Page 53 - Introduction to Mineral Exploration

36 A.M. EVANS & C.J. MOON

Replacement body tion of the orebodies. The principal materials
of Fe ore 100 m produced from skarn deposits are iron, copper,
tungsten, graphite, zinc, lead, molybdenum,
tin, uranium, and talc.
Fault
Concordant orebodies

Sedimentary host rocks
lgneous intrusion
Shale
Sandstone
Concordant orebodies in sediments are very
Limestone
important producers of many different metals,
being particularly important for base metals
and iron, and are of course concordant with
FIG. 3.5 Skarn deposit at Iron Springs, Utah. (After the bedding. They may be an integral part of the
Gilluly et al. 1959.)
stratigraphical sequence, as is the case with
Phanerozoic ironstones – or they may be
the preferred and more popular term. The epigenetic infillings of pore spaces or replace-
orebodies are characterized by the develop- ment orebodies. Usually these orebodies show
ment of calc-silicate minerals such as diopside, a considerable development in two dimen-
wollastonite, andradite garnet, and actinolite. sions, i.e. parallel to the bedding and a limited
These deposits are extremely irregular in shape development perpendicular to it (Fig. 3.6), and
(Fig. 3.5); tongues of ore may project along any for this reason such deposits are referred to as
available planar structure – bedding, joints, stratiform. This term must not be confused
faults, etc., and the distribution within the with strata-bound, which refers to any type or
contact aureole is often apparently capricious. types of orebody, concordant or discordant,
Structural changes may cause abrupt termina- which are restricted to a particular part of the

SURFACE

UPPER
QUARTZITES

T
T

T
T

T
0 150 m

Sulfide ore Pyrrhotite Albitization
Quartzite beds T Tourmalinization Chloritization
Footwall
Footwall breccia Diorites
conglomerate
Granophyre
FIG. 3.6 Cross-section through the ore zone, Sullivan Mine, British Columbia. (After Sangster & Scott 1976.)