6.0 GENERAL SUMMARY - INTERPRETATION
The previous sections have described, discussed and interpreted the considerable evidence that now exists for early copper mining on the Great Orme. A number of important factors have been identified that have been involved with the control of the mineralisation and correspondingly the extent and nature of those workings of Bronze Age origin. The amassed evidence has enabled a set of characteristic artefacts and mining features to be recognised, which are now considered to be representative of mining from this early period at the Great Orme. Comparisons with other known early mining sites mainly throughout Europe have also been completed.
The chronological development of the early workings will also be considered, and sequence of events proposed that are responsible for the mining evidence presently seen at the site.
6.2 Summarised Evidence for Early Mining
The various sections constituting this study are summarised in tables 5-8 and as a series of statements as below.
6.2.1 Literature Review - Evidence for Prehistoric Mining:
1. Two main ore types have been identified at sites in Europe and the Near East:
a) Calcareous host rocks, comprising limestones, dolomites and calcareous
mudstones with sulphide, oxide and carbonate copper ores.
b) Non calcareous host rocks with mainly sulphide copper ores of primary and
secondary origin.
However, these two categories are not always obvious if renewed mining activity
in more recent times has removed particular ores and host rocks.
2. Workings have a tendency to be more extensive in the calcareous host rocks,
especially where weathering and chemical alteration has produced a more friable
and rotted material. In contrast the typically harder non-calcareous rock types
have required greater effort for their removal and correspondingly display greater
evidence for firesetting.
3. In the past there has been a tendency to ascribe dates to a number of European sites
based on ceramic and typological evidence, although this is now being backed by
radiocarbon dating methods.
4. At a number of European sites (excluding Britain and Ireland) two phases of mining activity have been identified : Copper - Early Bronze Age and Late Bronze Age, while in Britain and Ireland mining evidence spans Early - Late Bronze Age. The lack of evidence for ore processing and smelting from the Cu-EBA period may indicate that only native copper or carbonate ores for pigments were exploited at this time.
5. Throughout Britain and Ireland there is a distinct lack of evidence for ore processing
and total lack of evidence for smelting when compared to other European sites.
Although this is as yet is unexplained, the likelihood that they do exist is very high.
The study strongly suggests that geological conditions of the ore deposit are the most important factors governing the extent and considerable size of the prehistoric mine workings at the Great Orme. These are summarised as follows:
1. The dominant factors controlling ore mineralisation are:
a). Structure - where the primary mineralisation has been directed along a series of
predominantly north-south fractures and joints, and to a lesser extent along east-
west fractures.
b). Lithology - where mineralisation is restricted to dolomitised limestones,
particularly those with a dominance of coarse grained calcite crystals
(calcarenites). This dolomitisation is further controlled by confining horizons of
non calcareous lithologies, such as mudstone and to a lesser extent sandstone,
which causes a lateral extension of dolomite replacement of limestone.
2. The principal ore is chalcopyrite, which has been oxidised and resulted in the
production of carbonate ores of mainly malachite and some azurite, hydrated iron
oxides of goethite, partly altered chalcopyrite and small amounts of arsenical
copper ores.
3. Oxidation of the chalcopyrite is thought to be related to rotting (dedolomitisation)
of the dolomites, especially in the immediate vicinity of the fractures. This process
was observed to be more developed nearer to surface, but did extend in certain
areas of the mine to depths of 130m. Similar rotting also occurs within some of the
mudstones and towards the base of the sandstone where calcareous material
occurs.
4. The underground surveys clearly indicate the complexity and extent of the early workings which conform directly to the geological conditions as described above. Workings were identified to vertical depths of 70m, extending laterally for 240m and covering an estimated area of 24000m2 .
6.2.3 Evidence for Prehistoric Mining
The artefacts and features described in this study indicate there is a characteristic set of criteria that are representative of prehistoric mining on the Great Orme, these are described below and in tables 5-8 where they are compared and contrasted with mining evidence from the 18-19th centuries.
1. The extent and shape of the majority of the early workings relate directly to the removal of ore material in the zone of rotting of the dolomites centred around the mineralised fractures and to a lesser extent in the adjacent mudstones. This is the principal reason explaining the unprecedented extent of the prehistoric working.
