Copper, lead and zinc by colorimetry after partial digestion with HNO3.
Ward, Frederick N., Lakin, Hubert. W., Canney, Frank. C., et al
Analytical methods used in geochemical exploration by the U.S. Geological Survey : a compilation of trace and semimicroanalytical methods of yielding semiquantitative data on geologic materials useful in geochemical prospecting for ore deposits