3.06    100    20     40     500

  8N         9         15     70     4.80    2.54    100    20     29     200

  8O         3         30     70     10.90   4.81    150    50     52     500

  8R         8         20     100    3.80    1.84    100    20     120    150

  12B        2         20     200    4.58    1.89    150    70     12     200

  12D        3         20     300    3.50    1.60    100    50     10     200

  12H        3         20     300    7.85    2.51    100    50     37     150

  12L        3         20     500    4.00    2.52    100    50     39     200

  12M        4         20     300    7.78    2.16    150    70     37     200

  12N        20        30     300    7.51    2.27    150    70     19     200

  12O        3         30     200    \--     5.75    150    100    55     1000

  12P        3         20     200    7.35    2.13    100    50     64     150

  21A        4         20     200    6.54    2.34    100    50     76     200

  21B        7         20     100    11.20   2.94    50     50     54     300

  21C        5         30     300    9.83    2.80    200    70     65     200

  21D        10        20     300    4.20    3.51    100    50     82     200

  21G        5         10     100    8.35    2.05    50     70     37     300

  31G        6         10     70     6.45    2.57    100    50     74     500

  31J        1         10     100    5.20    1.34    100    10     29     100

  31M        15        10     300    5.79    3.42    70     20     38     50

  125A       19        15     100    7.13    1.98    70     30     92     200

  125B       12        20     100    15.60   3.25    100    30     76     500

  125C       6         10     100    6.99    1.20    70     20     42     200

  125D       8         20     70     10.90   2.68    100    20     55     500

  125F       9         20     70     \--     \--     100    20     26     300

  126A       13        20     200    5.81    1.77    100    20     40     150

  126B       2         20     100    9.30    2.56    100    30     39     200

  126C       5         20     200    8.18    1.77    70     30     29     200

  127A       3         20     200    \--     7.85    100    50     66     200

  127B       3         20     200    7.60    2.57    100    20     72     200

  127D       5         20     150    7.56    3.30    100    30     100    300

  127G       6         20     100    8.55    2.85    100    50     92     200

  127H       7         15     150    7.52    2.76    100    30     53     200

  129D       5         20     100    9.80    3.23    100    20     56     200

  129J       3         15     70     6.66    2.82    100    20     65     100

  129K       4         15     70     8.35    4.57    100    70     110    200

  129M       2         20     100    9.15    4.79    100    50     130    200

  129O       7         20     100    10.00   3.97    100    50     55     100

  9A         6         10     200    4.52    2.16    50     30     59     200

  9B         3         10     200    4.40    1.45    100    30     70     150

  9C         4         15     200    6.05    2.48    100    50     75     300

  9D         4         20     150    7.47    1.95    100    20     90     300
  ---------- --------- ------ ------ ------- ------- ------ ------ ------ ------

**Table 2.**\--Mineral composition of sandstones, Minturn and Sangre de
Cristo Formations. Q, quartz; K, potassium feldspar; P, plagioclase; TF,
total feldspar; FM, fresh mica; AM, altered mica; C, carbonate cement;
HM, heavy minerals, RF, rock fragments; M, matrix \< 0.03 mm. Determined
by polarizing microscope, 300 points per thin section, by R. E.
Phillips. Blank (\--) values for feldspar varieties, too altered to
identify variety with confidence. Blank rows (\--, for samples 12B, 9A,
9B, 9C, and 9D), not analyzed.

  ---------- --------- ------ ------ ------ ------ ------ ------ ------ ------ ------
  Sample No. Q         K      P      TF     FM     AM     C      HM     RF     M

             Volume                                                            
             Percent                                                           

  7A         16        7      17     24     0      2      0      6      18     33

  8B         34        \--    \--    34     1      4      5      0      0      23

  8C         31        17     28     45     1      10     0      2      0      13

  8E         30        14     36     50     0      6      1      0      0      14

  8F         27        12     27     39     5      3      8      1      0      16

  8G         31        9      27     36     11     2      0      1      0      19

  8I         41        1      17     18     2      3      2      2      0      32

  8J         50        29     6      35     2      0      0      1      0      13

  8K         43        \--    \--    34     4      3      0      0      0      17

  8N         45        \--    \--    24     2      1      0      1      0      27

  8O         41        \--    \--    23     4      3      2      1      0      25

  8R         47        16     11     27     2      0      2      1      2      18

  12B        \--       \--    \--    \--    \--    \--    \--    \--    \--    \--

  12D        22        14     23     38     1      0      0      0      0      41

  12H        32        \--    \--    33     0      0      0      0      0      35

  12L        27        \--    \--    14     0      0      6      0      0      52

  12M        34        18     28     46     0      1      0      2      0      18

  12N        13        12     34     46     0      0      0      1      0      41

  12O        27        38     9      47     0      0      1      7      0      18

  12P        37        14     29     43     0      0      0      2      0      17

  21A        35        12     23     35     1      5      3      3      1      18

  21B        16        32     15     47     0      1      0      2      6      28

  21C        28        13     26     39     1      3      4      3      2      20

  21D        27        20     26     46     0      2      1      6      0      17

  21G        23        \--    \--    19     1      1      0      28     0      28

  31G        54        21     10     31     3      0      0      1      0      12

  31J        47        29     9      38     5      1      0      0      0      8

  31M        30        29     25     55     3      1      4      1      1      7

  125A       47        19     11     30     8      1      0      0      2      12

  125B       41        23     18     41     1      1      3      0      2      10

  125C       44        20     16     36     5      0      0      0      0      15

  125D       44        16     15     31     3      1      1      1      1      18

  125F       42        21     16     37     3      1      0      1      0      16

  126A       33        16     28     44     2      1      4      1      3      12

  126B       35        11     20     31     17     0      0      0      0      17

  126C       36        14     24     38     12     1      1      0      1      11

  127A       31        18     21     39     16     2      0      1      2      8

  127B       41        7      30     37     10     1      0      1      0      10

  127D       30        6      32     38     4      10     0      4      0      14

  127G       47        7      18     25     2      5      2      2      0      19

  127H       36        6      35     41     3      4      2      1      0      13

  129D       33        16     29     45     4      3      0      3      1      11

  129J       39        12     25     37     5      2      0      2      0      15

  129K       46        8      26     34     2      5      2      1      0      10

  129M       36        4      19     23     12     1      0      1      1      26

  129O       34        8      21     29     12     6      2      1      0      15

  9A         \--       \--    \--    \--    \--    \--    \--    \--    \--    \--

  9B         \--       \--    \--    \--    \--    \--    \--    \--    \--    \--

  9C         \--       \--    \--    \--    \--    \--    \--    \--    \--    \--

  9D         \--       \--    \--    \--    \--    \--    \--    \--    \--    \--
  ---------- --------- ------ ------ ------ ------ ------ ------ ------ ------ ------

![](media/image4.png){width="5.999305555555556in"
height="3.884027777777778in"}

**Figure 2.**\--Topographic and geologic map of sampled stratigraphic
section of Minturn and lowermost Sangre de Cristo Formations at Marble
Mountain (geology from Lindsey, Johnson, and others, 1986). Red dot,
sample location and number; green line, measured section; Qrf,
Quaternary rockfall deposits; Qpt, Pinedale till; PlPsc, Permian and
Pennsylvanian Sangre de Cristo Formation, Crestone Conglomerate Member;
PlPsu, Sangre de Cristo Formation, undivided; lPm, Pennsylvanian Minturn
Formation; cls, crinoidal limestone; bls, biohermal limestone; Xm,
Proterozoic X mafic igneous rock; Xqm, quartz monzonite; and Xgn,
gneiss.

![](media/image5.png){width="5.99375in" height="6.226388888888889in"}

**Figure 3.**\--Topographic and geologic map of sampled stratigraphic
section of Minturn Formation at Eureka Mountain (from Lindsey, Clark,
and Soulliere, 1985). Red dot, sample location and number; green line,
measured section; Qrf, Quaternary rockfall deposits; Qrg, rock glacier;
Tf, felsite dikes and sills; PlPsl, Permian and Pennsylvanian Sangre de
Cristo Formation, lower member; PlPsu, Sangre de Cristo Formation,
undivided; lPmu, Pennsylvanian Minturn Formation, upper part; lPml,
Pennsylvanian Minturn Formation, lower part.

![](media/image6.png){width="5.997916666666667in"
height="5.902777777777778in"}

**Figure 4.**\--Topographic and geologic map of sampled stratigraphic
section of Sangre de Cristo Formation at Eureka Mountain (from Lindsey
and Schaefer, 1984). Red dot, sample location and number; green line,
measured section; Qrf, Quaternary rockfall deposits; Qpt, Pinedale till;
Tf, felsite dikes and sills; PlPsc, Permian and Pennsylvanian Sangre de
Cristo Formation, Crestone Conglomerate Member; PlPsl, Sangre de Cristo
Formation, lower part; lPmu, Pennsylvanian Minturn Formation, upper
part; mls, marker limestone.

![](media/image7.png){width="5.999305555555556in"
height="8.152083333333334in"}

# 

**Figure 5.**\--Topographic and geologic map of sampled stratigraphic
section of upper Minturn and lower Sangre de Cristo Formation at Thirsty
Peak (geology from Lindsey, Soulliere, and Hafner, 1985). Red dot,
sample location and number; green line, measured section; Qrf,
Quaternary rockfall deposits; Qrg, rock glacier; Qpt, till of Pinedale
age; Tf, felsite dikes and sills; Trag, Oligocene granite of Rito Alto
Peak; Trat, Oligocene tonalite of Rito Alto Peak; PlPsu, Sangre de
Cristo Formation, undivided; lPm, Pennsylvanian Minturn Formation; mnls,
limestone of Mt. Neidhardt.

