ORES OF LEAD, ZINC, AND SILVER 99
N.N.E. and the other to W.N.W.; they contain quartz
and carbonates, galena, and silver ore; (2) the Noble-
Quartz veins are rich in silver, especially argentite (Ag,S),
and trend some to N.N.E. and others to E.N.E.; (3) the
Pyritic-Lead veins contain quartz, galena and blende, and
some copper ores; they generally trend to N.N.E. or N.E.
The younger lodes include the Barytic-Lead veins, and were
formed in fissures at a lower temperature than the others;
they trend W.N.W. ; their constituents, galena, blende,
Pyrite, quartz, fluorite, and barite, show extreme crustifi-
‘ation, as in the often-quoted Three Princes Lode. The
deep-seated origin of the Freiberg lodes is indicated by the
ores of uranium and radium. The lodes were formed during
the earth-movements near the end of the Paleozoic. The
Occurrence of these four different groups of lodes in the same
tountry rock is an argument against the formation of ores by
fateral secretion,
The lead and zinc mines of Clausthal in the Harz Mountains
of Centra] Germany were worked even earlier than those of
Freiberg. The field is in a fractured belt of Devonian and
Lower Carboniferous rocks broken by Hercynian faults.
Most of the lodes trend to W.N.W., and are connected by
cross-lodes at regular angles, so that the field is cut by inter-
secting fissures into rhomboids. The richest ore-bodies are
Where fissures intersect. The lodes have often a sharp foot-
wall, but may pass gradually into the country on the hanging
wall, They have been worked to the depth of 3000 feet.
The British lead mines 2 include various types of primary
lodes. They are mostly in the Ordovician and Carboni-
ferous rocks. The lodes in the Carboniferous Limestone
of the Pennine Range, at intervals from Derbyshire to
Northumberland, occur along steeply inclined faults, whence
horizonta] « flats” pass off along the more permeable beds.
The flats are replacement bodies, and if connected with the
fissures their ores are rich in zinc, which in the lodes increases
‘Ndepth, A lode is often rich in limestone, and becomes thin
Ad poor in shale or igneous rock, and remakes if it re-enter
! They are regarded as Miocene by von Koenen, Jahrb. preuss, geol.
Landesanst,, xiv, 1804, pp. 79, 81. The Hercynian age is supported by
EB, Hornung, Z.d.g.G., vii, 1903, p. 303.
G.S. Gr, Bris. Spec. Rep. Min. Res., Nos. 1%, 19-23, 26-6.
