144 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1902. [bull. 213. 
but more rarely, in the limestone just above it, and occasionally in 
fissures which cross it. 
The ore bodies have assumed various forms, and for convenience 
of discussion these forms have been divided into two general classes, 
vein deposits and bunch deposits. 
The vein deposits are so defined as to include all tabular ore masses, 
whether in true fissures or along joint or fault planes or shear zones. 
The ores may be found only in shoots within the planes which have 
controlled their form, but are characteristically of indefinite extent 
in one or two directions. 
The "bunch" deposits, on the other hand, are irregularly bounded 
masses of ore, from a few inches to a few feet in diameter, which 
usually are not obviously related to fractures or fissures or joint 
planes, but in form are much like basic segregations in igneous 
rocks — i. e., they generally have indefinite limits, grading from 
masses of practically pure ore at the center through leaner and leaner 
phases, into the entirely unmineralized inclosing country rock. 
These "bunches" are so numerous in certain parts of the field within 
the upper part of the greenstone that prospectors who have opened a 
number of them, 400 or 500 feet below the base of the limestone, have 
been led to conclude that a ledge of ore parallels the contact at this 
horizon. 
MIXES AND CLAIMS. 
In order to give an idea of the different types of deposits and the 
conditions of development, some of the best-known occurrences will 
now be described. 
Nicolai mine. — The Nicolai mine is located near the eastern part of 
the Chitina copper district, on Nicolai Creek, a few miles west of the 
Nizina River. The vein, a fissure with definite walls, is in the green- 
stone not more than 50 feet below the base of the limestone. It 
trends about N. 50° E. and dips 75° SE., and a displacement of not 
more than 50 feet has taken place along it. The main fissure, which 
may be traced for several thousand feet, although it shows no 
ore except near the place of discovery, is paralleled at distances of 
90 and 140 feet by two other fissures, which also contain copper min- 
erals. In the vicinity of a shaft which has been sunk in the process 
of development, the vein has a width of from 8 to 12 feet and is about 
equally divided by a horse of greenstone 3 or 4 feet across. The ore 
on either side of this horse is practically pure bornite with only a 
small amount of quartz associated in an irregular way. Locally there 
is a band of chalcopyrite lying next the hanging wall. 
In 1900, when the shaft had been sunk to a depth of 30 feet, ore 
from 2 to 4 feet in thickness was exposed throughout this depth. 
Bonanza claim. — This claim is located upon a high ridge between 
Kennicott Glacier and McCarthy Creek, and is about 8 miles west of 
the Nicolai mine. This vein also is a fissure, which cuts across the 
contact between the greenstone and the limestone, although for some 
