Alteration Mineralogy at the Cerro La Mina Epithermal Prospect, Patagonia, Argentina:

Field Mapping, Short-wave Infrared Spectroscopy, and ASTER Images

DIEGO F. DUCART, ALVARO P. CRSTA, CARLOS R. SOUZA FILHO Geosciences Institute, State University of Campinas, PO Box 6152, Campinas, SP, Brazil, 13083-970

JORGE CONIGLIO Department of Geology, National University of Rio Cuarto, PO Box 3, Rio Cuarto, Cba., Argentina, 5800

Short running title: Los Menucos Epithermal Alteration, Argentina

Abstract

The Cerro La Mina prospect, located in the Los Menucos area, Argentina, is currently being

explored for epithermal gold mineralization. Triassic-Jurassic hydrothermal activity produced intense

alteration of rhyolites, andesites, ignimbrites and tuffs of the Late Triassic Los Menucos Group, in the

Somn Cur Massif. A detailed surface map of the principal alteration assemblages at Cerro La Mina

was produced employing field mapping, supported by short-wave infrared (SWIR) field spectroscopy,

petrography, X-ray diffraction (XRD), and scanning electron microscopy (SEM).

Advanced argillic, argillic, and silicic alteration zones and their internal mineral assemblage

variations were recognized at Cerro La Mina. The silicification consists of massive bodies of fine-

grained quartz and minor vuggy quartz, locally containing disseminated aggregates of pyrite, and rutile.

Advanced argillic alteration of magmatic-hydrothermal origin occurs adjacent to the silicic alteration

zones, and can be subdivided into three mineral assemblages: (1) stage 1 alunite + quartz dickite

Corresponding author: ducart@ige.unicamp.br

1

kaolinite pyrophyllite diaspore rutile pyrite barite; (2) dickite + kaolinite pyrophyllite

diaspore pyrite barite; and (3) dickite + quartz diaspore. The advanced argillic and silicic

alteration grades to argillic alteration, comprising three mineral assemblages: (1) kaolinite dickite

quartz illite smectite; (2) kaolinite illite smectite ferroan clinochlore; and (3) illite quartz

muscovite kaolinite. Supergene alteration, which locally overprints the prior alteration zones, consists

of jarosite + hematite + goethite stage 2 alunite aluminium phosphate sulfate (APS) poorly-

crystalline kaolinite.

Consistent discrimination of the main alteration minerals of this prospect was also achieved by

means of satellite multispectral remote sensing. The application of image processing techniques,

specifically designed for mineral mapping, to selected spectral bands of the Terra/ASTER multispectral

sensor resulted in a detailed alteration map for the entire prospect. Comparison between the results

achieved through remote sensing with field data on the Cerro La Mina confirmed the accuracy of the

former.

The silicification and minor vuggy quartz, the abundant dickite, and the coarse-grained

hypogene alunite, among other advanced argillic alteration assemblages, suggest that Cerro La Mina

corresponds to a volcanic-hydrothermal leached environment, possibly controlled by permeable

lithologies. These characteristics led us to interpret this prospect as a possible lithocap similar to those

that typically host subsequent high-sulfidation mineralization.

Introduction

A number of epithermal gold deposits hosted by Triassic-Jurassic volcanic rocks have been

discovered in Argentinean Patagonia during the last decade. These deposits largely belong to the low-

sulfidation type associated with bimodal volcanism in back-arc settings. An example is the large Cerro

Vanguardia vein system, located in the Deseado Massif (Schalamuk et al., 1997). Epithermal gold

2

occurrences were identified at the Los Menucos area in 1998, in northern Somn Cur Massif (Franco

et al., 1999; Fig. 1A). One of the most prominent surface features in this area is the extensive

hydrothermal alteration associated with the Cerro La Mina prospect (Fig. 1B).

The alteration zones at Los Menucos have been analyzed by means of remote sensing methods

(Kruse et al., 2002; Crsta et al., 2003). Reflectance spectroscopy, which constitutes the basis of

multispectral remote sensing, provides an effective means of mapping fine-grained alteration minerals,

either in the field or from satellites and airplanes. When applied jointly with field mapping and other

conventional analytical methods (e.g., petrography, X-ray diffraction), this technique permits an

effective characterization of alteration zones. Field portable short-wave infrared (SWIR) spectrometers,

such as the PIMA (Portable Infrared Mineral Analyzer), are becoming increasingly used in

exploration programs, due to their effectiveness for alteration mapping. However, the literature on the

subject is scarce (e.g., Thompson et al., 1999; Herrmann et al., 2001; Yang et al., 2001; Sun et al.,

2001; Jones et al., 2005).

The aim of this study is to map the exposed alteration mineralogy of the Cerro La Mina

prospect employing field mapping, supported by field SWIR spectroscopy, petrography, X-ray

diffraction (XRD), and scanning electron microscopy (SEM). This study also assesses the use of SWIR

bands of the multispectral satellite sensor ASTER (Advanced Spaceborne Thermal Emission and

Reflection Radiometer) to map the spatial distribution of hydrothermal alteration minerals associated

with Cerro La Mina and other adjacent prospects at Los Menucos.

Geological Setting

The Somn Cur Massif, also known as the Northpatagonian Massif (Windhausen, 1931), is a

morphostructural unit consisting of Precambrian to Cambrian metamorphic, Paleozoic plutonic

intrusive, and Mesozoic to Cenozoic volcanic and subvolcanic rocks (Aragn et al., 1996; Fig. 1A).

3

The metamorphic rocks comprise gneiss and mica schist with an age range from Precambrian to

Cambrian (Ramos, 2004), and are intruded by Carboniferous and Permian granitoid bodies (Ramos and

Aguirre-Urreta, 2000).

Triassic-Jurassic volcanosedimentary rocks form an extensive plateau over the massif

(Llambas et al., 1984; Fig. 1A). In the Los Menucos region, they are included in the Los Menucos

Group (Labudia et al., 1995; Fig. 1B), which is composed of two members: Vera Formation at the

bottom (Labudia and Bjerg, 2001) and Sierra Colorada Formation at the top (Stipanicic et al., 1968).

Late Triassic ages were confirmed for the Los Menucos Group on the basis of Dicroidium fossil flora

(Labuda and Bjerg, 2001) and radiometric dating (Rapela et al., 1996).

Early Cretaceous continental sedimentary rocks overlie parts of the massif (Stipanicic et al.,

1968). Several events of volcanic activity extruded large volumes of mafic volcanic rocks that covered

most of the central part of the massif from Eocene to Pleistocene (Corbella, 1984).

