Page 302 - Handbook of Gold Exploration and Evaluation

266 Handbook of gold exploration and evaluation

Drowned strandline deposits have been identified offshore at various dis-
tances beyond the present shoreline of Seward Bay and nearly to the centre of
Chirikov Basin from the Siberian Chukotka Peninsular. The Nome drowned
strandline deposits are located at depths below sea level of about 11, 21 and 25
metres that probably represented stillstands at the time of their formation. A
general geological map of the Nome near-shore area shows the distribution of
gold in the surface sediments (Fig. 4.40).
The `modern' beaches were worked at various levels for distances up to 9 km
inland from the present shoreline during the gold rush days but became
uneconomic early in the twentieth century. The raised beaches were mined until
about 1963. An unsuccessful attempt was made to dredge shelf deposits in the
late 1980s, but after a promising start the operation was brought to a halt by
machinery failure. Recovered grades were lower than expected and although
losses were probably high, there appeared to be little hope of improvement. The
dredger (BIMA) used in this operation was ferried to Alaskan waters after being
shut down at the close of an Indonesian tin-dredging operation in 1985.
The widespread disposition of the Nome placers appears to have been due to
the role of glaciers in the dispersal and redistribution of low-grade auriferous
tills derived from provenances in mountains some distance north of Nome. Both
source rocks and segments of older placers in the coastal plain were sequentially
eroded and telescoped by the glaciers. When deposited on beaches, the weakly
auriferous tills were successively upgraded by wave action during each interval
of stillstand following uplift. Marginal gold accumulations are still worked
sporadically on Nome beaches when cliffs of glacial debris are eroded by violent
storms.