Reasons for Designation
For several millennia the western part of the South West Peninsula, namely
Cornwall and West Devon, has been one of the major areas of non-ferrous
metal mining in England. It is defined here as prospecting, extraction,
ore processing and primary smelting/refining, and its more important and
prolific products include copper, tin and arsenic, along with a range of
other materials which occur in the same ore bodies. Throughout much of the
medieval period most of the tin was extracted from streamworks, whilst the
other minerals were derived from relatively shallow openworks or shafts.
Geographically, Dartmoor was at the peak of its importance in this early
period.
During the post-medieval period, with the depletion of surface deposits,
streamworking gradually gave way to shaft mining as the companion to
openworking methods. Whilst mining technology itself altered little, there
were major advances in ore processing and smelting technologies. The 18th
century saw technological advances turning to the mining operations
themselves. During this period, Cornish-mined copper dominated the market,
although it was by then sent out of the region for smelting. The
development of steam power for pumping, winding and ore processing in the
earlier 19th century saw a rapid increase in scale and depth of mine
shafts. As the shallower copper-bearing ores became exhausted, so the mid
to late 19th century saw the flourish of tin mining operations, resulting
in the characteristic West Cornish mining complex of engine houses and
associated structures which is so clearly identifiable around the world.
Correspondingly, ore processing increased in scale, resulting in extensive
dressing floors and mills by late in the 19th century. Technological
innovation is especially characteristic of both mining and processing
towards the end of the century. In West Cornwall, these innovations relate
chiefly to tin production, in East Cornwall and West Devon to copper.
Arsenic extraction also evolved rapidly during the 19th century, adding a
further range of distinctive processing and refining components at some
mines; the South West became the world's main producer in the late 19th
century.
From the 1860s, the South West mining industries began to decline due to
competition with cheaper sources of copper and tin ore from overseas,
leading to a major economic collapse and widespread mine closures in the
1880s, although limited ore-extraction and spoil reprocessing continued
into the 20th century.
A sample of the better preserved sites, illustrating the technological and
chronological range, as well as regional variations, of non-ferrous metal
mining and processing sites, together with rare individual component
features, are considered to merit protection.
The Tolgus arsenic works survives very well, with little modification,
containing the best preserved example of a Brunton calciner known to
exist. The 20th century works contain a good range of surviving
components. The adjacent survival and limited reuse of the 19th century
arsenic works shows well the complexity and chronological depth often
present at such sites.
Details
The monument includes an early 20th century arsenic works which served the
Tolgus tin stream works north of Redruth. The monument also includes
adjacent remains of a 19th century calciner, flue and a collapsed chimney.
The works' Brunton calciner, one of the arsenic condensing chambers, and
the standing chimney are Listed Buildings Grade II.
The early 20th century calciner is understood to be the only surviving
complete example of a type that was developed by the Scottish engineer
William Brunton. Constructed on this site in about 1933, its function was
to roast off sulphur and arsenical contaminants from tin bearing ores. The
arsenious oxide in the fumes was collected for sale from condensers higher
up the slope. The fabric of the calciner is of reused granite blocks,
some forming quoins to the wall corners, with uncoursed granite rubble in
the upper section. Cream brick arches line the ground floor wall openings.
The ground floor on the north side has a brick faced recess containing the
calciner's twin grates, ash pans and damper door. The calciner has an
hipped slate roof, painted fascia boards and a cast iron rain-water
down-pipe on the north. The calciner's ground floor walling is reinforced
with vertical iron tie-bars to counter the thermal stresses when in use.
The eastern elevation contains the calciner's power arch which encloses
the drive gearing for the rotating hearth which survives above. The
calciner's exhaust opening and ore chute door are sited within the
southern elevation. The first floor retains its original iron hopper to
feed the rotating hearth, together with the floor's supporting beams and
ties. The first floor also served as a storage space in which the ore was
dried prior to being fed to the hearth below. The floor's access door is
on the west, opening to the trackway beyond. The fuel store attached to
the north of the calciner is constructed of cement-rendered concrete
blocks and shuttered mass concrete, and was built about the same time as
the calciner. The roof is only partly extant and is a mixture of
cement-asbestos sheeting and felt-clad planks supported by wooden `A'
frames that have been repaired in places.
Upslope from the calciner are the flues and condensers that connect with
the calciner, rising to a circular chimney 87m to the south west. The
flues are brick with coursed slate-stone rubble in places. The flues'
capping survives over some lengths, beneath a covering of earth and
vegetation. The first condenser in the line of flues has the remains of
seven brick baffles within, on which the arsenic would have accumulated
and been periodically removed for further processing and sale. The second
condenser, higher up the slope, is of a smaller three-baffle design and
may have been added later than the flues and condenser lower down the
slope. From the second condenser, a section of flue passes westwards under
the Old Portreath Road and continues for a further 38m to join the
circular chimney which bears the date 1933 and has a brick upper section.
A revetted trackway cut along the hillside north from the calciner
provided a sloping access ramp for the delivery of ores to the upper
drying floor and hopper space. The trackway varies in width from a maximum
8.4m wide turning area at its southern end beside the calciner, to a
minimum 4.5m at its northern extent.
The rear wall of an earlier 19th century calciner extends south from the
20th century one; its extant walling was reused as the rear of a lean-to
structure contemporary with the 20th century calciner. A line of tumbled
masonry and a cone of soot stained slate-stone rubble mark the positions
of a 19th century flue and chimney that ascended the hill slope
immediately west of the 20th century calciner and its access trackway:
some of the few surviving remains from arsenic calcining in the area
before 1900.
The surface of the modern metalled road is excluded from the scheduling,
although the ground beneath is included.
MAP EXTRACT
The site of the monument is shown on the attached map extract.
