U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2007-1095

Mineralogy from Cores in Prospect Gulch,

San Juan County, Colorado
Mineralogy from Cores in Prospect Gulch, 

San Juan County, Colorado

By Dana J. Bove, Raymond H. Johnson, and Douglas B. Yager

Open-File Report 2007-1095

U.S. Department of the Interior

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

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2007

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Suggested citation:

Bove, D.J., Johnson, R.H., Yager, D.B., Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado: U.S. 

Geological Survey, Open-File Report 2007-1095, 82 p.
iii

Contents

Abstract...........................................................................................................................................................1

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

Geologic Setting.............................................................................................................................................2

Hydrologic Setting .........................................................................................................................................3

Drilling Locations, Core Logs, and Oxidation Depth.................................................................................3

Mineralogy from Cores .................................................................................................................................3

References Cited............................................................................................................................................3

Appendix A. Core log for UPG-D ...............................................................................................................37

Appendix B. Core log for MPG-D ..............................................................................................................59

Appendix C. Core log for LPG-D ................................................................................................................72

Figures

1. Location of Prospect Gulch in the upper Animas River watershed.....................................5

2. Detailed alteration map of bedrock in Prospect Gulch and the surrounding area............6

3. Drill hole locations in Prospect Gulch.......................................................................................7

4. Depth of the partially oxidized zone in feet ..............................................................................8

5. Depth of the fully oxidized zone in feet .....................................................................................9

Tables

1. Drill hole locations and oxidation depths ...............................................................................10

2. Mineralogy in UPG-D samples from X-ray diffraction analyses.........................................11

3. Mineralogy in MPG-D samples from X-ray diffraction analyses........................................14

4. Mineralogy in LPG-D samples from X-ray diffraction analyses..........................................20

5. Mineralogy in H-4 samples from X-ray diffraction analyses...............................................26

6. Mineralogy in H-5 samples from X-ray diffraction analyses...............................................32

7. Mineralogy in H-6 samples from X-ray diffraction analyses...............................................34
iv

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

yard (yd) 0.9144 meter (m)

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

°C=(°F-32)/1.8

Vertical coordinate information is referenced to the North American Vertical Datum of 1929 

(NAVD 29).

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

SI to Inch/Pound

Multiply By To obtain

Length

centimeter (cm) 0.3937 inch (in.)

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

meter (m) 1.094 yard (yd) 

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

°F=(1.8×°C)+32

Vertical coordinate information is referenced to the North American Vertical Datum of 1929 

(NAVD 29).

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

In the late nineteenth century, San Juan County, Colorado, was the center of a metal mining boom in the San Juan 

Mountains. Although most mining activity ceased by the 

1990s, the effects of historical mining continue to contribute 

metals to ground water and surface water. Previous research by 

the U.S. Geological Survey identified ground-water discharge 

as a significant pathway for the loading of metals to surface 

water from both acid-mine drainage and acid-rock drainage. 

In an effort to understand the ground-water flow system in the 

upper Animas River watershed, Prospect Gulch was selected 

for further study because of the amount of previous data 

provided in and around that particular watershed. In support of 

this ground-water research effort, data was collected from drill 

core, which included: (1) detailed descriptions of the subsurface geology and hydrothermal alteration patterns, (2) depth of 

sulfide oxidation, and (3) quantitative mineralogy.

Introduction

In the late 19th, San Juan County, Colorado, was the 

center of a metal mining boom in the San Juan Mountains. 

Although most mining activity ceased by the 1990s, the effects 

of historical mining continue to contribute metals to ground 

water and surface water. These increased metal concentrations degrade stream-water quality and are toxic to fish and 

other aquatic organisms. As a result, viable fish and aquatic 

habitat is now more limited than what existed before mining 

(Besser and others, 2006). Since the 1990s, the local economic base has shifted away from hard-rock mining toward 

tourism with a focus on recreational opportunities. This new 

focus, as well as increased population downstream also has 

increased the demand for clean water. While streams in this 

area have low pH and elevated metal loads due to acid-rock 

drainage, the influence of acid-mine drainage due to historical 

mining activities has degraded preexisting ground-water and 

surface-water quality (Church and others, 2006). Determining 

the ground-water flow and associated dissolved-metal transport is critical to protecting ground-water and surface-water 

resources, determining the influence of acid-mine drainage 

compared to preexisting acid-rock drainage, and providing 

sensible remedial options.

Much of the San Juan Mountains is influenced by historical mining, and many surface-water samples (along with 

other data) have been collected in the upper Animas River 

watershed (fig. 1) by the U.S. Geological Survey (Church and 

others, 2006; http://amli.usgs.gov/reports/). Three goals of this 

watershed characterization project were to (1) characterize the 

surface-water quality, (2) identify abandoned mines that contribute the greatest metal loads to surrounding surface waters, 

and (3) determine premining water quality. The ultimate objective was to provide the necessary scientific information for 

public land managers to select effective remedial approaches 

that would improve watershed quality. Ground-water discharge 

has been identified as a significant pathway for the loading 

of metals to surface water from both acid-mine drainage and 

from acid-rock drainage (Church and others, 2006; Mast and 

others, 2006; Kimball and others, 2002; Kimball and others, 

2006). Understanding the ground-water flow and dissolved 

metal transport is essential in determining whether sampled 

metal loads to streams are related to acid-mine drainage or 

acid-rock drainage, and thus, whether or not an identified 

source of metal loading should be remediated.

In an effort to understand the ground-water flow system 

in the upper Animas River watershed, Prospect Gulch (fig. 1) 

was selected for further study because of the amount of data 

provided in and around that particular watershed (Church and 

others, 2006), including stream tracer studies (Kimball and 

others, 2002; Wirt and others, 1999, 2001) and detailed maps 

of hydrothermal alteration (Bove and others, 2006). In addition, many of the inactive mines within Prospect Gulch are on 

land managed by the Bureau of Land Management (BLM). 

An understanding of the ground-water flow system is critical 

in assisting them with their remedial efforts. In support of this 

ground-water research effort, data was collected from drill 

core, which included: (1) detailed descriptions of the subsurface geology and hydrothermal alteration patterns, (2) depth 

of sulfide oxidation, and (3) quantitative mineralogy. The data 

from these cores will be used to support the calibration of a 

ground-water model in this area and provide the basis for a 

holistic model of the hydrogeochemistry of Prospect Gulch. 

This report summarizes all of the core related mineralogy that 

was collected.

Mineralogy from Cores in Prospect Gulch, San Juan 

County, Colorado

By Dana J. Bove, Raymond H. Johnson, and Douglas B. Yager
Geologic Setting

The predominant rock types in the Prospect Gulch study 

area consist of intermediate- to silicic-composition igneous rocks. These rocks formed following formation of the 

28.2-Ma San Juan caldera, coincident with and (or) postdating formation of the 27.8-Ma Silverton caldera (Yager and 

Bove, 2002). Intermediate-composition lava flows and minor 

volcaniclastic sedimentary rocks that were deposited on the 

flanks of central vent volcanoes predominate this igneous 

sequence and are part of the Silverton Volcanics described 

by Lipman and others (1973). Silverton Volcanics lavas and 

volcaniclastic sediments shed from the adjacent volcanoes 

infilled the San Juan caldera volcanic depression to nearly a 

kilometer in thickness over an approximately 14-km-diameter 

area. Primary igneous minerals of the Silverton Volcanics 

intermediate-composition porphyritic lavas include, in relative 

order of abundance, plagioclase, quartz, hornblende, pyroxene, ± biotite, and opaque oxide minerals.

A regional propylitic alteration event affected much of 

the study area following caldera formation (Burbank, 1960). 

The propylitic alteration formed as the large thickness of lavas 

that infilled the San Juan caldera cooled and degassed, altering the primary igneous mineral assemblage to a secondary 

assemblage containing chlorite, ± epidote, ± calcite, ± pyrite, 

fine-grained muscovite, and iron oxide minerals. This propylitic assemblage was shown to have some acid-neutralizing 

capacity where it was not more intensely altered by later 

hydrothermal alteration events (Yager and others, 2005).

Prospect Gulch is located on the margin of the historic 

Red Mountain mining district, where ore deposits of silver, copper, lead, and zinc sulfides were discovered in 1881 

(Burbank, 1947) and is located near the northwest structural 

margins of the San Juan and Silverton calderas. This area is 

the locus for several small-volume plugs and dikes of dacite to 

rhyolite composition that intruded along the structural margins 

of the calderas, after caldera activity ceased. Isotopic ages of 

intrusions near Prospect Gulch indicate that they also formed 

several million years after eruption of the intermediatecomposition Silverton Volcanics lavas (unit Tsv as noted in 

Appendix core logs) during the Miocene Epoch, which are 

thought to have provided the heat source for the hydrothermal 

system that was responsible for mineralization and associated 

alteration in and adjacent to the Red Mountain mining district 

(Lipman and others, 1976; Bove and others, 2001).

Several alteration types formed contemporaneously with 

or shortly after intrusive activity at approximately 23 Ma 

(Bove and others, 2001), overprinting the regional propylitic 

assemblage and locally eliminating any acid-neutralizing 

capacity while introducing acid-generating minerals, especially pyrite. These assemblages are particularly evident in the 

vicinity of Red Mountain #3 (fig. 2) whose slopes drain into 

Prospect Gulch. The summit and slopes of Red Mountain #3 

are stained with secondary mineral coatings that are caused 

mainly by the oxidation and weathering of pyrite. The mineral 

coatings impart spectacular hues of red, yellow, and brown, 

which led to the naming of the Red Mountains.

The geology of the area and types of alteration vary 

substantially from north to south across the Prospect Gulch 

subbasin (Bove and others, 2006). The majority of intensely 

altered terrain is exposed along the northern part of the subbasin on south-facing slopes along and beneath the ridge that 

separates Dry Gulch from Prospect Gulch (fig. 2). Acid sulfate 

mineralization is exposed near Red Mountain #3 and is characterized by an acid-sulfate mineral assemblage that includes 

quartz, alunite, pyrophyllite (QAP assemblage), and pyrite. 

Pervasive silicification accompanied the acid sulfate alteration 

where it forms highly resistant ridges such as those exposed on 

Red Mountain #3. Poorly indurated and more easily weathered 

argillic (ARG assemblage) alteration occurs on the margins of 

the QAP assemblage; dickite (a waxy clay mineral in outcrop) is commonly associated with this assemblage. Pervasive 

quartz-sericite-pyrite (QSP assemblage) alteration, locally 

containing 10–20 volume percent pyrite where not oxidized, 

is the largest alteration type exposed in Prospect Gulch. The 

QSP assemblage commonly crops out topographically below 

or adjacent to the QAP and ARG assemblages. Similar to the 

ARG assemblage, the QSP assemblage (especially near the 

margins) is more readily weathered than the QAP assemblage. 

Surficial deposits including debris cones and talus that have 

formed below Red Mountain #3 incorporate clasts of the 

upslope QAP, ARG, and QSP assemblages.

In the southern part and lower one-third of Prospect 

Gulch, regional propylitic alteration dominates, although it is 

locally overprinted by narrow, more intensely altered zones 

of QAP and QSP assemblages that are exposed in northeasttrending gulleys in the upper part of the subbasin that drain 

toward the north into Prospect Gulch. Locally, surficial deposits involving mainly propylitically altered clasts, whose source 

is located along the ridge that separates Georgia Gulch from 

Prospect Gulch, are volumetrically important.

A general structural fabric is evident in and around 

Prospect Gulch based on interpretation of mapped veins (D.J. 

Bove, unpub. data, 2005; Bove and others, 2006). Northwest-, 

north-, and northeast-trending veins are evident along with 

another prominent set of east-west-trending veins. These veins 

may have formed along existing faults or formed contemporaneously with mineralization along structural zones of weakness. East-west-trending veins are not as common as their 

north-trending counterparts, but they do occur. Major structures, if present, are obscured largely by the intense alteration 

that has affected much of the northern subbasin. Additional 

detailed mapping is needed to determine offset of marker horizons along faults (if any are preserved) such as interbedded 

volcaniclastic units within the Silverton Volcanics. However, 

mapped offsets in the upper Prospect Gulch area are as much 

as 100 m (D.J. Bove, unpub. data, 2005)

 Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Hydrologic Setting

The stream in Prospect Gulch is approximately 2.4 km 

in length with an elevation change of 800 m. Average annual 

precipitation is about 114 cm with 94 cm occurring as snowfall (Wirt and others, 2001). As a result, most recharge into 

the ground-water system occurs in late May and early June 

during the spring snowmelt. Late June through September is 

dominated by summer thunderstorms, producing rainfall that 

provides additional ground-water recharge (Wirt and others, 

1999). Snow generally covers the ground surface in most of 

Prospect Gulch from October through early May, preventing 

any significant recharge to the ground water-system.

