Neville,
 
My geologist-mining consultant here, Willard P. Fuller, says that they did do
some ore roasting in the early years of the California Mother Lode -- the
1850s and 1860s -- but it never worked very well. It was mostly surface
roasting, just piling up the wood and crude ore, although Young (Western
Mining, 1970, U. Okla. Press) describes an 1850 roasting furnace using iron
tubes made from musket barrels (p.120). For refractory ores, the California
miners generally worked on the concentrates, not on the crude ore itself.
Fuller wonders if they ever experimented with chlorine leaching on
concentrates in New Zealand. It preceded the cyanide process (first used at
the Crown Mine, Karangahake, New Zealand, in 1889!) and could have perhaps
been more successful than roasting.
 
Young describes ore roasting kilns in the US Southwest that are beehive shaped
and located around old Spanish mine workings (p.67-68). These sound closer to
what you have.
 
At the Mother Lode copper-mining town of Copperopolis, they did some roasting
of copper ore at one phase in the 19th century. This was commonly used in
antiquity in the development of copper working in Cypress, Greece, Spain, and
Central Europe (and other places).
 
Good luck