Research paperCeramic behaviour of clays in Central Chile
Introduction
Chile contains a significant amount of industrial minerals and rocks whose deposits formed during various geological processes that occurred between the Paleozoic and Cenozoic eras. Chilean clays exploitation is very low with respect to the volume of their resources because they are solely used in handicraft and industrial ceramics for the Chilean domestic market.
In Chile, according to its National Service of Geology and Mining, there are approximately 188 deposits of clays. Of these, 27 deposits are found within the Metropolitan Region; the Libertador General Bernardo O'Higgins Region (Region VI of Chile) has 25, specifically kaolin, plastic clay, and common clay (Gajardo, 2000); in the Maule Region, there are 16 deposits.
The clay outcrops examined in the Metropolitan Region correspond geologically to an era between the Pleistocene and Holocene, and their petrogenetic origin is a result of detrital sedimentation. The weathering processes that formed kaolin deposits in Chile are related to kaolinization due to climatic and morphological conditions during the Upper Tertiary. These clays are used for the manufacture of refractory brick, aluminum sulfate, and cement.
The main deposits of common clays are found in the vicinities of large populated centers, undoubtedly those most numerous in the basin of Santiago. This basin is full of river materials: sands, gravels, and sediments related to the development of the large rivers that cross them; there are also fine materials, clays and silts, deposited in lagoon environments and very frequently developed towards the westernmost sector of the Central Depression, which was and currently is under conditions for the establishment of lacustrine environments.
The deposits in this region have been grouped into five sectors. Sector R13.1 contains 9 clay deposits whose origin is of supergene alteration, and are stratiform and/or irregular. Sector R13.2 has 11 kaolin deposits. Sector R13.3 has 3 deposits of common clays of a sedimentary clastic origin and stratiform. In sector R13.4, there are 2 deposits of common clays that are clastic sedimentary in origin and stratiform. The fifth sector, R13.5, the Metropolitan Region, has 1 deposit of common clay whose origin is supergenic alteration, and is stratiform and/or irregular. (Gajardo, 2000; SERNAPLAC-MINMETAL, 1979; SERNAGEOMIN-BRGM, 1994; Gajardo and Carrasco, 1997; Gajardo and Gutierrez, 1993; Meseguer et al., 2008).
The Libertador General Bernardo O'Higgins Region (Region VI of Chile) contains 25 deposits of clays, specifically kaolin, plastic clay, and common clay (Gajardo et al., 2003). We have divided the locations of these deposits into five sectors. Sector R6.1 has 6 deposits, of which 4 are kaolin and 2 deposits are plastic clays. Sector R.6.2 contains 2 deposits of common clays whose origin is sedimentary clastic and are stratiform. In sector R.6.3, there are 10 kaolin deposits. Sector R.6.4 contains 6 plastic clay deposits. The final sector, R.6.5, has only one kaolin deposit (Gajardo, 2000; SERNAPLAC-MINMETAL, 1979: SERNAGEOMIN-BRGM, 1994; Gajardo and Carrasco, 1997; Gajardo and Gutierrez, 1993).
In Region VI, there are deposits of sedimentary plastic clays corresponding to interstratified clastic strata. The origin of these clays is related to weathering processes of the metamorphic rocks in the Chilean Coast Range, whose product was deposited in sub-aquatic environments, probably marine, during the Upper Tertiary, along with the clastic sediments, conforming a sequence of total thicknesses >15 m that partially covers the metamorphic rocks in the area. The kaolin deposits in Region VI are found in the Litueche-La Estrella area, Coast Range of Region VI, and represent the product of the kaolinization of granite, which constitutes a kaolin stratum in a sub-horizontal position, covered by fine to coarse clastic material that extend towards the south of the Litueche-La Estrella area, always in the Coast Range and genetically related with the Coastal Batholith. The deposits of common clays in Region VI are located in the vicinities of the large populated centers. In Region VI, they are found in the basin of Rancagua and San Fernando, which are full of river materials: sands, gravels, and sediments related to the development of the large rivers that cross them; there are also fine materials, clays and silts, deposited in lagoon environments and very frequently developed towards the westernmost sector of the Central Depression, which was and currently is under conditions for the establishment of lacustrine environments (CORFO-INTEC, 1989; Pardo, 2011).
