Supergene and hydrothermal dispersion of heavy metals in wall rocks near ore bodies, Tintic District, Utah

Abstract

PART I, T. S. LOVERING.Preliminary work in the Tintic district, Utah, determined the relative distance of migration of ore metals in moist carbonate and silicic wall rocks near ore, and in ground water having a very sluggish circulation through mineralized ground. The analyses of efflorescences in the Tintic Standard mine openings at suitable localities indicated that under the conditions existing during the past 25 years lead has not moved perceptibly; gold has migrated only a few inches; copper has moved a few score feet at most and only in acid solutions; and zinc has traveled hundreds of feet, but not as far as some silver. Silver may travel far in the oxidized zone, but if it comes in contact with sulfides its migration is quickly halted.The chief chemical factors that influence the migration of metals in supergene solutions are the hydrogen ion concentration (pH) of hydrolysis of the metal ion, the solubility of sulfates of the metals, and the position of the metals in Schuermann's series if the solutions are in contact with sulfides for a considerable time.PART II, H. T. MORRIS.Primary dispersion gradients of lead, copper, and zinc, slightly modified by supergene solutions locally, have been recognized in the Tintic district, Utah, in hydrothermally altered wall rocks of gold- and silver-bearing lead-zinc-copper veins in monzonite and in dolomite near lead-zinc replacement ore bodies.The metal content of the rocks near ore seems to decrease logarithmically, and the plotted curves strongly suggest diffusion; the precipitation in the wall rocks at a short distance from the ore must have entailed a concomitant drop in concentration of the metal ions in the mineralizing solution, which in turn would tend to maintain the initial concentration gradient. The curves indicate a short-lived source.Evidence was found of supergene leaching and precipitation of zinc in the wall rocks near ore bodies in the oxidized zone above the water table, but lead is apparently static under surface conditions and reflects primary dispersion patterns. Copper appears to be relatively stable in a carbonate environment, but moves locally in hydrothermally altered monzonite.The dispersion patterns of lead in the oxidized zone--and locally the patterns of zinc and copper as well--are similar to those adjacent to primary sulfide ore bodies 700 feet below the water table and 2,600 feet below the surface.