A Mineralogical, Geochemical, and Geochronological Study of ‘Valencianite’ from La Valenciana Mine, Guanajuato, Mexico

Minerals

卷:11

Amabel Ortega-Rivera¹  Teresa Pi-Puig²  Jesús Solé² 

[1] Instituto de Geología, Universidad Nacional Autónoma de México, Estación Regional del Noroeste, Apartado Postal 1039, Hermosillo, Sonora 83000, Mexico;

[2] Laboratorio Nacional de Geoquímica y Mineralogía, Instituto de Geología, Universidad Nacional Autónoma de México, Ciudad Universitaria, Coyoacán, Ciudad de México 04510, Mexico;

关键词: alkali-feldspar;    adularia;    X-ray diffraction;    Rietveld refinement;    major-elements;    trace-elements;   

DOI  :  10.3390/min11070741

来源: DOAJ

【 摘 要 】

Valencianite has been described as a variety of K-feldspar (adularia) from La Valenciana mine, Guanajuato, Mexico, from which three samples were used for this study. We present new major and trace element analysis, X-ray powder diffraction with Rietveld refinement, and single-crystal ⁴⁰Ar/³⁹Ar ages of this classical mineral. A detailed review of major works on feldspars and relevant papers from adularia shows that the structure of this mineral has monoclinic and triclinic domains with variable degrees of Al/Si order that we have been only able to model by powder X-ray diffraction assuming the presence of monoclinic (~50%) plus triclinic (~50%) K-feldspar. The literature data show some extreme structural states for adularia obtained in the pre-Rietveld refinement era; these data are dubious and need to be reanalyzed. A triangular diagram using the relative development of {110}, {010} and {001} faces is proposed. The temperature of formation, the Na/K ratio, and the growth kinetics seem to be the main factors controlling the morphological changes in K-feldspar crystals. The geochemistry of valencianite shows an almost pure orthoclase composition, as is common in most adularia crystals, although compositions up to Or₉₀Ab₁₀ have been found. Measurement of thallium in adularia can be an exploration guide for ore deposits. The weighted mean of 15 ⁴⁰Ar/³⁹Ar analyses of one valencianite from La Valenciana mine gave an age of 30.43 ± 0.27 Ma (2 standard deviations). It is discussed whether valencianite can be considered a new mineral.

【 授权许可】

Unknown