Cerro La Mina prospect

The Cerro La Mina prospect, discovered by Iamgold Argentina mining company in 1998, is

currently undergoing exploration. The local geology comprises rocks of the Los Menucos Group. The

Vera Formation occurs in the western and northern sector of the study area (Fig. 2). This formation

consists of sandstones, siltstones, conglomerates, and fossiliferous tuffs, intercalated with minor dacitic

and rhyodacitic lavas, ignimbrites and rhyodacitic volcanic breccias near the top of the sequence

(Labudia and Bjerg, 2005). The Sierra Colorada Formation, predominantly volcanic and volcaniclastic,

hosts the main alteration zones and gold occurrences of the prospect. The volcanic stratigraphy is

complex, poorly constrained, and displays rapid facies variations. A flow-banded rhyolitic-dacitic-

andesitic lava complex occurs at Tripailao, Catrin, and Domo La Vbora areas (Figs. 2, and 3A, B, C).

The original textures of these volcanic rocks are mostly obliterated by intense hydrothermal alteration

4

on the surface (mainly silicification and advanced argillic alteration; Fig. 3D), but they are partially

preserved at depth. Rhyolitic-rhyodacitic welded ignimbrites (Fig. 3E), tuffs, and minor surge deposits

dominate the central and northeastern sector of the prospect (Fig. 2) and dip 5 to 10 to the southeast.

Andesites, which have been assigned to the Jurassic by Labudia and Bjerg (2005), intrude the rocks of

the Los Menucos Group at the north of the Brecha La Gorda area (Fig. 2). Isolated outcrops of

microdiorites, tentatively assigned to Jurassic by Lema et al. (2005), occur in the western sector.

Cerro La Mina includes an elongated northeast- to southwest-trending zone of intense

hydrothermal alteration covering nearly 27 km2. There are no geochronological data on this alteration.

However, it can be assigned to the Late Triassic or Jurassic, since the alteration affects Late Triassic

rocks of the Los Menucos Group, but the Jurassic andesites and microdiorites are unaffected.

Numerous northeast-striking hydrothermal breccias occur in the silicified lava complex (Figs. 2, and

3H). The hydrothermal breccias are poorly sorted, either matrix- or clast-supported, with angular to

subrounded fragments, cemented by finely crystalline quartz, hematite, and dickite (Fig. 3F, G). The

fragments are monolithologic and appear similar to the local wall rock. Locally, some fractures are

filled by chalcedony kaolinite. Some breccias contain gold at concentrations ranging from a few tens

of ppb up to 60 ppm.

Structural setting

The Los Menucos region is characterized by the presence of Triassic-Jurassic faults and/or

fractures with orientations mainly to the east, but locally to the northeast and southeast (Giacosa et al.,

2005; Fig. 1B). Some of the east- to northeast-striking structures correspond to dextral strike-slip faults

that offset laterally Precambrian and Cambrian metamorphic rocks, Carboniferous and Permian

granitoids, and Late Triassic volcanosedimentary rocks of the Los Menucos Group, with displacements

of less than 7 km (Giacosa et al., 2005). Cretaceous and younger rocks are not displaced by these faults.

5

In particular, the Cerro La Mina prospect lies between two east-oriented parallel dextral strike-slip

faults the La Laja fault in the northern part of the prospect and the Lagunitas-Cerro Bandera fault in

the south (Fig. 1B). In between these faults, there are several east-northeast- and southeast-striking

lineaments in the prospect area (Fig. 2). In the Catrin, Tripailao and Cerro La Antena areas,

hydrothermal breccias are related to the northeast-striking structures.

The presence of the volcanic complex at Tripailao, Catrin, and Domo La Vbora, in association

with some radial and circular lineaments, suggests the possibility that this area was an eruptive center

or a caldera (Lema et al., 2005) localized in a transtensional area related to a dextral strike-slip regime.

Some of these northeast-striking faults were subsequently reactivated in a post-alteration stage,

apparently associated with the formation of a graben or semi-graben (Labudia and Bjerg, 2005). They

have the same trend as the main alteration zones of the Los Menucos region (Aguada de Guerra, Cerro

Abanico, and Cerro La Mina) and a linear magnetic anomaly (Chernicoff, 1999). The northeast-striking

normal fault, located in the Catrin area, dismembers the intensely altered volcanic complex, leaving its

hanging-wall portion mostly covered by Quaternary sediments at the southeast (Fig. 2).

Methods

Field SWIR spectroscopy

SWIR spectroscopy allows rapid identification of minerals and variations in mineral

composition, even for fine-grained minerals. Portable spectrometers can therefore be used for mapping

the spatial distribution of alteration assemblages in the field. Readers are referred to Hunt and Ashley

(1979), Clark et al. (1990), and Thompson et al. (1999) for details on SWIR spectroscopy. Reflectance

spectra were acquired on over 1,000 samples collected at the surface, in order to determine the

alteration mineralogy of the Cerro La Mina prospect. Sampling was conducted along a regular grid,

with sample points spaced every 50 m along lines, with an interval of 200 m between lines, covering

6

the entire prospect (see Appendix 1). The PIMA portable SWIR spectrometer was used in this study,

with a spectral resolution of about 0.007 m and a spectral sampling interval of 0.002 m.

Mineral identification was based on wavelength, intensity, and shape of the main absorption

features in each spectrum, in comparison to reference spectra from the USGS digital spectral library

(Clark et al., 2003). The spectral analysis was carried out using SIMIS FeatureSearch 1.6 (Mackin,

2003) and ENVI 4.1 (Research System Inc., 2004, ENVI Users Guide, version 4.1, 1150 p.)

software. The results of mineral identification at each sampling point were organized using a MS-Excel

spreadsheet and then spatially distributed and displayed as an alteration map, through the use of

ArcMap 9.0 GIS software.

Results from spectral analysis were integrated with field geologic observations, combined with

petrological, textural, and mineralogical studies using transmitted and reflected light optical

microscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM).

SWIR ASTER processing

Descriptions and geological applications of the multispectral ASTER sensor have been

published by Abrams (2000), Crsta et al. (2003), Rowan et al. (2003), Souza Filho et al. (2003),

among others. We employed a version of the method proposed by Boardman and Kruse (1994), and

implemented in ENVI 4.1, involving the following steps: (1) ASTER data acquisition and

preprocessing; (2) correction of the images to apparent reflectance using the ACORN atmospheric

correction software; (3) linear transformation of the reflectance data to minimize noise using the

Minimum Noise Fraction transformation (MNF); (4) creation of a spectral library with end-member

spectra of alteration minerals, selected from the set of samples collect in the Los Menucos area and

measured with a PIMA spectrometer; (5) spatial mapping and abundance estimates for specific

mineral end-members using the Mixture Tuned Matched Filtering (MTMF) technique.

