The Nerrena or Little Bendigo Gold-field is situated immediately north-east of, and within
three miles of, the city of Ballarat. It occupies an area of country
about a mile square. Mining commenced on it in the "early fifties," and
the diggers of the time met with very rich and extensive deposits of
auriferous quartz gravels in the different gullies, and on the ranges
of the place. More than 200.000 ozs. of gold are said to have been
mined from these deposits, and the locality gen-rally was considered to
be very rich, if not the richest in the Ballarat district. As, with
the rest of the district, its rocks are composed of fine pained slates
and sandstones, classed as ordovician (lower Silurian) which have been
forced from a horizontal position and corrugated.
This
corrugation has the lines of its arches and troughs running almost due
north and south (about 10 degrees west of north). In parts of the field
the arches lean to the west, in others to the east. The corrugating of
these hitherto almost flat layers of rock fractmred them very much. By
some means or other they appear to have had various metallic substances
(associated with sulphur principally, and known as sulphides)
distributed through them. As soon as they became cool enough to be
breakable, these minerals and quartz were brought in solution and
deposited in the cracks. In this manner all the lodes in this State
appear to have been formed. Most of the fracture systems in the gold
country of the State is the result of a more or less twist application
of force to the rock masses. Accordingly all, more or less, have the
style of fracturing to be noted in a pine board, when it is twisted.
The Ballarat Gold-field shows the most pronounced form of this class of
compound fracturing on a large scale, and the Bendigo Gold-field the
least. Here, in Little Bendigo, which is really part of Ballarat East,
we have much compound fracturing, and, as a consequence, the lodes
are, for the most part, composed of bulges of quartz running nearly
north and south, and have wing- and fin-like veins of quartz going out
from one of their sides or the other. Each system, which includes as
many as five lines, has' been formed in the troughs between the arches
of the corrugation,. They occur at intervals of about a quarter of a
mile, in parallel lines.
As
far back as the year 1856, at a time when alluvial mining was in full
swing, quartz mining was commenced on the field. Numerous outcrops of
rich occurrences, belonging to the different quartz lodes, were met
with, and followed down to their terminals for returns as high as 5
ozs., and as low as 2 dwts. per ton. In most instances, as on other
fields, these occurrences, although but higher members in each line of
a series of such occurrences, were looked upon as the " all-in-all " of
the lode, and mining ceased as their terminations were teached. The
general application of the twisting movement, in bringing about the
pine-board sort of fracture, was not recognised. The popular idea
concerning lodes favoured the notion that a continuous, almost
vertical, and very rich lode was to be met with in the field somewhere.
"All this rich alluvial gold must have been thrown out of this kind of
lode, or lodes, or else, where did it come from ?" Few people
recognised that the lowering of the surface of the country was the wear
of ages. Experience, however, leads us to assume that most of, if not
all. the alluvial gold met with in the gold-fields of this State, has
been derived from the worn-away extents of quartz lodes, and that its
coarse and nuggety nature is due to the dip of the lode-receiving
crack, provided that the lode receptacle is associated with drains
from gold-slate. I sav gold-slate, because, although gold is at times
found "in quartz veins permeating sandstone, the largest portion of the
total yield of gold in the State, about £300,000,000,
has been found associated with a fine-grained slate. This slate is full
of drains, that is. lines of more or less vertical channels. (See
Plates III. and IV.) They occur between the slate and the sandstone,
and between the leaves of slate. The more defined channels of this
description are known as "indicators."
[Report sent in 1st Februarv, 1904.]