![](media/image8.png){width="5.9944444444444445in"
height="3.9659722222222222in"}

**Figure 6.**\--Topographic and geologic map of sampled stratigraphic
section of Sangre de Cristo Formation at North Taylor Creek (geology
from Lindsey, Scott, Soulliere, and DeAngelis, 1984; and Lindsey,
Soulliere, Hafner, and Flores, 1985). Red dot, sample location and
number; green line, measured section; Qrf, Quaternary rockfall deposits;
Qpt, till of Pinedale age; Qbt2, young till of Bull Lake age; Tf,
felsite dikes and sills; PlPsu, Sangre de Cristo Formation, undivided;
lPml, Pennsylvanian Minturn Formation, lower part; Xgn, Proterozoic X
gneiss.

# Petrography and classification

Sandstones of the Minturn and Sangre de Cristo Formations are arkosic.
Among sand-size detrital grains, rock fragments compose only a minor
part of the total; quartz-feldspar ratios vary from 30:80 to 80:30\--all
in the arkose range (Fig. 7A). On quartz-feldspar-lithic fragment
(Q-F-L) diagrams, these rocks plot in the field of continental tectonic
blocks of Dickinson (1985). Arkoses of the Minturn and Sangre de Cristo
Formations typically contain more than 10 volume percent (Fig. 7B)
matrix (defined as all grains \<0.03 mm) and ,thus, may be properly
considered arkosic wackes in the terminology of Gilbert (Williams and
others, 1954). A few percent calcite cement is common.

![](media/image9.pct){width="5.763888888888889in"
height="6.333333333333333in"}

**Figure 7.**\--Triangular diagrams showing petrographic classification
of sandstones from the Minturn and Sangre de Cristo Formations: A)
Q-F-L, quartz-feldspar-lithic fragments (terminology of McBride, 1963),
B) G-C-M, detrital grains-calcite cement-matrix (\<0.03 mm), and C)
Q-K-P, quartz-potassium feldspar-plagioclase.

Although their ratio varies somewhat, in general potassium feldspar
(including microcline) and plagioclase are subequal in abundance (Figs.
7C and 8). Arkose of the Sangre de Cristo Formation is consistently
plagioclase-rich; arkose from the Minturn Formation is more variable.
Potassium feldspar is fresh to variably altered, but plagioclase
exhibits dusty-looking alteration in nearly all thin sections examined
(Fig. 8). Detrital mica (as much as 18 volume percent, much of it
biotite) and minor amounts of heavy minerals, including oxidized
magnetite, sphene, zircon, and apatite, are also present. Most detrital
grains are angular, but subround to round quartz grains occur in the
Minturn and, rarely, in the lower part of the Sangre de Cristo Formation
(Figs. 8A-C). The composition and texture of detrital grains is
consistent with first-cycle derivation from the plutonic and gneissic
rocks that make up the Precambrian terrane of the region.

In thin sections of sandstone, coarse sand- and granule-size rock
fragments include both simple and compound monocrystalline quartz grains
and polycrystalline quartz (Fig. 9), intermediate-composition to
granitic plutonic rocks (Fig. 10) and, less commonly, gneiss, schist
(Fig. 10B), and sandstone. Most quartz, including simple monocrystaline
grains, exhibits undulose extinction (Fig. 9A). Compound monocrystalline
quartz (polygonized quartz of Young, 1976), composed of discrete
segments of undulose quartz, is common in coarse sandstone of the
Minturn Formation at Marble Mountain (Fig. 9C). Some compound quartz
grains contain deformation bands and small primary quartz crystals along
segment boundaries. Polycrystalline quartz is less common than
monocrystalline quartz in the Minturn Formation. Polycrystalline quartz
is composed of elongate quartz grains with sutured boundaries, numerous
small primary quartz crystals and, commonly, small amounts of mica. It
closely resembles polycrystalline quartz of medium metamorphic grade
described by Young (1976). A few grains contain abundant mica (quartz
mica schist fragment of Fig. 10B). The presence of mica indicates that
polycrystalline quartz grains were derived from metamorphic rocks, such
as gneiss, schist, and quartzite. Finally, a few quartz grains show
cockscomb structure indicative of derivation from quartz veinlets.

In outcrop, conglomerate beds contain clasts of all of the rock types
noted in thin sections of sandstones. Gneiss and intermediate to
granitic plutonic rocks are the most abundant rock types in the
Precambrian terrane of the Sangre de Cristo Range; pegmatite dikes,
mafic sills and dikes, and quartz veins are common in gneiss, and a thin
layer of metaquartzite crops out southeast of Marble Mountain (Lindsey,
Johnson, and others, 1986). Mafic sills and dikes cut the Precambrian
terrane, and orthoquartzite, sandstone, and limestone of Cambrian
through Devonian age also underlie the Minturn and Sangre de Cristo
Formations. Clasts of all of these rocks are seen locally in the Minturn
and Sangre de Cristo Formations. Quartz granules and pebbles are
abundant in the redbed facies of the lower Minturn Formation exposed
along the west side of the Sangre de Cristo Range. Otherwise, plutonic
rocks and gneiss are the dominant rock types in conglomerate beds of the
Minturn and Sangre de Cristo Formations.

The question of whether simple and compound undulose quartz predates
deposition of the Minturn and Sangre de Cristo Formations is difficult
to resolve. In unmetamorphosed sandstones, compound (polygonized) quartz
is interpreted as derived from low-grade metamorphic rocks (Young,
1976). However, much of the Minturn and Sangre de Cristo Formations were
affected by greenschist metamorphism during Tertiary time (Lindsey,
Andriessen, and Wardlaw, 1986). Metamorphism was weakest near Marble
Mountain and strongest on the western side of the Sangre de Cristo
Range. Near Crestone, where greenschist metamorphism is most evident,
compound quartz is predominant in Precambrian quartz monzonite of Silver
Plume age, in quartz granules of the lowermost Ordovician Harding
Sandstone, and in the quartz redbed facies of the Minturn Formation.
Possibly, compound quartz in the Minturn of the Marble Mountain section
predates deposition, but that on the west side of the range is an effect
of Tertiary greenschist metamorphism.

![](media/image10.png){width="6.0in" height="4.5in"}

**Figure 8.**\--Photomicrographs of sandstones in the Minturn and Sangre
de Cristo Formations: A) potassic arkosic wacke (21 pct potassium
feldspar, 10 pct plagioclase, 19 pct matrix) with angular to subround
quartz grains, sample 31G, medium sand, 1181 m below top, Minturn
Formation, Marble Mountain section; B) sodic arkosic wacke (9 pct
potassium feldspar, 27 pct plagioclase, 12 pct matrix) with subround and
round quartz grains, sample 8G, coarse sand, 826 m below top, Minturn
Formation, Marble Mountain section; C) sodic arkosic metawacke (18 pct
potassium feldspar, 28 pct plagioclase, 18 pct matrix) with metamorphic
epidote and angular to subround quartz grains, sample 12M, coarse sand,
264 m above base, Sangre de Cristo Formation, Thirsty Peak section; and
D) potassic arkosic wacke (32 pct potassium feldspar, 15 pct
plagioclase, 28 pct matrix), sample 21B, diamictite composed mostly of
angular sand in hematitic matrix, 583 m above base, Sangre de Cristo
Formation, Eureka Mountain section. All photos taken under plain
polarized light, potassium feldspar stained yellow by cobaltinitrite. Q,
monocrystalline quartz; CQ, compound monocrystalline quartz; RQ, rounded
quartz in (B); K, potassium feldspar; P, plagioclase, M, mica (biotite
marked, but muscovite also present); and R, plutonic rock fragment in
(D).

![](media/image11.png){width="6.0in" height="6.75in"}

**Figure 9.**\--Photomicrographs of quartz and other detrital grains,
very coarse sand to granule size, Minturn Formation: A) sample 125B,
1824 m below top, Minturn Formation, Eureka Mountain section; B) sample
31M, 665 m below top, Minturn Formation, Marble Mountain section; and C)
sample 31J, 1049 m below top, Minturn Formation, Marble Mountain
section. (A), (B), and (C), taken under plain polarized light,
correspond to (D), (E), and (F), respectively, taken under
cross-polarized light. Potassium feldspar stained yellow by
cobaltinitrite. Q, monocrystalline quartz; CQ, compound monocrystalline
quartz; PQ, polycrystalline quartz (some grains contain metamorphic
mica); K, potassium feldspar; P, plagioclase; CP, crushed plagioclase;
M, mica (labeled grains are biotite but muscovite also present); GR,
granite; and IG, intermediate-composition plutonic rock.

![](media/image12.png){width="6.0in" height="4.5in"}

**Figure 10.**\--Photomicrographs of plutonic and metamorphic rock
fragments, granule size, Minturn Formation: A) sample 31M, 665 m below
top, Minturn Formation, Eureka Mountain section; and B) sample 349 (not
analyzed), about 1080 m below top, Minturn Formation, near Eureka
Mountain section. (A) and (B), taken under plain polarized light,
correspond to (C) and (D), respectively, taken under cross-polarized
light. Potassium feldspar stained yellow by cobaltinitrite. QMS, quartz
mica schist; QP, quartz-plagioclase plutonic rock; Q, monocrystalline
quartz; K, potassium feldspar; P, plagioclase; CP, compound plagioclase
grain; and M, mica (biotite marked but muscovite also present).

