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 Wheal Kitty tin processing works contains a good, and relatively
complete, range of surviving structural components, illustrating well the
layout and construction of a tin ore processing works from the early 20th
century. The Brunton calciners and scrubber chamber also demonstrate how
19th century technology and build was readily incorporated where
appropriate and legally required to minimise arsenic pollution. The high
quality of the works' survival is further enhanced by the nearby survival,
beyond this scheduling, of parts of the shaft-head complex of buildings
around the works' ore-source, Sara's Shaft.
Details
The monument includes an early 20th century tin processing works which
served the Wheal Kitty mine at Goonlaze Downs, east of St Agnes in west
Cornwall.
The Wheal Kitty tin processing works was constructed during 1926-29, its
function being to process ore produced at the Wheal Kitty mine to extract
cassiterite using Californian stamps, classifiers, sand and slimes tables,
and circular buddles. Contamination was removed from the ore by the use of
calciners and chemical treatment. Discharge from the refining process was
treated in a tailings mill to recover the maximum amount of cassiterite
from the effluent. All the structures are now roofless and all the
machinery has been removed.
The tin processing works comprises three groups of buildings, being termed
the western and eastern mills for the purposes of this scheduling. The
third housed the tailings mill. The extant fabric of the buildings
comprises low cement-rendered concrete block walls; the upper walls and
roofs have been removed but were of corrugated steel sheets fixed to
timber frames, internally supported on concrete piers. The floors inside
the buildings are of screed concrete into which dipper-wheel pits and
sunken channels have been created, the former to elevate process material
to higher levels, and the latter to drain waste overflow from the
processing plant for disposal. The works' buildings contain numerous
concrete machine bases onto which sand and slimes tables and other
processing machinery were fixed.
The ore dressing methods used in the works involved both gravity and
chemical techniques. The western mill contained the primary ore dressing
machinery which consisted of a Californian stamps battery and classifiers,
with sand and slimes tables immediately in front. Chemical froth-flotation
cells were in use in the western mill to remove contaminating arsenical
sulphides from the processed ore. The eastern mill contained the secondary
ore processing and calcining machinery and four cement-rendered circular
convex buddles are positioned at the northern end. Two Brunton arsenic
calciners are located at the southern end of the eastern mill. A pair of
concrete coal chutes positioned at the rear of the calciners facilitated
the delivery of fuel to the storage area there. A concrete and masonry
arsenic flue connects the Brunton calciners to the arsenic scrubber
chamber approximately 103m to the north east. The scrubber chamber was
constructed to remove excess toxic gases from the calciner fumes by water
treatment and is a reuse of a 19th century building. A short length of
flue connects the scrubber chamber to a square concrete chimney
immediately to the east.
The tailings mill, sited approximately 50m to the north of the eastern
mill, screened the effluent from the latter to recover lost cassiterite.
Constructed on two levels, it contains concrete machine bases, a
dipper-wheel pit, and one visible cement-rendered circular convex buddle.
Two parallel channels constructed using concrete blocks link the eastern
mill to the tailings mill via a concrete settling tank. A sunken drainage
channel curves downslope to the north from the western mill which was used
for the disposal of process effluent at sea.
The St Agnes area was a significant producer of tin with rich deposits
being worked during the 18th century. Prospecting pits, lode-back pits and
openworks are extant in the area surrounding the tin processing works in
addition to the shafts associated with deep lode mining.
MAP EXTRACT
The site of the monument is shown on the attached map extract.
It includes a 2 metre boundary around the archaeological features,
considered to be essential for the monument's support and preservation.