The examined deposits are located in Region VI, in Cachapoal Province, and specifically in the Malloa commune. Geologically, they correspond to a period between the Oligocene and Miocene, and their origin depends upon the type of clays: the common clays were constituted by clastic sedimentation, the plastic clays by clastic sedimentation and supergenic alteration, while the kaolins were so by hydrothermal and supergenic alteration. This work examines the behavior of the ceramic clays from deposits located within the Malloa commune.
Cauquenes Province, located in the Maule Region, has eleven deposits according to the National Service of Geology and Mineralogy of Chile. The clays were formed by supergenetic alteration processes during the Paleozoic, which were transported and deposited in marshy lagoon environments. The maximum age of the sediment generation process in the deposits of plastic clay corresponds to the Middle Miocene, an age indirectly determined by the minimum age for the supergenic alteration process. Their minimum age must be prior to the morphostructural differentiation event of the Chilean Coast Range.
The deposits of sedimentary plastic clays located in Region VII are tabular bodies covered by clastic sediments, which is being exploited by the Fanaloza Corporation.
Refractory clays from the weathering of slate and schist of metamorphic basement rock are located in regions VII and VIII. The deposits are formed by strata with irregular thicknesses and dimensions, covered by clastic and clayish sediments. These are second best in refractory quality, after those from Montenegro. Those from Region VII (San José and San Miguel) and Region VIII (located between Lota and Carampangue) contain between 25 and 30% aluminum oxide and are used in the manufacture of refractory bricks in mixtures with higher quality clays (kaoliniferous bauxites and imported bauxites).
The refractory clays that follow those from Montenegro in terms of importance come from deposits formed in weathering processes of slate and schist of the metamorphic basement rock, and are located in regions VII and VIII. These deposits have a genesis that is common to the deposits of kaolin and plastic clays from weathering and correspond to the same supergene process related to favorable climatic and morphological factors that occurred during the Upper Tertiary.
The objective of this research is to review the mineralogical, physicochemical, and ceramic behavior of clays in the Pirque commune (Metropolitan Region), Malloa commune (Libertador General Bernardo O'Higgins Region, Region VI), and in Cauquenes Province (Maule Region, Region VII).
Section snippets
Materials and methods
Samples of each outcrop were taken according to standardised sampling procedures. The largest number of samples coincided with the largest amount of earth taken from the areas under exploitation (Sanfeliu, 1991a, Sanfeliu, 1991b). The sample number is refers the place in the deposit. Mine samples were sieved using a sieve of 63 μm. Mineralogical analysis of the samples was performed by X-ray diffraction (XRD). The process used in the mineralogical analysis is the fractionating method described
Chemical and mineralogical characterization of clays
Table 1 shows the chemical composition of studied clays. The samples analyzed by X-ray fluorescence from the outcrops examined in the Metropolitan Region possess high silica contents (59.60%), with aluminum oxide contents above 16.20% in all samples. The CaO content does not exceed 2.85%, which indicates a good sintering process and the possibility for their use in the manufacture of ceramic (stoneware and tiles). The high Fe2O3 content (6.35%) is responsible for the reddish color in the firing
Conclusions
Clays from Central Chile studied area can be classified into two groups according their mineralogical and chemical composition. The first group was characterized by the presence of high kaolinite content (samples 5, 7 and 8 from VII Region and sample 6 from the VI Region). Imported clays (ball-clays) from the UK and France by Spanish ceramic industry have similar behaviour that the clays here studied. The second group was characterized to have low content of kaolinite. Clays from the
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