Feldspar grains are commonly crushed (Fig. 9B), a feature that must have
formed after deposition, by compaction or tectonic stress.

The matrix of Minturn and Sangre de Cristo sandstone is composed mostly
of chlorite and sericite. These minerals also replace grains of
plagioclase and, less commonly, potassium feldspar, but in most cases
outlines of detrital grains are still visible. Detrital mica and rock
fragments also exhibit varying degrees of alteration to chlorite and
sericite. Evidently, alteration of unstable detrital grains was an
important source of matrix production. In redbeds, matrix and detrital
mica are replaced by red hematite (Figs. 8C,D).

Chemical classification of Minturn and Sangre de Cristo sandstones in
the system of Herron (1988) shows most samples falling in the field of
wackes (Fig. 11A). On the diagram log (SiO~2~/Al~2~O~3~) vs log
(K~2~O/Na~2~O), used by Pettijohn and others, 1972), all samples plot in
a narrow range of SiO~2~/Al~2~O~3~ and along a large range of
K~2~O/Na~2~O (Fig. 11B). The range in log K~2~O/Na~2~O extends into the
field of sodic arkose and graywacke (compare with Lindsey, 1999). Such
linear patterns are consistent with variable destruction of plagioclase
(and removal of Na~2~O) in a two-feldspar arkose, as would be expected
from weathering of plutonic and gneissic rocks. Finally, in the triangle
chemical classification of Blatt and others (1972), the Minturn and
Sangre de Cristo arkoses straddle the line between sodic and potassic
sandstones (Fig. 11C). None are particularly iron- or magnesium rich.

![](media/image13.pct){width="5.99375in" height="4.993055555555555in"}

**Figure 11.**\--Diagrams showing chemical classification of sandstones
from the Minturn and Sangre de Cristo Formations: A) log (FeTO3/K2O) vs
log (SiO2/Al2O3) (classification of Herron,1988), B) log (SiO2/Al2O3) vs
log (K2O/Na2O) (ratios of Pettijohn and others, 1972), and C) FeTO3+MgO
vs Na2O vs K2O (classification of Blatt and others, 1972).

# Mineral-chemical relationships

The mineral-chemical relationship of major components is evident by
strong positive correlation of some constituents (Fig. 12). Abundance of
quartz grains is correlated with SiO~2~ (Fig. 12A), abundance of
potassium feldspar plus mica grains with K~2~O (Fig. 12B), of
plagioclase with Na~2~O (Fig. 12C), and of detrital mica with LOI (loss
on ignition, including water and hydroxyl) (Fig. 12D). Of course, such
mineral-chemical relationships are imperfect because only the relative
abundance of minerals among detrital grains and cement can be estimated
in thin section. Presumably, stronger relationships would be observed if
the abundance of minerals in sandstone matrix was determined.

An important, indeed dominant, relationship seen in major oxide and
mineral abundance of Minturn and Sangre de Cristo arkoses, is the effect
of mixing (Fig. 13). As unstable feldspar grains were destroyed by
weathering and transport, the proportion of quartz (and silica)
increased. Thus, simple dilution of framework silicates with quartz
explains the inverse relationships between Al~2~O~3~ and SiO~2~ (Fig.
13A) and quartz vs other silicates (Fig. 13B). Additionally,
precipitation of calcite cement dilutes the concentration of other
constituents, including quartz. Although an inverse relationship between
calcite and quartz could not be demonstrated from thin section
estimates, such a relationship is supported by an inverse correlation
between CaO and SiO~2~ (Fig.13C). Other chemical constituents that are
likely to be contained within or associated with calcite, such as MnO
and P~2~O~5~, also vary inversely with SiO~2~ (Figs. 13D and E).
Possibly, the poor inverse relationship between calcite cement and
detrital quartz in thin section stems from spotty distribution of
cement. Chemical analyses should reflect relationships more accurately
because they were determined on splits of powder samples.

![](media/image14.pct){width="5.995833333333334in" height="4.95in"}

**Figure 12.**\--Diagrams showing effect of mineral abundance (detrital
grains) versus total oxide content: A) quartz vs SiO2, B) potassium
feldspar + mica vs K2O, C) plagioclase vs Na2O, and C) loss on ignition
(LOI) vs total (detrital) mica.

![](media/image15.pct){width="5.999305555555556in"
height="6.342361111111111in"}

**Figure 13.**\--Diagrams showing effects of mixing on abundance of
major oxides, detrital grains, and cement in the Minturn and Sangre de
Cristo Formations: A) Al2O3 vs SiO2, B) silicates except quartz vs
quartz, C) CaO vs SiO2, D) MnO vs SiO2, and E) P2O5 vs SiO2.

# Stratigraphic variation

Stratigraphic variation in mineral and chemical constituents is observed
in each measured section except the short section on North Taylor Creek
(Figs. 14 and 15). The most pronounced variation occurs in the Minturn
Formation at the Marble Mountain section. There, SiO~2~ decreases
whereas Al~2~O~3~ and Na~2~O increase from the bottom to the top of the
Minturn Formation (Figs. 14A, B, and C). Quartz decreases whereas
plagioclase and total silicates except quartz increase (Figs. 14D, E,
and F). The upward increase in Al~2~O~3~ and Na~2~O is accompanied by
increases in CaO, MnO, and P~2~O~5~ (Fig. 15). Undoubtedly, some CaO,
MnO, and P~2~O~5~ is present in calcite cement, suggesting that calcite
increases upward, also. Upward increase in calcite could not be
documented from thin section.

The same relationship, of decreasing quartz and increasing plagioclase,
is less well-developed but evident in the Eureka Mountain section (Fig.
14). Although the trend for detrital quartz is present, it is not
reflected in a trend for SiO~2~. Likewise, the trend for plagioclase is
not reflected by a corresponding trend for Na~2~O. Most of the
stratigraphic variation in detrital grains occurs within the Minturn
Formation; in contrast, the Sangre de Cristo Formation is more uniformly
arkosic. Compared to the Marble Mountain section, stratigraphic
variation in the Minturn Formation of the Eureka Mountain section is
much less. Overall, the Minturn of the Eureka Mountain section is more
arkosic than that of the Marble Mountain section.

An interesting detail is the overall upward increase in abundance of
detrital heavy minerals in all sections (Fig. 15D). Although estimates
of heavy mineral abundance are based on thin section counts where
abundance is dependent upon traversing only a few grains, a clear trend
in heavy mineral abundance is nevertheless evident. Upward increase in
heavy minerals, accompanied by detrital plagioclase, indicates that the
supply of heavy minerals was probably a function of the freshness of
detritus. Evidently, rapid erosion during Sangre de Cristo time enhanced
preservation of the original supply of heavy minerals.

The Thirsty Peak section is much shorter than the others, comprising
about 400 m of Minturn Formation and 650 m of Sangre de Cristo
Formation. Most stratigraphic trends seen in the other sections are not
evident in the interval represented by the Thirsty Peak section. The
abundance of Al~2~O~3~ declines upward (Fig. 14B), in contrast to upward
increases in CaO and MnO (Figs. 15A, C). These changes also correspond
to increasing distance from the Oligocene Rito Alto stock. Thus,
distinction between contact metamorphic and stratigraphic effects at the
Thirsty Peak section may be in doubt. The section does contain some of
the most soda-rich sandstones sampled, and all but one of these is
plagioclase-rich.

The North Taylor Creek section is too short (400 m) to reveal
significant stratigraphic variation. All four samples are sodic arkoses,
typical of the Sangre de Cristo Formation.

Stratigraphic plots of oxide ratios (Fig. 16) at each section are
consistent with trends in major oxides already noted. At the Marble
Mountain section, the ratios log (SiO~2~/Al~2~O~3~) and log
(K~2~O/Na~2~O) decline consistently toward the top of the Minturn
Formation (Figs. 16A and B), consistent with upward increase in the
proportion of quartz and decrease in the proportion of plagioclase. No
trends in log ratios are evident in the Eureka Mountain section. At the
Thirsty Peak section, log (K~2~O/Na~2~0) increases upward, opposite the
trend at the Marble Mountain section, and perhaps reflecting the
metamorphic aureole of the Rito Alto stock. No stratigraphic trends for
log (Fe~T~O~3~/K~2~O) are evident at any section (Fig. 16C). Major-oxide
log ratios were plotted because they are sometimes used in chemical
classification of sandstones (e.g., Lindsey, 1999).

![](media/image16.pct){width="6.0in" height="6.71875in"}

**Figure 14.**\--Stratigraphic variation of major oxides and minerals at
three sections in the Minturn and Sangre de Cristo Formations: A) SiO2,
B) Al2O3, C) Na2O, D) quartz, E) total silicates except quartz, and F)
plagioclase. Meter scale refers to stratigraphic distance above or below
the Minturn-Sangre de Cristo contact.

![](media/image17.pct){width="5.992361111111111in"
height="4.855555555555555in"}

**Figure 15.**\-- Stratigraphic variation of major oxides and heavy
minerals at three sections in the Minturn and Sangre de Cristo
Formations: A) log CaO, B) P2O5, C) MnO, and D) detrital heavy minerals.
Meter scale refers to stratigraphic distance above or below the
Minturn-Sangre de Cristo contact.

