K-Ar, delta O-18 and REE constraints on the genesis of ammonium illite from the Harghita Bai hydrothermal system, Romania

• Type: Article in International Scientific Journal
• Date: 2010

Authors

Clauer, N (Author) Other; Liewig, N (Author) Other; Bobos, I (Author) FCUP

Journal

Title: Clay Minerals

Vol. 45 No. 3

Pages: 393-411

ISSN: 0009-8558

Publisher: Walter De Gruyter

Indexing

ISI Web of Knowledge - 9 Citations

Scopus - 10 Citations

Scientific classification

FOS: Natural sciences > Chemical sciences

Other information

Authenticus ID: P-003-31G

DOI: 10.1180/claymin.2010.045.3.393

Abstract (EN): Ammonium illite and ammonium illite-smectite mixed layers, together with potassium illite, smectite and minute amounts of kaolinite were identified in hydrothermally altered andesite rocks from the Harghita Bai area of the Eastern Carpathians, Romania. K-Ar dating and oxygen isotope tracing, as well as rare-earth elemental analyses were made to provide new information on the timing and crystal-chemical processes characterizing the crystallization and further evolution of these illite-type mineral phases. The combined results suggest the occurrence of hydrothermal activity in two distinct episodes with nucleation of two generations of illite-type particles of different chemistry and morphology. About 9.5 Ma ago, potassium illite crystallized in alteration halos of the porphyry Cu system, probably at a temperature of similar to 270 degrees C from fluids having a delta O-18 of similar to 2.9 parts per thousand (V-SMOW). Associated smectite seems to have precipitated slightly later in external alteration halos at a similar temperature, but from fluids depleted in alkalis and with a different delta O-18. Alternately, ammonium-rich illite-smectite mixed layers formed very recently, less than similar to 1 million years ago at a temperature of similar to 90 degrees C from fluids of probable meteoric origin that altered the previously crystallized potassium illite, resulting in the crystallization of a new generation of ammonium illite-smectite mixed layers. Evidence of this dissolution-precipitation process is provided by a significant increase in the delta O-18 of the mixed-layer structures and by a significant change in their REE contents and distribution patterns. Occurrence of potassium in the ammonium-rich mixed layers probably relates to the progressive alteration of the first-generation potassium illite and a discrete concomitant take up of released K by the new NH4-rich interlayers of the ammonium mixed layered sequence.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 19