QUARTZ REPLACEMENT BY KEROLITE IN GRAPHIC QUARTZ-FELDSPAR INTERGROWTHS FROM THE VĚŽNÁ I PEGMATITE, CZECH REPUBLIC: A COMPLEX DESILICIFICATION PROCESS RELATED TO EPISYENITIZATION

DOSBABA, Marek and Milan NOVÁK. QUARTZ REPLACEMENT BY KEROLITE IN GRAPHIC QUARTZ-FELDSPAR INTERGROWTHS FROM THE VĚŽNÁ I PEGMATITE, CZECH REPUBLIC: A COMPLEX DESILICIFICATION PROCESS RELATED TO EPISYENITIZATION. Canadian Mineralogist. 2012, vol. 50, No 6, p. 1609-1622. ISSN 0008-4476. Available from: https://dx.doi.org/10.3749/canmin.50.6.1609.

Basic information

• Original name: QUARTZ REPLACEMENT BY KEROLITE IN GRAPHIC QUARTZ-FELDSPAR INTERGROWTHS FROM THE VĚŽNÁ I PEGMATITE, CZECH REPUBLIC: A COMPLEX DESILICIFICATION PROCESS RELATED TO EPISYENITIZATION
• Authors: DOSBABA, Marek (203 Czech Republic, belonging to the institution) and Milan NOVÁK (203 Czech Republic, guarantor, belonging to the institution).
• Edition: Canadian Mineralogist, 2012, 0008-4476.

Other information

• Original language: English
• Type of outcome: Article in a journal
• Field of Study: 10500 1.5. Earth and related environmental sciences
• Country of publisher: Canada
• Confidentiality degree: is not subject to a state or trade secret
• Impact factor: Impact factor: 1.180
• RIV identification code: RIV/00216224:14310/12:00064363
• Organization unit: Faculty of Science
• Doi: http://dx.doi.org/10.3749/canmin.50.6.1609
• UT WoS: 000314295200012
• Keywords in English: quartz kerolite replacement desilicification episyenitization contamination pegmatite serpentinite Věžná
• Tags: AKR, rivok

Abstract

Quartz replacement by kerolite (variety of talc) was examined in coarse- to medium-grained graphic intergrowths of quartz + feldspars (oligoclase An13-15Or3/orthoclase Or95-99Ab5-1) from the desilicated granitic pegmatite hosted in serpentinized apoharzburgite, at the locality Věžná I, western Moravia, Czech Republic. Pale brownish to white kerolite (Mg2.77-2.79Al0.09-010 Fe0.04 Si 4.05-4.08O10(OH)2.1.98H2O) forms aggregates, up to 2 cm in size, varying from massive fine-grained (1-10 m) to radial (needles up to ~1 mm long). Diffraction patterns exhibit a very broad peak at ~ 10 A (001) and a sharp peak at ~ 1.52 A (060). Kerolite does not swell at ethylenglycol atmosphere; cation exchange capacity (CEC) was 31+2.3 meq/100 g. Kerolite is a product of interaction between quartz and Mg-rich fluids originating from the host rock by the simplified reaction: 4SiO2 + 3MgCl2 + 6H2O = Mg3Si4O10(OH)2.2H2O + 6HCl. The process of kerolitization was evidently associated with albitization of oligoclase producing minor to trace amounts of Ba-rich K-feldspar, pectolite, analcime, natrolite, celadonite, monazite-(Ce) and niobian titanite, and possibly with vermiculitization of phlogopite. The simplified reaction including oligoclase, SiO2 released during kerolitization, and assuming immobility of Al was calculated as: 20(Na0.85Ca0.10K 0.05)Al1.15Si2.85O8 + 14SiO2 + 4.5H2O + 6NaCl = 21NaAlSi3O8 + 1KAlSi3O8 + 1NaCa2Si3O8 (OH) + 1NaAlSi2O6.H2O + 6HCl. This process likely proceeded at T ~ 100-300 C and P lt; ~ 0.5-1 kbar, under high activity of alkalis and low tectonic stress. Pseudomorphs of kerolite locally with rare relics of quartz were later almost completely removed because of surface weathering, which produced empty cavities in the graphic unit. Similar processes such as kerolitization of quartz at Věžná occur not only in granitic pegmatites but may operate in episyenites, where a direct dissolution of quartz and consequential formation of open vugs typically occurs.