Geology, mineralogy, origin and possible applications of some Argentinian kaolins in the Neuquen basin

Applied Clay Science 12 (1997) 27-42

Geology, mineralogy, origin and possible applications of some Argentinian kaolins in the Neuquen basin F. Craver0 a, I. Gonzalez b, E. Galan b,*, E. Dominguez a Departamento b Departamento

a

de Geologia-CONICET, de Cristalografia

Universidad National de1 SW, San Juan 670, 8000 Bahia Blanca, Argentina y Mineralogia, Facultad de Q&mica, Uniuersidad de Seuilla, Apartado 553, 41071 Seville, Spain

Received 22 February 1996; revised 17 October 1996; accepted 17 October 1996

Abstract The geology and genesis of three kaolin deposits (Las Mellizas, Chita and Misud), located in the Neuqutn basin were studied. Kaolin mineralogy and oxygen isotopic data indicate that kaolinite comes from a weathered area developed during the lower to middle Jurassic times; the kaolinite was then transported and deposited in a fluvial environment. I/Sm comes from in situ illite degradation. Kaolin properties are related to mineralogical and chemical composition and to compactation and cementation. Low plasticity of these kaolins is due to high degrees of compactation undergone, and plasticity increases as I/Sm content increases. Viscosity is related to pH: in low pH clay suspensions the edge faces are positively charged, so on stirring, they collide with the negative charged faces forming card-house structures, thus enhancing the viscosity. Cementation effects makes it difficult to get dispersed suspensions. As a ceramic raw material, these kaolins are considered stoneware clays. When kaolins with lower iron oxide content are mixed with quartz and feldspar, an optimum white stoneware is obtained at 1150°C. On this basis, the three deposits can be exploited to make stoneware products, but selected beds should be mined in order to obtain the best quality. Keywords:

kaolin; genesis: applications;

* Corresponding

Neuq&n

basin; Argentina

author. Tel.: + 34-5-4557 141.

0169-1317/97/$17.00 Copyright PZI SO169-1317(96)00035-X

0 1997 Elsevier Science B.V. AI1 rights reserved.

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1. Introduction In southern Argentina there are three main areas with kaolin deposits, two in Patagonia, in the provinces of Santa Cruz and Chubut and one in the province of NeuquCn (Fig. 1). The latter is not as well studied as the former ones, mainly because the kaolin is not suitable for use in fine ceramics and the paper industry. The NeuquCn

CHALLACO

Fig. 1, Geological

FORMATION

and geographical

setting of the kaolin deposits

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kaolin deposits are distributed in an area about 1000 km2 and are situated in a middle jurassic sedimentary continental sequence (Challac6 Formation). Production of kaolin began in 1940 and in recent years the average output has been over 40,000 ton/year of clay classified as refractory and plastic (Angelelli et al., 1976). Reserves are over 30,000,OOO ton. To the west of the study area, Dominguez (1988) described the geological setting and mineralogy of other kaolin deposits, and Allione et al. (1992) studied two deposits: Misud and La Beatriz, classified by them as plastic to semiplastic fire clays. The objective of this work is to contribute to the knowledge of the geology, mineralogy and technological properties of these kaolin deposits and to suggest the most suitable uses. To carry out this work, three deposits located in the eastern sector were chosen (Fig. 1) which contain kaolins of different qualities. Las Mellizas and Misud were selected because they represent two of the main mines still producing kaolin, and Chita because it has been mined underground and later abandoned due to clay rheology problems. Kaolin from Las Mellizas is used for making floor and wall tiles, that from the Misud deposit is used for manufacturing whiteware products, and the Chita kaolin was used for refractory products and for the rubber industry, from 1946 to 1976, and then from 1985 to 1993 the clay was used for whiteware products, but viscosity problems caused the exploitation to be discontinued.

