The Nome nugget., 1920-02-14
GRAVEL THAWInG BY
 COLD WATER PROCESS

Recent successful demonstrations of the utility of the cold water process Of thawing frozen gravels for mining nurposes has led to an investigation by the T.. $. Geological survey, the results of which are embodied In a report of that department showing the successful demonstrations of 1918 and cmbodyng the best information avail able regarding the methods Of opera tion and the various problems involv- ed Following is a digest of the state ment. The thawing of auriferous prayels by cold water instead of steam or hot water is of the greatest import ance to the Alaska gold industry and may bring about complete revolu- tion of thawing methods. owing to It's greatly lessened cost. The report says:
 The use of cold water-that is water at the normal summer tempera- ture of ponds, ditches and creeks-in thawing perpetually frozen muck and gravel is recent development that promises to be of value to the placer miners of Alaska. The idea Is per- haps not entirely new. but its appli- cation to mining was not successfully ,...,.,..,,+o tod ,,ptil tho sea son of 1918, The method is far from being estab- lished. and much experimental work remains to be done before it's real value and limitations are known. It promises to be an economic means of thawing ground for dredging and open-cut mining. The available data on the subject as given below are db- stracted from a report now in course of publication by the United states Geological Survey. Department of the Interior.
 Experiments were made during the season of 1917 for the Alaska Mines Corporation. near Nome, for the pur- pose of determining the most efficient and economical means of thawing the deep Nome gravels for dredging. Su- perheated steam at a temperature oi 600 degress Fahrenheit. steam ,at boiler = -.->.<r1-cs .2ot T~-s~ g. F" .s 1SO degrees Fahrenheit. and water at steam temperature of 52 degress Fah- ienheit. were used in the experiments.
 In the experiments in which steam and hot water were used three holes were drilled to bedrock at the points of an equilateral triangle 12 feet apart, and at point intermediate between them a test hole was drilled. which was cased and kept open to determine when the ground had thawed to the center. Shafts were sunk in the thawed ground, and drifts were run to the limits of the thawed area. In the tests in which hot water and steam at boiler temperature were used the thawed areas tended to come downward. leaving horses of unthaw- ed ground on bedrock. Superheated steam at 1000 degrees Fahrenheit thawed q mass of gravel 66 feet deep. 32 feet in diameter at the bottom, and 27 feet in diameter at the top. The thawed area was greatest on bedrock and where q clay stratum was encoun- tered the hole did not pinch.
 Two holes were thawed by the cold-water method. both single holes without tlfe test holes used in the foregoing experiments. One hole was 43la feet, and the other 50 feet deep. Both were 6-inch holes drilled to bed . rock with an Empire drill. A 2-inch pipe was inserted to bedrock. and T small gas engine, developing not moro than 30 pounds pressure, was used u force water down the pipe. The water was allowed to run from the bottom of the. pipe and flow over the surface, the circulating water thawins the ice out of the muck and gravel. As no test holes were used it was not possible to tell how rapidly the thaw- ing progressed until the ground began to slough in at the surface. This re- quired from five to six days. Tie shrinkage in the thawed ground was about one third, which represents the volume of ice present in the muck and gravel. The temperature of the water issuing from the hole was not taken. A shaft sunk in the thawed ground showed the holes to have passed thru a stratum of clay. The area thawed was in cross section like an hour glass, having width of g feet on bedrock, pinching to feet at the clay stratum,
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