7

To determine the effectiveness of ASTER images for mapping the alteration assemblages, one

cloud-free scene image was acquired over the Los Menucos region. The ASTER data were acquired

with radiometric and geometric corrections corresponding to level 1B (Abrams et al., 2002), and

georeferenced to UTM coordinates (Zone 19 South, datum WGS-84). The spectral bands

corresponding to the SWIR region (bands 4-9) were selected for further processing, due to the

occurrence in this spectral region of diagnostic spectral absorption features of clays, sulfates, and

phyllosilicates (Clark et al., 1990), minerals commonly present in Cerro La Mina hydrothermal

alteration zones.

ASTER data were converted from radiance at the sensor to atmospherically corrected,

reflectance at the surface, thus removing the interference of atmospheric gases and particulate

materials. Figure 4 shows a comparison of several pixel spectra extracted from the atmospherically

corrected ASTER image and ground spectra at the same locations at Los Menucos. In order to allow for

comparison, ground-based PIMA spectra were resampled at the same spectral resolution as ASTER.

The ASTER spectra show less deep absorption features if compared with the resampled PIMA spectra

at the same location, probably due to atmospheric attenuation effects, and/or because an ASTER

spectrum is the mean spectrum from a 30 x 30 m pixel area. A comparative analysis between the

equivalent spectra of different minerals resampled to ASTER resolution shows that, despite the

apparent similarities, there are some important diagnostic differences at wavelengths corresponding to

spectral bands 5, 6, and 7 (Fig. 4). These diagnostic differences are important for the identification and

mapping of the minerals by the Mixture Tuned Matched Filtering (MTMF) technique.

Alteration Mapping Results

The alteration at Cerro La Mina is widespread and mainly pervasive, and the relationships

between alteration assemblages are complex. Three main hydrothermal alteration zones have been

8

recognized: silicic, advanced argillic, and argillic (Table 1, and Fig. 5). Minor supergene advanced

argillic alteration is also present. For the convenience of understanding broad-scale patterns, each zone

is further divided into mineral assemblages. There is, however, some overlap in the occurrence of

associated minerals. In the absence of stable isotope data on sulfur-bearing minerals, the

characterization of the subzones according to the classification of Rye et al. (1992) is preliminary.

Silicic alteration assemblage

Mapping of silicification at Cerro La Mina is based on field observations, and petrography, as

quartz lacks diagnostic spectral features in the portions of the electromagnetic spectrum sampled by

ASTER and PIMA (Fig. 6B, sample Cm128). Silicification occurs mainly in the eastern and

southeastern sector of the prospect (Tripailao and Catrin areas) and appears limited to a few

stratigraphic units in the northeastern sector (Cerro La Antena area), where it is underlain by argillic

alteration assemblages (Fig. 5, and 7A). Permeable tuffs or volcaniclastic horizons were transformed

into massive bodies of fine-grained quartz and minor vuggy quartz (Fig. 7B), locally containing

disseminated aggregates of fine-grained pyrite and rutile.

Another type of silicification, composed mainly by quartz and chalcedony, is associated with

northeast-striking structures, with hydrothermal breccia matrix (Fig. 7C), and with fracture- and open

space-filling (Fig. 7D). The silicified structures range from a few tens of centimeters to approximately

1 m wide and, in places, contain up to 11 ppm Au.

Hypogene advanced argillic assemblages

The advanced argillic alteration occurs mainly in the Domo La Vbora, Catrin, Tripailao, and

Cerro La Antena areas. Within this advanced argillic alteration, three mineral assemblages can be

distinguished: (1) stage 1 alunite + quartz dickite kaolinite muscovite pyrophyllite diaspore

9

rutile pyrite barite, which occurs at Domo La Vbora area; (2) dickite + kaolinite quartz

pyrophyllite diaspore pyrite barite, which occurs between Domo La Vbora and Tripailao areas

and in the Cerro La Antena area; (3) dickite + quartz diaspore in the north and east of Tripailao and

in Domo Sur area (Fig. 5).

Stage 1 alunite appears as a medium- to coarse-grained (70 to 160 m), interlocking mosaic of tabular to platy crystals replacing feldspar and lithic clasts or lining cavities (Fig. 7E, F). Alunite

extends below the surface to a depth up of 160 m (determined in the drill core CMDD03). The

characteristics of the alunite, in addition to the associated high-temperature alteration minerals (e.g.,

dickite, phyrophyllite), are evidence of a magmatic-hydrothermal origin (e.g., Rye et al., 1992; Sillitoe,

1993; Hedenquist et al., 2000; Deyell and Dipple, 2005).

Alunite shows up in the SWIR spectra of samples 32192, 32156, and 32189 (Fig. 6B),

associated with kaolinite in sample 32160, and with kaolinite + dickite in samples 32187, 32286, and

32202, where the weak absorption features marked by arrows indicate a small proportion of alunite.

Chemical variations between K-, Na-, and Ca-bearing alunite are evident in the ~1.480 m spectral feature (Thompson et al., 1999). Almost all samples of the prospect indicate a K-bearing alunite

composition, and only a few are natroalunite. This was confirmed by scanning electron microscopy

analysis (SEM) in thin sections. SEM analysis of some alunites showed crystal compositional zoning,

from alunite to aluminium phosphate sulfate minerals (APS); a K-Na-(Ca)-bearing crystal core, which

probably corresponds to minamiite, natroalunite, and woodhouseite, is surrounded by a K-bearing

alunite rim (Fig. 7F).

Based on reflectance spectroscopy, and confirmed by XRD and petrographic analysis, we

identified kaolinite and dickite as part of the hypogene advanced argillic assemblage. Kaolinite occurs

as disseminations (Fig. 7G) and replaces biotite, feldspar phenocrysts, and lithic or pumice fragments

(Fig. 3E). Dickite is also disseminated in the matrix of hydrothermal breccia (Fig. 3F, G) and occurs as

10

vug-fillings (Fig. 7H), and as replacement of feldspar and biotite phenocrysts. Dickite extends below

the surface to depths up of 300 m (determined in drill the core CMDD05), which suggests a magmatic-

hydrothermal origin. Dickite veins locally cut the quartz-kaolinite-diaspore-pyrophyllite alteration to

the east of Cerro La Antena (Fig. 7I, J).