Drilling Locations, Core Logs, and 

Oxidation Depth

All drill hole locations with core data in Prospect Gulch 

are shown in figure 3 and table 1. The drill core locations for 

UPG, MPG, and LPG (upper, middle, and lower Prospect 

Gulch) were drilled in 2004 as part of a Raymond Johnson’s 

Mendenhall Postdoctoral Research Program with the USGS. 

Core locations labeled as M were core drilled in 1983 by 

Amoco Minerals (unpub. data) and locations labeled as H 

were rotary drilled by Caldedonia Resources in 1984 (unpub. 

data).

Original core logs for UPG, MPG, and LPG are provided 

in Johnson and Yager (2006). Additional detailed description 

of the cores for UPG, MPG, and LPG were completed as part 

of the sample collection process for mineralogy and are provided as appendices A through C. The depths of the partially 

oxidized zone and the fully oxidized zone are presented in 

figures 4 and 5, respectively.

Mineralogy from Cores

Quantitative mineralogy was determined by X-ray diffraction (XRD) for all samples and is presented in tables 2 

through 7. Ultimately, this mineralogy data will be used to better understand the rock/water interactions that are occurring in 

Prospect Gulch. The samples were prepared according to the 

methods described by Srodon and others (2001). In summary, 

3 g of sample were mixed with 0.333 g of an internal standard 

(zincite). The mixture was subsequently ground with 4 mL 

of methanol in a McCrone mill for 5 minutes, oven dried at 

85°C, passed through a 4 mm sieve, and then side-loaded into 

an aluminum holder to optimize random orientation. Samples 

were X-rayed from 5 to 65° 2θ with CuKα radiation (40 Kv, 

30 mA) using a Siemens D500 X-ray diffraction system with a 

graphite monochromator, 1° slits, a step size of 0.02° 2/θ, and 

a counting time of 2 s per step.

The XRD data were converted into wt% minerals using 

the RockJock computer software (Eberl, 2003). The program 

compares integrated X-ray intensities for minerals present in 

a sample with that of an internal zincite standard, and weight 

percents are calculated from previously measured mineral 

intensity factors (MIF’s; also referred to as reference intensity 

ratios, RIR’s). Integraged X-ray intensities for individual minerals were determined by fitting stored XRD patterns for pure 

mineral phases to the measured XRD pattern using the Solver 

option in Microsoft Excel. The Solver option minimized the 

degree of fit parameter between measured and calculated patterns by varying the intensities of the stored standard patterns 

by multiplying each of these patterns by a separate factor.

The RockJock technique has been checked for accuracy 

using artificial mixtures, and generally results are within 1 

to 2 wt % of actual values (Eberl, 2003). All mineral weight 

percentages presented in tables 2 through 7 were normalized 

to 100 %. X-ray amorphous material was determined to be 

negligible due to low backgrounds in the XRD patterns and 

the nature of the rock samples.

References Cited

Besser, J.M., Finger, S.E., and Church, S.E., 2006, Impacts 

of historical mining on aquatic ecosystems—An ecological risk assessment, in Church, S.E., von Guerard, P., and 

Finger, S.E., eds., Integrated investigations of environmental 

effects of historical mining in the Animas River watershed, 

San Juan County, Colorado: U.S. Geological Survey Professional Paper 1651.

Bove, D.J., Hon, K., Budding, K.E., Slack, J.F., Snee, L.W., 

and Yeoman, R.A., 2001, Geochronology and geology of 

late Oligocene through Miocene volcanism and mineralization in the western San Juan Mountains, Colorado: U.S. 

Geological Survey Professional Paper 1642, 30 p. http://

pubs.usgs.gov/of/1999/ofr-99-0347/.

Bove, D.J., Mast, M.A., Dalton, J.B., Wright, W.G., and Yager, 

D.B, 2006, Major styles of mineralization and hydrothermal 

alteration and related solid- and aqueous-phase geochemical signatures, in Church, S.E., von Guerard, P., and Finger, 

S.E., eds., Integrated investigations of environmental effects 

of historical mining in the Animas River watershed, San 

Juan County, Colorado: U.S. Geological Survey Professional Paper 1651.

Burbank, W.S., 1947, Red Mountain District, Ouray County in 

Vanderwilt, J.W., ed., Mineral resources of Colorado: State 

of Colorado, Mineral Resources Board.

Burbank, W.S., 1960, Pre-ore propylitization, Silverton 

Caldera, Colorado, in Geological Survey Research 1960: 

U.S. Geological Survey Professional Paper 400–B, article 6, 

p. B12–B13.

References Cited 
Church, S.E., von Guerard, P., and Finger, S.E., eds., 2006, 

Integrated investigations of environmental effects of historical mining in the Animas River watershed, San Juan 

County, Colorado: U.S. Geological Survey Professional 

Paper 1651, 6 plates, 1 DVD.

Eberl, D.D., 2003, User guide to RockJock–A program for 

determining quantitative mineralogy from X-ray diffraction 

data: U.S. Geological Survey Open-File Report 2003–78, 

40 p.

Johnson, R.H., and Yager, D.B., 2006, Completion reports, 

core logs, and hydrogeologic data from wells and piezometers in Prospect Gulch, San Juan County, Colorado: U.S. 

Geological Survey Open-File Report 2006–1030, http://

pubs.usgs.gov/of/2006/1030/.

Kimball, B.A., Runkel, R.L., Walton-Day, K.W., and Bencala, K.E., 2002, Assessment of metal loads in watersheds 

affected by acid mine drainage by using tracer injection 

and synoptic sampling — Cement Creek, Colorado, USA: 

Applied Geochemistry, v. 17, p. 1183–1207.

Kimball, B.A., Walton-Day, K., and Runkel, R.L., 2006, 

Quantification of metal loading by tracer injection and synoptic sampling, 1996–2000, in Church, S.E., von Guerard, 

Paul, and Finger, S.E., eds., Integrated investigations of 

environmental effects of historical mining in the Animas 

River Watershed, San Juan County, Colorado: U.S. Geological Survey Professional Paper 1651.

Lipman P.W., Fisher, W.S., Mehnert, H.H., Naeser, C.W., 

Luedke, R.G., and Steven, T.A., 1976, Multiple ages of 

mid-Tertiary mineralization and alteration in the western 

San Juan Mountains, Colorado: Economic Geology, v. 71, 

p. 571–588.

Lipman, P.W., Steven, T.A., Luedke, R.G., and Burbank, W.S., 

1973, Revised volcanic history of the San Juan, Uncompahgre, Silverton, and Lake City calderas in the western San 

Juan Mountains, Colorado: U.S. Geological Survey Journal 

of Research, v. 1, p. 627–642.

Manning, A.H., Solomon, D.K., and Sheldon, A.L., 2003. 

Applications of a total dissolved gas pressure probe in 

ground water studies: Ground Water, v. 41, p. 440–448.

Mast, M.A., Verplanck, P.L., Wright, W.G., and Bove, D.J., 

2006, Characterization of background water quality, in 

Church, S.E., von Guerard, P., and Finger, S.E., eds., Integrated investigations of environmental effects of historical 

mining in the Animas River watershed, San Juan County, 

Colorado: U.S. Geological Survey Professional Paper 

1651.

Srodon, J., Drits, V.A., McCarty, D.K., Hsieh, J.C., and Eberl, 

D.D., 2001, Quantitative mineral analysis by powder X-ray 

diffraction from random preparations: Clays and Clay Minerals, v. 49, p. 514–528.

Wirt, L., Leib, K.J., Bove, D.J., Mast, M.A., Evans, J.B., and 

Meeker, G.P., 1999, Determination of chemical-constituent 

loads during base-flow and storm-runoff conditions near 

historical mines in Prospect Gulch, upper Animas River

 watershed, southwestern Colorado: U.S. Geological Survey 

Open-File Report 99–159, 39 p.

Wirt, L., Leib, K.J., Bove, D., and Melick, R., 2001, Metal 

loading assessment of point and non-point sources in a 

small alpine sub-basin characterized by acid drainage—

Prospect Gulch, upper Animas River watershed, Colorado: 

U.S. Geological Survey Open-File Report 2001–0258, 36 p.

Yager, D.B., and Bove, D.J., 2002, Generalized geologic map 

of part of the upper Animas River watershed and vicinity, 

Silverton, Colorado: U.S. Geological Survey Miscellaneous 

Field Studies Map MF–2377, scale 1:48,000.

Yager, D.B., McCafferty, A.E., Stanton, M.R., Diehl, S.F., 

Driscoll, R.L., Fey, D.L., and Sutley, S.J., 2005, Net acid 

production, acid neutralizing capacity, and associated 

geophysical, mineralogical, and geochemical characteristics 

of Animas River watershed rocks near Silverton, Colorado: 

U.S. Geological Survey Open-File Report 2005, 78 p.

 Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Figure 1. Location of Prospect Gulch in the upper Animas River watershed.

Figure 1. 
H-5

Figure 2. Detailed alteration map of bedrock in Prospect Gulch and the surrounding area.

 Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
!

!

!

!

!

!

!

! !

! !

!

LPG-D

MPG-D

UPG-D 

H-5

H-4

RM-1 H-6

RM-2 

RM-3 

RM-4 

RM-6 

RM-5 

Figure 3. Drill hole locations in Prospect Gulch.

Figure 3. 
!

!

!

!

!

!

!

! !

!

!

!

99

85

34

45

75

70 250 

113 

387 

360 

110 

230 

Figure 4. Depth of the partially oxidized zone in feet. (Note that the 113-foot depth of the partially oxidized zone in RM-2 is the 

total depth of the hole.)

 Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
!

!

!

!

!

!

!

! !

! !

!

0

0

34

25

20

0 250 

113 

211 

225 

110 

230 

Figure 5. Depth of the fully oxidized zone in feet. (Note that the 113-foot depth of the fully oxidized zone in RM-2 is the total 

depth of the hole.)

Figure 5. 
Location Latitude 

(decimal

degrees) 

Longitude 

(decimal

degrees) 

Depth of 

partially 

oxidized 

zone (ft) 

Depth of 

fully 

oxidized 

zone (ft) 

UPG-D 37.8952827 -107.6848674 34 34 

MPG-D 37.8922303 -107.6811235 0 85 

LPG-D 37.8829656 -107.6677624 0 99 

RM-1 37.8976240 -107.6914280 250 250 

RM-2 37.8987050 -107.6925920 113 113 

RM-3 37.8995550 -107.6922720 211 387 

RM-4 37.9002040 -107.6911050 225 360 

RM-5 37.8979080 -107.6906400 230 230 

RM-6 37.8987730 -107.6906380 110 110 

H-4 37.8957820 -107.6808580 20 75 

H-5 37.8963210 -107.6812110 25 45 

H-6 37.8958660 -107.6804270 0 70 

Table 1. Drill hole locations and oxidation depths. (Note that total depth for RM-2 is 113 feet.)

[ft, feet]

10 Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Sample name: PGU-22 Sample name: PGU-38 

 

Alteration QPs Alteration QSP-P

Mineral

Normalized results 

Weight % Mineral 

Normalized results 

Weight % 

NON-CLAYS NON-CLAYS 

Quartz 56.7 Quartz 31.5 

Pyrite 6.9 Pyrite 8.5 

Alunite 0.7 Alunite 0.2 

Jarosite 2.1 Jarosite 0.2 

Hematite 0.0 Rutile 0.9 

Goethite 1.2 Svanbergite 2.1 

Anatase 0.1 Total non-clays 41.4

Rutile 1.1 

Maghemite 0.3 CLAYS:

Diaspore minor Illite/muscovite 34.1 

Svanbergite minor Pyrophyllite 22.4 

Total non-clays: 69.0 Total clays 56.5 

 FPF 0.1023 

CLAYS: TOTAL 100.0 

Illite/muscovite 4.7 

Pyrophyllite 26.3 

Kaolinite tr 

Total Clays: 31.0 

FPF 0.0987 

TOTAL 100.0 

Alteration type 

Alteration assemblage as 

mapped in fig. 2 

QPS Quartz-pyrophyllite with major sericite qap-s 

QPs Quartz-pyrophyllite with minor sericite qap-s 

QSP-P Quartz-sericite-pyrite with major 

pyrophyllite

qap-s 

QSP-p Quartz-sericite-pyrite with minor 

pyrophyllite

qsp 

QSP-Arg Quartz-sericite-pyrite with late kaolinite/dickite qsp 

Table 2. Mineralogy in UPG-D samples from X-ray diffraction analyses (sample number indicates depth in feet).

