Parys Mountain Research Articles

A new look at the Mona Complex (Anglesey, North Wales)

Re-examination of the Mona Complex (Anglesey, North Wales) has led to a radical re-interpretation of its stratigraphy, structure and geological history. The gneisses are regarded as representatives of an earlier continental basement, as Greenly (1919) originally proposed. In the northern part of Anglesey the Bedded Succession can be separated into 3 structural units. The South Stack Unit of Holy Island is overlain by the more highly deformed New Harbour Unit; the contact between these two units is interpreted as a thrust plane. A third unit, the Cemlyn Unit, outcropping in the NW, comprises the Church Bay Tuffs, Skerries and Gwna Groups of Greenly's succession, as well as greywackes and slates, correlated by Greenly with the New Harbour Group. However, the Cemlyn Unit is less deformed than the New Harbour Unit and their relationships may be unconformable. It is proposed that Greenly's Fydlyn Group does not form part of the Mona Complex but may be correlated with the Caradocian volcanics of Parys Mountain. No major structural discordance occurs between the Gwna Group and the overlying Ordovician rocks on the N coast. The time gap represented by this contact has also been reduced by recent fossil finds, which indicate that some members of the Mona Complex are of Cambrian Age. The implications of these discoveries are that there was no 'Irish Sea land mass' in the Anglesey area in the Lower Palaeozoic and that major structures in the complex previously attributed to a late Precambrian orogeny are of Caledonian age. Using the new structural and stratigraphic data, a synthesis of the sedimentary, tectonic and structural evolution of the complex is proposed, in the context of plate tectonics.

The age of mineralisation at Parys Mountain, Anglesey

Summary Borehole exploration of the mineralisation in the Ordovician and Silurian rocks of Parys Mountain, Anglesey has produced two hypotheses to explain the emplacement of the ore deposits. Mineralisation was either syngenetic, associated with volcanicity in the Ordovician, or epigenetic, occurring during or after the Caledonian orogeny. An outline of the geological evidence is given together with the results of K-Ar isotope age determinations on thirty-two core samples. Two isotopic events have emerged from the K-Ar determinations, 394±9 Ma and 353±7 Ma; these ages are discussed in the light of the evidence available.

The potential for evolution of heavy metal tolerance in plants

The effects of increase in copper contamination in potting compost/copper mine waste mixtures on the germination and growth of the following species has been examined: Agrostis tenuis, Poa trivialis, Lolium perenne, Dactylis glomerata, Cynosurus cristatus, Anthoxanthum odoratum, Arrhenatherum elatius, Plantago lanceolata and Trifolium repens. Copper tolerant A. tenuis from Parys Mountain was used as control. Plant dry weight and plant height decreased with increase in proportion of copper contaminated soil in the mixtures, a conspicuous characteristic was the continued survival and growth of some individuals and the death of others at 1-4, 1-8 and mine soil levels. Agrostis tenuis and Dactylis glomerata produced fully copper tolerant survivors at a frequency of 0·08 per cent. By contrast Poa trivialis, Lolium perenne, Arrhenatherum elatius and Cynosurus cristatus produced survivors having indices of tolerance ranging from 7 to 20 per cent, tolerance, values too low to be considered as fully copper tolerant. Plantago lanceolata, Anthoxanthum odoratum, and Trifolium repens, failed to produce any survivors at all. The heritability of copper tolerance in the selected material: Agrostis tenuis, Lolium perenne, Dactylis glomerata, Arrhenatherum elatius, and copper tolerant A. tenuis was determined. Heritability is discussed in terms of breeding value. The results suggested that while the evolution of tolerance would be easy in A. tenuis it would be difficult in species such as Lolium perenne. The data presented are interpreted as evidence that the exclusion of some species from mine areas is because of their inability to evolve metal tolerance.

The Mineral Industry in Wales — A Review of Production Trends, Resources and Exploitation Problems

The full range of mineral resources of economic significance is discussed. Reference is made to recent production trends and the reserves available for future working, taking into account the more obvious conflicting interests. The collieries of the South Wales coalfield are still the major source of employment within the mineralbased industries of Wales, but limestone production is now about equal to coal output and seems destined to far outstrip this in the future. Concentrated programmes of drilling and other exploratory work directed at the discovery of large, low-grade copper ore bodies at Parys Mountain, Anglesey and Coed-y-Brenin, to the north of Dolgellau in Merioneth, have been given great publicity on account of the scale of possible future mining operations and the associated environmental problems.

The Stratigraphy of the Ordovician rocks of Anglesey

AbstractArenig sandstones, grits and conglomerates rest unconformably on pre‐Cambrian rocks (the Mona Complex) and are of variable thickness and facies. Higher Arenig and Llanvirn shales, grits, conglomerates, shaly breccias and ironstones are related to contemporaneous fault movements, with abundant slump structures and rare turbidites. A pre‐Caradoc break in sedimentation was followed by deposition of shales, cherty shales, sandstones, breccias and conglomerates on Llanvirn, Arenig and pre‐Cambrian rocks. The Carmel Head Thrust acted as a major line controlling sedimentation, with upthrow to the north. Lower Silurian graptolitic shales at Parys Mountain rest on an acid volcanic group of Caradoc (?) age.

Pisanite from Parys Mountain, Anglesey

During the Manchester University's 1946 geological excursion to Anglesey, a visit was made to Parys Mountain. At this locality small quantities of an attractive light blue mineral were found capping pyrite veins and in clefts in the rock. Larger finds were obtained in an artificial cavern which extended for fifty or sixty feet into the south-east side of the excavated pit. A specimen weighing 2½ pounds and consisting of silicified shale veneered with the pale blue mineral was collected by the author and examined in the geological research laboratory at Manchester University during the session 1948–1949. The blue mineral was identified as pisanite, and this is the first record of pisanite as a British mineral.Parys Mountain is situated in the north-west of Anglesey close to Amlwch. Copper and to a smaller extent lead were mined throughout a period exceeding one hundred and fifty years, but operations have completely ceased since the first world war. The geological structure of the district need only be briefly outlined for the purpose of this study.

II.—Note on the Geological Age of the Shales of the Parys Mountain, Anglesey

The rocks of the Parys Mountain, which lies about two miles to the south of the town of Amlwch in Anglesey, were described in 1878 by the late Mr. T. Fanning Evans, H.M. Inspector of Mines, who regarded the Parys Mountain “as an outlying piece of ground, geologically identical with the region in which the great slate-mines of Festiniog occur, and from which it differs only in being developed on a much smaller scale, and in being highly metalliferous.”