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Where is the Gold in Wicklow’s Goldmine River district? – IMC Exploration
Gold Frenzy, the story of Wicklow’s gold – An excerpt from the book by Dr Peadar McArdle.
Dr McArdle, who recently retired as Director of the Geological Survey of Ireland, has had a long term interest in the history and origin of the Goldmine River gold deposits.
Text copyright Dr Peadar McArdle 2011.
Pt 12 – Where is the Gold in Wicklow’s Goldmine River district?
Where is the gold in the Goldmine River district? This was well illustrated on a map published in 1971 by Tom Reeves, a professional geologist by training, but better known to Irish consumers, until his recent retirement, as the Commissioner for Energy Regulation. The main focus of placer gold was along the Goldmine River itself, downstream of Ballinagore Bridge and there are additional occurrences reported from the stream at Knockmiller further east, here called the Eastern Goldmine River. These occur both east and ESE of the Ballycoog-Moneyteige ridge. There are further showings along the Coolbawn River wich flows northwest from Croghan Kinshelagh towards Annacurragh as well as along the Aughrim River and its tributaries immediately north and ENE of the Ballycoog-Moneyteige ridge. Further away, and less directly relevant to our story, are gold placer occurrences along the Avoca and Ow Rivers. The occurrences, as well as bedrock gold, all occur in close association with the outline of the zone of volcanic rocks which extends from Avoca district. Yes, even in 1801 Fraser really did get it right: there is indeed a link between volcanic bedrock and placer gold in this area.
We have an accurate knowledge of the extent of the original gold workings in the Goldmine River area because Thomas Harding, Surveyor, and his assistant undertook an arduous survey of the river, its tributaries and surrounding mountainous terrain. Harding was an accomplished and successful surveyor, residing on Prussia Street in Dublin, but he had to share the credit for his labours with several others. The resulting Mineralogical Map, published in December 1801, gives a fascinating insight into the extent of alluvial gold and workings, as well as the old (even then!) mine workings on Ballycoog-Moneyteige ridge. But then this was no ordinary map, being executed by command of His Excellency, Philip Earl of Hardwicke, Lord Lieutenant General and General Governor of Ireland. It was done under the direction of Richard Kirwan, who was Inspector General of Mines, and the Directors of His Majesty’s Goldmine: Abraham Mills, Thomas King and Thomas Weaver. Kirwan had visited its location back in 1796 and now, five years later, it was being published. It was certainly a good basis for presenting the new exploration strategy being proposed by the directors. It may have been intended for official eyes only – uneducated peasants could not be expected to glean much information from such a technical document. But then they wouldn’t have desired it either, all they would have wanted was free access to the workings again!
In the aftermath of any gold rush there is an understandable concentration on finding the bedrock source of the alluvial wealth. There will be references to the ‘Mother Lode’, suggesting that the bedrock source may be even more bountiful than the daughter alluvium. However in many cases this is not the case at all. The bedrock source may have been entirely eroded during the placer formation so that no bedrock ore remains. Alternatively, the main bedrock source may be buried below surface in a position that remains inaccessible – and undiscovered. For example, the placers of the Klondyke yielded over 12 million fine ounces of gold but the bedrock there has only produced 1,000 fine ounces. This has led, and not only in the Klondyke, to a frantic search for a myriad of alternative bedrock sources: a similar situation quickly developed in the Goldmine River valley....
To be continued…
Other books by Dr Peadar McArdle can be viewed on Amazon here
Gold Frenzy, the story of Wicklow’s gold pt 11 – IMC Exploration
Gold Frenzy, the story of Wicklow’s gold – An excerpt from the book by Dr Peadar McArdle.
Dr McArdle, who recently retired as Director of the Geological Survey of Ireland, has had a long term interest in the history and origin of the Goldmine River gold deposits.
Text copyright Dr Peadar McArdle 2011.
Pt 11 – Pocket history of Avoca’s volcanic history
We cannot identify the specific volcano responsible for the region’s volcanic rocks: it is either buried deep underground and out of sight or it was destroyed by subsequent geological events. But we do know it dominantly spewed out ashes, because plentiful evidence of them remains in the rocks around Avoca. Low viscosity magma like basalt will usually give rise to lavas that flow downhill with the speed and consistency of thick broth. Rhyolitic and similar high-viscosity magma, on the other hand, is generally very gas-rich and erupts explosively. Avoca’s magma was predominantly of rhyolitic composition and so gave rise to ashes. Ash clouds would have billowed skywards from the volcanic crater and spread out over the surrounding seas, dropping their ash loads onto the sea floor. The ashes became incorporated into seabed-hugging and sediment-charged water currents called turbidity currents, which surged rapidly downslope and lost their sediment load when they reached flat-lying seafloor in water depths of about 200 metres. Thus developed the sediments that now form the bulk of the Avoca rock sequence.
