Granulometric characteristics of gold in ore deposits of the northern Baikal-Patom Highland (Russia)

The median size of gold particles decreases from 2.5-3.0 to 1.0-1.25 mm fro m the north to south in the Lena placer ore district in the Baikal-Patom hi ghland. The predominance of large gold particles is obvious in quartz vein deposits. More than 50% of the gold has sizes of less than 0.05 mm in sulfi de and sulfide-veinlet deposits, and thin-dispersed gold (TDG) is mainly en closed in pyrite and insoluble carbonaceous matter (ICM). The gold content in ICM is up to 8-10 g/t. During dispersion of carbonaceous ores and metaso matites the concentration of TDG in ICM increases twofold, and the concentr ation process is of an adsorption nature. The predominance of isolated part icles of native gold in quartz vein deposits is provided by a Limited numbe r of Au crystallization centers in the quartz. In the sulfide-veinet deposi ts, fine gold and TDG is confined to numerous crystallization centers in su lfides and ICM. The fraction of TDG during exogene abrasion of primary and placer gold increases after achievement of the critical 10 mu m size of its particles.