Calamine brass a mixture of the virtually indistinguishable zinc ores smithsonite and hemimorphite) as the zinc component of brass. The resulting brasses, produced by heating a mixture of copper and calamine to a high temperature for several hours (allowing zinc vapor to distill from the ores and permeate the metallic copper), contained a significant amount of slag material resulting from the non-zinc components of calamine. The use of ore rather than metallic zinc also made it difficult to accurately produce the desired final proportion of copper to zinc. This process is known as cementation. Calamine brass was produced using proportions of two-sevenths
Pitinga mine By 1990 the mine directly employed 2,000 people, and indirectly perhaps as many as 40,000. Trees were cleared, the river diverted and dams and ponds built before the alluvium deposits were processed. Bucketwheel excavator dredges extracted material rich in cassiterite, which was pumped through pipes to floating processing plants that separated the tin ore. The cassiterite is concentrated on site, then shipped to Mamoré Mineração e Metalurgia in the southern state of São Paulo for casting. Columbite ore is also mined, concentrated and processed on site for use in production of FeNbTa metallic alloy. Up to 1990 a total of