Mining techniques in the 20th century
In the 1960s the search for a new mine at Parys Mountain recommenced. Exploration in the 1960s and 1970s was focused on the extension of the old open pit workings and was directed towards copper. This exploration utilised a variety of geological, geophysical and geochemical methods together with approximately 285 diamond drill holes totalling about 60,000 metres of drilling.
The modern phase of exploration of Parys Mountain began in the early 1980s when a new important polymetallic zinc, lead, copper, silver, gold area was identified about 1 kilometre west of the old workings.
Between 1988 and 1990 a shaft was sunk to a depth of 300 metres. About 1,000 metres of lateral development were completed on the 280 metre level. Drilling and underground development work from 1988 to 1990 resulted in the identification of the Engine, White Rock and Chapel zones containing a resource of 6.5 million tonnes with a combined base metal grade (zinc, copper and lead) of 10.3%.
Approximately 2,000 tonnes of development ore were successfully hoisted and processed through a pilot plant constructed on the site for metallurgical testing and concentrate production of about 200 tonnes was sold to the smelter at Avonmouth.
Major improvements in technology in recent years have had a significant impact on mineral exploration. Anglesey Mining has been at the forefront of the application and use of new methods and technologies and advanced instruments to help unravel the geological mysteries of Parys Mountain.
Over the past few years major lithogeochemical studies have been carried out at Parys Mountain. This work, which has been undertaken by Dr. Tim Barrett of Ore Systems Consulting of Vancouver in conjunction with Cardiff University of Wales and using the analytical laboratory at McGill University in Montreal, involved the re-examination of large quantities of drill core and outcrop. The work was significantly expanded during the year to include the current drilling and to extend to other parts of the property.
Lithogeochemistry depends on the observation that, although the chemical composition of rocks today may be very different to their original composition, certain of the elements within the rock are relatively immobile and do not change.
In order to apply lithogeochemistry it is necessary to accurately analyse rock using X-ray fluorescence and inductively-coupled-plasma mass-spectrometry or similar techniques.
Lithogeochemistry can not only identify rocks to the point where individual lava eruptions can be recognised, but the data can also provide information about the nature of the geological environment in which the volcanic activity occurred, such as a volcanic continental arc or rifted oceanic crust. Additionally, lithogeochemical data allow hydrothermal alteration to be characterised and quantified accurately using mass-change techniques.
The goal of all this is to identify and follow volcanic units and their contacts with each other and with the surrounding shales as doing so will lead to the area’s most likely to contain mineralisation.
Infrared Mineral Analysis
Mineral deposits are associated with hydrothermal alteration of the surrounding rocks. Such alteration commonly forms a halo around the mineralisation, providing an exploration target considerably larger than the deposit itself. The delineation and characterisation of hydrothermal alteration can therefore be of great value in mineral exploration for the identification and assessment of new targets.
Until recently, assessment of alteration assemblages was often difficult because of the fine grain-size of the minerals, and could only be accomplished by expensive and time consuming laboratory techniques. However, this problem can now be addressed using an instrument known as a PIMA (portable infrared mineral analyser), originally developed in Australia, which is a hand-held spectrometer which can provide important information on rocks, minerals and soils. The instrument is capable of detecting many of the minerals commonly found in hydrothermal alteration systems, such as clays, carbonates and sulphates
A recnt joint project was carried out in conjunction with the British Geological Survey, supported by the Department of Trade and Industry, using the PIMA to examine the nature and distribution of alteration in the volcanogenic massive sulphide rocks at Parys Mountain.
The PIMA was successful in detecting distinctive mineral assemblages related to geology and formed by the alteration of the host rocks during interaction with mineralising fluids at Parys Mountain.
Anglesey has been working closely with the British Geological Survey in the application of 3-D visualisation and virtual-reality models to mineral exploration and mine development. BGS staff have worked with Anglesey on a project under the Technology Access Programme of the Department of Trade and Industry on a model of the geology and mineralisation at Parys Mountain so that the underground geology can be better understood and new exploration can be targeted. All the significant historic and new data from Parys Mountain has now been loaded into the BGS Vulcan 3D modelling system. Completing this process was time consuming because of the amount of data involved. It is planned to continue the examination and review of this data using Vulcan.
Radio isotope dating
The volcanogenic massive sulphide (VMS) deposits at Parys Mountain were originally formed in the vicinity of large submarine volcanic centres with associated hydrothermal systems.
In an effort to determine the age and duration of hydrothermal and volcanic activity at Parys Mountain where mineralisation occurs at three levels within the succession, a special project using radio isotope geochronology has been undertaken with the British Geological Survey. This project utilises the very high precision method of uranium/lead dating of the mineral zircon. Because of the unique attributes of the uranium/lead decay system, it is possible to date rocks to within approximately 500,000 years even when the rocks are as old as 2,700 million years.
This technique has been applied to the deposits at Parys Mountain only recently but if it is proved to be successful its impact might have far reaching consequences for the understanding of the formation of these orebodies.
Palaeontology studies in conjunction with Leicester University were carried out in 1996 in order to help to determine the overall stratigraphic relationships at Parys Mountain. A review involving further evaluation of palaeontological data and examination of shale sequences has been completed in 1998. Determining the ages of the shale units at Parys Mountain will be very helpful in establishing the overall structural relations at the property. Systematic collections have not as yet been made from all of the property and a further phase of micro-paleontological dating forms part of the company’s plans.
The Parys Mountain property is the largest and the only undeveloped polymetallic mineral deposit in the United Kingdom. It contains an important identified geological resource of about 6.5 million tonnes with a grade of 5.3% zinc, 2.3% copper, 2.7% lead, 39 grams of silver and 0.32 grams of gold per tonne. A positive independent feasibility study was completed in 1990 and full planning permission obtained for a 1,000 tonne per day mine.
A complete geological reassessment of the property is being carried out and this has resulted in the development of new geological models which indicate that there is potential for the discovery of substantial additional mineral resources in areas east and north of the known resource largely unexplored to date.
A new exploration programme was launched in 1997 and four diamond drill holes were completed. The objective of the new exploration programme is to develop significantly larger mineral deposits at Parys Mountain.
Another exploratory drilling operation was beginning in 2005. This has extended the area over which Copper and zinc have been confirmed further northwards.