The spectra of dickite, kaolinite, and their mixtures can be clearly seen in Figure 6A. Typical

dickite spectra are seen in samples 32195, 32183, 32148, 32139, 14452, and 32757, whereas kaolinite

occurs in samples 32681, 32464, 32269, 32162, and 32922. Examples of mixtures of dickite + kaolinite

are seen in samples 32538 and 32264 (Fig. 6A), and kaolinite + dickite + quartz is seen in samples

32142 and 32757 (Fig. 6B). The kaolinite of Cerro La Mina corresponds mainly to highly-crystalline

varieties on the basis of the morphology of the 2.2 m double absorption feature in kaolinite spectra (Clark et al., 1990; Pontual et al., 1997c; Fig. 8A, B). Kaolinites with higher degrees of crystallinity

were identified in the north and northeastern sector of the prospect.

Under the microscope, dickite often shows stacks of well-ordered crystals, commonly larger

than the stacks of kaolinite crystals. The pyrophyllite and diaspore (Fig. 7K) occur as rare and isolated

fine-grained crystals; the reflectance spectra did not show their diagnostic absorption features without

removal of the background (hull quotient baseline correction: Pontual et al., 1997)

Argillic assemblages

The argillic alteration occupies a wide area in the northern sector of the prospect (Fig. 5).

Within this alteration, three zones of different mineral assemblages were identified (Table 1): (1)

kaolinite dickite illite quartz smectite in the center of the prospect; (2) kaolinite illite

smectite ferroan clinochlore in the northeast; (3) illite quartz muscovite kaolinite in the

northwest (Fig. 5).

11

The illite spectra of Cerro La Mina have sharp Al-OH absorption features within a wavelength

range from 2.196 to 2.208 m, which reflects a variation in composition from paragonitic illite (Na-rich) to regular illite (K-rich) (Pontual et al., 1997a). Muscovite spectra are present in samples 32297,

LM165, and LM29 (Fig. 6C), and illite was found in samples 14468 and 32294. A few spectra of

smectite were identified in samples from the north-northeastern part of the prospect (sample 32301,

Fig. 6C), generally mixed with illite (samples 14391 and 14410). A few spectra of samples collected in

the northern sector of the prospect indicate the presence of ferroan clinochlore (chlorite group; see

sample 32050 in Fig. 6C).

Supergene advanced argillic assemblages

In addition to the hydrothermal activity responsible for the stage 1 alunite, a second event of

supergene advanced argillic alteration has been documented at Cerro La Mina. The supergene

alteration is restricted to small areas in the prospect, in places achieving depths of about 30 meters;

their distribution is not shown in Figure 5.

Supergene argillic assemblages at Cerro La Mina are characterized by hematite + goethite

jarosite stage 2 alunite poorly-crystalline kaolinite aluminium phosphate sulfate minerals, in the

form of fracture and cavity fillings (Fig. 7L, M), as well as replacements of previous assemblages.

Stage 2 alunite forms very fine-grained anhedral crystal aggregates (1 to 10 m in size). The aluminium phosphate sulfate minerals (APS) are commonly enriched in PO4, Fe, Ca, In, Ba and Ce

(Fig. 7N). Jarosite is present in small amounts in reflectance spectra of samples containing dickite and

kaolinite, as indicated by arrows in spectra of samples 32139, 14452, and 32264 (Fig. 6A).

Alteration Mapping with ASTER

12

The results obtained from the ASTER image processing provided regional and local

information on the spatial distribution of the main alteration mineralogy (Fig. 9). The vegetation cover

in this arid region is minimal, which favored a remote sensing approach to mineral mapping. Three

major areas of alteration were clearly recognized: Cerro La Mina, Cerro Abanico, and Aguada de

Guerra (Fig. 9). A visual comparison between the results obtained from the ASTER data and the

alteration map of Figure 5 shows a satisfactory correlation of the spatial distribution of the main

alteration minerals at the Cerro La Mina prospect. Appendix 2 compares mineral assemblages

determined by reflectance spectroscopy, XRD and by ASTER processing.

Alteration minerals such as kaolinite, dickite, alunite, illite and quartz were mapped at the

Cerro La Mina prospect. The kaolinite-group minerals (in this case kaolinite or dickite) were mapped

mainly in the northeastern sector of the prospect. Alunite, surrounded by kaolinite and minor dickite,

was identified at Domo La Vibora. The Mixture Tuned Matched Filtering (MTMF) technique also

distinguished quartz in the Catrin area, where intense silicification occurs. The quartz was only

identified in image pixel spectra almost without absorption features, similar to that shown in Figure 4.

Similar positive results were also obtained for illite and muscovite at the Cerro Abanico

prospect. Muscovite surrounded by illite was detected in both the ASTER processing and in field

reflectance spectra. The other prospect where conspicuous alteration is shown by ASTER image

processing, Aguada de Guerra, has wide zones with dickite surrounded by kaolinite; minor alunite,

illite and quartz occur in the west and southwest. This prospect has not been investigated on the ground

but, based on the alteration pattern shown by ASTER mineral mapping, it is a potential target area for

epithermal mineralization.

Discussion and Conclusions

13

The use of field SWIR spectroscopy data, in support of field mapping, enabled us to identify the

main alteration assemblages related to the Cerro La Mina prospect. SWIR spectroscopy was able to

detect the main very fine-grained alteration minerals which occur at this prospect, including alunite,

kaolinite, dickite, illite, muscovite, smectite, and jarosite. Identification of isolated fine-grained

minerals, such as pyrophyllite and diaspore, was by petrographic analysis. In more intensely silicified

portions of the prospect, the presence of quartz tends to flatten the spectra in the SWIR, thus hindering

the identification of alteration minerals present in smaller amounts.

The SWIR spectra of kaolinites at Cerro La Mina correspond mainly to highly-crystalline

varieties. These varieties can be formed either by hydrothermal alteration processes or in lateritic

weathering environments (Pontual et al., 1997c). At Cerro La Mina, however, hydrothermal alteration

is the most likely origin for the kaolinite, due to its association with other high-temperature alteration

minerals (dickite, alunite, pyrophyllite) and the absence of deep weathering.

SWIR spectroscopy at Cerro La Mina also revealed variations in the composition of alunite

between K- and Na-bearing end members. Results presented by Stoffregen and Cygan (1990),

Stoffregen et al. (2000), and Deyell and Dipple (2005) suggest that substitution of K by Na in alunite is

favored at high temperatures and is spatially and genetically associated with ore (Hedenquist et al.,

2000), although this is also a function of the composition of the source fluids and the host rocks (Deyell

and Dipple, 2005).

