Reasons for Designation
Cobalt ores usually occur as vein minerals in association with other metals,
particularly nickel and copper. Although found in traces in most orefields, it
is only found in workable deposits in Cornwall, at Alderley Edge (Cheshire)
and in the Lake District. At Alderley Edge the ores are mostly impregnated
into the local sandstone. The refined metal is used in pigments.
Until the mid-19th century the pigment was produced in the form of azure or
`smalt' by concentrating and then calcining the ore, then grinding and melting
with fine quartz to form `zaffre', a yellow colour, named after saffron. This
was then converted to azure by grinding and melting with potash. In the later
19th century a more efficient process was developed in which the parent ore
containing cobalt, nickel, copper and iron was smelted to a `regulus' which
was then calcined and dissolved in hydrochloric acid. The iron and copper were
removed and the cobalt precipitated out with a bleaching powder, dried and
heated to produce pure cobalt oxide.
Copper was extracted in Britain intermittently from the Early Bronze Age
(about 2000 BC) until the early 20th century, after when the industry was
confined to by-product production and small scale reworkings of mines and
dumps. There is very limited evidence for copper mining before the 15th and
16th centuries, and most known sites are of later date, principally of the
industry's 18th and 19th century peak after it had been revitalised by
developments in smelting technology. In the 18th and 19th centuries, as
perhaps it had also been in prehistory, British production was important on a
European scale.
Nucleated copper mines are a prominent type of field monument produced by
copper mining. They consist of a range of features grouped around the adits
and/or shafts of a mine. The simplest examples contain merely a shaft or adit
with associated spoil tip, but more complex and, in general, later examples
may include remains of engine houses for pumping and/or winding from shafts,
housing, lodging shops and offices and power transmission features such as
wheel pits and leats. The majority of nucleated copper mines are of 18th to
20th century date, earlier mining being normally by rakes, opencuts and open
levels, and including scattered ore dressing features.
An essential part of a copper mining site is the ore works, where the mixture
of ore and waste rock extracted from the ground was separated (dressed) to
form a smeltable concentrate. The range of processes can be summarised as:
picking out clean lumps of ore and waste; hammering (breaking down lumps to a
smaller size by manual hammering or by mechanical crushing); jigging and
buddling (separation of finer material by washing away the lighter waste in a
current of water). Field remains of ore works include crushing devices,
separating structures and tanks and tips of distinctive waste from the various
processes, together with associated water supplies. Simple ore dressing
devices had been developed by the 16th century, but the large majority date
from the 18th to 20th centuries, when technology evolved rapidly.
During English Heritage's national evaluation of the copper industry, 130
sites were assessed. This is a highly select sample of the numbers of sites
that historically existed in England; although there are no national
estimates, for the south west alone an estimate has been made of over 10,000
sites. It is considered that protection by scheduling is appropriate for less
that 50, with alternative means of protection or management being considered
more appropriate for the other nationally important sites.
Although the cobalt processing at Alderley Edge was only working for a short
time, it is historically important as an example of the discovery and
application of the new 19th century technology in the preparation of metal
pigments. Beneath the overgrown ground level there will be the remains of the
buildings, tanks, mine workings and machinery which were associated with the
production of both copper and the minor metals, lead, nickel and cobalt at
this site. There are foundations of buildings, including offices, cottages,
furnaces and a cooling tower which may be located and identified by further
archaeological work. The site preserves an unique opportunity for the
development of an educational resource for future students.
Details
The monument includes the earthworks and buried remains of the metal ore
processing works adjacent to Wood Mine and West Mine on the western side of
Windmill Wood on Alderley Edge. The locations of the original Wood Mine and
West Mine entrances are included in the protected area as are the modern
entrances to each. The works were set up to process copper and lead ores and
later to extract cobalt from the copper ores a short time before 1860 by the
Alderley Edge Mining Company. The lead works were closed in 1863. Work at the
cobalt plant ceased in 1864 and production of copper was abandoned at this
site in 1878. Although only operating for a short time, the works processed
168,269 tons of copper ore and produced 3,200 tons of fine copper metal. In
addition, almost 100 tons of lead and 11 tons of cobalt-nickel were produced.
After 1878 the site stood idle until a new works was constructed, possible in
a different location, in 1914. This was sold off in 1926.
Among the metal extraction processes on this site, the production of cobalt is
of great interest in the history of mining and smelting in England and it is
believed that this processing site is unique. The copper ore from the mines
was first crushed and then fed into wooden leaching tanks where the copper was
removed by dissolution with hydrochloric acid. The resulting liquid was then
put into precipitating tanks where scrap iron was added to the acidic mixture
causing the iron to be dissolved at the expense of copper which precipitated
in a metallic state. The remaining solutions contained iron, manganese, nickel
and cobalt. These were treated by being concentrated and then evaporated to
produce a cobalt/nickel `speiss'some of which was sold on to manufacturers of
paint or enamels. Whilst the production of cobalt at this site is of
technological interest, documentary evidence suggests that a ready market for
the product was never found.
The features of the process which will survive here include the remains
of the wooden tanks for acid dissolution and precipitation, the bases of the
furnaces for heating the cobalt bearing solutions, the foundations of the
cooling tower for evaporating the heated mixture and the beds for the steam
engines which powered the entire process. In addition there are the remains of
the copper ore crushing machinery, the inclined tramways which brought the ore
from Wood Mine and West Mine, the offices and workshops of the processing
works and the accommodation for some of the senior artisans on the site. Also
on the site, within the monument, there are the remains of the pitheads and
shafts of several entrances to the ore-bearing veins in each mine. Notable
among these are the foundations for the winding engine houses of Wood Mine and
West Mine, the crusher and buddling floors of Wood Mine, and the dressing
floors common to the two mines located beside West Mine. The adit entrance
shaft for Wood Mine are located in the eastern side of the monument area at
SJ85457760 and the possible remains of the winding engine house for West Mine
are located on the western side of the site at approximately SJ85267753. The
machinery on these sites was finally sold off in 1926 when the mines finally
closed.
Immediately to the east of the central processing area were four cottages and
a well which may have been built for workers in the copper mines and were
still in occupation in 1950. At least one of these dated to 1747. Of these
only the brick foundations survive and they are included in the scheduling. To
the south of the central processing area there were massive hills of waste
sand from the copper processing and the remains of the largest sandhill are
also included in the scheduling.
All fence posts, gates and waymarkers are excluded from the scheduling,
although the ground beneath them is included.
MAP EXTRACT
The site of the monument is shown on the attached map extract.