[FPF, full pattern fit]

Table 2. 11
Sample name: PGU-40 Sample name: PGU-47 

 

Alteration QSP-p Alteration QSP-Arg

Mineral

Normalized results 

Weight % Mineral 

Normalized results 

Weight % 

NON-CLAYS NON-CLAYS 

Quartz 55.1 Quartz 39.3 

Pyrite 8.4 Pyrite 16.6 

Rutile 0.5 Jarosite 0.3 

Svanbergite minor Goethite 0.1 

Total non-clays: 64.1 Anatase 0.1 

 Rutile 1.0 

CLAYS: Svanbergite minor 

Illite/muscovite 31.7 Total non-clays: 57.3

Pyrophyllite 4.2 

Total Clays: 35.9 CLAYS:

FPF 0.0983 Dickite/kaolinite 11.1 

TOTAL 100.0 Illite/muscovite 31.7 

Total Clays: 42.7

 FPF 0.0997 

 TOTAL 100.0 

Sample name: PGU-90 Sample name: PGU-102 

 

Alteration QSP-P Alteration QPS

Mineral

 Normalized results 

 Weight % Mineral 

Normalized results 

Weight % 

NON-CLAYS NON-CLAYS 

Quartz 43.9 Quartz 43.4 

Pyrite 2.3 Pyrite 9.0 

Jarosite 1.0 Alunite 0.2 

Goethite 1.2 Jarosite 1.7 

Anatase 0.1 Goethite 0.6 

Rutile 1.2 Anatase 0.1 

Svanbergite minor Rutile 0.6 

Total non-clays: 49.7 Svanbergite minor 

Total non-clays: 55.6

CLAYS: 

Illite/muscovite 37.8 CLAYS:

Pyrophyllite 12.5 Dickite/kaolinite 3.9 

Total Clays: 50.3 Illite/muscovite 12.9 

FPF 0.0982 Pyrophyllite 27.6 

TOTAL 100.0 Total Clays: 40.4

 FPF 0.1013 

 TOTAL 100.0 

Table 2. Mineralogy in UPG-D samples—Continued.

12  Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Sample name: PGU-125 

Alteration QPS

Mineral

Normalized results 

Weight % 

NON-CLAYS 

Quartz 37.2 

Pyrite 19.9 

Alunite 1.0 

Jarosite 0.5 

Goethite 0.3 

Rutile 1.0 

Svanbergite minor 

Total non-clays: 59.9

CLAYS:

Dickite/kaolinite 1.8 

Illite/muscovite 17.9 

Pyrophyllite 22.2 

Total Clays: 38.3

FPF 0.0967 

TOTAL 100.0 

Table 2. Mineralogy in UPG-D samples—Continued.

Table 2. 13
Alteration type 

 

Alteration assemblage as 

mapped in fig. 2 

 

QP Quartz-pyrophyllite qap

QPS Quartz-pyrophyllite with major 

sericite 

qap-s

QSP Quartz-sericite-pyrite qsp

QSP-P Quartz-sericite-pyrite with major pyrophyllite qap-s

QSP-p Quartz-sericite-pyrite with minor pyrophyllite qsp

Sample name: PGM-67-70 Sample name: PGM-80 

 

Alteration QSP-P Alteration QSP-P

Mineral

Normalized results 

Weight % Mineral 

Normalized results 

Weight % 

NON-CLAYS NON-CLAYS 

Quartz 49.8 Quartz 45.2 

Anhydrite 0.1 Anhydrite 0.2 

Gypsum 0.7 Gypsum 0.7 

Goethite 0.1 Goethite 0.9 

Rutile 1.1 Maghemite 0.4 

Pyrite 9.0 Rutile 0.9 

Barite 1.6 Pyrite 7.1 

Alunite 0.5 Barite 0.6 

Jarosite 3.8 Alunite 0.3 

Diaspore 4.9 Jarosite 1.8 

Sphalerite 3.9 Diaspore 8.0 

Svanbergite 0.6 Svanbergite 1.4 

Total non-clays 76.1 Total non-clays 67.6

 

 

CLAYS: CLAYS:

disordered 

Kaolinite 0.1 

disordered 

Kaolinite 4.3 

ordered Kaolinite 2.4 ordered Kaolinite 2.6 

Pyrophyllite 18.0 Pyrophyllite 22.8 

Illite/muscovite 27.3 Illite/muscovite 2.6 

Total clays 23.9 Total clays 32.5

FPF 0.1113 FPF 0.0992 

TOTAL 100.0 TOTAL 100 

Table 3. Mineralogy in MPG-D samples from X-ray diffraction analyses (sample number indicates depth in feet).

[FPF, full pattern fit]

14  Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Sample

name: PGM-88 Sample name: PGM-100 

 

Alteration QP Alteration QSP-P

Mineral

Normalized results 

Weight % Mineral 

Normalized results 

Weight % 

NON-CLAYS NON-CLAYS 

Quartz 45.5 Quartz 42.4 

Gypsum 0.3 Pyrite 8.0 

Goethite 0.2 Anhydrite 0.1 

Rutile 0.7 Goethite 0.8 

Pyrite 5.1 Anatase 0.6 

Barite 0.4 Svanbergite 1.0 

Alunite 0.0 Total non-clays 52.9

Jarosite 0.2 

Diaspore 2.1 CLAYS:

Svanbergite 1.0 Illite/muscovite 34.0 

Total nonclays 55.5 Pyrophyllite 13.1 

Total clays 47.1

 FPF 0.1033 

CLAYS: TOTAL 100.0 

Pyrophyllite 44.5 

Total clays 44.5 

FPF 0.0979 

TOTAL 100 

Table 3. Mineralogy in MPG-D—Continued.

Table 3. 15
Sample name: PGM-108 Sample name: PGM-119 

 

Alteration QSP-p Alteration QP

Mineral

Normalized results 

Weight % Mineral 

Normalized results 

Weight % 

NON-CLAYS NON-CLAYS 

Quartz 37.1 Quartz 18.3 

Pyrite 4.8 Gypsum 0.3 

Anhydrite 0.3 Goethite 0.2 

Gypsum 0.3 Pyrite 12.0 

Jarosite 0.2 Jarosite 0.2 

Goethite 0.5 

Total nonclays 31.1

Anatase 0.2 

Rutile 0.3 CLAYS:

Svanbergite 1.4 Pyrophyllite 68.9 

Total nonclays 45.1 Total clays 68.9

 FPF 0.1012 

CLAYS TOTAL 100.0 

Illite/muscovite 47.8 

Pyrophyllite 7.1 

Total clays 54.9 

FPF 0.1011 

TOTAL 100.0 

 

Table 3. Mineralogy in MPG-D—Continued.

16  Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Sample name: PGM-133 Sample name: PGM-143 

 

Alteration QSP Alteration QSP-P

Mineral

Normalized results 

Weight % Mineral 

Normalized results 

Weight % 

NON-CLAYS NON-CLAYS 

Quartz 48.5 Quartz 46.6 

Anhydrite 0.2 Anhydrite 0.2 

Gypsum 0.4 Gypsum 0.1 

Goethite 0.4 Maghemite 0.3 

Rutile 0.7 Anatase 0.3 

Pyrite 7.4 Rutile 0.3 

Barite 0.3 Pyrite 10.4 

Alunite 0.2 Alunite 0.6 

Jarosite 1.2 Svanbergite 1.7 

Total nonclays 59.3 Total non-clays 58.8

 

CLAYS: CLAYS:

Illite/muscovite 40.7 Illite/muscovite 26.5 

Total clays 40.7 Pyrophyllite 13.0 

FPF 0.0999 Total clays 39.4

TOTAL 100.0 FPF 0.0937 

 TOTAL 100.0 

Table 3. Mineralogy in MPG-D—Continued.

Table 3. 17
Sample name: PGM-157 Sample name: PGM-166 

 

Alteration QSP-P Alteration QSP

Mineral

Normalized results 

Weight % Mineral 

Normalized results 

Weight % 

NON-CLAYS NON-CLAYS 

Quartz 35.5 Quartz 36.9 

Pyrite 11.8 Anhydrite 0.5 

Anhydrite 0.5 Gypsum 0.5 

Bassanite 0.1 Goethite 0.3 

Alunite 0.3 Maghemite 0.3 

Goethite 0.4 Rutile 0.8 

Anatase 0.1 Pyrite 11.2 

Rutile 0.7 Barite 0.3 

Ilmenite 0.1 Alunite 0.1 

Svanbergite 2.5 Total non-clays 50.9

Total nonclays 52.1 

 CLAYS: 

CLAYS:

disordered 

Kaolinite 1.1 

Illite/muscovite 37.4 Illite/muscovite 48.0 

Pyrophyllite 10.4 Total clays 49.1

Total clays 47.9 FPF 0.0967 

FPF 0.0988 TOTAL 100.0 

TOTAL 100.0 

 

Table 3. Mineralogy in MPG-D—Continued.

18  Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Table 3. Mineralogy in MPG-D—Continued.

Sample name: PGM-171 

Alteration QSP-p

Mineral

Normalized results 

Weight % 

NON-CLAYS 

Quartz 37.7 

Anhydrite 0.3 

Goethite 0.3 

Anatase 0.1 

Rutile 0.4 

Pyrite 12.1 

Barite 0.4 

Alunite 0.2 

Total non-clays 51.5

CLAYS:

disordered 

Kaolinite 0.1 

Illite/muscovite 43.4 

Pyrophyllite 5.0 

Total clays 48.5

FPF 0.1017 

TOTAL 100.0 

Table 3. 19
Alteration type Alteration assemblage 

 as mapped in fig. 2 

PROPA Propylitic with secondary albitization pr

WSP-PROP Propylitic to weak sericite pyrite wsp-pr 

WSP-PROPA

-WSP Propylitic (with secondary albitization) grading to weak sericitic wsp-pr 

WSP-QSP Weak sericite pyrite to quartz-sericite pyrite wsp-pr 

QSP Quartz-sericite-pyrite qsp

Sample name: PGL-13 Sample name: PGL-87.5 

 

Alteration

WSP-PROP (clast in 

ferricrete) Alteration WSP-PROP

Mineral

Normalized 

Weight % Mineral 

Normalized 

Weight % 

NON-CLAYS NON-CLAYS 

Quartz 34.9 Quartz 58.7 

Albite feldspar 4.0 Gypsum 0.2 

Andesine feldspar 2.3 Bassanite 0.2 

Gypsum 0.5 Jarosite 0.5 

Jarosite 2.0 Sanidine feldspar 10.0 

Goethite 9.0 Orthoclase feldspar 3.3 

Maghemite 1.7 Albite feldspar 11.3 

Apatite 0.6 Andesine feldspar 0.5 

Anatase 13.0 Pyrite 0.5 

Rutile 0.3 Total non-clays 85.2

Total non-clays 68.4 

CLAYS

CLAYS: disordered Kaolinite 2.5 

Illite/muscovite 31.6 Biotite 0.1 

Total clays 31.6 Illite/muscovite 10.5 

FPF 0.0931 Chlorite 1.6 

TOTAL 100.0 Total clays 14.8

 FPF 0.0996 

 TOTAL 100.0 

Table 4. Mineralogy in LPG-D samples from X-ray diffraction analyses (sample number indicates depth in feet).

[FPF, full pattern fit]

20 Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Table 4. Mineralogy in LPG-D—Continued.

Sample name: PGL-93 Sample name: PGL-103 

 

Alteration WSP-PROPA Alteration WSP-PROP

Mineral

 Normalized 

 Weight % Mineral

Normalized 

Weight % 

NON-CLAYS NON-CLAYS 

Quartz 34.5 Quartz 36.8 

Gypsum 0.3 Gypsum 0.1 

Bassanite 0.1 Bassanite 0.3 

Jarosite 0.2 Epidote 2.0 

Epidote 1.1 Sanidine feldspar 21.3 

Sanidine feldspar 7.3 Orthoclase feldspar 4.2 

Orthoclase feldspar 4.0 Albite feldspar 10.9 

Albite feldspar 33.1 Pyrite 2.1 

Andesine feldspar 0.3 Total non-clays 77.7

Pyrite 0.4 

Total non-clays 81.3 CLAYS

 disordered Kaolinite 3.6 

CLAYS Biotite 0.3 

disordered Kaolinite 1.6 Illite/muscovite 13.2 

Illite/muscovite 10.9 Chlorite 5.2 

Chlorite 6.1 Total clays 22.3

Total clays 18.7 FPF 0.1017 

FPF 0.1001 TOTAL 100.0 

TOTAL 100.0 

Table 4.  21
Table 4. Mineralogy in LPG-D—Continued.

