AT a previous meeting of the Broken Hill Branch of the Institute the writer reported the occurrence of two minerals in the sulphide zone of Block 14 Mine, both of them new to Broken Hill. They were wolfram and scheelite. The former-wolframa tungstate of iron and mangenese gave on assay 42 % tungstic acid. The latter-scheelite-a tungstate of lime gave 35 % 'tungstic acid. Both these samples contained zinc and lead sulphides, and clean specimens of wolfram gave 64 % W03 ; scheelite gave 70 % W03. An estimation of the lead in these samples revealed the fact that the presence of tungsten in the ore seriously interfered with the ammonium-molybdate assay for lead, giving low results according to the amount of tungsten present in the ore. The sample under review, when. assayed under ordinary conditions gave a negative value for lead, but on removal of the tungsten shewed 9.8 % Pb. The reason for this interference is shewn on an examination of the reactions which occur in the assay