Abstract A physically realistic exposure model for expressing the exposure of “disseminated inclusive” mineral grains from a binary petrologic system has been applied to gold ore leaching operations. The relationship between gold exposed ratio ( F E), gold grain size ( d), ore particle size ( D), and grain boundary fracturing factor ( P), is expressed as: f E (K) = P K 3−(K−2) 3 K 3 +(1−P) K 3−(K−1) 3 K 3 K= D d This equation facilitates calculation of the grain size of gold particles, which is difficult to obtain by direct measurement, as in the extraction of flour gold disseminated in sulfide or quartzite matrix. Thus, the economic benefit may be given by optimizing the grinding operation for gold liberation relative to gold recovery. The grain size of gold particles in the Chinkuashih gold mine located in Keelung, Taiwan was determined as 0.6–2.9 μm, 0.4–2 μ and approximately 10 μm for the Penshan, Hsumei and Buffalo districts, respectively. Furthermore, this model was also demonstrated to be suitable for gold samples of gold mine operations from other parts of the world.