2. Geologic setting and deposits description This area, located about 60 km southeast of Zapala, is part of the NeuquCn Basin and lies on the northwestern limb of the Cerro Lotena-Cerro Granito anticline (Fig. 1). The landscape is characterized by a relatively flat morphology. The clay bearing formation strikes about N75-100” and dips 8-10N. These gently dipping Jurassic strata are covered by flat lying sedimentary cretaceous deposits and tertiary basalts. The basement of the NeuquCn Basin consists of a Carboniferous-Permian complex (Leanza, 1990) intruded in highly metamorphosed rocks Precambrian to Lower Paleozoic in age (Digregorio and Uliana, 1980). A huge rhyolitic volcanic event, Choiyoi Group (Upper Carboniferous-Upper Triassic), overlies the older rocks. The infill of the basin is characterized by three marine-continental sedimentary cycles, which were deposited from early Jurassic up to Cretaceous time. The clay deposits are located in the first cycle, Cuyano group, with a total thickness of 2500 m. This group comprises three formations characterized by distinct facies: Los Molles (deep sea), Lajas (littoral) and Challac6 (continental). The Challac6 formation, Later Upper Bajocian to Middle Bathonian in age, is characterized by a sequence of facies, interpreted by Zavala (1993), as an anastomosed fluvial system; this formation comprises two main facies, the coarser facies is built up of fining-upward crossbedded conglomeratic sandstones, with sharp erosional bases and the finer one of clay sized sediments, grey, red or purple in color with sandstone intercalations. It is in this facies where the kaolin deposits occur.

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In the Las Mellizas deposit the only kaolin bed is located on a small hill, where a mine 300 m long was opened. The clay bed is massive to laminated, about lo-15 m in thickness, and gray to purple in color. Toward the top of the bed, sandstone lenses are quite common. Over the clay lies a thick sequence (about 6 m in thickness) of amalgamated, fining-upward crossbedded conglomeratic sandstones. Based on drill hole data, the resources are over 2,000,OOO ton (Dominguez, 1992). The Chita deposit consists of two main kaolin levels and is lenticular in shape. The lower level (NSF), the more regular, is about 2 m thick, massive, and brownish red in color. Pyrite (Py) is present as a replacement of plants debris or disseminated in the clay. The upper level (HC), the more irregular one, is also about 2 m thick but has lateral variations and clay-sized very pure kaolinitic lenses. It is very thinly laminated and is grey in color which becomes red on exposure because of iron oxide coatings. Because a thick sequence of very hard sandstone overlies the clay the deposit was mined underground (for about 20 year) in an area of about 1000 m X 200 m. This mine was exploited from 1946 to 1976. In 1985 it was reopened, and produced about 600 ton/month until 1993. The reserves are about 120,000-150,000 tons. Misud, the largest deposit in the area, is along the eastern border of a 4 km long East-West trend of kaolin mines, where Chita is the westernmost. The mine covers an area of about 1200 m X 600 m. It is comprised of several beds with a total clay thickness of about 20 m. Drill data show several intercalated sandstones lenses. The clay is overlain by a thick sandstone sequence (8-10 m). At present, only one bed is exploited, the APM112, which is grey and massive. Another bed, the APMl13 is yellow to reddish in color but is not in production. This mine was opened in 1976 and since then it has produced 3200 ton/month.

3. Materials

and methods

Representative samples (about 10 kg) of kaolin from each deposit were collected using a combination of both a channel and chip method. Samples were labeled: LM from Las Mellizas, NSF and HC from Chita, APM 112 and APMl13 from Misud. After splitting, mineralogical and chemical composition, grain size distribution, texture, plasticity, viscosity and pH as well as firing behavior were determined. For mineralogical composition by XRD a Phillips X-ray diffractometer PW 1130/90 at 20 mA and 40 kV, with Ni filtered Cu Ka radiation, was used. The whole sample and < 2 pm mineralogy were determined by standard quantitative methods and data from Schultz (1964), Biscaye (1965) and Martin Pozas (1975) on random and glycolated oriented samples (less than 2 Frn), respectively. Because the relative proportion of I/Sm increases in the fraction less than 0.2 pm (Hewer et al., 19761, the identification of these minerals was made on glycolated oriented samples. The fraction < 0.2 Km was obtained by centrifuging at 2400 rpm during 35 min (Moore and Reynolds, 1989). Kaolinite crystallinity was measured following the Stoch method, in which the presence of quartz does not interfere (Galan et al., 1994). The major elements chemical composition was determined using different techniques depending on the type of element analyzed. For SiO, calorimetry and gravimetry and