So where would Avoca’s volcano fall on the scale of recent volcanic eruptions? Probably somewhere in the middle, outshone by examples such as Mount St Helen’s and Krakatoa. Think of the 1990’s Montserrat eruptions in the Caribbean in order to imagine the overall scale and setting.
But where are the metals for which Avoca (and indeed Croghan Kinshelagh) is famous? We know that mining took place in the vicinity of the Vale of Avoca since at least 1720. The suggestions of earlier outputs of metals extend back to Ptolemy’s time but alas are based on speculation, however tantalising. The recorded Avoca production amounts to 16 million tonnes of copper ore containing 0.6 percent copper and 5 percent sulphur. Even more prolonged, but on a smaller scale, was the output of iron ore from the Ballycoog-Moneyteige ridge on the northwest flank of the Goldmine River Valley. These workings are believed to have been operated by the Vikings and I have a suspicion their output may have been used in the Dublin of their era.
The Avoca mine frequently had but marginal profitability, especially since it re-opened in 1958, and it required Government support in its final years. Most ore was extracted from the intensive workings of West Avoca, which reached a depth of 300m below surface, but the environmental impact was greater in East Avoca where shallower workings were more extensive. The main open pits, which contributed over 30 percent, were in East Avoca. At least one of the open pits, Cronebane, gave rise to extensive waste which formed a significant dump that was subsequently used to partially backfill the pit itself. The Ballymurtagh Open Pit in West Avoca became a landfill facility for County Wicklow in the 1980’s before finally closing some years ago...
To be continued…
Other books by Dr Peadar McArdle can be viewed on Amazon here
Gold Frenzy, the story of Wicklow’s gold pt 10 – IMC Exploration
Gold Frenzy, the story of Wicklow’s gold – An excerpt from the book by Dr Peadar McArdle.
Dr McArdle, who recently retired as Director of the Geological Survey of Ireland, has had a long term interest in the history and origin of the Goldmine River gold deposits.
Text copyright Dr Peadar McArdle 2011.
Pt 10 – Volcanic Rock Formations
The volcanic rock parallel extending from the Croghan Kinshelagh area to Avoca and Rathdrum has been studied by geologists since Fraser’s map first appeared so that we have a good understanding of their age and how they formed. Mind you, not all rocks are uniformly well exposed so our knowledge of them is a bit uneven. Nevertheless over the last thirty years we have learned how they fit into the global kaleidoscope of changing continental and oceanic shapes and positions, a sequence of patterns which has been predicated by plate tectonics and seismic events. Sadly the consequences are determined as much by the effectiveness of the local construction codes as they are by the intensity of the seismic event itself. The Earth is a truly vibrant organism and we are not always in harmony with it.
One implication of this context is that Wicklow’s landscapes have been far from constant throughout its geological history. The widespread siltstones and sandstones all accumulated at a time when deep sea covered the Wicklow area. Land would not have been visible in any direction over most of the period that sediments formed and yet the influence of the land would have been discerned. For this region was part of an ocean, Iapetus Ocean, which formed here (and was in time destroyed) long before there was any hint of the emergence of the modern-day Atlantic Ocean. The sediments were deposited on the southeast continental margin of this long-vanished Iapetus Ocean and were subsequently churned up and re-deposited in deeper water. This was achieved through the operation of sediment-laden deep-sea currents triggered by earthquakes or major storms. While considerable thicknesses of sediment were thus laid down in a matter of days, there could have been time lapses of centuries between each pulse. The different nature of the rocks formed reflects the different sources tapped for sediment over time.
But inexorably, although imperceptible to an individual observer, the ocean itself was now contracting in size and the continents on opposing margins were approaching each other. They would eventually collide with each other, but before that happened, a series of volcanoes would develop in between, like beads strung out on a gigantic necklace which marked their junction. These volcanoes gave rise to the diversity of associated volcanic rocks, including those in Fraser’s golden zone of southwest Wicklow. The opposing continental margins did crash into each other, with one causing the other to sink deep into the Earth’s interior. All of the pre-existing rocks were stressed and heated, with the finer grained sediments developing a slaty cleavage. As increased heat partially melted the descending rock sequence, the resulting liquid magma buoyantly ascended along fault lines and fractures in the Earth’s crust, forming the considerable bodies of granite for which Wicklow is celebrated. This was the final act in the destruction of the Iapetus Ocean: the forces of plate tectonics would soon be realigned in a new European configuration that would lead to the next phase in Earth’s enthralling history.
