The report on the Beldon partnership's ore is pretty clear. The ore did
n't look too good because it was small and consisted of a mixture of galena
(blue ore) and carbonate ore (grey ore). The reporter was surprised when
it smelted (ran) as well as it did and also the yield was better than
anticipated. Carbonate ores can be expected to smelt more easily than
sulphides as they break down to litharge at relatively low temperatures (I
think somewhere around 400-500 degC). The percentage of lead is always
lower in carbonate ores 77% vs 87% for the pure mineral and less if the
carbonate is hydrated, so yields would be lower.
I'm not sure how that ties up with silver. Even high quantities of silver
should make no difference to lead smelting. The term 'soft' lead means
that it has low levels of hardening impurities such as Fe, Cu, Sb, Sn, As,
Ni. Fe normally comes out on remelting so is not a big problem. The
others will cause problems with cupellation and are normally removed from
asssay samples when above 2-3%. Some of the hardening impurities
(particularly Cu) will upset the Pattinson or Rozan refining processes as
they form drosses which come out slowly and incompletely. The impurity
level in the silver-rich crystals will be disproportionatel;y high. Lead
from English slag hearths was nearly always hard and would have had a lower
Ag content than ore hearth lead.
I think that Raistrick said that ore from Braithwaite Hall in south
Wensleydale mine was high in silver and was sent to Bollihope, near
Stanhope rather than to West Burton for smelting and refining..
Richard Smith
3M UK Bracknell,
Environment, Safety and Security [log in to unmask]
Tel: 01344-858154 (Trim. 8-230-2154)
Fax: 01344-858367 (Trim. 8-230-2367)
|