1918.] The N.Z. Journal of Science and Technology. 
383 
The Factors influencing Gold-deposition in the Bendigo Goldfield, by 
F. L. Stillwell. Commonwealth of Australia , Advisory Council of Science 
and Industry Bulletin No. 4; 68 pp., 1917. 
This bulletin is in many respects one of the most valuable papers on the 
Bendigo Goldfield that has appeared. Following an introduction, which refers 
mainly to previous geological work, is a general outline of the main features 
of the field. The lode-containing rocks are sandstones and slates of Ordo¬ 
vician age. With these are thin bands of limestone which is of secondary 
origin, and which in many places has cone-in-cone structure. A large mass 
of granodiorite a few miles south of Bendigo, which is intrusive into 
the Ordovician sediments, is considered to be of Devonian age. The 
monchiquite dykes found in “ centre country ” are of Middle Tertiary 
age, but are distinct from the basaltic rocks of Victoria. A small area of 
volcanic agglomerate with pseudo-glacial characters occurs four miles 
south of Bendigo. The only other rocks of the district are Tertiary and 
Quaternary gravels. 
The auriferous quartz lodes, or c " reefs,” occur in the Ordovician sedi¬ 
ments characteristically along the anticlinal axes of folds. They are con¬ 
sidered to be of the same age as or slightly younger than the faults, which 
latter are of great importance in connection with the formation of the lodes. 
The nature of the ore-bodies is fully described, and the terms “ saddle 
reef,” “ trough reef,” “ leg reef,” “ fault reef,” and “ spur ” are explained. 
In addition to quartz, ankerite, siderite, calcite, chlorite, muscovite, and 
feldspar occur as gangue minerals. Gold, arsenopyrite, pyrite, pyrrhotite, 
zinc blende, galena, stibnite, chalcopyrite, and carbon are present in variable 
amount. The quartz of the saddles has been formed mainly by fissure¬ 
filling, but in the leg reefs the replacement of the country by quartz has 
been an important process. The quartz lodes are believed to be of Devonian 
age, and to have been formed by solutions given off by the granitic intrusions 
in the Ordovician rocks. Dr. Stillwell believes that the solutions were 
forcibly injected similarly to the injection of igneous rocks. The gold in the 
lodes is almost wholly primary, and ‘was deposited as the metal, and not 
as a sulphide or a telluride. The relation of the faulting to the reefs is 
discussed, and emphasis is placed on the genetic relationship between them. 
The gold shoots are described. The author points out that detailed study 
of each shoot is necessary, but that, unfortunately, in most cases the data 
are scanty. He rejects in whole or in part most of the theories advanced 
to account for the distribution of the gold, but views with some favour 
the hypothesis that the faults have influenced the deposition of the gold in 
the main lode-channels. Dr. Stillwell considers that replacement of 
country by quartz near fault-planes provides the best general explanation 
of the richly auriferous shoots. The gold was precipitated by the carbon 
of the country, this not being acted on by the silica-bearing solutions. 
“ The above explanation of a gold shoot is confined at present to the 
leg reefs, and cannot yet be discussed in regard to the spurry reefs and 
saddle reefs.” 
In view of the prominence given in recent years to the impoverishment 
that in general takes place in lodes in depth, it is surprising that 
Dr. Stillwell makes no mention of this subject. The mines of Bendigo 
are among the deepest gold-mines of the world, and a discussion by so 
keen an observer as Dr. Stillwell on the influence of depth on the nature 
and size of the quartz bodies could not have failed to be of the greatest 
interest both to the student and to the miner. J. H. 