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31

for the other elements atomic absorption spectrometry was used. Grain size distribution was determined on < 100 pm samples with a Micromeritics 5000 Sedigraph. Kaolin textures and kaolinite morphology were observed by SEM and TEM. Atterberg limits were used for plasticity determination. Viscosity was measured in an aqueous suspension with about 69% solids concentration with a Brookfield viscometer, at 10 rpm with spindle 3, and pH was measured in a distilled water suspension containing 10% solids concentration. Previous to the determination of firing properties, chemical data were plotted in the triangular diagram of Fabbri and Fiori (1985) in order to test the possible applications of these clays in ceramic. Samples whose chemical compositions are not represented in the defined application fields were corrected with addition of feldspars and quartz up to reach an appropriate composition. Ceramic tests consisted of firing samples and mixtures before cited from 1000 up to 1200°C. The highest heating temperature was 1200°C because according to the technical properties, color, and composition of these materials they are not appropriate for porcelain and refractories. Sample discs of about 2 X 1 cm2 were prepared with a hydraulic press. Linear shrinkage, loss on ignition and water absorption capacity were determined at each temperature according to the Spanish Normative (UNE 61-033-75). XRD was performed on the fired bodies to determine the high temperature phases and SEM was also used to study the mineral phases formed and microstructures.

4. Results 4. I. Kaolin characterization The samples are mainly composed of quartz and kaolinite with low to medium crystallinity (Stoch index ranges between 1.36-0.79), and interstratified I/Sm, which was present in three samples (Table 1). Quartz content decreases in the finer fractions, except in samples NSF and HC, indicating that it is very fine grained or microcrystalline. Goethite was detected in only one sample (NSF). Electron microscopy analyses show that almost all the samples are constituted of kaolinite crystals arranged in face to face patterns (Fig. 2), but, as in the LM sample, swirl patterns are also present (Fig. 3). Kaolinite crystals are pseudohexagonal with sizes as fine as 0.1 pm (Fig. 4). When the laminated structure of sample HC is seen by SEM and scanned with EDAX, layers of quartz + kaolinite alternating with others of kaolinite + iron oxides are clearly exposed. In Fig. 5 a mica type crystal shows “open borders”. The chemical data (Table 1) correlate with the mineralogical composition, and the silica and alumina contents agree with the quartz and kaolinite contents. Iron content is high, but iron oxides were detected by XRD only in one sample (NSF), which means that iron could be present as amorphous oxides or hydroxides. The grain-size distribution (Table 1) shows that the samples from the Chita mine (NSF and HC) are the finest, with 60-70% < 2 pm. Both the high amounts of the tine fraction and the same amount of quartz in the bulk kaolin and in the < 2 pm fraction clearly indicate that this mineral is very fine grain sized or microcrystalline. APM113

LMT <21*m

APMl12T <2pm APM113T <2 I*rn

NSFI<2 pm HCT <2 firn

Las Mellizas

Misud

Chita

19 11 11 12

81 89 89 87

64 96 95 97 60.00 59.00 48.00 49.00

64.00 47.00 48.00 45.00

57.00 57.00

II 88

23 12

36 4 5 3

SiO,

K

Q

0.23 0.42 0.15 0.12 0.10 0.38 0.08 0.19

25.00 31.00 33.00 34.00

0.24 0.16

NazO

24.00 36.00 30.00 34.00

27.00 28.00

42%

(%)

(%I

0.84 1.16 0.62 0.70

0.75 0.74 0.50 0.50

1.13 0.18

K,O

of the samples studied

Chemical analysis

and grain size distribution

Mineralogy

0.29 0.28 0.19 0.25

0.18 0.16 0.25 0.23

0.59 0.40

CaO

0.30 0.45 0.19 0.22

0.21 0.32 0.21 0.24

0.42 0.50

MgO

4.57 3.98 6.13 4.13

1.93 3.08 8.99 7.38

4.15 4.21

Fe&

9.78 10.47 12.41 12.02

9.00 12.31 12.61 13.10

10.89 9.88

L.I.

100.88 100.72 100.62 100.51

100.30 100.03 100.85 100.57

101.42 100.33

Total

57 69

23 92

41

39

42

34

32

73

<2 pm

91

52

91

39

pm 81

20-2

< 20 pm

(%)

Grain-size

I/Sm is present in the < 0.2 pm fraction of LMT (5%), NSFT ( < 5%) and HCT (traces). Goethite was detected in NSF. Q = quartz; K = kaolinite; L.1. = loss on ignition.