![](media/image18.pct){width="5.992361111111111in"
height="3.920138888888889in"}

**Figure 16.**\-- Stratigraphic variation of major oxide log ratios at
three sections in the Minturn and Sangre de Cristo Formations: A) log
(SiO2/Al2O3), B) log (K2O/Na2O), and C) log (FeTO3/K2O). Meter scale
refers to stratigraphic distance above or below the Minturn-Sangre de
Cristo contact.

# Petrogenetic models derived from factor analysis

Petrogenetic models were derived from interpreting results of a
multivariate statistical technique called principal components (factor)
analysis (Table 3). The following discussion is based on two experiments
with geochemical data on 50 sandstone samples of the Minturn and Sangre
de Cristo Formations. The first experiment involved 17 quantitatively
determined variables, including major oxides, loss on ignition (LOI),
and trace metals. The second experiment used the same variables and 12
additional semi-quantitatively determined trace elements. Methods are
described in an Appendix, with supporting data tables 4-11.

In the first experiment, the first three factors are of principal
petrologic interest; they can be interpreted as representing important
petrologic processes of placer concentration, chemical maturity, and
destruction of plagioclase (Table 3). Factor 1, the concentration of
iron-titanium placer minerals, probably reflects alluvial concentration
near sediment source, although reworking by marine currents in the
Minturn Formation may have played some role. Heavy minerals were
observed to increase in abundance upsection, and to be most abundant in
the mostly fluvial, near-source Sangre de Cristo Formation. Factor 2,
the abundance of potassium feldspar and mica (both largely detrital),
probably reflects degree of weathering and destruction in the source
area and during transit. Thus, both factors 1 and 2 appear to be
measures of provenance.

**Table 3**.\--Summary of factor interpretations based on log-contrast
principal components analysis (see Appendix for explanation of method
and supporting tables 4-11).

+----------+-----------------+--------------------+-------------------+
| **Factor | **Mineral or    | **Oxides and       | **Factor          |
| Number** | chemical        | elements (factor   | interpretation**  |
|          | group**         | loading \> 0.50)** |                   |
+----------+-----------------+--------------------+-------------------+
| **First  |                 |                    |                   |
| ex       |                 |                    |                   |
| periment |                 |                    |                   |
| (17va    |                 |                    |                   |
| riables: |                 |                    |                   |
| major    |                 |                    |                   |
| oxides,  |                 |                    |                   |
| LOI, and |                 |                    |                   |
| trace    |                 |                    |                   |
| m        |                 |                    |                   |
| etals)** |                 |                    |                   |
+----------+-----------------+--------------------+-------------------+
| **Factor | Iron-titanium   | Fe~T~O~3~, TiO~2~, | Near-source       |
| 1**      | oxides          | P~2~O~5~, and Th   | placer            |
|          | (detrital       |                    | concentration     |
|          | grains)         |                    | (provenance)      |
+----------+-----------------+--------------------+-------------------+
| **Factor | Potassium       | SiO~2~, Al~2~O~3~, | chemical maturity |
| 2**      | feldspar and    | K~2~O              | (provenance)      |
|          | mica (detrital  |                    |                   |
|          | grains)         |                    |                   |
+----------+-----------------+--------------------+-------------------+
| **Factor | Chlorite and/or | MgO, LOI vs Na~2~O | Detrital mica or  |
| 3**      | mica versus     |                    | matrix vs         |
|          | plagioclase     |                    | plagioclase       |
|          | (detrital       |                    | (provenance or    |
|          | grains)         |                    | metamorphism)     |
+----------+-----------------+--------------------+-------------------+
| **Factor | Manganese       | MnO and Zn vs Mo   | Holocene          |
| 4**      | oxides vs       |                    | weathering of     |
|          | molybdenite     |                    | mineralized rock. |
+----------+-----------------+--------------------+-------------------+
| **Factor | \--             | Pb                 | Uninterpreted     |
| 5**      |                 |                    | unique factor.    |
+----------+-----------------+--------------------+-------------------+
| **Factor | \--             | U                  | Uninterpreted     |
| 6**      |                 |                    | unique factor.    |
+----------+-----------------+--------------------+-------------------+
| **Second |                 |                    |                   |
| ex       |                 |                    |                   |
| periment |                 |                    |                   |
| (29      |                 |                    |                   |
| va       |                 |                    |                   |
| riables: |                 |                    |                   |
| 17 from  |                 |                    |                   |
| first    |                 |                    |                   |
| ex       |                 |                    |                   |
| periment |                 |                    |                   |
| plus**   |                 |                    |                   |
|          |                 |                    |                   |
| **12     |                 |                    |                   |
| s        |                 |                    |                   |
| emi-quan |                 |                    |                   |
| titative |                 |                    |                   |
| trace    |                 |                    |                   |
| ele      |                 |                    |                   |
| ments)** |                 |                    |                   |
+----------+-----------------+--------------------+-------------------+
| **Factor | Mafic vs base   | Cr and V vs Cu and | Uninterpreted     |
| 1**      | trace metals    | Pb                 | factor, possibly  |
|          |                 |                    | representing      |
|          |                 |                    | mineralization.   |
+----------+-----------------+--------------------+-------------------+
| **Factor | Potassium       | SiO~2~, Al~2~O~3~, | Chemical maturity |
| 2**      | feldspar and    | K~2~O, Ba, and La  | (provenance)      |
|          | mica (detrital  | vs Co              |                   |
|          | grains)         |                    |                   |
+----------+-----------------+--------------------+-------------------+
| **Factor | Iron-titanium   | Fe~T~O~3~, TiO~2~, | Near-source       |
| 3**      | oxides and      | P~2~O~5~, Th, and  | placer            |
|          | zircon          | Zr vs Be           | concentration     |
|          | (detrital       |                    | (provenance)      |
|          | grains)         |                    |                   |
+----------+-----------------+--------------------+-------------------+
| **Factor | Manganese       | MnO vs Mo          | Holocene          |
| 4**      | oxides vs       |                    | weathering of     |
|          | molybdenite     |                    | mineralized rock  |
+----------+-----------------+--------------------+-------------------+
| **Factor | Chlorite and/or | MgO, LOI, B, and   | Detrital mica or  |
| 5**      | mica            | Ni vs Y            | matrix formation  |
|          |                 |                    | (provenance or    |
|          |                 |                    | metamorphism)     |
+----------+-----------------+--------------------+-------------------+
| **Factor | Th-U mineral vs | Th, U, and Zn vs   | Destruction of    |
| 6**      | plagioclase     | CaO, Na~2~O, and   | plagioclase       |
|          |                 | Sr                 | (provenance or    |
|          |                 |                    | metamorphism?)    |
+----------+-----------------+--------------------+-------------------+

Factor 3 is the most interesting (and puzzling) of all: it reflects an
inverse relation between MgO and LOI vs Na~2~O. Na~2~O abundance is, in
large part, a measure of detrital plagioclase and, thus, factor 3 may
represent plagioclase destruction, either before or after deposition. At
first glance factor 3 might be interpreted as post-depositional
destruction of plagioclase to produce magnesian chlorite matrix.
However, because matrix is not correlated with the abundance of any
other component, including MgO and LOI, interpretation of factor 3 as
post-depositional alteration of plagioclase to produce matrix would seem
to be excluded. If so, factor 3 might also be an indicator of sediment
provenance. LOI is related to abundance of detrital mica, although a
better correlation might (speculatively) have been produced if all mica
were included. Here, it is probably best to keep in mind the risk of
interpreting random effects when too many factors are preserved for
rotation (Jackson, 1993).

Factor 4 in the first experiment clearly represents the effect of
molybdenum and base-metal mineralization near the Rito Alto stock (Table
3). Anomalous metal values were detected in sandstone from the Thirsty
Peak section. The unique factors 5 (Pb) and 6 (U) are not of petrologic
interest. Both elements are present only in crustal background
quantities. Lead and uranium were shown to co-vary in
uranium-mineralized rocks from this region (Lindsey and Clark, 1995).
Notable is the apparent near-complete lack of participation of trace
heavy metals Cu, Pb, and Zn in any sandstone-forming process.

Tables summarizing a second experiment, utilizing 12 semi-quantitatively
analyzed trace elements in addition to the variables included in the
first experiment, are given in Tables 8-11 of the Appendix. Although
some differences between the results of the first and second experiment
are evident, the three petrologic factors of interest to provenance
interpretation are present in both (compare tables 7 and 11). In the
second experiment, the trace elements Ba and La are seen to load on the
factor for potassium minerals, probably because both elements substitute
for potassium. Thorium and zirconium load on the factor for
iron-titanium oxides, as would be expected for concentration of heavy
minerals. Calcium oxide and Sr load with Na~2~O on factor 6 of the
second experiment, suggesting Sr substitution in plagioclase. In the
second experiment, new factors appear for mafic vs base trace metals
(factor 1, uninterpreted) and chlorite and/or mica (MgO, LOI, B, and
Ni\--factor 4, possibly representing detrital minerals or alteration
during greenschist metamorphism). These differences illustrate the
uncertainties of factor analysis in petrologic interpretation.

The petrologic models derived from factor analysis must be viewed as
incomplete. In addition to variable outcomes of factor analysis, the
analysis only accounts for available chemical data. For example, the
process of redbed formation through oxidation of ferromagnesian minerals
and deposition of ferric oxide cement and grain coatings was not
identified because data on ferric versus ferrous iron is not available.
Moreover, the method of log-contrast principal component analysis
(Reyment and Savazzi, 1999), used here, is designed to eliminate forced
negative correlations among chemical elements. However, some negative
(inverse) relationships do reflect processes that increase the
proportion of major constituents such as quartz (during weathering and
transport) and calcite (during cementation).

