need help identifying a rock!

[george barakat]

i dug up a rock from a depth of 1 meter approx. the rock is covered with a smooth brownish coating and its inside is extremely yellow. i ran my gold detector over it , and it givr me a positivr sign for the presence og gold!! this is very surprising to me . can anoyne explain what type of rock is this? and how come am i geeting a sign for the presecse of gold from it?
below is a google docs link to pictures of the rock after crushing it into small chuncks.
https://drive.google.com/open?id=0B4vb9x0JJoIiaVpmV1hLSnpYa0k