MINERALOGY, PARAGENESIS, AND MINERAL ZONING OF THE BULLDOG MOUNTAIN VEIN SYSTEM, CREEDE DISTRICT, COLORADO

The Bulldog Mountain vein system, Creede district, Colorado, is one of four major epithermal vein systems from which the bulk of the distric t's historical Ag-Pb-Zn-Cu production has come. Ores deposited along t he vein system were discovered in 1965 and were mined from 1969 to 198 5. Six temporally gradational mineralization stages have been identifi ed along the Bulldog Mountain vein system, each with a characteristic suite of minerals deposited or leached and a characteristic distributi on within the vein system; some of these stages are also strongly zone d within the vein system. Stage A was dominated by deposition of rhodo chrosite along the lower levels of the Bulldog Mountain ore zone. Stag e B in the northern parts of the ore zone is characterized by abundant fine-grained sphalerite and galena, with lesser tetrahedrite and mino r chlorite and hematite. With increasing elevation to the south, stage B ores become progressively more barite and silver rich, with alterna ting barite and fine-grained sphalerite + galena generations; native s ilver +/- acanthite assemblages are also locally abundant within south ern stage B barite sulfide ores, whereas chalcopyrite and other Cu and Ag sulfides and sulfosalts are present erratically in minor amounts. Stage C in the upper and northern portions of the ore zone is characte rized by abundant quartz and fluorite, minor adularia, hematite, Mn si derite, sphalerite, and galena, and major leaching of earlier barite; to the south, some barite and sulfides may have been deposited. Stage D sphalerite and galena were deposited in the upper and northern porti ons of the ore zone; a barite- and silver-rich facies of this stage ma y also be present in the southern portions of the vein system. Late in stage D, mineralogically complex assemblages containing chalcopyrite, tetrahedrite, polybasite, bornite, pyrargyrite, and a variety of othe r sulfides and sulfosalts were deposited in modest amounts throughout the vein system. This complex assemblage marked the transition to stag e E. During stage E, the final sulfide stage, abundant botryoidal pyri te and marcasite with lesser stibnite, sphalerite, and sulfosalts were deposited primarily along the top of the Bulldog Mountain ore zone. S tage F, the final mineralization stage along the vein system, is marke d by wire silver and concurrent leaching of earlier sulfides and sulfo salts; this stage may reflect the transition to a supergene environmen t. The sequence of mineralization stages identified in this study alon g the Bulldog Mountain system can be correlated with corresponding sta ges identified by other researchers along the OH and P veins, and the southern Amethyst vein system. Mineral zoning patterns identified alon g the Bulldog Mountain vein system also parallel larger scale zoning p atterns across the central and southern Creede district. The complex v ariations in mineral assemblages documented in time and space along th e Bulldog Mountain vein system were produced by the combined effects o f many processes. Large-scale changes in vein mineralogy over time pro duced discrete mineralization stages. Short-term mineralogical fluctua tions produced complex interbanding of mineralogically distinct genera tions. Fluid chemistry evolution within the vein system produced large -scale lateral zoning patterns within certain stages. Hypogene leachin g substantially modified the distributions of some minerals. Finally, structural activity, mineral deposition, and mineral leaching modified fluid flow pathways repeatedly during mineralization, and so added to the complex mineral distribution patterns within the vein system.