But let us revert to the necklace of volcanoes which will feature prominently in our story. We are now entering the Ordovician Period, a fascinating phase in Earth’s evolution, which lasted from 488 to 444 million years ago, a relatively extensive period of 56 million years. At the global level, the Earth was a very different place than it is today. Continents were all clustered in the Southern Hemisphere, and this is where the northern and southern halves of Ireland would eventually come together as the Iapetus Ocean finally closed. There was a very complex array of volcanoes, which were fed an abundant supply of lavas due to some spectacularly intensive convection, or ‘hot spot’, operating in this part of the Earth’s mantle. It was right in the middle of this fascinating Ordovician Period, about 450 million years ago, that the volcanic rocks of the Croghan Kinshelagh and Avoca district were formed..
To be continued…
Other books by Dr Peadar McArdle can be viewed on Amazon here
Gold Frenzy, the story of Wicklow’s gold pt 7 – IMC Exploration
Gold Frenzy, the story of Wicklow’s gold – An excerpt from the book by Dr Peadar McArdle.
Dr McArdle, who recently retired as Director of the Geological Survey of Ireland, has had a long term interest in the history and origin of the Goldmine River gold deposits.
Text copyright Dr Peadar McArdle 2011.
Pt 7 – The likely source of gold lies in the mountain’s quartz vein.
When work resumed in September 1800, First Lt Weaver came into his own. The Commissioners now recommended to the Government that work be extended beyond the simple collection of alluvial gold to include a search for any gold bearing veins in the bedrock. The Government, like any government might do, had finally abandoned any pretence that it was focussed only on preventing the assembly of mobs. Let’s go for gold! Weaver worked on the assumption that the alluvial gold would be sourced in quartz veins on the higher ground surrounding Croghan Kinshelagh Mountain.
In their report, the Commissioners described the progress of the workings and the weight and value of gold recovered in considerable detail. They also investigated reports of gold occurrences in all neighbouring streams and recorded their relative success. Because gold sometimes adhered to quartz, they concluded that quartz veins were the source of the gold – and very likely some of the many such veins occurring on Croghan Kinshelagh mountain itself. The workings were not without their own tribulations, for the authors reported that their utensils (at Monaglogh): “were destroyed by some persons unknown, for the discovery of whom a reward of 20 guineas was offered without producing the desired effect and the trial was not resumed.” While minor compared to the events of May 1798, clearly the neighbours had not entirely acquiesced in their imposed state of inactivity.
Convinced that a viable bedrock gold source lay in quartz veins on the higher slopes of Croghan Kinshelagh, the Commissioners proposed to continue working the river bed, opening trenches and even tunnelling until this idea had been fully tested. Indeed they had one daring if risky idea: to open a tunnel, at right angles to the principal direction of the veins, straight through the mountain at the highest level where gold had been discovered in the river bed. While the other proposed workings could be relied upon to produce a profit, this new concept was much more risky.
In considering the programme of work recommended by Abraham Mills and co-workers, the Government had the weighty views of eminent scientist and President of the Royal Irish Academy, Richard Kirwan. In his report, published as an appendix to that of Mills and co-workers, he was complimentary about the operations themselves: “As to the method of extracting gold from the sand, none, I believe, can be more ingeniously contrived nor more successfully applied, than that employed by Mr Mills. The real interest, however, would have been his views on the source of the gold, the future of the operation and especially in the proposed tunnel. He did not disappoint.
He agreed the likely source of gold lay in the mountain’s quartz veins but concluded that the gold was derived not by modern river action but “by ancient inundations; I say ancient, because modern inundations convey none, as Mr Mills (at my request) having tried has experienced.” Modern rivers, in his view, did not have the power to move downstream nuggets of the sizes known from Goldmine River. He was not averse to prospecting on a limited scale being undertaken in the upper reaches of the various streams and ravines. But as to the idea of driving a tunnel straight through the mountain to the other side, well he was very cautious.
This must have been sweet music to the economical ears of those in HM Treasury! Nowadays a cost-efficient set of boreholes would be attempted, but that option was not available to Weaver and tunnelling techniques were primitive, slow and expensive. Kirwan appended a later note (dated 1 October 1801), after the mountain had been surveyed, indicating the proposed tunnel would be 8,862ft (2.72km) in length. He concluded, “The expense I cannot estimate” – another damning uncertainty in the eyes of HM Treasury. The tunnel was never driven.
To be continued…
Other books by Dr Peadar McArdle can be viewed on Amazon here