Sample name: PGL-109 Sample name: PGL-119 

 

Alteration PROPA Alteration WSP-QSP

Mineral

Normalized 

Weight % Mineral 

Normalized 

Weight % 

NON-CLAYS NON-CLAYS 

Quartz 18.8 Quartz 48.0 

Gypsum 0.1 Goethite 0.1 

Bassanite 0.1 Rutile 0.2 

Hematite 0.2 Sanidine feldspar 0.2 

Maghemite 1.7 Albite feldspar 5.6 

Apatite 0.3 Pyrite 1.4 

Sanidine feldspar 16.5 

Orthoclase feldspar 7.8 Total non-clays 55.6 

Albite feldspar 36.9 

Andesine feldspar 3.4 CLAYS 

Pyrite 0.1 disordered Kaolinite 0.2 

Total non-clays 86.0 Biotite 0.8 

 Illite/muscovite 35.9 

CLAYS Chlorite 7.5 

disordered Kaolinite 1.1 Total clays 44.4 

Chlorite 7.7 FPF 0.0972 

Illite/muscovite 5.2 TOTAL 100.0 

Total clays 13.9 

FPF 0.0993 

TOTAL 100.0 

22  Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Table 4. Mineralogy in LPG-D—Continued.

Sample name: PGL-129 Sample name: PGL-136.5 

 

Alteration WSP-QSP Alteration WSP-QSP

Mineral

 Normalized 

 Weight % Mineral 

Normalized Weight 

%

NON-CLAYS NON-CLAYS 

Quartz 42.2 Quartz 44.1 

Goethite 0.4 Albite feldspar 11.5 

Rutile 0.3 Pyrite 5.1 

Orthoclase feldspar 0.4 Rutile 0.2 

Albite feldspar 5.1 Total non-clays 60.8 

Pyrite 4.4 

 CLAYS: 

Total non-clays 52.7 Illite/muscovite 35.0 

 Chlorite (CCa-1) 4.2 

CLAYS Total clays 39.2 

disordered Kaolinite 10.3 FPF 0.1136 

Illite/muscovite 29.6 TOTAL 100.0 

Chlorite (CCa-1) 7.6 

Total clays 47.4 

FPF 0.0999 

TOTAL 100.0 

Table 4.  23
Table 4. Mineralogy in LPG-D—Continued.

Sample name: PGL-142.5 Sample name: PGL-149 

Alteration QSP Alteration WSP-QSP

Mineral

Normalized 

Weight % Mineral 

Normalized 

Weight % 

NON-CLAYS NON-CLAYS 

Quartz 52.9 Quartz 45.2 

Pyrite 2.0 Goethite 0.2 

Rutile 0.2 Maghemite 0.0 

Total non-clays 55.1 Rutile 0.1 

Sanidine feldspar 6.6 

CLAYS: Orthoclase feldspar 2.6 

disordered 

Kaolinite 3.1 Albite feldspar 8.3 

Illite/muscovite 33.6 Pyrite 2.2 

Chlorite (CCa-1) 8.1 Total non-clays 65.1 

Chlorite (CCa-3) 1.2 

Total clays 44.9 CLAYS 

FPF 0.1004 disordered Kaolinite 8.5 

TOTAL 100.0 Illite/muscovite 23.8 

Chlorite (CCa-1) 2.6 

Total clays 34.9 

FPF 0.1002 

TOTAL 100.0 

24  Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Table 4. Mineralogy in LPG-D—Continued.

Sample name: PGL-159 

Alteration WSP-PROPA

Mineral

Normalized 

Weight % 

NON-CLAYS 

Quartz 33.5 

Bassanite 0.3 

Magnetite 0.2 

Rutile 0.4 

Sanidine feldspar 8.9 

Orthoclase feldspar 3.6 

Albite feldspar 39.6 

Andesine feldspar 3.3 

Pyrite 1.2 

Total non-clays 80.9 

CLAYS

disordered Kaolinite 1.5 

Biotite 8.2 

Illite/Muscovite 5.2 

Chlorite 4.2 

Total clays 19.1 

FPF 0.0997 

TOTAL 100.0 

Table 4.  25
Sample name: H4-164 Sample name: H4-166 

 

Lithology

Dark clast-supported 

breccia Lithology Medium gray lavas 

Alteration QAp Alteration QAp

Mineral

Normalized results 

Weight % Mineral 

Normalized results 

Weight % 

NON-CLAYS NON-CLAYS 

Quartz 51.0 Quartz 60.4 

Anhydrite 1.8 Anhydrite 2.1 

Gypsum 0.0 Bassanite 0.5 

Jarosite 0.0 Goethite 0.1 

Magnetite 0.0 Maghemite 1.4 

Hematite 0.0 Anatase 0.0 

Maghemite 1.9 Rutile 1.1 

Anatase 0.0 Pyrite 4.8 

Rutile 0.7 Alunite 17.2 

Pyrite 10.9 Natroalunite 6.4 

Alunite 14.6 Total non-clays 94.0

Natroalunite 9.3 

Diaspore 3.0 CLAYS

Svanbergite 1.7 Pyrophyllite 6.0 

Total nonclays Total clays 6.0

94.8 FPF 0.0993 

CLAYS TOTAL 100 

Pyrophyllite 5.3 

Total clays 5.3 

FPF 0.0971 

TOTAL 100 

Alteration 

type 

Alteration assemblage 

as mapped in fig. 2 

 

QAP Quartz-alunite-pyrophyllite qap

QAp Quartz-alunite with minor pyrophyllite qap

Pyroph-a Pyrophyllitic with minor alunite qap

QSP-p Quartz-sericite-pyrite with minor pyrophyllite qsp

QPS Quartz-pyrophyllite with major sericite qap-s

Table 5. Mineralogy in H-4 samples from X-ray diffraction analyses (sample number indicates depth in feet).

[FPF, full pattern fit]

26  Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Table 5. Mineralogy in H-4—Continued.

Sample name: H4-164 Sample name: H4-166 

 

Lithology

Dark clast-supported 

breccia Lithology Medium gray lavas 

Alteration QAp Alteration QAp

Mineral

Normalized results 

Weight % Mineral 

Normalized results 

Weight % 

NON-CLAYS NON-CLAYS 

Quartz 51.0 Quartz 60.4 

Anhydrite 1.8 Anhydrite 2.1 

Gypsum 0.0 Bassanite 0.5 

Jarosite 0.0 Goethite 0.1 

Magnetite 0.0 Maghemite 1.4 

Hematite 0.0 Anatase 0.0 

Maghemite 1.9 Rutile 1.1 

Anatase 0.0 Pyrite 4.8 

Rutile 0.7 Alunite 17.2 

Pyrite 10.9 Natroalunite 6.4 

Alunite 14.6 Total non-clays 94.0

Natroalunite 9.3 

Diaspore 3.0 CLAYS

Svanbergite 1.7 Pyrophyllite 6.0 

Total nonclays Total clays 6.0

94.8 FPF 0.0993 

CLAYS TOTAL 100 

Pyrophyllite 5.3 

Total clays 5.3 

FPF 0.0971 

TOTAL 100 

Alteration 

type 

Alteration assemblage 

as mapped in fig. 2 

 

QAP Quartz-alunite-pyrophyllite qap

QAp Quartz-alunite with minor pyrophyllite qap

Pyroph-a Pyrophyllitic with minor alunite qap

QSP-p Quartz-sericite-pyrite with minor pyrophyllite qsp

QPS Quartz-pyrophyllite with major sericite qap-s

Table 5.  27
Table 5. Mineralogy in H-4—Continued.

Sample name: H4-267 Sample name: H4-580 

 

Lithology

Dark matrix-supported 

breccia Lithology 

Dark clast and matrix-supported 

breccia 

Alteration Pryoph-a Alteration QAp

Mineral

Normalized results 

Weight % Mineral 

Normalized results 

Weight % 

NON-CLAYS NON-CLAYS 

Quartz 1.9 Quartz 45.3 

Anhydrite 0.1 Maghemite 1.0 

Gypsum 0.1 Anatase 0.2 

Jarosite 0.0 Rutile 0.7 

Magnetite 0.6 Pyrite 7.6 

Hematite 0.2 Alunite 27.1 

Maghemite 0.0 Natroalunite 11.5 

Anatase 0.0 Svanbergite 1.0 

Rutile 0.8 Zunyite minor 

Pyrite 16.2 

Total nonclays 95.7

Alunite 6.7 

Svanbergite 2.2 CLAYS

Total non-clays 26.7 Pyrophyllite 4.3 

Total clays 4.3

CLAYS FPF 0.1061 

Pyrophyllite 71.2 TOTAL 100 

Total clays 71.2 

FPF 0.1124 

TOTAL 100 

 

28  Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Table 5. Mineralogy in H-4—Continued.

Sample name: H4-602 Sample name: H4-649 

 

Lithology

Dark clast-supported 

breccia Lithology Dark breccia; feint texture 

Alteration QAp Alteration QAp

Mineral

Normalized results 

Weight % Mineral 

Normalized results 

Weight % 

NON-CLAYS NON-CLAYS 

Quartz 54.8 Quartz 52.3 

Anhydrite 2.2 Anhydrite 1.8 

Gypsum 0.0 Maghemite 2.2 

Jarosite 0.0 Anatase 0.0 

Magnetite 0.0 Rutile 0.7 

Hematite 0.0 Pyrite 12.7 

Maghemite 1.8 Alunite 10.5 

Anatase 0.0 Natroalunite 12.3 

Rutile 0.6 Svanbergite 1.8 

Pyrite 6.3 Total non-clays 94.9

Alunite 11.5 

Natroalunite 14.9 CLAYS

Svanbergite 2.5 Pyrophyllite 5.1 

Total non-clays 94.7 Total clays 5.1

 FPF 0.1009 

CLAYS TOTAL 100 

Pyrophyllite 5.3 

Total clays 5.3

FPF 0.1011 

TOTAL 100 

Table 5.  29
Sample name: H4-655 Sample name: H4-690 

 

Lithology

Gray matrix-supported 

breccia Lithology Medium gray lavas 

Alteration QAP Alteration QSP-p

Mineral

Normalized results 

Weight % Mineral 

Normalized results 

Weight % 

NON-CLAYS NON-CLAYS 

Quartz 30.3 Quartz 41.1 

Anhydrite 2.5 Anhydrite 0.3 

Gypsum 0.3 Anatase 0.1 

Maghemite 1.9 Rutile 0.6 

Anatase 0.2 Pyrite 12.1 

Rutile 0.8 Alunite 0.1 

Pyrite 18.9 Total non-clays 54.3

Alunite 20.0 

Natroalunite 13.1 CLAYS

Svanbergite 0.8 Illite/Muscovite 41.2 

Total non-clays 88.4 Pyrophyllite 4.6 

Total clays 45.7

CLAYS FPF 0.0979 

Pyrophyllite 11.6 TOTAL 100 

Total clays 11.6 

FPF 0.0969 

TOTAL 100 

Table 5. Mineralogy in H-4—Continued.

30 Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Table 5. Mineralogy in H-4—Continued.

Sample name: H4-711 Sample name: H4-720 

 

Lithology Gray breccia Lithology 

Gray matrix supported 

breccia 

Alteration QPS Alteration QAP

Mineral

Normalized results 

Weight % Mineral 

Normalized results 

Weight % 

NON-CLAYS NON-CLAYS 

Quartz 33.6 Quartz 44.1 

Anhydrite 0.2 Anhydrite 1.1 

Gypsum 0.1 Gypsum 0.1 

Jarosite 0.3 Magnetite 0.5 

Maghemite 0.3 Hematite 0.2 

Rutile 0.7 Rutile 0.8 

Pyrite 11.1 Pyrite 9.4 

Alunite 0.4 Alunite 6.3 

Total non-clays 46.6 Natroalunite 11.3 

Total non-clays 73.8

CLAYS 

Illite/Muscovite 24.4 CLAYS

Pyrophyllite 29.0 Illite/Muscovite 1.1 

Total clays 53.4 Pyrophyllite 25.1 

FPF 0.0993 Total clays 26.2

TOTAL 100 FPF 0.9989 

 TOTAL 100 

Table 5.  31
Table 6. Mineralogy in H-5 samples from X-ray diffraction analyses (sample number indicates depth in feet).

[FPF, full pattern fit]

Alteration type 

Alteration assemblage 

as mapped in fig. 2 

 

QSP Quartz-sericite-pyrite qsp

QAp qap

Sample name: H5-20 Sample name: H5-25 

 

Lithology Light gray lavas Lithology Light gray lavas 

Alteration QSP Alteration QSP

Mineral

Normalized results 

Weight % Mineral 

Normalized results 

Weight % 

NON-CLAYS NON-CLAYS 

Quartz 40.7 Quartz 44.6 

Gypsum 0.1 Anatase 0.6 

Jarosite 12.0 Pyrite 2.2 

Anatase 0.5 Total non-clays 47.3

Pyrite 0.1 

Total non-clays 53.3 CLAYS

 Illite/Muscovite 52.3 

CLAYS Pyrophyllite 0.3 

Illite/Muscovite 46.4 Total clays 52.7

Pyrophyllite 0.3 FPF 0.1064 

Total clays 46.7 TOTAL 100 

FPF 0.1010 

TOTAL 100 

32  Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Table 6. Mineralogy in H-5 samples—Continued.