Sample

chemical composition,

Deposit

Table 1 Mineralogy,

F. Crauero et al/Applied

Clay Science 12 (1997) 27-42

Fig. 2. Kaolinite crystals arranged in face to face patterns.

fine clay size and chemical amc punt of the qua rtz, points

content does not agree with the high kaolinite amount showed by XRD composition, indicating the poor dispersability of this sample. The large fraction 20-2 pm in sample APM112, coupled with the high amol mt of out that this mineral is present mainly in this fraction.

Fig. 3. Swirl pattern in sample LM, from Las Mellizas deposits.

34

F. Crauero et al. /Applied Clay Science 12 (1997) 27-42

Fig. 4. Kaolinite crystals showing pseudohexagonal

4.2. Technological

properties

shapes.

and industrial applications

The Atterberg plasticity index (Fig. 6) shows that these kaolins are not very plastic. The normal plasticity index for ceramic kaolins is about 30-35 (Konta, 1980). Sample LM and those from the Chita mine (HC and NSF) are the most plastic and have acceptable molding properties. According to the clay workability chart of Bain and Highly (1978) they could by used for pottery and bricks. On the other hand, samples APMl12 and 113 are not appropriate due to poorer cohesion. This different plastic

Fig. 5. Mica type crystal showing open borders.

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35

properties

bricks t I

I

I

I

10

20

30

40

50

plasticity index 0

APM112

0

NSF

)(

AF’M113

0

LM

A

HC Fig. 6. Clay workability

chart (after Bain and Highly, 1978).

50% Fe203

+ Tie0

0

100% Si02

Apt.4112

N2o3 a = red stoneware b, b’, W

Fig. 7. Triangular diagram studied are plotted.

. = white

of Fabbri

stoneware (german. english, french)

and Fiori (1985) where SiO, /Al,O,

/total

oxides of raw materials

36

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behavior is mostly related to the mineralogy rather than to kaolinite crystallinity, which is very similar for all the samples. The measured pH values, Las Mellizas 8.32, APMll2 8.70, APMl13, 7.35, NSF, 4.8

(a)

Las

Mellizas

NSF

L.S/W.A.(%)

L.S/W.A.(%) ._ 10.

8.

8-

6h44-

2-

2.,<,_

$00

950

1000105011001150

O(“1””

120012501300

900

950

Temperature -Linear

Shrinkage

+Water

1000 1050 1100 1150 1200 1250 1

Temperature absorption

-Linear

Shrinkage

HC

+-Water

absorption

APM112

L.S/W.A.(%)

L.S./W.A

(%)

14.

14Y loS6-

642-

$00

950

1000 1050

J

1100 1150 1200 1250 1300

9”IOO 950 I

Temperature ‘Linear

Shrinkage

+Water

1000 5 1050 I 1100 1 1150 I 1200 I 1250 I I

Temperature absorptcon

‘Linear

shrinkage

+Water

absorption

Fig. 8. (a) Sintering diagrams of samples LM from Las Mellizas deposits, NSF and HC from the Chita mine and APMI 12 from Misud deposits. (b) Sintering diagrams of sample APM113 from a Misud deposit and the mixtures with quartz and feldspar of samples LM (Las Mellizas), NSF (Chita) and APM I12 (Misud).

F. Cravero et al. /Applied

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APM113

LM

L.S/W.A.(%) 12

I

I

4

$00

950

31

mixture

L.S/W.A.(%)

I

I

0

!

I

I

1000 1050 1100 1150 1200 1250 1300

Temperature ‘Linear

Shrinkage

NSF

+Water

Temperature absorption

-Linear

Shrinkage

APM112

mixture

+Water

absorption

mixture

L.S/W.A.(%)

L.S/W.A.(%)

14-

12-

10864-

2-I>, $00

950

Temperature -Linear

Shrinkage

+-Water

1000 1050 1100 1150 1200

1250

10

Temperature absorption

‘Linear

Shrinkage

+Water

absorption

Fig. 8 (continued).

and HC 4.70, denote that the Las Mellizas

and Misud (APM112 and APMl13) samples are slightly alkaline, whereas the samples from the Chita mine are definitely acidic. The pH of the clay suspension is related to the edge surface electric charge (Rand and Melton, 1976). The low pH values are related to positively charged edges, which would be expected in samples from the Chita mine.

