The gold item was 0.4 centimetres in diameter and weighed 0.6 grams, senior official Arnat Bamrungwong said yesterday.
He gave no details on the beads.
The dig would take 20 days and would be extended if the work was not completed by then, he said.
The department had reached an agreement with the owner of the 3.5-rai field, Wi Thabsaeng, to allow the area to be explored by three of its offices.
The deal reportedly included the promise to plant palm trees on the land and restore it to its original condition, after the field was completely dug up by locals hoping to get rich.
A team of 11 surveyors and archaeologists sifted a 10-metre square area.
The depth would be extended layer by layer in 20cm steps.
A huge crowd gathered at the pit to look on.