Abstract

Fissure-filling and replacement Pb-Zn-Cu-Au-Ag ores of the Mayflower mine occur in calcareous sedimentary and intrusive wall rocks over a vertical interval of 3,000 feet. The ores are exceptional in the district for their chalcopyrite and gold content and for the unusual associated gangue minerals anhydrite, chlorite, and hematite. High oxygen fugacities are indicated for many stages of mineralization. Sphalerite compositions are highly variable in the range 0.09 to 5.9 weight percent Fe, an indication of large fluctuations in sulfur fugacity. Silver is carried in tetrahedrite-tennantite (0.2 to 16 wt %), enargite (0.5 to 0.8 wt %), in coupled substitution with Bi + Sb in galena (0.02 to 2.9 wt %), and in the minerals argentite, matildite, chalcocite, and bornite. Content of As, Se, Te, and other minor elements is small. Fractionation of Cd between sphalerite and coexisting galena is relatively consistent whereas the fractionation of Mn between sphalerite and galena is variable; calculated temperatures of formation are high and unreliable.

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