Ore Generation, Alteration, and Fluid Processes at the Top of a Buried Intrusion in the Ward Zinc-Silver-Copper-Lead District, White Pine County, Nevada

The easterly slopes of Ward Mountain, south of Ely, NV
(Fig. 1) in the southern Egan Range, have yielded polymetallic
ores from Carboniferous-age sedimentary rocks since the
l870s. From l866 through the 1940s about 90,000 tonnes, and
in the l960s about 64,000 tonnes of silver-rich base metal ores
were produced from shallow workings and adits. In the late
l960s, core drilling tested an aeromagnetic anomaly and
encountered extensive concealed silver-lead and zinc-coppersilver
mineralization in multiple deep Mississippian and
Devonian carbonate units. Further drilling by four different
companies encountered the top of a concealed quartz monzonite
pluton, named the Ward stock. Skarn, consisting of
anhydrous calc-silicate minerals cut by later chloritic and
clay alteration, is distributed irregularly in the overlying carbonates.
Metal distribution is zoned, changing from high silver-
to-lead ratio telluride-sulfide mineral assemblages near
surface to copper and higher zinc/lead sulfide ores in the
deepest skarns. Hasler et al. (1991) and Gonzales (1988)
describe the sediment-hosted high temperature carbonate
replacement deposits (CRD) and skarn sulfide mineralization
in more detail.