Bendigo, Victoria.

The most important auriferous areas of Victoria occur in long and comparatively narrow belts, striking, practically with the enclosing Lower and Upper Silurian rocks, northerly and southerly. Bendigo occupies one of these belts.

For detailed descriptions of this district, reference is made to the monograph of E. J. Dunn, published by the Victorian Mines Department at Melbourne, 1893, and to the papers of Mr. Rickard in Vols. XX. and XXII. of these Transactions.

The New Chum Railway Mine.—The first of the mines selected for this inquiry was the New Chum Railway Company's mine, one of the deepest on the New Chum reef, which is one of the three most productive anticlinal axes in Bendigo.^† On the 2498-foot level of this mine, a cross-cut extends 265 feet east from the main shaft, and at the end of it, a winze was sunk to a further depth of 360 feet; and on driving about 12 feet east at the bottom of this winze, the west leg of a saddle-reef was struck. At the time of my visit, January, 1895, this showed about 4 feet of laminated quartz, yielding 1.5 ounces of gold per ton, and was the deepest pay-ore exposed in Australia up to that time. (A later discovery has been reported from Lansell's "180" mine on the same anticlinal, at a depth more than 3000 feet.) Samples were taken along the above-mentioned cross-cut from the shaft to the winze (see a to q, Table page 4 I.). At 190 feet from the shaft, a slide or slight fault was crossed, from the sides of which three samples, two of slate (l, m) and one of sandstone (k) were taken. At the bottom of the winze, 2858 feet from the surface, three samples of slate (s, t, u) and one of sandstone (r) were taken close to the reef, to show the difference, if any, between the country-rock in close proximity to a reef and that further away. Table I. gives the results of the examination of the samples to determine their gold-contents per ton, and their percentage of sulphur and of carbon, and Diagram 1 shows them graphically.

The South St. Mungo Mine.—The second Bendigo mine selected for investigation was that of the South St. Mungo Co., situated on the New Chum line of reef, but presenting a modification of the saddle-reef type, in which the lode fills a more or less continuous fissure in "center-country," i.e., along an anticline such as is usually occupied by the saddle-reefs. The possible effect of this variation in lode-form and structure upon the distribution of gold in the reef and rock respectively, was the reason of choosing this mine for study. In this case the lode follows a nearly N.—S. anticline, and dips slightly E. It has been worked to 1180 feet depth, and carries an enormous quartz body, 20 to 60 feet wide, with a remarkably small percentage of sulphides (chiefly pyrite and blende, with traces of galena). At the 1180-foot level I saw in January, 1895, this immense mass of white, splintery quartz. On the 610-foot level a body of quartz 60 feet wide was worked throughout the whole length of the claim, and this level alone is said to have paid over £50,000 in dividends. The cross-cut at the 1180-foot level, which struck the reef 128 E. of the shaft, was sampled (see Table II. and Diagram 2). By reason of the steep dip of this lode, the cross-cuts from the shaft to it are comparatively short. But a prospecting cross-cut driven E. 302 feet at the 610-foot level gave an opportunity for getting samples further from the lode (see Table III.).

Tables I., II. and III. show a striking connection between the percentage of sulphur (as sulphides) and the contents of gold in any sample, especially from the slates; the sandstones, particularly at a distance from the reef, sometimes containing large crystals of non-auriferous pyrite. The sandstones generally carry much less sulphide than the slates, and the sulphides page 5 in sandstone are rarely, while those in the slates are usually, auriferous. (See analyses e, h, i and r in Table I. and the whole series in Table III.)

A marked inverse relation between auriferous contents and distance from the lode is observed. The zones of country-rock containing appreciable quantities of gold are confined to 50 or 60 feet on each side of the lode.

Samples from the vicinity of a slight fault, even at some distance from a main reef, contain much more gold and sulphides than the adjoining rocks, away from the fault.

Another remarkable fact which seems unaccountable is that the samples of slate from the New Chum Railway Co.'s mine (Table I.) show a striking increase in carbon as the reef is approached. Mr. L. A. Samuels, an experienced mine-manager in Bendigo, has assured me that this is a common phenomenon on the line of another reef in that district.

Finally, it is observable that the mine-samples (of 4.48 pounds) in which sulphides did not occur contained no gold or silver.