Hi,
Another interesting thing to take into account is that you don't need to
assume that arsenic content is intentional, through the use of copper
sulphides. There are secondary copper arsenates such as olivenate,
clinoclase, cornubite, cornwallite, as well as antimony oxides like
stibiconite that result from weathering of copper sulphides.
Thus you can get arsenic and antimony into tools without having to
intentionally exploit copper sulphides, as is normally assumed. The arsenic
and antimony content in this scenario could be simply the result of the
exploitation of available ores in a region. This ores could be mixed
together (they can occur together) with copper carbonates like malachite
and azurite.
In this acenario there's no real difference in timelines. It all depends on
the type of ores available locally. Purer copper in tools could be the
result of either the use of native copper (if available) or simply the use
of a deposit where secondary copper arsenates and antimony oxides do not
occur together with the more common copper oxides.
The interesting thing about this is that you don't need the very high
temperatures (1250-1300C) needed to get the copper from primary minerals in
a one-step process, neither do you need a preliminary roasting process of
fahlerz at around 800C that leads to loss of arsenic. All you need is a
mixture of copper oxides and secondary copper arsenates at a temperature of
around 700C to get copper arsenic alloys by diffusion of arsenic into solid
copper.
Richard Thomas is the one that has been doing work in this scenario. You
can check out Paul Budd's article "Recasting the Bronze Age" available on
the internet (just use Google), where he summarizes this matter very
well.
Pedro Pereira
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