Dear Yitzhak
You have had some interesting replies. I would like to suggest that you look at a book published some years ago which deals with copper mining and smelting in ancient Africa:
Herbert, Eugenia W. Red Gold of Africa - copper in Pre-colonial History and Culture. University of Wisconsin Press, Madison, 1984.
Pages 63-64 I believe are pertinent as it deals with smelting in the Niari Basin of Angola. "In the case of copper, a certain amount of previously smelted lead was always added to the charge. The result was a highly malleable metal looking rather like tin. It was then smelted a second time with a new and heavy admixture of copper ore." It continues that after creating ingots of this second smelt the ingots were melted a third time specifically with more charcoal and "heated to precise colour, presumably to eliminate the greater part of the added lead." On cooling the metal "took on a beautiful red copper colour." Could it be that your artefact was created from the intermediate and lead rich smelt?
I have been working on the mineralogy and archaeology of an ancient "copper mine' known as the Olifantspoort copper mine no 47/73 which was excavated in 1973. It has always puzzled me why a copper mine? Yes it does contain mineable quantities in pre-historical terms of copper with the dominant ores being carbonates however so far I seem to be showing that on a mineral species ratio of visually identified species there are more lead minerals present than copper. This raises a question of whether the lead was smelted and used in a similar manner to the Niari Basin lead.
Regards
Graham Reeks
-----Original Message-----
From: Arch-Metals Group [mailto:[log in to unmask]] On Behalf Of Yitzhak Vassal
Sent: Saturday, October 11, 2014 9:15 PM
To: [log in to unmask]
Subject: Polymetallic lead/copper ore
Dear list,
I'm currently working on an early artifact of copper mixed with lead (the lead is mostly concentrated between grains and can reach up to %70). Our fundamental assumption is that it represent a deliberate mix of copper and lead metal, but does anyone is familiar with a polymetallic lead/copper ore used in antiquity? Is this a valid possibility to take into account?
Many thanks in advance,
Yitzhak Vassal
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