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Alteration of Ilmenite in the Cretaceous Sandstones of Nova Scotia, Southeastern Canada

Published online by Cambridge University Press:  01 January 2024

Georgia Pe-Piper ,
David J. W. Piper  and
Lila Dolansky
Georgia Pe-Piper*
Affiliation:
Department of Geology, Saint Mary’s University, Halifax, N.S., Canada B3H 3C3
David J. W. Piper
Affiliation:
Geological Survey of Canada (Atlantic), Bedford Institute of Oceanography, PO Box 1006, Dartmouth, N.S., Canada B2Y 4A2
Lila Dolansky
Affiliation:
Department of Geology, Saint Mary’s University, Halifax, N.S., Canada B3H 3C3
*
*E-mail address of corresponding author: [email protected]
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Abstract

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Most detrital ilmenite grains in sandstones of the Chaswood Formation are completely altered to pseudorutile, leucoxene and rutile. The textural, chemical and mineralogical changes involved in alteration were tracked using electron microprobe analyses, backscattered electron images, and elemental maps. Ilmenite grains (Ti/(Ti+Fe) ≈ 0.48) alter patchily to pseudorutile (Ti/(Ti+Fe) 0.5–0.7) with volume loss, forming a porous structure and this process continues with the development of leucoxene (Ti/(Ti+Fe) 0.7–0.9). Within the pseudorutile and leucoxene, stubby prismatic rutile crystals have been precipitated. Si and A1 occur in the altered ilmenite, either (1) inherited from original quartz and muscovite inclusions in the parent crystal or (2) as kaolinite altered from muscovite inclusions or precipitated in the pore space, under pedogenic or early diagenetic conditions. Distribution of alteration phases has been related to facies and diagenetic variations. With increasing amounts of leaching in different types of paleosols, there was increasing alteration of pseudorutile to leucoxene. In light gray mudstones and interbedded sandstones with diagenetic kaolinite that formed beneath the water table from percolating meteoric water, most leucoxene was converted to rutile. Burial diagenesis (to vitrinite reflectance values >0.4%) also promoted the change from leucoxene to rutile. The alteration of ilmenite is an important source of Fe for diagenetic minerals in the Chaswood Formation and correlative offshore deltaic and marine facies of the Scotian basin.

Keywords

AlterationDiagenesisIlmenitePseudorutileRutile
Type
Research Article
Information
Clays and Clay Minerals , Volume 53 , Issue 5 , October 2005 , pp. 490 - 510
Copyright
Copyright © The Clay Minerals Society 2005

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