Note, on the Formntion of Gold Ore. — ran Kraotz. 107 
moved from each other, and it is, on the other hand, altogether 
likely that it is this very class of rocks whose presence serves 
as the invariable associate and rni.soti iVetre of gold deposits. 
In Australia Howitt in particular has shown the intimate 
connection between the auriferous quartz veins of Swift's 
creek and certain dioryte eruptives.* At that locality the 
auriferous quartz veins occur at the contact of dioryte and 
schists, and Howitt explains their formation as a phenomenon 
accompanying the dioryte eruption. Similar conditions obtain 
in the newly discovered gold fields of Coolgardie, near Perth, 
as I am informed by Dr. Chas. Chewings. The gold-bearing 
formation is fissured by numerous eruptive rocks, among which 
porphyry and dioryte dykes predominate, and practical ex- 
-perjence lias shown that richness in gold depends upon proxi- 
mity to the eruptive masses. In the Urals, also, as I am told 
by Prof. Futterer, the presence of gold depends upon the 
occurrence of eruptive rocks and tectonic disturbances. 
We may perhaps look upon the auriferous character of 
rocks which are associated with dioryte as analogous to the 
formation of tin ore deposits near granite areas. f It is to be 
expected that similar lat^r acid eruptives will also be found 
to have been accompanied by auriferous solutions. In this 
category we may place the rocks of the andesyte and trachyte 
class of Dilln in Hungary and Guanaco in Chili. Here like- 
wise the gold occurs in silicified belts of the rock or in cracks 
filled with quartz, and usually associated with pyrite. Gold 
does not appear to be genetically related with rocks which are 
much more basic than those of the dioryte group; but alwa3's 
with those more acid. Thus we find it occasionally associated 
with quartz trachytes and dacites. 
Summarizing the above arguments we may find: Gold us- 
ually comes from the interior of the €»,rth in acid solutions in 
company with acjd eruptive rocks like dioryte. The form of 
the dissolved gold salt cannot be determined. In precipita- 
ting the gold from- its solutions the sulphids. pyrite particu- 
larly, and to a subordinate degree copper, arsenic, lead and 
*•' The diorites and granites of Swift's Creek and their contact-zooe 
with the auriferous deposits."' Melbourne, 1879. 
tRosenbusch, Mikrosk- Phvsiogr. 3d Ed. Vol. II, p. 258: Vogt, 
Zeit. f. prakt, Geo!. 1892, p. 479. 
