failure of supplies from Russia during the Russo-Japanese war of 1905 gave
fresh impetus to Welsh mines, but this time the greatest contribution came
from the neighbourhood of Rhiw, at the western end of the Lleyn Peninsula.
In this region, irregular bodies of ore, situated between a massive sill
of dolerite below and a
lave flow above occur in some mudstones in the Arenig division of the
Ordovician System. The mudstone being softer than the associated igneous
rock was greatly disturbed – folded and shattered, during a period of mountain
building movements, so that the ore – bed was broken into many separate
bodies, the content of which varies from as much as 30,000 tons. The
thickest masses were about 30 feet thick, having been built up by
distortion of a bed originally from 8 to 10 feet thick, but as they were
steeply inclined they appeared, in shafts driven vertically through them,
to be twice as thick as they really were.
There were two groups of mines, a southern group including Nant Gadwen
mine near Llanfaelrhys, and a northern group about a mile away, including
the Rhiw and Benallt mines. Ore was being raised as early as 1894, and
before the last of them Benallt closed in 1945, they had produced
over 195,000 tons of ore. At first, only a few hundred tons a year were
raised, but between 1905 and 1907 the output rose to more than 20.000 tons
a year. For the next few years most of the ore was obtained from levels
driven from an incline at the Nant mine, the most in one year being about
10,300 tons in 1918. The mine has been inactive since 1925. The ore, which
was worked from several levels driven off a main incline, came all from
one ore body.
Benallt mine was found to have a particularly complex geological
structure, due to folding and faulting, and the ore bodies occurred in a
disconnected manner. The character of the original sediments was changed
by mineral solutions that invaded the rock as a concomitant of the
and the ore consists mainly of manganese silicates with oxides of
and iron, is manganese carbonate, so characteristic of the other mines, is
present only in significant quantity.
was obtained from opencast workings until, due to the inclination of
strata, the amount of over-burden became excessive and inclines were drive
into the ore-bearing beds. Eventually several shafts were sunk, one of
which was deepened in 1941 from 60 to 130 feet, and the ore was obtained
from headings driven from the shaft at three levels, it was allowed to
gravitate to the lowest level and from this was hoisted to the surface.
Exploratory work shortly before the mine closed in 1945 produced negative
results although, having regard to the nature and distribution of the ore
bodies, this does not preclude the possibility that they may occur at
Gwaith Mango Nant Gadwen.
Yn y dechrau carriwyd y mango gyda mulod i Borth Cadlan I’w
lwytho ar longau hwylio bach. Yn ymyl Groeslon mae cae o’r
enw cae mulod ac yma byddai’r mulod yn cael eu cadw.
Adeiladodd William Jones, rheolwr cynta’r gwaith, Groeslon
gan ddefnyddio cerrig mango.
Adeiladwyd y lanfa yn 1902/3 ar gost o £182.
‘Rhiw’oedd enw’r tren bach a ddoi a’r mango lawr o waith
Benallt i’r lanfa ym mhorth Ysgo.
Yn 1906 cloddiwyd 10,000 tunnell o fango yn Nant Gadwen.
Ym mis Mai 1918 cafodd pump llong eu llwytho mewn wythnos.
Mercher 22 – Llwytho’r SS JJ Monk – 55 rownd.
Sadwrn 25 – Llwytho SS Florence – 60 rownd.
Llun 27 – Llwytho Anne - 66 rownd.
Mawrth 28 – Llwytho Agnes Ellen – 300 tunnell.
Mercher 29 – Llwytho Florence – 200 tunnell.
Yn 1919 gwnaeth y gwaith elw o £8,542.
Caewyd gweithfeydd Nant Gadwen am y tro olaf ar ddydd Llun
17eg o Awst 1925.
Ar ddydd llun yr 11fed o Orffennaf 1927 llwythwyd 340
tunnell o fango ar yr SS Daisy. Mae’n bur debyg mai hon oedd
y llong olaf i ddefnyddio glanfa Porth Ysgo.
Yn ystod oes y gwaith cynhyrchwyd 45,644 tunell o fango.
Tynnwyd y lanfa i lawr yn 1933.
Doedd dim damweiniau angeuol yn y gwaith ond collodd un dyn
ei fraich mewn damwain. Claddwyd ei fraich ym mynwent
Llanfaelrhys. Blynyddoedd yn ddiweddarch pan fu farw’r gwr
bu iddo gael ei gladdu ym mynwent Nebo ym mhentre Rhiw.
Nant Gadwen Manganese Mines.
first the ore was taken by donkeys to Porth Cadlan where it
was loaded on to small sailing ships at low tide. There is a
field at Groeslon called “Donkey Field” where they were
William Jones the first manager of the mine built Groeslon
The jetty at Porth Ysgo was constructed in 1902/1903 at a
cost of £182.00.
The little train that brought the ore down to the jetty from
Benallt was called “Rhiw”
10.000 tons of ore was mined at Nant Gadwen in 1906.
In May 1918 five ships loaded at the Porth Ysgo jetty in a
Wednesday 22 – Loading the SS J J Monks 55
Saturday 25 – Loading SS Florence 60 round.
Monday 27 – Loading SS Anne 66 round.
Tuesday 28 – Loading Agnes Ellen 300 tons.
Wednesday 29 – Loading the Florence 200 tons.
In 1919 the mine made a profit of £8.542
Nant Gadwen mines shut down for the last time on Monday 17th
The SS Daisy loaded 340 tons on Monday 11th July
1927. This could have been the last ship to load at the
Porth Ysgo jetty.
Nant Gadwen produced 45.644 tons of manganese in its
The jetty was finally demolished in 1933.
There were no fatalities at the mine, but one man lost his
arm in an accident. His arm was buried at Llanfaelrhys
church, and many years later he was interned at Nebo chapel