78 ALASKAN MINERAL RESOURCES IN 1904. [bull. 259. 
than the hrown, is composed of slate intricately intruded hy small dikes 
of very fine-grained diorite, the whole being impregnated with sul- 
phides in the same way as the ordinary ore. 
The value of the material mined varies from $1 to $5 and even $10 
or more per ton, though in the course of development a great deal of 
less valuable rock is extracted, and in working the open pits large 
amounts of worthless slate must be moved, much of which goes with 
the ore to the stamps. In general the average value of the rock has 
been a few cents over $2 for the past two or three years. From 60 to 
75 per cent of the gold is free milling, and the concentrates, which the 
mill records show to be about 2 per cent of the material treated, assay 
from $30 to $50 per ton. 
SHAPE OF THE OKE BODIES. 
The impregnation of the dikes in which the ore occurs is, for the 
most part, so general, and the presence of at least small amounts of 
gold is so constant, that it is impossible to recognize any well-defined 
masses which may property be distinguished as ore shoots. Though 
the values are by no means uniformly distributed, from the assay plan 
they do not appear to occur in any regular way, and indeed the dis- 
tinction between ore and rock too lean to pay for extraction is often 
the matter of only a few cents. The actual differences in gold tenor | 
of several contiguous samples taken from the ore are usually much 
greater than the difference between the average of any considerable 
block of ore and the contents of intervening masses of poor rock. In 
several places mere joints or seams may be noted separating the ore 
and the poor material, and it frequently happens that blocks of the 
latter, which show assays from a trace up to $1, are entirely surrounded 
by ore averaging $2 or more. Structural limitations, such as joints, 
however, are difficult of observation, because the sides of the drifts 
are everywhere covered with dust. 
In general, the best ore is that which contains the greatest number 
of quartz and calcite veinlets, and though their absence is not an infal- 
lible indication of valueless material, it seems that the irregular distri- 
bution of the gold has resulted mainly from original differences in the 
amount of crushing and the consequent varying permeability of the 
rock. Where the metasomatic replacement of the diorite by secondary 
albite is absent, the sulphides usually replace such minerals as horn-' 
blende or mica, and it is suspected that in these cases the gold content 
is ordinarily low. 
In planning the position of stopes the assay charts often enable the 
miners to locate the pillars in relatively poor material, but as a rulei 
the low-grade rock is not found to persist for the whole distance 
between two mine levels. The largest masses, which have been left 
because of their leanness, are on the foot-wall side of the south dike 
