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194 THE DIAMOND
Bagagem
river one and a half miles to the west, are full of old excavations of
diamond workers. The soil near Agua Suja church is alluvial with
patches of ferruginous gravel. The basal strata are of mica-schist and
contain quartz, muscovite, altered tourmalines and almandine garnets.
The heaviest pan-residues from this rock are magnetite, ilmenite,
rutile, tourmaline, staurolite, and zircon. Large deposits are found in
hollows in the hills. An examination of the rear wall of an excavation
in one of these deposits, which illustrates their general character in
this neighborhood is given by L. F. Gonzaga de Campos, as follows:
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The
ferruginous clay, like the " red earth" of S. Paulo and the wet
diggings of Africa, leaves a residue on washing of ilmenite, magnetite,
apatite, an abundance of hydrated oxides of iron, and water-worn quartz
pebbles. The gorgulho contains fragments of quartz crystals, brown
iron, hydroxide pebbles, needle-emerald (tourmaline) and fragments of
rutile. Usually this carries few diamonds, but larger ones than the
more prolific upper parts of the deposits. The " Star of the South"
was found in a ferruginous clay above the gorgulho. The clay-schist "
secundina" usually overlays the diamondiferous beds. It is rather soft
and plastic but not easily disintegrated. Diamonds are
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