Sirius Minerals, the firm looking to develop a potash mine near York, has described new assay (test) results at the site as 'strong'.One of the holes being drilled showed "a consistent overall seam thickness compared to the "mother" hole with approximately 50m total polyhalite mineralisation."Other drilling is described as "progressing well".Chris Fraser, Managing Director and Chief Executive Officer of Sirius said: "These assay results of the third new hole of the York Potash drilling program have delivered yet another thick intersection of high-grade polyhalite in the Shelf Seam."He added: "These assays continue the strong results obtained from the drilling program, and combined with the results of the Detailed Scoping Study confirm the world-class nature of the York Potash Project."The market wasn't impressed however, Sirius's stock had dropped 2.3% by 12:00.BS