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MINING-HISTORY  November 2012

MINING-HISTORY November 2012

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Subject:

Geevor Mill in 1961

From:

Tony <[log in to unmask]>

Reply-To:

The mining-history list.

Date:

Mon, 12 Nov 2012 21:56:14 -0000

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (104 lines)

Sorry if I have told this tale to the List before, but my memory is getting
to that stage when I can recall things which happened 50 years ago better
than I remember in detail what I did last year! Anyway, I hope you find it
of interest.

Cheers,

Tony Brewis

 

 

Geevor Mill

 

In March 1961, during a postgraduate year studying mineral processing at the
Royal School of Mines, I accompanied a group of final-year mineral
processing students on a week spent visiting processing plants in the
southwest of England, starting at the lead-zinc Imperial Smelter in
Avonmouth and going on to several china clay works, South Crofty and Tolgus
Tin. We ended up being shown round the mill at Geevor.

The first thing we saw before entering the Geevor mill was a heap of rusty
steel grinding-mill balls in the yard - the ball charge was topped up from
time to time, we were told, and these were the stock waiting to be used.
Inside the mill we studiously followed the process flow, the shaking tables
and Frue vanners being of particular interest. As we descended the
occasional flight of stairs from one floor level to the next, I was
particularly  impressed with the excellent quality of the smooth wooden
handrails, polished to perfection by years of use. 

With the noise of the ball mill, and a steady slow hammering from lower
down, some of the foreman's explanations as he guided us through the plant
were difficult to hear. However, there was soon a providential power cut,
and apart from his talking all was quiet except for a gentle background
sound of running water. Suddenly all his explanations became crystal clear. 

On the lowest floor of the mill we came to the final stage of the process.
On one side was a conical concrete buddle, while on the other there was a
row of large wooden barrels, alongside each of which hung a large wooden
mallet, moved (when the power was on) by cams on overhead lineshafting. The
barrels, we were told, were kieves. 

Having been taught that the important thing in representing  a milling
process was drawing the flowsheet, we were all perplexed at this stage
because we could not see any obvious route for the material flow. One of the
students asked our guide for an explanation - did the flow take place from
buddle to kieve or from kieve to buddle?

"Ah!" said our guide, "Well, tis like this"

He took a shovel and scooped up some of the material lying on the surface of
the buddle, together with a film of water. A deft  back-and-forth and
side-to-side shaking movement made the fine particles divide in a trice into
two areas, one dark grey, one a light brown. He drew a line between the two
with his fingertip to emphasise the boundary. "This 'ere is the tin" he
said, pointing at the darker area, "And that there is the iron oxide".

"Now," he said "you remember that heap of rusty steel balls outside in the
yard?" We assured him we did. "Well," he explained "when we put those into
the mill, the rusty iron oxide gets knocked off and they become shiny again,
but smaller.  When we next sort the charge of balls in the mill, some go
back outside and get rusty again. Over time, they get smaller and smaller.
That's what happens here" he explained.

"Jim there can take a sample as I have just done and, looking at it, he
knows just how much tin there is in this concentrate to the nearest percent
and decides what to do with it. It may go to the buddle first and then to
the kieve, or what's been in the kieve can go back to the buddle. In time,"
he emphasised, "just like the rust on those balls, and the way they get
smaller as the rust is knocked off them, this iron oxide gets knocked around
so much between buddle and kieve  that in the end it gets so small it just
vanishes, and we're left with the tin!"

At that moment the power came back on, the ball mill restarted and the
mallets renewed thumping the kieves loudly. All opportunity to ask questions
was lost in the din. 

The iron oxide "just vanishes"?? But he was the foreman, so with his years
of experience he must have known. We looked admiringly at the stream of
water in the launder taking the "vanished" iron oxide tailings out to be
discharged. 

Some doubt in our minds as to the complete efficiency of the system was
aroused  shortly afterwards when, once outside, we saw another plant  lower
down the hill treating the Geevor mill tailings on a set of round frames.
Presumably the man who had gone to the trouble of building the roundframes
was collecting enough  tin to make a profit??

Things were very different when, as editor of Mining Magazine, I went back
to Geevor in 1982 and included a description of the mine and plant in the
November issue of that year within an article on metal mining in the UK
(Geevor mill is referred to on page 407). No mention of any kieves then!

 


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