Geology, alteration, and mineralization at the Western World Lakes Cu-Zn prospect, Yuba County, California

Abstract

The Lower Volcanic Unit of the Jurassic aged Smartville Complex hosts the Western World Lakes massive sulfide deposit and other mineral prospects. The complex is a sequence of volcanoclastic sediments, pillowed lavas, sheeted dikes, and plutonic rocks similar to ophiolites found worldwide. At least four metamorphic and alteration events were responsible for the prehnite-pumpellyite metamorphic mineral assemblage developed in the complex. All lavas near the massive sulfide deposit are metamorphosed to a greenschist facies metamorphic mineral assemblage. Weakly altered Footwall unit lavas are locally sodium depleted and copper and zinc enriched. Strongly altered sodium depleted lavas are more abundant in the Gossan Hill unit and are weakly copper depleted. The massive sulfide body consists of primary pyrite, chalcopyrite, sphalerite, tetrahedrite, galena, hematite, pyrrhotite, electrum, and secondary covellite, bornite, chalcocite, and digenite. The massive sulfide, alteration, and metamorphism exhibit characteristics diagnostic of volcanogenic style mineralization.