ORES OF PLATINUM 69 
igneous origin. Platinum, however, is found in a great 
variety of rocks and usually in those that have undergone 
hydrothermal alterations and contain secondary sulphides. 
It is associated with serpentine, an altered ultra-basic rock in 
the Urals and British Columbia. In South America, in 
Columbia, where platinum was first discovered and which 
has been second only to Russia in output, it comes from 
gabbro along the Choco River and is found as nuggets inter- 
grown with chromite on the Condoto River. In New Zealand 
alluvial platinum has been derived from dunite, and in 
Spain from peridotite. It occurs in diorite in Walhalla, 
Victoria; in quartz-monzonite and pegmatite in Nevada; 
In pyroxene-syenite at Franklin, British Columbia; and in 
altered bands beside basic intrusions in Mexico. It is 
generally associated with chalcopyrite and pyrites as at 
Lydenburg, Sudbury, and Franklin, British Columbia, and 
with gold, silver, and copper ores as at Walhalla. It is in 
many places a constituent of quartz-veins, as in Nevada, 
the Waterberg Sandstone in the Transvaal, the Gympie 
goldfield in Queensland, and New Zealand. In Nevada, 
Near the Boss Mine, platinum was introduced with copper 
Minerals along fault planes, probably in Carboniferous times 
after intrusions of quartz-monzonite. It is frequently found 
In nuggets, which weigh up to 25 lb. in the Urals, and over 
3 Ib. in Columbia ; and nuggets are usually due to secondary 
toncentration. The introduction of platinum by solution 
hasbeen claimed by L. Hundeshagen (77. I.M.M., xiii, 1904, 
P. 550), for the ore at Sepongi in Sumatra, for an intrusion 
or granodiorite that produced wollastonite and garnet, was 
ollowed by the entrance of solutions carrying platinum, 
topper, and gold. 
, The age of the chief platinum occurrences is Upper Palexo- 
1c. The pre-Paleozoic coigns of gneiss and schist have 
Fie no platinum of commercial importance. The igneous 
the s of the Urals that contain platinum are post-Devonian ; 
2 ek Nevada are late Carboniferous or Permian. The 
a unk in the Waterburg Sandstone of the Transvaal is 
a arroo (i.e. at least post-Triassic). The most numerous 
north, occurrences are in western North America, in the 
Moy, ern Andes in Columbia and Equador, the Appalachian 
ntains of the eastern United States, the Hercynian folds