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Earth Science Conservation Review
| Aughnagon Quarry | Down |
| Site number: | 574 | ||
| ESCC: | ED | ||
| Locality Type: | Quarry (disused) | Status: | ASSI |
| Grid Reference: | J14452505 Centroid | ||
| Google maps: | 54.16174,-6.24861 | ||
| County: | Down | Council area: | Newry, Mourne & Down District Council |
| Period: | Devonian, Silurian | ||
| Stages: | Lower Devonian | ||
| Lithostrat: | Newry Igneous Complex | ||
| Site Description | |
|---|---|
| Highlights: | |
Exposures in Aughnagon Quarry demonstrate the relationship between contact metamorphosed country rock and a variety of intrusive igneous bodies that comprise the middle pluton of the Newry Igneous Complex. | |
| Introduction: | |
Aughnagon Quarry is located approximately 2.5km south-southwest of Mayobridge, on the B7 Chapel Hill Road. The Newry & Mourne District Council, whose permission should be sought before entering, are currently using Aughnagon Quarry as a landfill site. Geologically, the rocks at Aughnagon are located at the southern margin of the middle pluton of the Newry Igneous Complex. Aughnagon Quarry appears to have been opened sometime after the publication of the first edition of the Newry (Sheet 60) one-inch to the mile geological map (Geological Survey of Ireland, 1876). The area was mapped as granite and quartziferous porphyry (elvanite) in contact with a zone of metamorphosed Silurian country rock. Metamorphosed country rock is described on the map key as indurated and is shown as a zone up to 1km wide. Hull (1881) did not elucidate the nature of the indurated country rock in this area. However, elsewhere, for example at Slieve Croob, it was described as described as "mica schist"(Egan, 1872), and at Shannaghan Hill it was described as "large masses of fine grit" retaining original dips and displaying the characteristics of fused (mobilized) sediment at (Reynolds, 1934 and 1936). On the map, the contact between 'indurated' country rock and granite is shown to dip steeply to the southeast, almost parallel to the strike of bedding in the surrounding Silurian sediments. Values of dip for bedding within the country rock are variable, but generally steep (45° to 70°) and are predominantly to the southeast. Reynolds (1934; 1936) classified the rocks at this site as granodiorite based on the mineralogy, i.e. rich in quartz, plagioclase feldspar, alkali feldspar, biotite mica and hornblende. Reynolds' classification and terminology withstand scrutiny under the modern classification scheme of Streckeisen (1976). Systematic sampling, thin section petrology and geochemistry (Grant, 1961; Meighan and Neeson, 1979 Neeson, 1984) has revealed composition zoning within the granodiorite plutons of the Newry Igneous Complex. Granodiorite at the margins of the middle pluton is more acid than granodiorite at the centre of the intrusion. This configuration is described as "reverse zoning". The opposite case ("normal zoning") is seen in the northeast and southwest plutons. | |
| Description: | |
The northern face of Aughnagon Quarry (a 300m long section) exposes a zone of contact between igneous rocks belonging to the middle pluton and metamorphosed Silurian country rock. Most of the section is in greywacke and shale country rock that has been altered to biotite-hornfels (Meighan, pers. comm., 1999). Original sedimentary bedding is generally undisrupted, but some evidence of fused (mobilised) sediment can be observed seen close to the intrusive contact. At least two main intrusive rock types are represented in the western 50m of section. The earlier intrusive is a porphyritic rhyolite that occurs at the main pluton contact. Thin sections show the rock to contain plagioclase phenocrysts and large crystals of biotite (that show a preferred orientation) in a quartz rich matrix (Meighan, pers. comm., 1999). The main body of igneous rock is a medium to coarse-grained, unfoliated granodiorite containing quartz, plagioclase and alkali feldspar, biotite and a small amount of hornblende (Meighan, pers. comm., 1999). The granodiorite is more acid in composition than that which makes up the central part of the middle pluton. A 'tongue' of granodiorite extends from the main granodiorite body into the country rock. The contact between country rock and granodiorite is sharp with no sign of chilling. Late stage, fine-grained aplite veins and very coarse-grained pegmatite pods are numerous. Small crystals of an unusual mineral, molybdenite, are visible in the pegmatite pods. | |
