Evolution of mineralizing fluids in the Zn-Pb-Cu(-Ag+-Au)skarn and epithermal deposits of the world-class San Martin district, Zacatecas,Mexico

摘要

Mineralizing fluids at the San Martin skarn show an evolution characterized by prograde and retrograde associations.The prograde mineral associations consist of(1)a massive garnet zone,(2)a tremolite+-garnet zone,and(3)a late association of quartz,sphalerite,calcite and fluorite lining the vugs in the garnet zone.The fluids of the prograde associations exhibit decreasing temperatures of homogenization(Th)and variable salinities.The fluids of the massive garnet zone have salinities of approx 36 wt.% NaCl equiv.and Th of 645 to 570 deg C,corresponding to pressures of approx 1055 bar.At the tremolite+-garnet zone,Th range from 438 to 354 deg C.In the late association at the endoskarn,the following evolution can be drawn:(a)salinities of 50 to 42 wt.% NaCl equiv.,and Th of 455 to 346 deg C in quartz,(b)salinities of approx 46 wt.% NaCl equiv.,and Th of 415 to 410 deg C in sphalerite,(c)salinities of 50 to 37 wt.% NaCl equiv.,and Th of 479 to 310 deg C in calcite,(d)salinities of 33 to 28 wt.% NaCl equiv.and of 24 to 22 wt.% KC1 in fluorite,and(e)two types of fluids with salinities of approx 2 and 39 wt.% NaCl equiv.and Th approx 344 and 300 deg C,respectively,in later saccharoidal quartz segregations.The retrograde mineral associations comprise pervasive propylitic alteration to carbonization,and mantos with sulfides.Fluids in epidote have salinities of approx 7.6 wt.% NaCl equiv.and Th of 287 to 252 deg C,and in calcite have salinities of 9.2 to 1 wt.% NaCl equiv.and Th of 188 to 112 deg C.Fluids in the sulfide assemblages in the mantos have salinities of 8 to 3 wt.% NaCl equiv.and Th approx 300 deg C,with corresponding pressures of approx 94 bar.Fluids in late epithermal veins close to the intrusive body have salinities of 10 to 5 wt.% NaCl equiv.and Th of 275 to 200 deg C,and distal veins show salinities of 2 to 1 wt.% NaCl equiv.and Th of approx 160 deg C.