Consistent discrimination of the main alteration minerals of this prospect was also possible by

means of satellite-based multispectral remote sensing. The application of image processing techniques

specifically designed for mineral mapping to the ASTER SWIR bands allowed us to produce an

alteration map for the entire prospect, including other adjacent hydrothermal alteration zones (Cerro

Abanico and Aguada de Guerra). Comparison between the results achieved through remote sensing

with field data confirmed the accuracy of the ASTER interpretations, despite inherent limitations of

14

ASTER data in terms of relatively limited spectral and spatial resolutions. Among the details seen in

the ASTER SWIR bands were differences in the degree of crystallinity of kaolinite. Highly-crystalline

kaolinite was mapped in the northern and eastern portions of the Cerro La Mina prospect, and

confirmed by field spectral analysis. However, minerals with similar reflectance spectra, such as

kaolinite and dickite, could not be discriminated.

The main hydrothermal alteration zones at the Cerro La Mina prospect comprise silicic and

advanced argillic assemblages in the southwest, and argillic assemblages in the northeast. The patches

of advanced argillic alteration to the southwest of Domo La Vbora (Domo Sur area) may represent the

remnants of a much broader advanced argillic zone, which was subsequently partly eroded. In addition,

the original extent of the silicification to the southeast of Catrin seems to have been truncated by a

northeast-striking normal fault.

The occurrence at surface and to depth of silicification with vuggy quartz, abundant dickite,

coarse-grained hypogene alunite and other hypogene advanced argillic assemblages suggests that Cerro

La Mina corresponds to a volcanic-hydrothermal leached environment (Arribas, 1995; Hedenquist et

al., 2000) and may be a possible lithocap similar to those that typically host subsequent high-sulfidation

mineralization (e.g., Sillitoe, 1995; Hedenquist et al., 1998; Hedenquist et al., 2000).

Acknowledgements

This project was supported by the So Paulo State Research Foundation (FAPESP) through a

PhD grant given to D.F. Ducart (04-07077-0) and a research grant (02-07978-1). A.P. Crsta and C.R.

Souza Filho were supported by research grants from the Brazilian National Research Council (CNPq).

This project would not have been developed without the support of F. Azevedo (Iamgold Argentina),

who also provided overall assistance throughout the project. Iamgold and Barrick mining companies

are thanked for field support and geological data, as well as for allowing publication of their data. The

15

original manuscript was greatly improved by early reviews made by J. Hedenquist and R. Bedell,

whom the authors would like to thank. We are grateful for the detailed corrections, comments, and

advice of Economic Geology editor, M. Hannington, and two reviewers, J. Perell and A.J.B.

Thompson. R. Anglica, from the Federal University of Par, Brazil, is acknowledged for conducting

XRD analyses. We thank D. Silva for assistance in SEM analyses, B. Palacios for petrographical

support, and M.F. Oyola for reviewing the manuscript.

References

Abrams, M., 2000, The Advanced Spaceborne Thermal Emission and Reflection Radiometer

(ASTER)- Data products for the high spatial resolution imager on NASA's EOS-AM1 platform:

International Journal of Remote Sensing, v. 21, no. 5, p. 847-861.

Abrams, M., Hook, S., and Ramachandran, B., 2002, ASTERs user manual Version 2: Jet

Propulsion Laboratory/National Aeronautics and Space Administration (JPL/NASA).

[Available from:

]

Aragn, E., Iiguez Rodriguez, A.M., and Benialgo, A., 1996, A calderas field at the Marifil

Formation, new volcanogenic interpretation, Norpatagonian Massif, Argentina: Journal of

South American Earth Sciences, v. 9, no. 5, p. 321-328.

Arribas, A., 1995, Characteristics of high-sulfidation epithermal deposits, and their relation to

magmatic fluid, in Thompson, J.F.H., ed., Magmas, Fluids and Ore Deposits: Mineralogical

Association of Canada, Short Course Series, v. 23, 419454.

Boardman, J.W., and Kruse, F.A., 1994, Automated spectral analysis- A geologic example using

AVIRIS data, north Grapevine Mountains, Nevada: Thematic Conference on Geologic Remote

16

Sensing, 10th, Ann Arbor, Michigan, U.S.A., Environmental Research Institute of Michigan,

Proceedings, MI, p. 407-418.

Chernicoff, C., 1999, Intepretacin geolgica-geofsica preliminar del rea de Los Menucos, Provincia

de Ro Negro: Instituto de Geologa y Recursos Minerales, SEGEMAR, Serie Contribuciones

Tcnicas, Proyecto Ro Negro N 1, Buenos Aires, Argentina, 32 p..

Clark R.N., King T.V.V., Klejwa M., Swayze G.A., and Vergo, N., 1990, High spectral resolution

reflectance spectroscopy of minerals: Journal of Geophysical Research, v. 95, no. 8, p. 12653-

12680.

Clark, R.N., Swayze, G.A., Wise, R., Livo, K.E., Hoefen, T.M. Kokaly, R.F., and Sutley, S.J., 2003,

USGS digital spectral library splib05a: U.S. Geological Survey Open-File Report, 03-395.

[Available from: ]

Corbella, H., 1984, El vulcanismo de la altiplanicie del Somuncur, in Ramos, V.A., ed., Geologa y

Recursos Naturales de la Provincia de Ro Negro: Congreso Geolgico Argentino, 9, Buenos

Aires, Argentina, Relatorio v. 1, no. 10, p. 267-300.

Crsta, A.P., Souza Filho, C.R., Azevedo, F., and Brodie, C., 2003, Targeting key alteration minerals in

epithermal deposits in Patagonia, Argentina, using ASTER imagery and principal component

analysis: International Journal of Remote Sensing, v. 24, no. 21, p. 42334240.

Deyell, C.L., and Dipple, G.M., 2005, Alunite natroalunite solid-solutions - equilibrium mineral fluid

calculations and their application to the El Indio-Pascua Belt (Chile-Argentina): Chemical

Geology, v. 215, p. 219-234.

Ducart, D.F., 2004, Caracterizao da alterao hidrotermal associada s ocorrncias aurferas de Los

Menucos, Argentina, por meio de tcnicas de sensoriamento remoto e espectroscopia de

reflectncia: Campinas, State University of Campinas, Brazil, MSc. Dissertation, 86 p.

17

Franco, S., Puente, N., Varela, C., and Gemuts, I., 1999, Mineralizacin aurfera en el distrito Los

Menucos, Rio Negro, in Zappettini, E.O., ed., Recursos minerales de la Republica Argentina:

Instituto de Geologia y Recursos minerales SEGEMAR, Buenos Aires, Argentina, Anales 35,

p. 893-894.

