Adsorption of Cu, Zn and Pb near sulfide deposits by hydrous manganese—Iron oxide coatings on stream alluvium

Abstract

Hydrous oxides of Mn and Fe scavenge several base metals in the surficial environment by adsorption and coprecipitation. Results of laboratory investigations suggest increased adsorption compared to coprecipitation where higher concentrations of metal ions exist in solution, such as generally occur near an oxidizing mineral deposit. Stream cobbles with hydrous oxide coatings, collected from the Valley and Ridge Province in northwestern Virginia, were immersed in prepared aqueous solutions of CuZnPb for 50 hr. Substantial quantities of each metal were absorbed from solution. Considerably greater proportions of the newly adsorbed metal could be extracted by ammonium citrate than background concentrations of metal initially present in the coatings. Analysis of hydrous oxide coatings collected at varying distances upstream and downstream from a small CuZnPb-sulfide deposit produced similar results. Following the same analytical procedure, considerably greater proportions of the total Cu and Zn were extracted by ammonium citrate from samples near the mine than from those upstream or at a greater distance downstream. If adsorption of metal by hydrous oxides is generally more important compared to coprecipitation where higher concentrations of metal ions are available in solution, the relation might be of practical value. The sulfide deposit is clearly delineated if Cu and Zn extracted by ammonium citrate is expressed as a percent of total Cu or Zn. Previous studies have shown that similar deposits are not clearly delineated by analysis of hydrous oxides unless ratios of metal to Mn or Fe are calculated.