2. Bone appears to be the principal tool material, especially where rotting was at its most advanced. Present studies indicate that generally larger bone components such as ribs and limb bones were selected for use as tools. Identified species include cattle and pig and to a lesser extent sheep, goat, deer and horse.
3. Stone tools were likely to have been used to a lesser extent than the bone implements, being chiefly employed in crushing separated ore rather than for direct ore removal. However, as rock strength increased (ie. less rotting) such tools would have seen greater use.
4. Firesetting was probably utilised for removing the less or non-rotted ore-bearing dolomite, particularly as the depth of the workings increased. Charcoal as well as timber fuel sources may have been used.
5. Bronze tools are likely to have been employed in the deeper workings, particularly where harder ore-bearing dolomites occurred which could not be worked with bone tools. Increasing availability of bronze in MBA to LBA times may also have encouraged the use of such tools.
6. The early workings produce characteristic spoils which differ in composition, component size/shape and degree of sorting from spoils of the 18-19th centuries. Typically they posses higher proportions of fines and more obvious sorting than recent spoils.
7. A proportion of the workings contain calcite speleothems, which are often well developed (up to 300mm thick) and have provided suitable material for uranium series dating.
8. Evidence of spoil backfilling to certain passages and stone stempling to surface trench workings suggests an organised system of mining, with maximised backfilling of waste rock, while maintaining access. It is also likely that ventilation was controlled during firesetting.
9. The distribution of tools and differences in strength of the ore-bearing dolomite would seem to indicate, as expected, that early mining techniques improved as ore material was sought at greater depths. This is also partly supported by younger C14 dates with increasing depths.
10.Differences in tool type and mining techniques found throughout the early workings hint that it may be possible to identify separate phases of mining activity within the Bronze Age period.
1. Documentary evidence suggests there are at least four potential sites where ores may have been processed in the early period. Of these, one site at Ffynnon Galchog has been excavated and produced material and artefacts bearing many similarities to Bronze Age mining evidence from the Pyllau valley. However, the single C14 date from the site suggests otherwise, indicating a Dark age period.
2. There is at present a total lack of any evidence from the Great Orme or surrounding district, as is the case throughout the British Isles, to suggest any roasting or smelting of ores from the prehistoric mines of the Pyllau valley.
3. Of the “washing sites” so far investigated, all are recognisable by their hummocky appearance and presence of dolomitic sands and gravels which contrasts with the surrounding ground. The presence of metallophytes and copper tolerant plants at these locations is also a useful indicator of mine derived material.
4. Conservative estimates of ore production from the Great Orme during prehistory suggest that quantities of produced copper metal could be in the region of 175 tonnes.
6.3 Chronological Development of Early Mining
It is concluded that geological and mineralogical factors were extremely important in dictating the extent of the early workings at the Great Orme. By understanding these conditions and relating them to the morphology of the workings and the nature of contained artefacts and features it has been possible to deduce a likely sequence of events that are responsible for the mine workings presently identified in the Pyllau valley.
It is proposed that copper carbonate ores contained within rotted dolomite were the first to be exploited, probably during a period between 2300-2000 BC. These brightly coloured ores, following the north-south veins, would have been easily identified at the surface, contrasting markedly with the yellow-brown dolomitised limestones. As excavation proceeded a series of largely parallel trench workings were formed, clearly seen at surface today where removal of surface spoil has exposed these features (plate 2). Simple tools of bone and wood would have been more than adequate for ore removal, with harder fragments of dolomite or massive ore necessitating occasional use of stone hammers. Deposits of this type were likely to have been removed rapidly during this initial period, and may have included ores other than malachite-azurite, such as the identified arsenical secondary minerals of olivenite and clinoclase. It is likely that the removal of ores confined to the rotted dolomite would have been fairly rapid. Greater difficulty must have been experienced in removing the ores from the less rotted dolomite, which must have prompted the use of different mining techniques. It is therefore likely that carbonate and particularly sulphide ores in the harder dolomite host rocks were initially deliberately left.