| Importance: | |
The Aughnagon Quarry and neighbouring smaller quarry constitute a site of national importance offering access to outcrops where the relationship between contact metamorphosed Silurian country rock and granodiorite can be demonstrated | |
| Interpretation: | |
At this site, and in the surrounding area, heat from the middle pluton of the Newry Igneous Complex has caused contact metamorphism of the Silurian greywacke and shale country rock. The result is a biotite-hornfels which extends for up to 1km from the margin of the granodiorite pluton. The absence of an obvious foliation within the granodiorites in this area is anomalous to comparable sites at the margin of the northeast pluton. This indicates the possibility of a different emplacement mechanism for the middle pluton. Comparison of marginal and more central granodiorite compositions indicates that the middle pluton is reversely zoned. The variety of granodiorites observed could be evidence that several injections of magma were involved in the formation of the middle pluton; this is a feature regarded as common to the formation of each of the plutons that together constitute the Newry Igneous Complex (Meighan and Neeson, 1979). | |
| Conclusions: | |
These quarried exposures demonstrate the relationship between contact metamorphosed country rock and a variety of intrusive igneous bodies that comprise the reversely zoned middle pluton of the Newry Igneous Complex. | |
| Notes: | |
For information and references on other sites within the Newry Igneous Complex see the following sites: Key Site 568 - Ardglass, Co Down Key Site 569 - Slieve Croob Key Site 570 - Shannaghan Hill Key Site 571 - Ballymagreehan Quarry Key Site 572 - Rathfriland Key Site 573 - Gransha Key Site 575 - Goraghwood Quarry Key Site 576 - Newry By-pass Key Site 577 - Cam Lough Quarry Key Site 578 - Kearney Point Key Site 579 - Ballyhalbert Pier For general information and references on the Caledonian Igneous Complexes of N. Ireland, and for directions to other regional sites, see the following site: Key Site 595 - Introduction to the Caledonian Igneous Complexes of N. Ireland | |
| Keywords | |
|---|---|
| Minerals: | Molybdenite |
| Rocks: | Granodiorite, Greywacke, Hornfels, Pegmatite, Shale, Aplite |
| Structures: | Caledonian, pluton, mobilisation |
| Relations: | Intrusion, Contact metamorphism |
| Access | |
|---|---|
| Approach: | Aughnagon Quarry is located approximately 2.5km south-southwest of Mayobridge, on the B7 Chapel Hill Road. |
| Management: | |
Aughnagon Quarry is an active landfill with steep quarry faces. Newry & Mourne District Council manage the landfill and permission will be needed to gain access. If the site is to be preserved, it will be particularly important to advise the Council of the importance of the exposure that occurs at a high level within the quarry. Despite the abundance of rock exposure, there is a need to restrict hammering or sampling particularly in the contact zone. The rocks of the Newry Igneous complex are considered to be prospective for a number of minerals including base metals and gold. Licensed mineral exploration and production has previously been carried out in Counties Armagh and Down. The area which includes this site is likely to attract further exploration activity. | |
| Threats: | Sensitive to over-sampling or hammering. |
| Uses | |
| Uses: | Landfill site |
| Map(s): | GEOLOGICAL SURVEY OF IRELAND, 1876. 1:63,360 Geological Sheet 60 (Newry). Dublin, Ordnance Survey for Geological Survey of Ireland. | ||
| Record type: | ESCR report | ||
| Entered by: | E M Porter | ||
| Last updated: | 03 MAR 2001 | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Aughnagon Quarry, County Down, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=574. Accessed on 2026-11-04. |
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