I
noticed similar effects in the Ballarat East field, but there the
application of the twist forces being different to those that operated
here, the deviation of the
line
of each fracture from the trough is to the east. (See Fig. 3). It is
interesting to note in this connexion, that in all systems of fracture
(now known as lode systems) the pattern of the general structure is
reproduced in detail. It could hardly be otherwise, since the detail
and general structure are both due to one and the same application of
force.
After
the corrugation of the Maldon field and the formation of its lode
lines, many breaks took place in the lines of arches and troughs. These
fractures appear to have been occasioned by a thrust from the north
resisted by unseen abut-ments below the surface south of the field.
This effect is to be seen in the form of breaks across the country.
They are known as cross-courses. The main lines of fracture, known as
lode lines, have been widened considerably in places by this movement.
Areas of compound fracture have also been widened, and a general zigzag
irregularity has been given to the lode systems and their minor parts.
The centre of this disturbance was somewhere in the region of the
present Eaglehawk Consolidated mine, and it extended north to the Union
Company's area; thence north-east. South, it extended to the South
German Extended Company's area; thence south-west. Associated with
these cross breaks in the country there have been hundreds of feet of
displacement to the rocks and their lodes. Another effect of this
movement was that in widening areas of compound fracture it created
many extra receptacles for the drainage from the gold-slate. In other
words, it tended to distribute the gold, rather than to concentrate it.
Thus, great quantities of patchy, low-grade ore, from which the richer
parts have in some instances been mined, remain to be worked.
The
general conditions which govern the deposition of gold in all our
fields, may be observed here. The nature of the fracturing of the rock
layers has permitted the creation of many receptacles for the storage
of gold, and I found; in all instances that, in some form or other,
partial obstruction to the drainage downward was essential to the
formation of rich situations. The alternate layers of slate and
sandstone seldom exceed 5 feet in width. The average width appears to
be about 2 feet. Some widths of slate have been permeated with
sulphides, more than have others. I noticed in more than one mine the
presence of that slate and sandstone so noticeable in all the
gold-fields off the State, in which are small spots distributed as
caraway seeds appear in a cake. These spots represent specks of
sulphide (principally of iron) which have been partly decomposed
(oxidised, that is, rusted), and thus give the rock a spotted
appearance. The descending water has travelled between the slate and
sandstone formations more freely than in the slate itself. Here, from
an inch to say J- of an inch in width, is a defined passage? in which
"mundic" (sulphide of iron) has been deposited in cubes and ins