Sample name: H5-30 Sample name: H5-36 

 

Lithology Gray lavas Lithology 

Gray matrix-supported 

breccia 

Alteration QSP Alteration QSP

Mineral

Normalized results 

Weight % Mineral 

Normalized results 

Weight % 

NON-CLAYS NON-CLAYS 

Quartz 40.0 Quartz 27.3 

Anhydrite 0.2 Anhydrite 0.0 

Gypsum 0.0 Gypsum 0.6 

Barite 0.3 Jarosite 0.7 

Goethite 0.4 Anatase 0.5 

Pyrite 7.9 Pyrite 8.4 

Total non-clays 48.9 Total non-clays 37.6

 

CLAYS CLAYS

Illite/Muscovite 51.1 Illite/Muscovite 62.4 

Total clays 51.1 Total clays 62.4

FPF 0.1117 FPF 0.1017 

TOTAL 100 TOTAL 100 

Sample name: H5-386 Sample name: H5-434 

 

Lithology

Gray matrixsupported breccia Lithology Gray matrix-supported 

breccia 

Alteration QAp Alteration QSP

Mineral

Normalized results 

Weight % Mineral 

Normalized results 

Weight % 

NON-CLAYS NON-CLAYS 

Quartz 52.3 Quartz 42.0 

Anhydrite 1.8 Anhydrite 0.3 

Maghemite 1.5 Gypsum 0.0 

Anatase 0.2 Anatase 0.8 

Rutile 0.9 Rutile 0.0 

Pyrite 3.1 Pyrite 2.0 

Alunite 25.7 Alunite 0.1 

Natroalunite 10.1 Total non-clays 45.2

Total non-clays 95.4 

CLAYS

CLAYS Illite/Muscovite 53.5 

Pyrophyllite 4.6 Pyrophyllite 1.3 

Total clays 4.6 Total clays 54.8

FPF 0.0991 FPF 0.1016 

TOTAL 100 TOTAL 100 

Table 6.  33
Table 7. Mineralogy in H-6 samples from X-ray diffraction analyses (sample number indicates depth in feet).

[FPF, full pattern fit

Alteration type 

Alteration assemblage as 

mapped in fig. 2 

QSP-p

Quartz-sericite-pyrite with minor 

pyrophyllite qsp

QSP-P

Quartz-sericite-pyrite with major 

pyrophyllite qap-s

QPS Quartz-pyrophyllite with major sericite qap-s

QPs Quartz-pyrophyllite with minor sericite qap-s

Sample name: H6-80 Sample name: H6-87 

 

Lithology Medium gray lavas Lithology Dark gray lavas 

Alteration QSP-p Alteration QSP-p

Mineral

Normalized 

Weight % Mineral

Normalized 

Weight % 

NON-CLAYS NON-CLAYS 

Quartz 35.7 Quartz 30.0 

Anhydrite 0.3 Anhydrite 0.5 

Gypsum 0.6 Gypsum 0.2 

Jarosite 0.4 Hematite 0.1 

Maghemite 0.5 Maghemite 1.4 

Anatase 0.1 Anatase 0.0 

Rutile 0.2 Rutile 0.4 

Pyrite 10.0 Pyrite 10.6 

Total non-clays 47.8 Total non-clays 43.2

 

CLAYS CLAYS

Illite/Muscovite 49.4 Illite/Muscovite 53.4 

Pyrophyllite 2.8 Pyrophyllite 3.4 

Total clays 56.8

Total clays 52.2 FPF 0.1201 

FPF 0.0969 TOTAL 100 

TOTAL 100 

34  Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Table 7. Mineralogy in H-6—Continued.

Sample name: H6-451 Sample name: H6-458 

 

Lithology Dark gray lavas Lithology 

Dark clast-supported 

breccia 

Alteration QPS Alteration QSP-P

Mineral

Normalized 

Weight % Mineral 

Normalized 

Weight % 

NON-CLAYS NON-CLAYS 

Quartz 34.1 Quartz 35.0 

Anhydrite 0.3 Anhydrite 0.2 

Gypsum 0.3 Anatase 0.3 

Goethite 0.3 Rutile 0.4 

Rutile 0.8 Pyrite 10.8 

Pyrite 8.1 Total non-clays 46.7

Bassanite 0.2 

Alunite 0.6 CLAYS

Jarosite 0.1 Illite/Muscovite 38.4 

Total non-clays 44.9 Pyrophyllite 14.8 

Total clays 53.3

CLAYS FPF 0.0985 

Illite/Muscovite 24.7 TOTAL 100 

Pyrophyllite 30.4 

Total clays 55.13 

FPF 0.0967 

TOTAL 100 

Table 7.  35
Table 7. Mineralogy in H-6—Continued.

Sample name: H6-460 

Lithology Dark clast-supported breccia 

Alteration QPs

Mineral

Normalized 

Weight % 

NON-CLAYS 

Quartz 37.8

Jarosite 0.1

Anatase 0.0

Rutile 0.6

Pyrite 10.0

Alunite 0.3

Total non-clays 48.8

CLAYS

Illite/Muscovite 7.4

Pyrophyllite 43.8

Total clays 51.2

FPF 0.0967

TOTAL 100

36  Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Interval from 22 to 30.6 ft. (material above 22 ft. 

was unconsolidated and not cored)

Interval from 22 to 27 ft comprised of altered dacite porphyry 

intrusive rock (Tdp) that becomes brecciated near 26.5 ft. The 

dacite porphyry (which could be a large boulder-sized clast 

in breccia) is cut at high angle by a light gray, finer grained, 

matrix-supported breccia. The matrix-supported breccia is 

comprised of clastic material (generally <1-4 mm) but tends 

to envelop a larger clast of Tdp and dark gray silicified rock 

(up to 5 cm) near its top. The Tdp clast has very irregular 

and somewhat embayed margins. Although difficult to 

discern, the breccia could have an intrusive matrix; discerning this from a fine clastic matrix is impossible without thin 

sections. Both Tdp and breccias are moderately silicified and 

strongly pyrophyllite-altered. Remnant biotite in Tdp has 

mostly altered to sericite, however sericite is relatively minor 

compared to pyrophyllite in entire interval. There are several 

small faults/fractures with slickensides. A small, high angle 

fault dipping about 45° cuts the dacite porphyry near 22.8 ft. 

This small fault zone (~2 cm wide) is brecciated and contains 

angular clasts of altered Tdp that range from several mm’s to 

as much as 2-3 cm. The associated breccia is suspended in 

a yellow-brown, oxidized clay matrix (fig. 1a). Clay in this 

fault zone is dominantly dickite or kaolinite with perhaps 

some pyrophyllite. Two other similar brecciated zones associated with fractures occur at 23.5 ft (~4cm), 24 ft (~5cm), 

and 25.5 ft. Fractures and brecciated fault zones contain two 

generations of clay (fig. 1b). The youngest clay is yellowbrown and highly oxidized. X-ray diffraction (XRD) studies 

indicate that these clays contain abundant jarosite, major finegrained muscovite or illite (R3 ordering and < 10% smectite 

interlayers)–referred from hereon as sericite–with minor to 

moderate amounts of dickite. The yellow clay is predated by 

white clay that commonly fills the same fractures or broken 

zones (fig. 1b). The later white clay is commonly waxy looking and offset slightly by fractures that contain jarositic, yellow clay. These white clays are comprised of major amounts 

of dickite, minor to major pyrophyllite (harder varieties may 

contain more pyrophyllite), and very minor sericite. Dark 

gray and highly silicified clasts become more abundant at 27 

ft. The breccia is still matrix-supported (light gray breccia 

matrix), however the dark silicified clasts are as much as 50 

% of this breccia. The dark silicified clasts are up to about 5 

to 6 cm. Clast margins are commonly rounded but can be very 

irregular, perhaps owing to alteration by the hydrothermal 

fluids or fluidized light gray breccias. The silicified clasts 

also contain moderate amounts of pyrophyllite and minor sericite. A larger brecciated but more coherent 1 foot “clast” of 

the dark silicified rock shows a high angle but very irregular 

contact with light gray, matrix-supported breccia at 29 ft. The 

body of this silicified clast is internally shattered and broken 

(non-rotated breccia), but also becomes net-veined by finer 

breccia from 29.5 to 30.5 ft. White, hard and waxy looking 

pyrophyllite with some dickite (as described above) fills fractures and formed as a replacement locally adjacent to broken 

and brecciated fractures. Minor to moderate amounts of fine 

pyrite tends to be more abundant in the finer grained, matrixsupported breccias. Overall pyrite content in the entire interval ranges from about 3 to 7 %. Original pyrite is irregularly 

oxidized in this core interval, especially adjacent to oxidized 

fracture/rubble zones (fig 1c). Jarosite and goethite is abundant and commonly localized along this and similar fractures 

zones. A 1-2 cm light gray, “bleached zone” borders the high 

angle fracture in figure 1c. Similar bleached zones are present 

in other core intervals. These bleached zones can easily be 

mistaken as darker clasts with irregular margins suspended in 

the light gray, matrix- supported breccia. These textures will 

be noted in ensuing descriptions as “bleached zone textures”

Appendix A. Core log for UPG-D

Appendix A. Core log for UPG-D  37
c

h

 Fig. 1c 

Fig. 1a 

Fig. 1b 

22 ft. 

30.6 ft. 

23.5 ft. 

22.8 ft. 

22.4 ft. 

38  Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Interval from 30.6 to 38.8 ft.

Breccia continues in this core interval; multiple periods of 

brecciation make paragenesis quite complex. Matrix-supported 

breccia continues from 30 to 33 ft, however, silicified clasts 

are less common. Instead, there are a number of clasts of varying lithology with highly reacted margins. “Bleached zone” 

breccia textures are again localized adjacent to a 5-6 cm, 

jarosite/goethite oxidized fracture zone near 31ft. These textures may give rise to the dark, irregular and wispy dark margin (~1cm) around the light gray, angular clast (3 cm) at 30.8 

ft. Spectral data suggest light and darker zones in “bleached 

zones” are similarly altered. Similar complex textures and true 

breccias continue to about 33.5ft. Bleached zones are accentuated around four to five oxidized and clay-lined fractures. The 

oxidized and clay-lined fracture zones are generally < 0.5 cm 

wide with dips from horizontal to high angles; slickensides 

are present along some of these fractures and appear to postdate some of the jarosite-stained clays. The presence of high 

temperature clays in these late fractures (dickite and pyrophyllite) and later slickensides, suggest that they formed during 

later stages of the hydrothermal system. Jarosite and goethite 

staining may generally reflect later and low temperature acid 

weathering. At 30.6 ft through 34 ft there are abundant fractures filled with late jarositic clay as described above. Oxidation continues with jarosite and some goethite along with 

abundant clays along fractures to about 34 ft. Below this zone 

the strong oxidation greatly diminishes. Coarse grained, clastsupported breccia dominates in interval from 33.5 to 35 ft. 

Clasts are angular to subangular (5-15 cm), dark and silicified 

(likely altered lavas), and suspended in a light colored, matrixsupported breccia; clasts in the matrix breccia are generally 

irregular in shape, have subangular to subrounded margins, 

and are < 1cm; clasts in the finer matrix are mostly rotated 

pieces of the dark silicified rock that are healed in a light tan 

to white, silicified and sericite/pyrophyllite-altered matrix (fig 

1d). The percent of larger silicified clasts greatly decreased 

from 35 to 38.8 ft as the matrix-supported breccia component 

becomes dominant. However, silicified clasts in the matrixsupported breccia become coarser grained and elongate in 

places, with subparallel orientations (length 4 to 5 cm and 

width about 1 cm or less; fig. 1e). This entire core interval is 

mostly unoxidized and contains abundant fine-grained pyrite 

(averaging 8-10%).

30.6 ft. 

38.8 ft. 

Fig. 1e (37 ft.) 

Fig. 1d (35 ft) 

Appendix A. Core log for UPG-D  39
Interval from 38.8 to 47 ft.

These rocks are also hydrothermally brecciated (fine lavas 

unless otherwise noted) as noted at the bottom of the last core 

interval; breccia textures are also similar. The clasts are irregular and silicified and commonly elongate. The breccias range 

from matrix-supported to clast-supported. There are approximately four or five fracture zones with abundant yellow 

jarosite and associated clays as described above. Rocks in this 

interval are mildly to moderately silicified with sericite gradually becoming much greater than pyrophyllite in the clay portion; near 47 ft, pyrophyllite is absent and sericite dominates 

these moderately silicified rocks; there are also some fractures filled with white clay consisting mostly of pyrophyllite 

47 ft. 