# Conclusions

Sandstones of the Minturn and Sangre de Cristo Formations range from
sodic to potassic arkose. Arkose of the Sangre de Cristo Formation is
consistently plagioclase-rich; arkose from the Minturn Formation is more
variable. Most are matrix-rich (arkosic wackes). Only a few percent rock
fragments, mostly intermediate to granitic plutonic rocks, gneiss, and
schist, are present. All of the rock fragments seen in sandstone are
present in interbedded conglomerate, consistent with derivation from
Precambrian gneiss and plutonic rocks like those exposed in the present
Sangre de Cristo Range.

Relative abundances of detrital minerals have a strong influence on the
relative abundance of major oxides: detrital quartz is correlated with
SiO~2~, all other detrital minerals (totaled) with Al~2~O~3~, potassium
feldspar plus mica with K~2~O, and plagioclase is correlated with
Na~2~O. Thus, major oxide content is a good predictor of detrital
mineralogy and arkose type, even though contributions from matrix and
cement make these relationships less than perfect.

Mixing of varying proportions of major detrital minerals and mineral
cements, reflected also in major oxide composition, produces inverse
relationships that have petrologic meaning. The abundance of quartz (and
SiO~2~) is enhanced by weathering and transport, which destroys feldspar
and rock fragments. The result is an inverse relationship between quartz
and all other silicate detritus and, thus, between SiO~2~ and Al~2~O~3~.
Weathering also preferentially destroys plagioclase (and removes Na~2~O)
over potassium feldspar. As fresh detritus is weathered from gneiss and
plutonic rocks and transported in the fluvial environment, it becomes
potassium feldspar- as well as quartz-rich. Stratigraphic variation in
major detrital minerals, especially apparent in the Marble Mountain
section, may indicate varying degrees of weathering or reworking in the
marine environment.

The composition of sodic and potassic arkoses in the Minturn and Sangre
de Cristo Formations can be explained entirely in terms of sediment
provenance. Rapid uplift and erosion, and rapid transit through a
fluvial (alluvial fan) system (Lindsey and Schaefer, 1984; Lindsey,
Clark, and Soulliere, 1986), produced plagioclase-rich sodic arkose rich
in iron-titanium oxides and other heavy minerals during deposition of
the Sangre de Cristo Formation and some beds of the Minturn Formation.
During deposition of the Minturn Formation in the Marble Mountain
section, weathering in the source area and on alluvial plains during
transit was sufficient to destroy some plagioclase and reduce the
quantity of total feldspar relative to quartz. Reworking, probably on a
shallow marine shelf, also enhanced the proportion of quartz and
produced rounded quartz grains. In contrast, the Minturn Formation of
the Eureka Mountain section shows much less plagioclase destruction and
quartz enrichment than the Marble Mountain section, probably because
much of the sand of the Eureka Mountain section was flushed into deeper
water by turbidity flows. The lower 1,500 m of the Minturn in the Eureka
Mountains section contains numerous intervals of sandstone interpreted
to have been deposited by turbidity flows (Lindsey, Clark, and
Soulliere, 1985; 1986).

Differences in arkose provenance in the Sangre de Cristo Range, among
formations and among sections, can be explained in terms of rates of
uplift, erosion, and transport of detritus to its final site of
deposition. A dry climate, whether present or not, is not required to
produce the sodic arkoses of the Sangre de Cristo Formation. Fossil
plants in the Minturn indicate the presence of coal-swamp vegetation, at
least locally (Lindsey, Clark, and Soulliere, 1985). Plant fossils are
not common in the Sangre de Cristo Formation of the Sangre de Cristo
Range, but preservation of remains is less likely in the alluvial fan
depositional environment of that formation.

# Acknowledgements

C. A. Brannon, R. F. Clark, and R. A. Schaefer assisted in measuring
sections and collecting samples in the field. Sandstone samples were
analyzed by J. S. Mee and D. F. Siems for major oxides and loss on
ignition; by J. M. Motooka for Cu, Mo, Pb, and Zn; by R. J. Knight for
Th and U; and by E. F. Cooley for other trace elements. R. E. Phillips
determined modal mineralogy of sandstones in thin section. G. P. Meeker
and I. Brownfield provided facilities and assistance in obtaining
photomicrographs. D. H. Knepper, Jr., and W. H. Langer reviewed the
manuscript. All are, or were at the time work was performed, employees
of the U.S. Geological Survey.

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# Appendix: Log-contrast principal components analysis and factor interpretation\--a description of the method and tables summarizing two experiments

As a supplement to the above-described data analysis, a combination of
principal components and factor analysis was used to search for
relationships among chemical elements that might be useful in petrologic
interpretation. Principal components and factor analysis are described
by Reyment and Savazzi (1999) and Cooley and Lohnes (1962),
respectively. A number of experiments using various methods of principal
components and factor analysis were conducted on chemical data on
sandstones of the Minturn and Sangre de Cristo Formations. It is
important to realize that, in factor analysis, multiple methods,
solutions, and interpretations are possible. Choices among methods,
number of principal components to rotate, and alternative factor
interpretations affect the outcome. However, after repeated
experimentation, some consensus is generally possible. The following
discussion summarizes two experiments, using the method of log-contrast
principal components analysis (method of Reyment and Savazzi, 1999),
followed by rotation of principal components and factor interpretation.
The results are considered to be representative, although by no means
identical, for the experiments conducted. The first experiment presented
here utilized data on 50 sandstone samples, for which 17 quantitatively
determined chemical constituents (major oxides, loss on ignition, and
trace metals) were available. The second experiment utilized the same
data, but added data on 12 semi-quantitatively determined trace
elements. In both experiments, steps in the analysis were:

1)  Data preparation\--Values below the limit of analytical detection
    were replaced and a centered log-ratio correlation matrix was
    calculated.

2)  Principal components analysis\--A principal components analysis was
    performed on a centered log-ratio correlation matrix with unities in
    the diagonal. The correlation matrix was solved for its latent roots
    (eigenvalues) and a new matrix specifying uncorrelated vectors
    (principal component axes) was calculated.

3)  Selection of principal components\--In the first experiment, the
    first six principal components were selected for rotation, based on
    eigenvalues \> 1, maximum communalities for log-ratios, and ease of
    interpretation. In the second experiment, six principal components
    were selected for rotation to allow comparison with the first
    experiment.

4)  Rotation of principal components\--Principal component axes were
    rotated to new, orthogonal (uncorrelated) axes using the Kaiser
    Varimax criterion.

5)  Factor interpretation\--Rotated principal components were
    interpreted as petrologic processes, based on factor loadings, and
    supported by analysis of mineral-major oxide correlation and
    stratigraphic distribution.

The method of log-contrast principal components analysis (Reyment and
Savazzi, 1999) was used instead of standard R-mode principal components
(factor) analysis (Cooley and Lohnes, 1962) for compositional data.
Although the author has found it to be a useful guide to identifying
petrologic processes, standard R-mode factor analysis of compositional
data is not always satisfactory because the theoretical sum of values in
each row (sample) of the data matrix is 100 percent. This property,
referred to as the \"constant sum problem\" in geochemistry (Chayes,
1960), constrains the values of correlation coefficients. Correlations
are not free to range between -1 and +1. Correlations for major
constituents are forced toward negative values. Moreover, when the
number of constituents is reduced and recalculated to 100 percent as is
done, for example, during conversion to a volatile-free basis, the
correlations change. Solutions to the constant sum problem have been
proposed, only to be declared invalid upon subsequent investigation, and
the problem does not seem to be completely resolved. The method employed
here, termed \"log-contrast principal components analysis\" (Reyment and
Savazzi, 1999), is a newly proposed solution for the constant sum
problem.

Although Reyment and Savazzi (1999) provide a convenient DOS program
that performs a log-contrast principal components analysis and a
traditional (R-mode) principal components analysis for comparison, I
also used the program \"Statview\" to permit analysis of large data
matrices and to extend the analysis to rotation of principal components.
Using either program, a new matrix of log-ratios is calculated by
dividing each cell of a row by the geometric mean of that row and
converting the result to its logarithm. A new covariance matrix, termed
the \"centered log-ratio covariance matrix,\" is calculated from the
log-ratio matrix, and a corresponding centered log-ratio correlation
matrix is computed (Table 4). The new correlation matrix is a measure of
proportionality between the original variables (columns). Raw data may
be expressed either as \"percent,\" \"parts per million,\" or both, if
consistent within columns. Finally, in principal components analysis,
the centered log-ratio correlation matrix is solved for its roots.
Centered log-ratio correlation coefficients are not comparable to
correlation coefficients calculated from raw data, but the results of
the principal components analyses (latent roots and vectors that specify
factor loadings) can be inspected for similarities and differences. In
the present analysis, I have relied exclusively on the method of
log-contrast analysis.

Selection of the number of principal components to preserve for rotation
and factor interpretation is not always obvious, as in the present case.
Criteria for selection are discussed by Jackson (1993). The number of
principal components selected for rotation can be based on 1) eigenvalue
magnitude greater than one, 2) the point on the eigenvalue distribution
curve where an obvious change in magnitude occurs (root curve method),
3) eigenvalue distribution curve compared to eigenvalues calculated from
random data (broken-stick distribution), 4) maximum communalities under
various rotation scenarios, and 5) trial interpretation of rotated
factors. Criteria (1), (4), and (5) were used here.

