Andradite and magnetite in contact-metamorphosed Chalk near Portmuck, Islandmagee, County Antrim

Research output: Contribution to journalArticleResearchpeer-review

Abstract

Skarn mineralisation was first reported 70 years ago by the mineralogist G. P. L. Walker at several coastal localities near Portmuck on the Islandmagee peninsula in eastern County Antrim. Described here is mineralisation associated with a 4 m wide Palaeogene dolerite dyke intruded through Cretaceous chalk. Along the dyke margin is a decimetre thick, dull-grey band of massive magnetite-calcite rock which, in thin section, has a clustered granular texture. In nearby marble, 2–3 mm diameter brown euhedral crystals of andradite garnet occur in close association with nodules of flint that have been metamorphosed to micro-crystalline quartz. Analyses by EDX indicate that the andradite is close to the ideal end-member, Ca3Fe2(SiO4)3, with minor substitution of Mg and Al. Flint is likely to be the source of silica for the crystallisation of andradite, whereas iron was probably introduced by hydrothermal fluids derived from the basaltic magma that formed the nearby sill-dyke complex.
Original languageEnglish
Pages (from-to)21-26
Number of pages6
JournalJournal of the Russell Society
Volume21
Publication statusPublished - 1 Nov 2018

Fingerprint

andradite
chalk
dike
magnetite
flint
mineralization
skarn
diabase
marble
hydrothermal fluid
thin section
sill
Paleogene
garnet
substitution
crystallization
calcite
silica
texture
magma

Cite this

@article{71ee7ed46efc4659a67c86efddb20d41,
title = "Andradite and magnetite in contact-metamorphosed Chalk near Portmuck, Islandmagee, County Antrim",
abstract = "Skarn mineralisation was first reported 70 years ago by the mineralogist G. P. L. Walker at several coastal localities near Portmuck on the Islandmagee peninsula in eastern County Antrim. Described here is mineralisation associated with a 4 m wide Palaeogene dolerite dyke intruded through Cretaceous chalk. Along the dyke margin is a decimetre thick, dull-grey band of massive magnetite-calcite rock which, in thin section, has a clustered granular texture. In nearby marble, 2–3 mm diameter brown euhedral crystals of andradite garnet occur in close association with nodules of flint that have been metamorphosed to micro-crystalline quartz. Analyses by EDX indicate that the andradite is close to the ideal end-member, Ca3Fe2(SiO4)3, with minor substitution of Mg and Al. Flint is likely to be the source of silica for the crystallisation of andradite, whereas iron was probably introduced by hydrothermal fluids derived from the basaltic magma that formed the nearby sill-dyke complex.",
author = "Norman Moles",
year = "2018",
month = "11",
day = "1",
language = "English",
volume = "21",
pages = "21--26",
journal = "Journal of the Russell Society",
issn = "0263-7839",

}

Andradite and magnetite in contact-metamorphosed Chalk near Portmuck, Islandmagee, County Antrim. / Moles, Norman.

In: Journal of the Russell Society, Vol. 21, 01.11.2018, p. 21-26.

Research output: Contribution to journalArticleResearchpeer-review

TY - JOUR

T1 - Andradite and magnetite in contact-metamorphosed Chalk near Portmuck, Islandmagee, County Antrim

AU - Moles, Norman

PY - 2018/11/1

Y1 - 2018/11/1

N2 - Skarn mineralisation was first reported 70 years ago by the mineralogist G. P. L. Walker at several coastal localities near Portmuck on the Islandmagee peninsula in eastern County Antrim. Described here is mineralisation associated with a 4 m wide Palaeogene dolerite dyke intruded through Cretaceous chalk. Along the dyke margin is a decimetre thick, dull-grey band of massive magnetite-calcite rock which, in thin section, has a clustered granular texture. In nearby marble, 2–3 mm diameter brown euhedral crystals of andradite garnet occur in close association with nodules of flint that have been metamorphosed to micro-crystalline quartz. Analyses by EDX indicate that the andradite is close to the ideal end-member, Ca3Fe2(SiO4)3, with minor substitution of Mg and Al. Flint is likely to be the source of silica for the crystallisation of andradite, whereas iron was probably introduced by hydrothermal fluids derived from the basaltic magma that formed the nearby sill-dyke complex.

AB - Skarn mineralisation was first reported 70 years ago by the mineralogist G. P. L. Walker at several coastal localities near Portmuck on the Islandmagee peninsula in eastern County Antrim. Described here is mineralisation associated with a 4 m wide Palaeogene dolerite dyke intruded through Cretaceous chalk. Along the dyke margin is a decimetre thick, dull-grey band of massive magnetite-calcite rock which, in thin section, has a clustered granular texture. In nearby marble, 2–3 mm diameter brown euhedral crystals of andradite garnet occur in close association with nodules of flint that have been metamorphosed to micro-crystalline quartz. Analyses by EDX indicate that the andradite is close to the ideal end-member, Ca3Fe2(SiO4)3, with minor substitution of Mg and Al. Flint is likely to be the source of silica for the crystallisation of andradite, whereas iron was probably introduced by hydrothermal fluids derived from the basaltic magma that formed the nearby sill-dyke complex.

M3 - Article

VL - 21

SP - 21

EP - 26

JO - Journal of the Russell Society

T2 - Journal of the Russell Society

JF - Journal of the Russell Society

SN - 0263-7839

ER -