38.8 ft. 

and lesser dickite. Breccias in interval from about 40 to 47 ft. 

become more clast-supported and clasts are highly elongate 

and subparallel. Elongate clasts are mostly dark and silicified, 

and most do not appear to be rotated. Although the matrix is 

still clastic, bleached zone textures (as described in interval 

22 to 30.6 ft.) may also be present. Darker clasts are highly 

silicified with pyrophyllite greater than sericite; alteration 

in the lighter altered matrix becomes dominated by sericite. 

There is late, white, and translucent to waxy-looking sericite 

that cements the breccia clasts at about 58 ft. Both clasts and 

especially breccia matrix contains abundant, finely disseminated pyrite (7-16 %). Pyrite abundances are similar to that in 

the intervals above, with jarosite and goethite largely confined 

to the few local, clay-filled fracture zones.

40 Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Interval from 47 to 58 ft.

Similarly complex breccias to that described in above intervals. 

Subparallel clast textures as above with some more equant 

silicified clasts to 52 ft. Lighter gray, matrix-supported and finer 

grained breccias dominate from 52 to about 54.5 ft. Back into 

coarser grained breccias that are largely clast-supported in interval from 54.5 to 58 ft. Clasts in this interval are largely bimodal: 

dark and silicified as above, and with relic porphyry texture. 

47 ft. 

58 ft. 

Both clast types are as much as 4-5 cm and have angular to 

irregular and embayed margins. Some of the porphyritic and 

altered clasts have white waxy sericite in fractures; these white 

fractures or clay healed zones are truncated at clast margins. 

The lighter, finer grained breccia and porphyritic clasts are moderately silicified and have sericite and minor pyrophyllite. Finegrained pyrite is unoxidized in this interval, averaging about 

10%. One moderately dipping, oxidized clay-lined fracture cuts 

the finer matrix-supported breccia at 53 ft.

Appendix A. Core log for UPG-D  41
58 ft. 

67 ft. 

fractures in interval to from 58 to 64 ft.; a steeply dipping 

fracture at 64 ft. is jarositic and clay lined and has a slickensided slip face. A breccia and rubble zone with abundant 

jarositic clay continues from the footwall of the fault to 

66.7 ft. Jarositic clay is abundant throughout the rubble, 

clasts, and matrix of this footwall interval. The earlier 

formed, white dickite/pyrophyllite-rich clay is also abundant in this interval. Clasts in the breccia/rubble zone are 

1 to 3 cm and of the same alteration type and lithology as 

that on the hanging wall of the small fault. Although pyrite 

is highly oxidized in the brecciated rubble from about 54 to 

67 ft., it is unoxidized and abundant from 58 to 64 ft.

Interval from 58 to 67 ft.

Rocks are dark, highly brecciated and highly silicified; 

clays are comprised of sericite and minor pyrophyllite. 

There are several 1 to 3 mm-wide fractures filled with the 

white soft clay. The white clay consists of dickite with 

minor to moderate pyrophyllite. The late, yellow-brown, 

jarositic clay fills some of the same fractures, but post-dates 

the white clays. Clay XRD studies verify similar compositions to the jarositic clays described above (major R3 

sericite; minor to moderate dickite, and abundant jarosite). 

There are approximately two jarositic and clay-lined 

42  Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Interval from 67 to 75 ft.

Highly silicified and very dark breccias (fine lavas) from 

67 to 68 ft.; these rocks are broken and highly fractured in 

this interval; this zone reflects the margins of the interval 

described from 64 to 66.7 ft. Jarositic clay also is present 

along fractures from 67 to 68 ft. From 68 to 72 ft. the rock is 

dominated by highly silicified and sericitic altered lavas; primary texture is nearly obliterated. Dark gray, massive silicification diminishes from 69 to 72 ft. Relic texture of sericitic 

altered lavas (light gray zones) becomes more recognizable 

in this 3-ft. interval. The lighter colored, sericitic altered 

lavas in this zone are cut by abundant stockwork-like fine 

quartz ± pyrite veinlets. Rather than a chaotic stockwork, 

these dense veinlets tend to be more subparallel and have 

moderate dips. The rocks become very dark and highly silicified from 72 to 75 ft. and appear to be highly brecciated and 

mostly clast-supported. However, the breccia texture in this 

silicified interval is more difficult to discern. There are some 

small vugs that average about 0.5 cm in this last silicified 

interval. Fine-grained pyrite averages more than 8-10% in 

this entire core interval.

67 ft. 

75 ft. 

Appendix A. Core log for UPG-D  43
Interval from 75.8 to 83.5 ft.

Interval is similar to above; however, this zone is all highly brecciated and contains zones of very coarse, clast-supported breccia. Some of the breccia clasts are 15 to 20 cm across and are 

subrounded to subangular. However, there is some finer breccia 

that is largely matrix-supported. There are four or five strongly 

fractured and broken zones in the entire core interval. All of 

these fractures and broken zones localized the jarositic clay. The 

nature of breccia and alteration in this interval is quite similar 

to that described from 38.8 to 47 ft. The breccia clasts are dark 

and highly silicified; sericite is the dominant clay in the lighter 

matrix dominated portions. Pyrite, as noted above, is finely 

disseminated and highly abundant, probably on the order 10% 

or more. There are also some pyritic veins that cut throughout 

this entire interval. There are several zones with fractures that 

contain the white dickite/pyrophyllite clay as described above. 

These clays are late paragenetically, but pre-date the yellowbrown jarositic clays. The relative paragenesis of these late clays 

remains consistent with that observed in previous core intervals.

75.8 ft. 

83.5 ft. 

44  Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Interval from 83.5 to 91 ft.

There is a high angle, brecciated fracture zone at 83 ft. with 

the late jarositic clay. Rocks are mostly brecciated in this 

entire interval, however, the breccia textures are more difficult 

to discern and probably fine grained. The breccia clasts tend 

to have irregular margins; breccia dominates to about 89 ft. 

Light gray, sericitic altered lavas and likely some breccias are 

present form 89 to 91ft. These rocks are cut by abundant, very 

dark, stockwork quartz ± pyrite veinlets. The margins of the 

veinlets are rather diffuse with widths ranging for 1-2 mm up 

to 0.5 cm. Although these still approximate “stockwork” fabric, many veinlets are roughly subparalell with moderate dips. 

The dips of these and other veinlets throughout this core may 

be influenced by foliation. With exception of the darker more 

silicified zones and clasts, lighter colored rocks in this interval 

are moderately silicified and are dominated by sericitic clays 

with a trace of pyrophyllite; towards the bottom of the interval 

pyrophyllite increases. Fine pyrite is abundant in this interval 

but decreases to about 2-4% in the last 2 to 3 ft.

83.5 ft. 

91 ft. 

Appendix A. Core log for UPG-D  45
Interval from 91 to 98.5 ft.

Highly brecciated lavas continue; these are cut by abundant, 

very dark, stockwork quartz ± pyrite veinlets (see description from 89-91 ft.). The rocks become darker and massively 

silicified from 95-96 ft. Dark quartz veinlets with diffuse 

margins emanate from the silicified zone at 95 ft. and cut the 

lighter gray, more sericitic altered, brecciated lavas. Highly 

broken and probably small fault zones are present at 95, 96 

and 97 ft. These zones contain late jarositic clay mixed with 

minor clasts. The late, white dickite/pyrophyllite clay is also 

present in these zones. Although this interval is highly brecciated, much of the breccia texture is difficult to discern. Except 

in the dark and highly silicified zones, sericite is much more 

abundant than pyrophyllite. Pyrophyllite increases toward the 

bottom of this interval. Pyrite is abundant, as described above.

91 ft. 

98.5 ft. 

46  Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Interval from 98.5 to 106 ft.

Breccia as described above from 98.5 to 99 ft. Interval then 

grades into brecciated dacite porphyry (Tdp) at about 100 ft.; 

breccias alternate with Tdp to 101 ft. Dacite porphyry is dominant from 101 to about 106 ft. The feldspar phenocrysts in the 

altered dacite porphyry are white, sericite and pyrophyllitealtered; whereas, the aphanitic groundmass is predominantly 

quartz-pyrophyllite-altered; pyrophyllite is more abundant 

than sericite in the dacite groundmass. The dacite porphyry is 

net veined by breccia or fine-grained breccia zones (described 

below). There are several fracture zones within this interval; 

fracture at 100 ft. is high angle and contains jarositic clay. 

Another high angle fracture at 103 ft. contains white, waxylooking dickite and pyrophyllite. As described above, these 

fracture filling clays are paragenetically late; jarositic staining 

is minimal. A high angle, jarosite-lined fracture is also present 

at 105 ft. This fracture contains some pyrophyllite-kaolinite; 

these clays are coated by the later jarosite. Most of core interval, with exception of brecciated Tdp zones, is moderately to 

highly silicified. The more silicified zones are finely vuggy in 

places. Dacite porphyry zones contain less disseminated pyrite 

than breccias, but still average roughly 5% or more. Interval 

from 101 to ~106 ft. is characterized by zones with irregular, 

almost stockwork-like pyrite veinlets; veinlet margins are very 

diffuse and irregular. Most of these veinlets measure up to 4 

to 5 mm but some are as much as 1 cm across. Breccia within 

this interval is mostly matrix-supported to but ranges to clast 

supported; breccia clasts are commonly subrounded generally 

less than 1 cm across.

98.5 ft. 

106 ft. 

Appendix A. Core log for UPG-D  47
Interval from 106 to 114.5 ft.

The Tdp intrusion (or block of intrusive dacite net veined by 

breccia) continues to about 110 ft. The bottom of Tdp interval 

has a gradational contact with breccia that coarsens away form 

the contact. Breccia in interval below has subangular clasts 

ranging from 15 to 30 cm across that are in turn suspended 

in a matrix-supported breccia. There are several high angle 

fracture zones that contain kaolinite and pyrophyllite; the rest 

of the interval is highly silicified with abundant disseminated 

pyrite. Sericite is generally more abundant than pyrophyllite in 

the more silicified intervals. Alteration of Tdp is similar to that 

described in the previous interval.

106 ft. 

114.5 ft. 

114.5 ft. 

48  Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Interval from 114.5 to 123 ft.

This zone is largely coarse-grained, clast-supported breccias that alternate with more matrix-supported hydrothermal 

breccias. The clasts are highly silicified as observed in above 

breccia intervals. Breccias are also moderately to highly silicified with sericite much more abundant than pyrophyllite in the 

clay fraction. Late pyrophyllite and kaolinite are present along 

a number of fracture zones in this interval. Later jarosite lines 

these fractures as well.

114.5 ft. 

114.5 ft. 

123 ft. 

Appendix A. Core log for UPG-D  49
Interval from 123 to 131.5 ft.

Interval is highly brecciated with textures similar to above. 

Breccias are highly silicified with sericite much more abundant than pyrophyllite to about 125 ft. However, at 126 ft., 

sericite and pyrophyllite are approximately subequal. There 

is a substantial high angle fracture at 128 ft. that is lined 

with thin kaolinite and pyrophyllite and a later thin jarositic 

clay. Another similar fracture zone is present at about 129 ft. 

There is also abundant vug-filling pyrite that fills the matrix 

around breccia clasts. The pyrite that fills these smaller 

and irregular matrix vugs in the matrix is euhedral but still 

relatively fine-grained.

123 ft. 

131.5 ft. 

50 Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Interval from 131.5 to 138 ft.

Interval contains highly silicified, coarse-grained, clast-supported 

hydrothermal breccias. Clasts are generally angular to subrounded. Most of the clasts are highly silicified. Pyrophyllite 

abundance in this silicified interval increases to about 135 ft. and 

is more abundant than sericite. There is a high angle fracturefilling veinlet that contains relatively fine to medium grained, 

potassium alunite and lesser pyrophyllite at 134 ft. At 135 ft., 

pyrophyllite and lesser alunite are present as the major alteration 

phases–as always less than quartz. Some of the breccias have a 

matrix healed with alunite and pyrophyllite. The alunite abundance is probably greater than pyrophyllite in these healed breccia 

zones. There are also some minor vuggy zones that contain late 

pyrite in some of these breccias; there is also some fine-grained 

but euhedral pyrite that appears to post-date the alunite veinlets.

131.5 ft. 

138 ft. 

Interval from 138 to 153 ft.

Complex and multi-generational hydrothermal breccias. 

