“Flecks of gold” is the usual phrase. One wouldn’t get excited about a single fleck, though.
[A]nd it is from this region that rumors thicken of the discovery of gold--not gold as it exists in masses, or imbedded [sic] in the primeval rock, but merely little flecks of gold, from the size of flax seed down to all manner of small gunpowder grains...
(Shelby County Herald (Shelbyville, MO), 13th Oct 1875, pg.1)
By a casual look ... can be seen flying particles of dust similar to flecks of gold...
(Champaign County Gazette (Champaign, IL), 29th May 1872)
But prospectors and assayers didn't talk much about gold in those terms; they talked about it more like sugar, as specific quantities and weights of nuggets or dust.
[A] traveler can get off his horse in the bed of any mountain stream, where the hills on either side are of gravelly red clay, and the slate creeps out in the bed of the gully, and there, in an hour's washing, he is sure to get some gold, sometimes a vial, sometimes two, three, or ten dollars [sic] worth. But the gold is scattered in all the hills of clayey and slatey formation...
(New Orleans Crescent (New Orleans, LA), 1st Jan 1849, pg.4)
I assayed about sixty ounces of the said gold, deposited in the form of dust, by T A Minard, and when melted and assayed, the total proved to be 895 [thousandths purity].
(Baltimore Sun (Baltimore, MD), 1st Jan 1849, pg.4)