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For vizice sity measurement, it was difficult to get dispersed 70% solid suspensic jns, thexefc )re on 11y comparative data were obtained. Sample APM112 has the lob rest vi: XOSi ItY, absout 180-200 cps which decreases to 144 when adding 0.3 ml defloccul ant

Fig. 9. SEM observations

of heating the NSF mixture sample at (a) lOOO”C, (b)

1lOO”C, and (c) 1200°C

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(Calgon). The viscosity of sample LM was too high to allow any measurements but with the addition of 2 ml of deflocculant the viscosity was 1300 cps. It was impossible to get suspensions containing 70% solids for samples HC and NSF. Regarding the color (red, gray, purple) and the high iron oxide content, these kaolins cannot be used in fine ceramics. Due to their chemical composition, they could be considered as ceramic raw material for stoneware (Konta, 1980; Konta, 1995) but according to Fabbri and Fiori raw materials should be modified in order to be closer to the ideal chemical composition. Chemical data of raw samples plotted on the triangular diagram proposed by Fabbri and Fiori (1985) showed that samples LM and APM 112 fit into the white stoneware field; sample NSF is very close to the edge, HC not far beyond it, and APM 113 quite far from it (Fig. 7). The latter two samples have the highest total oxides content. Taking into account the ideal composition for an optimum white stoneware product according to those mentioned authors (SiO, = 72%, Al,O, and total oxides = 8%) the samples that are within or near to the white stoneware field (APM112, LM, NSF) were blended with feldspar and quartz. For sample LM, 53% clay was mixed with 26% feldspar and 21% quartz, for APM112, 53% clay was mixed with 36% feldspar and 11% quartz, and for NSF, 55% clay was mixed with 28% feldspar and 17% quartz. The firing tests performed on raw samples and on mixtures as well showed the optimum gressification temperature. These data were plotted on sintering diagrams, (Fig. 8a and b). For raw samples maximum linear shrinkage was around 8% at 12OO”C, except for APM 112 (6%). For mixtures linear shrinkage values decrease to around 6%. Absorption water capacity is 4% or less for all the samples fired at 1200°C except for samples APM 112 (8%). These values are appropriate for stoneware and whiteware (Burst, 1991). Concerning to the mineralogical composition of fired bodies, it is to be noted that mullite could be identified by XRD at ca. 1100°C (pseudomullite, according to Burst, 1991) and mullite content, crystallinity and size increased at 1200°C. At the same time cristobalite also started to be detected at 1100°C and amorphous silica (the main component observed at 1000°C) decreased abruptly towards 1200°C. For the mixtures, feldspar was detected up to 1100°C and cristobalite formation was delayed up to 1200°C or later (APM 112) increasing the content of mullite and the mullite/cristobalite ratio from 1, for the raw materials, up to 2/l in the mixtures. The microstructures of fired bodies were typical those of dominant amorphous materials, with non-defined geometrical forms and high intergrain and fracture porosity which at 1200°C decreases by sintering (Fig. 9a-c).

5. Discussion Regarding the origin of the kaolinite, Dominguez (1988) suggested that this mineral could have come from an altered surface developed on the Choiyoi group, which was present in the main source area of the basin at the time the Neuqdn basin developed. The conglomeratic beds that are above and below the clay are composed of rhyolitic volcanic clasts and minor amounts of granitic clasts. The SEM textures (edge to edge

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Clay Science 12 f 1997) 27-42