Rocks are highly silicified and clays consist largely of pyrophyllite; alunite is minor. White fracture-filling pyrophyllite 

is common. The breccias are mostly clast-supported with 

subangular to angular clasts; the larger clasts are up to about 

15 cm across. Clasts are comprised of multiple lithologies 

with different degrees of silicification. There are some later, 

mostly matrix-supported hydrothermal breccias that cut 

the coarser grained breccias; these later breccias generally 

have finer grained clasts. Pyrite throughout this interval is 

relatively fine-grained and commonly cements the breccia 

matrix. There are many voids and vuggy areas between 

clasts. The vuggy areas are partially filled with finer grained 

pyrite. There are also late pyritic veinlets. These veinlets are 

about 3-4 mm and cross-cut breccia clasts and matrix. The 

lithologies and textures of the clasts are difficult to distinguish; however they are likely to be fine-grained lavas (Tsv). 

Breccias become clast-supported in the interval from 151 to 

153 ft. The clasts appear to be mostly non-rotated and comprised largely of fine-grained lavas of the Silverton Volcanics 

(Tsv); some of the altered feldspar phenocrysts are recognizable in the clasts. Clasts in this interval range from 10-15 cm 

across. A fracture at 149 ft. contains the yellow oxidized clay 

that is predominantly jarositic with abundant sericite and 

minor kaolinite/dickite. There is another low angle fracture 

at 157 ft. with the same yellow clay assemblage.

Appendix A. Core log for UPG-D  51
138 ft. 

145.5 ft. 

145.5 ft. 

153 ft. 

52  Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Interval from 153 to 176.3 ft.

Coarse-grained, clast-supported breccias are dominant from 

153-157 ft. These coarse grained breccias have late, finegrained and prismatic quartz and some drusy quartz crystals 

lining vugs. The vugs are up 4-5 cm across; minor finegrained pyrite post-dates the quartz in these vugs. Interval 

from 157-176.3 ft. is characterized by fine-grained breccias 

and some brecciated lavas; the lavas are cut by abundant 

1-3 mm pyrite veinlets. Rocks in this entire interval are 

highly silicified, strongly sericitized, and contain minor 

pyrophyllite. Late fracture-filling pyrophyllite becomes more 

abundant in the lower parts of this core interval. Fine-grained 

pyrite typically exceeds 8-10%.

153 ft. 

160.5 ft. 

Appendix A. Core log for UPG-D  53
160.5 ft. 

168 ft. 

168 ft. 

176.3 ft. 

54  Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Interval from 176.3 to 190.7 ft.

This interval is mostly fine-grained lavas and brecciated lavas 

as above; however, breccias become slightly more prevalent. 

Rocks are highly silicified and sericitized, and contain minor 

pyrophyllite. Pyrite is abundant and occurs in clots after mafics and along tiny fractures and veinlets. The lavas textures are 

still easily discerned due to pyrite pseudomorphs after mafic 

phenocrysts. Pyrite content 10-12%.

176.3 ft. 

184 ft. 

184 ft. 

190.7 ft. 

Appendix A. Core log for UPG-D  55
Interval from 190.7 to 223.8 ft.

Rocks comprised mostly of moderately to highly silicified, 

Qsp-altered lavas and brecciated lavas. The breccias are less 

abundant in this interval. Fine-grained, porphyritic textures are 

readily discerned in this interval. There are several intervals 

with stockwork pyrite veinlets averaging 1-3 mm. There 

are a few zones that are more brecciated; these intervals are 

highly silicified and are commonly vuggy. The vuggy areas 

are similar to that described in the previous core intervals. 

There are several fracture zones filled with very fine-grained, 

white kaolinite/dickite. Several fractures also contain the late 

jarositic clay as described above. Fractures filled or lined by 

these late clays are mostly high angle.

198.8 ft. 

190.7 ft. 

56  Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
206.5 ft. 

198.8 ft. 

213.9 ft. 

206.5 ft. 

Appendix A. Core log for UPG-D  57
219.8 ft. 

213.9 ft. 

223.8 ft. 

219.8 ft. 

58  Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Appendix B. Core log for MPG-D

Interval from 67 to 75.3 ft. (material above 67 ft. 

was unconsolidated and not cored)

Entire interval is moderately silicified (50-55% quartz), Qspaltered breccias. These rocks are overprinted by late-stage 

clay alteration comprised of pyrophyllite with minor dickite. 

Pyrite content averages about 10% in the unoxidized rock; 

sphalerite is locally abundant (4-5%). Interval from 67-67.5 

ft. is jigsaw breccia with non-rotated and corroded clasts 

(Tsv lavas); open/vuggy areas in breccia matrix (2-5mm) 

filled by white pyrophyllite rich clay and pyrite. These open 

areas/vugs are filled with two generations of white clay. 

The earliest is snow white and somewhat waxy; this clay is 

comprised of an intimate mixture of dickite and kaolinite. 

A layer of paragenetically younger white clay (fine sugary 

appearance), containing only pyrophyllite, is the latest clay 

in this vug-filling sequence. The latest pyrophyllitic clay 

alternates paragenetically with an abundance of fine but 

euhedral pyrite. A few crystals of dark-green, fine-grained 

(< 2mm), botryoidal sphalerite, are latest in this vug-filling 

sequence. This breccia transitions into (or perhaps is cut by) 

matrix-supported breccia to 70 ft.; these breccias contain a 

few larger, subrounded, and more sporadic clasts (1-2 cm). 

These more coherent breccias lack open space or vugs and 

are cut by a few discontinuous white veinlets (1-3 mm) filled 

with white pyrophyllite ± dickite. These breccias contain 

blebs of fine-grained pyrite and are cut by a relatively low 

density of pyrite veinlets as well. Interval from 70-72 ft. is 

comprised of coarser breccias as described above with late 

white clays in open matrix and a sphalerite-rich zone from 

70 to 71 ft. Paragenesis is same as above, however the dark 

green sphalerite is much more abundant and is up to 0.75 mm 

in width. Rather than veins, theses sphalerite grains fill open 

space in the breccia matrix. The sequence here establishes 

that base-metal sulfide deposition followed brecciation and 

very late stages of acid-sulfate alteration. Rock from 71 to 75 

ft. is finer matrix-supported breccia and brecciated lavas. An 

uneven fracture (~25o dip) cuts the coarser breccias at ~70 ft. 

and has a 2 cm iron-stained zone surrounding it. The fracture 

surface also localized a relatively thin clay-rich zone (1-3 

mm). Two small fractures with similar 20-25 degree dips 

localized oxidation at 71 ft. (very thin oxidation) and at 72 

ft. (banded oxidation about 3 cm). A very steep, clay-lined 

fracture cuts fine breccias/lavas at 73 ft. The fracture surface 

is clay-lined and strongly coated with goethite, jarosite, and 

hematite. The footwall of the fracture/fault localized highly 

clay altered rubble to 75 ft. Banded oxidation is present on 

both margins of this fractured zone.

67 ft. 

75.3 ft. 

Appendix B. Core log for MPG-D  59
Interval from 75.3 to 83.5 ft.

Mix of alternating coarse and fine-grained breccias/brecciated lavas as described above. The breccias are all compact 

and tight without open space in matrix. This zone is slightly 

less silicified, and is not cut by late, white clay-filled veinlets. These Qsp-altered rocks are also overprinted by about 

20% pyrophyllite and contain about 7-8% fine-grained pyrite. 

There are about five prominent fractures (30-50o dips, multiple 

directions) that localized jarositic and goethitic oxidation as 

described above (75; 76.5; 77; 77.5; 78 and 80 ft.). Fractures 

at 75 and 80 ft. localized clay and some breccia. Note that 

there is light gray oxidative bleaching (1 cm) around a couple 

of these fractures.

75.3 ft. 

83.5 ft. 

60 Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Interval from 83.5 to 91.6 ft.

Medium gray, moderately silicified, quartz-pyrophyllitealtered, coarse-grained and clast-supported breccias. There 

is very rare to minor amounts of sericite in this interval. 

Breccias are very complex, multigenerational, and clasts have 

a variety of shapes and are varied alteration types. Many of 

the clasts are subrounded to subangular; some have corroded 

margins. Pyrite concentration bands thinly surround many of 

the clasts. There is fine open space between some clasts, creating a slight vuggy appearance in places. White pyrophyllitic 

clay is prevalent as fillings in these spaces. White pyrophyllite 

and fine pyrite are abundant and form tight fillings throughout much of the breccia matrix. Moderately dipping fracture 

zones with iron staining and clay alteration are present at 85 

and 86.8 ft. Two shallow dipping fractures localized gray clay 

alteration, but no oxidation occurs near 88 ft. Fine-grained 

pyrite in this interval averages about 5-6% and is present 

mostly in the breccia matrix but rarely in veinlets.

83.5 ft. 

91.6 ft. 

Appendix B. Core log for MPG-D  61
Interval from 91.6 to 99.3 ft.

Breccia from above interval almost immediately transitions 

into light to medium gray, Qsp-altered and mildly silicified 

lavas (Tsv). This core interval has some very interesting 

textures created by diffuse pyrite flooding/alteration that 

localized along near vertical fractures; these diffuse zones are 

as much as 1 cm wide. The dark, near vertical pyritic zones 

branch into similarly wide and diffuse zones; these zones are 

at low angles to the core. These diffuse zones are subparallel 

to a low to moderate density of thin pyritic veinlets (1-3mm) 

that have more defined margins. The orientation of these 

veinlets/pyrite zones are likely subparallel to foliation. The 

fine porphyritic texture of the lavas is moderately obscured 

and matrix pyrite is in small blebs (1-2 mm). Average pyrite 

content in this zone is 5-8%.

91.6 ft. 

99.3 ft. 

62  Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Interval from 99.3 to 106.8 ft.

Interval is fairly similar to previous, however density of 

pyritic veinlets is increased and orientations may be in more 

conjugate sets. A very steep fracture zone with some clay and 

breccia cuts the core between 101 and 102 ft. The fracture is 

lined with medium gray clay. Another more moderately dipping fracture at 105 ft. separates altered lavas in the hanging 

wall from clast-supported breccia in the footwall to 106.8 

ft. The fracture is very sharp and has localized whitish-gray 

clay (dickite with pyrophyllite) and some breccia in this 

1-2 cm zone. Several other fractures faces in this interval have 

localized thin white clay comprised of dickite, pyrophyllite, 

and minor sericite. These fracture faces have also localized 

abundant fine-grained pyrite and very fine-grained sphalerite. 

Pyrite content in this interval averages 8-10%.

99.3 ft. 

106.8 ft. 

Appendix B. Core log for MPG-D  63
Interval from 106.8 to 115 ft.

Medium gray, Qsp-altered lavas (Tsv) are dominant to 111 

ft. Textures are somewhat similar to that in interval from 

93.7 to 99.4 ft. Qsp-altered breccias ranging from matrix 

to clast-supported are present in interval from 111 to 115 

ft. Pyrite flooding is more abundant throughout this breccia 

interval. White veinlets of pyrophyllite/dickite sporadically 

cut the entire core interval. Pyrophyllite alteration generally 

becomes more abundant from top to bottom of entire core 

interval. Pyrite content increases from about 5% in altered 

lavas to about 10-12% in the breccias.

106.8 ft. 

115 ft. 

64  Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Interval from 115 to 122 ft.

Very dark gray-blue, strongly pyrophyllite-altered assortment 

of hydrothermal breccias. Breccia textures and sizes are 

typical of above zones, tending toward more coarse-grained 

and clast-supported. Rocks are very soft and easily scratched 

owing to pervasive replacement by pyrophyllitic clay. A few 

discontinuous white pyrophyllite/dickite veinlets cut the 

breccia Fine-grained pyrite is abundant in this interval and 

ranges from 10-15%.

115 ft. 

122 ft. 

Appendix B. Core log for MPG-D  65
Interval from 122 to 130 ft.

Medium gray to gray-blue, Qsp and pyrophyllite-altered breccias; low to moderate silicification. Clast-supported breccia 

is darker gray (due to higher pyrite concentrations) and has 

entrained larger clasts of altered Tsv lavas (0.2 to 0.3 m). The 

clast-supported “matrix” that supports the larger clasts contains 

variously altered, subrounded to subangular clasts (4-8 mm). 

Fine-gained pyrite is localized in the matrix of these breccias 

and in places outlines the larger clast margins. The Tsv clasts 

are characterized by evenly distributed pyrite blebs (<1 mm). 

White pyrophyllite/dickite and associated fine pyrite in-filled 

breccia void space in the interval around 126 ft. Wispy and 

discontinuous veinlets of the same white clay are also common 

in the entire core interval. Pyrite content is roughly 8-10%.

122 ft. 

130 ft. 

66  Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Interval from 130 to 137.3 ft.

