Page 49 - Introduction to Mineral Exploration

32 A.M. EVANS

Tin ores and of mercury in solid solution in the ten-
nantite, remained unknown for several years
At mines where separate concentrates of and the smelting of concentrates from this
cassiterite and copper–zinc–arsenic sulfides mine at a custom smelter in Belgium presum-
(often as a minor byproduct) are produced, ably produced a marked mercury anomaly over
cassiterite coated with stannite (Cu 2 FeSnS 4 ) a substantial part of western Europe. A mer-
will pass into the sulfide concentrate.
cury separation plant was then installed at
Gortdrum and a record production of 1334
Zinc loss flasks was reached in 1973.

Lead–zinc ore from a new orebody was tested
by being processed in a mill at a nearby mine. Sulfur in coal
Despite being apparently identical to the ore at Of the three sulfur types in coal (organic,
the mine, substantial zinc losses into the tail- sulfate, and sulfide) the sulfide is usually pres-
ings occurred. It was discovered with the use ent as pyrite and/or marcasite. If it is coarse-
of an electron probe microanalyzer that the grained then much can be removed during
siderite in the gangue carried 8–21% Zn in washing, but many coals, e.g. British ones, have
solid solution. such fine-grained pyrite that little can be done
to reduce the sulfur content. Such coals are no
longer easily marketable in this time of con-
Mercury impurity
cern about acid rain.
In 1976 Noranda Mines Ltd cut its copper–
gold–silver concentrate purchases from Con-
solidated Rambler Mines Ltd, Newfoundland 2.3 FURTHER READING
by nearly 50% because of “relatively high
impurities” (Anon 1977). The major impurity General techniques in applied mineralogy are
was mercury. An electron probe investigation well discussed in Jones’ Applied Mineralogy –
showed that this occurred in solid solution A Quantitative Approach (1987). Hutchison’s
(1–2%) in the minor sphalerite in the ore. By Laboratory Handbook of Petrographic Tech-
depressing the zinc in the flotation circuit the niques (1974) is also an invaluable book, as is
mercury content of the concentrate was virtu- Zussman’s (1977) Physical Methods in Deter-
ally eliminated. minative Mineralogy. Those working on pol-
Probably the first mine to recover mercury ished sections should turn to Ore Microscopy
from copper concentrate was Rudnany in and Ore Petrography by Craig and Vaughan
Czechoslovakia where it occurs in tetrahedrite. (1994) and the online atlas of Ixer and Duller
At the former Gortdrum Mine in Ireland the (1998). References to techniques not covered by
presence of cinnabar in the copper–silver ore, these books are given in the text of this chapter.