Tony -
Malachite has also been worked in Russia, mainly at various mines
in the Urals, certainly since the early 18th century (and
probably long before that), and used among other things for some
superb decorative inlay work for the Tsars and aristocracy - as
well as large pieces being used to make giant vases (like the
British equivalent, the Blue John vases at Chatsworth). Some of
the mines have an interesting history, being worked by a variety
of companies at different times. One mine, which I have visited
recently, was operated by a British-owned company 'Lena
Goldfields' on lease from the Bolshevik government in the 1920s.
My Russian hosts told me that there is evidence nearby for the
deposit having been worked more than 2000 years ago.
- Steve Henley
----- Original Message -----
From: "Tony Brewis" <[log in to unmask]>
To: "List" <[log in to unmask]>
Sent: Saturday, August 26, 2000 7:10 PM
Subject: Re: Copper terms/malachite
> Richard Kelham asks if there was any commercial exploitation of
> malachite, a copper carbonate/hydroxide.
>
> Yes, very much so. Being a nicely coloured stone, it may well
have
> been the origin of the Bronze Age, when early people built
their
> hearths of the nice green stone and discovered smelting. The
black
> oxide, when heated with charcoal, yields metallic copper.
>
> One of the earliest "commercial" examples was the use of
malachite
> by the Zimbabwe Empire, which produced copper currency from
> malachite deposits at Kansanshi and Bwana Mkubwa.
>
> Typically, malachite forms near the surface in the zone
penetrated
> by air and groundwater, so converting the original sulphide
minerals
> in an "oxide capping". At Malanjkand in India, for example,
malachite
> was the dominant copper mineral near the surface, and at
Chambishi,
> Zambia, there was malachite to a depth of 50 metres.
>
> The "problem" of malachite for modern technology is that the
flotation
> process works best on sulphide minerals, so malachite is lost
to tailings.
> Some reagents will collect it, but generally the upper zones of
ore which
> contained it were known generally as "refractory" ores. In
modern times
> such ores were worked at the Aljoujt mine in Mauritania,
between 1970
> and 1983, using a furnace system known as TORCO ( Treatment Of
> Refractory Copper Ores). Once the open-pit had worked its way
through
> the upper zone of ore, which graded 2.7% copper, the furnace
was
> closed down.
>
> Tony Brewis
>
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