40 GRAVEL AND PLACER MINING IN ALASKA. [bull. 263. 
per cent lower. In all parts of Alaska drill holes should be not less 
than 100 feet apart, on account of the unequal distribution of the gold. 
Geologic conditions at Oroville, or in other dredging fields of flood- 
plain character, are radically different. There the ratio of holes is 1 
to an acre or 1 to 5 acres. 
Shallow bench gravels can occasionally be prospected by diverting 
a high stream or water from a ditch in a direction transverse to the 
gold-bearing channel. The water will ground sluice a trench to bed 
rock, thus crosscutting the ground. Such prospecting is done in the 
Fortymile district, and an example of it was seen on Gold Bottom 
Creek, in the Council district of Seward Peninsula. 
Bench gravels covered by heavy overburden are usually prospected 
by drifts. Drifts require timbering and are more expensive than 
shafts, but give a more satisfactory test of the ground. In rich pay 
streaks the running of prospect drifts often more than pays the cost. 
Owners of claims sometimes get their ground partly prospected by 
letting out the right to drift to two or more men, who pay a royalty 
on the gold they take out. In the Nizina district a 20 per cent royalty 
is charged on prospect work. 
When ground is prospected by shafts the distance between the shafts 
varies, although the variation is not so great as when the prospecting 
is none by drill holes. The practice in Alaska varies according to the 
work, the resources of the owner, and the depth of the ground. Where 
the gold has not traveled far and in consequence the values are spotted, 
shafts should be sunk 30 to 50 feet apart, but such close work is never 
done. Twenty shafts to a 20-acre claim are common. Shallow ground, 
6 to 18 feet deep, can be well and cheaply prospected in the winter 
months. Deep ground, as in the Fairbanks field, is expensive to pros- 
pect, and the prospect shafts do not average four to a claim. The 
cost of sinking shafts in the various camps is given below. 
Twenty shafts, 3^ by 6 feet and 12 feet in depth, timbered in thawed 
ground, or untimbered in frozen ground, cost from $1,200 to $2,000. 
If steam thawing is employed, the outfit, consisting of a 6-horsepower 
boiler, three or four steam points, steam hose, and pipe connections, 
will cost from $300 to $500. Hot stones, hot water, and wood fires 
are more generally employed in prospecting ground in the remote 
camps. The hardest ground to prospect is that which is partly frozen. 
For example, in the Birch Creek and Fortymile districts shafts 15 
to 25 feet in depth penetrate frozen ground and require no timbering 
until they are within 5 feet of bed rock, when a rush of water is fre- 
quently encountered. The entire labor of sinking the shaft through 
the overlying barren material may be lost, as the shaft may^ be flooded 
before pay gravel is reached. 