Giacosa, R., Lema, H., Busteros, A., Zubia, M., Cucchi, R., and Di Tommaso, I., 2005, Tectnica

transcurrente asociada al Trisico de Los Menucos - Macizo Nordpatagnico, Rio Negro:

Congreso Geolgico Argentino, 16, La Plata, Argentina, Tomo I, p. 363-366.

Hedenquist, J.W., Arribas, A., Reynolds, T.J., 1998, Evolution of an intrusion centred hydrothermal

system: Far Southeast-Lepanto porphyry and epithermal Cu-Au deposit: Economic Geology, v.

93, p. 373404.

Hedenquist, J.W., Arribas, A., Jr., and Gonzales-Urien, E., 2000, Exploration for epithermal gold

deposits: Reviews in Economic Geology, v. 13, p. 245277.

Herrmann, W., Blake, M., Doyle, M., Huston, D., Kamprad, J., Merry, N., and Pontual, S., 2001, Short

wavelength infrared (SWIR) spectral analysis of hydrothermal alteration zones associated with

base metal sulfide deposits at Rosebery and western Tharsis, Tasmania, and Highway-Reward,

Queensland: Economic Geology, v. 96, p. 939-955.

Hunt, G.R., and Ashley, R.P., 1979, Spectra of altered rocks in the visible and near infrared: Economic

Geology, v. 74, p. 16131629.

Jones, S., Herrmann, W., and Gemmell, J.B., 2005, Short Wavelength Infrared Spectral Characteristics

of the HW Horizon - Implications for Exploration in the Myra Falls Volcanic-Hosted Massive

Sulfide Camp, Vancouver Island, British Columbia, Canada: Economic Geology, v. 100, p.

273294.

Kruse, F.A., Perry, S.L., and Caballero, A., 2002, Integrated multispectral and hyperspectral mineral

mapping, Los Menucos, Rio Negro, Argentina, part II - EO-1 Hyperion/AVIRIS Comparisons

18

and Landsat TM/ASTER Extensions: JPL Airborne Geoscience Workshop, 11th, Jet Propulsion

Laboratory, p. 1-5.

Labudia, C.H., and Bjerg, E.A., 2001, El Grupo Los Menucos- redefinicin estratigrfica del Trissico

superior del Macizo Nordpatagnico: Revista de la Asociacin Geolgica Argentina, Argentina,

v. 56, no. 3, p. 404-407.

2005. Geologia del Grupo Los Menucos, Comarca Nordpatagnica, Argentina: Congreso

Geolgico Argentino, 16, La Plata, Argentina, Actas, Tomo I, p. 233-238.

Labudia, C.H., Llambas, E.J., Rapela, C.W., and Artabe, A., 1995, El Trisico de Los Menucos-

procesos volcnicos y sedimentarios: Segunda Reunin del Trisico del Cono Sur, Baha

Blanca, Argentina, Actas, p. 17-21.

Llambas, E.J., Caminos, R., and Rapela, C.W., 1984, Las plutonitas y vulcanitas del Ciclo Eruptivo

Gondwnico, in Ramos, V.A., ed., Geologa y Recursos Naturales de la Provincia de Ro

Negro: Congreso Geolgico Argentino, 11, San Juan, Argentina, p. 85-118.

Lema, H., Busteros, A., Giacosa, R., Dalponte, M., Godeas, M., Zubia, M., 2005, Geologa del

Complejo Los Menucos Macizo Norpatagnico, Provincia de Ro Negro: Congreso Geolgico

Argentino, 16, La Plata, Argentina, Actas, Tomo I, p. 27-32.

Mackin, S., 2003, SIMIS-FeatureSearch 1.6. Spectrometer Independent Mineral Identification Software

- User manual and tutorial: SIMIS Solutions S.L., England. 90 p.

Pontual, S., Merry, N., and Gamson, P., 1997a, G-Mex - spectral analysis guides for mineral

exploration- Spectral interpretation field manual: Kew, Victoria 3101, Australia, Ausspec

International Pty. Ltd., v. 1, 169 p.

1997b, G-Mex - Epithermal alteration systems: Kew, Victoria 3101, Australia, Ausspec

International Pty. Ltd., v. 4, 55 p.

19

1997c, G-Mex - Regolith logging: Kew, Victoria 3101, Australia, Ausspec International Pty. Ltd.

v. 8, 60 p.

Ramos, V.A., 2004, La Plataforma Patagnica y sus relaciones con la Plataforma Brasilera, in

Mantesso-Neto, V., Bartorelli, A., Carneiro, C.D.R., and Brito-Neves, B.B., Geologa do

Continente Sul-Americano- Evoluo da Obra de Fernando Flvio Marques de Almeida: Beca

Produes Culturais Limitada [Brazil], 673 p.

Ramos, V.A., and Aguirre-Urreta, M.B., 2000, Patagonia, in Cordani, U.J., Milani, E.J., Thomaz Filho,

A., Campos, D.A., eds., Tectonic Evolution of South America: International Geological

Congress, 31st, Rio de Janeiro, p. 369-380.

Rapela, C.W., Pankhurst, R.J., Llambas, E.J., Labudia, C., and Artabe, A., 1996, Gondwana

magmatism of Patagonia- inner Cordilleran calc-alkaline batholiths and bimodal volcanic

provinces: International Symposium on Andean Geodynamics, 3rd, St. Malo, ORSTOM

editions, Colloques et Seminaires, Paris, France, p. 791794.

Rowan, L.C., Hook, S.J., Abrams, M.J., and Mars, J.C., 2003, Mapping hydrothermally altered rocks at

Cuprite, Nevada, using the Advanced Spaceborne Thermal Emission and Reflection Radiometer

(ASTER), a new satellite-imaging system: Economic Geology, v. 98, p. 1019-1027.

Rye, R.O., Bethke, P.M., and Wasserman, M.D., 1992, The stable isotope geochemistry of acid sulfate

alteration: Economic Geology, v. 87, p. 225-262.

Schalamuk, I.B., Zubia, M., Genini, A., and Fernandez, R.R., 1997, Jurassic epithermal Au-Ag deposits

of Patagonia, Argentina: Ore Geology Reviews, v. 12, p. 173-186.

Sillitoe, R.H., 1993, Epithermal models - Genetic types, geometric controls and shallow features, in

Kirkham, R.V., Sinclair, W.D., Thorpe, R.I., and Duke, J.M., eds., Mineral deposit modeling:

Geological Association of Canada, Special Paper, v. 40, p. 403-417.