Six principal components were selected for rotation and interpretation.
Selection of such a large number of principal components risks
interpreting random effects (Jackson, 1993) but, in the present case,
solutions involving fewer components yielded low communalities and posed
difficulties for interpretation. (Communality is the sum of the squared
factor loadings, and is a measure of the degree to which a particular
solution accounts for the variance of a variable, in this case a log
ratio). The first two eigenvalues account for almost half of the total
variance (Table 5) and, if low communalities for many log-ratios were
ignored, a simple two-factor solution could be considered. The
eigenvalue curve (not shown) becomes flat after the fourth root and 67
pct of the total variance is included, but communalities of some log
ratios remain low. In contrast, the first six eigenvalues account for
more than 80 pct of total variance (Table 5) and all communalities
exceed 0.70 (Table 6). Results of rotating 6 principal components are
summarized in Table 7.

Tables summarizing a second experiment, utilizing 12 semi-quantitatively
analyzed trace elements in addition to the variables included in the
first experiment, are given in Tables 8-11.

**Table 4.**\--17X17 centered log-ratio correlation matrix, log ratio
data, Minturn and Sangre de Cristo Formations. N = 50; X, row geometric
mean of original data matrix.

  --------------- ------------ ------------ --------------- --------- --------- ------------ ----------- ------------ --------------
                  Log          Log          Log             Log       Log       Log          Log         Log          Log
                  (SiO~2~/X)   (Al~2~O~3~   (Fe~T~O~3~/X)   (MgO/X)   (CaO/X)   (Na~2~O/X)   (K~2~O/X)   (TiO~2~/X)   (P~2~O~5~/X)
                               /X)                                                                                    

  Log (SiO~2~/X)  1.00         .883         .214            .186      -.455     -.118        .827        -.042        -.342

  Log             .883         1.00         .343            .329      -.353     .129         .715        .037         -.077
  (Al~2~O~3~/X)                                                                                                       

  Log             .214         .343         1.00            .506      -.528     -.247        .211        .695         .238
  (Fe~T~O~3~/X)                                                                                                       

  Log (MgO/X)     .186         .329         .506            1.00      -.319     -.307        .033        .348         .212

  Log (CaO/X)     -.455        -.353        -.528           -.319     1.00      .476         -.473       -.308        .037

  Log (Na~2~O/X)  -.118        .129         -.247           -.307     .476      1.00         -.281       -.232        .174

  Log (K~2~O/X)   .827         .715         .211            .033      -.473     -.281        1.00        -.058        -.303

  Log (TiO~2~/X)  -.042        .037         .695            .348      -.308     -.232        -.058       1.00         .507

  Log             -.342        -.077        .238            .212      .037      .174         -.303       .507         1.00
  (P~2~O~5~/X)                                                                                                        

  Log (MnO/X)     -.246        -.236        -.248           -.284     .392      .076         -.096       -.238        -.104

  Log (LOI/X)     .309         .226         .268            .492      -.356     -.599        .346        .282         -.039

  Log (Cu/X)      -.431        -.493        -.492           -.390     .157      .183         -.391       -.385        -.095

  Log (Mo/X)      .001         -.074        -.270           -.223     .053      .171         -.169       -.341        -.206

  Log (Pb/X)      -.268        -.470        -.287           -.340     -.047     -.206        -.117       -.126        -.196

  Log (Th/X)      .389         .401         .596            .252      -.495     -.231        .346        .473         .084

  Log (U/X)       -.029        -.021        .342            .247      -.278     -.462        .038        .152         -.053

  Log (Zn/X)      .029         -.055        .221            .004      -.413     -.290        .185        .210         .001
  --------------- ------------ ------------ --------------- --------- --------- ------------ ----------- ------------ --------------

  --------------- --------- --------- -------- -------- -------- -------- ------- --------
                  Log       Log       Log      Log      Log      Log      Log     Log
                  (MnO/X)   (LOI/X)   (Cu/X)   (Mo/X)   (Pb/X)   (Th/X)   (U/X)   (Zn/X)

  Log (SiO~2~/X)  -.246     .309      -.431    .001     -.268    .389     -.029   .029

  Log             -.236     .226      -.493    -.074    -.470    .401     -.021   -.055
  (Al~2~O~3~/X)                                                                   

  Log             -.248     .268      -.492    -.270    -.287    .596     .342    .221
  (Fe~T~O~3~/X)                                                                   

  Log (MgO/X)     -.284     .492      -.390    -.223    -.340    .252     .247    .004

  Log (CaO/X)     .392      -.356     .157     .053     -.047    -.495    -.278   -.413

  Log (Na~2~O/X)  .076      -.599     .183     .171     -.206    -.231    -.462   -.290

  Log (K~2~O/X)   -.096     .346      -.391    -.169    -.117    .346     .038    .185

  Log (TiO~2~/X)  -.238     .282      -.385    -.341    -.126    .473     .152    .210

  Log             -.104     -.039     -.095    -.206    -.196    .084     -.053   .001
  (P~2~O~5~/X)                                                                    

  Log (MnO/X)     1.00      -.130     -.150    -.242    -.126    -.222    .083    .245

  Log (LOI/X)     -.130     1.00      -.423    -.466    -.168    .249     .284    .418

  Log (Cu/X)      -.150     -.423     1.00     .291     .288     -.403    -.394   -.317

  Log (Mo/X)      -.242     -.466     .291     1.00     -.043    -.395    -.186   -.514

  Log (Pb/X)      -.126     -.168     .288     -.043    1.00     -.180    -.105   .030

  Log (Th/X)      -.222     .249      -.403    -.395    -.180    1.00     .370    .187

  Log (U/X)       .083      .284      -.394    -.186    -.105    .370     1.00    .262

  Log (Zn/X)      .245      .418      -.317    -.514    .030     .187     .262    1.00
  --------------- --------- --------- -------- -------- -------- -------- ------- --------

**Table 5.**\--Eigenvalues (roots) of 17X17 log-ratio correlation
matrix.

  ----------------- ----------------- ----------------- -----------------
                    Magnitude         Variance          Cumulative
                                      Proportion        Variance
                                                        Proportion

  Value 1           5.157             .303              .303

  Value 2           2.610             .154              .457

  Value 3           2.041             .120              .577

  Value 4           1.691             .099              .676

  Value 5           1.178             .069              .745

  Value 6           1.010             .059              .804

  Value 7           .707              .042              .846

  Value 8           .599              .035              .881
  ----------------- ----------------- ----------------- -----------------

**Table 6.**\--Communalities for orthogonal rotations, 6 principal
components, 17 variables.

  ---------------------------------------- ------------------------------
                                           h^2^

  Log (SiO~2~/X)                           .951

  Log (Al~2~O~3~/X)                        .951

  Log (Fe~T~O~3~/X)                        .801

  Log (MgO/X)                              .814

  Log (CaO/X)                              .778

  Log (Na~2~O/X)                           .829

  Log (K~2~O/X)                            .861

  Log (TiO~2~/X)                           .795

  Log (P~2~O~5~/X)                         .725

  Log (MnO/X)                              .832

  Log (LOI/X)                              .880

  Log (Cu/X)                               .698

  Log (Mo/X)                               .779

  Log (Pb/X)                               .725

  Log (Th/X)                               .725

  Log (U/X)                                .839

  Log (Zn/X)                               .702
  ---------------------------------------- ------------------------------

**Table 7.**\--Six-factor orthogonal solution, 17 variables, Varimax
rotation.

  --------------- ---------- ---------- ----------- ----------- ----------- ----------
  Proportion      Factor 1   Factor 2   Factor 3    Factor 4    Factor 5    Factor 6

  Log (SiO~2~/X)  .007       **.958**   .125        -.049       .125        -.004

  Log             .173       **.856**   .069        -.077       .405        -.119
  (Al~2~O~3~/X)                                                             

  Log             **.786**   .211       .157        .064        .168        .286
  (Fe~T~O~3~/X)                                                             

  Log (MgO/X)     .359       .056       **.730**    -.109       .363        .075

  Log (CaO/X)     -.463      -.506      -.267       -.010       .392        -.288

  Log (Na~2~O/X)  -.046      -.078      **-.619**   -.170       .364        -.526

  Log (K~2~O/X)   -.037      **.900**   .092        .192        -.041       .057

  Log (TiO~2~/X)  **.841**   -.109      .185        .199        .048        .010

  Log             **.605**   -.402      .032        .096        .248        -.356
  (P~2~O~5~/X)                                                              

  Log (MnO/X)     -.441      -.234      -.327       **.555**    .349        .216

  Log (LOI/X)     .061       .239       **.802**    .403        .042        .110

  Log (Cu/X)      -.269      -.354      -.163       -.360       -.499       -.308

  Log (Mo/X)      -.255      -.016      -.182       **-.819**   -.048       .082

  Log (Pb/X)      -.126      -.178      -.080       .084        **-.815**   -.025

  Log (Th/X)      **.650**   .416       -.053       .168        .019        .313

  Log (U/X)       .172       -.058      .153        .115        .124        **.868**

  Log (Zn/X)      .123       .092       .099        **.770**    -.180       .209
  --------------- ---------- ---------- ----------- ----------- ----------- ----------

**Factor 1**\--Iron-titanium oxides (detrital grains)\--Fe~T~O~3~,
TiO~2~, P~2~O~5~, and Th\--placer concentration (provenance).

