Greisen and post-greisen alteration in the Sao Vicente de Pereira kaolinite deposit, Portugal

• Type: Article in International Scientific Journal
• Date: 1998

Authors

Bobos, I (Author) Other; Gomes, C (Author) Other

Journal

Title: Canadian Mineralogist

Vol. 36

Pages: 1615-1624

ISSN: 0008-4476

Publisher: Mineralogical Association of Canada

Indexing

ISI Web of Knowledge - 11 Citations

Scopus - 14 Citations

Scientific classification

FOS: Natural sciences > Earth and related Environmental sciences

Other information

Authenticus ID: P-001-6KH

Abstract (EN): The Sb Vicente de Pereira kaolinite deposit, located at the northwestern border of the Ossa Morena zone, in Portugal, is the site of important hydrothermal alteration, developed at the expense of migmatitic rocks and related to a system of Hercynian polyphase deformation and shear zones. Two stages of hydrothermal alteration are evident: 1) greisen-type alteration is represented by quartz + muscovite containing F and Cl, and by quartz + tourmaline; 2) post-greisen alteration and advanced argillic alteration led to the formation of well-ordered or poorly ordered kaolinite. The quartz + muscovite assemblage was investigated by XRD and electron-microprobe analyses. The mica shows intermediate characteristics between muscovite and lepidolite. It has a relatively low content of Si (3.10-3.20 apfu), a high proportion of Al-VI, a very low Fe content, and an absence of Mg. Quartz-tourmaline-rich greisen occurs in veinlets that cross-cut migmatites showing advanced argillic alteration. Two generations of tourmaline having different morphologies and different Fe contents can be identified. Well-ordered kaolinite formed at the expense of muscovite exhibits a "bookIet" morphology, as revealed by SEM and TEM observations. The hydration of well-ordered kaolinite led to halloysite 7 Angstrom. Results of O and H isotopic analyses attest to the formation of kaolinite from metamorphic pore-fluid.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 10