20

1995, Exploration of porphyry copper lithocaps, in Mauk, J.L., and St. George, J.D., eds.,

Proceedings of Pacific Rim Congress, 1995, Carlton, Victoria: Australasian Institute of Mining

and Metallurgy, p. 527-532.

Souza Filho, C.R., Tapia Calle, C.H., Crsta, A.P., and Xavier, R.P., 2003, Infrared Spectroscopy and

ASTER imagery Analysis of Hydrothermal alteration Zones at the Quellaveco Porphyry-

Copper deposit, Southern Peru: Proceedings of the American Society for Photogrammetry and

Remote Sensing (ASPRS), Annual Conference, 1-12 (CD-ROM).

Stipanicic, P.N., Rodrigo, F., Baules, O.L., and Martnez, C.G., 1968, Las formaciones presenonianas

en el denominado Macizo Nordpatagnico y regiones adyacentes: Revista de la Asociacin

Geolgica Argentina [Argentina], v. 23, no. 2, p. 67-98.

Stoffregen, R.E., and Cygan, G.L., 1990, An experimental study of Na-K exchange between alunite

and aqueous sulfate solutions: American Mineralogist, v. 75, p. 209220.

Stoffregen, R.E., Alpers, C.N., and Jambor, J.L., 2000, Alunite-jarosite crystallography,

thermodynamics, and geochronology, in Alpers, C.N., Jambor, J.L., and Nordstrom, D.K., eds.,

Reviews in Mineralogy and Geochemistry, Sulfate minerals - Crystallography, Geochemistry,

and Environmental Significance: Mineralogical Society of America, Washington, D.C., v. 40, p.

453-479.

Sun, Y., Seccombe, P.K., and Yang, K., 2001, Application of short-wave infrared spectroscopy to

define alteration zones associated with the Elura zinc-lead-silver deposit, NSW, Australia:

Journal of Geochemical Exploration., v. 73, no. 1, p. 11-26.

Thompson, A.J.B., Hauff, P.L., and Robitaille, A.J., 1999, Alteration mapping in exploration-

application of short-wave infrared (SWIR) spectroscopy: Society of Economic Geologists

Newsletter, v. 39, p. 1, 16-27.

21

Windhausen, A., 1931, Geologa Argentina, in Peuser, J., ed., Geologa Histrica y Regional del

Territorio Argentino: Lda Buenos Aires, Argentina, v. 2, p. 1-645.

Yang, K., Browne, P.R.L., Huntington, J.F., and Walshe, J.L., 2001, Characterising the hydrothermal

alteration of the Broadlands-Ohaaki geothermal system, New Zealand, using short-wave

infrared spectroscopy: Journal of Volcanology and Geothermal Research, v. 106, p. 53-65.

22

Fig. 1: A. Simplified geological map of Somn Cur Massif in northern Patagonia, and adjacent geological provinces,

(modified from Aragn et al., 1996; Ramos and Aguirre-Urreta, 2000). The rectangle in the northern part of the massif

indicates the location of Figure 1B. B. Simplified geological map of Los Menucos region (based on Giacosa et al., 2005;

Lema et al., 2005; Labudia and Bjerg, 2005; this study). Abbreviations: LLF = La Laja Fault, LCBF = Lagunitas-Cerro

Bandera Fault

23

24

Fig. 2. Simplified geological map of Cerro La Mina prospect, Los Menucos area. The upper left inset shows the regional

location of Cerro La Mina, Cerro Abanico, and Aguada de Guerra prospects. Geological and structural data are based on

unpublished reports of Iamgold, and also from Ducart (2004), Giacosa et al. (2005), Lema et al. (2005), Labudia and Bjerg

(2005), and this work. Abbreviations: LLF = La Laja Fault, LCBF = Lagunitas-Cerro Bandera Fault.

.

25

26

Fig. 3. Photographs and photomicrographs of rocks in the Cerro La Mina prospect. A. View of andesitic lavas of the

Sierra Colorada Formation, Catrin area, next to an elongated zone with silicification surrounded by argillic alteration.

Width of view ~200 m. B. Rhyolite and andesite from the drill holes CMDD05 at 49 m and CMDD03 at 121 m,

respectively (see drill holes location in Figure 2, Catrin area). C. Flow-folded rhyolite lava, Domo La Vbora. D.

Photomicrograph (transmitted light, crossed polarizers) of a possible rhyolite with hydrothermal alteration obliterating

the original texture but preserving the embayment of a quartz phenocryst (sample LM122). E. Welded ignimbrite with

fiammes and lithic or pumice fragments completely altered to kaolinite, in the Cerro La Antena area. F. Hydrothermal

breccia with angular fragments cemented by dickite + quartz, Catrin area. G. Hydrothermal breccia with Fe-oxides and

dickite in the matrix, Catrin area. The clasts are highly silicified rhyolite, now fine-grained quartz. H. Hydrothermal

breccia body striking to the northeast, cutting silicified rhyolites; Catrin area. Abbreviations: dk = dickite, Fe-ox = Fe-

oxides, qtz = quartz.

27

28

Fig. 4. Comparison of field PIMA spectra resampled to ASTER spectral resolution, with atmospherically corrected

ASTER pixel spectra at the same geographic locations. ASTER SWIR bands (4-9) were employed, covering the 1.600-

1.430 m spectral range. The ASTER spectra show less deep absorption features if compared with the resampled PIMA spectra at the same location, however the differences at wavelengths corresponding to spectral bands 5, 6, and 7 between the

ASTER spectra are diagnostic for the mineral identification and mapping by the Mixture Tuned Matched Filtering (MTMF)

technique. Abbreviations: mxl kaolinite = moderately-crystalline kaolinite, hxl kaolinite = highly-crystalline kaolinite.

29

30

Fig. 5. Simplified distribution of alteration zones and mineral assemblages of the Cerro La Mina prospect. This map was

produced using PIMA spectroscopy, field mapping, petrography, and ASTER data. Abbreviations: al = alunite, brt =

barite, chl = chlorite, dia = diaspore, dk = dickite, ill = illite, kln = kaolinite, ms = muscovite, py = pyrite,

pyr = pyrophyllite, qtz = quartz, rt = rutile, sme = smectite.

31

32

Fig. 6. Reflectance spectra of altered samples from Cerro La Mina prospect. A. Spectra of advanced argillic and argillic

alteration mineralogy. Arrows indicate a small proportion of jarosite. B. Spectra of advanced argillic and silicic alteration

mineralogy. Arrows indicate a small proportion of alunite. C. Spectra of argillic alteration mineralogy. Arrows indicate a

small proportion of ferroan clinochlore.

