Some aspects of the geochemistry of sphalerite, Central City District, Colorado

Economic geology of the Idaho Springs district, Clear Creek and Gilpin Counties, Colorado

“…The zonal pattern of the ores of the Idaho Springs district is part of a regional pattern and is an extension of the southeast side, of the concentric pattern recognized in the Central City district (Sims and others, 1963;Sims and Barton, 1961; To explain the zonal pattern, we postulate^ in general accord: with Sims and coworkers, that altering and ore-bearing solutions emanated from a magmatic source in two distinct stages. First, after districtwide fracturing the juvenile solutions moved outward from the source, altering the wallrocks, and forming pyrite veins throughout most of the district; this process'decreased in intensity with distance from the source.…”

“…As shown in table 10 (p. 88), the darker sphalerite contains about 4 percent of iron by weight, which is considerably less than the maximum iron content of sphalerite from the Central City district (Sims and Barton, 1961;. The darkest sphalerite grains from the Idaho Springs district show marked color zoning, however, and the maximum iron con-tent undoubtedly exceeds the maximum listed in table 10.…”

“…In the Chicago Creek area, as postulated by Harrison and "Wells (1959, p. 43), copper-rich ores were deposited before lead-zinc-rich ores, in accord with a sequence of fracturing. In the Central City district, however, as suggested by Barton (1961, 1962) and Sims and others (1963), there was only one stage of base-metal mineralization, which probably followed a period of districtwide refracturing, and the different kinds of base-metal-ores-owe their main characteristics to different pressure-temperature conditions. If the copper-rich and lead-zinc-rich ores formed in sequence, as postulated by Harrison and Wells (1959, p. 43), one would expect to find successive bands of such ores in the symmetrically banded veins, such as the Lincoln and Houston veins, which apparently remained open from the pyrite stage through the base-metal stage.…”

“…X-ray studies indicate that the pinkish variety is true enargite and not luzonite (Paul B. Barton, written commun. to P. K. Sims, 1961).…”

“…The pattern is also denned by carbonate gangue that increases in amount radially from the core area, by barite that increases from the peripheral zone outward, and by average silver-gold ratios that increase radially. Details of this zonal pattern are given by Sims, Drake, and Tooker (1963) and by Sims and Barton (1962). The zonal pattern in the Idaho Springs district is less well defined and is not concentric.…”