The Pine Creek mine, located 27 km west of Bishop, California, contains scheelite-bearing skarns found at and near the contacts between a septum of Paleozoic metasedimentary rocks and a mid-Cretaceous quartz monzonite pluton. Underground and surface mapping and drill core logging have suggested that skarn formation and accompanying metal deposition should be characterized as a series of events over a range in temperatures overprinting several different rock types.Metamorphism caused the formation of barren, iron-poor calc-silicate marbles and hornfelses, which were subsequently replaced by iron-rich calc-silicate and ore minerals during metasomatism. High-temperature metasomatism was characterized by the formation of garnet-quartz, garnet-pyroxene, and idocrase-wollastonite-pyroxene zones from marble; by pyroxene-plagioclase + or - garnet skarns from biotite and calc-silicate hornfels; and by pyroxene-plagioclase-quartz rock from quartz monzonite. These high-temperature assemblages were locally over-printed by hydrosilicate alteration characterized by biotiteoplagioclase-magnetite replacement of garnet, amphibole-quartz-chalcopyrite + or - calcite (epidote) replacement of garnet-pyroxene (plagioclase) skarn, and calcite-quartz-epidote-chlorite-fiuorite replacement of wollastonite-idocrase. Contemporaneous alteration of quartz monzonite comprised quartz-biotite-chalco-pyrite veins and locally pervasive biotitization. The latest, lowest temperature alteration con-sisted of vertical pipes of quartz-calcite-zeolite, which cut and altered all other rock types.Patterns of ore deposition were intimately tied to original lithologies and alteration types. Initial scheelite deposition accompanied high-temperature metasomatism of marble but not of hornfels or quartz monzonite. In the early-formed skarn, scheelite is concentrated toward the marble replacement front and depleted away from marble. Molybdenite is concentrated in quartz-rich masses near intrusive contacts and in quartz-garnet veins cutting across metaso-matized hornfels. Scheelite was remobilized and deposited in association with hydrosilicate alteration of skarn and hornfels. Copper was deposited with hydrosilicate alteration, particularly in association with amphibole-quartz calcite replacement of garnet-pyroxene skarn. The sequence of events inferred at Pine Creek appears to be similar to those found in other tungsten skarns from around the world.

First Page Preview

First page PDF preview
You do not currently have access to this article.