The
main and tributary channels of circulation of the golden parts are
here, I notice, associated with the fine-grained slate known as
gold-slate, which, although much altered in its texture by a soaking in
a hot solution of quartz and sulphides (giving it the appearance of
quartzite), is very much in evidence in the Stawell mines.
These
leg lines of formation must have originally been lines of compound
fracture, rather than lines of long, continuous, clean break, for
liquids carrying quartz, sulphides, silver, and gold, appear to have
saturated the whole rock-layers, and then to have commenced a further
concentrating process when the rock-fracturing period arrived.
I
noticed in the Magdala workings, where tributary currents of drainage
had been subject to partial stagnation long enough to allow of the
deposition of a long " block" (they call these " makes " in other
mining centres), there are extensive formations of milky-white quartz,
of no value as far as gold is concerned.
These
great and small, rich and poor, occurrences, with the country on their
foot-wall side and a black slate known as " magpie " (on account of the
thousand and one little fractures in it filled with white quartz) on
their hanging-wall side, together with dyke material locally known as
elvan, constitute the lode masses in Stawell, and it is found
frequently that a point in the "magpie" part of the lode has been
chosen for the deposition of gold. On looking for evidence concerning
circulating passages and their obstructions here, I found in all
instances that the " magpie " situation of gold is in close-fractured
slate that impeded circulation along a line of passage, in a, wide part
of which quartz had been deposited, a consequent deposition of minerals
forming "magpie" slate and creating a situation in the latter for gold.
This refers to the leg formations known as verticals. There is an
irregular contorted kind of lamination (book-like layers) throughout
the whole of the formations, much after the same pattern as in the Lord
Nelson mine at St. Arnaud, and many other mines of this State.
All evidences available for my inspection bear out the idea
(1) that obstruction to circulation is the main factor in bringing
about deposition of minerals in payable form ; (2) that the nature of
the cracking a field has been subject to, had all to do in arranging
the relative positions of these points to each other ; and (3) that the
angle of the floor of the favoured position to the vertical, or
direction of gravity, dominates whether or not the gold is deposited in
nuggety or comparatively fine particles. Of course, there are in some
fields formations of quartz in which gold is peppered in fine particles
throughout the quartz. By " fine," I do not mean gold particles too
minute to be saved by ordinary mechanical mill processes. The causes
which evidently brought about the solidification of these quartz and
sulphide masses may have governed the size of particles and their
distribution in the mass. I have noted more than one instance in my
experience where an apparently sudden cooling of quartz and sulphide
solutions had resulted in a deposition of gold and sulphide of iron in
fine particles bunched in streaks just over the most favoured position
of deposit—the gold in the most favoured position being in larger
particles and more solid.
The
Magdala works have been pushed ahead on full widths of this 300 feet
long by 30 feet wide " settling pit," as it were. From the 1,400-ft.
level up to the 900-ft. level, the lode was payable. As mentioned,
pillars of stone have been left in this stoped country as supports to
the roof of the loie, and these have to be taken out some day before
the stopes are filled. The town water service is laid through the
works; the air, owing to shaft connexions, is good; and, as with the
Lord Nelson mine at St. Arnaud, there