**Factor 2**\--Potassium feldspar and mica (detrital grains)\--SiO~2~,
Al~2~O~3~, K~2~O\--chemical maturity (provenance).

**Factor 3**\--Chlorite and/or mica (detrital grains or matrix) versus
plagioclase (detrital grains)\--MgO, LOI vs Na~2~O\--if detrital mica vs
plagioclase destruction, then provenance; if matrix vs plagioclase
destruction, then greenschist metamorphism or burial diagenesis.

**Factor 4**\--Manganese oxides vs molybdenite\--MnO and Zn vs
Mo\--weathering of mineralized rock.

**Factor 5**\--Pb\--Uninterpreted unique factor.

**Factor 6**\--U\--Uninterpreted unique factor.

**Table 8.**\--29X29 centered log-ratio correlation matrix, log ratio
data, Minturn and Sangre de Cristo Formations. N = 50; X, row geometric
mean of original data matrix.

  --------------- ------------ --------------- --------------- --------- --------- ------------ ----------- ------------ -------------- ---------
                  Log          Log             Log             Log       Log       Log          Log         Log          Log            Log
                  (SiO~2~/X)   (Al~2~O~3~/X)   (Fe~T~O~3~/X)   (MgO/X)   (CaO/X)   (Na~2~O/X)   (K~2~O/X)   (TiO~2~/X)   (P~2~O~5~/X)   (MnO/X)

  Log (SiO~2~/X)  1.00         .822            -.042           -.087     -.473     -.165        .799        -.189        -.390          -.251

  Log             .822         1.00            .078            -.028     -.328     .187         .682        -.075        -.036          -.186
  (Al~2~O~3~/X)                                                                                                                         

  Log             -.042        .078            1.00            .319      -.488     -.221        .063        .686         .290           -.181
  (Fe~T~O~3~/X)                                                                                                                         

  Log (MgO/X)     -.087        -.028           .319            1.00      -.351     -.416        -.187       .186         .109           -.341

  Log (CaO/X)     -.473        -.328           -.488           -.351     1.00      .528         -.440       -.173        .152           .443

  Log (Na~2~O/X)  -.165        .187            -.221           -.416     .528      1.00         -.268       -.080        .312           .200

  Log (K~2~O/X)   .799         .682            .063            -.187     -.440     -.268        1.00        -.117        -.268          -.053

  Log (TiO~2~/X)  -.189        -.075           .686            .186      -.173     -.080        -.117       1.00         .590           -.075

  Log             -.390        -.036           .290            .109      .152      .312         -.268       .590         1.00           .075
  (P~2~O~5~/X)                                                                                                                          

  Log (MnO/X)     -.251        -.186           -.181           -.341     .443      .200         -.053       -.075        .075           1.00

  Log (LOI/X)     .213         .107            .194            .404      -.299     -.532        .291        .268         .014           -.068

  Log (B/X)       .085         .053            .174            .600      -.389     -.567        .061        .007         -.089          -.157

  Log (Ba/X)      .629         .458            -.171           -.150     -.249     -.144        .552        -.275        -.356          -.129

  Log (Be/X)      .180         .201            -.176           -.147     .099      .078         .225        -.491        -.233          .089

  Log (Co/X)      -.482        -.457           .167            .353      -.089     -.058        -.450       -.066        -.078          -.186

  Log (Cr/X)      -.233        -.392           .039            .544      -.076     -.420        -.325       -.004        -.247          -.149

  Log (Cu/X)      -.305        -.266           -.290           -.336     .237      .344         -.244       -.112        .141           .019

  Log (La/X)      .504         .517            -.058           -.426     -.052     .121         .440        -.156        -.138          -.108

  Log (Mo/X)      .011         -.036           -.251           -.271     .101      .233         -.152       -.239        -.086          -.151

  Log (Ni/X)      -.034        -.097           .126            .735      -.402     -.415        -.122       -.143        -.151          -.459

  Log (Pb/X)      -.147        -.262           -.091           -.301     .059      .011         .016        .115         .061           .046

  Log (Sc/X)      -.181        -.123           .299            .263      -.146     -.104        -.370       .246         .014           -.182

  Log (Sr/X)      -.040        .035            -.429           -.214     .497      .403         -.145       -.376        -.040          .121

  Log (Th/X)      .271         .287            .543            .089      -.440     -.190        .269        .448         .127           -.156

  Log (U/X)       -.240        -.275           .254            .070      -.200     -.384        -.070       .151         .030           .165

  Log (V/X)       .304         .076            .018            .274      -.276     -.449        .164        -.239        -.467          -.250

  Log (Y/X)       -.212        -.195           -.097           -.325     .255      .265         -.218       -.204        -.205          .092

  Log (Zn/X)      .043         .014            .298            -.037     -.304     -.139        .223        .310         .143           .326

  Log (Zr/X)      .252         .141            .256            -.068     -.426     -.111        .157        .425         .032           -.452
  --------------- ------------ --------------- --------------- --------- --------- ------------ ----------- ------------ -------------- ---------

  --------------- --------- ------- -------- -------- -------- -------- -------- -------- -------- --------
                  Log       Log     Log      Log      Log      Log      Log      Log      Log      Log
                  (LOI/X)   (B/X)   (Ba/X)   (Be/X)   (Co/X)   (Cr/X)   (Cu/X)   (La/X)   (Mo/X)   (Ni/X)

  Log (SiO~2~/X)  .213      .085    .629     .180     -.482    -.233    -.305    .504     .011     -.034

  Log             .107      .053    .458     .201     -.457    -.392    -.266    .517     -.036    -.097
  (Al~2~O~3~/X)                                                                                    

  Log             .194      .174    -.171    -.176    .167     .039     -.290    -.058    -.251    .126
  (Fe~T~O~3~/X)                                                                                    

  Log (MgO/X)     .404      .600    -.150    -.147    .353     .544     -.336    -.426    -.271    .735

  Log (CaO/X)     -.299     -.389   -.249    .099     -.089    -.076    .237     -.052    .101     -.402

  Log (Na~2~O/X)  -.532     -.567   -.144    .078     -.058    -.420    .344     .121     .233     -.415

  Log (K~2~O/X)   .291      .061    .552     .225     -.450    -.325    -.244    .440     -.152    -.122

  Log (TiO~2~/X)  .268      .007    -.275    -.491    -.066    -.004    -.112    -.156    -.239    -.143

  Log             .014      -.089   -.356    -.233    -.078    -.247    .141     -.138    -.086    -.151
  (P~2~O~5~/X)                                                                                     

  Log (MnO/X)     -.068     -.157   -.129    .089     -.186    -.149    .019     -.108    -.151    -.459

  Log (LOI/X)     1.00      .506    .046     -.116    -.228    .063     -.271    -.109    -.435    .155

  Log (B/X)       .506      1.00    -.100    -.098    .186     .379     -.367    -.228    -.386    .435

  Log (Ba/X)      .046      -.100   1.00     .165     -.389    -.094    -.372    .508     -.028    -.033

  Log (Be/X)      -.116     -.098   .165     1.00     .035     -.263    -.070    .131     .020     .000

  Log (Co/X)      -.228     .186    -.389    .035     1.00     .364     .158     -.511    .038     .493

  Log (Cr/X)      .063      .379    -.094    -.263    .364     1.00     -.368    -.326    -.272    .612

  Log (Cu/X)      -.271     -.367   -.372    -.070    .158     -.368    1.00     -.224    .353     -.243

  Log (La/X)      -.109     -.228   .508     .131     -.511    -.326    -.224    1.00     -.103    -.275

  Log (Mo/X)      -.435     -.386   -.028    .020     .038     -.272    .353     -.103    1.00     -.063

  Log (Ni/X)      .155      .435    -.033    .000     .493     .612     -.243    -.275    -.063    1.00

  Log (Pb/X)      -.034     -.223   -.314    -.009    .097     -.232    .390     -.206    .051     -.295

  Log (Sc/X)      -.267     .121    -.015    -.408    .251     .343     -.079    -.142    .055     .216

  Log (Sr/X)      -.371     -.199   .381     .194     -.068    -.074    .031     .193     .035     -.112

  Log (Th/X)      .199      .070    -.050    -.084    -.234    -.043    -.236    .246     -.370    -.043

  Log (U/X)       .242      .086    -.222    .168     -.007    .025     -.193    -.043    -.140    .011

  Log (V/X)       -.059     .314    .427     .003     .112     .445     -.418    .052     -.044    .341

  Log (Y/X)       -.443     -.402   .024     -.033    -.036    .048     -.085    .242     .169     -.259

  Log (Zn/X)      .454      .087    -.112    -.109    -.112    -.196    -.148    -.039    -.416    -.151

  Log (Zr/X)      .080      -.081   .069     -.449    -.281    .058     -.125    .240     .002     -.021
  --------------- --------- ------- -------- -------- -------- -------- -------- -------- -------- --------

  --------------- -------- -------- -------- -------- ------- ------- ------- -------- --------
                  Log      Log      Log      Log      Log     Log     Log     Log      Log
                  (Pb/X)   (Sc/X)   (Sr/X)   (Th/X)   (U/X)   (V/X)   (Y/X)   (Zn/X)   (Zr/X)

  Log (SiO~2~/X)  -.147    -.181    -.040    .271     -.240   .304    -.212   .043     .252

  Log             -.262    -.123    .035     .287     -.275   .076    -.195   .014     .141
  (Al~2~O~3~/X)                                                                        

