Silver Smelting in Peru 2000 Years Ago
Tuesday, 13. October 2009, 08:54:48
On the shores of Lake Titicaca, in what is now Peru, silver was mined and smelted as early as around 2000 years ago - at Huajje. The site of Huajje is a 128,000-m3 mound located on the northern shores of Lake Titicaca, in the centre of the resource-rich Puno Bay. Huajje is situated in a region famous since Colonial times for the rich Laicacota silver ore mines located above the city of Puno.
Huajje, where the new excavations have taken place, was probably first a village that later grew out to become an important centre around 100 A.D. About 500 years later it was incorporated into the Tiwanaku state. The Incas expanded to the area in the 15th century followed by the Spaniards (looking for El Eldorado, and thus gold and not silver) after 1532. During this time-span silver was produced in Huajje.
Evidence of silver production—including crucibles, matte, slag, and vitrified ceramics characteristic of high temperature processing—was found in every level in the 22 m test unit from 0.30 m to 4.80 m below the modern surface.
The steps required for silver extraction include mining, beneficiation (i.e., crushing of the ore and sorting of metal-bearing mineral), optional roasting to remove sulfur via oxidation, followed by smelting, and cupellation. During smelting, silver and lead-rich ores are combined in the furnace. The lead ore acts as a collector for the silver metal, securing better separation of silver from the gangue (i.e., mineral impurities in the silver-bearing ore). Smelting produces metal, typically a silver-containing lead (bullion) containing variable amounts of metal sulfides (matte), and slag. Matte is defined as a matrix of metal sulfides with only minor amounts of silicates. Slag, by definition, has a matrix of silicates, sometimes with minor inclusions of matte or metal.
The data suggest the following pattern: the smelting of a rich silver ore conducted elsewhere (likely the site of Punanave), followed by transportation of the raw bullion to a central and well-supervised site (in this case, Huajje) for further processing. Re-melting of the raw bullion in crucibles here would result in the separation of matte that may have been mixed with the bullion, and a partial oxidation of lead metal, forming lead silicate slag in the crucible through reaction with quartz mineral. The refined bullion from this operation would then have been fit for cupellation to pure silver.
Note:
A crucible is a ceramic or metal container in which metals or other substances may be melted or subjected to very high temperatures.
Cupellation is a process used to separate noble metals such as gold or silver from base metals such as lead.
A cupel is a shallow, porous container in which gold or silver can be refined or assayed by melting with a blast of hot air, which oxidizes lead or other base metals.
Reference:
Schultze et al.
Direct evidence of 1,900 years of indigenous silver production in the Lake Titicaca Basin of Southern Peru
PNAS 2009
doi: 10.1073/pnas.0907733106
In Norwegian:
Huajje, where the new excavations have taken place, was probably first a village that later grew out to become an important centre around 100 A.D. About 500 years later it was incorporated into the Tiwanaku state. The Incas expanded to the area in the 15th century followed by the Spaniards (looking for El Eldorado, and thus gold and not silver) after 1532. During this time-span silver was produced in Huajje.Evidence of silver production—including crucibles, matte, slag, and vitrified ceramics characteristic of high temperature processing—was found in every level in the 22 m test unit from 0.30 m to 4.80 m below the modern surface.
The steps required for silver extraction include mining, beneficiation (i.e., crushing of the ore and sorting of metal-bearing mineral), optional roasting to remove sulfur via oxidation, followed by smelting, and cupellation. During smelting, silver and lead-rich ores are combined in the furnace. The lead ore acts as a collector for the silver metal, securing better separation of silver from the gangue (i.e., mineral impurities in the silver-bearing ore). Smelting produces metal, typically a silver-containing lead (bullion) containing variable amounts of metal sulfides (matte), and slag. Matte is defined as a matrix of metal sulfides with only minor amounts of silicates. Slag, by definition, has a matrix of silicates, sometimes with minor inclusions of matte or metal.
The data suggest the following pattern: the smelting of a rich silver ore conducted elsewhere (likely the site of Punanave), followed by transportation of the raw bullion to a central and well-supervised site (in this case, Huajje) for further processing. Re-melting of the raw bullion in crucibles here would result in the separation of matte that may have been mixed with the bullion, and a partial oxidation of lead metal, forming lead silicate slag in the crucible through reaction with quartz mineral. The refined bullion from this operation would then have been fit for cupellation to pure silver.
Note:
A crucible is a ceramic or metal container in which metals or other substances may be melted or subjected to very high temperatures.
Cupellation is a process used to separate noble metals such as gold or silver from base metals such as lead.
A cupel is a shallow, porous container in which gold or silver can be refined or assayed by melting with a blast of hot air, which oxidizes lead or other base metals.
Reference:
Schultze et al.
Direct evidence of 1,900 years of indigenous silver production in the Lake Titicaca Basin of Southern Peru
PNAS 2009
doi: 10.1073/pnas.0907733106
In Norwegian:
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