33

34

Fig. 7. Photographs, photomicrographs and back-scattered electron (SEM) images of altered rocks in the Cerro La Mina

prospect. A. Inactive kaolin quarry located in the Cerro La Antena area, northeastern part of the prospect. Intensely silicified

ignimbrites forming resistant caps on the hills. This silicification grades downward to argillic alteration. B. Vuggy quartz in

the Catrin area. Width of view ~20 m. C. Hydrothermal breccia with subangular to subrounded fragments cemented by

quartz, Catrin area. D. Chalcedony apparently filling a fracture or open space, west of the Cerro La Antena. E.

Photomicrograph (transmitted light, uncrossed polarizers) of stage 1 alunite and quartz, apparently filling a vug (sample

LM125b). F. SEM image of zoned stage 1-alunite, with a K-Na-(Ca)-bearing core and K-bearing rim (sample LM125b). G.

Ignimbrite intensely altered to kaolinite + quartz, Cerro La Antena. H. Photomicrograph (transmitted light, crossed

polarizers) of stacks of dickite filling a vug, surrounded by kaolinite + quartz (sample LM099). I. Ignimbrite intensely

altered to massive kaolinite-quartz with dickite veins, western of Cerro La Antena. J. Photomicrograph (transmitted light,

uncrossed polarizers) of a fracture filled with kaolinite and cut by a late dickite veinlet. The wall rock corresponds to a

rhyolite with intense silicic alteration (sample LM108). K. Photomicrograph (transmitted light, uncrossed polarizers) of a

euhedral diaspore crystal (amostra LM125a). L. Symmetrical halos of goethite + hematite jarosite (dark colors) around a

fracture, overprinting ignimbrite with argillic alteration (mainly kaolinite + quartz). Cerro La Antena. M. SEM image of Fe-

oxides and gold in a vug (sample LM119). N. SEM image of an aggregate of APS minerals (sample LM119).

Abbreviations: al = alunite, APS = aluminium phosphate sulfate minerals, Au = gold, brt = barite, dia = diaspore, dk =

dickite, cha = chalcedony, Fe-ox = Fe-oxides, kln = kaolinite, qtz = quartz, rt = rutile.

35

36

Fig. 8. A. Variation of the structure of the double absorption features (doublet) at 2.2 m in kaolinite spectra, versus

increasing crystallinity from bottom to top of the figure (modified from Pontual et al., 1997C). B. Some kaolinite spectra of

Cerro La Mina showing the increasing crystallinity from bottom to top of the figure. Highly-crystalline kaolinite was

identified in the north and northeastern sector of the prospect.

37

38

Fig. 9. Spectral Mixture Tuned Matched Filtering (MTMF) classification results draped over the ASTER band 3 of Los

Menucos region. The white rectangle indicates the location of the Cerro La Mina prospect. Some dark gray areas represent

topographic shadows, which prevent the orbital sensor from receiving sufficient signal to determine the mineralogical

composition of the surface.

39

40

Table 1. Summary of the alteration zones recognized at Cerro La Mina prospect.

Alteration zone

Alteration subzone Mineral assemblages Alteration style Distribution

qtz py vg qtz rt Pervasive Widespread, mainly in the south, southeast and center of the prospect; caps the argillic alteration in the Cerro La Antena area

Silicic

qtz + cha Veinlets, structure-controlled, breccia matrix

Locally, mainly in the eastern part*

al (APS) + qtz dk kln ms pyr dia rt py brt

Pervasive, breccia matrix Domo La Vbora area

dk + kln + qtz pyr dia py brt Pervasive, breccia matrix Between Domo La Vbora and Tripailao areas, and also in Cerro La Antena area

Hypogene

dk + qtz dia Pervasive, breccia matrix East and north of Tripailao, and Domo Sur area

Advanced argillic

Supergene hem + gt + qtz jar al APS kln Veinlets, pervasive Locally, overprinting the other alteration*

Argillic kln dk ill qtz sme Pervasive Center part

kln ill sme chl Pervasive Northeastern part; underlying the silicic alteration in the Cerro La Antena area

ill qtz ms kln Pervasive, veinlets Northwestern and western part

Abbreviations: al = alunite, APS = aluminium phosphate sulfate minerals, brt = barite, cha = chalcedony, chl = chlorite, dia

= diaspore, dk = dickite, gt = goethite, hem = hematite, ill = illite, jar = jarosite, kln = kaolinite, ms = muscovite, py =

pyrite, pyr = pyrophyllite, qtz = quartz, rt = rutile, sme = smectite, vg qtz = vuggy quartz. (*) These alteration subzones

occur locally; therefore, their distribution is not showed in Figure 9.

41

Appendix 1

Spatial distribution of the samples used for spectral analysis in the Cerro La Mina prospect. Petrography, DRX, and SEM

analyses were applied in some of these samples.

42

43

Appendix 2

Comparison of mineral assemblages derived from XRD, reflectance spectroscopy and ASTER processing of the same samples and locations.

44

Sample UTM-W UTM-S XRD analysis Reflectance spectroscopic ASTER processing

LM9 569061 5473230 Quartz (major), dickite (minor), kaolinite (trace) Quartz, dickite, goethite Quartz

LM10 569038 5473240 Quartz (minor), kaolinite (minor), dickite (minor) Quartz, kaolinite, dickite Quartz

LM11 569002 5473259 Quartz (major), dickite (minor), kaolinite (minor) Dickite, kaolinite Quartz

LM15 568774 5473491 Quartz (major), calcite (minor) Quartz, calcite Quartz

LM18 568655 5473721 Kaolinite (major), quartz (minor) Kaolinite, quartz Kaolinite, quartz

LM19 568638 5473751 Kaolinite (major), dickite (minor), quartz (minor) Kaolinite, dickite Kaolinite

LM20 568636 5473855 Kaolinite (major), dickite (major), quartz (minor), smectite (trace)

Kaolinite, dickite Kaolinite

LM22 568589 5473967 Quartz (major), kaolinite (major), dickite (minor), alunite (minor)

Kaolinite, dickite, alunite Kaolinite

LM24 568450 5474071 Dickite (major), quartz (minor), kaolinite (minor), alunite (minor)

Dickite, kaolinite, alunite Kaolinite, alunite

LM28 568261 5474344 Kaolinite (major), quartz (minor), alunite (minor), illite (trace)

Alunite, kaolinite Alunite

LM29 568169 5474367 Illite (major), alunite (major), quartz (minor), kaolinite (minor)

Alunite, illite, kaolinite Alunite

Note: minerals detected using XRD, but not recognized by the spectral analysis, may be present in small amounts, or do not

have absorption features in this wavelength interval (e.g., quartz).

45