Breccias continue as above but are very dark gray due 

to increase in silicification (50-55% quartz. Interval is 

dominantly Qsp-altered with less pyrophyllite (similar to 

that described above). Rock is locally vuggy and these 

open spaces are either empty or filled with white clay 

(pyrophyllite). Several high-angle fractures at present at 132; 

134; 136 and 137 ft with some slickensides and later filling 

by white clays. Pyrite content ranges from 7-10%.

Sample at 136’ has an important paragenesis: Dark Qspaltered and more silicified breccia containing very fine pyrite 

(or a very large clast of previously brecciated rock) is cut by or 

perhaps supported in another breccia (clay alteration is possibly sericite). The later breccia (or matrix to the coarse breccia 

clast) is healed and/or replaced by a flesh colored mixture of 

pyrophyllite and minor natroalunite (if pyrite is present, it is 

very fine grained, sparse, and intermingled in alunite). All are 

cut by a 1-2 mm fracture filled with white pyrophyllite. The 

white clay in this and similar late fractures alternate paragenetically with abundant fine-grained pyrite. This late generation 

of pyrite accounts for the majority of pyrite in this interval.

130 ft. 

137.3 ft. 

Appendix B. Core log for MPG-D  67
Interval from 137.3 to 145. 8 ft.

Breccia similar to that described above to 138.5 ft. Interval 

from 138.5 to 145.8 ft. is cut by four prominent fractures. Three 

of these are associated with clay-altered breccias and broken 

zones. Clay-altered breccia zones localized late pyrophyllite 

alteration. A high angle fracture with a smooth clay face is 

present at 138.5 ft. There is a slightly broken and fractured zone 

filled with white pyrophyllite clay (2-3 mm) that is concentrated 

along the fracture surface. The high angle fracture intersects 

a near horizontal fracture at 138.3 ft.; this fracture has a 2 cm 

brecciated and clay altered zone that localized later pyrophyllite. There is a relatively undisturbed wedge of silicified rock 

between the two fractures. A 45o fracture at 143 ft. is lined by 

thin, white pyrophyllitic clay but no associated breccia. A highly 

broken, brecciated and fractured zone is present from 144 to 145 

ft. This zone has fragments with intervening clay altered and 

finely brecciated matrix that is overprinted by late pyrophyllite. 

Pyrite from ranges from about 8-10% in entire interval; sericite 

predominates over pyrophyllite in the entire interval.

137.3 ft. 

145.8 ft. 

68  Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Interval from 145.8 to 154.8 ft.

Entire interval is highly broken and shattered; broken and 

clay-lined fracture surfaces noted throughout. See descriptions 

for broken zones in above interval (137.3 to 145. 8 ft.).

145.8 ft. 

154.8 ft. 

Appendix B. Core log for MPG-D  69
Interval from 154.8 to 163 ft.

Dark gray, clast-supported breccias with larger Tsv lava clasts 

(4-6 cm). Remnant texture of breccias and Tsv clasts is still 

discernible. Breccia that is present between larger Tsv clasts 

is darker due to a greater abundance of fine pyrite. Darker and 

more indurated breccias are moderately to highly silicified and 

Qsp-altered; lighter and more broken zones are Qsp-altered, 

minor to moderately silicified, and are overprinted by more 

pyrophyllite. A few broken zones are localized about fractures; 

minor to moderate density of discontinuous, white, pyrophyllite 

veinlets cut the breccias. Pyrite content varies from 12-14%.

154.8 ft. 

163 ft. 

70 Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Interval from163 to 173 ft.

As above to 167 ft. Exceptions are that Tsv clasts are even 

larger—still suspended in breccia as described above. Rocks 

to 167 ft. are dark-gray, Qsp-altered, and contain 12-14% 

finely disseminated pyrite. Breccias are mostly soft, broken 

rubble to 173 ft. A very high angle fracture spans interval 

from 172-173 ft.; another at 172 ft. is likely associated with 

rubble and clay altered brecciation (breccias and rubble may 

be fracture/fault related and alteration post-dates brecciation). 

Rubble zones have minor pyrophyllite overprint. Entire 

interval averages 10-12% fine-pyrite.

163 ft. 

173 ft. 

Appendix B. Core log for MPG-D  71
Appendix C. Core log for LPG-D

Interval from 8.3 to 13.6 ft. (material above 8.3 ft. 

was unconsolidated and not cored)

Zone with coarse alluvial ferricrete. Contains rounded 

to subrounded, cobble and pebble-sized clasts cemented 

by massive to laminated iron-oxide matrix. XRD confirms crystalline iron-oxide phases in matrix to be almost 

entirely goethite; schwertmannite is not present. Clasts are 

predominantly Tsv porphyritic lavas that range from propylitic to weak sericitic-altered. Mafics in weak sericitic-altered 

clasts have altered to epidote and chlorite; plagioclase is 

metastable with some sericitic alteration. There is some 

bleaching of fresher Tsv lava clasts marginal to more matrix 

supported ferricrete zones. This is related to acid weathering; 

there is generally no discernable change in clay alteration in 

these more bleached intervals.

8.3 ft. 

18.6 ft. 

72  Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Interval from 18.6 to 35 ft.

Alluvial ferricrete as above. Consists of cobbles and subrounded to angular pebbles in an iron-oxide cemented matrix. 

Reverse grading in pebble layers between subrounded cobbles. 

Most clasts are propylitic-altered Tsv lavas with some larger 

quartz-alunite and quartz-pyrophyllite-altered clasts (latter two 

alteration lithologies from about 28-30 ft.).

18.6 ft. 

35 ft. 

Appendix C. Core log for LPG-D  73
Interval from 35 to 73.7 ft.

 Glacial till? Angular to subrounded pebble to cobble-sized 

clasts in a gray brown, clay-rich matrix cement. Fine-grained 

(< 1 mm) pyrite in clayey matrix is mostly unoxidized; matrix 

is moderately indurated. Clasts are largely propylitic to weak 

sericitic altered Tsv lavas.

35 ft. 

48.6 ft. 

48.6 ft. 

68 ft. 

74  Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Interval from 73.7 to 88.7 ft.

Saprolitic top of Tsv lava bedrock. Top several feet of core 

is rubbly and clay altered, with abundant light brown-yellow 

clays (sericite and kaolinite). Rock below saprolite is highly 

fractured and broken Tsv; alteration ranges from propylitic to 

weak sericitic with jarosite and goethite that replaced pyrite 

along fractures. Fine-grained pyrite is sparse in groundmass. Quartz vein at about 85 ft.; vein is 1 cm wide with 

cockscomb texture and is iron-stained. Similar quartz vein is 

present at bottom of this interval; vein is associated with clay 

(possibly sericite).

68 ft. 

89.2 ft. 

73.7 ft. 

88.7 ft. 

Appendix C. Core log for LPG-D  75
Interval from 88.7 to 108 ft.

Highly fractured, propylitic to weak sericitic-altered Tsv lavas. 

Secondary albite is abundant in these rocks (10-30%). Contains 

plagioclase phenocrysts (<1-2 mm) replaced by chlorite and 

epidote. Interval cut by moderately dense network of 1-2 mm 

quartz-pyrite veinlets; late white kaolinite is present along fracture 

surfaces. Goethite and hematite also are present along some fractures faces. Fine-grained pyrite is present mostly along fractures 

but is sparse (< 1%) in the groundmass; overall content is 1-3%. 

Tsv lavas become a bit more coarsely porphyritic at 107-108 ft. 

with plagioclase up to 2 cm; phenocrysts aligned along foliation.

89.2 ft. 

99.6 ft. 

99.6 ft. 

108 ft. 

76  Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Interval from 108 to 117 ft.

Propylitic-altered Tsv lavas with strong secondary albitization 

(>35 % albite); chlorite is abundant and minor epidote is 

present locally. Rock is intensely fractured in a few intervals; 

pyrite (<1 mm) is present on fracture surfaces and in some 

narrow quartz-pyrite veinlets, some also with sericite. Pyrite 

content is < 1%.

108 ft. 

117 ft. 

Appendix C. Core log for LPG-D  77
Interval from 117 to 127 ft.

Entire interval is highly fractured and broken; weak sericitic 

to Qsp-altered Tsv lavas. Plagioclase (only about 5 % albite 

remains) is mostly altered to sericite and minor chlorite 

(epidote appears to be partially to wholly replaced). Mafics to 

sericite but some chlorite remains. Rocks are weak to moderately silicified. Irregular and thin pyrite veinlets are sporadic, 

some with quartz. Pyrite abundance is 1-2%. This altered zone 

marks the upper alteration halo of hydrothermal alteration/

veining centered around a strong fracture zone at 140-142 ft. 

(see description below).

117 ft. 

127 ft. 

78  Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Interval from 127 to 135.3 ft.

Matrix-supported breccias; Qsp and moderately silicified; 

contain abundant subangular clasts that are rather evenly 

distributed. Clasts tend to be fairly even in size, averaging 

about 0.5 cm; clasts were derived from a dark gray, fine or 

chalcedonic quartz-altered rock; the dark gray clasts comprise 15-20% of the brecciated rock. Rocks cut by local 

dark gray, chalcedonic quartz flooded zones (up to 1 cm) 

that were localized along angular fractures. Note the near 

vertical, dark, chalcedonic quartz-flooded fracture (2-3 cm) 

at 134 ft.; this zone has very diffuse margins. This feature 

continues to 139 ft. in the next core interval. Fine-grained 

pyrite abundance is 4-5%.

127 ft. 

135.3 ft. 

Appendix C. Core log for LPG-D  79
Interval from 135.3 to 144 ft.

Matrix-supported breccia with dark, evenly distributed clasts 

continues to 142 ft. These breccias are weak sericite-pyrite 

altered, contain partially altered k-spar and secondary albite, 

are moderately silicified, and have metastable chlorite. The near 

vertical chalcedonic quartz vein tapers out at 138 ft. Matrix-supported breccias appear to grade into a coarse-grained, clast-supported breccia in the interval from 139 to 142 ft. The texture 

in the 139-142 ft. interval is obscured by strong overprint of 

medium to dark gray, chalcedonic silicification (> 52 % quartz; 

feldspars completely altered to sericite; chlorite still present 

along fractures). A near vertical, 0.5 cm fracture is filled by 

milky open-space quartz (vein composed of anhedral crystals). 

The white quartz vein cuts both the coarse breccia interval 

and finer matrix-supported breccia (143-144 ft.). The matrixsupported breccia at 143-144 ft. appears to be a gradational 

transition from the coarser breccia. In summary: hydrothermal? 

breccia is localized in the interval from 127-151.5 ft. A coarse 

breccia is localized at the core of this zone and grades into finer 

breccias on both margins. Chalcedonic quartz is localized along 

fractures and post-dates brecciation. The coarse breccia interval 

from 139-142 ft. has localized dark chalcedonic quartz flooding; this may be equivalent to that seen along strong vertical 

fracture from 139-142 ft. Episodes of brecciation and chalcedonic silicification are post-dated by fracture-filled quartz vein. 

The white quartz vein is offset ~ 0.5 cm by a small normal fault 

at 141 ft. Hydrothermal alteration and quartz veining appears 

to have been localized near the coarse core of the breccia zone 

that extends from 127 to 151 ft. Qsp alteration and silicification extends about 12 ft. on either side of this zone. Question: 

what/where is the source of the evenly distributed breccia 

clasts? Fine-grained pyrite content is 5-6% to about 139 ft. and 

diminishes to < 2% from 139 to 144 ft.

135.3 ft. 

144 ft. 

80 Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado
Interval from 144 to 151 ft.

Qsp to weak sericitic-altered, moderately silicified breccias 

(weak sericite-pyrite altered, contain partially altered k-spar, 

secondary albite, and chlorite along fractures); 1 mm pyrite (as 

fracture-fillings and in sporadic quartz veins) <1-2%. Breccias 

still contain 0.5-1 cm silicified clasts. Fracture with slickensides at 151 ft.

144 ft. 

152.9 ft. 

151 ft. 

Appendix C. Core log for LPG-D  81
Interval from 151 to 159 ft.

Breccias transition into weak sericitic to propylitic-altered, 

flow-foliated lavas (Tsv) at 151.5 ft; lavas contain 1 mm 

wide phenocrysts. Rocks are strongly albitized. Albite 

and k-spar are weak to moderately sericitized. Biotite is 

metastable and along with other mafics is partially altered 

to chlorite and epidote. Moderately dense fracture network 

is filled with dark chalcedonic quartz and pyrite (not quite 

stockwork texture). Late, white kaolinite is also present 

along many of these fractures. Tsv lavas are cut by mediumgrained, clast-supported hydrothermal breccia at 159 ft. 

Breccia has very sharp margins. Fine pyrite < 1-2%. 

152.9 ft. 

159 ft. 

82  Mineralogy from Cores in Prospect Gulch, San Juan County, Colorado