It is possible that some gold deposits present mineralized bands with different types of sulphides and gangue minerals, and it is common the association of gold with some minerals. For example, five distinct bands may be counted and proceeding from each wall inward to the center, each of these bands has an almost perfect counterpart on the opposite side of the vein. The first band, that next to the wall, may contain quartz and pyrite; its inner edge is outlined by the crystalline terminations of quartz prisms. The succeeding band is composed of blende and chalcopyrite; the chalcopyrite grows more abundant toward the inner edge and, in fact, forms two subsidiary bands separated by a thin band of sphalerite. The next layer, a thin band, contains quartz and chalcopyrite. It is followed by a narrow band of sphalerite, which in turn is followed by a thicker band of quartz that contains fine grains of disseminated chalcopyrite, and locally fails to join with its corresponding band on the opposite side, leaving an open crystalline cavity at the center.
On one wall of the gold vein may be a narrow secondary vein, evidently a reopened fissure. Its walls are outlined by narrow bands of quartz and galena, between which is an oxidized mass of iron and magnesia carbonates, and quartz. The narrow quartz bands may form the walls of this little gold vein have locally been broken, and pieces of the wall now lie at varying angles across the vein, embedded in the vein filling. On the opposite wall of the main vein a fragment of country rock may be included in and surrounded by the vein material of the large vein.
Considering this information, the history of the mineralization of this particular gold vein may be deduced. A fracture was formed in the country rock and filled by solutions carrying zinc and iron sulphides. Fracturing continued and cross fissures on a small scale were opened. The forces, of whose presence this first fracturing was a preliminary, finally succeeded in producing an open fracture measured by the width of the vein described, and solutions carrying silica, iron sulphide, a trace of zinc sulphide, and lead, circulated through the open spaces thus afforded. Along both walls gold, quartz and pyrite were precipitated simultaneously, and continued to be precipitated, apparently, until solutions ceased to circulate, or ceased to carry sulphur, iron and silica, for the boundary between the first band and the succeeding one is sharp both in demarcation and in mineral content. When mineralizing waters next flowed past the walls, the blende and chalcopyrite were deposited, and it is evident that, although copper, sulphur and iron were present during the remainder of the history of the vein, though growing markedly less toward the end, the blende and silica content fluctuated, first a layer of one and then of the other being precipitated. Parts of the vein along the center were probably never completely filled, not because there was a lack of material, but because deposition fortuitously isolated geode-like open spaces within which the circulation ceased. The small vein at the edge of the large one points to a recurrence of fracturing, and the advent of carbonated waters, carrying silica also; it marks a distinct change in the solutions, with the cessation of which the mineralization closed.