  Log             -.091    .299     -.429    .543     .254    .018    -.097   .298     .256
  (Fe~T~O~3~/X)                                                                        

  Log (MgO/X)     -.301    .263     -.214    .089     .070    .274    -.325   -.037    -.068

  Log (CaO/X)     .059     -.146    .497     -.440    -.200   -.276   .255    -.304    -.426

  Log (Na~2~O/X)  .011     -.104    .403     -.190    -.384   -.449   .265    -.139    -.111

  Log (K~2~O/X)   .016     -.370    -.145    .269     -.070   .164    -.218   .223     .157

  Log (TiO~2~/X)  .115     .246     -.376    .448     .151    -.239   -.204   .310     .425

  Log             .061     .014     -.040    .127     .030    -.467   -.205   .143     .032
  (P~2~O~5~/X)                                                                         

  Log (MnO/X)     .046     -.182    .121     -.156    .165    -.250   .092    .326     -.452

  Log (LOI/X)     -.034    -.267    -.371    .199     .242    -.059   -.443   .454     .080

  Log (B/X)       -.223    .121     -.199    .070     .086    .314    -.402   .087     -.081

  Log (Ba/X)      -.314    -.015    .381     -.050    -.222   .427    .024    -.112    .069

  Log (Be/X)      -.009    -.408    .194     -.084    .168    .003    -.033   -.109    -.449

  Log (Co/X)      .097     .251     -.068    -.234    -.007   .112    -.036   -.112    -.281

  Log (Cr/X)      -.232    .343     -.074    -.043    .025    .445    .048    -.196    .058

  Log (Cu/X)      .390     -.079    .031     -.236    -.193   -.418   -.085   -.148    -.125

  Log (La/X)      -.206    -.142    .193     .246     -.043   .052    .242    -.039    .240

  Log (Mo/X)      .051     .055     .035     -.370    -.140   -.044   .169    -.416    .002

  Log (Ni/X)      -.295    .216     -.112    -.043    .011    .341    -.259   -.151    -.021

  Log (Pb/X)      1.00     -.294    -.199    -.028    .075    -.491   -.224   .164     -.021

  Log (Sc/X)      -.294    1.00     .008     .093     -.030   .333    .065    -.231    .119

  Log (Sr/X)      -.199    .008     1.00     -.537    -.517   .091    .077    -.451    -.382

  Log (Th/X)      -.028    .093     -.537    1.00     .317    .035    .000    .236     .436

  Log (U/X)       .075     -.030    -.517    .317     1.00    -.148   .111    .329     .069

  Log (V/X)       -.491    .333     .091     .035     -.148   1.00    .132    -.258    .021

  Log (Y/X)       -.224    .065     .077     .000     .111    .132    1.00    -.154    .135

  Log (Zn/X)      .164     -.231    -.451    .236     .329    -.258   -.154   1.00     .145

  Log (Zr/X)      -.021    .119     -.382    .436     .069    .021    .135    .145     1.00
  --------------- -------- -------- -------- -------- ------- ------- ------- -------- --------

**Table 9.**\--Eigenvalues (roots) of 29X29 log-ratio correlation
matrix.

  ----------------- ----------------- ----------------- -----------------
                    Magnitude         Variance          Cumulative
                                      Proportion        Variance
                                                        Proportion

  Value 1           5.491             .189              .189

  Value 2           4.780             .165              .354

  Value 3           3.852             .133              .487

  Value 4           2.520             .087              .574

  Value 5           1.945             .067              .641

  Value 6           1.832             .063              .704

  Value 7           1.340             .046              .750

  Value 8           .972              .034              .784

  Value 9           .880              .030              .814

  Value 10          .784              .027              .841

  Value 11          .715              .025              .866

  Value 12          .596              .021              .887

  Value 13          .509              .018              .905

  Value 14          .461              .016              .921
  ----------------- ----------------- ----------------- -----------------

**Table 10.**\--Communalities for orthogonal rotation, 5-7 principal
components, 29 variables. h^2^(5), communality for rotation of five
components.

  --------------------- ---------------- ---------------- ----------------
                        h^2^(5)          h^2^ (6)         h^2^ (7)

  Log (SiO~2~/X)        .914             .915             .917

  Log (Al~2~O~3~/X)     .723             .811             .875

  Log (Fe~T~O~3~/X)     .605             .613             .762

  Log (MgO/X)           .731             .813             .832

  Log (CaO/X)           .725             .799             .813

  Log (Na~2~O/X)        .641             .737             .800

  Log (K~2~O/X)         .823             .829             .830

  Log (TiO~2~/X)        .761             .842             .848

  Log (P~2~O~5~/X)      .441             .735             .764

  Log (MnO/X)           .671             .694             .696

  Log (LOI/X)           .661             .692             .772

  Log (B/X)             .635             .678             .684

  Log (Ba/X)            .693             .700             .718

  Log (Be/X)            .413             .437             .839

  Log( Co/X)            .596             .629             .727

  Log (Cr/X)            .725             .726             .782

  Log (Cu/X)            .660             .696             .706

  Log (La/X)            .669             .669             .675

  Log (Mo/X)            .466             .598             .599

  Log (Ni/X)            .742             .743             .771

  Log (Pb/X)            .486             .603             .645

  Log (Sc/X)            .581             .591             .591

  Log (Sr/X)            .566             .795             .797

  Log (Th/X)            .623             .634             .696

  Log (U/X)             .459             .666             .734

  Log (V/X)             .714             .723             .727

  Log (Y/X)             .631             .761             .766

  Log (Zn/X)            .611             .612             .617

  Log (Zr/X)            .621             .679             .777
  --------------------- ---------------- ---------------- ----------------

**Table 11**.\--Six-factor orthogonal solution, 29 variables, Varimax
rotation.

  ------------------ ----------- ----------- ----------- ----------- ----------- -----------
                     Factor1     Factor2     Factor3     Factor4     Factor5     Factor6

  Log (SiO~2~/X)     .071        **.901**    -.143       -.218       .148        .087

  Log (Al~2~O~3~/X)  -.027       **.863**    .086        -.076       .153        -.173

  Log (Fe~T~O~3~/X)  .114        .015        **.666**    .005        .188        .348

  Log (MgO/X)        .428        -.251       .215        -.116       **.711**    .033

  Log (CaO/X)        -.154       -.350       -.208       .414        -.382       **-.540**

  Log (Na~2~O/X)     -.374       -.005       .117        .088        -.446       **-.615**

  Log (K~2~O/X)      -.088       **.832**    -.184       -.003       .173        .258

  Log (TiO~2~/X)     -.136       -.076       **.869**    .138        .120        .170

  Log (P~2~O~5~/X)   -.359       -.169       **.643**    .266        .119        -.279

  Log MnO/X          -.151       -.157       -.209       **.747**    -.209       -.038

  Log (LOI/X)        -.018       .196        .085        .311        **.642**    .369

  Log (B/X)          .366        -.049       -.005       .060        **.715**    .166

  Log (Ba/X)         .360        **.697**    -.243       -.049       -.070       -.135

  Log (Be/X)         -.095       .179        **-.615**   .133        .024        .010

  Log (Co/X)         .110        **-.664**   -.103       -.335       .230        .014

  Log (Cr/X)         **.685**    -.431       .007        -.099       .224        .107

  Log (Cu/X)         **-.660**   -.308       -.093       -.304       -.159       -.196

  Log (La/X)         .118        **.703**    .003        .082        -.393       -.024

  Log (Mo/X)         -.253       -.093       -.190       **-.579**   -.350       -.175

  Log (Ni/X)         .459        -.241       -.069       -.396       **.555**    .065

  Log (Pb/X)         **-.697**   -.192       -.106       -.089       .002        .248

  Log (Sc/X)         .483        -.254       .431        -.290       -.088       -.124

  Log (Sr/X)         .166        .072        -.294       .134        -.154       **-.797**

  Log (Th/X)         .064        .324        **.518**    .041        -.022       **.504**

  Log (U/X)          .020        -.212       .007        .285        -.084       **.730**

  Log (V/X)          **.771**    .155        -.182       -.257       .059        .045

  Log (Y/X)          .311        -.117       -.049       .040        **-.799**   .088

  Log (Zn/X)         -.250       .107        .188        .465        .182        **.503**

  Log (Zr/X)         .050        .290        **.543**    -.344       -.219       .361
  ------------------ ----------- ----------- ----------- ----------- ----------- -----------

**Factor 1**\--Mafic vs base trace metals\--Cr and V vs Cu and
Pb\--uninterpreted factor, possibly representing mineralization.

**Factor 2**\--Potassium feldspar and mica (detrital grains)\--SiO~2~,
Al~2~O~3~, K~2~O, Ba, and La vs Co\-- chemical maturity (provenance).

**Factor 3**\--Iron-titanium oxides and zircon (detrital
grains)\--Fe~T~O~3~, TiO~2~, P~2~O~5~, Th, and Zr vs Be\--near-source
placer concentration (provenance).

**Factor 4**\--Manganese oxides vs molybdenite\--MnO vs Mo\--weathering
of mineralized rock.

**Factor 5**\--Chlorite and/or mica\--MgO, LOI, B, and Ni vs Y\--if
detrital mica, then provenance; if matrix, then greenschist metamorphism
or burial diagenesis.

**Factor 6**\--Th-U mineral vs plagioclase\--Th, U, and Zn vs CaO,
Na~2~O, and Sr\--destruction of plagioclase (provenance or
metamorphism).