Minera Quarry Trust

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Designed & Hosted by Step IT Solutions Ltd.

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Project 1—Geology

AIMS

 

1.  To conserve and enhance features, which illustrate many aspects of historical geology, sedimentation, structural geology, mineralisation and landscape development.

2.  To present the geological features as a resource in the teaching of earth sciences.

3.  To raise the awareness of local communities, and the public in general to the vital importance that geology has played in the landscape and in the industrial history of the area.

 

BACKGROUND

 

Quarrying at Minera has exposed a variety of rock types formed from largely marine sediments in the late Ordovician (~ 450 Ma) and early Carboniferous  ( ~ 350 Ma ) periods of geological time. Ordovician mudstones contain shelly fossils with small corals. Their steep dip and marked cleavage reflect the effects of continental collision and uplift during the Caledonian mountain building episode. Shallow water pebbly limestones were the first sediments to be laid down by tropical seas of the early Carboniferous over the eroded surface of older rocks. The ‘unconformity’ surface is clearly visible in the northern quarry. The thick sequence of limestones, most admirably displayed in the southern quarry, contains a rich variety of sedimentary features recording the changing environments and volcanic events of the times. Marine fossils are common and are particularly diverse in the upper, darker limestones. During the ‘Variscan Orogeny’ earth movements caused fracturing and dislocation of the rocks. Emplacement of ores of lead and zinc followed infiltration of the fissures by mineral containing brines.

 

THEMES TO DEVELOP

 

1.          Place the age of the Minera rocks in context in the expanse of earth history, outlining the structure of geological time, and the essential characteristics of the geological periods.

2.          A description of the rocks, the environments which produced them, and the creatures which lived in the ancient seas.

3.          The story of continents; drift, collision, mountain building, erosion, earthquakes, seas, faulting, mineralisation.

4.          Relate geology to landscape, agriculture, industry and settlement in a Minera context with its quarries of various rocks, mining for lead/zinc and for coal etc.

 

MEANS

 

1.          Intervene where necessary by excavation, drainage and management of vegetation to conserve and enhance features of value.

2.          Create a geology trail with adequate footpaths linking the main features of interest, which will be described on a series of information boards.

3.          Research the geology of the immediate area by observation, appropriate collecting and literature search producing an archive and a collection of high quality specimens to form the basis to develop displays within an interpretation centre.

MQT/PR1/Draft1/20.2.06

1.  The southern quarry provides a classic section through much of the ‘Loggerheads’ and ‘Cefn Mawr’ Limestones. Features include prominent ‘bentonite clays’ recording volcanic events, re-emergence horizons, textural changes etc.

2.  The exposure of the unconformity between cleaved late Ordovician mudstones and the ‘Leete Limestone’ formation in the northern quarry is an important feature designated as a regionally important geodiversity site (RIGS).

3.  This low-angle normal fault in the eastern quarry is a feature of the ‘White Vein’ of the Minera Lead Mines and is also a ‘RIGS’. Lead ores in quartz gangue occur in a series of tension fissures in the ‘footwall’

4.  One of many coral types found at Minera this ‘lithostrotion’ is common in the Lower Carboniferous