Abstract
Halloysite deposits in Argentina have been identified in the province of Río Negro (Patagonia). The mineralized area occurs as altered zones in Eocene volcanic–pyroclastic rocks, dacitic to rhyolitic in composition. A comprehensive study of these deposits was carried out by means of mineralogical, geochemical and isotopic analyses.Intense weathering has transformed the whole rock to a white mass composed of 75% –90% halloysite+kaolinite, with cristobalite, tridymite, and quartz, as the main non-clay minerals. Ferruginous beidellite and titanium minerals are also present in minor amounts.The halloysite–kaolinite ratio ranges from 75 to 25 to 100–0. Due to the alteration of very dense rocks, halloysite morphology is predominantly spheroidal. Tubular halloysite is the main constituent in more porous rocks, but the latter are scarce in the area.Because of the predominance of the spheroidal type, the use of halloysite as HNT (halloysite nanotube) is not feasible. Nonetheless, this mineral can be modified by different organic molecules, and used to remove pollutants such as emulsified hydrocarbons and heavy metals. A special product made with this halloysite is used as sunscreen when sprayed on fruits in areas of intense solar radiation. The whiteness of this mineral is not very high due to the amount of titanium oxide present in its composition (about 1%). Nevertheless, titanium oxide is present as individual particles, so it could be removed by a mechanical process.New applications for spheroidal halloysite are currently being investigated. Moreover, depending on the price and demand, the tubular halloysite of low grade deposits could be exploited.
Highlights
Halloysite is defined by the presence or evidence of past occurrence of interlayer water in a mineral with a kaolin-type structure (Churchman and Carr, 1975)
Past detailed studies on different parts of Mamil Choique and Buitrera deposits demonstrated that the mineralogy in the Mamil Choique deposits comprises halloysite, kaolinite, with impurities such as tridymite, cristobalite, quartz, iron-rich beidellites, and iron oxides
Characterization Large and small “pockets” of rocks altered to halloysite are found along a 50 km area in a W–E direction, but no structural control has been detected (Fig. 1)
Summary
Halloysite is defined by the presence or evidence of past occurrence of interlayer water in a mineral with a kaolin-type structure (Churchman and Carr, 1975). In Argentina, small and low grade deposits are located in the area of Mamil Choique and Buitrera, Patagonia, Argentina (Cravero et al, 2009, 2012). The extension of the alteration, the high halloysite/rock ratio, not common in this type of deposit, and the formation of halloysite rather than kaolinite in different rocks at the same time and with different morphologies make these areas of interest to contribute to the understanding of the formation conditions of halloysite (Cravero et al, 2012). Taking into consideration that spheroids are the predominant morphology, some attempts were made in order to determine possible applications of these halloysites (Fernández et al, 2009a, 2009b, 2013, 2015). To carry on this study, XRD, DTA-TG, chemical and isotopic analyses, petrography, surface chemical modifications, and technological measurements were all used
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