ORES OF LEAD, ZINC, AND SILVER 10;
been worked to a depth of 1800 feet. It was capped by an
Iron gossan which stood as a ridge above the plains, and was
"pegged ” out as a tin lode, A shaft was sunk and instead
of tin found rich deposits of silver. The arid nature of the
Country had led to secondary enrichments so large that
their yield caused a serious fall in the price of silver. The
UPper part of the lode was famous for its beautiful minerals,
and its many new species of iodides, bromides, and chlorides,
which survived owing to the arid climate. The treatment
of the ore was troublesome, and led to the invention of the
flotation process to separate the rhodonite and blende,
Which are of the same specific gravity.
The lode is in pre-Pal®ozoic gneiss and schists, which
contain sillimanite and abundant garnets that are earlier
than the ores, A bulge on the side of the lode and some
Secondary arches of quartz led to its description as a
saddle-lode (E. F. Pittman, 1892; J. B. Jacquet, Mem.
GCSNSW. No. 5, 1804, and Beck, Rec. G.S.N.S.W., vii,
1900, p. 27). The footwall has vast slicken-sided surfaces,
and the author in 1904 (Melbourne Argus, and Science Pro-
87€sS, 1906, p. 131) explained the formation as a fault lode
enlarged by metasomatic action at the shallow depth in-
dicated by the abundant fluorite. The lode is a steeply
inclined sheet which tapers downwards. This view has been
demonstrated in the monograph on the field by C. W. Andrews
(Mem, GSNSW., Geol., No. 8, 1922), who has shown that
the silicates in the lode were formed in connection with the
faulting,
SECTION B. SecoNDARY ORES
(¢) Disseminatep Orgs or Mississippi—The Mississippi
valley (Fig. 34) contains important lead and zine ores in
Paleozoic limestones free from igneous rocks. The ores have
been the subject of long controversy as to whether they were
formed by ascending or descending solutions. The field
of Joplin “in S.W. Missouri is in Carboniferous limestone.
The fields ip S.E. Missouri consist of pre-Pal®ozoic rocks
Covered by Tepresentatives of all the systems from the
Cambrian to Upper Carboniferous. Its lead and zinc ores
Are mainly in Cambrian rocks, which include in ascending
order, the Lamotte Sandstone, the Bonneterre Dolomite,