arrangements and swirl patterns) clearly indicate a detrital origin and the clay mineralogy, mainly kaolinite, along with quartz and traces of feldspars (Dominguez, 1988) correlates with the proposed source. Craver0 and Chivas (unpublished data, 1992) found that the oxygen isotope composition of kaolinites from eight different clay deposits in the Challaco formation range from 15 to 16% which indicates that the kaolinite came from a weathered surface. Taking all the above data into account, the weathered surface must have been developed on Choiyoi rocks during the Lower to Middle Jurassic. Zavala (1993) considered that the Challaco formation was deposited as an anastomosed fluvial system. In this environment, the clay deposits represent the alluvial plain deposits. According to the SEM textures, the clay deposition was the result of kaolinite flocculation in an aqueous medium (Keller, 1978); furthermore, the laminated texture of kaolin HC could be related to the deposition in a lacustrine type environment with climatic oscillations, thus depositing on the one hand kaolinitic laminae during a calm season in which no sediments were fed to the lake and on the other hand quartz rich layers where quartz was supplied during a stormy or rainy season. For I/Sm an origin other than detrital is proposed. SEM (Fig. 5) shows a mica type mineral with open borders that are frayed causing it to resemble smectite layers; therefore it seems that the mixed layer mineral could be formed after mica or illite degradation. The illite itself is common in a kaolinization profile, and could have been eroded and transported with the kaolinite. Regarding kaolin properties, the plasticity is not as high as was expected from the fine-grain size and the I/Sm content. Nevertheless, there is a clear relationship between plasticity and I/Sm: the higher the plasticity index the higher the I/Sm content. As in the AMP1 12 sample the low plasticity value is related to the high quartz content (35%); in the other samples, the high degree of compactation and the effect of diagenesis seems to be the best explanation (Konta, 1980). In samples APMl13 and HC this is enhanced by the presence of iron oxides acting as a cement between the kaolinite particles. Viscosity or flow behavior is also affected by the high degree of compactation, which makes dispersion difficult. The high viscosity obtained in samples from the Chita mine (NSF and HC), under the test conditions used, can be related to positively charged surfaces (low pH values), which, when stirred collide with the negative charged surfaces, produce a card-house structure. However, note that the expandable clay content, particle size, morphology and particle size distribution of the kaolin can also contribute significantly to the viscosity. Both the mineralogical and chemical compositions indicate that the best application for most of these clays seems to be for stoneware, but, due to the high iron oxides content, samples APMl13 and HC cannot be used for making such a product. Sintering features show that in sample LM the vitrification interval is reached at about 105O”C, which is too low for a kaolin because the I/Sm and iron oxides present act as fluxes. At 1OOO”C, sample LM has a high linear shrinkage and begins to melt at about 1200°C; however, when it is mixed with quartz and feldspar, the initial vitrification interval moves to 1150°C and at 1200°C there is still open porosity. Due to the kaolin purity, sample APMl12 did not reach the vitrification point in the analyzed range, but when this sample was mixed with quartz and feldspar the vitrification point is reached at 1150°C as in the former sample. Sample APMl13 almost melts at 12OO”C, like sample

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LM, due to its high iron oxide content. Raw sample NSF and its mixture almost the same temperature, but the mixture shows less linear shrinkage.

41

vitrified

at

6. Conclusions The kaolins studied were formed in a fluvial environment (Challaco formation) and represent deposits on an alluvial plain. Kaolinite and illite were eroded from a weathered area developed on Choiyoi rocks during Lower to Middle Jurassic. The I/Sm came from illite degradation. Physical properties are closely related to the mineralogical and chemical composition as well as to compactation and cementation, which are diagenetic effects. Low plasticity is due to the high degree of compactation, and plasticity increases as the I/Sm content increases. Viscosity is related to both the degree of compactation that makes dispersion difficult and to pH; the lower the pH the more viscous the clay. As a ceramic raw material, these kaolins can be considered as stoneware clays. The best white stoneware products are obtained when the raw kaolin is mixed with quartz and feldspar, mainly in samples LM, APM112 and NSF, which have more economical interest. Based on all the above results the three deposits can be exploited for ceramic white stoneware utilization. In the Las Mellizas deposit the entire thickness of clay can be exploited but in the Misud mine only level APMl12 and in the Chita mine level NSF can be exploited. Mineralogical and chemical composition analyses are important properties for a good quality control of these kaolins. The values of the vitrification range indicate that the kaolin samples are generally vitrified at low temperature, and the vitrification interval is short.

Acknowledgements The authors are grateful to Dr. H.H. Murray for reviewing the paper. Our gratitude is also expressed to Piedra Grande S.A. who always cooperated with the research. Part of this work was carried out in Spain on the basis of a post-doctoral fellowship granted by the EU to F.C.

References Allione, J.L., Pettinari, G., Giaveno, M.A. and Chiacchiarini, P., 1992. Caracterizaci6n de niveles arcillosos presentes en mina Misud y La Beatriz, Dept. Zapala. Prov. Neuqutn. IV Congr. Geol. Econ., C6rdoba, Argentina, Actas: 226-240. Angelelli, V., Schalamuk, I.B. and Arrospide, A., 1976. Los yacimientos metaliferos y rotas de aplicacidn de la regi6n Patagonia Comahue. Secretaria de Estado de Mineria, Buenos Aires, An., 18. Bain, J.A. and Highly, D.E., 1978. Regional appraisal of clay resources challenge to the clay mineralogist. In: M.M. Mortland and V.C. Faxmer (Editors), Proc. Int. Clay. Conf. Elsevier, Amsterdam, pp. 437-446.

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