SciELO - Scientific Electronic Library Online

 
vol.42 issue3Sr-stratigraphy and sedimentary evolution of early Miocene marine foreland deposits in the northern Austral (Magallanes) Basin, ArgentinaA silicoflagellate from the middle Albian of Austral Basin, Argentina author indexsubject indexarticles search
Home Pagealphabetic serial listing  

Services on Demand

Journal

Article

Indicators

Related links

  • On index processCited by Google
  • Have no similar articlesSimilars in SciELO
  • On index processSimilars in Google

Share


Andean geology

On-line version ISSN 0718-7106

Abstract

RICHTER, Stefan; GOTZE, Jens; NIEMEYER, Hans  and  MOCKEL, Robert. Mineralogical investigations of agates from Cordon de Lila, Chile. AndGeo [online]. 2015, vol.42, n.3, pp.386-396. ISSN 0718-7106.  http://dx.doi.org/10.5027/andgeoV42n3-a06.

In the present study a first found of agates in Chile is reported from the Cordón de Lila region in northern Chile. The agates occur as veins and lenses in altered Permian volcanic rocks. The rock composition is rhyodacitic/dacitic consisting of a fi ne-grained K-feldspar-quartz groundmass with phenocrysts of plagioclase (An50-60) and pyroxene (augite). The volcanic host rocks show strong features of alteration and brecciation. Results of XRD, polarizing microscopy and cathodoluminescence (CL) microscopy and spectroscopy point to a late- to postvolcanic formation of the agates by hydrothermal fluids and SiO2 which was released during the alteration of unstable minerals and volcanic glass. Strongly varying agate micro-textures and the appearance of euhedral quartz crystals with pm-sized growth lamellae (so called Bambauer quartz) indicate fluctuations in the physico-chemical conditions (SiO2 concentration, pH) during alteration and agate formation. Another indication for the alteration processes is the occurrence of secondary calcite in the agate-bearing rocks.

Keywords : Cordón de Lila; Volcanic rocks; Mineralogy; Geochemistry; Agate.

        · abstract in Spanish     · text in English     · English ( pdf )

 

Creative Commons License All the contents of this journal, except where otherwise noted, is licensed under a Creative Commons Attribution License