Systematic mineralogy - Mineralogy for Petrologists - page 166

frequently contains (sometimes submicroscopic) inclusions of chalcopyrite
which is a result of the replacement of zinc by copper in the lattice. Sphaler-
ite show various habits (in German sphalerite is blende and means deceiving
or misleading) both at the macroscopic and microscopic scale, depending on
its chemical composition (especially its content of iron, cadmium and man-
ganese) and its more or less development of crystals: large limpid crystals,
zoned concretions, microcrystalline and compact, transparent (“honey” or
“ruby sphalerite”) to almost opaque sphalerites.
Sphalerite is a hydrothermal mineral of medium to low temperature. It
is most often associated with pyrite, pyrrhotite, galena, chalcopyrite, some-
times sulfosalts, and in some deposits, barite and/or fluorite. It is mined in
many ore types: massive sulphides, skarns (especially molybdenum skarns),
veins associated with Porphyry Copper, meso-to epithermal veins, strati-
form deposits of the Mississippi Valley type (where it is most abundant in
carbonate environment that in clastic ones).

3.7.4 Scheelite
CaWO 4 and wolframite (Fe, Mn)WO 4 are the major ores of tungsten. There
is a continuous solid solution between scheelite and powellite MoWO 4 .
Scheelite is a mineral of the skarns associated with granodiorites and
monzodiorites. It appears at the main stage of skarn formation where it is
accompanied by numerous calcic minerals (described in the chapter 3-4). It
occurs in both hedenbergite skarns in the andradite skarn. It also appears in
the late hydrothermal stages of skarns where it is associated with sulphides:
arsenopyrite, pyrrhotite, etc. Scheelite also occurs in pegmatites and hydro-
thermal veins with wolframite ( sulphides). Sometimes wolframite

and scheelite are in reactional association, scheelite replacing wolframite or
the reverse.

+ quartz +

3.7.5 Cassiterite
SnO 2 is the main ore of tin. Iron (ferrous and ferric) can substitute to tin.
Cassiterite also contains tantalum and niobium and lesser amounts Mn, Ti
and Sc.
Primary deposits of cassiterite are associated with granites ( s. s .), leu-
cogranites and alkali-feldspar-granite. It may appear at the magmatic stage
and tardi-magmatic stage (pegmatites with cassiterite, wolframite, topaz,
beryl, etc.), but its main deposits are rather associated with the hydrother-
mal stage:

￿ greisens with lepidolite/muscovite, topaz, tourmaline, wolframite,
scheelite, molybdenite, arsenopyrite, Bi-Nb-Ta;