and COPPER DEPOSITS OF MOUNT- WRANGELL REGION. 147 
MENDENHALL 
AND 
SCHRADER 
flakes, sometimes intimately associated with chaleocite. The latter 
mineral occurs with the native copper and in minute crevices which 
seem to be later than the general alteration and silicification. 
NORTHERN DISTRICT. 
North of the volcanic pile of the Wrangell Mountains, in the valleys 
of the Copper, of the two forks of the Tanana River, called the 
Nabesna and the Chisana, and of the White River, native copper has 
been reported from time to time, and the reports have been substan- 
tiated by prospectors and others who have brought out nuggets of 
the metal. 
GEOLOGY. 
The geologic conditions under which the copper occurs in the 
northern district are different from those which prevail in the Chitina 
Basin. Although the Nicolai greenstone, which is the great copper 
reservoir for the southern field, is probabty present, it does not play 
the important part that it does south of the mountains. 
A great calcareous series, which is believed to be equivalent to the 
Chitistone limestone, is clearly recognized over a large area. It has 
been affected by complex structures in the northern as in the southern 
district, and after its deformation and erosion Mesozoic beds have 
been deposited unconformably upon its edges, and the still later lavas 
of Mount Wrangell have buried many of its outcrops. In these 
respects its history is similar to that of the equivalent beds to the 
south. The essential difference, however, is in its relation to the 
basic igneous rocks. Instead of being clearly deposited conformably 
upon the surfaces of earlier flows, it has been extensively cut by later 
intrusives, and the contacts with these diabases, which are altered in 
many cases to greenstones, seem to be the loci for the accumulation 
of native copper and other copper ores. One occurrence, of no 
economic importance, is known in an altered mass of diorite. 
OCCURRENCES OF COPPER ORE. 
The evidence at present available, although incomplete, is better 
than that upon which earlier judgments were based. It does not indi- 
cate that these northern occurrences have much commercial value. 
A brief description of some of them follows: 
Monte Cristo Creek and California Gulch are respectively western 
and eastern tributaries of the Nabesna River, which they join within 
3 or 4 miles of the foot of the glacier. A mass of altered diorite 
occurs in this region, and along the lines of fracture in this diorite 
there occur sporadically films and blotches of malachite, which is prob- 
ably derived from a little chalcopyrite contained in the altered rock. 
In the mountains just east of California Gulch fragments of low- 
w grade copper ore, consisting essentially of pyrrhotite and copper 
