CHAPTER II!

ORIGIN, FORM, AND DISTRIBUTION OF IRON ORES

Tron ore deposits form in many ways and assume various shapes, but
most deposits originate either as sediments or precipitates or else as direct
products of igneous action. A third important group of iron ore deposits
includes those which have been produced by the prolonged decay, under
special conditions, of great volumes of rock whose iron content is preserved,
whereas other constituents are largely carried away. The sediments and
precipitates tend to occur in beds, though in some cases only greatly modified
parts of the beds constitute the iron ore deposits. The sediments
and precipitates generally are associated with bedded strata and may
be of any geological age. The limonites or bog iron ores are a special
class of the precipitates and are deposited at the surface of the earth by
waters which leach iron from rocks that may be of igneous or sedimentary
origin. A special feature of the sediments and precipitates, that is, the
bedded ores, is that when they do occur within a geological formation
they tend to be a constant feature of the formation, although only locally
may they be rich enough in iron to constitute an ore.

The iron ores that have formed as direct products of igneous action
oceur, as hardly need be said, in regions where igneous products are
manifest, but not all regions so characterized are the sites of iron ore
deposits. The iron ores of this group in some cases occur in masses within
or adjacent to the parent rock of which they are only a special phase. In
other cases they form vein-like bodies or they occur as impregnations or
replacements somewhat younger than the associated igneous rock and
situated within it or some other neighbouring body of rock. Many of the
impregnations and replacements are irregular of form, but some preserve
the bedded structure of their host and thus simulate bedded deposits.

From the foregoing general remarks it is apparent that iron ores of
special types are likely to characterize considerable regions and that it is
to be expected that other extensive regions may be barren of such ores.
There is a very special connexion between the presence or absence of iron
ore and the general geological history of any given region. This general
condition is exemplified in the case of British Columbia and Yukon terri-
tory. The Rocky mountains, which define the greater part of the east
border of British Columbia, are formed of folded and faulted strata ranging
in age from Precambrian to Tertiary. Igneous rocks are rare and occur
mainly in only two limited areas. There is, therefore, reason to suppose
that iron ores of igneous origin will only rarely, if ever, be found in the

Rocky mountains. In the extreme southwest, adjacent to Columbia River
valley, on Bull river and Sand creek (lo ality 42, Figure 2), limited deposits
of hematite have been found. On Bull river, the hematite is associated
with a dark, basic dyke; on Sand creck, it occurs in what seems like a thin
hed with which are associated masses of vein quartz. These two deposits
possibly are igneous products. They are the only iron ore occurrences as

1By G. A. Young,