A suite of metallic minerals that occur in the extensive shear zone systems of Giant Yellowknife Gold Mines' property has been studied. The members of this suite appear to have been formed during three separate periods of mineralization from hydrothermal solutions having a magmatic origin. The introduction of these solutions is believed to have been effected by dilation of the shear zones that accompanied deformation of the surrounding rocks. The metallic minerals were probably formed from these solutions by a combination of reaction with, or replacement of, preexisting minerals, and precipitation in spaces opened by dilation.Each of the mineralization periods is believed to have been characterized by a group of minerals and an environment of deposition different from those of the other two periods. Minerals formed during the first period are pyrite and arsenopyrite. Sphalerite, chalcopyrite and minor pyrrhotite were formed during the second period of mineralization and sulphides and sulphosalts containing Pb and Sb were the dominant minerals formed during the third and last period. The P-T conditions during mineralization are believed to have varied progressively from intense during the first period (temperatures exceeding 500 degrees C accompanied by high pressures) to relatively mild during the third and last period (temperatures below 350 degrees C and fairly low pressures). Since most of the gold is believed to have been introduced and deposited during the first mineralization period, the ore deposit is classed as hypothermal.The most common and hence most important association of gold in the ores is with arsenopyrite. This association is believed to be a product of time and space rather than the result of any type of chemical affinity. Other less common associations are with pyrite, gangue minerals, and the younger sulfides and sulfosalts. The mineral aurostibite is believed to be a reaction product formed by the interaction of S-deficient antimonial solutions with pre-existing gold.There is a strong possibility that some of the gold was originally deposited in solid solution in pyrite and arsenopyrite. However, it seems unlikely that much of it now exists in such a state although there may still be appreciable ultrafine, dispersed gold intermixed with these sulfides.