Thanks Jeff, I was thinking pyrite. I didn’t find this one. A mate of mine found it in Pine Creek, NT in a dry creek bed. He’s not a prospector and was just walking with his family and spotted it. I think it broke his heart when I told him i thought it was pyrite.Without the benefit of any standard mineral tests and just by the look, I’ll have a go with a sulphide mineral such as pyrite (iron);or chalcopyrite (copper iron). If under a high power hand lens the crystals are cubic then it would most likely be pyrite. A hot oxidizing flame test against it should show green if it was chalcopyrite.
These ores can also be auriferous.
If it is from an existing mine dump just look up mining records to see what was being mined.
If you have discovered an unknown seam of the material, it may be worth your while to take it to your states museum for identification. You don’t have to disclose the exact place you found it If you feel you may be onto something.