Eventually the early miners must have realised that ore-bearing material could be followed from the sides or bases of the trench workings, principally where the veins intersected confining strata such as mudstone. These situations allowed the ore deposits to be mined underground following both the vein and the underside of the confining strata. With increasing depth improvements in mining methods followed, seeing firesetting and more intensive use of stone hammers as a means to enlarge passage ways and remove ore from the harder dolomites.
The opencast may have been part of this early development, representing the removal with minimum effort of an ore body of considerable size. Alternatively, and more likely, the ore body constituting the opencast could have been worked initially as a series of interconnecting workings. Eventually, supporting masses of ore were removed with the resulting instability demanding complete removal of both ore bearing and barren rock resulting in the formation of an opencast feature.
As mining progressed below surface and within the opencast, the large volumes of spoil generated would require disposal, which at first is likely to have been tipped at the perimeter of the developing ore field. With progressive expansion, greater volumes of material were generated, which required a more organised system of disposal, with subsequent backfilling of trench workings and associated passages. In certain areas stone stemples were fitted to span the trenches allowing access through the base of the working and at the same time maximising filling operations above. Radiocarbon dates from contexts within the opencast and associated workings and from underground sites to a depth of 30m, suggest that these areas were being worked between 1500-1100BC. The grouping of dates around this period may also indicate this was the main phase of mining at the site. It is proposed that chalcopyrite ores were exploited during this period. This certainly would seem possible as malachite is often intimately associated with oxidised chalcopyrite-goethite and may therefore have been more easily mined as a mixed ore rather than separating the two components. Craddock (pers. comm.) has suggested that the presence of hydrated iron oxides such as goethite may indeed have aided with the smelting and slagging of chalcopyrite ores. Northover (1989) also proposes there was a notable change in bronze artefact composition at this time, suggesting that chalcopyrite ores were being mined and smelted for metal production centred around 1300BC.
The degree of rotting within the dolomite and to a lesser extent in the mudstones becomes less pronounced with increasing depth, so reducing the effectiveness of bone tools. This is confirmed sometimes by the complete absence of bone tools in particular workings even though stone hammers and fireset charcoal are common. Workings of this type may be considered to represent later stages of exploitation during the Bronze Age, where perhaps bronze tools were necessary for selective removal of harder ore-bearing rock. Some of the metal pick marks observed in these areas originally thought to have been due to iron tools from recent centuries may alternatively therefore have been produced by bronze tools. This is particularly true in some of the deeper workings (eg. location 35) where removal of harder ore- bearing dolomites and sandstones suggests mining techniques had improved sufficiently to allow ore extraction in these areas
It is not unreasonable to assume that reworking to some extent of previously neglected ores would have been possible. Activity of this type itself destroys earlier phases of mining, and if concentrated on surface may have been responsible for the destruction of any primary workings that could have provided the earliest datable evidence. Secondary working has been proposed at Mount Gabriel (O'Brien 1994) where exploitation of low grade sulphide ores is considered to be representative of improvement in smelting during the Middle Bronze Age. This however may not be necessarily true at the Great Orme, because some mining reports last century specifically state that quantities of "yellow ore" (chalcopyrite) were removed from the side walls of certain "old welsh" workings.
Later stages of mining are represented by increasing depths and advancement northwards into the hillside beneath Bryniau Poethion, and supported by the date of 1410-922calBC from location 5. It is likely that the production of spoil from these operations caused the opencast to be partly backfilled, at the same time retaining access to those workings immediately beneath via a system of retaining walls and stone-stempled trench workings. Eventually the majority of the carbonate and oxidised sulphide ores were removed, coinciding with the natural extent of the mineralised ground to about 40m below Vivians shaft. The presence of perched water tables and decrease in the extent of ore-bearing rotted dolomite also contributed to the cessation of mining and as well as to the introduction of iron as the new metal.
Renewed activity in Romano-British to Dark Age times has been hinted at, but as yet sufficient evidence does not exist to confirm this. If found, such evidence is more likely to indicate reworking rather than new exploitation, simply because the technology to drive shafts and tunnels into the harder ore bearing dolomite did not exist. The advent of gunpowder would be the deciding factor for the exploitation of such ores.
