Chapter I A GEOENVIRONMENTAL MODEL FOR POLYMETALLIC VEIN DEPOSITS: A CASE STUDY IN THE COEUR D’ALENE MINING DISTRICT AND COMPARISONS WITH DRAINAGE FROM MINERALIZED DEPOSITS IN THE COLORADO MINERAL BELT AND HUMBOLDT BASIN, NEVADA

A case study on drainage from polymetallic vein deposits in the world-class Coeur d’Alene mining district in northern Idaho is presented. The initial discussion focuses on our conceptual geoenvironmental model for these deposits, and then proceeds to examine the composition of waters, particularly those draining from adits and tailings piles within the district. The relative importance of the amount of reacting pyrite and carbonate minerals on drainage composition is discussed from a theoretical viewpoint and then compared with observed compositions from the district. Comparisons of drainage composition and reacting pyrite to carbonate ratios are made with diverse types of ore deposits, including polymetallic vein deposits, in Colorado and with polymetallic vein deposits in Nevada. The results indicate that drainage from polymetallic vein deposits has highly variable pH (i.e., acidic to basic) and concentrations of sulfate, metals, and arsenic. These observations are largely due to variable amounts and types of sulfide minerals and predicted ratios of reacting pyrite to carbonate minerals that range from near zero to just under 20/1. The dominant dissolved base metal in these waters is zinc (Zn)